Reproductive System
READING ASSIGNMENT: Chapter 17, Clinical Anatomy and Physiology for Veterinary Technicians
Chapter 12, An Illustrated Guide to Veterinary Medical Terminology (might be helpful)

                                      The Female Reproductive Tract   

The female tract consists of paired ovaries, ovaducts and uterine horns. The uterine horns merge to form the body of the uterus which continues on as the cervix and then the vagina. It ends at the external opening the vulva. The broad ligament suspends the female reproductive tract from the body wall.  

femalerepro.gif (11363 bytes)
Graphics reprinted with permission by the copyright owner, Hill's Pet Nutrition Inc.

a) ovary  b)  ovarian artery and vein  c) suspensory ligament   d)  uterine horn
e & f) colon and rectum   g)  urinary bladder    h) ureter

Parts of the female reproductive tract:

The ovaries:
The ovaries produce the ova (eggs) and hormones. They are located caudal to the kidneys and are suspended from the body wall by part of the broad ligament. The ovarian pedicle contains the ovarian artery and vein. That part of the broad ligament that suspends the ovaries is termed the suspensory ligament.

The oviducts:
The oviduct is the small tube which extend from the ovary to the uterine horns. The oviduct carries the ova into the uterine horn. At the end nearest the ovary a funnel like structure, the infundibulum catches the ovum when it "drops" from the ovary.

The uterine horns:
The uterine horns are lined with a vascular and glandular mucosa and contain smooth muscle. There is species variation in the relative size of the uterine horns, species having "litters" often have larger and longer horns. The embryo is implanted here.

Species variation in uterine horn anatomy
A)  cat   B) cow   C)  horse   D)  human (notice the less distinct horns in species normally giving birth to one or two babies).

The body of the uterus:
The body of the uterus is formed by joining of the two uterine horns.

The cervix:
The cervix contains connective tissue and muscle which forms a firm tube like sphincter. The cervix is usually "closed", because the muscular sphincter contracts and closes the  cervix. The cervix acts as a barrier to foreign substances except during fertilization and birth when the sphincter is relaxed or opened.

The vagina:
The vagina extends caudally from the uterus and is located within the pelvic canal. This is the area where sperm are deposited during breeding, in many species this is also the area where the urinary tract opens via the urethra.

The vulva:
The vulva is the external opening of the female reproductive tract.

 a) What structures are removed for the ovariohysterectomy (spay)?


Hormones involved in the female reproductive cycle:

Several hormones regulate estrus, the reproductive cycle in female animals. 
The time of hormone secretion and their actions vary slightly among species. 
For example the female cat is a "reflex or induced ovulator" - she does not drop an egg (ovulate) until after breeding, thus her hormonal timetable is somewhat different than other species.

Follicle stimulating hormone: 
Follicle stimulating hormone (FSH) initiates the growth of the follicle (the ova and its support cells). It is secreted from the anterior pituitary gland.

Luteinizing hormone: 
Luteinizing hormone (LH) also stimulates the growth of the follicle, in addition it stimulates the rupture of the ova from the ovary. 
It assists in the conversion of the area where the ova ruptured (on the ovary) into the "temporary" endocrine gland the corpus luteum. This process is termed luteinization. LH is also secreted by the anterior pituitary.

Estrogen is secreted by the ovary. It functions to prepare the uterus for pregnancy and causes the female secondary sexual characteristics.

b) What are female secondary sexual characteristics?

Progesterone is secreted from the corpus luteum or "yellow body", the area that the ova was ruptured from the ovary, early in pregnancy. Later in pregnancy progesterone is secreted by the placenta. Progesterone is responsible for maintaining pregnancy.

Certain prostaglandins are essential in the reproductive cycle at specific points. The lysis (destruction) of the corpus luteum, rupture of the follicle, and uterine contractions at birth are all also stimulated by reproductive prostaglandins, such as F2Alpha.

Control of the female reproductive cycle:

A complex sequence of secretions regulates the estrus cycle in the female.
The FSH and LH levels are controlled by a feedback loop involving estrogen and progesterone. Basically, FSH and LH production is decreased when progesterone levels rise. 
This is logical because during pregnancy progesterone is high and there is no need for estrus cycling or production of ova.

Although there is considerable difference between species regarding the levels and times that the various hormones are secreted the following graph demonstrates the basic relationship between the blood levels of the four hormones.

female hormonegraph.tif (45778 bytes)
The small vertical line on the horizontal axis represents ovulation.
a)  estrogen  b)  FSH  c)  LH  d)  prostaglandin F2A

The phases of the estrus cycle:

The estrus cycle is divided into four different phases, the length of the various phases is different between species. The species variations are studied in Animal Breeds and Behavior (VET 116).

1) Proestrus:
This phase involves the development of the reproductive tract and follicle and the secretion of estrogen, this "get ready" phase is regulated by FSH and LH.

