The Greeks proposed that:

1.     the fetus arose from menstrual blood and was activated by seminal fluid,

2.     sex determination depended on the darkness of the coagulum,

3.     heat was required to achieve a male fetus (preg during hot month of add heat)Snakes sex can change by adding heat, and

4.     the right side of the body was more active and nobler which indicated that males were produced there.

a.     the right ovary produces males and the left ovary females,

b.     ovaries alternate in activity, so to determine the sex of the offspring just not the sex of the last child, count the menstrual cycle between them.  If you had a son and 10 cycles between f-m-f-m-f-m-f-m-f-m.

conducted the first artificial insemination in the dog.

used the vaginal smear as a bioassay for estrogen.

purified estrogen from urine of pregnant women

It has been estimated to get 1 mg of estrogen it would take about 4 tons of pig ovaries

: in fact, most of what they discovered we take for granted today.

Some people think that science and experiments are all exact and very thoroughly planned out.  Hopefully that is true most of the time, but I’ll tell you a couple of stories about past experiments that are a bit different.

decided that he would isolate this compound from the urine of pregnant cows.  They collected tubs of urine from the cows at the dairy barn and took it to the lab.  Now the smell of the urine was bad enough, but when they concentrated the urine by boiling it, the smell was almost unbearable.  Come to find out, there is very little, if any, estrogenic material in pregnant cow urine.

he and his colleagues were trying to freeze sperm from roosters to aid the artificial insemination industry.  They were attempting to add sugar to the mixture without much success.  Polge decided to have one more try so he used a bunch of different types of sugars to see which would work best.  The next day he found out that one of the sugars had almost magical properties and the sperm could be frozen then thawed and remain alive.  When he went to see which sugar was responsible (because he didn’t record it at the time), he found that the labels on the bottles of sugar solution that he used had all fallen off.  So he had no idea what the sugar was.  They had to chemically analyze the solutions that were mixed with the sperm to finally find out that it was glycerol that he had added.

is the testis

The testis is paired and in the domestic animals are located in the scrotum.  Some animals, like the elephant and the whale, have abdominal testes

is to produce

(1) sperm and

(2) testosterone

are formed in the testes by the process of spermatogenesis and we’ll talk about that in a week or so.  Once the sperm are formed they leave the testis through the epididymis.

1.     to absorb liquid,

2.     to store sperm (which may mature during this storage), and

3.     to possibly resorb defective sperm.

It takes 7-13 days for sperm to get through the epididymis. (use male to much less fertail because of not having enough time to mature)

The vas deferens transports sperm from the tail of the epididymis to the urethra.  The vas deferens has a muscular wall that contracts at ejaculations, forcing the sperm up and out.

vas deferens then pass through the seminal vesicles

seminal vesicles

Just past the point where the bladder empties into the urethra you’ll find the prostate gland.  This gland supplies volume for the semen and in the bull is responsible for most of the odor of the semen.

The urethra then runs through the penis to the outside of the body.

1. Scrotal muscles

2. Sweat glands

3. Pampiniform plexus

1.     Scrotal muscles 

(a)   the cremaster muscles line the inside of the scrotum and pull the testicles up toward the body in cold weather.

(b)  Tunica dartos muscles are inserted into the skin of the scrotum in such a way that when the muscles contract, it makes the skin fold to conserve heat.

2.     Sweat glands (scrotum)

testis itself is made up of these convoluted tubules

The tubules themselves are very convoluted and can be up to 1m in length.  The tubules are responsible for formation of the sperm cells.  IN the man there may be as many as 1200 seminiferous tubules in each testis.

The seminiferous tubules themselves are

made up of several cell layers:

1.     noncellular layer – makes up the boundary of the tube

2.     smooth muscle layer – responsible for peristaltic movement

3.     Sertoli cells – surround the undeveloped germinal cells and give them nutritive support.

The lumen of the siminiferous tubule is fluid filled and the spermatozoa are moved along with the fluid by both the peristaltic movement of the seminiferous tubules and the continued addition of fluid to the lumen.  The seminiferous tubules empty into the Rete testis, which leads to the epididymis.

area in between the seminiferous tubules

This area contains blood vessels, lymph vessels, nerves, and leydig cells.

is made up of fibroblasts and collagen.

is a capusul that surrounds testis

1.     fibroelastic – bull, boar, and ram, not much erectile tissue (penis doesn’t become erect the sigmoid flexure becomes rigid and pushs penis out of the sheath.

