Term
| Stages of Cytodifferentiation part 1 |
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Definition
| 1. Primordial germ cells A. Appear in the posterior endodermal wall of the secondary yolk sac at the end of the 3rd week (text says 24 days). B. These large cells stain intensely for alkaline phosphatase activity. ameboid movement to the presumptive gonadal region by the 5th week. Migration is facilitated by stem cell factor |
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Term
| Stages of Cytodifferentiation part 2 |
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Definition
| C. Approximately 1,000 PGCs migrate to the gut tube, then rostrally by ameboid movement to the presumptive gonadal region by the 5th week. Migration is facilitated by stem cell factor acting as a positive factor for B. These large cells stain intensely for alkaline phosphatase activity." |
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Term
| Stages of Oogenesis pre natal part 1 |
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Definition
| 1. Primordial germ cells differentiate into oogonia which further proliferate and form clusters of oogonial cells. These clusters become surrounded by flat epithelial cells (follicle cells) derived from ovarian epithelial cells by the end of the third month. |
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Term
| Stages of Oogenesis pre natal part 2 |
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Definition
| 2. By the 4th month, some oogonia have differentiated into primary oocytes which begin Meiosis I up to prophase I. Prophase I may last 40-50 years (until ovulation). 3. Oocyte maturation inhibitor (meiotic inhibitory factor) is secreted by follicular cells, traverses to the oocytesvia gap junctions, and prevents primary oocytes from progressing past prophase I (diplotene stage). |
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Term
| Stages of Oogenesis pre natal part 3 |
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Definition
| 4. The number of germ cells rises rapidly so that by the 5th month, there are ~7 X 106 PGCs + 1o oocytes 5. By 7th month, oogonia have either degenerated or differentiated into primary oocytes which are now individually surrounded by follicular cells (primordial follicle). " |
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Term
| Oogeneisis post natal development: how many oocytes will be ovulated? |
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Definition
| 105. B. Postnatal development 1. At birth, 0.7-2.0 X 106 primary oocytes; at puberty, ~4 X 105. 2. Only ~ 500 will be ovulated." |
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Term
| Oogeneisis post natal development part 1 |
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Definition
| Primary 3. With each ovarian cycle, several primordial follicles mature. A. Primary oocyte increases in size. B. Flat follicular cells proliferate, become cuboidal, and form stratified epithelium. These are now granulosa cells and the follicle is now a primary follicle. |
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Term
| Oogeneisis post natal development part 2 |
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Definition
| 4. A non-cellular membrane, the zona pellucida, forms from glycoproteins secreted by both the oocyte and granulosa cells.There are three major proteins within the zona pellucida: ZP1, ZP2, and ZP3. Null mutations of ZP3 in mice resulted in no zona pellucida. Transgenic mice rescued with human ZP3 restored structural integrity of the zona pellucida." |
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Term
| Oogeneisis post natal development part 3 |
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Definition
| "5. Intracellular spaces begin to coalesce between granulosa cells and a fluid filled cavity, the antrum, forms. The follicle is now a secondary follicle. 6. Cumulus oophorus- mound of granulosa cells surrounding the primary oocyte in the secondary follicle. 7. Follicle matures, increases in size, and is now a tertiary or Graafian follicle. |
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Term
| Oogeneisis post natal development part 4 |
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Definition
| 8. Usually only 1 of several follicles is ovulated; the rest become atretic. "9. Gap junctions between the follicle cells and the oocyte disintegrate, and the primary oocyte resumes Meiosis I near ovulation and results in a secondary oocyte and the 1st polar body. 10. Meiosis II is initiated immediately after Meiosis I and is arrested at metaphase until fertilization." |
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Term
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Definition
| Spermatogenesis (PGC to fully mature spermatozoa) A. PGCs differentiate into spermatogonia. Spermatogonia function as stem cell precursors - producing new spermatogonia after division. B. Spermatogonia undergo several rounds of cell division withincremental differentiation until they are classified as primary spermatocytes. This process takes about 16 days. C. Primary spermatocytes complete Meiosis I to form secondary spermatocytes. After Meiosis II it is a spermatid. Four functional cells are produced (no polar bodies). |
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Term
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Definition
| D. Spermatid cytokinesis is incomplete, leaving cytoplasmic bridges within a group of spermatids. This results in waves of similarly differentiated spermatocytes within regions of the seminiferous tubules. E. Spermiogenesis - maturation of spermatids into spermatozoa takes about 24 days " |
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Term
| Stages of Spermiogenisis part 1 |
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Definition
. Maturation occurs in close association with Sertoli cells that line seminiferous tubules and create the blood-testis barrier."
2. |
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Term
| Stages of Spermiogenisis part 2 |
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Definition
| 2. Maturation events A. Formation of acrosome from Golgi apparatus which contains enzymes to digest path to oocyte cell surface. B. Nuclear condensation by use of protamines C. Morphological changes include loss of cytoplasm, formation of the head containing the nucleus and acrosomal vesicle, formation of the neck containing the centriole for flagellar organization, formation of the midpiece containing mitochondria, and formation of the flagellar tail. |
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Term
| Stages of Spermiogenisis part 3 |
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Definition
| F. ~64 days from spermatogonium to mature spermatocyte. G. Up to 10% of spermatozoa are morphologically abnormal and usually have decreased motility. (2 heads, 2 tails, etc.)" |
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Term
| Preperation for ovulation? part 1 |
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Definition
| A. Follicular and thecal cells produce estrogens which causes stimulation of proliferationof cells of uterine lining (uterine proliferative stage). B. Graafian follicle grows and matures under influence of FSH. C. Due to the LH surge and production of prostaglandins, a surface area of the ovary becomes avascular where follicle will be ovulated. This avascular spot is called a stigma. D. Meiosis I is completed just prior to ovulation and Meiosis II begins but is arrested again until fertilization. E. The ovarian wall is ruptured and the oocyte with surrounding cumulus oophorus is released. F. Cumulus oophorus cells rearrange around oocyte and are now cells of the corona radiata. |
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Term
| Preperation for ovulation? part 2 |
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Definition
| G. Follicular cells left behind differentiate into luteal (yellow) cells. Cells hypertrophy on ovary surface and accumulate lipid (why?) to form corpus luteum (yellow body). H. LH initially maintains the corpus luteum which in turn produces progesterone which maintains uterine lining through the secretory stage. |
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Term
| Preperation for ovulation? part 3 |
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Definition
| I. If no fertilization occurs, the corpus luteum degenerates into fibrotic scar tissue called the corpus albicans (white body). Progesterone levels decline resulting in menstrual bleeding. If fertilization occurs, the corpus luteum is maintained by hCG (human chorionic gonadotropin – the basis of most pregnancy tests) secreted by embryo trophoblast cells. The corpus luteum is maintained until ~ 4th month then slowly degenerates. Progesterone levels are then maintained by the embryo portion of the placenta (formerly trophoblast cells). |
