6 6 and 11 4 Human Reproduction How

6. 6 and 11. 4 Human Reproduction

How do humans reproduce? Sexual reproduction— Process in which two gametes come together to form one fertilized cell that contains genetic information from both parental cells

Female Reproductive System Drawings must include ovary oviduct uterus cervix vagina endometrium

Identify the components of the female reproductive system. Drawings must include ovary oviduct uterus cervix vagina endometrium

Female Menstrual Cycle: Hormones Involved 1. Follicle Stimulating Hormone (FSH) 2. Estrogen 3. Luteinizing Hormone (LH) 4. Progesterone

Female Menstrual Cycle FSH stimulates the development of follicles The developing follicle then secretes estrogen Estrogen stimulates the thickening of endometrium Estrogen also stimulates LH secretion LH induces ovulation and development of the Corpus luteum

Female Menstrual Cycle cont. Corpus luteum then secretes progesterone Progesterone causes further thickening of endometrium in preparation for fertilized egg implantation Progesterone and estrogen inhibits the secretion of LH or FSH to prevent further ovulation Falling progesterone levels at the end of the cycle allow FSH production to start next menstrual cycle

Female Reproductive Hormone Interactions FSH leads to estrogen production Estrogen spike induces LH production LH leads to progesterone production Progesterone and estrogen inhibit LH and FSH Reduction of progesterone stimulates FSH and LH production

Oogenesis Mitotic divsion produces oogonium Oogonia become primary oocytes Primary oocytes divide by meiosis I to form one polar body and one secondary oocyte Meiosis II produces one polar body and one ovum Polar bodies (there actually three) are not viable and break down

Structure of Placenta is composed of fetal and maternal tissues Villi increase surface area for blood flow Capillaries in placental villi share blood between mother and fetus

Function of Placenta secretes estrogen and progesterone to maintain uterine lining (this was job of corpus luteum) Placenta allows gas / nutrient exchange between fetus and mother Placenta allows antibodies to go from mother to fetus Placenta secretes hormone HCG which stimulates development of the fetus

Role of the Hormone Testosterone Development of external reproductive structures Sperm production Development of secondary sex characteristics like deepening of voice, pubic hair and muscle growth

Male Reproductive System Drawings must include penis scrotum prostate gland urethra/urinary tract seminal vesicle bladder testes epididymis Vas deferens erectile tissue

Identify the components of the male reproductive system. Drawings must include penis scrotum prostate gland urethra/urinary tract seminal vesicle bladder testes epididymis Vas deferens erectile tissue

Structure of Sperm Acrosome Contains enzyme that breaks down coating of egg Head with nucleus Contains DNA Tail Allows sperm to move Middle piece with mitochondria Numerous mitochondria power movement of sperm

Spermatogenesis Mitotic divsion produces large numbers of Spermationia Spermatogonia become primary spermatocytes Primary spermatocytes divide by meiosis I to form haploid secondary spermatocytes Meiosis II produces haploid spermatids These spermatids differentiate (grow tail and other features) into sperm Sertoli Cells provide nutrients to the developing sperm FSH, testosterone and LH all needed for spermatogenesis; Sperm mature in the epididymis where they gain the ability to move

Expanded Spermatogenesis Diagram

Ejaculation Fluid added to sperm by seminal vesicle Contains nutrients (glucose) and mucus for protection from acidity of vagina Additional fluid added to sperm by prostate gland

Fertilization Sperm enters oviduct and swims toward egg Sperm is attracted to egg When sperm contacts egg, it releases enzymes which break down the jelly-like coating of the egg. Membranes of egg and sperm fuse and sperm (head) penetrates egg membrane ending in fertilization See image on next slide

Fertilization Diagram

Embryo Development Prior to Implantation Fertilized egg is called a zygote The cells divides by mitosis The first divisions occur while zygote is still in the oviduct Mitosis continues until a ball of cells is formed called a blastocyste Implantation of blastocyste in uterine wall occurs up to seven days after fertilization See image on next slide

Diagram of Embryo Development Prior to Implantation

What surrounds the fetus as it grows? Amniotic sac, which contains Amniotic fluid

Hormones Involved with Birth Process Estrogen hormone from ovaries induces oxytocin receptors on uterus Oxytocin hormone from fetus stimulates uterus to contract (during labor) Oxytocin also stimulates placenta to make Prostaglandin Increase in Prostaglandin stimulates more Oxytocin and Prostaglandin (positive feedback) More oxytocin present = more contractions occur

In vitro Fertilization (IVF) The oocytes/eggs are mixed with sperm in culture dishes Incubated for several days to allow the fertilized eggs to start developing When they have developed into embryos of at least eight cells each, the embryos are carefully inserted into the woman’s uterus and allowed to implant What are some ethical issues surrounding IVF? Can cause financial barriers (IVF is expensive!) Usually extra fetuses are created, which may be destroyed later There are risks with the drug treatment women are given

IB Exam Question 1. Draw a labelled diagram of an adult female reproductive system. (6 marks) Award [1] for each of the following structures, clearly labelled and drawn in the correct position relative to the other organs, up to [6 max]. ovary; oviduct; uterus; cervix; vagina; endometrium;

IB Exam Question 2. Explain how hormones control the menstrual cycle in human females. (8 marks) FSH stimulates the development of follicles; The developing follicle then secretes estrogen stimulates the thickening of the uterus lining estrogen also stimulates LH secretion; LH surge causes ovulation and development of the Corpus luteum; The Corpus luteum then secretes progesterone; progesterone causes further thickening of the uterus lining in preparation for fertilized egg implantation; progesterone / estrogen also inhibits the secretion of LH / FSH to prevent further ovulation falling progesterone levels at the end of the cycle allow FSH production to start next menstrual cycle

