Testicular Function Flashcards
At which point in development is the male reproductive system distinguishable from the female reproductive system?
Week 7.
Which cells are the precursors to the reproductive systems?
What ploidy are these cells?
- Primordial germ cells.
- Diploid cells.
What is the role of the Y chromosome in the determination of male sex?
- The Y chromosome has a control gene that triggers the male developmental pathway; it doesn’t code for the masculine traits.
- This gene is the SRY gene, and it codes an architectural transcription factor.
What is an architectural transcription factor?
A transcription factor that alters the structure of DNA to allow other transcription factors to act upon it (rather than directly activating the DNA itself).
What is the cause of females with XY chromosomes and males with XX chromosomes?
Deletion or mutation of the SRY gene.
List the processes that occur from weeks 3-7 of reproductive development in a male.
1 - Coelomic epithelial cells arrive at the gonadal ridges of the embryonic dorsal wall.
2 - They penetrate deeply into the developing testis and proliferate.
3 - These are the cells that express SRY.
4 - They form the primitive sex cords.
5 - Primordial germ cells migrate to the primitive sex cords.
6 - The sex cords envelop the primordial germ cells.
From which cells are Sertoli cells derived?
Coelomic epithelial cells.
From which structures are seminiferous tubules formed?
Primitive sex cords that have enveloped the primordial germ cells.
Other than coelomic epithelial cells and primordial germ cells, which cells migrate to the developing testis from weeks 3-7 of male reproductive development?
What is the fate of these cells?
- Cells from the mesonephric primordia.
- They form the vasculature, leydig cells and myoid cells.
What are primordial germ cells called once they become enveloped within seminiferous tubules?
Prospermatogonia.
What cellular event occurs in primordial germ cells once they become enveloped within seminiferous tubules?
Meiosis is inhibited.
List the structures / cells that exist between seminiferous tubules.
1 - Vasculature.
2 - Clusters of Leydig cells.
When does SRY stop being expressed?
What directs further development of the male reproductive system?
- Once seminiferous tubules have formed.
- The testes direct further development via androgens and anti-Mullerian hormone (AMH).
At which point in development are the testes in their final pre-pubertal form?
At which point in development is the male reproductive system in its final pre-pubertal form?
- The testes finish developing by ~week 8.
- The male reproductive system finishes developing by ~week 12.
List 2 roles of the male reproductive system at puberty.
1 - To produce sperm.
2 - To produce hormones.
List the two compartments of post-pubertal testis.
Which cells are present in these compartments?
1 - Intraseminferous compartments of the seminiferous tubules (Sertoli cells).
2 - Interseminiferous compartments (Leydig cells).
What is the function of the Sertoli cells in the seminiferous tubules of the post-pubertal testis?
To produce sperm.
What is the function of the Leydig cells in the seminiferous tubules of the post-pubertal testis?
To produce androgens.
List the 3 subcompartments of the intraseminiferous compartment.
Where are these compartments?
1 - The lumen in the centre of the seminiferous tubule.
2 - The adluminal compartment surrounding the lumen of the seminiferous tubule.
3 - The basal compartment by the outer basement membrane of the seminiferous tubule.
Where is the blood-testis barrier?
Between the adluminal and basal compartments of the seminiferous tubules.
List the junctions that form the blood-testis barrier.
Which cells are being linked together by these junctions?
1 - Adherens junctions.
2 - Gap junctions.
3 - Tight junctions.
- These junctions are linking adjacent Sertoli cells.
When does the blood-testis barrier form?
Why is this important?
- During puberty prior to the onset of spermatogenesis.
- This is important because the role of the blood-testis barrier is to keep mature sperm away from the immune system.
Other than separating the immune system from mature sperm, what is the other role of the blood-testis barrier?
To selectively transport ions and small molecules into the seminiferous tubule.
What is the rate of production of sperm?
100 million per day.
List the phases of spermatogenesis.
1 - Proliferation.
2 - Division by meiosis.
3 - Differentiation.
Describe the proliferation phase of spermatogenesis.
1 - At puberty, prospermatogonia are reactivated and are then known as ‘As spermatogonia’.
2 - As spermatogonia undergo mitosis in the basal compartment of the seminiferous tubule to produce another As spermatogonium (renewal) and an ‘A spermatogonium’.
3 -The A spermatogonia undergo mitosis to produce B spermatogonia.
4 - B spermatogonia undergo mitosis to produce primary spermatocytes.
Describe the division phase of spermatogenesis.
1 - The primary spermatocytes move from the basal compartment of the seminiferous tubule through the blood-testis barrier into the adluminal compartment.
2 - Here, they undergo the first meiotic division over the course of 24 days to form diploid secondary spermatocytes.
3 - They then undergo the second meiotic division over the course of 24 hours to form haploid round spermatids.
Give an overview of the differentiation phase of spermatogenesis.
1 - Round spermatids elongate to form elongated spermatids.
2 - Elongated spermatids become mature spermatozoa.
- The maturation process includes formation of specialised sperm structures:
1 - Acrosome.
2 - Flagella.
3 - Centrioles.
4 - Mitochondria.
5 - A nucleus.
6 - Cytoplasm.
From which structure is the acrosome formed?
The golgi apparatus.
What is contained within the acrosome?
Hydrolytic enzymes that facilitate the acrosome reaction.
Where on the acrosome is the receptor for fusion with the egg cell found?
On the inner acrosomal membrane.
From which structures do sperm flagella develop?
Briefly describe the process of flagellum development.
- Centrioles
- One centriole migrates to the opposite end of the cell to the nucleus, and one stays proximal to the nucleus.
