Male Reproductive Tract Flashcards
What are androgens?
The major class of C-19 sex steroid hormones in males, with distinct structural and functional features:
- Beta-hydroxylated C-17
- Ketone structure at C-3
What are SRY genes?
Sex determining genes region Y.
Can cause expression of testis determining factor, TDF.
If TDF is expressed = embryonic development of testes
If TDF is not expressed = development of ovaries
Describe embryonic male development.
2 hormones produces by the developing testes change the developmental pathway of the internal genitalia from the default female to the male phenotype.
- The developing testes maintains the Wolffian duct system, which develops into the epididymis and male reproductive tract.
- Anti-Mullerian hormone (AMH) is produced by Sertoli cell type, causing regression of the Mullerian duct system and prevents development of the female internal genitalia.
- Prenatal testosterone from the Leydig cells of the testes masculinise the external genitalia to becomes penis and scrotum.
How can androgens be synthesised?
From cholesterol by progesterone.
How can oestrogen be synthesised?
Testosterone converted into oestrogen by aromatase enzymes.
Androstenedione converted into oestrogen by aromatase enzymes.
What is DHT and its function?
Peripheral conversion of testosterone to 5 alpha-dihydrotestosterone (DHT), which is much more biologically active.
This is vital for the maturation of the male external genitalia during development and for maintenance of reproductive function in the adult.
What is adrostenone?
Testosterone is inactivated by the liver and one of the products produced is adrostenone, which has no hormonal activity, but has an important role in pigs as a sexual attractant produced by boars to attract sows for mating.
Boars that produce too much of these is responsible for boar taint, an unpleasant taste from the meat of sexually active boars.
Describe the organisational mode of andorgens.
Organisational/determinative effects of steroids are totally or only partially irreversible. For example:
Mammals other than primates exposure to androgens during the perinatal period is important for having an organisational effect to matching areas of the brain involved in control for reproduction and behaviour.
Describe the activational effects of androgens.
Activational/regulatory effects of steroids are reversible. Such as:
- Maintenance of spermatogenesis
- Maintenance of activity of accessory sex glands
- Anabolic effects
- Erectile capacity
- Secondary sexual characteristics, such as antler growth ]male-specific behaviour and aggression and increased physical activity
Means that energy does not need to be wasted in seasonal breeders for maintaining reproductive capacity outside breeding period when androgen levels fall.
What is the link between castration and androgens?
Used to control reproduction and behaviours in domestic species. DUe to lack of adnrogens, there is:
- Decreased sexual motivation and sexual behaviour
- Decrease in ‘undesirable’ behaviours – fighting, roaming and urine spraying in cats
But castration after puberty often does not eliminate these behaviours completely.
Give a brief overview of spermatogenesis.
- Spermatogenesis occurs in seminiferous tubules.
- Spermatozoa collected into rete testis.
- Efferent ducts reabsorb fluid and concentrate sperm.
- Epididymis matures and stores sperm.
- Deferent duct transports sperm to pelvic urethra at ejaculation.
Describe and name scrotal species.
Androgen hormones, such as testosterone, cause descent. These have effect on the gubernaculum and suspensory ligament:
Pigs, cattle, goats, sheep, felids, canines, primates, rodents, etc.
- Cattle, horse, pig and sheep prenatal descent normally completed by a few weeks postnatally.
- Cat and dog postnatal descent completed in first few months.
Define cryptorchidism.
A failure one or both testes to descend and causes sterility if bilateral and has increased risk of neoplasia.
Name some non-scrotal species.
Birds
Elephants
Dolphins
Hedgehog
What is the importance of the pampiniform plexus?
Pampiniform venous plexus surrounds testicular artery and functions as a counter current heat exchanger, and the exchange of other things, like testosterone.
Describe the first stage of spermatogenesis - spermatocytogenesis.
- First stage is known as spermatocytogenesis – spermatogonia develop into spermatocytes. It is initiated by asymmetric divisions of spermatogonia stem cell to generate a replacement stem cell and a spermatogonium.
- Spermatogonium undergoes several rounds of mitotic proliferative division, helping to generate the large numbers of spermatogonia that are required to meet the normal sperm production rate.
- After a species specific number of mitotic divisions, spermatogonia become spermatocytes in meiosis.
- After the 2nd mitotic division, the spermatocytes becomes haploid spermatids and enter a process of differentiation known as spermiogenesis.
- Spermiation causes them to be placed into the seminiferous tubular lumen.
Define and the describe the process of the 2nd stage of spermatogenesis - spermiogenesis.
Converts a non-motile round cell into a highly efficient DNA vehicle.
- Begins in golgi phase by alignment of centrioles and golgi apparatus on opposite sides of the nucleus, which determines the cell’s polarity. Golgi apparatus dramatically increases in synthetic activity during this phase, and the nuclear DNA undergoes packaging and becomes highly condensed.
- During the cap phase, the golgi apparatus expands to form a cap IV anterior part of the nucleus. One of the centrioles elongates to start forming the tail.
- In the acrosomal phase, the cap expands to form the acrosome, which becomes the anterior half of the chromosome. While mitochondria migrate to the midpiece region when residual cytoplasm is removed.
- In the last phase, the unnecessary cytoplasm is removed and condensed following residual bodies. Tail continues to elongate. Mitochondria wrap tightly along the proximal region of the tail, forming the helical mitochondrial sheath.
Describe the role of Sertoli cells in spermatogenesis.
Engulf the developing spermatogeneic cells, controlling and coordinating spermatogenesis.
- Sertoli cells mediate the effect of testosterone on follicle stimulating hormone on spermatogenesis, as there are no hormone receptors on developing spermatogenic cells themselves.
- Sertoli cells also involved in remodelling the cytoplasm of spermatids by phagocytosising the residual cytoplasm.
- The stem cells, a mitotically dividing spermatogonia, are found in the basal compartment between the basement membrane that surrounds the seminiferous tubule and the tight junctions between the Sertoli cells.
- As they become spermatocytes and enter meiosis, they move past junctions and into the ad luminal compartment.
- Spermatids differentiate into spermatozoa and released into Sertoli cells and tubule in spermiation.
What is the blood-testis barrier?
Junctional complexes between Sertoli cells from blood-testis barrier.
- Mitosis occurs in basal compartment near basal lamina.
- Meiosis occurs in the adluminar compartment, on the other side of the tight junctions to protect from immune system and cytotoxins.
- Also allows a different seminiferous tubular fluid microenvironment for the late stages of spermatogenesis.
Infection can hide behind this barrier.
Describe spermatogenic cycle and spermatogenic wave in the continuous production of spermatozoa.
The duration of the spermatic cycle is the interval between cohorts of spermatogonia entering spermatogenesis. Is a quarter of the time taken to complete spermatogenesis.
Stage of spermatogenic cycle is staggered in neighbouring regions of seminiferous tubule.
Describe the morphology of mammalian spermatozoa.
- Head contains nucleus with highly condensed chromatin covered by acrosomal cap – hyaluronidase and acrosin.
- Middle contains packed spiral of mitochondria.
- 9 outer dense fibres
- Axoneme – 9 and 2 flagella arrangement which extends into tail.