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Term
| Preperation for ovulation? part 3 |
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Definition
| J. After ovulation, fimbriae and cilia of Fallopian tube guide the oocyte into the tube. K. Over the next 3-4 days, muscular contractions and ciliary movements transport the oocyte to the uterus." |
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Term
| Final step of spermatozoa maturation? part 1 |
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Definition
| A. Spermatozoa are aided in movement by muscular contraction of the uterus to the ampulla of Fallopian tube where fertilization usually occurs. B. Capacitation 1. Occurs in female reproductive tract. 2. Removal of glycoprotein covering over the acrosomal process 3. Involves a change in cholesterol:phospholipid ratio in membranes over acrosomal vesicle. |
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Term
| Final step of spermatozoa maturation? part 2 |
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Definition
| 4. Takes ~ 7 hours. 5. Capacitated spermatozoa can pass through corona radiata. |
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Term
| Steps of fertilization? part1 |
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Definition
| Fertilization 1. Spermatozoa have a cell surface protein on the head region that binds to a species-specific protein on the zona pellucida. The protein - ZP3 – is a 83kd glycoprotein. ZP3 binds to sperm cell surface proteins. A. In a mouse ZP3- mutant carrying human ZP3, human sperm do not bind. Why not? Mouse-specific glycosylation of human ZP3 and/or higher order interactions among ZP1, 2, 3 lead to species-specific sperm binding." |
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Term
| Steps of fertilization? part 2 |
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Definition
| "B. Sperm binding triggers a Ca2+ influx, a resulting increase in pH and a signal transduction cascade leading to the acrosome reaction - fusion of acrosomal vesicle membrane with sperm plasma membrane and release of degradative enzymes (eg. membrane-bound acrosin) to penetrate the zona pellucida." |
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Term
| Steps of fertilization? part 3 |
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Definition
| "2. After spermatozoon binding to oocyte cell surface, permeability of zona pellucida changes due to release of lysosomal enzymes from cortical granules under oocyte plasma membrane (cortical reaction). ZP proteins may be degraded (zona reaction) resulting in a block to polyspermy." |
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Term
| Steps of fertilization? part 4 |
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Definition
| 3. Once spermatozoon and oocyte membranes contact, they fuse. In humans, head and tail enter oocyte. Flagellum disintegrates. Mitochondria in midpiece also disintegrate - all mitochondria with its DNA are maternally derived." |
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Term
| Steps of fertilization? part 5 |
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Definition
| "4. Oocyte then finishes Meiosis II. 5. Oocyte becomes metabolically active. 6. Sperm nucleus decondenses as the protamines are replaced with histones - sperm pronucleus. 7. Each pronucleus replicates its DNA and pronuclei fuse to form single nucleus with 46 chromosomes. 8. 50-60% of fertilized eggs are aborted. 40-50% of these due to chromosomal abnormalities. |
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Term
| 9. Results of fertilization: |
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Definition
" A. Restoration of diploid chromosome number.
B. Sex of embryo is determined.
C. Cleavage of zygote is initiated.
D. Metabolic activation of the egg possibly due to a rise in pH." |
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Term
| "General features of human zygote cleavage? part 1 |
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Definition
| 1. Definition - cell division without increase in total cell volume. 2. Cells resulting from early cleavage are blastomeres - regulative cells with approximately equal developmental potential. This is in contrast to mosaic development in which blastomeres have restricted developmental potential. |
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Term
| "General features of human zygote cleavage? part 2 |
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Definition
| 3. First cleavage occurs at ~ 30 hours. Cleavages are asynchronous and rotational. 4. After several cleavages, the blastomeres form an asynchronous ball called a morula. |
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Term
| "General features of human zygote cleavage? part 3 |
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Definition
| 5. After the 3rd cleavage, blastomeres develop tight junctions and form a compact ball of cells. This rearrangement, or compaction, segregates inner cells from outer cells. The adhesion molecule, E-cadherin, present on adjoining cell surfaces, mediates compaction and antibodies to E-cadherin prevent compaction. Inner cells develop gap junctions for intercellular transport of small metabolites. |
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Term
| "General features of human zygote cleavage? part 4 |
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Definition
| 6. Inner cells form the inner cell mass (ICM) giving rise to the embryo and outer cells form the outer cell mass (OCM) giving rise to extraembryonic structures." |
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Term
| "Blastocyst formation? part 1 |
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Definition
1. Fluid enters through zona pellucida and accumulates intercellularly to form a cavity called the blastocele. The embryo is now called a blastocyst."
"2. ICM (embryoblast) is at one pole (embryonic pole). OCM flattens and becomes trophoblast. |
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Term
| "Blastocyst formation? part 2 |
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Definition
| "3. Trophoblast cells away from the ICM (abembryonic pole) produce strypsin on cell surface projections to degrade the zona pellucida "shell". 4. The pluripotential regulative blastomeres of the mammalian ICM has allowed the generation of embryonic stem (ES) cells and transgenic animals." |
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Term
| "Events of blastocyst implantation part 1 |
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Definition
| . Trophoblast cells over the ICM secrete collagenase and plasminogen activator - proteases to aid in penetrating the uterine epithelium at ~ day 6. The trophoblast is highly invasive, readily degrades the uterine epithelium and embeds the blastocyst into the endometrium. Implantation usually occurs first at the embryonic pole — side of the blastocyst with the ICM. |
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Term
| "Events of blastocyst implantation part 2 |
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Definition
| 2. Blastocyst contact with the endometrial epithelium induces trophoblast cell proliferation. Proliferation is stimulated by LIF (leukemia inhibitory factor) — a cytokine in the interleukin family. The named is derived from inhibition of growth and stimulation of differentiation of a murine leukemia cell line. LIF knockout mice have normal blastocysts in the uterus but they do not implant." |
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Term
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Definition
| 1. Normally implantation occurs in the posterior or anterior wall of the uterus. 2. Placenta previa (5:1,000 births) is caused by implantation at the internal os of the uterus and the growing placenta comes to cover the opening." |
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Term
| Risk factors for placenta previa include |
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Definition
| 1. Prior placenta previa (4-8%) 2. Ceaserian section 3. Maternal age (Women over 30 years have three times higher rate than women under 20 years.) 4. Multiple fetuses 5. Induced abortion |
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Term
| Potential complications of placenta previa include: |
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Definition
| 1. Maternal hemorrhaging (0.03% mortality) 2. Rh factor incompatibility 3. Fetal anemia 4. Intrauterine growth retardation (IUGR) |
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Term
| What is ectopic pregnancy? |
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Definition
| Ectopic pregnancies - implantation outside of uterus. |
