T2 l9The testis and spermatogenesis Flashcards
what is the space outside the testis
Tunica vaginalis
what are the 2 main products from the testis
Spermatozoa
Hormones
where does spermatogenesis occur
Seminiferous tubules which are vascularised stroma containing Leydig cells
what is the process of spermatogenesis
(-some testosterone passes through to the seminiferous tubules
-converted to dihydrotestosterone by 5a-reductase in Sertoli cells )
Testosterone synthesised from acetate and cholesterol by Leydig cells
4 – 10 mg testosterone secreted daily
Principally into blood vessels but also lymph
- Androgens are required for spermatogenesis
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anatomy look at slide 3
how was it
what is the pituitary control of androgen and spermatozoa production & Proof
Proof: Removal of pituitary (hypophysectomy) causes testes to shrink and spermatogenesis to arrest
At puberty, androgens rise and spermatogenesis commences
LH stimulates Leydig cells to produce androgens (which are required for spermatogenesis)
FSH stimulates Sertoli cells and is required for spermatogenesis
describe the seminiferous tubules
- surrounded by myoid cells
- then a layer of basement membrane
- Sertoli cells and spermatogenic cells within the tubules
- Physiological barrier formed by gap and tight junctioned complexes between Sertoli cells
- Creates a basal compartment containing spermatogonia
- whilst spermatocytes,spermatids and spermatazoa are in a separate adluminal compartment
what are the 3 processes that spermatogenesis occurs in
- Mitotic proliferation to produce lots of cells
- Meiotic division to generate genetic diversity
- Cell modelling to package chromosomes for delivery to the oocyte
describe the first phase of spermatogenesis
- 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
describe the second stage of spermatogenesis
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
Describe the third stage of spermatogenesis (look at pic for relevant number coord on slide 21)
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
describe the spermatogenic cycle
We considered generation of sperm from a single spermatogonium
Once this process has started, new stem cells at the same location don’t start generation of clones again for a few days
The interval is constant at around 16 days, the process by which the stem cell population controls, or is controlled is unknown
The time for completion of spermatogenesis is 64 days, so there are four successive sets of clonal development (at four separate stages of the process) in one place at one time – and that’s what we see when we look down the microscope
describe the spermatogenic wave
If the seminiferous tubules are dissected longitudinally, adjacent synchronised clones of spermatogenesis are seen
What occurs after spermatogenesis
Spermatozoa wash into the rete
Through the vasa efferentia
Into the 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 does spermatozoa mix with to form the components of semen
Spermatozoa mixed with secretions from seminiferous tubules, epididymis etc.
Addition of secretions from prostate, seminal vesicles and bulbourethral glands at time of ejaculation
