Lecture 5 + 6 - 2017 Flashcards
How is the testes an exocrine gland?
It secretes spermatozoa.
How is the testes an endocrine gland?
It secretes testosterone.
What happens in the early stages of testes development?
Germ cells are set outside the developing embryo (on the yolk sac - posterior side). These have to migrate to the embryo and they start to form the testes.
After the germ cells migrate to the embryo what happens?
They migrate up and around to the developing hindgut (connected to the dorsal part of the mesentery) and split outside of where the aorta is developing and come to lie on either side of the genital ridges (pelvic cavity). The germ cells come in and take up with the epithelial cells that cover the genital ridge. The epithelial cells wrap around the germ cells.
What do the epithelial cells form?
Sertoli cells - which nourish and feed developing stages of germ cells (spermatogonia).
What does the interstitial tissue between cords form?
Leydig cells and myoid cells.
What do the germ cells form?
Spermatogonia.
When do the testis descend?
7-8 months in utero (7-8month fetus).
How does this occur?
The testes go from an intra-abdominal position to a position outside of the body. It occurs via a ligament (gubernaculum) that shortens and drags the testicles down, this is all under the control of AMH.
What are gonocytes?
Primitive germ cells that become spermatogonia (only present in ealry life).
What are spermatogonia?
They come from germ cells that are essentially differentiated pre-sperm cells that replicate by mitosis.
What are sertoli cells?
These come from epithelial cells, that sit in the lumen of tubule that help to develop pre-sperm cells.
What are leydig cells?
These come from interstitial stromal tissue and their function is to produce testosterone.
What are myoid cells?
These come from interstitial stromal tissue and their function is to contract.
How does AMH contribute to the descent of testes?
Controls movement within the abdominal cavity and down to the inguinal ring.
How does testosterone contribute to the descent of testes?
Testosterone controls the movement from the ring to the sac.
What other factors affect the embryonic development of the testes?
Stem cell factor is important in driving migration, if there is inadequate SCF then the primordial germ cells will die.
What happens will the primordial germ cells migrate?
They follow fine enteric nerves and do not always enter or stop at the testes e.g. ectopic - in the pancreas where they always form oocytes.
Where are germ cell tumours found?
- 93% in testis.
- 4% in ovaries.
- 3% are ectopic (not in gonads).
- Most common site is in the CNS - keep on migrating and survive into CNS.
Where is testosterone produced?
Leydig cells.
Describe the initial production of testosterone by embryonic leydig cells?
This initial production is not dependent on stimulation by LH (7-8 weeks).
What happens at 14 weeks gestation in terms of testosterone production?
The production of testosterone becomes LH (pituitary)/hCG (placenta) dependent.
List the testosterone levels throughout a boys life?
- 13-15 weeks = 2ng/ml.
- 5-6 months = 0.8ng/ml.
- 2 months post partum = 2-3ng/ml (mini puberty).
- 3-4 months post partum = 0.5ng/ml.
- pre-puberty = 0.1ng/ml.
- post-puberty = 2-3ng/ml.
- Adult = 3-9ng/ml (4-10mg/daily).
Why is there high levels of testosterone at mini puberty?
This is to do with gonadal programming that pre-programmes testicular tissue and gonadal tissue - into a routine so that it occurs at puberty. Also important in causing sertoli cell proliferation and promoting differentiation of gonocytes into dark AD-spermatogonia.
Where do sertoli cells sit?
On the basement membrane, they span from the bm to the lumen of the seminiferous tubules.
What do sertoli cells do?
They nourish spermatogonia, resorb the excess cytoplasm (residual body), produce seminiferous tubule fluid and mantain the spermatogonial cell niche.
Where are spermatids embedded?
Deeply into the sertoli cells.
Describe the sertoli-to-sertoli junctional complex?
Tight junction that contributes to the blood-testis barrier. It prevents WBC from sensing developing gametes (perceived as foreign bodies due to genetic cross over).
Describe the sertoli-to-spermatid junctional complex?
Adhesion device that resides in deep recess within apical cytoplasm. Germ cells can slide through the tight junction. Before the junction mitosis occurs, after the junction, meiosis and cytodifferentiation occur.
What is the transit time of sperm from the basal lamina to the lumen?
74 days.
What is the time between waves of developinbg spermatozoa?
16 days.
What is cryptorchidism?
Failure of testes to descend.
- Unilateral = one testis.
- Bilateral = both testes.
What are the types of cryptochidism?
- Incomplete: testes is on the right track to descend but gets stopped and lodges in inguinal canal.
- Maldescent: testes goes to anterior wall of abdomen, perineum or thigh.
What are the consequences of cryptorchidism?
- Infertility - this is due to the increased temperature in the body. Spermatogonia require lower temperature (2 degrees).
- Risk factor for testicular cancer - 3-4 fold increased risk.
What are the four phases of spermatid development?
- Golgi phase.
- Cap phase.
- Acrosomal phase.
- Maturation phase.
Describe the golgi phase?
Spermatids start out as rounded cells and the proteins go into the golgi and accumulate into vesicles which fuse and form pro-acrosomal granules (from acrosome) The pro-acrosomal granules contain digestive enzumes for ZP of egg (important for fertilisation).
Describe the cap phase?
The granules (from the golgi phase) keep fusing until they form a cap of acrosomal material (acrosome) which is bound by the membrane.
Describe the acromsomal phase?
The shape of the cell starts changing - starts to elongate (centrioles elongate to become a tail) and oval. The acrosome spreads down over the nucleus.
Describe the maturation phase?
The spermatids are released into the lumen with the tails of the spermatid in the lumen, with the heads embedded in the sertoli cells. The sertoli cells phagocytose the cytoplasm of the spermatid.