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Term
|
Definition
| B. Most (95%) ectopic implantations occur in the Fallopian tube, usually in the ampulla. Sometimes it occurs in the isthmus of the tube (near the uterine cavity). These implantation sites lead to tubal pregnancies. C. Implantation can occur on the ovary resulting in a primary ovarian pregnancy. This occurs with a frequency of about 0.5% of ectopic implantations." |
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Term
| Can eptocic pregnancy occur in abdominal cavity? |
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Definition
| D. It can occur in the abdominal cavity, particularly on the peritoneal lining of the rectouterine cavity (Douglas’ pouch). This constitutes about 1.5% of ectopic implantations." |
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Term
| Can implantation occur in cervix? |
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Definition
| E. Implantation can occur in the cervix. This occurs at a frequency of about 0.3% of ectopic implantations. F. Contributing factors to ectopic implantations include pelvic imflammatory disease (PID) due to gonorrhea or chlamydia infection which causes inflammation and scarring of the epithelial lining of the Fallopian tube and uterus. The incidence of ectopic pregnancies rises to 6.4%. Endometriosus also contributes to increased incidence of tubal pregnancies. |
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Term
| Formation of the bilaminar germ disk:(part1) |
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Definition
| The ICM reorganizes (probably by delamination) and differentiates into two cell layers. 1. Hypoblast - layer of cuboidal cells next to the blastocele. 2. Epiblast - layer of columnar cells next to the growing amniotic cavity. The epiblast may form from the inner most cells of the ICM. |
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Term
| Formation of the bilaminar germ disk:(part2) |
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Definition
| 2. The trophoblast differentiates and there is the first establishment of uteroplacental circulation. A. Trophoblast cells differentiate into 2 layers: |
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Term
Formation of the bilaminar germ disk:(part3)
What are the layers? |
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Definition
| 1. Cytotrophoblast layer - mononucleated cells surrounding the blastocyst. 2. Syncytiotrophoblast layer - a highly invasive multinucleated layer that first appears at the embryonic pole then develops around the embryo. Cells from the cytotrophoblast proliferate and fuse into a syncytium. The invasiveness leads to complete embedding of the blastocyst into the uterine endometrium." |
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Term
| Formation of the bilaminar germ disk:(part4) |
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Definition
B. By day 9, large vacuoles appear in the syncytiotrophoblast and these begin to fuse to form lacunae (large open areas within the syncytium). This is known as the lacunar stage."
C. By day 12, the syncytiotrophoblast erodes the epithelium of enlarged maternal capillaries called sinusoids and blood enters the lacunae. |
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Term
| Formation of the bilaminar germ disk:(part5) |
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Definition
| D. By day 13, local proliferation of trophoblast cells causes columns of trophoblast cells to extend into the syncytiotrophoblast forming primary villi. E. Maternal endometrium near the implantation site becomes more edematous and accumulates glycogen and lipid. This is the decidual reaction. |
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Term
| Formation of the bilaminar germ disk:(part6) |
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Definition
| 3. Further trophoblast development A. Primary villus — a fingerlike extension of cytotrophoblast and overlying syncytiotrophoblast B. Extraembryonic mesoderm then fills the core of the primary villus to form a secondary villus. |
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Term
| Formation of the bilaminar germ disk:(part7) |
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Definition
| C. Mesodermal cells then differentiate into blood vessels and blood cells to form a tertiary villus. D. Capillaries connect with chorionic plate and connecting stalk to form the embryonic placental circulatory system. |
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Term
| Formation of the bilaminar germ disk:(part8) |
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Definition
4. Formation of the amniotic cavity
A. Begins by cavitation as a narrow cleft within the ICM (becoming the epiblast layer) at the embryonic pole. The cavity then temporarily comes in contact with the cytotrophoblast." |
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Term
| Formation of the bilaminar germ disk:(part9) |
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Definition
| B. Epiblast cells, called amnioblasts, next to the amniotic cavity migrate dorsally along the cytotrophoblast, form the amniotic membrane, and line the amniotic cavity. |
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Term
| Formation of the bilaminar germ disk:(part10) |
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Definition
| 5. Formation of the primitive (primary) yolk sac Hypoblast cells next to the cytotrophoblast begin to migrate ventrally along the cytotrophoblast ventrally and form a thin membrane called the exocoelomic or Heuser’s membrane made of extraembryonic endoderm to enclose the exocoelomic cavity or primitive (primary) yolk sac. |
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Term
| Formation of the bilaminar germ disk:(part11) |
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Definition
| 6. Formation of extraembryonic mesoderm and the chorionic cavity". A. A new cell population forms from hypoblast cells and/or existing extraembryonic endoderm. These cells come to lie between the exocoelomic cavity and the cytotrophoblast. These cells differentiate into a loose connective tissue called the extraembryonic mesoderm. |
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Term
| Formation of the bilaminar germ disk:(part12) |
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Definition
| B. Cavities form within the extraembryonic mesoderm and they coalesce to form the extraembryonic coelom or chorionic cavity." |
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Term
| Formation of the bilaminar germ disk:(part13) |
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Definition
| C. Mesoderm next to the trophoblast is called extraembryonic somatopleuric mesoderm or extraembryonic somatopleure. Mesoderm next to the primitive yolk sac is called extraembryonic splanchnopleuric mesoderm or extraembryonic splanchnopleure. |
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Term
| Formation of the bilaminar germ disk:(part14) |
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Definition
| D. The cavity will eventually extend all around the embryo within the blastocyst except at the embryonic pole where the connecting stalk suspends the embryo in the chorionic cavity and will become the umbilical cord." |
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Term
| Formation of the bilaminar germ disk:(part15) |
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Definition
| 7. Formation of the secondary yolk sac A. A second wave of hypoblast cells migrates toward the abembryonic pole and forms a smaller cavity called the secondary (definitive) yolk sac. Portions of the primitive yolk sac are pinched off during this process and are retained as exocoelomic cysts." |
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Term
| Formation of the bilaminar germ disk:(part16) |
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Definition
"B. The secondary yolk sac is a site of hematopoiesis and PGC formation
**Connecting stalk, which later becomes the ambilicle chord. |
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Term
| When does the embryonic period occur? |
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Definition
| The embryonic period occurs during the 3rd to 8th week of development. |
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Term
| What is the embryonic period characterized by? |
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Definition
| It is characterized by: A. Period of organogenesis when 3 germ layers give rise to specific structures (organs). B. Major changes in the shape of the embryo due to growth in specific regions, embryonic folding, and organogenesis. C. By the end of the 8th week, major external body features are recognizable |
