9.4 Regulating the Reproductive System

The Reproductive System

to unite a single reproductive cell from a female

with a single reproductive cell from a male

Both male and female reproductive systems

include a pair of gonads to produce:

1. reproductive cells (sperm, eggs)

2. sex hormones (regulate the reproductive system)

Male Reproductive System

Testes: produce and store large amount of sperm cells

Penis: deposits sperm in the female reproductive tract

The Y Chromosome

contains a gene called testis-determining factor (TDF),

which produces male sex hormones (androgens) that

initiate development of the male sex organs in the fetus

Maturation of the Male Reproductive

System

born with an immature set of reproductive organs

at puberty (10 to 13 years of age):

hypothalamus produces gonadotropin-releasing hormone (GnRH)

anterior pituitary gland releases

1. follicle-stimulating hormone (FSH) and

2. luteinizing hormone (LH)

cause the testes to produce sperm and release testosterone

Testosterone: development of sex organs and secondary sex

characteristics (eg. facial hair, muscle development)

Negative Feedback Loop

To keep the level of sperm production constant

Hypothalamus releases GnRH

Anterior pituitary releases FSH and LH

FSH causes the testes to produce sperm and

to release a hormone called inhibin

Inhibin acts on the anterior pituitary to inhibit

the production of FSH

FSH levels drop, testes release less inhibin

Negative Feedback Loop

To maintain secondary sex characteristics

Hypothalamus releases GnRH

Anterior pituitary releases FSH and LH

LH causes interstitial cells in the testes to

release the hormone testosterone

Promotes development of muscle and facial

hair

Testosterone acts on the anterior pituitary to

inhibit the release of LH

Aging in the Male Reproductive System

Healthy males can be fertile for their entire lives

some men may experience andropause – a drop in

testosterone level (around the age of 40)

Symptoms: a decrease in sperm production, fatigue,

loss of muscle mass, and possible depression.

Female Reproductive System

includes a pair of gonads (ovaries)

produce only a limited number of

reproductive cells (ova)

fertilization occurs in the oviduct

fetal development takes place in

the uterus

vagina is both the organ of sexual

intercourse and the birth canal

Oogenesis

The Ovaries

produce eggs inside the follicles

Ovulation: each month, a follicle matures and ruptures, releasing a

mature egg into a tube called the oviduct

the egg can survive in the oviduct for up to 24 hours after ovulation

Projections called fimbriae sweep the egg toward the oviduct

oviduct is lined with cilia, which beat to create a current that carries

the egg through the oviduct to the uterus

The Uterus

a muscular organ that holds and nourishes a developing fetus

endometrium: the lining of the uterus, has blood vessels to provide

nutrients for a fetus

If fertilization occurs, the fertilized egg (zygote) moves through

the oviduct to the uterus and implants in the endometrium, and

embryo begins to develop.

Unfertilized eggs do not implant. The endometrium disintegrates,

and its tissues and blood flow out the vagina.

The Uterus

Maturing of the Female Reproductive

System

born with an immature set of reproductive organs

puberty begins between 9 and 13 years of age

FSH and LH act on the ovaries to produce the female sex hormones estrogen and progesterone

These hormones are involved in a reproductive cycle and stimulate the development of secondary sex characteristics

Regulation of the Female Reproductive

System – Menstrual Cycle

a reproductive cycle, approx. 28 days long

ensures that an egg is released at the same time the uterus is most receptive to a fertilized egg

If the egg (ovum) is not fertilized within 24 hours of being released from the ovary, fertilization can no longer occur uterine lining is shed and the cycle will begin again.

controlled by estrogen and progesterone

composed of two interconnected cycles:

1. the ovarian cycle (takes place in the ovaries)

2. the uterine cycle (takes place in the uterus)

The Ovarian Cycle

Each follicle contains a single, immature egg

At birth, a female has about 2 million follicles

at puberty only 400 000 viable

only 400 will develop into a mature follicle and release an egg

2 stages: the follicular stage and the luteal stage

The Ovarian Cycle -

Follicular stage

anterior pituitary secretes FSH

FSH stimulates one follicle to mature

maturing follicle releases estrogen and progesterone

Estrogen: 1. inhibits anterior pituitary from secreting FSH

2. triggers release of gonadotropin-releasing

hormone (GnRH)

GnRH stimulates the anterior pituitary to secrete LH

LH triggers ovulation: follicle bursts, releasing its egg.

Ovulation marks the end of follicular stage

The Ovarian Cycle –

Luteal stage

Once the egg is released

LH causes the follicle to develop into a corpus luteum

corpus luteum secretes progesterone and estrogen

inhibit LH and FSH production in the anterior pituitary

corpus luteum degenerates

progesterone and estrogen levels drop

increased FSH secretion from the anterior pituitary

Follicular stage:

anterior pituitary: FSH ↑

one follicle matures

estrogen and progesterone ↑

Estrogen FSH↓ , GnRH ↑

LH ↑ Ovulation

Luteal stage:

LH corpus luteum

progesterone and estrogen ↑

LH and FSH ↓

corpus luteum degenerates

progesterone and estrogen ↓

FSH ↑

The Uterine Cycle

build-up of blood vessels and tissue in the endometrium

prepares the uterus to receive and nurture a fertilized egg

The Uterine Cycle

build-up of blood vessels and tissue in the endometrium

prepares the uterus to receive and nurture a fertilized egg

If fertilization occurs:

fertilized egg implants in the thickened endometrium

high Progesterone: maintains the endometrium to support the fetus

high estrogen: prevents maturation of other follicles

If fertilization does not occurs:

corpus luteum degenerates

estrogen and progesterone levels drop

the endometrium breaks down and menstruation begins

The Uterine Cycle

begins on Day 1 of menstruation

corpus luteum has degenerated

progesterone and estrogen: low

Menstruation lasts for 5 days

At the end of menstruation, the

endometrium is very thin

A new follicle is maturing during

this time and releasing estrogen.

The Uterine Cycle

On day 6:

high levels of estrogen cause the

endometrium to begin to thicken

On day 14 (after ovulation):

corpus luteum releases progesterone

rapid thickening of endometrium

Between days 15 and 23:

endometrium can double or triple in

thickness

Aging and the Menstrual cycle

The number of viable follicles decreases with age

decrease in estrogen and progesterone

menstrual cycle becomes irregular, and eventually stops altogether

(menopause) around age 50

Menopause: mood changes, high cholesterol levels, decreased bone

mass, “hot flashes”, greater risk of cancer of the reproductive organs.

Hormone replacement therapy (HRT)

delivers low doses of estrogen with or without progesterone

not widely used due to increased risk of heart disease, blood

clots, breast cancer, and dementia

Endocrine Disruptors

Substances that interfere with the normal functions of hormones

disturb the development and reproduction of organisms by

mimicking natural hormones or by blocking their effects

Any endocrine disruptor that

mimics estrogen can cause

feminization in male organisms

many come from sewage and

mill wastes

can also be found in cosmetic

products such as nail polishes

Endocrine Disruptors

Substances that interfere with the

normal functions of hormones

disturb the development and

reproduction of organisms by

mimicking natural hormones or by

blocking their effects

Any endocrine disruptor that

mimics estrogen can cause

feminization in male organisms

Many endocrine disruptors come