2.     vascular – horse and man, largely erectile tissue

3.     os penis – dog, cat, rats, and mice, bone (baculum)

Upon sexual stimulation the penis becomes erect by filling with blood. Depending on the species, the blood filling is more important. In animals with a fibroelastic penis like the bull filling with blood causes the sigmoid flexure to straighten out, but in the horse it is very important.  Blood pressure in the erect penis can reach 7000 psi which is quite remarkable.

 is a spongy erectile tissue, which is continuous with the veins of the penis.  Filling of this area causes erection.

 spongy erectile tissue surrounds the urethra.

the number of sperm and volume of the ejaculate varies by species also:

                         Volume ofSperm (mL)                      Sperm Concentration

Bull                              3-8                                                     3-16 billion

Ram                            .8-1.2                                               1.3-3.6 billion

Boar                          150-300                                               30-90 billion

Stallion                       30-100                                                 6-40 billion

 During natural insemination the female can be bred more than one time, so the number of sperm utilized to fertilize one egg could be immense. 

The two types of cell division are:

1.     mitosis

2.     meiosis

Mitosis occurs in somatic or body cells and certain germ or reproductive cells. Mitosis results in the duplication of the original cell (called 2n or diploid).

            If we look at the nuclear changes that occur during the process of mitosis, we’ll see that it has been divided into five phases.  The process of mitosis is a continual process so these phases are artificial.

1.     Interphase

 2.     Prophase

 3.     Metaphase

 4.     Anaphase

 5.     Telophase

is the stage between all divisions; no chromosomes are visible.  Cells spend about 4/5 of their life in this stage.  The cell life can be diagramed to a cell cycle.

                       m = mitosis

                      G1,  G2 = gap phase

                       s  = synthetic phase

is the phase that starts when the chromosomes become visible.  The chromosomes have already duplicated at this time to form 2 chromatids, which are joined together at the centromere.  As prophase continues, the chromatids become shorter and thicker.  The nuclear membrane begins to disappear and a system of microfibers called asters (spindle) begins to form from the centrioles.

The chromosomes become oriented on the spindle fibers on an equatorial plane.  With a sudden division of the centromeres, metaphase is completed.

The chromatids separate and move toward the centrioles on the spindle fibers. The cell begins to pinch off.

The nuclear membrane begins to reform and further pinching-off occurs.  The spindle fibers disappear as the cell wall is completed and the nuclear membrane is fully formed.  The chromosomes become longer and thinner and eventually become undetectable.

The second type of cell division   This occurs only in certain germ cells such as primary spermatocyte > secondary spermatocyte > spermatid/ primary oocyte > secondary oocyte > ootid.  Meiosis results in two cells with only half the normal number of chromosomes,  called IN or haploid.  So for example, in cattle there are 60 chromosomes (30 pairs) in sperm and oocytes there are only 30 chromosomes.

                        Cattle = 60             Sheep = 54

                        Swine = 40             Horses = 64

The chromosomes in the primary spermatocyte are contracted and also spherical.  When they lose this tension, meiosis proper starts.

Leptotene – The chromosomes are in a bouquet with the centromere ends in a single limited area just inside the nuclear membrane

Zygotene – The homologous chromosomes pair up.

Pachytene – Chromosomes divide into 2 chromatids and each is connected by the centromere forming a tetrad.

Diplotene – Crossing over of portions of the two homologous chromosomes occurs forming a chiasma (crossover point)

Diakinesis – the tetrad separates.

the chromatids lie on the equatorial plate; the centromere does not divide.

each chromosome is still made up of two chromatids, the 2 members of the tetrad separate to opposite poles.

Telaphase

chromatids contract, but remain visible and the nuclear membrane reforms, cell membrane pinches off.

because the chromatids remain visable a true interphase does not occur.  When the tension is released from the chromatidsthe second prophase of meiosis begins.

chromosomes orient on the equtorial plate.  The centromere divides and the two chromatids separate.

The chromatids separate to the opposite poles.

chromosomes become undetectable, the nuclear membrane reforms and the cell membrane pinches off.

1.     Sertoli cells -provide nutrients to the developing germ cells.

2.     Developing germ cells-The germ cells undergo a series of cell divisions and morphological changes

1.     Stem cells (spermatogonia) – a series of cell divisions occur resulting in the primary spermatocyte.

2.     Spermatocytes > meiosis > spermatids  This process is called spermatocytogenesis.

3.     Spermatids > maturational changes > spermatozoa   This process is called spermiogenesis.

Ao spermatogonia > A₁ > A₂ > A₃ > A_{4  >}  Intermediate spermatogonia > Type B spermatogonia.

 The type B spermatogonia divides once or twice to produce primary spermatocytes >secondary spermatocytes >spermatid.

