1. SZM2.6 ANIMAL PHYSIOLOGY Physiology of reproduction Lecture 5, Week 6 1

2. This week contents Male reproduction & its control Female reproduction & its control Fertilization, gestation and parturation Lactation, lactogenesis and galactogenesis Mammogenesis 2

3. Overview of reproduction Role of the male  produce sperm  introduce sperm into the female body Role of the female  produce ova  receive sperm & provide for union of the gametes  harbor an embryo/foetus and give birth  nourish offspring 3 Primary sex organs = gonads: ovaries and testes Secondary sex organs= everything else related to reproduction

4. Male Sex Hormones Are called androgens, of which testosterone is the most abundant. Testosterone is secreted in foetus until birth, and then not again until puberty, after which it is continuously secreted.

5. Actions of Testosterone Stimulates the development of the male reproductive organs. Causes the testes to descend. Responsible for male secondary sexual characteristics (deep voice, body hair, thickening of the skin, and so forth).

6. Hormonal Control of Male Reproductive Functions Hypothalamic and Pituitary Hormones –At the time of puberty, the hypothalamus controls the many changes that lead to the development of a reproductively functional adult. –The hypothalamus releases gonadotropin-releasing hormone (GnRH), –GnRH triggers the production of the gonadotropins, luteinizing hormone (LH), and follicle-stimulating hormone (FSH) from the anterior pituitary.

7. Hormonal Control of Male Reproductive Functions LH promotes the development of interstitial cells of the testes and they, in turn, secrete male hormones (testosterone). FSH stimulates the supporting cells of the seminiferous tubules. FSH and testosterone stimulate spermatogenesis.

8. 8 Hormonal Control of Female Reproductive Functions

9. Female Sex Hormones At about 10 years of age, the hypothalamus begins to secrete more GnRH, which in turn stimulates the anterior pituitary to produce LH and FSH. At puberty, the ovaries synthesize estrogens in response to FSH. Estrogens are responsible for the female secondary sexual characteristics, such as breast development, increased adipose tissue deposition and increased vascularization of the skin. Ovaries also secrete progesterone, which triggers uterine changes during the menstrual cycle.

10. Female Reproductive Cycle The menstrual cycle is characterized by monthly changes in the uterine lining that lead to menstrual flow as the endometrium is shed. A menstrual cycle is started by FSH, which stimulates the maturation of a follicle in the ovary. Follicular cells surrounding the developing oocyte secrete estrogen, which is responsible for maintaining secondary sexual characteristics as well as the thickening of the uterine lining. Ovulation is triggered by a mid-cycle surge in LH. Following ovulation, follicular cells turn into a glandular corpus luteum that secretes increasing amounts of estrogen and progesterone.

11. Female Reproductive Cycle cont. If pregnancy does not occur, the corpus luteum degenerates, hormone levels decline, and the uterine lining disintegrates and is shed. During the cycle, estrogen and progesterone inhibit the increased release of FSH and LH; when estrogen and progesterone levels fall, the secretion of FSH and LH increases.

12. 12 Fertilization, gestation & parturation (labour)

14. Gestation Gestation period begins with fertilization and end with parturition of foetus Gestation consist 3 class : ovum period embryo period foetus period 14

15. 15 Conception/ fertilization After ejaculation into the vagina, sperm swim to meet an egg – Sperm live 5-7 days (need cervical mucus) – Eggs live about 12-24 hours, so conception only occurs during this short window – Fertilization occurs in the fallopian tube Events leading to fertilization: Sperm binds to receptors on zona pellucida Acrosomal reaction – enzymes digest a slit Sperm passes through zona Fusion of a single sperm’s plasma membrane with oocyte’s plasma membrane Cortical reaction: sperm receptors destroyed in zona so no more enter; sperm nucleus engulfed by egg’s cytoplasm Fertilization occurs at the moment the chromosomes from the male and female gametes unite

16. Blastocyst with blastocoele cavity Morula solid ball of cells Cleavage Early division of zygote into multiple cells without increase in size, partitions contents Zygote

17. 17 Implantation Blastocyst floats for 2 days: “hatches” by digesting zona enough to squeeze out 6-9 days post conception - burrows into endometrium

18. 18 Formation of Placenta Both contribute: Trophoblast from embryo Endometrial tissue from mother Not called placenta until 4th month Embryonic blood circulates within chorionic villi, close to but not mixing with mother’s blood Nutrients to baby Wastes to mom