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Term
|
Definition
| formation of the neural tube |
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Term
| What are the steps of Neurlation?(part 1) |
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Definition
A. At the end of gastrulation, the cranial end of the embryo is broader than the caudal end.
B. The notochord (derived from embryonic mesoderm) causes the overlying ectoderm to thicken forming the neural plate. This portion of ectoderm is called neuroectoderm." |
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Term
| What are the steps of Neurlation?(part 2) |
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Definition
| C. By the end of the 3rd week, the lateral neural plate elevates dorsally to form neural folds on either side of a depressed neural groove. D. Fusion of the neural folds begins in the cervical region and the folds zipper together in both cranial and caudal directions. Fusion of the folds creates a tube -the neural tube. |
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Term
| What are the steps of Neurlation?(part 3) |
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Definition
| E. The holes at the cranial and caudal ends of the neural tube are the anterior (cranial) and posterior (caudal) neuropores, respectively. The cranial end closes on approximately day 25. The caudal end closes on approximately day 27. " |
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Term
| What are the steps of Neurlation?(part 4) |
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Definition
F. Failure of the anterior neuropore to close results in anencephaly.
G. Failure of more caudal neural tube and associated vertebral arches to close results in spina bifida. |
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Term
| What do Neural crest cells do? |
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Definition
| oon after (possibly at the same time) neural fold fusion, cells at the dorsal end of the newly formed neural tube migrate out of the neural tube (NT). These neural crest cells contribute to a diverse array of cell types and structures. |
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Term
| What are the types of Neural Crest cells? Where do they form?(part 1) |
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Definition
| 1. Ganglia - some cranial ganglia, dorsal root ganglia, and enteric ganglia 2. Schwann and glial cells 3. Meninges - pia mater and arachnoid. |
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Term
| What are the types of Neural Crest cells? Where do they form?(part 2) |
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Definition
| 4. Melanocytes 5. Medulla of the adrenal gland 6. Portions of bone and connective tissue of the head 7. Conotruncal region of the heart 8. Odontoblasts involved in tooth formation |
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Term
| Name the two ways neural crest pathways migrate within the embryo? |
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Definition
1. The dorsal pathway is taken by melanocytes.
2. The ventral pathway is taken by cells that contribute to ganglia, heart, etc." |
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Term
| What do Neural crest cells exemplify? |
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Definition
| Neural crest cells exemplify a common event in embryonic development - cell migration. Numerous genes are currently being identified that mediate neural crest cell, and possibly other cell type, migration and survival during migration. |
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Term
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Definition
| 1. The c-kit receptor is a molecule expressed by different types of migrating cells. It binds the ligand, steel. |
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Term
| What do mutations in c-kit receptor or steel genes result in? |
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Definition
| 2. Mutations of either the c-kit or steel genes results in abnormalities of cells or structures derived from migrating cell types. A. Sterility may result from lack of PGC migration. B. Abnormal pigmentation due to abnormal neural crest cell migration. |
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Term
| What is Hirschsprung’s Disease?(part 1) |
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Definition
| (related to c-kit receptors) Frequency of occurrence is 1:5,000. 2. Characterized as a congenital disorder in which a segment of the colon is abnormally dilated. Therefore, it is sometimes given the descriptive name, megacolon." |
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Term
| What is Hirschsprung’s Disease?(part 2) What is it due to? |
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Definition
| "3. The condition is due to a constriction of the colon in a more distal segment relative to the zone of dilation. Constriction is due to a lack of enteric ganglia (neural crest cell derived) in a segment of descending colon. The lack of ganglia causes continuous smooth muscle constriction. Symptoms include failure to pass meconium, constipation, vomiting, and abdominal distention in the first year |
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Term
| What is DiGeorge Syndrome ? |
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Definition
| E. DiGeorge Syndrome 1. The syndrome is due to a partial deletion of chromosome 22 2. It is characterized by hypoplasia and decreased function of the thymus and thyroid with some cardial septal defects. It is caused by an abnormality in cranial neural crest cell development |
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Term
| Neural crest study conducted how? |
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Definition
| F. Derivatives of neural crest cells are determined by cell tracing and lineage studies using latex beads, dyes, etc. and by chick/quail chimeras |
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Term
| What has Neural Crest studies shown? |
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Definition
. 1. Single cell labelling has shown that many neural crest cells are multipotent, suggesting that cell specification may arise during and/or after migration.
2. Cranial versus caudal neural crest cells are specified rather early in development. |
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Term
| Ectodermal derivatives that begin to form during the embryonic period include? |
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Definition
| A. Central nervous system B. Peripheral nervous system C. Sensory epithelium of the eye, ear, and nose D. Epidermis including hair and nails E. Pituitary gland F. Mammary gland G. Derivatives of neural crest cells |
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Term
| In initial embryonic period the mesoderm can be divided into which three portions? |
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Definition
| Initially during the embryonic period intraembryonic mesoderm can be divided into three major portions - paraxial mesoderm, intermediate mesoderm, and lateral plate mesoderm." |
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Term
| What is the paraxial mesoderm? |
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Definition
| 1. Paraxial mesoderm appears as a thickened mesoderm next to the neural tube and notochord. |
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Term
| When does segmentation of paraxial mesoderm occur?(part 1) |
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Definition
2. Segmentation of unsegmented paraxial mesoderm generally occurs in a cranial to caudal direction.
A. The first pair of somites appears in the cervical region on ~ day 20. B. Thereafter, somites form at a rate of 3 pairs/day up to 42-44 pairs. |
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Term
| When does segmentation of paraxial mesoderm occur?(part 2) |
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Definition
| C. The number of somite pairs is the primary means of determining embryonic age from the 3rd to 4th week of development. After 4 weeks, age is typically determined by crown-rump length. D. Cells of the somites will eventually form dermis, skeletal muscle, and vertebrae. |
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Term
| What is Intermediate mesoderm? What does it give rise to? |
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Definition
1. In more cranial regions, intermediate mesoderm will give rise to nephrotomeswhich will form part of the kidney. "
- In more caudal regions, intermediate mesoderm will give rise to nephrogenic cords which will form genital ridges. |
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Term
| What is Lateral plate mesoderm? Where does it form?(part 1) |
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Definition
| 1. Cavities form and coalesce within the lateral plate mesoderm to form the intraembryonic coelom. This is initially continuous with the extraembryonic coelom or chorionic cavity. |
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Term
| What is Lateral plate mesoderm? Where does it form?(part 2) |
|
Definition
| 2. The intraembryonic coelom divides the lateral plate mesoderm into mesodermal layers associated with either ectoderm or endoderm. A. Mesoderm associated with ectoderm is called somatopleure or somatic mesoderm or parietal mesoderm. This mesoderm forms the body wall. |
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Term
| What is Lateral plate mesoderm? Where does it form?(part 3) |
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Definition
| B. Mesoderm associated with endoderm is called splanchnopleure or splanchnic mesoderm or visceral mesoderm. This mesoderm forms the gut wall and mesothelial and serous membranes that will line the peritoneal, pleural, and pericardial cavities |
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Term
| What happens to lateral plate mesoderm during the 3rd week? |
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Definition
| 3. During the 3rd week, angioblasts from extraembryonic splanchnic mesoderm next to the yolk sac form angiogenic cell clusters." |
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Term
| What do cells on the inside of the clusters form? |
|
Definition
| A. Cells on the inside of these clusters form circulating blood cells. B. Cells on the outside of the clusters form endothelial cells of the blood vessels which fuse to form longer embryonic blood vessels." |
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Term
|
Definition
| D. Mesoderm forms (at least part of): 1. Muscle - striated and smooth 2. Cartilage 3. Bone 4. Blood 5. Dermis 6. Portions of the spleen, kidney, gonads, and adrenals |
