Term
| What is different about horses in embryonic development vs other mammals? |
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Definition
| it is a blastocyst when it enters the uterus (a morula in other mammals) |
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Term
| Approximately how long is the oviduct? |
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Definition
| 20-30cm depending on the species |
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Term
| What does the trophoblast of the blastocyst do? |
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Definition
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Term
| What steps of embryonic development |
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Definition
1. Zygote travels along uterine horn, doubling in the number of cells each day until 8-celled
2. Morula enters uterus
3. Morula develops into early blastocyst
-trophoblast will form chorion
4. Inner cell mass will become the fetus
4. Endoderm formed after 7-8 days
5. Blastocyst expands & hatches |
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Term
| What are the general steps required for implantation in the uterus? |
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Definition
Recognition (apposition)
Contact (adhesion)
Formation of placenta (invasion) |
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Term
| What is required for placentation to take place? (5) |
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Definition
Concepus must:
-move to proper location in uterus
-stimulate endometrial histotroph production
-prevent luteolysis (Requires P4)
-inhibit maternal immune system
-establish a placenta |
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Term
| What are some strategies for retaining luteal function during early gestation? |
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Definition
-rats: mating triggers luteotrophin release (LH + prolactin)
-primates release chorionic gonadotrophin
-antiluteolyic mechanism in farm animals
All of these allow maternal recognition of pregnancy |
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Term
| Describe the antiluteolytic mechanism of a cow/ewe |
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Definition
Conceptus elongation triggers an increase in interferon protein production, which is recognized by the endometrium
-blocks transcription of oxytocin receptors
-no PGF2-alpha produced
-corpus luteum is not destroyed |
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Term
| What happens if conceptus elongation does not occur? |
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Definition
-oxytocin binds to oxytocin receptor in the uterus
-PGF2alpha secretion increases in the uterine vein
-PGF2alpha is transferred to ovarian artery
-luteolysis is initiated |
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Term
| What role do interleukins play in embryonic development? |
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Definition
LIM (leukemia inhibitory factor)
-expressed by endometrium
-proliferation/differentiation/survival of blastocyst
IL-11
-anti inflammatory effects
-major role in implantation |
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Term
| Describe chorionic attachment in a bovine pregnancy |
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Definition
-microvillar interdigitation form 'mini'velcro (early attachment)
-chorionic invasion of endometrial glands form maxi velcro (21-50 days) |
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Term
| What membrane is involved in the direct attachment of the fetus to the endometrium? |
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Definition
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Term
| What are the different types of placenta? Why is this important? |
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Definition
Haemochorial
-chorion comes in direct contact with maternal blood (human)
Endotheliochorial
-maternal endometrial blood vessels are bare to their endothelium and these come in contact with the chorion (dogs, cats)
Epitheliochorial
-maternal epithelium of the uterus comes in contact with the chorion (pigs, cows)
With direct contact with blood, it is possible to transfer large molecules like antibodies from mother to fetus |
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Term
| Describe placental transport of various molecules |
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Definition
-water & lipid soluble molecules diffuse across epithelium
-AAs, Ca, glucose, vitamins require active transport as they are essential, may need to move against concentration gradients
-diffusion of free FA's depends on species |
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Term
| How does the early embryo transport material? |
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Definition
| uses the allantois initially, then the placenta once formed |
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Term
| Why is active transport of some molecules across the placental membranes important? |
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Definition
-need for glucose increases and digestive capacity of mother decreases as fetus grows
-need to maximize the amount of energy the fetus can receive |
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Term
| What are the 6 layers of the placenta? |
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Definition
fetal endothelium
fetal connective tissues
fetal chorionic epithelium
maternal endometrial epithelium
maternal endothelium |
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Term
| What peptide hormones does the placenta release? |
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Definition
Gonadotrophic hormones: stimulate CL
Lactogenic hormones: stimulates growth of mammary tissue during pregnancy
Relaxin: prevents uterine contraction (with progest.) loosens cervix connection tissue & pelvis ligaments |
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Term
| What hormone is the key to maintaining pregnancy? How is it made? |
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Definition
progesterone
made from cholesterol by the placenta |
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Term
| How is estradiol-17B created towards the end of the pregnancy? |
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Definition
| -fetal adrenal gland produces dehydroandrosterone sulfate which is converted to E-17B by trophoblasts |
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Term
| Why are trophoblasts unable to convert C21 to C19 steroids (estrogen precursors)? |
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Definition
| they do not have the required enzyme 17-alpha hydroxylase |
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Term
| What are some procedures that might induce abortion? |
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Definition
hypophysectomy
ovariectomy
lutectomy
luteolysis
P4 antibodies
These all inhibit progesterone production, unless the placenta is well developed enough to synthesize it itself |
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Term
| Where does progesterone come from throughout the pregnancy of a sow or cow? |
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Definition
produced by corpus luteum
-placenta will take over in the last month of gestation in cows |
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