19. 19 Sugars, fats and oxygen diffuse from mother’s blood to foetus Urea and CO2 diffuse from foetus to mother Maternal antibodies actively transported across placenta= passive immunity Most bacteria are blocked Many viruses can pass including rubella, chickenpox, HIV Many drugs and toxins pass including alcohol, heroin, mercury, antibiotics Placental secretion of hormones – Progesterone and HCG (human chorionic gonadotropin, the hormone tested for pregnancy): maintain the uterus – Estrogens and CRH (corticotropin releasing hormone): promote labor From mother to child and vice versa

20. 20 Childbirth Gestational period: averages 266 days Parturition: the act of giving birth: 3 stages of labor 1.Dilation: 6-12h (or more in first child); begins with regular uterine contractions and ends with full dilation of cervix (10cm) 2.Expulsion: full dilation to delivery – minutes up to 2 hours 3.Placental delivery: 15 minutes Dilation of cervis; head enters true pelvis Late dilation with head rotation to AP position Expulsion: head first safest as is largest part Delivery of the placenta

21. Parturition= The Process of Childbirth The mechanisms signaling the onset of labor are not clearly understood, although several theories exist. Potential role of progesterone?: - decreasing progesterone prior to labor would allow uterine contractions to occur - however, there is no decline in progesterone before labor in humans - some studies suggest there is a decline in uterine progesterone receptors, resulting in decreased progesterone action, leading to labor

22. Potential Role of Oxytocin in Parturition? Oxytocin causes uterine contraction. However, oxytocin levels do not increase until after labor starts, according to more recent studies. Oxytocin may play a role in uterine contraction following labor, resulting in decreased blood loss.

23. Potential Role of Relaxin in Parturition? Relaxin acts on the cervix, causing dilatation and softening. In some animals relaxin increases before labor starts. In humans, relaxin is high beginning early in pregnancy and stays elevated until labor. Relaxin does act to soften connective tissues, such as the ligaments connecting the pelvic bones, to allow increase in size of the birth canal. Relaxin also decreases uterine contractility during pregnancy.

24. Potential Role of Prostaglandins in Parturition Prostaglandins cause dilation and softening of the cervix. Prostaglandins also cause uterine contractions. The levels of prostaglandins increase in fetal membranes before the onset of labor. It is believed that some (unknown) signal from the fetus causes increased prostaglandin production from fetal membranes, which then act on the uterus and cervix to initiate labor.

25. 25 Mammogenesis, Lactation, lactogenesis & galactogenesis

26. Mammogenesis = term used to describe the development of the mammary gland. Mammary (breast) growth occurs. The size and weight of the breast increases. Preparation for milk production

27. Mammary glands –Are present in both males and females. –Are not a component of the reproductive system. –Contain epithelial tissue that secrete milk. »Milk drains into a series of ducts opening at the nipple. Modified sweat glands Respond to hormonal stimulation Lymph drains into parasternal and axillalry lymph nodes

28. 28 Hormones acting on mammary glands during various physiological conditions

29. Lactation Lactation is the delivery of milk from the mammary gland. There are 4 main stages of lactation, controlled by different hormones: 1. milk synthesis in alveolar cells 2. secretion of milk from alveolar cells to alveolar lumen 3. maintainance of established milk production and release into alveolar lumen 4. milk ejection: movement of milk from alveoli into the duct system and out of the breast

30. Milk Synthesis Milk Synthesis= Production of breast milk is stimulated by increased levels of prolactin (pituitary) and human placental lactogen (from the placenta) during pregnancy. Milk release from alveolar cells is inhibited by the high levels of progesterone and estrogen during pregnancy. Estrogen and progesterone also act with prolactin to increase alveolar duct growth during pregnancy.

31. Lactogenesis Lactogenesis= secretion of milk from alveolar cells into the alveoli of the breast. Stimulated by prolactin, and occurs after parturition when estradiol and progesterone levels are decreased.

32. Galactopoiesis and Milk Ejection Galactopoiesis= the maintenance of established milk production, caused by prolactin. Milk Ejection= movement of milk from alveolar ducts into the main duct system and out of the breast. Induced by oxytocin. Oxytocin causes contraction of myoepithelial cells in the breast, causing milk release.

33. Regulation of Oxytocin & Prolactin During Lactation Oxytocin levels increase due to suckling of the breast by the infant. In addition, sight, sound, or thought of the infant can also increase oxytocin levels, causing milk ejection. Prolactin release is also increased by suckling of the breast by the infant (but not by audiovisual stimuli). Associated with suppression of dopamine release.

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