IB Exam Question HL Only 3. Describe the structure and function of the placenta. (6 marks) placenta is composed of fetal and maternal tissues; villi increase surface area; capillaries within placental villi share blood between mother and fetus; placenta also secretes estrogen and progesterone to maintain uterine lining (formerly, this was job of corpus luteum); placenta allows gas / nutrient exchange between fetus and mother; placent allows has passive immunity / antibodies from mother; placenta also secretes the hormone HCG which stimulates development of the fetus;

IB Exam Question 4. List 3 roles of testosterone males. (3 marks) Development of external reproductive structures Sperm production Development of secondary sex characteristics like deepening of voice, pubic hair and muscle growth

IB Exam Question 5. Draw a labelled diagram of an adult male reproductive system. (6 marks) Award [1] for each two of the following structures clearly drawn and correctly labelled. Connections between organs must be correct for full marks. penis; scrotum; prostate gland; urethra/urinary tract; seminal vesicle; bladder; testes; epididymis; sperm duct / Vas deferens; seminiferous tubules; erectile tissue;

IB Exam Question 6. How can testis tissue be distinguished from ovary tissue, when seen using a light microscope? (1 mark) A. B. C. D. Testis tissue has a layer of muscle fibres and ovary tissue does not. Testis tissue is cooler than ovary tissue. Testis tissue contains tubules and ovary tissue does not. Testis tissue contains pain receptors and ovary tissue does not. Correct answer: C

IB Exam Question HL Only 7. Draw a labelled diagram of a mature sperm. (3 marks) For a diagram of a mature sperm, award [1] for each of the following structures clearly drawn and labelled correctly. acrosome; head with nucleus; tail; middle piece with mitochondria;

IB Exam Question HL Only 8. What is the function of Sertoli cells? (1 mark) A. B. C. D. They nourish sperm. They produce testosterone. They nourish interstitial cells. They form the basement membrane. Correct answer: A

IB Exam Question HL Only 9. Production of semen involves a series of processes, which in total take many weeks to carry out. Outline the processes involved in semen production from the start of sperm formation (spermatogenesis) to ejaculation. (9 marks) cell division of diploid cells by mitosis produces large numbers of Spermationia growth of spermatogonia form larger cells called primary spermatocytes; these primary spermatocytes divide by meiosis I to form haploid secondary spermatocytes a second division (meiosis II) produces haploid spermatids these spermatids differentiate (grow tail and other features) into sperm Sertoli cells provide nutrients to the developing sperm FSH, testosterone and LH all needed for spermatogenesis; sperm mature in the epididymis where they gain motility (ability to move); fluid added to sperm by seminal vesicle (during ejaculation); this fluid from seminal vesicle contains nutrients / mucus; additional fluid added to sperm by prostate gland (during ejaculation)

IB Exam Question 10. Compare the processes of spermatogenesis and oogenesis. HL Only (7 marks) Similarities both involve meiosis; LH / FSH involved in both; Differences testes versus ovaries; spermatogenesis until death versus oogenesis until menopause; spermatogenesis continuously versus oogenesis in a cycle; millions of sperm daily versus one egg per month; spermatogenesis involves equal divisions (all viable) versus oogenesis involves unequal cell / cytoplasm divisions resulting in smaller polar bodies; polar bodies are not viable and break down spermatogenesis involves Sertoli /nurse cells versus oogenesis does not;

IB Exam Question HL Only 11. Where does human fertilization most frequently occur? (1 mark) A. B. C. D. Ovary Oviduct Uterus Vagina Correct answer: B

IB Exam Question HL Only 12. Outline the process of fertilization in humans. (5 marks) sperm enters oviduct (fallopian tube) and swims toward egg sperm attracted to egg When sperm contacts egg (usually in the oviduct) it releases enzymes which break down the jelly-like coating of the egg. this is called the acrosome reaction. membranes of egg and sperm fuse and sperm (head) penetrates egg membrane ending in fertilization;

IB Exam Question HL Only 13. Outline early embryo development in the human until implantation in the uterus. (4 marks) fertilized egg called a zygote; cells divides by mitosis; first divisions occur while zygote is still in fallopian tube/oviduct; division continues until a ball of cells is formed called a blastocyste; implantation of blastocyste in uterine wall occurs up to seven days after fertilization;

IB Exam Question HL Only 14. Outline the process of birth and its hormonal control, including the changes in progesterone and oxytocin levels and positive feedback. Estrogen hormone from ovaries induces oxytocin receptors on uterus Oxytocin hormone from fetus stimulates uterus to contract Oxytocin also stimulates placenta to make Prostaglandin Increase in Prostaglandin stimulates more Oxytocin and Prostaglandin (positive feedback)

IB Exam Question 15. Outline the process of in vitro fertilization (IVF). (4 marks) The oocytes/eggs are mixed with sperm in culture dishes and incubated for several days to allow the fertilized eggs to start developing When they have developed into embryos of at least eight cells each, the embryos are carefully inserted into the woman uterus and allowed to implant

IB Exam Question 16. Discuss the ethical issues associated with IVF. (3 marks) Can cause financial barriers There are often, many surplus fetuses conceived as a result of IVF. Some of these may be destroyed through this process There are risks with the drug treatment women are given