(In the bull, the process of development from spermatogonia to spermatid takes about 45 days.)

he actual cell division between cells during spermatogenesis is incomplete which leaves cellular bridges between the cells.  This is for communication between cells so that there is synchronous development.

      The process of spermatogenesis results in 512 spermatids form each spermatogonium.

The development of the spermatid to the spermatozoa is called spermiogenesis and this is a maturational process.

1) condensation of nuclear chromatin (Nuclear condensation );

2) the development of the acrosomal cap; and

3) formation of the sperm tail.

  Development of the acrosomal cap

The acrosome plays an important role in fertilization.  It originates from the Golgi complex within the spermatid.  This process can be divided into three parts:

a.Golgi phase

b. Cap phase

c. Acrosomal phase

  possibly before meiosis occurs in the spermatocyte, the Golgi apparatus seems to synthesize protein granules called proacrosomal granules.  These fuse together to form a single acrosomal granule.  The acrosomal granule surrounded by the fused Golgi then migrate toward the nucleus and become attached to it.

The acrosome spreads out over the nuclear membrane, becoming flattened.  This forms a double layered cap.

The acrosome indents into the nuclear membrane, reshaping it.  Any extra cytoplasm from the Golgi is displaced to behind the nucleus and the head is rotated toward the basement membrane.

Formation of the tail

At the end of the second meiotic division, the two centrioles formed don’t disappear --  they migrate to the position opposite the Golgi apparatus, just beneath the cell membrane.  The distal centriole is located perpendicular to the cell membrane and the proximal centriole is above the distal at a right angle to the cell membrane.

gives rise to the tail of the spermatozoa.  The tail begins as an inner pair of microtubules surrounded by nine pairs of microtubules give rise to nine pairs of course outer fibers.  These are much larger than the original microtubules.

The mitochondria of the spermatid migrate down the cytoplasm to form a double helical coil around the midpiece of the sperm.  The mitochondria are lined up end to end

Release of the spermatozoa from the Sertoli cell to the lumen of  the seminiferous tubule is called Spermiation.  When the spermatozoa is released, the residual body,  which is the entire cytoplasm of the original spermatid,  breaks off leaving a cytoplasmic droplet at the neck of the sperm.  So if we look at the sperm, it’s made up of;     1)  Head       2) Midpiece      3) Tail

(As we said already, the sperm are released into the retetestis and moved along by the fluid pressure up into the epididymis.)

Research has shown that the pattern of development of spermatozoa from spermatogonia is very organized.  In the bull, about 7 billion spermatozoa are released from Sertoli cells each day.  If you take a cross section of the seminiferous tubule, you’ll see several stages of development with the least developed near the basement membrane and the highest at the top.  The coordination of the development between cells may be caused by ; 1) cytoplasmic bridges 2) Sertoli cells 3)Release of residual bodies by spermatozoa

The rete testis empties into the epididymis.  Remember that the function of the epididymis was to;

1)             absorb water            2)             allow the sperm to mature

Sperm are moved through the epididymis by muscular contrations of the duct wall.  The time required to pass through the epididymis is :

                                       Bull – 7 days                      ^ ­ frequency of

Boar – 12  days                      ejaculation transit v

                                Ram – 16 days                             time by 10-20%

A)            loss of cytoplasmic droplets

B)            gain of fertilization ability

C)            potential for sustained motility

The droplet is left when the residual body breaks off during spermiation and is located at the neck of the sperm

During passage through the epididymis, the droplet moves down the neck almost to the tail.  It is believed that the droplet is moved by the sperm, basically doubling on itself, and the droplet translocates.

There is also a change in the droplet itself during the passage through the epididymis. At the head of the epidiymis, the droplet is full of membrane-bound vesicles, But at the tail of the epidiymis the number of vesicles are reduced and some of them have collapsed on themselves. This indicates that the vesicles are being used either by the sperm or by the droplet itself. At the tail of the epididymis the droplet is shed by being pinched off.

Structure of the acrosome may change.  In some species this change is quit marked—like the guinea pig:

                                    caput

                                    cauda

            But in other species the change isn’t noticable-

            Bull:                caput

                                    cauda

permability goes down with the passage through the epididymis.  There’s a change in the specific gravity of the sperm

   Caput                        1.0918                          may be due to the change in

Cauda                        1.3519                              the cytoplasmic droplet.

The electrical charge of the sperm itself changes.  This was tested by putting sperm collected from different parts of the epididymis in an electric field and see which way they migrated. 

Anode  (+)  and Cathode  (-). 

