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IB Biology (Core and Extension)
Copyright 2008 PresentationFx.com | Redistribution Prohibited | Image © 2008 clix/sxc.hu | This text section may be deleted for presentation.
6.6.1 Draw and label diagrams of the adult male and female reproductive systems.
Male & Female DifferencesMales produce sperm cells at a constant rate
starting from sexual maturityFemales are born with a set number of viable
eggs & one is matured every 28 days after puberty
the excretory system of the females does not cross the reproductive system like in males
Females follow a complicated sexual cycle where one ovum matures approx. every 28 days
Male Reproductive System
The Sperm’s Journey
1. Spermatogenesis in the testis
2. Maturation in the epididymis
3. Carried along vas deferens
4. Fructose for energy & protective mucus picked up at seminal vesicle
5. Prostate adds fluids to neutralise acid in the vagina
6. Ejaculation through the penis, via the urethra
The scrotum
The sac that contains the testesTestes descend during the last 2 months
of fetal development The temperature of the scrotum is a few
degrees cooler than the body temperatureAllows for sperm development
If the testes do not descend the male will be sterile
Vas Deferens
Carries sperm from the testes to the ejaculatory duct
The ejaculatory duct is a tubule formed at the union of the vas deferens and the seminal vesicle ducts and opening into the urethra
Seminal Vesicles
• Mucous to protect sperm in vagina
• Some nutrients, including sugars for energy
6.6.4 List three roles of testosterone in males
Functions of Testosterone
Copyright 2008 PresentationFx.com | Redistribution Prohibited | Image © 2008 clix/sxc.hu | This text section may be deleted for presentation.
Female Reproductive System
Protecting the reproductive system is a real sperm-killer:•Vagina is acidic, killing bacteria and sperm•Tightly-closed cervix has a mucus plug, catching pathogens & sperm
6.6.2 Outline the role of hormones in the menstrual
cycle, including FSH (follicle stimulating hormone), LH
(luteinizing hormone) estrogen and progesterone
Menstrual Cycle
• Puberty– Hormonal cycle
• About every 28 days• To release an egg (ovum)
– Possible fertilization• Implantation into the inner lining of the uterus
– Inner lining (endometrium) is rich with blood vessels
– Lining breaks down if no implantation– Menstrual bleeding
Hormones from the brain• Hypothalamus
– Regulatory center of menstrual cycle
• Produces gonadotrophin releasing hormone– Targets the pituitary
• Pituitary reduces & secretes 2 hormones– Follicle stimulating hormone
(FSH)– Luteinizing hormone (LH)
Menstrual Cycle Hormones
Graafian follicles
• A spike in FSH & LH leads to ovulation– Release the oocyte from
the Graafian follicle– Progesterone maintains
the integrity of the endometrium
What next?
No pregnancy
• Corpus luteum begins to break down
• Leads to a decline in both progeterone and estrogen levels
• Vascular endometrium canpt be maintained and blood vessels rupture and menstruation begins
Pregnancy
• Progesterone levels remain high
• Embryo implants• Negative feedback to
hypothalamus– Does not produce GnRH– FSH & LH levels not
conducive to the production of another Graafian follicle
Sex Hormones
6.6.5 Outline the process of in-vitro fertilization (IVF)
In-vitro fertilization (IVF)
• Natural fertilization typically occurs in fallopian tubes 24-28 hours after ovulation
• Zygote begins to divide by mitosis and takes several more days to travel down the Fallopian tube
• Embryo reaches the endometrium and implants
Reasons for pregnancy problems
• Males with low sperm counts
• Males with impotence (failure to achieve or maintain an erection
• Females who cannot ovulate normally
• Females with blocked Fallopian tubes
Steps of an IVF procedure
1) After determining suitability for IVF, FSH and LH are given to stimulate multiple egg release
2) These eggs are collected
3) Eggs are fertilized with father’s sperm, in a dish, and incubated. This is “IVF”
Steps of an IVF procedure4) After incubation, viable blastocysts are selected
and developed into embryos.
5) Guidelines state that up to 3 embryos can be selected for implantation. Hopefully one or more will ‘take’. There is a risk of multiple pregnancy.
6) After bedrest & a month or so, a pregnancy test is administered. If positive, pregnancy continues as normal. If not, a woman may wait a few months and attempt another cycle
Steps to IVF
6.6.6 Discuss the ethical issues associated with IVF
Arguments for IVF The right to have children Embryos that are visibly not healthy in early stages
can be eliminated from consideration for implant Genetic screening is possible on embryos before
implantation to eliminate the chance of passing on some genetic diseases
Improving medical technology makes it safer than ever before
Some governments cover costs Unused embryos can be stored & used later, donated
or as a source of stem cells
Arguments against IVFReligion: is it playing God?The risk to the mother & fetuses of multiple
pregnanciesExtreme costs can be associated with IVFEmotional cost of failure can be high, especially
with all the extra hormonal loadDoes termination of excess embryos count as
ending a human life? Complex legal issues concerning the use of frozen
embryos when couples split up
11.4.1 Annotate a light micrograph of testis tissue to show the location and function of interstitial cells (Leydig cells), germinal epithelium cells, developing spermatozoa and Sertoli cells
Mature Sperm and Egg
11.4.2 Outline the processes involved in spermatogenesis within the testis, including mitosis, cell growth, the 2 divisions of meiosis and cell differentiation
Spermatogenesis
• Production of male sperm in the testis
• Small and motile• Produced throughout
the life of a sexually mature male
Spermatogenesis
Spermatogenesis
Spermatogenesis
Spermatogenesis
• Important Definitions– Spermatogonia = sperm-producing cells found
in the seminiferous tubules– Spermatocytes = a cell that arises from
division of spermatogonia during spermatogenesis
– Spermatid = an immature sperm cell that arises from division of a spermatocyte
Spermatogenesis
• Sertoli cell = a cell that provides metabolic and mechanical support to developing sperm cells, nourish the development of sperm cells until they are mature
• Epididymis = structures located along the posterior border of the testis, consisting of coiled tubules that store sperm cells, develops motility (swimming ability)
Spermatogenesis
11.4.3 State the role of LH, testosterone and FSH in spermatogenesis
Hormonal control of spermatogenesis
• FSH is produced and releases by the anterior (frontal) pituitary and stimulates meiosis of the primary spermatocytes, giving secondary spermatocytes (now haploid).
Hormonal control of spermatogenesis• LH is also produced &
reaches the interstitial cells of the testis
• Stimulates testosterone production
• Testosterone stimulates the final meiotic division & differentiation of spermatids to form mature sperm cells
Semen Production
11.4.4 Annotate a diagram of the ovary to show the location and function of germinal epithelium, primary follicles, mature follicle and secondary oocyte.
The Ovary• Germinal epithelium – outer layer, produces
primary follicles, constant cell division• Primary follicles – location for development of
oocyte• Mature follicle – contains the oocyte, ready for
ovulation