2) Estrus:
This phase also termed "heat" is the period of sexual receptivity. Ovulation occurs here, when the egg is dropped from the ovary and fertilization also occurs. 
At ovulation FSH drops and LH surges or increases.

3) Metestrus:
In this phase progesterone is secreted from the corpus luteum. If fertilization and implantation occur then the normal reproductive cycle is suspended during pregnancy.

4) Diestrus: 
This is a period of hormonal inactivity between the next estrus cycle.

"Without" estrus, this is a prolonged period of hormonal inactivity.



OOgenesis.tif (23962 bytes) 
Oocysts developing at peripheral area of ovary
a)  enlarged fluid filled follicle  
b)  ovum rupturing from follicle  
c)  corpus luteum "yellow body"

Oogenesis is the development of the ova or egg inside the ovary. 
Only a small number of ovum mature in the female lifetime, compared to sperm production in the male. It is estimated that about 400 ova mature in the lifetime of a human female, compared to approximately 5 million sperm that are produced in one ejaculate of the human male. 
Oogenesis occurs after puberty and involves cellular sexual reproduction, termed meiosis. 
During meiosis, (unlike mitosis), four cells are formed. 
In females only one viable cell (ova) results, that particular ova has received most of the cytoplasm during meiosis and it is able to nourish the developing embryo until it is implanted in the uterus.

The number of unfertilized ova is probably decreased in species that are "reflex ovulators." The rupture of the ovum in these species occurs after breeding due to a neuroendocrine reflex that stimulates the release of L.H. from the anterior pituitary. This occurs in the cat, ferret, and rabbit and reduces the number ova dropped.

There is a continual secretion of progesterone from the corpus luteum  to "maintain" pregnancy. (See the unit on embryology for description of early pregnancy). 
During later gestation the progesterone is produced by the placenta. The attachment of the fetus to the uterus varies among species. 
In the dog and cat the fetal placenta is attached to the uterus only around the middle (in a belt like fashion) of the fetus. This is termed zonary placentation. 
In the horse and hog the entire placenta is attached throughout its surface, this is diffuse placentation. 
In cattle and other ruminants the placenta and uterus are fused together at "buttons" (the fetal cotyledeons and maternal caruncles.) This is termed cotyledonary placentation.

placentas.tif (30569 bytes)


Near the end of pregnancy the fetus secretes A.C.T.H. (Adrenocorticotropic hormone) which stimulates increased cortisol levels in both the fetus and the mother. The cortisol is believed to then stimulate prostaglandin and estrogen secretion from the uterus. 
This in turn stimulates the secretion of oxytocin which causes uterine contractions and birth. Oxytocin also causes milk letdown and passing of the afterbirth.


Mammary glands and milk production

mammarygland.tif (31466 bytes)Cross section of mammary gland

Mammary glands are modified sweat glands. There is species variation in the numbers, location and anatomy of the glands.

Mammary glands are composed of connective tissue (to provide support and structure ), blood vessels, lymphatic vessels and glandular tissue. The mammary gland contains alveoli (somewhat like the lungs) where milk is stored and secreted. The alveoli are connected by a duct system and empty into the teat.
Milk is composed of: 

Specialized enzyme systems in the mammary glands transform blood components to milk (milk fat, sugars, and proteins). The actual mechanisms of this transformation not well understood.

The variation between species in different components of the milk can be seen below.species             fat%           protein%      lactose%      ash%

cat                                7.1.                10.1                4.2             0.5

dog                               9.5                  9.3                 3.1             1.2

horse                            1.6                  2.4                 6.1            0.5  

Jersey cow                   5.5                  3.9                 4.9            0.7

c)  What does this tell us about substituting different milk sources for newborns?
What is mastitis?


                                The male reproductive system

malerepro.gif (16982 bytes)
Graphics reprinted with permission by the copyright owner, Hill's Pet Nutrition Inc.

a)  urinary bladder  b)  testicular vessels  c)  ureter  d)   colon  e)  rectum
f)  prostate gland  g)  pelvic symphysis  h)  spermatic cord   i)  ductus deferens
j)  testicle  k)  penis  l)  bulbus glandis  m)   prepuce

The male reproductive system consists of:
The paired testicles, surrounded by a "skin sac" the scrotum.
The epididymis which extends from each testicle. It is a long tubule where the sperm mature and are stored.
The ductus deferens (also called the vas deferens) is the tubular continuation of the epididymus into the urethra. The urethra is the common passageway for both urine and semen.
The accessory sex glands (these vary among species) including the prostate gland (present in all domestic animals), the bulbourethral gland and the vesicular glands.
The penis, which carries the semen into the female reproductive tract, and the protective skin surrounding the penis, the prepuce.

