Chapter4 (Gametogenesis) Flashcards
What is gametogenesis?
Gametogenesis is the production of haploid gametes by diploid multicellular
organisms through the process of meiosis.
What is Oogenesis ?
Production of female gametes
What is spermatogenesis?
Production of male gametes
Where does Oogenesis occur?
With in the follicle of the ovary
In spermatogenesis primordial germ (germinal epithelial cells) cells divide repeatedly by mitosis to form
diploid spermatogonia
spermatogonium increases in size (2x) to form
a primary spermatocyte (sperm mother cell).
the 1st meiotic division in spermatogenesis gives rise to
two secondary spermatocyte,
the 2nd meiotic division in spermatogenesis gives rise to
a group of four spermatids.
spermatid, unspecialised cells,
differentiates Into
a spermatozoon with
characteristic head and tail.
Sperms are produced at the rate of
about 120 million per day.
Maturity of a given sperm takes
about 70days (2months).
Where does spermatogenesis takes place?
The walls of somniferous tubules
The primordial germ cells are formed from
the germinal epithelium lining the outside of the tubule.
The final transformation of spermatids to spermatozoa takes place in what part of the wall?
The part of the wall immediately adjacent to the lumen.
heads of the developing sperms are enveloped by
large sertoli cells,
Where does sperm derive their nourishment from?
sertoli cells,
The sperm _____ project into the fluid filled lumen of the tubule.
tails
What is the length of sperm?
2.5micro meter long.
What does the head of a sperm contains and describe the content?
- the nucleus which contains the haploid number of chromosomes.
- the acrosome, a large lysosome which contains hydrolytic enzymes which will be involved in the penetration of the layers of cells surrounding the egg immediately before fertilization.
The short neck of the sperm contain
a pair of centrioles lying perpendicular to each other.
The middle piece is the first part of the tail and is enlarged by
the presence of many mitochondria.
The sperm swims at what speed ?
About 1 - 4mm per minute.
Spermatogenesis is controlled by
the hypothalamus and the anterior pituitary gland working together.
The hypothalamus secretes
gonadotrophins-releasing hormone (GRH)
What stimulates the anterior pituitary?
gonadotrophins-releasing hormone (GRH)
The two gonadotrophins are
follicle stimulating hormone (FSH) and luteinising hormone (LH).
FSH stimulates spermatogenesis by
stimulating sertoli cells to complete the development of spermatozoa from spermatids
Function of the luteinising hormone
stimulates the synthesis of the hormone testosterone by the leydig cells (interstitial cells) of the testis.
Function of the Testosterone
stimulates growth and development of the germinal epithelial cells (spermatogonia) to form sperms, and also works with follicle stimulating hormone to stimulate the sertoli cells.
increase in the level of testosterone cause a backward effect of
decrease in secretion of gonadotrophins-releasing hormone from the hypothalamus.
Inhibin negative feedback causes
Inhibition of follicle stimulating hormone
Testosterone negative feedback causes
inhibition of LH
Primordial germ cells, divide to form
oogonia during development of foetus
oogonium becomes enveloped by a layer of
follicle cells (granulosa cells).
The structure of the oogonium envelope by a layer of follicle cell (granulosa cells) is called
Primordial follicle
At birth there are about _____ of these follicles,between ______primary follicles in each ovary, but only 200 to 400 complete their development.
- 2 million
- 200,000 and 400,000
Undeveloped primordial follicle degenerate into
atretic follicles
primary oocyte, remains at ______ of meiosis I throughout childhood.
prophase
cells from the stroma of the ovary form further layers outside the primary oocytes known collectively as
the theca.
As the primary follicle develops, a fluid is secreted by the _____ which contain
- granulosa cells
- ostrogen
What is the anthrum?
A fluid-filled space in the follicle of the ovum
Oestrogen stimulates growth of
the follicles, which eventually becomes a mature follicle
When does the secondary oocyte undergoes the second meiotic division l
At fertilization
The cortical granules of the eggs form
a layer just beneath the surface.
The yolk is concentrated towards
the lower end of the egg, away from the nucleus.
What is the animal pole of the egg?
The non-yolky end with the nucleus and active cytoplasm
The more inert yolky end is the
vegetative pole.
What provides a source of nourishment for the embryo?
The yolk
For eggs without yolk nourishment is supplied by
separate yolk filled cells or by a nutritive tissue surrounding the embryo.
the inner membrane of the egg is the _____
Plasma membrane
the outer egg membrane is the
vitelline membrane
Feedback effect of oestrogen
- stimulates, repair and develop the lining of the uterus, the encometrium.
- inhibits the secretion of follicle stimulating hormone..
What is the target of luteinising hormone in females
it causes ovulation.
After ovulation, the remaining part of the graafian follicle is stimulated by______ to develop into the _____
- luteinising hormone
- corpus luteum (yelfow body).
Released of progesterone is associated with
a rise in body temperature. of the female just after ovulation.
The corpus luteum secrete
ostrogen, as well as progesterone
What happens if fertilization does not occur?
the corpus luteum starts to degenerate about day 28
What causes menstruation (the period)?
the breaks down of endometrium
What is the primary location for storage and development of sperm cells
Epididymis
Ovulation in occur on what day of the menstrual circle ?
14th
Sperm is viable from _____ to _____ in the female genital tract
24 to 72hrs
Oocytes is viable from ____ to ____hours
12 to 24hrs
The first meiotic division in spermatogenesis gives rise to
Secondary spermatocyte
The second meiotic division in spermatogenesis gives rise to
Spermatids
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