oogenesis

Question 1

Primordial follicle

Answer 1

it is the earlier stage of development, it is formed during the fetal life. it is composed of an oocyte 1 blocked at prophase 1 of meiosis and surrounded with few follicular.

Question 2

The primary follicle

Answer 2

the oocyte is now surrounded with more follicular cells

Question 3

The secondary follicle

Answer 3

the follicular cells from several layers composing “granulosa”. oocyte 1 is now surrounded with a thick membrane called “zona pellucida”

Question 4

the tertiary or cavitary follicle

Answer 4

the granulosa presents several small cavities, the follicle is now surrounded with a fibrous membrane called “theca”

Question 5

the mature or Graafian follicle

Answer 5

the granulosa presents one unique and large cavity called “atrium” filled with follicular liquid. the follicle is now surrounded with 2 fibrous membranes: the internal and external theca

Question 6

yellow body or corpous luteum

Answer 6

at time of ovulation, graafain follicle bursts to release oocyte 2 blocked at metaphase 2 into the oviduct. the ruptured follicle( granulosa+ theca internal and external) in the ovaries becomes yellow body that secretes hormones.

Question 7

White body or corpous albician

Answer 7

at the end of the cycle, yellow body becomes white body and degenerates.

Question 8

What is oogenesis?

Answer 8

it is the change of a germ cell called “oogonia, one oogonium” having 2n chromosomes into a haploid called oocyte having n chromosome.

Question 9

Multiplication phase

Answer 9

it starts during the fetal life, in the ovaries of the fetus, initial germ cell or oogonia undergoes successive mitosis to increase in number to reach several million, then multiplication stops completely.

Question 10

Growth phase

Answer 10

the oogonia begin to increase in size. also interphase takes place for DNA to duplicate and oocytes 1 are produced having 2n chromosomes and every chrs is of 2 chrd

Question 11

Maturation phase

Answer 11

• oocytes 1 start meiosis 1 and are blocked at prophase 1.
• at birth, only 5 to 6 million of oocytes 1 remain and form primordial follicles, they will remain in a resting period till puberty.
• from the age of puberty and periodically, a certain number of primordial follicles which were at rest from birth will resume their development cycle.
• 4 months before menstruation one primordial follicle becomes cavitary follicle and from day 0 till day 14 cavitary follicle becomes graafain follicle.
• few hours before ovulation, oocyte 1, completes its first meiotic division and gives rise to 2 unequal cell: oocyte 2 of n chrs (2 chrd/chrs) and a polar body of n chrs.
• the oocyte 2 starts its second meiotic division and stops at metaphase 2.
• at time of ovulation, oocyte 2 is released from graafain follicle to oviduct where fertilization may take place.
• if fertilization takes place, then oocyte 2 continuous meiosis 2 and gives rise to 2 unequal cells: an ootid of n chrs of 1 chrd and a second polar body then ootid unties with the sperm cell to form a fertilized ovum that becomes a zygote.
• it no fertilization, then oocyte 2 survives only for24 hrs, then degenerates.