Lecture 4 - Gametogenesis Flashcards
What happens once the primordial germs cells migrate to the primitive gonad in the indifferent stage?
They proliferate via mitosis
Meiosis occurs (genetic variation)
Then cytodifferentiate into mature gametes (ova or sperm)
How does Oogensis differ too spermatogenesis in terms of the number of gametes produced per cycle?
Oogenesis = 1 Ovum + 3 polar bodies (polar bodies dont go on to produce anything)
Spermatogenesis = 4 gametes per cycle
What is the cell called when the 2 haploid cells fertilise forming a diploid cell?
Conceptus
What are the 2 functions of meiosis?
Reduce chromosome number in the gamete to 23
Ensures gametes are genetically varied/unique
How is genetic variation created in gametogenesis/meiosis?
Crossing over of the homologous areas of non sister chromatids
Independent assortment of the homologous chromosomes/bivalent
What is the crossed over region of the recombinant chromosomes called?
Chiasm a
Where does spermatogenesis occur?
Seminferous tubules
What are the 2 compartments of the seminferous tubules?
Basal compartment
Adluminal compartment
What cells reside in the basal compartment of the basal compartment?
Germs cells that carry out spermatogenesis
What is the blood testis barrier?
What is its function?
Where Sertoli cells form a barrier separating the environment for cytodifferentiation and the adluminal compartment
It prevents the immune system setting up an immune response against the sperm cells
What is the function of the Sertoli cells?
Provide the nutrients to the germ cells to carry out cytodifferntiation to become sperm cells
What structures do sperm move through starting with the Seminferous tubules?
Seminiferous tubules -> rete testis -> ductili efferentes -> epididymis -> vas deferens -> urethra
What is the point of the rete testis then the ductili efferentes?
Concentrates the sperm
What are spermatogonia?
Male germ cells/raw material for spermatogenesis
What type of division does spermatogonia undergo to renew?
Mitosis
What are the 2 types of spermatogonium?
Ad spermatogonium
Ap spermatogonium
What is Ad spermatogonium?
d for Dark sperm
Resting/reserve stock
What is Ap spermatogonium?
P for pale sperm
Active/ maintain stock, from puberty onwards produces Type B spermatogonia
What do Type B spermatogonia give rise to?
Primary spermatocytes
What is the process by which Type B spermatogonia produce spermatids?
Type B spermatogonia -> -> primary spermatocytes meiosis I -> secondary spermatocytes -> meiosis II -> 4 haploid spermatids
What is spermiogenesis?
When the spermatids produced mature produceing the finial mature spermatozoa
What is the spermatogenic cycle?
The TIME taken for reappearance of the same stage within a given segment of a seminiferous tubule n the spermatogenesis cycle
What is the spermatogenic wave?
The DISTANCE between the same stage of spermatogenesis in the seminiferous tubule
What is spermiation?
When spermatids are released into the lumen of seminferous tubules
The spermatids are non-motile until they reach the epididymis, how do they move to th epididymis?
Sertoli cell secretions assisted by peristaltic contraction
How are sperm adapted for fertilisation?
Many mitochondria
Tail has dynin protein responsible for motility
What parts of the male reproductive tract contribute the most to the male ejaculate volume?
Seminal vesicle (70%)
Secretions of prostate (25%)
Sperm via vas deferens (2-5%)
Bulbourethral gland / Cowper gland
What is contained in the secretions of the prostate and what is their importance?
Zinc needed for sperm to become motile
Proteolytic enzymes
What is sperm capacitation?
Where the conditions in the female genital tract stimulate the final maturation of the sperm allowing it to bind to the zona pellucida of the oocyte to initiate the acrosome reaction
What gets removed from the sperm membrane to allow it to bind to the zona pellucida?
Glycoproteins
Cholesterol
For IVF why must the sperm be put in capacitation media?
Capacitation media mimics the environment of the femal reproduction tract which provides the conditions to allow the sperm to bind to the zona pellucida
How do oocytes mature?
Germ cells migrate to gonadal cortex and differentiate into oogonia
Oogonia proliferate by mitosis
3rd month oogonia are in clusters surrounded by ovary flat epithelial cells
Primary oocytes formed by oogonia entering meiosis nad arresting in meiosis I
What is it called when primary oocytes begin to degenerate?
Atresia
What is the structure called when primary oocytes get surrounded by a layer of flat epithelial cells called follicular cells?
Primordial follicle
What are the stages that oocytes go through when maturing?
Preantral
Antral
Preovulatory
What occurs in the Preantral stage of oocyte maturtity?
As the primordial follicles grow the flat single epithelial cells forms a cuboidal stratified epithelium
These stratified epithelial cells are called Granulosa cells
What is the function of the granulosa cells (stratified epithelium) in the Preantral stage?
Secrete layer of glycoprotein on oocyte forming the Zona pellucida
What occurs during the Antral stage of oocyte development?
Fluid filled spaces appear between the granulosa cells forming the antrum
What is the inner layer of cells called surrounding the Antrum?
What is the outer layer surrounding the antrum?
Inner secretory layer = theca interna
Outer fibrous layer = theca externa
What is the function of the theca externa (outerfibrous layer of antrum)?
Produces androgens
What is the function of the theca interna (inner secretory layer)?
Converts androgens to oestrogen
What occurs during the preovulatory stage?
Surge in LH induces preovulatory growth phase
One cell receives most of the cytoplasm from the other then enters meiosis II and then arrests
If the oocyte enters into arrest at meiosis II when does it actually complete the cycle?
Once it gets fertilised
What leads to the production of LH in the preovulatory stage?
Hypothalamus makes GnRH
Which stimulates Anterior Pituitary to make LH
What hormones stimulate rapid growth of the follicle?
FSH and LH
What is the mature follicle called?
Graafian follicle
What leads to the oocyte to extrude and break free from the ovary?
LH increases collagenase activity and prostaglandins increase the response to LH
This leads to local muscles contractions in the ovarian wall
What structure do the remaining granulosa and theca interna cells become once the oocyte breaks from the ovary?
Corpus luteum
What is the function of the corpus luteum?
Secretes oestrogen and progesterone
Stimulates uterine mucosa to enter secretory stage in prep for embryo implantation
Look at slide 20 to identify the corpus luteum
What happens to the corpus luteum if fertilisation doesn’t occur?
Degenerates and becomes a fibrotic scar tissue structure called the corpus albicans
How does the released oocyte get transported once it ruptures from the ovary?
Fimbriae sweep over the surface of the ovary collecting it into the fallopian tube
Fallopian tube lined with cilia which rhythmically beat the oocyte along with peristaltic muscular contractions
Why does menstrual bleeding occur if fertilisation doesn’t occur?
The corpus luteum degenerates into the corpus albicans which doesn’t produce progesterone leading to the bleeding
If fertilisation occurs, what prevents the degeneration of the corpus luteum?
Developing embryo produces Human Chorionic Gonadotropin hormone which prevents its degeneration
So the Corpus luteum contiues to produce progesterone until the secretion of progesterone by the placenta becomes enough
Compare spermatogenesis and oogenesis in terms of where the stages of it are completed?
Spermatogenesis = all stages complete in the testes
Oogenesis = last stage of meiosis 2 occurs in the oviduct in the ampulla area