           % oriented toward anode

caput              13%                                          So there is a negative

corpus            90%                                                charge on the

cauda              98%                                                sperm cell.

,  they must first attach to it; so two different tests have been conducted to determine this ability

1 Agglutination test- On other card

2 Egg attachment-if put sperm in with an egg,  can determine the percent attached

distal cauda     28.6

                                           Ejaculated sperm  55.0

 if put sperm into a solution can determine how much agglutination occurs between the sperm.

caput -                                                            - = no agglutination

corpus +                                                         + = agglutination

cauda  +++

Cold shock is the ability of the sperm to survive a drop of temperature and remain viable.  

**** look at experiment about 4 rams exposed to cold shock****

(They also looked at the percentage of sperm that still had cytoplasmic droplets attached  and They concluded that the higher the percent of cytoplasmic droplets, the greater the resistance to cold shock.)

caput – 0%

cauda   84%

while there is also a difference in the concentration of sperm in the different areas.

            So there are many differences between areas of the epididymis and it takes 7-13 days for the sperm to pass through these ducts.

AI has been practiced for the last 50 years.  In the U.S., AI is most widely used on dairy farms.  Beef cattle producers tend not to use AI unless they are producing purebred seedstock and AI in sheep and swine is not practiced very often.  AI is frowned upon in horse production because of the possibility of falsifying the sire of a foal.

                                Sperm Concentration

 Bull                                3-16 billion

 Ram                               1.6-3.6  “    “

 Boar                               30-90    “    “

 Stallion                             6-40    “    “

            Using AI, at least in cattle, they package about 10 million sperm per package; so in the case of the bull above, we could get 300-1600 inseminations out of that one ejaculate.  So you can see the impact a great bull could have on the cattle population using AI. To get the 300-1600 inseminations, the semen has to be diluted or extended and frozen or preserved.

1. Nutrients- an energy source required aerobic and anaerobic metabolism

2

A good semen extender must have the following characteristics:

Nutrients- an energy source required aerobic and anaerobic metabolism.

Buffering capacity – to reduce the change in pH.  As the metabolic activity increases the pH decreases.  Cooling also has an effect on pH.

Protection against cold shock and freezing damage – egg yolk,  lipoproteins and glycerol are common

Toxicity – should be isosmotic with blood for freezing

Bacterial control – the extender should be sterile as well as adding supplemental antibiotics to stop the growth of bacteria

Cost effective – if the extender costs more then the semen is worth, then the producer won’t buy it

Semen is stored frozen on liquid N2 which has a temperature of –320°F.  Semen has been stored for up to 20 years and remain fertile.

The freezing process varies depending on the company that is packaging the semen, but basically it involves ;

1. cooling slowly to decrease the metabolism

2.glycerate slowly – the glycerol replaces some of the water in the sperm to decrease ice crystal formation in the cells.

Freezing and thawing kills at least 20% of cells.

Semen Collection 

Semen is the combination of sperm and fluid from the testes, excurrent ducts and the accessory sex glands that make up the ejaculate.

Characteristics of the ejaculate are influenced by frequency of ejaculation, sexual preparation, season, breed and sire differences

Semen is made up of sperm from the testes and Seminal fluid serves as a vehical for transport and provides nutrients.

***look at origin of the seminal plasma in boar and bull***

sperm are diluted with the seminal plasma.  These secretions stimulate the almost motionless cells into vigorous motile activity.  This stimulation may be due to the dilution effect, the increased O2 partial pressure or specific substances, like fructose.

In the bull and ram, ejaculation is very rapid and the ejaculate consists of only one fraction; but in other species like the boar, stallion and dog, copulation extends over a longer period of time and the ejaculate has distinct fractions.

Stallion

The semen of the stallion is composed of three fractions, which are ejaculated in sequence.  It takes 10 – 30 seconds to complete ejaculation.

1st fraction -Thin watery, almost no sperm- mainly from urethral and cowpers glands (44% of volume)

2nd fraction- Thin, non-viscous milky, speam rich fraction (33% of total volume)

3rd fraction - Very viscous, highly glatinous, littlor no sperm, mainly seminal vesicle secreation.

As the stallion dismounts from the mare, a small amount of fluid drips from the penis.  This is not a representative sample of ejaculate and it comes from the urethra

Boar

Ejaculate in the boar is a prolonged process that may take from 3-30 minutes.  Boar semen is ejaculated in 3 fractions.

