SPERM: ORIGINS AND ROLES Flashcards
Describe the structure of sperm?
it has a head, body and tail.
it has an acrosomal cap on top of the nucleus, centrioles below the nucleus and mitochondria encircling the flagella
why do sperm have an acrosomal cap?
it contains degratative enzymes that can read down the zone pellucida
why do sperm have centrioles?
it has a role in maturing sperm, linking the head to the tail and beating the tail
why do sperm have mitochondria?
to produce energy for the movement of sperm
describe the structure of sperms head?
the head is flattened and contains little cytoplasm with the nucleus taking u most of the space`
why do the testis sit outside the body?
to regulate the temperature to support the spermatogenesis.
what are the testis roles?
1) making sperm and 2) making androgens.
describe the route that the spermatozoa take out of the testis?
they leave the seminiferous tubules and go into the rete testis and then the vasa efferentia then the epididymis and then the vas deferens
what is the vasa efferentia?
the several highly convoluted tubules that lead from the rete testis to the vas deferens and form the head of the epididymis
where abouts in the testis do you find the leydig cells?
within the septa- the gaps between the seminiferous tubules
which cells surround the seminiferous tubules?
myoid cells outside and a layer of Sertoli cells on the inner epithelia
whats in the gaps between the sertoli cells?
developing spermatogonia
where in the testis does spermatogonia start and finish?
starts at the basal compartment and finishes at the luminal compartment
what are the 4 stages of spermatogenesis?
mitotic division
meiosis 1
meiosis 2
cytodifferentiation/spermiogenesis
describe stage 1) mitotic division of spermatogenesis?
proliferating spermatogonia stem cells divide to form 16 clone of spermatogonia A1 which divid to produce a spermatogonia A2 which divide to produce spermatogonia A3 which then divide to produce spermatogonia A4. type A4 spermatogonis divide to produce intermediate spermatogonium which divides to produce a spermatogonium type B which then didvides to produce a resting primary spermatocyte
how many A1 cells can be formed from a spermatogenic stem cell?
16
describe step 2) meoisis of spermatogenesis?
the primary spermatocyte divides to generate a secondary spermatocyte (cytoplasmic bridge remains)
describe step 3) meiosis 2 of spermatogenesis?
the secondary spermatocytes divide to produce 4 early spermatids (cytoplasmic bridge remains)
describe step 3) cytodifferentiation of spermatogenesis?
Spermatids start to acquire the sperm morphology.
The Golgi apparatus assembles to one of the polar regions of the sperm, starts to condense and form the acrosome vesicle on top of the nucleus.
The centrioles migrate to the distal pole of the cell, from the most distal region we see an elongation and growth of a flagellum.
The mitochondria begin the coalesce around the developing microtubule. We also see the loss of excess cytoplasm to form the final, functional typical sperm morphology.
when does the cytoplasmic bridge break?
when the final functional spermatozoa form
how long does it take for spermatogenesis to occur?
74
how long is one cycle of the seminiferous tubules?
16 days
where do sperm gain motility?
in the epididymis
how many final functioning spermatids form from a spermatogenic stem cell?
512 (assuming there are no cell losses on the way)
how many sperm would be considered normal in a semen sample?
how many of these are motile?
> 15 million per ml
over 40% have motility
what is oligozoospermia?
low sperm count
what is aspermia?
complete absence of semen following ejaculation
what is azoospermia?
complete absence of sperm within the semen
what is asthenozoospermia?
low sperm motility
what is teratozoospermia?
abnormal sperm morphology
what is globospermia?
when the sperm have rounded heads and no acrosome- can be caused by a higher than body temperature
what is gonadal function controlled by?
the hypothalamic-pituitary axis
what happens at puberty to the hypothalamus?
it starts producing hourly pulse secretions of GnRH
what does GnRH act on?
the pituitary to cause secretion of LH and FSH
what does LH do?
stimulates Leydig cells to produce testosterone which has a negative feedback effect on LH by acting on the hypothalamus
what does testosterone do?
it binds to receptors on Sertoli cells and is converted to dihydrotestosterone
it maintains and supports proliferation
what do Sertoli cells produce?
what does this do?
inhibin B which negatively regulates the FSH receptor and positively regulates the Leydig cells
what does FSH do?
binds to receptors on sertoli cells which stimulates production and expression of androgen receptor so testosterone can influence these cells
what is the common precursors of steroid hormones?
acetate -> cholesterol
how can testosterone be converted to oestradiol?
by aromatase (found in testes, liver, fat and brain)
whats the function of the bulbourethral duct?
produces mucus to lubricate the urethra so sperm can leave and lubricate the penis to enable coitus.
whats the function of the seminal vesicle?
produce most of the fluid that makes up semen. They also produce fructose (for sperm metabolism), ascorbic acid (vitamin C to prevent oxidative damage) and have an alkaline pH to neutralise the acidity in the female reproductive tract.
whats the function of the prostate gland?
secretes prostate-specific androgen (prevents sperm from aggregating), ions such as Cl-, Ca+, Mg2+, Na2+ to maintain osmotic balance of the fluid.
what’s the average volume of semen?
2-5 mls
whats is the composition of semen?
spermatozoa, fructose, inositol, citric acid, glycerylphosphocholine and prostaglandins
what does the prostate secrete?
prostate specific androgen, acid phosphatase, protease, and citric acid
what could 2 reasons for the enlarged prostate be?
benign prostate hyperplasia or a malignant prostate cancer
how can we treat prostate cancer?
by reducing the size of the prostate
e.g. GnRH antagonists, andorgen receptor antgonists or a reductase inhibitor
describe the physiology of an erection?
Sensory stimulation occurs, we then see an increase in production of nitrous oxide from the endothelium of the penis. This stabilises the soluble guanyl cyclase. Net result is vasodilation if arteries and corresponding constriction of the veins which leads to a high pressure-low efflux system= enlargement of the penis
what is guanyl cyclase?
enzyme that catalyses the conversion of GMP into cGMP
describe the physiology of detumescence?
Once sensory stimulation is gone, NO levels fall so we see the expression of PDE5 (catalyses cGMP to GMP). This inhibits production of cAMP which enables vasoconstriction, allowing venous supply to enlarge and produce a high efflux system so the erection becomes flaccid.
what are some drug types for erectile dysfunction?
Phosphodiesterase inhibitors
Prostaglandin agonists
Dopamine receptor agonists
