B110 Female Reproductive Anatomy & Physiology

1. B110 Female Reproductive Anatomy & Physiology

2. Bovine Female Reproductive Parts Estrous Cycle Female Reproductive Process Corpus Luteum Development Embryo and Fetal Development Lesson Outline

3. Bovine Female Reproductive Parts

4. Bovine Female Reproductive Parts

5. Close up of the Cervix

6. Estrous Cycle • Estrus occurs when estrogen levels are high and the female has produced an egg and is receptive to the male. • Over a period of time, many changes take place in the reproductive system in response to changing hormone levels. These changes in normal open females repeat approximately every 21 days. This regular repetition is called the estrous cycle.

7. Pre-Estrus Phase • The hypothalamus which is a region at the base of the brain, produces the hormone gonadotrophin. • The hormone gonadotrophin triggers the pituitary gland (which is attached to the hypothalamus) to start estrus. • The pituitary gland starts the estrus cycle by producing follicle stimulating hormone, and luteinizing hormone.

8. Pre-Estrus Phase • Follicle stimulating hormone (FSH) - Just as the name suggests, this hormone is responsible for stimulating the growth of follicles on the ovaries. • This starts the first phase of estrus. • The second hormone produced by the pituitary gland is luteinizing hormone (LH) – This hormone causes a mature follicle to rupture or ovulate. • LH also helps maintain the pregnancy by stimulating the production of progesterone by the corpus luteum (CL) which starts the second phase of estrus.

9. Follicle Development & Estrogen Production(Estrus Cycle Phase I) • The ovaries are the primary organs in a cow's reproductive tract. They function to produce eggs and to produce hormones (estrogen and progesterone). • At the beginning of estrus, one ovary has a large follicle. • Follicles are fluid filled, blister like structures that contain developing oocytes or eggs. • Over time, greater than 95% of the other follicles on the ovary regress and die without ovulating and are replaced by new crops of growing follicles. • The largest follicle present on the ovaries is termed the "dominant follicle ".

10. Follicle Development & Estrogen Production(Estrus Cycle Phase I)

11. Estrous Cycle (Phase I) • The cells lining the follicle are producing the hormone estrogen. • Estrogen is transported in the blood stream to all parts of the cow's body, causing the animal to come into estrus. • Ovulation occurs when the follicle ruptures or "ovulates" releasing the egg into the large open end of the oviduct that surrounds the ovary. This funnel-like structure called the infundibulum keeps the ova from falling into the body cavity.

12. Female Reproductive Process • Oviducts, as their name implies, carry the cow's eggs or ova. The oviducts are also commonly referred to as the fallopian tubes. • It is within the upper segment of the oviduct that fertilization occurs.

13. Ovary & Oviduct

14. Estrus Cycle (Phase II) Corpus LuteumDevelopment & Progesterone Production • After ovulation, over the next 5-6 days, new cells grow in the void or crater left on the ovary where the follicle was located. • These cells grow to form the corpus luteum (CL), which is the other structure found on the ovarian surface.

15. Estrus Cycle (Phase II) • The corpus luteum forms in the crater left on the ovary after ovulation. • The outside of a CL is usually dark red in appearance, yet a cross section reveals a bright yellow to yellow-orange interior. • This is where the term “corpus luteum" (Latin for "yellow body") originates.

16. Estrus Cycle (Phase II)

17. Corpus Luteum Development • The CL produces another hormone, progesterone. • Progesterone prepares the uterus for pregnancy by thickening the uterine walls, providing nourishment for the developing embryo and causes a thick plug to form in the cervix, preventing access of bacteria or viruses into the uterus. • Progesterone also prevents the animal from returning to estrus by blocking the release of follicle stimulating hormones from the pituitary gland in the brain.

18. Corpus Luteum Development • Follicle stimulating hormone, or FSH, as its name implies, stimulates the growth of follicles. • Rapid follicle growth usually results in estrogen production that would bring the animal back into heat and terminate the pregnancy. • The corpus luteum production of progesterones to block FSH is a very important aspect of maintaining the pregnancy.

19. Estrous Cycle • During days 16 -18 of the estrus cycle, the uterus searches for the presence of a growing embryo. • If no embryo is detected, the uterus begins to produce another hormone called prostaglandin. • Prostaglandin begins to destroy the CL. • When the CL is destroyed, no more progesterone is produced and the pituitary gland begins to secrete FSH. • This rise in follicle stimulating hormone initiates the selection of a new follicle which is to grow to a large size, produce estrogen, and bring the animal back into estrus.

20. Embryo and Fetal Development • For the first 4-5 days following insemination or breeding, the egg moves in the oviduct toward the uterus. • While floating free in the uterus, several membranes are produced by the new embryo. Collectively, these membranes are referred to as the placenta. • The growing placenta produces a chemical that stops production of prostaglandin by uterus.

21. Embryo and Fetal Development • At about 30 days of gestation, the placenta begins to attach to the uterus at several points. • The placental sides of these attachment points are called cotyledons. • The uterine side has caruncles. • The attachment of cotyledons to caruncles is very similar to velcro. • This greatly increases the surface area within the attachment point. • The placenta is a sack surrounding the developing calf which is attached to the umbilical cord on the calf. • Surface area within attachment points is important to allow for exchange of nutrients and waste products between calf and mother.

22. Embryo and Fetal Development

23. Embryo and Fetal Development

24. Summary Diagram Hypothalamus 1. Gonadotrophin Pituitary Gland 2. (LH) Causes the follicle to rupture & creates the CL 3. (FSH) Creates a follicle Ovary Follicle 4. Estrogen: Causes the animal to come into heat CL 5. Progesterone: Prepares uterus for pregnancy & blocks (FSH) Egg Uterus Unfertilized Egg Fertilized Egg Placenta 7. Placenta: Blocks Prostaglandin prod.) 6. Prostaglandin: Destroys the CL and stops progesterone prod.