The process of a male gamete (sperm) fertilizing a female gamete (egg or ovum)

The process of a male gamete (sperm) fertilizing a female gamete (egg or ovum)

The cellular union between each gamete ensures that half the genetic makeup of the resulting zygote is derived from each parent.

Ensures genetic variationDimorphism – different body forms of males

and females Hormones play a role in both development

and regulation of sexual physiology

The Reproductive System produces gametes The structures of the male and the female

reproductive system are adapted for production and release of the gametes In Females: Nurtures and protects the developing

embryo

The release of LH (Luteinizing Hormone) stimulates cells to produce increased amounts of testosterone. (Signaled by Hypothalamus)

Testosterone causes the male physical changes associated with puberty Together with FSH (Follicle-Stimulating

Hormone) stimulates the development of sperm

Diagram: Page 199

Figure 6.19

Erectile Tissue

Menstrual Cycle – the process of egg formation

and release One ovary “usually” produces and releases

one mature ovum every 28 days. The purpose is for fertilization and

implantation Implantation must occur in a highly

vascular endometrium Cycle is regulated by the hypothalamus

The highly vascular endometrium is not maintained if there is no implantation The breakdown of blood vessels leads to

menstruation Menstruation = not pregnant

Ovaries – Primary reproductive organ in females

The hypothalamus produces a hormone known as gonadotrophin releasing hormone (GnRH)

The target of GnRH is the pituitary gland and results in 2 hormones into the blood stream. LH (Luteinizing Hormone) and FSH (Follicle-

Stimulating Hormone) stimulates ovaries Ovaries produce estrogen

EstrogenEstrogen Target tissue is the

endometrium of the uterus Results makes

endometrium is making it highly vascular

Estrogen causes the female physical changes associated with puberty

FSH & LHFSH & LH Produce structures within the ovaries

known as Graafian Follicles Ovaries contain follicle cells and the

reproductive cells known as oocytes FSH & LH arrange these cells into a

structure known as Graafian Follicles

FSH & LHFSH & LH A spike of these hormones causes ovulationA spike of these hormones causes ovulation

Zona Pellucida – an inner ring of follicle cells andZona Pellucida – an inner ring of follicle cells and

a glycoprotein membrane that a glycoprotein membrane that

accompanies the oocyte.accompanies the oocyte. This entire structure is known as a follicle and This entire structure is known as a follicle and

typically enters the Fallopian tube typically enters the Fallopian tube

The outer ring of follicle cells remain within the ovary They produce a hormone: Progesterone Corpus Luteum – structure formed after the

same follicle cells continue to divide and fill in the area left by

ovulation Progesterone is continually produced for 10 –

12 days

Progesterone Maintains the thickened, highly vascular

endometrium As long as progesterone is produced

enometrium will not beak down waiting for implantation

Estrogen and progesterone are negative feedback for hypothalamus

Hypothalamus does not produce GnRH, so FSH and LH are not produced, Graafian Follicle is not produced

If there is no pregnancy the corpus luteum breaks down Declines in both progesterone and estrogen The highly vascular endometrium will not

be maintained Capillaries and small blood vessels begin to

rupture and menstruation begins The drop in progesterone and estrogen

signals the hypothalamus to secrete GnRH and the process begins again

Natural fertilization usually occurs in the Fallopian Tubes 24 – 48 hours after fertilization

Some couples cannot bear children because: Males with low sperm count Males with impotence Females who cannot ovulate Females with blocked Fallopian Tubes

In-vitro fertilization is a fairly new technology used to overcome these issues

Steps of an IVF Procedure To prepare women are injected with

FSH for 10 days This ensures ovulation when you want

Several eggs are harvested surgically Man ejaculates in a container to collect

sperm for fertilization Harvested eggs are mixed with sperm

in culture dishes

Steps of an IVF Procedure Microscopic observation reveals which ova

are fertilized and if the early development appears normal and healthy

Usually 2 or 3 healthy embryos are introduced into the woman’s uterus for implantation

The procedure is expensive and using one embryo presents a high risk of failure That means you have to repeat the procedure

More embryos implanted increases the chances of success: oh and multiple fetuses…..

Healthy not planted embryos can be frozen

Ethical Issues For: It enables couples who would otherwise be

unable to have children to have a family Embryos that are visibly not healthy in the

early stages of development can be eliminated from implantation

Genetic screening is possible Technology will advance and lead to

further benefits in reproductive biology Superbaby???

Ethical Issues Against: Embryos produced during culturing, not

implanted are either frozen or destroyed There are complex legal issues concerning the

use of those frozen embryos when couples split up

Genetic screening of embryos could lead to society choosing desirable characteristics

IVF bypasses natures way of decreasing the genetic frequency of that reproductive problem

Multiple births………