Male reproduction tract Flashcards
What are the exocrine and endocrine productions of the testis?
Exocrine - spermatozoa
Endocrine - testosterone
What are the cell types in the testis?
Gonocytes - primordial germ cells in the testis (only following fetal development) that become spermatagonia, only present in early life up to minipuberty
Spermatogonia - germ cells, replicate by mitosis, the differentiate to become sperm
sertoli cells
Leydig cells
myoid cells - conractile
What is the path of the primordial germ cells during development?
They migrate from the yolk sac to the gonadal ridges which is near where the kidney develops (via the hindgut).
They are driven by stem cell factor along the path of neurons (enteric neurons) to the testis.
Those that leave the path die due to loss of stem cell factor. Ectopic germ cells can be the origin of germ cell tumours (93% of germ cell tumours are in the testis, very rare in females). Those few germ cell tumours that are not in the testis are developed from primordial germ cells that got lost. These are usually in the CNS because the cells are following the nerves.
What do the leydig cells do?
The produce testosterone in response to LH in adults and fetuses. Found outside the seminephrous tubules, interstitial cells, main product is androgen (testosterone).
During sex differentiation at 7 weeks, the embryonic leydig cells produce testosterone but this is not initiated by LH stimulation or hCG.
At 14 weeks this switches.
Fetal leydig cells hve a different stem cell to adult leydig cells.
When does minipuberty occur?
2 months postpartum, increase in testosterone production.
Perhaps important for masculinization of male brain, promoting sertolic cell proliferation, prooting gonocyte differentiationm
What do sertoli cells do?
Sertoli cells - epithelial cells in the tubule. They wrap up sperm cells
Promote spermatogenesis.
Help the developing pre-sperm,
Promote post-mitotic development of sperm precursors.
They nourish spermatogonia,
help remove remaining debris from sperm development,
maintain the spermatogonia stem cell niche (for their survival).
Produce seminephrous tubule fluid for movement.
There is a direct relationship between the number of sertoli cells and the number of sperm.
They also promote the blood testis barrier to prevent anti-testis antibody development. The protect sperm against the immune system
What are the two phases of testicle descent and what are the ligaments holding the undeveloped testis called?
Two phases: the transabdominal phase (10-15 weeks) and the lnguinoscrotal phase (25-35 weeks)
The testis form in the gonadal ridge in the lumbar region suspended between two ligaments, the caudal and the gubernaculum.
How do the testis move during development?
Two phases: the transabdominal phase (10-15 weeks of gestation) and the lnguinoscrotal phase (25-35 weeks of gestation)
Transabdominal phase:
The testis form in the gonadal ridge in the lumbar region suspended between two ligaments, the caudal and the gubernaculum.
As the fetus develops the gubernaculum does not elongate and so it anchors the testis to the pelvis area as the fetus grows. Thus, the testis are maintained anchored lower in the abdomen. Later on, testosterone induces the release from the caudal ligament. Insulin-like-3 then causes the migration toward and elongation of, the inguinal canal.
Insulin like 3 is produced by leydig cells.
Linguinoscotal phase
Dependent on androgens
Descent through the inguinal canal
What is cryptorchidism?
When the testis are not in the right place. Failure to descend. It can be unilateral or bilateral
Incomplete cryptorchidism - testis go to the anterior abdominal wall, thigh or perinium. It affects 1-9% of term and 30% of pre-term babies.
Variance with race.
Usually self corrects. Can get surgery (orchidopexy)
It leas to infertility because of temp.
Is a risk factor of testicular cancer. 3-4 fold increased risk.
Breast-feed babies are less likely to remain cryptorchid
Higher rates of cryptorchisism in Maori children - 20% more likely, NZ Pacific and Asian boys are protected.
What happens to the testis at puberty?
The chords develop a lumen and become seminiferous tubules.
Significant increase in spermatoagonia proliferation
Beginning of sperm production
What are the three phases of spermatogenesis?
Mitotic division (division is symmetrical, one becomes sperm and the other remains as a spermatogonia). This occurs in the basal compartment of the seminiferous tubules. When this division is complete, one of the divided spermatogonia (linked to other spermatogonia) moves from the basal compartment of the seminiferous tubule through the sertoli cells, which form the blood testis barrier, and to the adlumen. The sertoli cells allow entry and then close behind. In the adlumen the spermatgonia are now primary spermatocytes. They then undergo meiosis.
Meiotic division - after miosis 1 when the cells have 23 chrmosomes the cells are called secondary spermatocytes. These then move further through into the lumen. The then rapidly complete meiosis II to give spermatids. Still linked together at this point.
Cytodifferentiation (spermiation, smermIOgenesis) - androgen dependent. spermatids are still round cells at this point. Needs to develop swimming and fertilisation capabilities. Only need the facilities to complete these two tasks. Looses cytoplasm that is not needed in residual body. Spermatozoa (sperm) then move to the lumen
Mature sperm are pulled back towards the basement membrane.
How is spermatogenesis controlled hormonally, positive and negative?
GnRH in the hypothalamus goes into the pituitary and induces the production of LH and FSH.
LH - acts on leydig cells outside the seminifirous tubules and induces them to produce testosterone, which is important for secondary sexual characteristics (balding, aggression, libido, secondary hair growth). The testosterone can also be used to produce dihydrotestosterone
FSH - acts on the sertoli cells inside the seminiferous tubules in direct contact with the spermatogonia. It induces them to produce androgen binding protein. Most of it goes into the blood to transport testosterone and dihydrotestosterone around. Some goes into the seminiferous tubule.
Some of the androgen binding protein stays in the seminiferous tubule and maintains the testosterone concentration, which is essential for cytodifferentiation.
Negative feedback - testosterone feedsback to the hypothalamus to inhibit the production of GnRH resulting in decreased FSH and LH. The sertoli cells also produce inhibin which feedsback on the anterior pituitary to inhibit FSH production.
What is the delay between sperm production?
Spermatogenic wave
Sperm is created in waves with sperm at different points of development. The cycle moves forward every 16 days. Produced in waves. In each segment the development of sperm is ahead of the previous segment.
What is the pathway for semen to be ejaculated?
It is in the seminiferous tubules, and the myoid cells contract pushing the semen and the fluid down the tubules. The tubules connect together forming the rete testes which has efferents to the epididymis (now in one tube). The epididymis is 7.5 cm long with 4-6 m of tubule, very convoluted.
Sperm in the epididymis is concentrated (from 5x10^7 to 5x10^9 /ml. Takes 10-14 days to pass through. Fluid is reabsorbed by stereocillia.
Sperm gains motility and the capabiliy to fertilise in the epididymis. This process is finished in the female reproductive tract
From the epididymis to the vas deferens (45 cm long) through the inguinal over the top of the bladder to the ejaculatory duct at the prostate gland to the urethra.
What are the layers of the vas deferens?
Three muscle layers: the inner longitudinal, middle circular and outer longitudinal. These surround an epithelial lining.
Just before joining the ejaculatory duct the vas deferens has a region called the ampulla, which becomes enlarged and folded with many crypts. It’s function is to store sperm.