1. Sperm-free – clear liquid, no sperm, fluid comes from accessory glands (5-20%)

2. Sperm-rich – milky color (30-50%)

3. Gel phase – The gelatinous material makes up 20-30% of ejaculate.  The function of the gel phase may be to plug up the female reprodutive tract to stop the lossof sperm

Semen Packaging

Ampules – various sizes

½ cc french straw

¼ cc

¼ continental straw

Microencapsulated semen -  sperm were enclosed in a membrane that would break down when inserted into the female.

Actual semen collection

1.              Artificial vagina

2.              Electroejaculator

is probably used more commonly during semen collection.  The artificial vagina is made up of –

1.              Hard plastic case

2.              Rubber liner

3.              Collecting cone

4.              Collecting tube

Warm water is filled between the case and liner (water should be a little above body temperature) to give the animal the feeling that he’s inseminating the cow.  The collection tube should be insulated in some way to protect the sperm from cold shock.  One way is to immerse the tube in warm water

The bull must be trained to collect, so it takes some time to accomplish this. The bull is brought into the room with either a restrained female or steer.  (In fact, AI studs use steers because they are larger and can withstand the weight of the bulls better.)

The bull is allowed to mount the female and should be encouraged to dismount and remount several times.  This is called false mounting, and it has been shown to increase the number of sperm per ejaculate.

As the bull thrusts the penis, it is directed into the artificial vagina by the technician and the semen is collected.

An added danger when collecting semen from the bull is at ejaculation.  The bull may actually leave the ground, so the technician can get stepped on if not careful.  Also bulls have been known to fall off the teaser animal, so the technician needs to be aware. 

When bulls are collected frequently (up to 4 times a week), they can lose interest in the collection procedure; so to guard against this, the AI stud may want to change things around to keep the bulls’ interest.  Things that can be done would be to –

1.         Use different teaser animals,

1.              Change the location or position of the teaser,

2.              Use more then one teaser

3.              Warm up pen ( have bull watch collection before it)

also semen can be collected using electroejaculation

Frequency of Ejaculation

Semen can be collected quite frequently.  Today AI studs usually collect semen four times (2  x  a day with 3 or 4 days rest) each week.  This gives the bull a rest period, as well as maintain libido (or sexual interest).  Studies have been conducted where bulls were collected daily for up to 32 weeks with no adverse effect in sperm motility, morphology or fertility.

can take measures of semen(on other card)

semen samples can be accepted or rejected on the basis of a variety of laboratory tests.  The tests are aimed at putting out a product of the highest quality and fertility.

1.Volume and appearance     2.Concentration of spermatozoa

3.Motility                              4. Ratio of live to dead sperm

5.Morphology

  Volume gives an indication of the number of sperm present.  Appearance can also indicate concentration, but also can tell if contaminating substances such as dirt, hair, blood or urine is present.  The semen should be milky white in appearance.

Examining the form or shape of the sperm can be conducted at the same time as live/dead counting.  The types of abnormalities have been broken down into two categories:

1.Primary abnormalities – any abnormality involving the head

2. Secondary abnormalities – abnormalities with the midpiece or tail

Very fertile males usually produce semen with less then 20% abnormals, and fertility tends to decrease as the percentage of abnormalities increase.

Male Reproductive Failure

Reproductive failure in the male is mainly involved with spermatogenesis, but could also encompass lack of libido or improper endocrine impulses or responses. 

cryptorchid

(male repro failure)

- first problem that the male could encounter would be if the testes didn’t descend into the scrotum either totally or partiall

- A cryptorchid doesn’t produce sperm cells and it is thought to be caused by the heat of the body effecting spermatogenesis

-experimentally make a male cryptorchis, there will be histological changes in the testes within two days; and by two weeks only Sertoli cells and spermatogonia will be present.  The testes will function normally again if they haven’t been in the abdomen too long.

heating the testes

(male repro failure)

-If the animal is exposed to temperatures above 37°C for long periods of time, this will have an adverse effect on spermatogenesis.

-The cells that are most sensitive to the effect of heat seem to be primary spermatocytes during pachytene and young spermatids

-Heat, whether environmental or body, seems to effect testosterone production.  There is a moderate decrease in blood levels of testosterone, but this has no effect on libido

Cold Effect on Testies 

(male repro failure)

Nutrient supply

(male repro failure)

Energy and protein lack

(Male repro failure)

Essential fatty acid deficient Diets

(Male repro failure)

Vitamin deficiencies

(male repro failure)

Naturally occurring abnormalities

(Male repro failure)

Klinefelter’s Syndrome

(Male repro Failure)

 This condition comes from the male having an extra X chromosome, which may have been a problem during spermatogenesis.  The effected individual has small nonfunctional testes.  The Leydig cells show decreased function.

