gametogenesis Flashcards
What is gametogenesis?
The process by which the mature gametes are formed from the primitive germ cells
What is gametogenesis in females called?
Oogenesis
What is the gametogenesis in males called?
Spermatogenesis
Where does gametogenesis occur?
In the gonads
What happens to the cytoplasm in primitive germ cells during gametogenesis?
In the ovum, the cytoplasm increases
In the sperm, the cytoplasm decreases
What happens to the nucleus of primitive germ cells during gametogenesis?
It undergoes mitotic division to reduce the number of chromosomes it has to itself
When does spermatogenesis start ?
At puberty and continues till old age
How many days does it take for a spermatogonium to develop into a mature spermatozoon?
Approx 74 days
How many sperm cells are produced daily?
Around 300 million
Where does spermatogenesis occur?
In the seminiferous tubules in the testis and completed in the epididymis
What do sertoil cells do ?
Support and protect the germ cells,
Participate in nutrients and assist in the release of mature spermatozoa
What hormone regulates spermatogenesis?
LH
What does LH do in men ?
Stimulate testosterone production and promote spermatogenesis
What does FSH do in men?
Stimulate testicular fluid production and synthesis of androgen receptor proteins
What is the purpose of spermatogenesis?
To reduce number of chromosomes from diploid to haploid
Change the shape of the germ cells to produce a highly motile sperm
Production of a large number of sperms
Determine the sex of the sperm
What are the stages of spermatogenesis?
Spermatocytogenesis
Spermiogenesis
What is spermatocytogenesis?
The process by which primitive germ cells differentiate into spermatids
What is spermatocytogenesis?
The process by which primitive germ cells differentiate into spermatids
How many chromosomes are in spermatogonial stem cells?
46
Where are spermatogonia cells found ?
In the Walls of the seminiferous tubules of the testis, supported by sertoil cells
What is produced when spermatogonial stem cells undergo mitotic division?
Spermatogonia type A
What happens to spermatogonia type A?
It’s continues to divide to give spermatogonia type B
What happens to spermatogonia type B ?
Divides by mitosis to give primary spermatocytes
What happens to primary spermatocytes?
They undergo 1st meiotic division to produce two secondary spermatocytes ,
What happens to secondary spermatocytes?
They undergo 2nd mitotic division to produce two spermatids
22+X
22+Y
What is spermiogenosis?
The morphological unstructural changes resulting in the transformation of spermatids into spermatozoa
How is the sperm head formed?
Condensation of the nucleus
Shedding most of the cytoplasm
Formation of acrosomal cap from Golgi apparatus around half of the nucleus
How is the middle piece of the sperm formed?
Formed from mitochondrial sheet
What is the junction between the head and the middle piece of the sperm called?
The neck
How is the tail of the sperm formed?
It is formed by elongation of one of the centrioles
What is oogenesis?
production of a mature ovum ready for fertilization
What does oogenesis occur?
In the cortex of the ovary
What is the aim of oogenesis?
Reduction of number of chromosomes from diploid to haploid
Increase the size of the ovum from 30 to 120 microns
What cells divide by mitosis and differentiate into oogonia?
PGCs
Primordial germ cells
What are primary oocytes?
Enlarged oogonia
When so all the primary oocytes start prophase of meiosis 1?
Near the time of birth
What are primordial follicles?
Flat epithelial cells that surround the primary oocytes
How many primary oocytes are there at birth ?
0.7 to 2 million
How many oocytes are present at the beginning of puberty?
Approximately 400,000
How many oocytes will be ovulated?
Fewer than 500
What are the two processes of oogenesis?
Maturation of the primary oocyte itself
Maturation of the follicular cells
How is the primary follicle formed?
The maturation of the follicular cells
The simple flat epithelium which surrounds the primary oocyte begins to grow
It changes from flat to cuboidal epithelium
Proliferate to produce stratified epithelium of granulosa cells
Where do granulosa cells rest?
Basement membrane
How is the Zona pellucida formed?
Granulosa cells and the oocyte secrete and layer of Glock proteins on the surface of the oocyte
What do the cells of the theca folliculi organize into ?
Inner layer ~ theca interna
Outer layer ~ theca externa
How was the secondary follicle formed?
The maturation of the follicular cells
Fluid-filled spaces appear between granulosa cells which coales forming The antrum
What is the cumulus oophorus ?
The layer of granulosa cells that surround the oocyte ~ after the second follicle formation, these cells stay intact and form the cumulus oophorus
What does LH do?
When the secondary follicle is mature, It’s induces the preovulatory growth phase
What is the result at the end of meiosis one?
Maturation of his primary oocytes itself
The secondary oocyte receives most of a cytoplasm
The first polar body receives small amount of cytoplasm
What is the result at the end of meiosis one?
Maturation of his primary oocytes itself
The secondary oocyte receives most of a cytoplasm
The first polar body receives small amount of cytoplasm
How long does the cell stay in metaphase during meiosis 2 before ovulation?