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Term
| Explain Initial development of endoderm during the embryonic period. |
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Definition
A. The endodermal germ layer forms the lining of the gut and gut-associated organssuch as the liver and pancreas.
B. Endoderm-derived cells also form the epithelium of the respiratory tract. |
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Term
| What does embryonic folding achieve? |
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Definition
| Embryonic folding transforms the somewhat two-dimensional trilaminar embryo into three dimensions. It spatially organizes the basic body plan of the developing embryo. |
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Term
| Explain Cephalocaudal (craniocaudal) folding?(part 1) |
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Definition
| 1. Folding in the cephalocaudal axis is due to differential growth in the length of the embryo. |
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Term
| Explain Cephalocaudal (craniocaudal) folding?(part 2) |
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Definition
| 2. Cephalocaudal folding brings the oropharyngeal and cardiogenic regions ventrally and caudally to their appropriate positions for further development." |
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Term
| Explain Cephalocaudal (craniocaudal) folding?(part 3) |
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Definition
| 3. The leading edge of the caudal movement in the cephalic folding is the septum transversum, the initial separation of the thoracic and abdominal cavities |
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Term
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Definition
1. Lateral folding is due to differential growth of the somites and neural tube.
2. As a result of lateral folding, the gut becomes enclosed. |
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Term
| What does lateral folding achieve? |
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Definition
| 3. Lateral folding reduces communication between the gut and the yolk sac to a thin vitelline duct. |
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Term
| What does embryonic folding do? What happens to the two membranes? What are there names? when does it occur? |
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Definition
| Embryonic folding closes off the intraembryonic coelom. The oropharyngeal membrane ruptures in 4th week and the cloacal membrane ruptures in the 7th week." |
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Term
| What happens in the fetal period? what is it characterized by? |
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Definition
| The fetal period occurs from the end of the 8th week to the end of gestation ~38 weeks (40 weeks from last menstruation). The fetal period is characterized by maturation and growth of organ systems. |
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Term
| What happens during the 2nd trimester? 3rd trimester? |
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Definition
| During the 2nd trimester (months 4-6), the fetus grows primarily in length. In contrast, during the 3rd trimester, the fetus primarily gains weight. At 8 weeks of development (end of the embryonic period), the embryo weighs about 8g. At 38 weeks (end of the fetal period) the fetus weighs about 3400g - an increase of 425 times. |
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Term
| What happens at 8 weeks to? |
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Definition
| At 8 weeks of development (end of the embryonic period), the embryo weighs about 8g. At 38 weeks (end of the fetal period) the fetus weighs about 3400g - an increase of 425 times. |
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Term
| What happens to body proportions and when? |
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Definition
| Relative bodily proportions also change during the fetal period. At 9 weeks, the fetus head is approximately one-half the crown rump length (CRL). By birth, the head is typically one-fourth of the CRL." |
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Term
| What effects fetal growth?(part 1) |
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Definition
| A. Glucose and amino acids that freely cross the placenta. B. Insulin and human growth hormone are hormones with major roles in fetal growth. C. Gestational diabetes can significantly increase fetal weight, but is detectable with a glucose tolerance test |
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Term
| What effects fetal growth?(part 2) |
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Definition
| D. Risk factors for intrauterine growth retardation (IUGR) — fetal weight within the lowest 10% of normal. 1. Cigarette smoking affects weight during the last 6-8 weeks. 2. Multiple fetuses 3. Poor nutrition 4. Placental dysfunction/abnormal uteroplacental circulation |
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Term
| What are the major hallmarks at 12 weeks of development? |
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Definition
| A. Primary ossification centers appear in long and cranial bones. B. External genitalia are visible by ultrasound. C. Urine is produced and excreted into the amniotic fluid. |
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Term
| What happens at 13 to 16 weeks? |
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Definition
| A. Eyes move anteriorly but do not open until ~26 weeks. B. Ears move cranially to their final position. C. Beginnings of fetal movement." |
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Term
| What covers the fetus around 13 to 16 weeks? |
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Definition
| The fetus becomes covered with lanugo - fine hair. The fetus also becomes covered with vernix caseosa - white, fatty substance secreted by sebacious glands. Lanugo helps hold it to the skin. Vernix caseosa protects the fetal skin from amniotic fluid. |
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Term
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Definition
| to produce red blood cells |
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Term
| When does Erythropoeisis occur? Where does it occur? |
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Definition
(13 to 16 weeks)
Erythropoeisis occurs at several sites throughout the fetus.
A. It occurs in the fetal liver for several weeks at the start of the fetal period. B. It then occurs in the spleen until approximately week 28. C. Thereafter, it occurs in the bone marrow. |
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Term
| What is quickening? WHen does it occur? |
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Definition
| arly fetal movements felt by the mother begins to occur around weeks 17- 20 |
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Term
| When is surficant produced? What does it do? |
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Definition
| At approximately 24 weeks, lung surfactant is made. Surfactant decreases lung air sac surface tension and therefore allows opening of the air sacs. This significantly increases premature fetal viability. |
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Term
| What are common fetal diagnostic tests?(part 1) |
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Definition
| A. Amniocentesis - withdrawal of 30-40cc of amniotic fluid 1. Alpha-fetoprotein (also in maternal blood) tests for failure of the neural tube to close. 2. Karyotype for gross chromosomal abnormalities. 3. Screen for specific heritable diseases |
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Term
| What are common fetal diagnostic tests?([part 2) |
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Definition
B. Chorionic villous sampling - biopsy of the fetal portion of the placenta provides cells that can be cultured for karyotyping and more extensive genetic screening.
