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Topic 6 and 11 – Human Health and Physiology

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1 Topic 6 and 11 – Human Health and Physiology
Topic 6.6/ Reproduction

2 Sexual Reproduction - Overview
Basic process: make gamete (sperm) fertilizing a female gamete (egg or ovum) Cellular union ensures that half of the genetic make-up of the resulting zygote is from each parent. Bigger purpose: ensure genetic variation in the species. Male and female reproductive systems adapted for sex cell production and release. Female reproductive system ideal location for fertilization and development of embryo then fetus until birth

3 SPERM: acrosome, haploid nucleus, flagellum, and mitochondria
EGG: cytoplasm, haploid nucleus, zona pellucida, follicle cells, and plasma membrane

4 Male reproductive system
Vas deferens scrotum

5 Light micrograph of testis

6 Spermatogenesis within the testis
Occurs within small tubes called seminiferous tubules. Near outer wall of seminiferous tubules are germinal epithelial cells called spermatogonia.

7 Spermatogenesis MEIOSIS MITOSIS
Spermatogonia undergo meiosis to produce spermatozoa (sing. Spermatozoon). Meiosis is reduction division. Spermatogonia = 46 = 2n Spermatozoa = 23 = n 23 homologous pairs of chromosomes becomes 23 chromosomes Spermatogonia undergo mitosis to duplicate. Sperm cell production starts at puberty and continues throughout life. Millions produced each day and mitosis replaces cells that become spermatozoa.




11 http://highered. mcgraw-hill

12 Three main roles of testosterone
Development of male genitalia during embryonic development. Development of secondary sex characteristics during puberty. Maintains sex drive. * Although males typically experience a slight lowering of sperm count as they age, fertility in males has been documented in individuals as old as 94.

13 Outline the role of the epididymis, seminal vesicle and prostate gland in the production of semen.

14 Female reproductive system
Fallopian tube cervix

15 Outline the role of hormones in the menstrual cycle, including FSH, LH, estrogen, and progesterone
OVERVIEW implantation… Puberty in females marked by hormonal cycle known as the menstrual cycle. On average lasts 28 days. Times release of egg (ovum) for fertilization and implantation in inner lining of the uterus (endometrium). Endometrium must be rich with blood vessels (highly vascular) to occur. No implantation results in lose of highly vascular endometrium. Breakdown of vessels creates menstrual bleeding. Sign that pregnancy has not occurred.










25 Hormones from the brain
Hypothalamus (regulatory center of the menstrual cycle) Gonadotrophin releasing hormone (GnRH) Triggers pituitary to release follicle stimulating hormone (FSH) and luteinizing hormone (LH) These hormones target the ovaries

26 Effects of FSH and LH on the ovaries
One effect increases production/secretion of estrogen. Target tissue is endometrium to increase blood vessels. Another effect is the production of follicle cells and true reproductive cells within the ovary (oocytes). Chemical stimulation from FSH and LH create mature follicle cells.

27 Micrograph of ovary with magnified oocyte and follicle.



30 Structure known as follicle and enters fallopian tube after ovulation.
FSH and LH cont… Spike in hormone levels leads to ovulation (release of oocyte from follicle). Inner ring of follicle accompanies oocyte along with glycoprotein coat (zona pellucida). Structure known as follicle and enters fallopian tube after ovulation.

31 http://msjensen. cehd. umn

32 Progesterone Outer ring of follicle cells remains in ovary.
Produce/secrete hormone progesterone. Creates glandular structure: corpus luteum. Corpus luteum produces progesterone for days after ovulation. Progesterone maintains thickened, highly vascular endometrium. Continued progesterone production keeps endometrium from breaking down and allows embryo to implant. Negative feedback signal to hypothalamus: will not produce GnRH with high levels of estrogen and progesterone. FSH and LH remain at levels that DO NOT produce mature follicle cells.

33 No pregnancy… Corpus luteum breaks down and both progesterone and estrogen levels decrease. Blood vessels of endometrium begin to rupture and menstruation begins. Drop in progesterone and estrogen signals hypothalamus to secrete GnRH Menstrual cycle begins again



36 – Compare the processes of spermatogenesis and oogenesis, including the number of gametes and the timing of the formation and release of gametes.