- The centriole distal to the nucleus elongates to form an axoneme, which becomes the main structural component of the flagellum.
What is the importance of the proximal centriole of a sperm cell?
Upon entry of the sperm into an egg cell, the proximal centriole is donated to the egg to form the spindle for the first cell division of the embryo.
What is the midpiece?
What is the function of the midpiece?
- The helically arranged structure of mitochondria that forms around the first part of the flagellum.
- It provides the flagellum with ATP.
What is the function of protamines?
Why is this important?
- They replace the function of histones in order to pack DNA more tightly into the sperm.
- Sperm DNA therefore does not have nucleosomes (as these require histones).
- This is important to ensure that the sperm is streamlined.
What is a residual body?
What happens to it after it forms?
- The superfluous cytoplasm released by a sperm in order to produce a more streamlined cell shape.
- It is phagocytosed by Sertoli cells.
Which process occurs after spermatogenesis?
What does this involve?
- Spermiation.
- This is the release of sperm into the lumen of the testis.
How long does spermiation take?
What controls the duration of spermation?
- 64 days.
- The duration of spermiation is controlled by a process intrinsic to the germ cells themselves.
What is the spermatogenic wave?
The phenomenon whereby different seminiferous tubules enter spermatogenesis at different times, ensuring that there is not a burst of sperm released into the lumen every 64 days, but rather a continuous flow.
What is the main male androgen?
List 3 other hormonal products of the testis.
- Testosterone.
1 - Oestrogens.
Cytokines:
2 - Inhibin.
3 - Anti-Mullerian hormone.
Into which substance is testosterone converted in the seminiferous tubules?
Which cells mediate this process?
Which enzyme is necessary to do this?
- Dihydrotestosterone.
- Sertoli cells.
- 5 alpha reductase.
What is the fate of dihydrotestosterone?
- Some binds to androgen receptors in Sertoli cells to stimulate spermatogenesis.
- Some binds to androgen-binding protein (ABP), a carrier protein.
List 2 functions of antigen binding protein.
1 - To form a store of testosterone within the testis.
2 - To carry testosterone to the cells lining the reproductive tract.
Which cells produce inhibin?
Sertoli cells.
What is the function of inhibin?
It suppresses FSH production by the anterior pituitary gland.
Which cells produce anti-Mullerian hormone?
Sertoli cells.
What is the function of anti-Mullerian hormone?
It has an embryonic role in the development of the reproductive system.
Where in the testis does LH bind?
What is its effect?
- To LHCG receptors on Leydig cells.
- It induces testosterone production.
- Testosterone moves to the tubules and binds to the androgen receptor on Sertoli cells to stimulate spermatogenesis.
Where in the testis does FSH bind?
What is its effect?
- To FSH receptors on sertoli cells.
- It induces expression of androgen receptors.
- It also stimulates production of inhibin and androgen-binding protein.
List the feedback molecules produced by the effects of FSH and LH.
- LH results in the production of testosterone, which feeds back to the hypothalamus.
- FSH results in the production of inhibin, which feeds back to the hypothalamus.
List the sperm maturation processes that occur between release of sperm from the testis and contact with an egg.
Where do these processes occur?
Why are these processes necessary?
1 - Maturation (in the epididymis).
2 - Capacitation (in the female tract).
- These processes are necessary because sperm released from the testis are:
1 - Immotile.
2 - Unable to recognise / bind to an egg.
What is the epididymis?
The tube through which all sperm pass after being released from the testis.
How does the epididymis affect the composition of sperm?
Which hormone controls this?
- Most of the fluid of the sperm is reabsorbed in the epididymis, making the sperm 100x more concentrated.
- Fluid reabsorption is controlled by oestrogen.
How long does sperm passage through the epididymis take?
10-14 days.
Which cell lines the epididymis?
What is their role?
Which hormone drives the activity of these cells?
- Pseudostratified columnar epithelium.
- They modify the sperm passing through the epididymis by conjugating and modifying proteins to the sperm surface.
- The activity of these cells is driven by androgens.
List the segments of the epididymis.
List the functions that the epididymis confers on the sperm cells at each segment.
1 - Caput (head - motility).
2 - Corpus (body - fertilising ability).
3 - Cauda (tail - no functional change to the sperm. It is part of the storage of sperm).
Into which structure do sperm pass after the epididymis?
What is the function of this structure?
- The vas deferens.
- It is a storage reservoir for sperm.
Which structure is the target of vasectomies?
The vas deferens.
What is semen?
Sperm mixed with seminal plasma.
What is the average concentration of sperm in ejaculated semen?
~200 million sperm per 2.5mls (average ejaculate volume).
List 4 functions of seminal plasma.
1 - Transport.
2 - Nutrition.
3 - Buffering of pH.
4 - Antioxidants.
*Seminal plasma is also the means of transport of STIs.
Where is seminal plasma produced?
1 - Seminal vesicles.
2 - Prostate.
3 - Bulbourethral glands.
- These are sac-like accessory glands.
What is semenogelin?
Why is this useful?
- A fibrinogen-like substrate produced by seminal vesicles that cause ejaculate clotting.
- This keeps the semen in the cervical mucus.
What prevents ejaculate clotting in the male reproductive tract?
The presence of enzymes that break down semenogelin.
List 2 components of the semen that are produced by the prostate.
1 - Alkaline secretions that are high in zinc.
2 - Enzymes for ejaculate clotting and liquefaction.
List 2 functions of the bulbourethral glands.
1 - Lubrication.
2 - Neutralisation (important as urine also passes through the urethra).
List the 2 components of capacitation.
1 - Hyperactivation of the tail.
2 - Acrosome reaction.