C. Ultrasound
1. Used to monitor formation of organs and skeletal |
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Term
| what does ultra sound measure? |
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Definition
A. Abdominal circumference
B. Head circumference
C. Femur length
D. Foot length |
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Term
| What are common fetal diagnostic tests?([part 3) |
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Definition
| Magnetic resonance imaging (MRI) for more detailed imaging of organs and structures." |
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Term
| Formation of the chorionic membrane and chorionic cavity(part 1) |
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Definition
| The chorionic membrane lines the chorionic cavity or extraembryonic coelom. This cavity begins to form by coalescence of spaces within the extraembryonic reticulum and extraembryonic mesoderm at about day 12. |
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Term
| Formation of the chorionic membrane and chorionic cavity(part 2) |
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Definition
| Extraembryonic mesoderm associated with cytotrophoblast forms the chorionic membrane. The origin of this extraembryonic mesoderm is uncertain. It is derived from either migration of cells from the epiblast or bydelamination of hypoblast cells. The chorionic cavity expands to encompass the embryo except at the connecting stalk which will become the umbilical cord. |
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Term
| Explain the formation of the amniotic membrane and cavity.(part 1) |
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Definition
| A. On day 8, fluid begins to accumulate between cells of the epiblast. As a result, some epiblast cells are displaced toward the embryonic pole and form the amniotic membrane. These cells are called amnioblasts and the cavity is the amnion. |
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Term
| Explain the formation of the amniotic membrane and cavity.(part 1) |
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Definition
| As the amnion grows in volume, amnioblasts migrate along the cytotrophoblastic roof and contribute to growth of the amniotic membrane. Ultimately the thin amniotic membrane consists of a single layer of extraembryonic ectodermal cells lined by nonvascularized extraembryonic mesoderm." |
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Term
| What does the embryonic cavity do? What can the amniotic cavity do by week 8? (part 2) |
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Definition
| By week 8, the amniotic cavity encompasses the embryo and acquires several functions: 1. Fluid absorbs shocks 2. Fluid prevents adherence to the amniotic membrane 3. Allows for fetal movement and growth 4. Temperature regulation" |
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Term
| Explain the formation of the amniotic membrane and cavity.(part 3) |
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Definition
| C. Growth of the amnion pushes the yolk sac (vitelline duct) and connecting stalk together. These eventually become incorporated into the umbilical cord. The yolk sac and vitelline duct usually disappear by birth. The amniotic membrane eventually grows to cover the umbilical cord. |
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Term
| How much amniotic fluid is at birth? |
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Definition
| There is 0.5 to 1 liter of amniotic fluid at birth. |
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Term
| Where does amniotic fluid originate from?(part 1) |
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Definition
| 1. Primarily from the maternal blood in chorion leave by transport across the amniotic membrane. 2. Across the embryonic/early fetal skin before keratinization. |
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Term
| Where does amniotic fluid originate from?(part 2) |
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Definition
| 3. Fetal respiratory tract 4. The fetal urinary system produces and excretes urine which is mostly water since waste is cleared by the circulatory system back to the maternal circulation. |
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Term
| What is the composition of amniotic fluid? |
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Definition
| 1. 99% water 2. Fetal epithelial cells which can be examined by amniocentesis and karyotyping 3. Protein such as alpha-fetoprotein A. High alpha-fetoprotein indicates a neural tube defect. B. Low alpha-fetoprotein may indicate chromosomal abnormalities like Trisomy 21 (Down Syndrome). 4. Fatty acids, amino acids, etc" |
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Term
| How is amniotic fluid replaced? How often? |
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Definition
| Amniotic fluid is replaced every 3 hours. The fluid is resorbed through the amniotic membrane back to the maternal circulation and by fetal swallowing of amniotic fluid (~400cc/day). This fluid is absorbed through the fetal gut and goes back to the maternal circulation as well. |
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Term
| What does amnion expansion do? |
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Definition
| Amnion expansion eliminates the chorionic cavity and the amniotic and chorionic membranes may fuse. |
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Term
| How are the chorionic and amniotic membranes different? |
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Definition
| However, the two membranes differ visually. The chorionic membrane is thicker and not as clear. The amniotic membrane, because of its requirement for fluid exchange, is thinner and therefore more transparent |
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Term
| What are some abnormal developments of the amnion/amniotic fluid? What is less then normal amounts? What can happen? |
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Definition
Less then 400cc A. It may be caused by a failure in fetal kidney development (renal agenesis) and/or an obstruction in the urinary system (obstructive uropathy) resulting in no fetal contribution to the amniotic fluid.
B. Complications include malformations due to insufficient room for development of the thorax and limbs as well as decreased potential for movement. |
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Term
| What can too much fluid cause? How much is too much? |
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Definition
| Too much amniotic fluid (1500-2000cc) is termed polyhydramnios (hydramnios). It is indicative of malformations affecting the ability of the fetus to swallow amniotic fluid. Possible malformations include anencephaly and/or esophageal atresia |
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Term
| What does Amniotic band syndrome cause? |
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Definition
| 3. Amniotic band syndrome - a strip of amniotic membrane can become detached and wrap around a fetal structure (often a limb). The structure can become constricted and can even be cut off by tightening of the amniotic band. This condition occurs in about 1:1200 live births |
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Term
| What are fraternal twins called and identical? |
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Definition
| dizygotic(fraternal) and monozygotic. |
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Term
| How do Dizygotic twins arise? |
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Definition
| 1. Arise from 2 or more eggs and 2 or more sperm. |
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Term
| How often do dizygotic twins occur?(prob not on test) |
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Definition
| 2. Occurs at a frequency of approximately 8-10/1000 with significant regional variations. In the Taiwanese population dizygotic twins occur at a frequency of 1.4/1000, whereas in Nigeria the frequency is approximately 45/1000. |
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Term
| When and why does twinning occur more often? |
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Definition
| 3. Incidence of dizygotic twinning increases with maternal age up to about age 37. 4. There are familial (genetic) tendencies for dizygotic twinning. |
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Term
| How many chorionic membranes exist in dizygotic twins? |
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Definition
| . There are two chorionic membranes which may fuse later in gestation. 7. There are two placentas which may fuse depending on the relative positions of implantations and placental growth." |
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Term
| how do Monozygotic twins arise? |
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Definition
| Arise from fertilization of a single egg by a single sperm. |
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Term
| What are frequencies of monozygotic twins? |
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Definition
| 2. The frequency of monozygotic twins is approximately 3/1000 with no significant variation in different populations or maternal age. |
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Term
| How does monozygotic twinning result? |
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Definition
| 3. Monozygotic twinning results from a split of embryonic cells, most likely of the inner cell mass. Complete monozygotic twins reflect the regulative versus mosaic development of higher vertebrates |
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Term
| WHat is shared by monozygotic twins? |
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Definition
| 4. The extraembryonic and even embryonic structures that are shared by the developing monozygotic twins directly reflects the stage and extent of splitting of the original embryonic cell mass or developing embryo. |
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Term
| What is shared when a split occurs at 2 cell stage? |
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Definition
| A. A split at the 2 cell stage results in separate amnions, chorions, and placentas (which may later fuse). |
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Term
| What is shared when a split of the inner cell mass? |
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Definition
| B. A split of the inner cell mass results in separate amnions but a common chorion and placenta. |
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Term
| What does an incomplete split of inner cell mass result in? |
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Definition
| C. An incomplete split of the inner cell mass or a split at later stages (eg. bilaminar disc stage) may result in common amnion, chorion and placenta. Unfortunately, incomplete splitting of the bilaminar disc may result in conjoined twins. |
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Term
| what is frequency of conjoined twins? |
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Definition
| 1. The frequency of conjoined twins in general is 1-2/50,000 births and 1/600 sets of twins. 2. A higher frequency occurs in female twins than male twins. A higher frequency occurs in female twins than male twins |
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Term
| What are shared duplicated images of each other? |
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Definition
| 3. The specific shared (conjoined) regions and/or organs depends on the region of the inner cell mass or bilaminar disc that did not completely separate. 4. Shared, duplicated organs are mirror-images of each other — Bateson’s rule." |
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Term
| How is waste excreted in development? (Formation of placental villi ) |
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Definition
| During the 1st week of development, simple diffusion of nutrients and waste is sufficient for development of the zygote. As the embryo grows in volume, the need for a circulatory system arises for efficient exchange of gases, nutrients, and waste. |
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Term
| When does this process occur?(Formation of placental villi ) |
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Definition
| This process begins on approximately day 9 by the formation of trophoblastic lacunae within the syncytiotrophoblast. Maternal capillaries are eroded and blood fills lacunar spaces |
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Term
| Formation of villi part 3? |
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Definition
| By this time, extraembryonic mesoderm has developed underneath the cytotrophoblast layer and this mesoderm induces local regions of the cytotrophoblast to proliferate and extend toward the lacunae with a covering of syncytiotrophoblast. |
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Term
| What are syncytiotrophoblasts are termed ?(Formation of placental villi ) |
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Definition
| 3. These initial extensions of cytotrophoblast into syncytiotrophoblast are termed primary villi (primary stem villi). Each individual extension is a primary villus. |
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Term
| What happens after the extension of syncytiotrophoblasts?((Formation of placental villi )(part 1) |
