Reproduction IB Biology Topic 6.6

Transcription

1 Outcomes Reproduction IB Biology Topic Draw and label diagrams of the adult male and female reproductive systems Outline the role of hormones in the menstrual cycle, including FSH (follicle stimulating hormone), LH (luteinizing hormone), estrogen and progesterone Annotate a graph showing hormone levels in the menstrual cycle, illustrating the relationship between changes in hormone levels and ovulation, menstruation and thickening of the endometrium List three roles of testosterone in males Outline the process of in vitro fertilization (IVF) Discuss the ethical issues associated with IVF. Where do babies really come from? The Male Reproductive System Interesting Sperm facts! Daily sperm production by a healthy man: million! Contents of average ejaculation: 50 million (25 million moving, 20 million deformed) Maturation time: 72 days! Swimming speed: 8 inches per hour Survival time inside a woman s body: 2-7 days! Testes: produces sperm cells and testosterone Seminiferous tubules: produces immature sperm cells (inside testes) Epididymis: matures and stores sperm cells in coiled tubules Vas deferens: Carries sperm from the epididymis to its junction with the urethra

2 Seminal vesicle: Secretes fructose into the semen which provides energy for the sperm Prostate gland: secretes an alkaline buffer into the semen to protect the sperm from acidic environments of the vagina Cowper s gland: secretes mucus-rich fluids into the semen that may protect the sperm from acids in the urethra Urethra: carries the semen during ejaculation also carries urine from the bladder to the exterior of the body Penis: deposits sperm into the vagina during ejaculation and contains the urethra. Production of Sperm Video Female Reproductive System health/male-reproductive-system/adam htm Vagina: Extends from the cervix to the external environment. It provides a passageway for sperm and menstrual flow and functions as the birth canal. Cervix: Is located between the vagina and uterus. The cervix is the opening that sperm must pass through in order to get to an egg. A baby must also go through the cervix as it exits the uterus and enters the vagina. Uterus: The uterus is a muscular organ. An egg that has been fertilized will implant itself into the uterus lining and will continue to develop in the uterus throughout the pregnancy. It is involved in menstruation

3 Fallopian Tubes: The fallopian tubes extend off the upper sides of the uterus and lead up to the ovaries. They have 20 to 25 finger-like structures on their ends that hover just above the ovaries and work to collect the mature egg when it is released. They will then carry the ovum to the uterus. It is in the fallopian tubes that fertilization of the egg will take place. Ovaries: Women have two ovaries, one on each side of the uterus. Ovaries are the storing house for the egg follicles; every month, one of these egg follicles will mature and release an egg into the fallopian tubes. The ovaries are also responsible for producing estrogen and progesterone, which are vital for proper reproductive function. A woman is born with all of the eggs she will every have for her entire lifetime Hormones in Puberty When a female reaches the age of puberty the hypothalamus releases gonadatropin releasing hormone (GnRH) which activates the pituitary gland to secrete and release follicle stimulating hormone (FSH) and lutenizing hormone (LH). Follicle Stimulating Hormone The FSH is carried in the blood to the ovaries where it stimulates follicle development. As the follicles develop they secrete the hormone estrogen which initiates the development of the endometrium. An increase in the concentration levels of estrogen trigger the pituitary to shut down secretions of FSH (negative feedback). The estrogen has a positive effect on the production and secretion of LH and the level rises which causes ovulation to occur.

4 After ovulation the LH directs the transformation of the follicle cells into a functioning corpus luteum and the Luteal phase of the menstrual cycle begins. The corpus luteum secretes both progesterone and estrogen and these hormones work together to build up and maintain the uterine lining (endometrium). Egg Production Video health/female-reproductive-system/adam htm Negative Feedback The estrogen and progesterone levels are now high and they send a message back to the hypothalamus which decreases the levels of GnRH. The decreased GnRH means the pituitary will decrease the levels of LH and FSH being released (negative feedback). Menstruation The drop in the levels of LH and FSH cause the corpus luteum to deteriorate. This slows down production of estrogen and progesterone which results in the beginning of menstruation. Annotate a graph showing hormone levels in the menstrual cycle, illustrating the relationship between changes in hormone levels and ovulation, menstruation and thickening of the endometrium.

5 Menstrual Cycle Animation nimations/content/ovarianuterine.html The Birth Control Pill Birth control pills contain progesterone or estrogen and progesterone. They prevent ovulation since high levels of estrogen and progesterone inhibit the release of FSH and LH so the follicles do not develop and ovulation does not occur. The birth control pill does not protect from STIs! Testosterone Testosterone is a hormone produced in the testes of males and it has several roles it performs in the body. During fetal development the testes secrete testosterone which causes the development and growth of the male genitalia including the penis.

6 Testosterone and puberty When a male reaches the age of puberty, testosterone will stimulate the development of secondary sex characteristics in males such as growth of facial and pubic hair, growth of the skeletal muscles and an enlarged penis. Testosterone and Reproduction Testosterone plays an important role in adulthood in the maintenance of sex drive of the male. This is important because it encourages males to have sexual intercourse and reproduce, passing their genes on to the next generation. So list 3 roles of testosterone: Prenatal development of male genitalia Secondary sexual characteristics at puberty Sex drive and aggression In Vitro Fertilization In vitro fertilization is a process that can be used for couples who cannot conceive children on their own for various reasons. The female undergoes drug therapy for three weeks (one injection per day) to stop her normal menstrual cycle. Then she is injected with high doses of follicle stimulating hormone (FSH) once a day for days to encourage the development of many follicles in her ovaries. 36 hours prior to the collection of her eggs she is injected with another hormone, HCG which causes the eggs to loosen within the follicles and mature. Before the eggs are harvested the man must provide sperm by ejaculating into a cup. The semen is processed and the healthiest sperm are collected.

7 A device is inserted through the vagina to collect the eggs from the female which are then mixed with the sperm in a shallow dish and placed in an incubator. The eggs are checked for fertilization and 2 or 3 embryos are chosen for implantation. The embryos are implanted in the uterus using a long plastic tube. The female will then undergo a pregnancy test to see if any of the embryos have implanted in the endometrium. If the test is positive she will then undergo an ultrasound to see if the pregnancy is continuing normally. Ethical issues associated with IVF There are ethical issues surrounding IVF similar to the issues surrounding contraception and family planning. There is also great variety in human societies around the world in terms of views of IVF as a result of cultural and religious diversity. We will explore both sides of the argument. Ethical Arguments For IVF Couples who are unable to have children on their own can have their own biological child Ethical Arguments Against IVF If the reason for infertility in the parents is inherited then there is the potential to pass the infertility to the child and the agony the parents endured will be repeated in their child. Ethical Arguments For IVF The screening of embryos for genetic diseases could reduce the amount of suffering from those diseases. Parents willing to go through IVF have a strong desire to have their own biological child and will likely be very loving parents. Ethical Arguments Against IVF The mixing of sperm and egg often produces more embryos than are needed and the extra embryos are disposed of and this could be considered killing new human life. The embryos that are selected to be implanted are chosen by embryologists so this could be viewed as humans deciding whether new life survives or dies. IVF increases the chances of multiple births which can carry health risks for both the mother and the children.