Sertoli Cell-Only Syndrome 

(male repro failure)

Testicular feminization

(male repro failure)

Mumps Orchitis

(male repro failure)

X-irradiation

(male repro failure)

– Whole body or localized irradiation can produce damage to the testes.  The A spermatogonia seem to be the most effected because they are eliminated after X-irradiation.  Very high doses of irradiation can effect the spermatids, spermatocytes and spermatozoa.  Testosterone production is unaffected but Sertoli cells numbers can be reduced.

Not caused naturally

Chemical damage

(Male repro failure)

Chemical damage can effect the testis directly.  Heavy metals such as:

1. Cadmium,

2. Mercury, and

3. Lead

can have very marked effects on the testes.  And there are many other compounds that I won’t mention that can affect spermatogenesis.

Not caused naturally

1.              ovaries

2.              infundibulum

3.              oviduct

4.              uterus

5.              cervix

6.              vagina

7.              vulva

The ovaries are responsible for the production of the gametes or ova and the reproductive hormones estrogen and progesterone.  The size and shape of the ovaries varies with species, with the cow and sheep having almond-shaped ovaries, the horse ovary is bean-shaped and the sow ovaries are shaped like a cluster of grapes.

1.              medulla – which contains connective tissue and an extensive nervous and blood system.

2.              cortex (contains the oogonia) – is responsible for egg formation and hormone production.

1.              follicle – which contains the developing oocyte and is responsible for estrogen production.

2.              corpus luteum – or yellow body that is responsible for progesterone production.

 is a membranous structure that either surrounds the ovary as

in the sow or sits next to the ovary.  The function of the infundibulum is to catch the egg and funnel it into the oviduct.  In animals where the infundibulum is open, at the time of ovulation it seems to sweep over the surface of the ovary trying to bee at the proper postion to catch the egg.

The oviduct itself is a very convoluted tube that leads from the infundibulum to the uterus.  It is divided into two sections:

1.              ampulla

2.              isthmus

The ampulla is the upper half of the oviduct and fertilization takes place here.

The ampula contains ciliated cells that act to move the ova along down the oviduct.

are to 1) incubate the fetus and

2) expel the fetus at parturition. 

The uterus also undergoes dramatic size changes from breeding to parturition.   In the cow at breeding, the heifer’s whole reproductive tract will fit in the palm of your hand; but at parturition, that same uterus will fill a wheelbarrow

After parturition, the uterus goes through a process of involution, where it decreases in size to try and rejoin its original size and shape

is a very important structure that acts as a barrier to the outside.  As we already said, the uterus is a great incubator; so if bacteria got in, they would have a field day.  So the cervix acts to keep contaminants out of the uterus.  The cervix is made up of a fibroelastic connective tissue that in domestic animals is arranged in rings.  Those rings fit into each other to act as a barrier.  The cervix is tightly closed at all times, except during estrus and parturition. 

The cervix also produces mucus that acts to further block the entrance.  During estrus the mucus is very thin and watery, but most of the time it is very thick.

 is made up of three components, but we’ll lump them all together as the vulva. The individual components are:  1) labia majora, 2) labia minora,  3) clitoris.

The labia again act as barriers to the outside.  They produce an oily substance which probably acts to remove contaminants and lubricate the tissue. The clitoris has the same embryological gives better results at conception.

is the study of hormones or chemical messagers throughout the body.  The field of endocrinology has really expanded over the last 10-20 years, and the definition of a hormones has become very cloudy.  A hormone is a substance produced in the body that has a regulatory effect on specific cells or organs. reproductive physiology there are basically four types of hormones.  They are: 1)Releasing factors/hormones,  2) Gonadotropin hormones3)Steroid hormones 4) Miscelleneous  

that are produced by the reproductive organs and are involved in secondary sexual characteristics, maintenance of the reproductive organs and regulation of the reproductive cycle

are hormones produced mainly by the gonads, but the adrenal glands and placenta can also produce them.  Steroids are derived from a common precursor, and synthesis begins with either acetate or cholesterol from the blood.  The steroid molecules important for reproduction are:

Estrogen – produced by either the ovary or placenta – 18C – 280

Progesterone – produced by the ovary, placenta in some species 21C and the adrenal gland – 310

Testosterone – produced by the testis – 19 carbons. –290

Produced by various organs or cells that effect reproduction

-Placental Hormones ( Placental lactogen, PMSG,HCG) Uterine Hormones (Prostaglandins) others (Relaxin, Inhibin)

These compounds are peptide

hormones, which are molecules made up of amino acids.  The compounds produced are:

            GnRH – gonadotropin releasing hormones, decapeptide

            TRH – thyrotropin releasing hormone, tripeptide

            PRF – prolactin releasing factor

            PIF – prolactin inhibiting factor

            CRF – corticotropin releasing factor

            GHRF – growth hormone releasing factor

            GHIF – growth hormone inhibiting factor (somatostatin)

 are hormones produced or secreted by the pituitary gland.  These compounds can be peptides, polypeptides, protein or glycoprotein in structure.