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Definition
4. By day 16, extraembryonic mesoderm invades the core of primary villi making them secondary villi.
5. At the end of the 3rd week, extraembryonic mesoderm within the villi and in the chorionic plate differentiates into circulating blood cells and the endothelial cells of blood vessels. These are tertiary villi." |
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Term
| What happens after the extension of syncytiotrophoblasts?((Formation of placental villi )(part 2) |
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Definition
| "6. The blood vessels anastomose (fuse) with embryonic vessels in the connecting stalk - two arteries and one vein within the umbilical cord. This (with the newly beating embryonic heart) establishes a functional uteroplacental circulation |
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Term
| What are the three layers must initially cross? ((Formation of placental villi )(part 3) |
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Definition
| 7. Therefore, gases, nutrients, waste, water, etc. must initially cross 3 cell layers of a mature villus. A. Endothelium of the villous capillaries B. Cytotrophoblast which becomes intermittent later in pregnancy. C. Syncytiotrophoblast" |
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Term
| "Nomenclature and fate of the decidua: What happens to decidua?(part 1) |
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Definition
| 1. Blastocyst implantation initiates the decidual reaction in the stroma (under the epithelium) of the uterus. Stromal cells accumulate lipid and glycogen. The stroma thickens and blood vessels invade the area making it highly vascularized. The endometrium is called the decidua. |
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Term
fate of the decidua: (part 2)
Relative to the site of implantation and the growing embryo and its associated cavities, the decidua has 3 areas? (part 1) |
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Definition
| A. Decidua basalis - the area of thickened decidua next to the embryonic pole or point of implantation. This will form the maternal part of the placenta. |
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Term
fate of the decidua:
Relative to the site of implantation and the growing embryo and its associated cavities, the decidua has 3 areas?(part 2) |
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Definition
B. Decidua capsularis - the area of decidua next to the abembryonic pole. This decidua becomes thin as the embryo and its extraembryonic cavities push out into the uterine cavity.
C. Decidua parietalis - rest of the decidua." |
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Term
fate of the decidua: (part 3)
What happens to decidua during 4-5 month? how are deciuda capsular is eliminated? |
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Definition
| 3. During months 4-5, the decidua capsularis is eliminated by being pushed next to the decidua parietalis, closing off the uterine cavity. Tertiary villi form from the embryonic around to the abembryonic pole. By the end of the 4th week, tertiary villi cover the entire chorion. |
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Term
| fate of the decidua: (Part 4) |
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Definition
| As the embryo grows into the uterine cavity, villi on the chorion at the abembryonic pole are compressed against the decidua capsularis. These villi atrophy, leaving a smooth chorion again. This is the chorion laeve. The chorionic region at the embryonic pole still retaining villi is the chorion frondosum which is the fetal contribution to the placenta. |
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Term
fate of the decidua: (part 5)
Is the placenta is both maternally and fetally derived
? what is it composed of? |
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Definition
| A. Basal plate - maternal layer of decidua basalis and cytotrophoblast B. Chorionic plate - fetal side |
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Term
fate of the decidua: (part 6)
WHat happens to decidua basal is as it grows? |
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Definition
| In months 4-5, tissue of the decidua basalis begins to grow into the intervillous spaces formed by fusion of lacunae. The growing tissue creates decidual septa (divisions). The areas within these septa are called cotyledons. There are typically 15 to 25 cotyledons in a placenta. The septa do not completely close off the intervillous spaces. The placenta itself is 15-25cm in diameter, 3cm thick, and 500-600g." |
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Term
| Where does implantation occur? How does placenta previa occur? |
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Definition
1. Normally implantation occurs in the posterior or anterior wall of the uterus
2. Placenta previa (5:1,000 births) is caused by implantation at the internal os of the uterus and the growing placenta comes to cover the opening. |
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Term
| Placental function: What happens to placenta by 11th week? |
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Definition
| 1. By the 11th week the placenta, in particular the syncytiotrophoblast, takes over production of estrogen and progesterone from the corpus luteum. |
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Term
Placental function:
Where does placental circulation begin? |
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Definition
| 2. Placental circulation begins at maternal arteries (about 100) which are spiral in shape and exhibit high blood pressure. They lead into the intervillous spaces within the cotyledons. Blood shoots out the open ends of the spiral arteries to fill the intervillous spaces, and returns via the open-ended maternal decidual veins. |
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Term
Placental function:
How much blood does a fully mature placenta have ? How often recirculated? |
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Definition
| A fully mature placenta has about 150cc of blood within the intervillous spaces, and it is recirculated about four times per minute |
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Term
Placental function:
What is placentas function? |
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Definition
| 3. Exchange of materials A. Villous branching within the placenta provides up to 10-11 square meters of surface area for exchange of gases, etc. |
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Term
|
Definition
| B. Besides gases, nutrients (eg. amino acids, glucose), steroid hormones, and waste, maternal antibodies also pass through the placenta to provide the fetus passive immunity for several months after birth. The fetal component of the placenta does not express major histocompatibility complex molecules. Therefore, potential for recognition of the fetal portion of the placenta by the maternal immune system is reduced." |
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Term
| What is erythroblastosis fetalis?(part 1) |
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Definition
| This condition can occur when the mother is Rh- and the fetus is Rh+. (Rh is a highly immunogenic molecule on the surface of RBCs.) If fetal RBCs mix with maternal blood, the mother forms antibodies which can traverse the placenta and lead to hemolysis and anemia. Severe cases also have greatly increased bilirubin which may cause fetal cerebral damage. Usually fetal blood only mixes with maternal blood at birth, so the first Rh+ infant is often unaffected. |
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Term
| What is erythroblastosis fetalis?(part 2) |
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Definition
| However, a second Rh+ fetus may be further compromised. An Rh+ fetus with erythroblastosis fetalis compensates for hemolysis by increasing production of erythroblasts which differentiate into RBCs - hence the name, erythroblastosis fetalis. |
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Term
| What risks exist to the placenta? What can cross it? |
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Definition
D. Viruses that can cross the placenta:
1. Rubella - German measles
2. Cytomegalovirus - mononucleosis
E. Some bacteria (eg. syphilis) can cross the placenta." |
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Term
| What can alcohol do to the fetus? |
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Definition
| . Chronic alcohol consumption increases the risk of fetal alcohol syndrome. |
|
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Term
| What can cocaine do the fetus? |
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Definition
| A. May lead to fetal/newborn addiction. B. Preterm labor occurs in 25% in women using cocaine compared to 8% in women without cocaine. This is possibly due to increased constriction of placental blood vessels and/or increased contractility of the uterus. Abnormal blastocysts occur at a significant frequency and most are probably never realized to exist. Other abnormal blastocysts persist |
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Term
|
Definition
| Gestational trophoblastic tumors (GTTs) encompass a number of neoplastic disorders derived from trophoblastic cells. Such disorders include partail and complete hydatidiform moles, as well as choriocarcinomas |
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Term
|
Definition
Hydatidiform Mole B. GTTs are uncommon and have a high cure rate (90-95% for choriocarcinomas). C. Hydatidiform moles occur in 0.1-0.5% of pregnancies. About 80% of GTTs are non-malignant hydatidiforms.
