Reproduction

IB Biology (Core and Extension)

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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

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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