W4 - Spermatogenesis Flashcards
What are testes?
Produce sperm and store it.
Produce hormones which regulate spermatogenesis.
Lie in scrotum outside body cavity….optimum temperature for sperm production 1.5-2.5oC below body.
Overheating of testes reduces sperm count.
Well-vascularised, well-innervated.
Normal volume of testes approximately 15-25ml
measured by orchidometer…
Testis is 90% seminiferous tubules, site of
spermatogenesis.
600m long in each testis! Tubules are tightly
coiled.
Tubules all lead to epididymis and ultimately
vas deferens.
What is the composition of Sertoli cells, tight junctions & adluminal compartments?
Primary germ cells or spermatogonia
on the basement membrane
Walls of tubule made up of tall
columnar endothelial cells Sertoli
cells. Tight junctions between these
form Adluminal compartment.
Allows specific enclosed environment
for spermatogenesis which is filled
with secretions from Sertoli cells.
Spaces between the tubules are filled
with blood and lymphatic vessels,
Leydig cells and interstitial fluid.
Leydig cells are the ones responsible for secreting androgens and testosterone.
What are the stages of spermatogenesis?
Spermatogonia:
Germ cell on basement membrane, capable of mitotic or meiotic division to produce primary spermatocytes or more spermatogonia by mitosis. They are diploid. Under a microscope, these are called ‘A dark’ - because some are dark, some pale and some pale but different. There is always spermatogonia in men - can be replenished. When they turn pale microscopically, they have committed to become sperm. These will become B spermatogonia.
Primary spermatocytes:
They move into the adluminal compartment and
duplicate their DNA to produce sister chromatids
which exchange genetic material before entering
meiosis I. They are 46XY diploid.
Secondary spermatocytes:
Secondary spermatocytes have undergone meiosis I to give 23X + 23Y haploid number of chromosomes arranged as sister chromatids.
Spermatids:
Meiosis II occurs to give 4 haploid spermatids. Round spermatid to elongated spermatid differentiation.
Spermatozoa:
Mature sperm extruded into the lumen.
What is spermatogenesis?
New cycle every 16 days, entire process takes approximately 74 days.
- Mitotic proliferation of spermatogonia.
- Meiosis and development of spermatocytes.
- Spermiogenesis, elongation, loss of cytoplasm, movement of cellular contents.
Each cell division from a spermatogonium to a spermatid is incomplete - the cells remain connected to one another by cytoplasmic bridges forming a syncytium allowing synchronous development.
Syncytia at various stages of development throughout seminiferous tubule giving continuous supply.
What is the Steroid production in the testes?
Leydig cells contain LH receptors and
primarily convert cholesterol into androgens.
Intra-testicular testosterone levels are 100x
those in plasma.
Androgens cross over to and stimulate Sertoli
cell function and thereby control
spermatogenesis.
Sertoli cells contain FSH receptors and
converts androgens to oestrogen.
FSH establishes a quantitatively normal
Sertoli cell population.
Androgen initiates and maintains sperm
production.
What interferes with negative feedback?
If someone were to take anabolic steroids, this is going to affect the HPG axis and reduce FDH/LH from pituitary leading to testicular atrophy.
What is the difference between Oogonia and Spermatogonia?
Oogonia all laid down in foetus.
Begin meiosis to make oocyte before birth.
Cannot make more oogonia by mitosis.
Limited supply.
Spermatogonia laid down in foetus.
Begin meiosis to make spermatocyte after puberty OR…
Divide mitotically to make more spermatogonia.
Lifetime supply.
How does erection and ejaculation work?
Vasodilation of the corpus cavernosum. Partial constriction of the venous return. During erection, there is dilation of the arterial supply into these spongy tissues. The penis then becomes filled with blood and an erection occurs.
Autonomic nervous system causes co-ordinated smooth muscle contractions of vas deferens, glands and urethra.
Parasympathetic control- erection
Sympathetic nervous system control:
-movement of sperm into epididymis,
-vas deferens, penile urethra (emission)
Somatic nervous system (perineal branch of the pudendal nerve from nerve roots S2–S4)
- Expulsion of the glandular secretions & evacuation of urethra.
pneumonic: point, shoot and score
Parasympathetic control, sympathetic control and somatic
How does the arterial blood flow in erections work?
How does ejaculation work?
300 million sperm produced per day on average.
- 3,500 per second so 9 million during this lecture
approximately 120 million in average ejaculate
Normal ejaculate volume is 1.5ml - 6ml.
- around one third to just over a teaspoon full
Initial portion of the ejaculate is most sperm rich.
99.9% lost before reaching ampulla of the uterine tube.
- around 120,000 sperm get near to egg, only one enters
Seminal fluid consists of secretions from:
- seminal vesicles, prostate, bulbo-urethral gland combined with epididymal fluid
What is seminal fluid?
Bulbo-Urethral Gland
Produces a clear viscous secretion
high in salt, known as pre-ejaculate.
This fluid helps to lubricate the
urethra for spermatozoa to pass
through, neutralizing traces of acidic
urine and to reduce friction.
Seminal Vesicles
Secretions comprise 50-70% of the
ejaculate. Contains proteins,
enzymes, fructose, mucus, vitamin C
and prostaglandins. High fructose
concentrations provide energy source.
High pH protects against acidic
environment in vagina.
Prostate
Secretes milky or white fluid roughly
30% of the seminal fluid. Protein
content is less than 1% and includes
proteolytic enzymes, prostatic acid
phosphatase and prostate-specific
antigen which are involved in
liquefaction. High zinc concentration
500–1,000 times that in the blood is
antibacterial.
How does semen analysis occur?
Sperm is jelly like and viscous. In the first 20mins the sperm liquifies. Proteases liquifies them. This allows them to ejaculate close to the cervix and leave it there. After about 20mins when everything calms down, it liquifies and the highly concentrated part is able to swim up the cervix. If it was liquid from the beginning, it might all just run out.
<15million/ml means it is a sub fertile situation = oligospermia.
Azoospermia is when there is no sperm at all.
>40% sperm should be swimming in a way they are going somewhere.
>58% of the sperm needs to be alive.
>4% of the morphology is normal
A lot of the sperm but low quality.
>7.2 pH
Leucocytes <1 million/ml
What is Spermatozoon?
Nucleus - DNA, almost no cytoplasm, tightly packed.
Acrosome - full of enzymes - cuts through egg membrane
Mirochondrial sheath - full of energy to swim, so for tail
Tail - Arrangement of 9 pairs of fibres longitudinally through the sperm tail.
Using the energy of the mitochondria, these fibres slide against one another in a whiplash motion, which drives the sperm forward.
How are sperms produced?
Lobules drain into the rete testis and eventually to the epididymus to be ejaculated out through the vas difference.
If we take a section of the semi-neferous tubule, the sperm matures on the outer edge and slowly moves towards the lumen. They move along the lumen to get to the epididymus. On the semineferous tubule, the spermatogonia are diploid cells. These cells can divide through mitosis. A proportion of them at any given time will commit to meiosis and they become primary spermatocytes. Then they undergo meiosis and become haploid cells to become sperm. This process is mediated by the sertoli cells.
What is the hypothalamic/pituitary/gonadal axis in males?
Hypothalamus produces GnRH, which sends a signal to the pituitary to release LH and FSH, which affects the testes and makes testosterone and some oestrogen. The testosterone (DHT) feeds back negatively to hypothalamus and pituitary. This is not cyclical. There is a bit of everything there.
