Reproduction

Male reproductive system

Female reproductive system

The menstrual cycle Prepares the ovaries for ovulation and

the uterus for implantation.

Starts at the age of puberty.

Each cycle lasts on average 28 days.

The purpose of the menstrual cycle is to release an egg or ovum (ovulation) for possible fertilization and later implantation into the endometrium.

This inner lining of the uterus is not maintained if there is no implantation.

The breakdown of the blood vessels leads to the menstrual bleeding (menstruation) of a typical cycle.

Hormones and the menstrual cycle: The

hypothalamus is the regulatory center of the

menstrual cycle.

Produces the gonadotrophin

releasing hormone (GnRH).

The target tissue for this hormone

is the nearby pituitary gland

results in the production and secretion of two hormones into

the bloodstream:

follicle stimulating hormone (FSH)

luteinizing hormone (LH).

The target tissues for these hormones are the

ovaries

Effects of FSH and LH on the ovaries:

• target tissue is the endometrium.

Increase the production and secretion of estrogen

Effects of FSH and LH on the ovaries:

• target tissue is the endometrium.

Increase the production and secretion of estrogen

• contain an oocyte surrounded by an inner ring of follicle cells and a glycoprotein membrane coat known as the zona pellucida

Production of structures within the ovaries known as Graafian follicles.

Effects of FSH and LH on the ovaries:

• target tissue is the endometrium.

Increase the production and secretion of estrogen

• contain an oocyte surrounded by an inner ring of follicle cells and a glycoprotein membrane coat known as the zona pellucida

Production of structures within the ovaries known as Graafian follicles.

• the release of the follicle (with the oocyte) from the Graafian follicle.

A spike in the production of FSH and LH leads to ovulation:

Effects of FSH and LH on the ovaries:

The outer ring of the Graafian follicles remain.

These cells will continue to divide to form a glandular structure known as the corpus lutheum which will produce the hormone progesterone.

This hormone will maintain the thickened, highly vascular endometrium for 10 to 12 days.

Effects of FSH and LH on the ovaries:

If there is no pregnancy, the corpus luteum eventually breaks down and there will be a decline of the progesterone and estrogen levels.

The capillaries and blood vessels begin to rupture and menstruation begins.

During pregnancy, the presence of estrogen and progesterone are negative feedback signals to the hypothalamus, inhibiting the production of GnRH and of a new Graafian follicle.

As the levels of these hormones fall, the hypothalamus begins to secrete GnRH and thus another menstrual cycle begins

Hormones in males:

In males, the hypothalamus also produces the hormone GnRH, whose target tissue is the pituitary gland that will secrete FSH and LH.

FSH´s target tissue is the epithelium of the testis to produce spermatogenesis. LH targets the testes tissue to produce testosterone. This hormone is needed in order to:

• Form male genitalia, • Ensure the development of male secondary sex characteristics, and • Help maintain the male sex drive.

In-vitro Fertilization:

Some couples are unable to bear children for a wide variety of possible reasons, including:

Males with low sperm count

Males with impotence (failure to achieve or maintain an erection)

Females who cannot ovulate normally;

Females with blocked Fallopian tubes.

Reproductive technologies have been developed to overcome these situations. One of them is in-vitro fertilization (IVF)

Steps of an IVF include:

Inject the woman with FSH for 10 days to ensure the production of several Graafian follicles

Surgical harvest of the eggs (oocytes

The man ejaculates in a container to obtain sperm cells and these are mixed in separate culture dishes.

Fertilized ova (2 or 3) are introduced into the woman´s uterus for implantation.

Ethical issues concerning IVF

Arguments for IVF Arguments against IVFEnables couples who would otherwise be unable to have children to have a family.

Embryos that are produced during culturing, but are not implanted are either frozen or destroyed.

Embryos that are visibly not healthy in early stages of development can be eliminated from consideration for implantation.

There are complex legal issues concerning the use of those frozen embryos when couples split up.

Genetic screening is possible on embryos before implantation to eliminate the chance of passing on some genetic diseases.

Genetic screening of embryos could lead to society choosing desirable characteristics.

IVF technology will advance and lead to further benefits in reproductive biology.

Some reproductive problems of an individual are genetically passed on and IVF bypasses nature`s way of decreasing the genetic frequency of that reproductive problem

  Multiple births and the problems associated with multiple births are more likely with IVF than with natural conception.

Questions:

Imagine a panel put together to debate the pros and cons of IVF. Give three pro or con arguments that would be likely to be given by each of the following panel members.

Health insurance executive

Man or woman who needs IVF to have a child.

Religious representative

Administrator from an IVF clinic.

One method of birth control known as tubal ligation involves tying off and then surgically cutting the Fallopian tubes (oviducts). This is considered to be a permanent form of birth control even through it is sometimes possible to surgically reverse the procedure. Do a web search on the male equivalent of this procedure which is known as a vasectomy.

How is a vasectomy performed?

Should a vasectomy be considered a permanent form of birth control?

Sources

Damon, A., McGonegal, R., Tosto , P., & Ward, W. (2007). Biology Higher Level. New Jersey: Pearson.

http://www.shropshireivf.nhs.uk/about-fertility/reproductive-system.asp

http://click4biology.info/c4b/6/hum6.6.htm

http://www2.estrellamountain.edu/faculty/farabee/biobk/biobookreprod.html

http://ynaija.com/teen/teen-y-health-girls-only-this-is-what-really-goes-on-in-your-body-28-days-in-a-month-look/

http://cnx.org/content/m44841/latest/

http://www.lifemartini.com/how-does-obesity-affects-fertility/

http://www.mindfully.org/Health/2005/In-Vitro-Fertilization14nov05.htm