IV) Female Reproductive System C) Menstrual Cycle

IV) Female Reproductive SystemC) Menstrual Cycle

the ovaries contain about 400’000 follicles at puberty. many follicles develop during each female

reproductive cycle but usually only one becomes dominant and reaches maturity.

remaining follicles deteriorate and are reabsorbed within the ovaries.

Between the ages of 12 and 50 years, approximately 400 eggs will mature in a women’s life.

IV) Female Reproductive SystemC) Menstrual Cycle remaining follicles deteriorate and are reabsorbed within the

ovaries. Between the ages of 12 and 50 years, approximately 400 eggs will

mature in a women’s life.

menopause the termination of the female reproductive years

and a drop in the production of female hormones. a few follicles remain. older follicles are presumed to have a greater

chance of genetic damage.

Ovary

Hypothalamus

Pituitary

Corpus LuteumGrowing Follicle

estrogen progesterone, some estrogen

ovulation

FSH

increased estrogen at midcycle stimulate

LH secretion

Gonadotropin Releasing Hormone

LH

Increases progesterone, estrogen after ovulation

inhibit FSH, LH secretion

- -

-

+

IV) Female Reproductive SystemC) Menstrual Cycle

Feedback Control of the Menstrual Cycle the hypothalmus-pituitary complex ultimately

regulates the production of estrogen and progesterone.

in females the gonadotropins, FSH and LH regulates the control of estrogen and progesterone which are produced in the ovaries.

progesterone and estrogen in turn regulate FSH and LH through negative and positive feedback.

IV) Female Reproductive SystemC) Menstrual Cycle in females the gonadotropins, FSH and LH regulates the

control of estrogen and progesterone which are produced in the ovaries.

progesterone and estrogen in turn regulate FSH and LH through negative and positive feedback.

the onset of puberty is signalled by the release of GnRH (gonadotropin-releasing hormone) from the hypothalamus

GnRh activates the pituitary gland. the pituitary gland is the site of production

and storage of FSH and LH

IV) Female Reproductive SystemC) Menstrual Cycle

GnRh activates the pituitary gland. the pituitary gland is the site of production and storage of

FSH and LH during the follicular phase blood carries FSH to the ovaries

stimulating follicular development follicles within the ovaries secrete estrogen

~ this initiates the development of the endometrium.

~ rising estrogen provides negative feedback to pituitary gland to shut off FSH secretion

the follicular phase ends and the rise of the estrogen levels stimulates LH producing cells of the pituitary gland.

~The spike in LH secretion causes ovulation.

IV) Female Reproductive SystemC) Menstrual Cycle

the follicular phase ends and the rise of the estrogen levels stimulates LH producing cells of the pituitary gland.

~The spike in LH secretion causes ovulation.

after ovulation the remaining follicular cells under the influence of LH are transformed into the corpus luteum. (The luteal phase begins)

cells of the corpus luteum secrete both estrogen and progesterone (further increases the development of the endometrium)

the build up of estrogen and progesterone trigger a second negative feedback that inhibits the release of both FSH and LH

IV) Female Reproductive SystemC) Menstrual Cycle

cells of the corpus luteum secrete both estrogen and progesterone (further increases the development of the endometrium)

the build of estrogen and progesteron trigger a second negative feedback that inhibits the release of both FSH and LH

without gonadotropic hormones the corpus luteum begins to deteriorate (slows estrogen and progesterone production)

the drop in ovarian hormones signals the beginning of menstruation.

some birth control pills are high doses of progesterone that inhibit ovulation.

IV) Female Reproductive SystemC) Menstrual Cycle

Hormones Location Description of Function

Estrogenfollicle cells

(ovary)

inhibits growth of facial hair, intiates secondary sexual characteristics, and causes thickening of the endometrium

Progesteronecorpus luteum

(ovary)

inhibits ovulation, inhibits uterine contractions, firms the cervix, and stimulates the endometrium

Follicle-stimulating Hormone (FSH)

pituitary stimulates the develoment of the follicle cells in the ovary

Luteinizing Hormone (LH)

pituitary stimulates ovulation and the formation and maintenance of the corpus luteum.

V) Fertilization, Pregnancy and Birth

V) Fertilization, Pregnancy and BirthI) Fertilization

I) Introduction fertilization occurs when there is a union

between a sperm cell and a secondary oocyte in a fallopian (oviduct) tube

the fertilized oocyte completes development and becomes the fertilized ovum (called a zygote)

V) Fertilization, Pregnancy and BirthI) Fertilization the fertilized oocyte completes

development and becomes the fertilized ovum (called a zygote)

about 500 million sperms are ejaculated during intercourse

150 million to 300 million sperm travel through the cervix into the uterus.

a few hundred reach the fallopian tube. several sperm attach to the outer edge

of the ovulated oocyte and one sperm cell fuses with it.

V) Fertilization, Pregnancy and BirthI) Fertilization

V) Fertilization, Pregnancy and BirthI) Fertilization

it takes between three and five days for the fertilized egg to travel the 10 to 12 cm of the fallopian tube during this time it undergoes many cell

divisions in a process called cleavage cleavage involves equal divisions of the cells of

zygote without an increase in size.

