HumanReproduction

Topic 6.6: Human Health and Physiology I

Assessment Statements6.6.1 Draw and label diagrams of the adult male and female reproductive systems.6.6.2 Outline the roles of hormones in the menstrual cycle, including FSH (follicle stimulating hormone), LH (luteinizing hormone), oestrogen, and progesterone.6.6.3 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.6.6.4 List three roles of testosterone in males.6.6.5 Outline the process of in-vitro fertilization (IVF).6.6.6 Discuss the ethical issues associated with IVF.

Human Reproduction

The common purpose of the male and female reproductive systems are to produce offspring.

1. The functions of the male reproductive system are to produce spermatozoa (sperm), secrete sex hormones, and transfer sperm to the reproductive system of the female.

2. The functions of the female reproductive system are to produce ova (eggs), secrete sex hormones, receive sperm from the male, provide sites for fertilization, implantation and development of the embryo and fetus, facilitate birth and secrete milk from mammary glands.

Fast Facts

The reproductive period of the female is between puberty (about age 12) and

menopause (about age 50).

Males will typically experience a slight lowering of sperm count as they age but fertility in males

has been documented in individuals as old as 94.

A Review of Meiosis

Meiosis in Males and Females

The Female Reproductive System

Male Reproductive System

3 Roles of Testosterone in Males

1. Determines and directs the development of male genitalia during embryonic development.

2. Ensures the development of secondary sex characteristics during puberty (facial hair, pubic hair, deepening of voice, testicle growth, skeletal muscle growth, etc.).

3. Stimulates sperm production.4. Maintenance of male sex drive throughout

the lifespan.

Testosterone

The Menstrual Cycle Prepares the Ovaries for Ovulation and the Uterus for Implantation

Starting at puberty (roughly 12 years of age), human females begin a hormonal cycle known as

the menstrual cycle.1. The purpose of the (28 day) menstrual cycle is

to time the release of an egg or ovum (ovulation) for fertilization and implantation into the endometrium (inner lining of the uterus).

2. Implantation must occur when the uterine lining (endometrium) is highly vascular.

3. No implantation/pregnancy leads to the breakdown of the endometrial blood vessels and menstrual bleeding.

Hormones from the BrainThe hypothalamus is the regulatory center of the

menstrual cycle. The hypothalamus produces a hormone know as

gonadotrophin releasing hormone (GnRH). The target tissue of GnRH is the nearby pituitary

gland and it results in the pituitary producing and secreting hormones into the blood stream:

1. Follicle Stimulating Hormone (FSH): Targets the ovaries.

2. Luteinizing Hormone (LH): Targets the ovaries.

Effects of FSH and LH on the Ovaries

The hormones FSH and LH have several effects on the ovaries:1. Increase in the production/secretion of estrogen

by the follicle cells of the ovary.2. Estrogen enters the bloodstream and targets the

endometrium of the uterus—increasing the blood vessels of the endometrium.

Hormonal Feedback Loops and Homeostasis

FSH and LH also result in the production of structures within the

ovaries known as Graafian follicles. Follicle cells are the true reproductive cells and the true reproductive cells known as oocytes.Under the chemical stimulation of FSH and LH, the

follicle cells and oocytes take on an arrangement known as a Graafian follicle.

1. FSH level rises and stimulates follicle development and estrogen secretion by the follicle cells.

2. Estrogen makes the follicle cells produce more FSH receptors, becoming more receptive to FSH.

3. This positive feedback makes estrogen levels rise & stimulate endometrial repair.

4. Estrogen levels rise to a peak and stimulate LH secretion by the pituitary gland.

5. LH rises to a peak and causes the egg to be released from the follicle (Ovulation).

6. LH causes the follicle cells to secrete less estrogen (neg. feedback) and more progesterone. After ovulation, LH causes the follicle to develop into the corpus luteum.

7. The corpus luteum secretes large amounts of progesterone, causing the uterus to prepare for the embryo.

8. High progesterone/estrogen levels inhibit FSH and LH secretion (neg. feedback) because FHS/LH initially stimulated estrogen/progesterone secretion.

9. Progesterone and estrogen levels fall if no embryo is formed. Eventually, the levels are low enough to allow FSH and LH secretion.

10. FSH levels rise again, staring the next menstrual cycle.

In-Vitro Fertilization (IVF) - Technology

Some couples are unable to bear children for a variety of reasons:

1. Males with low sperm counts.2. Males who are impotent (unable to achieve or

maintain an erection).3. Females who cannot ovulate normally.4. Females with blocked Fallopian Tubes.5. Endometriosis.6. Unexplained causes.

In-Vitro = “Within the Glass”

Steps of an IVF Procedure

Steps of an IVF Procedure1. A woman is usually injected with FSH for about 10 days

ensuring the development of Graafian follicles within her ovaries. Several eggs (oocytes) are surgically harvested.

2. The man ejaculates into a container to obtain sperm cells needed for fertilization.

3. The harvested eggs are mixed with sperm cells in separate culture dishes.

4. Microscopic observation reveals which ova are fertilized and if early development is normal/healthy.

5. Two or three healthy embryos are selected and introduced into the woman’s uterus for implantation. The procedure is expensive and implanting more than one embryo is more cost effective and increases the risk that at least one embryo will implant in the uterus.

6. Cultured healthy embryos that are not implanted can be frozen and used later if another implantation is required.

Ethical Issues Concerning IVF (Pro)

IVF enables couples who would otherwise be unable to have children to have a family.

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

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

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

Arguments IVF (Con) Embryos produced during culturing but not

implanted are frozen or destroyed. The legal issues are complex regarding couples

that have separated or divorced. Genetic screening of embryos could promote the

selection of ‘desirable’ traits. Some reproductive problems of an individual are

genetically passed on and IVF bypasses nature’s way of decreasing the genetic frequency of the disorder.

Multiple births and the problems/costs associated with multiple births are more likely with IV than natural concpetion.