             Luteinizing hormone (LH)  30,000 MW glycoprotein

            Follicle Stimulating hormone (FSH)  32,000 MW glycoprotein

            Prolactin (Prl)  23,000 MW protein

Growth hormone (GH) 22,000 MW protein

Adrenocorticotropic hormone  (ACTH)  39 amino acids

Melanocyte Stimulating hormone (MSH)

Thyroid Stimulating hormone (TSH)

Oxytocin – octapeptide  (1000 MW)

Vasopressin

Steriod Hormones

• produced mainly by the gonads
• adrenal glands and placenta can produce them too
• derived from a common precursor-synthesis begins with either acetate or cholestreol from the blood

Steriod molecules important for reproduction

• Estrogen- produced by either the ovary or placenta (18 C-280 MW)
• Progesterone- produced by the ovary, placenta in some species 21C and the adrenal gland 310 MW
• Testosterone- produced by the testis (19C, 290 MW)

Miscellaneous Hormones

Placental hormones (placental lactogen, PMSG,HCG), Uterine Hormones (Prostaglandins), others (relaxin, inhibin)

is an interesting organ that lies just below the hypothalamus in an area called the sella turcica.  The pituitary is surrounded by a membrane called the dura mater—which when translated, means tough mother.  But the pituitary lies outside of the blood-brain barrier -

The interesting part of the pituitary is that it is composed of two separate types of tissues.  During embryonic development, a portion of neural tissue is combined or surrounded by oral ectoderm or tissue that goes on toform the pituitary with the neural portion forming the neurohypopohysis or posterior pituitary and the oral portionforming the adenohypophysis or anterior pituitary.

 has direct neural attachments with the brain nuclei that produce oxytocin and vasopressin, so it actually acts as a storage organ, secreting the compounds on demand.

has no neural connection, which should make you ask “How do the neural signals from the hypothalamus reach the anterior pituitary?”  This takes place through the hypophysial portal system.  If you remember from your physiology class, a portal system is one where the arterial blood vessels form a capillary network and then go on to supply an organ or tissue.  The pituitary has this type of system.  Neurons carrying releasing factors end in close proximity to the hypophyseal vessels.  The releasing factors are picked up and transported by the blood to stimulate or inhibit release of the approriate hormone.  This type of control is called Neurohumoral, because the nervous signal controls the humoral response

is an octapeptide, and it is synthesized in the hypothalamus stored in the posterior pituitary.  Recently it has been shown that oxytocin is also produced in the corpus luteum of the cow,  ewe and human.  Oxytocin stimulates muscle contraction in smooth muscles, such as the uterus

**look at the reflex of Oxytocin**

1.              milk letdown

2.              induced parturition  (pictocin)

3.              retained placenta

FSH

(Pituitary gonadotropins )

:  In females, FSH stimulates growth and maturatiuon of follicles; and in the presence of LH, stimulates estrogen production.  It is used in superovulation of cattle (inject 2x daily)

LH

(Pituitary gonadotropins )

Luteinizing Hormone is also a glycoprotien molecule that is produced in basophilic pituitary cells.  It also has two subunits (a & b).  The molecular weight of LH is approx. 30,000.  LH is secreted in pulses that occur at hourly intervals.  This is called tonic release.  Just prior to ovulation, LH secretion is different – you get the preovulatory surge of LH, which can last 6 to 12 hours.

:  in the female LH stimulates progesterone production by the corpus luteum, works with FSH to stimulate estrogen production by the follicle and stimulates ovulation,

In the male, LH stimulates the Leydig cells to produce testosterone.  Some people call LH in the male Interstitial cell stimulating Hormone (ICSH).

Prolactin

(Pituitary gonadotropins )

            is a protein molecule of about 24,000 molecular wight.  It is produced by the acidophils of the pituitary.

            Function:  Prolactin is called the lactogenic hormone.  It is involved in mammary development and milk production but doesn’t actually cause either.  In reproduction, prolactin is important in the rat and mouse for corpus luteum function and maintenance.  This has not been proven in domestic animals though.