V) Fertilization, Pregnancy and BirthI) Fertilization

as a result of cleavage the cells of zygote become progressively smaller.

by the time it reaches the uterus the zygote has developed into a fluid filled structure called a blastocyst.

V) Fertilization, Pregnancy and BirthI) Fertilization

the blastocyst consists of an outer sphere of cells from which the extraembryonic structures develop and an inner cell mass, from which the embryo develops.

once in the uterus the blastocyst becomes attached to the wall of the endometrium, a process referred to as implantation.

V) Fertilization, Pregnancy and BirthII) Preventing Polyspermy

contact and fusion causes ion channels to open in the egg’s plasma membrane. this allows sodium ions to flow into the egg.

this changes the membrane potential (depolarization) occurs within about 1-3 seconds after sperm binds. prevents additional sperm from fusing with egg’s

plasma membrane. this is called “fast block to polyspermy”

V) Fertilization, Pregnancy and BirthII) Preventing Polyspermy

membrance depolarization last for about a minutes Within seconds after the sperm binds to egg cortical granules

fuse with the eggs plasma membrane. this initiates the cortical reaction.

the reaction causes a fertilization envelope to form that resists the entry of additional sperm.

this is a longer term reaction is called “slow block to polyspermy”

Fig. 47-4EXPERIMENT

10 sec afterfertilization

1 sec beforefertilization

RESULTS

CONCLUSION

25 sec 35 sec 1 min500 µm

10 sec afterfertilization

20 sec 30 sec500 µm

Point ofsperm

nucleusentry

Spreadingwave of Ca2+

Fertilizationenvelope

Fig. 47-4a

EXPERIMENT

10 sec afterfertilization

25 sec 35 sec 1 min500 µm

Binding of sperm to egg

Acrosomal reaction: plasma membranedepolarization (fast block to polyspermy)

Increased intracellular calcium level

Cortical reaction begins (slow block to polyspermy)

Formation of fertilization envelope complete

Increased intracellular pH

Fusion of egg and sperm nuclei complete

Increased protein synthesis

Onset of DNA synthesis

First cell division

1

Se

co

nd

s

2

3

68

10

4

20

30

501

2

40

34

10

5

20

3040

9060

Min

ute

s

V) Fertilization, Pregnancy and BirthIII) Structures that Support the Developing Embryo

in humans, four days after fertilization, the zygote becomes an embryo.

after the eighth week of pregnancy the zygote is referred to as a fetus.

for the pregnancy to continue, menstruation cannot occur.

a shedding of the endometrium would also mean a shedding of the embryo from the uterus.

V) Fertilization, Pregnancy and BirthIII) Structures that Support the Developing Embryo

the problem: to prevent menstruation progesterone and estrogen

levels must remain high. high level of these hormones have a negative

feedback effect on the secretion of gonadotropic hormones.

LH levels must remain high to sustain the corpus luteum.

If the corpus luteum deteriorates the levels of estrogen and progesterone drop stimulating uterine contractions and endometrium shedding.

V) Fertilization, Pregnancy and BirthIII) Structures that Support the Developing Embryo

the solution: the blastocyst secretes hormones

the outer layer of the blastocyst gives rise to two structures:

the chorion and the amnion the chorion produces the hormone human

chorionic gonadotropic hormone (hCG) this hormone maintains the corpus luteum

for the first three months of pregnancy

V) Fertilization, Pregnancy and BirthIII) Structures that Support the Developing Embryo

the chorion produces the hormone human chorionic gonadotropic hormone (hCG)

this hormone maintains the corpus luteum for the first three months of pregnancy

the corpus luteum continues to produce progesterone and estrogen which maintains the endometrium

hCG levels in the urine is what a pregnancy test detects.

the amnion is a fluid filled extraembryonic structure.

V) Fertilization, Pregnancy and BirthIII) Structures that Support the Developing Embryo

Amniotes

Embryos of birds, other reptiles, and mammals develop in a fluid-filled sac in a shell or the uterus

Organisms with these adaptations are called amniotes

During amniote development, four extraembryonic membranes form around the embryo: The chorion functions in gas exchange The amnion encloses the amniotic fluid The yolk sac encloses the yolk The allantois disposes of waste products

and contributes to gas exchange

Amniotes

Embryo

Amnion

Amnioticcavitywith

amnioticfluid

Shell

Chorion

Yolk sac

Yolk (nutrients)

Allantois

Albumen

V) Fertilization, Pregnancy and BirthIII) Structures that Support the Developing Embryo

between the amnion and the embryo is the amniotic cavity.

the amniotic cavity is a fluid filled sac that insulates the embryo, and later the fetus, protecting it from infection, dehydration, impact and changes in temperature.

The extraembryonic coelom is a fluid filled space between the amnion and the chorion.

by the second week of pregnancy the yolk sac forms beneath the embryo (there is no yolk).

this is the site of early red blood cell production and later it contributes to the primitive digestive tract.

V) Fertilization, Pregnancy and BirthIII) Structures that Support the Developing Embryo

cells from the embryo and endometrium combine to form the placenta

the placenta allows for the exchange of materials between the mother and embryo

at four months of pregnancy the placenta begins to produce estrogen and progesterone

V) Fertilization, Pregnancy and BirthIII) Structures that Support the Developing Embryo