Approximately 3 hours
How long after ovulation does the cell degenerate if not fertilized?
24 hours
What is the ovarian cycle controlled by?
The hypothalamus
Where is GnRH produced and what does it do?
Produced in the hypothalamus
Epsom salts of the anterior pituitary gland which secretes gonadotropins
What are the two types of gonadotrophins ?
FSH and LH
How many days does it take to complete one ovarian cycle?
28
What are the three phases of the ovarian cycle?
a. follicular phase
b. Ovulation
c. luteal phase
Describe the pre-opulatory phase ( the follicular phase)
It’s the first half of ovarian cycle
At the beginning the anterior pituitary secretes FSH
Normally only one follicle reaches maturity and only one oocyte is ovulated - the others degenerate
FSH also stimulates maturation of follicular cells
The growing full of cells secretes estrogen
Feedback effects on the anterior pituitary
FSH secretion stops
The generation of primary follicles
What is ovulation?
It is the rupture of the Graafian follicle with extrusion of the ovum from the surface of the ovary
How many days before the next menstruation does ovulation happen?
Exactly 14 days
Does ovulation occur during pregnancy?
No
What is the name of the degenerated follicles?
Corpus atreticum
What happens in ovulation during the LH surge?
Graffian follicle will enlarge and become nearer to the surface
The follicle enters the preovulatory stage
The primary oocyte complete meiosis one to form the secondary outside and small polar body
Meiosis 2 is also initiated but the oocyte stops in metaphase for 3 hours before ovulation
What is the stigma?
When the surface of the ovary begins to bulge locally a vascular spot called the stigma appears on the apex
What hormone increases collagenase activity?
LH
What causes muscular contractions in the ovarian wall?
An increase in Prostaglandin due to LH surge
How is Corona radiata formed?
The oocyte, In metaphase phase of meiosis 2, is discharged from the ovary together with a large number of cumulus oophorus cells some of them arrange themselves around the zona pellucida to form the Corona radiata
Describe the luteal phase
It is the second half of the cycle
Due to LH, the ruptured graafian follicle is transformed into a yellow body called Corpus luteum
The corpus luteum secrete progesterone and a bit of estrogen to inhibit FSH and LH
Progesterone causes the uterine mucosa to enter the progestational stage in preparation for implantation of the embryo
What happens if fertilization does not occur?
The corpus luteum lives for 9 days only after ovulation, then shrinks and degenerates forming a fibrotic scar tissue called Corpus albicans
This leads to decrease the level of progesterone in the blood precipitating menstrual bleeding
What happens if fertilization does occur?
Degeneration of the Corpus luteum is prevented by hCG secreted by the embryo
The Coopers luteum continues to grow and forms the corpus luteum of pregnancy
Luteal cells continue to secrete progesterone until the end of the fourth month of pregnancy
Why is progesterone important?
It is essential to maintain pregnancy
The removal of the corpus luteum before the fourth month usually leads to an abortion
What happens at the end of the fourth month of pregnancy?
The corpus luteum of pregnancy regress slowly as secretion of progesterone by the placenta becomes adequate for maintenance of pregnancy
What are three layers that the wall of the uterus consists of?
Endometrium or mucosa - lining the inside wall
Myometrium - a thick layer of smooth muscle
Perimetrium - peritoneal covering of the outside wall
What is the uterine cycle?
The monthly cichlid changes comparing in the endometrium in response to cyclic changes which occur simultaneously in the ovaries during ovarian cycle
What are the stages that the uterine endometrium pass through?
Follicular or proliferative phase
Secretory or progestational phase
Menstrual phase
Describe briefly the follicular phase
Begins at the end of the menstrual phase and is under the influence of estrogen and parallel growth in the ovarian follicles
Briefly describe the secretory phase
Begins approximately 2 to 3 days after ovulation in response to progesterone produced by Corpus Luteum
Briefly describe what happens in the menstrual phase
The fertilization does not occur shedding of the endometrium occurs
If fertilization does occur the endometrium assists in implantation and formation of the placenta
What happens to the uterus at the time of implantation?
The mucosa of the uterus is in the secretory phase during which the uterine glands and arteries become coiled and the tissue becomes succulent
What are the three layers that form in the uterus at the time of implantation?
A superficial compact layer
An intermediate spongy layer
A thin basal layer
Where does the human blastocyte implant?
In the endometrium along the anterior and the posterior wall of the body of the uterus
At the time of implantation, what happens if the oocyte is not fertilized?
Venules and sinusoidal spaces gradually become packed with blood cells
During the menstrual phase blood escapes from the superficial arteries and pieces of the stroma and glands breakaway
During the following three or four days the compact and spongy layers are expelled and the basal layer is the only part of the endometrium that is retained
What are the arteries that supply the basal layer with blood ?
Basal arteries