Androgens

(Gonadal Steroids)

-       stimulating the last stages of spermatogenesis

-       stimulating growth and development of accessory sex glands

-       stimulates sexual behavior (libido)

-       has a protein anabolic effect

Estrogens

(Gonadal Steroids)

The production of estrogen by a tissue has brought about a theory called the 2 – cell theory.  It seems to require two cell types to produce estrogen.

Female> LH> theca cells> testosterone > follicular cells>estrogen.

Male > LH > Leydig cells> testosterone > sertoli cells> estrogen.

Estrogens have several functions:

- Act on CNS for behavioral estrus (in cow and ewe P₄ is needed)

- Stimulate duct growth of mammary gland

- Have feedback effects on hypothalamus (neg on tonic center, pos on preovulation center)

- Increase calcium uptake and ossification of bone

- Maturation of epiphyseal plates (in ruminants have protein anabolic effects)

Progesterone

(Gonadal Steroids)

is produced by the luteal cells of the corpus luteum. It is also produced by the adrenal cortex and the placenta. Progesterone is a 21 carbon compound with a molecular weight of 310. It is transported in the blood by a binding protein

Progesterone is often used to prevent abortions. It is one of the main ingredients of birth control pills.

called hormone of pregnancy

                        Prepares uterus for implantation

                        Increases secretory glands of endometrium

                        Decreases motility of uterus

Decreases secretion of LH

Plays a role in the induction of estrus

Stimulates lobulo alveolar growth of the mammary gland

Human Chorionic Gonadotropin (HCG) 

(miscellanous hormone)

HCG has mostly LH like activity with slight FSH activity. It is very potent in causing ovulation and will stimulate the Leydig cells of the testis to produce testosterone. It functions in the woman to stimulate the formation and maintenance of the corpus luteum of pregnancy. This hormone is what pregnancy tests are based on. In home pregnancy tests or professional tests, antibodies to HCG react with the hormone to cause a color change in the kit to indicate pregnancy.

Pregnant Mares Serum Gonadotropin (PMSG)

(miscellanous hormone)

 also called Equine Chorionic Gonadotropin (ECG) – This is a glycoprotein of about 68,000 MW seen in the pregnant mare. It is produced by specialized structures called endometrial cups in the placenta. It is first seen in the mare’s blood at about day 40 of pregnancy. Values peak at approximately day 60 and then decline until day 170, after which it is undetectable.

 It has mainly FSH like functions, so it stimulates follicular development in females and sperm production in males. In the mare, it stimulates the formation of accessory follicles after conception which then turn into accessory corpora lutea to produce extra progesterone to maintain the pregnancy.

It is used commercially to induce super ovulation in cattle. It is very potent, but results are quite variable.

Placental Lactogen

(miscellanous hormone)

Placental Lactogen is produced by the fetal portion of the placenta. The molecular weight in most species is 22,000 but in the cow it is 32,000 and the rat has a 40,000 MW form. It is only produced by some species (ruminants, rodents, humans) and its’ function is still unknown. It has growth hormone and prolactin like activities. It has been suggested to be involved in nutrient partitioning during pregnancy.

Relaxin

(miscellanous hormone)

Relaxin is a polypeptide hormone of approximately 5700 MW and it is made up of two subunits. It is secreted by the corpus luteum of pregnancy, as well as the placenta and uterus in smaller amounts.

Function – It stimulates the cervix and vagina to dilate at birth. In the guinea pig it causes separation of the pubic symphasis.

Inhibin

(miscellanous hormone)

 – This compound is also called folliculostatin. It is produced by the sertoli cells of the male and the granulosa cells of the female. The structure is unknown and the mechanism of release is unknown.

Function – It inhibits release of FSH from the pituitary.

Prostaglandins

(miscellanous hormone)

Prostaglandins- this is a group of 20 carbon fatty acids. They act locally and are rapidly degraded. The compounds that we are most interested for reproduction are PGE2 and PGF2a.

                                    PGE2                                                PGF2a 

                                    luteotropic                                    luteolytic

                                    vasodilator                                    vasoconstrictor

Prostaglandins are involved at the ovarian level with ovulation. If you inject aspirin ( a prostaglandin synthesis inhibitor) into the follicle just before the LH surge you prevent ovulation

PGF2a has been used to synchronize estrus mostly in cattle. The only problem is that it doesn’t work during the first 5 days of the estrous cycle.

There are three control points for endocrine secretion. The brain (hypothalamus), the pituitary and the target organ. How is each contol point controlled? This occurs by a mechanism called feedback, which can be either negative or positive.

 – The size, shape or electrical charge of protein hormones prevents them from easily getting into a cell. Because of this the protein hormone receptors are found on the outside cell membrane. The receptors use a lock and key mechanism that will only respond to the hormone that fits.