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………