37 SPERMATOGENESIS OOGENESIS Millions of sperm cells are produced every day. Typically, one secondary oocyte is ovulated per menstrual cycle. Four gametes are produced for each germinal cell which begins meiosis. One gamete is produced for each germinal cell which begins meiosis. The resulting gametes are very small. The resulting gametes are very large. Occurs within testis. Occurs within ovaries. Spermatozoa are released during ejaculation. Secondary oocyte is released during ovulation. Haploid nucleus results from meiosis. Spermatogenesis continues all through life (starting at puberty). Ovulation starts at puberty, occurs with each menstrual cycle, then stops during menopause.


39 In-vitro fertilization
Woman injected with FSH to ensure many mature follicles are present. Oocytes harvested surgically and sperm is donated from the male parent. Eggs and sperm mixed and observations are made to identify fertilized eggs. Two or three healthy embryos introduced to uterus for implantation. Typically more than one embryo is implanted to ensure success.

40 Fertilization Millions of sperm are ejaculated into a female’s vagina.
Sperm absorb fructose present in semen for added energy. Some sperm get through cervical opening (cervix separates the vagina from the uterus). Some of these sperm make it to the Fallopian tubes. In the middle of the menstrual cycle a secondary oocyte may be present in the Fallopian tube. Very small percentage of sperm ever make it to the oocyte.

41 Interesting facts Females Males
Average number of sperm per ejaculate (in millions) - Man: 280 - Pig: 8000 - Rabbit: 280 Fruit flies have some of the largest gametes of any animal Fertile life of sperm (in hours) - Man: - Rabbit: - Pig: Time to fertilization (in minutes) - Woman: 5-68 - Pig: 15 - Rabbit: few minutes Only about 200 sperm will survive to fertilization Ovaries can release eggs simultaneously One ovary can release multiple eggs

42 How did it begin!? Typical location for fertilization is within one of the Fallopian tubes. Takes many sperm to get through the follicle cell layer. Several sperm reach zona pellucida and release the hydrolytic enzymes within the acrosome. First sperm to the plasma membrane fuses both membranes together. Cortical reaction initiated.






48 Early embryo development
Fertilization triggers the zygote to begin a mitotic division (first division occurs ~24 hours after fertilization). First 5 days mitotic divisions; moving within Fallopian tube to the uterus. Mitotic divisions increase, embryo reaches uterine cavity and is ~100 cells in size The embryo, at implantation, is a ball of cells known as a blastocyst.



51 human chorionic gonadotrophin (HCG)
Role of HCG in early pregnancy Pregnancy tests HCG is the hormone that home pregnancy kits test for. This hormone can only be produced by an embryo and this is a positive indicator for pregnancy. Corpus luteum: remaining follicle layer in the ovary that secretes estrogen and progesterone. If no fertilization the corpus luteum ceases hormone production after 14 days. A week after fertilization occurs the embryo implants on the endometrium. Soon after implantation the embryo begins secreting HCG. HCG enters mothers blood. Targets corpus luteum to continue hormone production. Maintenance of endometrium. Later estrogen and progesterone production is caused by placenta.

52 The placenta Before and just after implantation the yolk is responsible for nutrient release. A result of implantation is the creation of the placenta by the embryo and the endometrium. Two fetal blood vessels within umbilical cord carry fetal blood to the placenta. Fetal blood exchanges materials with the maternal bloodstream and another fetal blood vessel returns the blood to the fetus. Returning blood has been oxygenated and nutrients have been added while in the placenta.

53 Exchange of materials between mother and fetus
Materials passed from fetus to mother within the placenta Materials passed from mother to fetus within the placenta Carbon dioxide Oxygen Urea Nutrients (glucose, amino acids, etc.) Water Hormones (e.g. HCG) Hormones Vitamins, minerals Alcohol, many drugs, nicotine (if taken by mother during pregnancy) Some viruses such as German measles, HIV (if mother is infected)

54 Placenta structure and function
Rich blood supply: deoxygenated blood and waste out via umbilical arteries, oxygenated blood and useful materials in via umbilical vein. Intervillus space is where nutrient/waste exchange occurs. Placenta has large surface area and many RER and vesicles for hormone production (HCG, estrogen, and progesterone). Placenta also produces anti- immune substances…. WHY???

55 Amniotic sac and amniotic fluid
Main purpose is support and protection of the fetus. Cushioning for protection. Environment for free movement for developing muscles and skeleton (w/o the added strain of gravity) Thermal stability. Fluid contains embryonic cells that can be tested for chromosome abnormalities (amniocentesis).





60 Quick Review

61 Major events of vaginal birth
Major hormone changes Opening of the cervix to 10cm Babies position is head- first, face down Shoulder typically widest part to pass through birth canal Once the placenta is expelled it is referred to as afterbirth Lactation begins soon after birth

62 Questions???

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