The Testicles:
The testicles are composed of tightly coiled tubes, the seminiferous tubules. 
There are about 900 per testicle, which are separated by connective tissue septa. 
The tubules produce the spermatozoa or "sperm".  Millions of spermatozoa are produced daily in most healthy, young male mammals. 
The spermatozoa develop from "stem cells" which line the seminiferous tubules. 
These cells first divide by mitosis, then later some cells will undergo meiosis to become spermatocytes, which finally divide to form the sperm.
After the sperm are formed in the tubules they are carried to the epididymis in fluid. There are also "support cells" inside the tubules, the sertoli and leydig cells. The testicle is surrounded by two layers of connective tissue, the tunics.

seminiferoustubule.tif (52406 bytes)
Cross section of semineferous tublue
a) center of the tubule with formed spermatocytes 
b)  stem cells

During development of the male the testicles "descend" from inside the abdomen, through an opening (the inguinal canal) into the scrotum. In livestock most males are born with descended testicles; in dogs the testicles descend shortly after birth normally. 
When the testicles do not descend the animal is termed cryptorchid. If the testicle remains inside the abdomen the animal is usually sterile, since the high temperature inside the body inhibits the development of the sperm. Sometimes the testicles will descend only partially and stop at the inguinal canal. These animals are usually fertile.

sperms.tif (20933 bytes)
Various shapes of sperm
#1)  bull  #2) dog  #3)  rat  #4)  avian

The scrotal temperature is about 2 degrees C cooler than the body temperature.

d)  What significance does this have for male animals with undescended testicles?

testicle.tif (49430 bytes)

a) head of epididymus 
b)  testicular vessels
c)  spermatic cord (vas deferens and testicular vessels)

The epididymis:
The epididymis is divided into three portions, the head, body and tail, which are easily visible attached to the testicle. In the male human the coiled epididymus is about 18 feet in length. It is the storage and maturation area for sperm (for about one month) before ejaculation.

The spermatic cord:
The spermatic cord (which is severed and ligated during castration) contains the testicular artery and vein, nerves, lymphatic vessels, the cremaster muscle, and the ductus deferens.

Accessory sex glands:
The accessory sex glands secrete fluid which contain sugars and vitamins to nourish the spermatozoa. About 90% of the ejaculate is fluid from the accessory glands.

The Penis:
The penis is the tube-like structure which contains a common passageway for the urinary and reproductive tract, the distal "free" part of the penis is called the glans. The penis contains erectile tissue which fills with blood and becomes enlarged during breeding. There is considerable variation among species in the shape, size and even location of the penis.

Hormonal regulation

From the hypothalamus, the gonadal releasing factor travel to the pituitary gland which secretes FSH and LH.(Yes, males do secrete follicle stimulating hormone)
The FSH stimulates the development of the sperm. The LH stimulates the production of testosterone.
The Leydig cells of the testicles produce testosterone. It is secreted in small amounts in fetus and neonate, then increases greatly at puberty.Testosterone (also called androgen) causes the typical male sexual characteristics including: increase muscle mass (up to 50% more than female), increase calcium (in the bone) and bone thickness, increase numbers of red blood cells and increase metabolic rate.

In the dog, the enlarged part of the penis the bulbus glandis, assists in the "tying" process during breeding. This is the unique feature of canine copulation when the male is trapped inside the female vagina.

Textbook Assignment
Clinical Textbook for Veterinary Technicians by Bassert and McCurnin

Please answer these questions and return answers by e-mail to Dr. Bidwell @ abidwell  Assignment will be “spot checked” and logged in and answered e-mailed back to student after receiving assignment. The student is responsible for noting the correct. The questions might be included on exams

Reproduction – chapter 17

1. What makes the reproductive system very different in its function compared to other body physiological systems?

2. What are the 2 ways that animals can have the exact same genetic make up?

3. Why don’t the ova and sperm have diploid numbers of chromosomes in their nuclei?

4. If the interstitial cells of a stallion were nonfunctional what would he lack?

5. What is the function of the cremaster muscle?

6. Define orchiectomy.

7. What is the heat exchange mechanism of the testicles?

8. How many layers of tissue surround the testicles?

9. Which cells “nurse” the developing spermatozoa?

10. List 4 structures inside the spermatic cord.

11. Which common domestic species doesn’t have bulbourethral glands?

12. Which species has the largest prostate gland?

13. From looking at diagram 17-14, which species has a uterus that appears to support multiple embryos (liters)?

14. Define multiparous.

15. Explain induced ovulation and list 3 species that are induced ovulators.

 16. What does the statement “the cervix is open at both ends of the cycle” mean?

17. Name a monoestrus female.



Answers to italized questions.

a) What structures are removed for the ovariohisterectomy (spay)?  The ovaries, oviducts and horns of the uterus

b) What are female secondary sexual characteristics?  Breast development, increased deposits of fat etc.

c)  What does this tell us about substituting different milk sources for newborns?
What is mastitis?  It is not giving the young animal a balanced diet.  Mastitis is inflammation of the mammary glands, a common disease in dairy cattle.

d)  What significance does this have for male animals with undescended testicles?   These animals are usually sterile, since the higher temperature within the body causes death of the sperm.


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