- All GTTs are characterized by high hCG levels." |
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Term
| What increases molar incidence? |
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Definition
| : D. Molar incidence increases with extremes in maternal reproductive age: incidence is increased in women younger than 20 and older than 40 years. Incidence is also increased with prior molar pregnancies, lower socioeconiomic status, and certain ABO blood groups. Paternal age does not appear to be a significant factor in the incidence. |
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Term
| What happens to cells that complete hydatidiform? |
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Definition
| "E. Cells of a complete hydatidiform mole can be diploid - usually the result of a sperm fertilizing an oocyte with a degenerated female pronucleus (46XX). The paternal chromosomes may duplicate resulting in a diploid cell - an extreme example of the phenomenon of paternal imprinting. There is no embryoblast. It is further characterized by diffuse trophoblastic hyperplasia and diffuse villous edema. |
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Term
| What happens to partial hydatidiform? |
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Definition
| F. Partial hydatidiform moles have partial embryoblast development and are usually triploid with 2 sets of paternal chromosomes (dispermic fertilization) of a normal oocyte (69XXY). Trophoblastic hyperplasia and villous edema are focal. |
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Term
| What do hydatdiform trophoblast cells secrete? |
|
Definition
| G. Hydatidiform trophoblastic cells secrete hCG to maintain pregnancy giving an abnormally high hCG — a partial basis for diagnosis particularly for complete hydatidiform moles. |
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Term
|
Definition
| Moles are usually spontaneously aborted in the second trimester. However, remnants of trophoblastic cells may (5-10%) form tumors resulting in persistent trophoblastic disease. Tumors are usually benign, but sometimes become malignant choriocarcinomas characterized by extensive vascularization and uterine bleeding. |
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Term
| Events of Gastrulation(1) |
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Definition
| . A primitive streak begins to develop at ~day 15 at the posterior (caudal) end of the bilaminar blastodisc. It proceeds anteriorly (rostrally, cranially). |
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Term
| Events of Gastrulation(2) |
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Definition
| The streak establishes bilateral symmetry (left vs right) and cranial vs caudal (anterior vs posterior) polarity. Transplantation of the caudal region of an pre-gastrulating embryo into another embryoblast results in another A/P axis by at least partial formation of another primitive streak." |
|
|
Term
| Events of Gastrulation(3) |
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Definition
| Content: "2. The streak becomes a primitive groove with a thickened anterior end called Hensen’s node, or primitive node, |
|
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Term
Events of Gastrulation(4)
What is gene expressed in primitive node? |
|
Definition
| Henson’s node or primitive node is an organizer for gastrulation. The gene, nodal, is expressed at the primitive node. Nodal mutations do not form a normal primitive streak and gastrulation is abnormal." |
|
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Term
| Events of Gastrulation(5) |
|
Definition
| As Hensen’s node regresses posteriorly, epiblast cells move toward the midline, obtain a bottle-like morphology, and invaginate into the space between the overlying epiblast and hypoblast |
|
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Term
| Events of Gastrulation(6) |
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Definition
| 5. Invaginating cells displace the hypoblast cells to become the definitive endoderm — one of the germ layers. |
|
|
Term
| Events of Gastrulation(7) |
|
Definition
| 6. Invaginating cells fill in the space between the epiblast and forming endoderm to become the embryonic mesodermal germ layer cells (~ day 16). |
|
|
Term
| Events of Gastrulation(8) |
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Definition
| 7. The remaining epiblast cells become the ectodermal germ layer." |
|
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Term
| Events of Gastrulation(9) |
|
Definition
| Therefore, 3 germ layers are organized at gastrulation. 9. Invaginating cells migrate laterally and anteriorly. Generally, the first to invaginate in ends up the most lateral. This can be shown by fate mapping by cell tracing or lineage analysis using quail/chick chimeras |
|
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Term
| What regions do not have mesoderm after gastrulation? |
|
Definition
| Regions that do not have mesoderm after gastrulation: 1. Oropharyngeal membrane (Buccopharyngeal membrane) - oral opening 2. Cloacal membrane - anal opening" |
|
|
Term
| Notochordal Process(part 1) |
|
Definition
| The notochordal process is formed by cells that invaginate through Hensen’s node and migrate rostrally. This tube is initially hollow but then fuses into the underlying endoderm layer. A transient opening is then created between the amnion and the yolk sac. |
|
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Term
| Notochordal Process(part 2) |
|
Definition
| This opening is the neurenteric canal. The cells of the notochordal process then egress from the endoderm layer and form a solid rod called the notochord. |
|
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Term
| What does notochord form? |
|
Definition
| the notochord itself forms the nucleus pulposus in fetal/young intervertebral dics and these cells are replaced later in life by other cells of mesodermal origin." |
|
|
Term
| Where does development generally occur now? |
|
Definition
| Development now in general occurs in a rostral to caudal gradient. Developmental defects are associated with abnormal primitive streak formation and abnormal gastrulation. |
|
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Term
| What are Sacrococcygeal teratomas? Caused by? Characteristics? |
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Definition
| 1. Sacrococcygeal teratomas A. 1:37,000 births; most common tumor in newborns. B. More frequent in female newborns. C. Caused by persistence of pluripotent primitive sacrococcygeal region. D. Derivatives of all 3 germ layers are often evident |
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