L9 - sperm production Flashcards
What are the function of the testis?
to produce spermatozoa and hormones
Describe the compartments of the testis
seminiferous tubules which is where spermatogenesis occurs.
there is a vascularised stroma containing leydig cells
Where/how is testosterone made?
Made by leydig cells from acetate and cholesterol.
lipid soluble so some passes through the tubules and converted to dihydrotestosterone by 5a-reductase in sertoli cells
What role does the pituitary ?
production of androgens and spermatazoa are related functionally.
removal of pituitary causes testes to shrink and spermatogenesis to arrest.
LH stimulates leydig cells to produce androgens which are needed for spermatogenesis
FSH stimulates sertoli cells and needed for spermatogenesis
Describe the structure of the seminiferous tubules
surrounded by myoid cells
then a layer of BM
there are sertoli cells and spermatogenic cells withinthe tubules
physiological barrier formed by gap and tight junctions between sertoli cells which creates a basal compartment containing spermatogonia, whilst spermatocytes, spermatids and spermatazoa are in a separate adluminal compartment
Describe the process of spermatogenesis?
1 - MITOTIC PROLIFERATION - to produce lots of cells
2- MEIOTIC DIVISION to generate genetic diversity
3- CELL MODELLING to package xomes for delivery to the oocyte
stage 1 - mitosis
Germ cells of immature testis (prospermatogonia) are reactivated at puberty to undergo rounds of mitosis in the basal compartment of the tubule
From this self regenerating population emerge groups of cells called A1 spermatogonia which undergo a series of divisions to form a clone of cells
Finally after the last round of division, the clone divide to form resting primary spermatocytes
Within this mitotic phase of division, although nuclear division is completed, cytoplasmic division is not, so all of the primary spermatocytes resulting from the division of a spermatogonium are linked by cytoplasmic bridges
stage 2 - meiosis
Resting primary spermatocytes push through sertoli cell junctions into adluminal compartment
Enter meiotic prophase
Paired homologous chromosomes form contacts at pachytene, break, swap segments and rejoin
Very sensitive to damage at this time
First division ends with separation of homologous chromosomes to opposites ends of the meiotic spindle, cytoplasm divides forming short-lived secondary spermatocytes
These quickly divide to form haploid spermatids
stage 3 - packaging
cytoplasmic remodelling of spermatid
5.Tail for forward propulsion
4: Midpiece with mitochondria for energy
3: Nucleus with packaged chromosomes
2: Cap region forms for sperm-oocyte fusion
1: Acrosome forms to penetrate oocyte
A small residual body is the dustbin for unwanted cytoplasm, later eaten by sertoli cell
spermatogenic cycle control
spermatogenesis completion takes 64 days
episodic fertility
small regions seem to be activated together, in wedges around the tubule
What happens in the final stages of maturation?
spermatozoa wash into the rete
through the vasa efferentia
into epididymis where fluid is absorbed and sperm concentrated
in the rete they can twitch - by the cauda epididymis they can swim
the process is dependent on androgen stimulation
What are the components of semen?
spermatozoa are mixed with secretions from the s tubules, epididymis etc
also additional secretions from prostate, seminal vesicles and bulbourethral glands at time of ejaculation
what are the cellular components of sperm?
cellular components include - spermatazoa epithelial cells from tract spermatogenic cells leucocytes
what are the fluid components of sperm?
provide a fluid vehicle for spermatozoa
nutrition - fructose/sorbitol
buffer
antioxidants - ascorbic acid
what does the endocervix do?
secretes mucus with cyclic variation
has macromolecular network of mucin fibrils to guide spermatozoa?
oestrogen stimulates watery mucus
progresterone inhibits secretory activity
sperm can penetrate from day 9, peak at time of ovulation
