The Testis and Spermatogenesis Flashcards
1
Q
Review the structure of the Testis
A
2
Q
What is the function of the Testis?
A
- produce spermatozoa and hormones in discrete compartments
3
Q
What are the compartments of the testis?
A
- inside the Lobulues are
- Seminiferous tubules where spermatogenesis occurs
- between the tubules are
- Vascularised stroma containing Leydig cells
- where testosterone is synthesised
- Vascularised stroma containing Leydig cells
4
Q
How does hormone production work in the Testis?
A
- Testosterone synthesised from acetate and cholesterol by Leydig cells
- 4-10mg testosterone secreted daily
- mainly into blood vessels but also into the lymph
- some testosterone passes through the seminiferous tubules and is converted to
- Dihydrotestosterone by 5-alpha-reductase in Sertoli cells
- Androgens are required for spermatogenesis
5
Q
Explain the organisation of the seminiferous tubules
A
- 30-80 cm long
- Total length c 540m
- Peripheral myoid cells
- Then basement membrane
- Sertoli cells and spermatogenic cells within the tubules
- a physiological barrier is formed by the gap and tight-junctions complexes between Sertoli cell
- this creates a basal compartment and ca separate adluminal compartment
6
Q
What are the three key phases of Spermatogenesis?
A
- Mitotic proliferation to produce lots of cells
- Meiotic division to generate genetic diversity
- Cell modelling to package chromosomes for delivery to the oocyte
- a large number of spermatozoa are produced: 300-699 gram per testis per second
7
Q
Go over the Mitotic phase of spermatogenesis
A
- Germ cells of immature testis (prospermatogonia) are reactivated at puberty to undergo rounds of mitosis in the basal compartment of the tubule
- A spermatogonia emerge from these germ cells to undergo a series of divisions to form a clone of cells
- after the last round of division, the clone divide to form resting primary spermatocytes which inhabit cavities formed in Sertoli cell cytoplasm
- although nuclear division is completed, the cytoplasmic division is not, so primary spermatocytes are linked by cytoplasmic bridges
8
Q
Go over the Meiosis in spermatogenesis
A
- Resting primary spermatocytes push through Sertoli cell junctions into the 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,
- the cytoplasm divides forming short-lived secondary spermatocytes
- These quickly divide to form haploid spermatids
9
Q
Go over the Packaging parts in Spermatogenesis
- function of parts of the sperm
A
Cytoplasmic remodelling of spermatid takes place to give the following
- 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
- the small residual body is the dustbin for unwanted cytoplasm, later eaten by sertoli cell
10
Q
Explain the spermatogenic cycle
A
- 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
11
Q
How is the spermatogenic cycle controlled?
A
- If all spermatogonia were activated on 11th birthday, mature spermatozoa would be produced every 16 days.
- Result: episodic fertility
- If the spermatogonia were activated randomly then continuous production could occur
- In fact, small regions seem to be activated together, in wedges and helices around the tubule
- the seminiferous tubules show that adjacent synchronised clones of spermatogenesis are seen - so staged spermatogenesis, gives an illusion of continuous spermatogenesis
12
Q
Where do spermatozoa finally mature?
A
- 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
13
Q
What are the components of semen?
A
- Spermatozoa are mixed with secretions from the seminiferous tubules, epididymis etc.
- addition of secretion from the prostate, seminal vesicles and bulbourethral glands at the time of ejaculation to give about
- 3 ml per human is produced
- Cellular components
- Spermatozoa
- Epithelial cells fro the tract
- Spermatogenic cells
- Leucocytes (presents risk of HIV transmission)
14
Q
What is the function of the fluid components of semen?
A
- provide a vehicle for spermatozoa
- nutrition (fructose, sorbitol)
- Buffer against vaginal acidity
- Antioxidants, (ascorbic acid hypotaurine)
15
Q
What does the endocervix do?
A
- Secretes mucus with cyclical variation
- The macromolecular network of mucin fibrils ? guiding spermatozoa
- Oestrogen stimulates watery mucus
- Progesterone inhibits the secretory activity
- Sperm can penetrate from day 9, peak at time of ovulation
21
Q
How is the morphology of sperm assessed?
A
- Visual inspection of the sperm
- the WHO classes greater than 4% of sperm having normal form is acceptable
