Lecture 2: Male tract, spermatogenesis and endocrine control, vasectomy and torsion Flashcards
What are the different cell types in the testis
Gonocytes: primitive germ cells only present up to mini puberty
Spermatogonia: pre sperm cell germ cells that replicate by mitosis
Sertoli cells: epithelial cells within lumen of tubule
Leydig cells: interstitial cells outside the tubule lumen
Myoid cells: surround the tubules to help spermatid movement
What makes up the blood-testis barrier and why is it important
Tight, adherens and gap junctions between sertoli cells form a physical barrier between the inside of the seminiferous tubule and the rest of the testis – spermatocyte and spermatogonium . This is to stop the production of anti sperm antibodies which would cause infertility as spermatocytes that have undergone meiosis and are not recognised as “self” cells.
From what cells do germ cell tumours originate from and what is the path of their migration
Germ cell tumours arise from primordial germ cells: either become oocyte or sperm. 93% in the testis. 3% ectopic bc of those that don’t stop at the testis
Primordial germ cells arise from yolk sac 3-4 weeks post conception, and migrate to gonadal ridges via the hind gut which requires stem cell factor from enteric nerves to drive it otherwise they die.
What is the main job of Leydig cells and how does it change from 7-8 weeks to 14 weeks +
Leydig cells produce testosterone (T)- needed for testes descent, spermatogenesis, conversion to 5DHT for 2ndary sexual characteristics.
Embryonic Leydig cells have different progenitors compared to Adult Leydig cells.
(7-8wks) T produced in response to placental hCG, independent from LH stimulation as pituitary gland not there yet.
14wks T produced dependent on LH (pit) and hCG.
What is mini puberty, when is it and why important
A rise in testosterone levels at 2-3 months post partum caused by losing the placenta which loses (-) feedback so testosterone goes to reach a new homeostatic level
Important for masculinising the neonatal brain, promoting sertoli cell proliferation (related to fertility) and promoting differentiation of the gonocytes into AD-dark spermatogonia
What are the two phases of the moving testes
1. 10-15 wks
2. 25-35 wks
and what is important for both,
- Transabdominal: testis is held between the caudal ligament superiorly and gubernaculum inferiorly in the lumbar region of the abdo wall
a) testosterone causes regression of the caudal ligament; the gubernaculum doesn’t elongate as the fetus grows up
b) INSL-3 from leydig cells causes migration of gubernaculum towards and dilation of the inguinal canal - Inguino-scrotal phase: moving through inguinal canal: androgen is important
What is cryptorchidism, treatment and complications of non treatment
- Premature, Maori, non-breastfed highest risk, pacific and asian less risk,
Cryptorchidism is failure of testes to descend: unilateral or bilateral, or maldescent- into ant abdo wall, perineum, thigh.
Treatment: most self correct within 3 months due to mini puberty providing androgens for 2nd phase, but if not can be surgically corrected at 9months with orchidoplexy.
Comp: Infertility due to excess temperature not good for spermatogenesis and increased risk (3-4x) for testicular cancer.
What is testicular torsion
When testicle rotate , twisting the spermatic cord, causing reduced blood flow= sudden and severe pain and swelling in most commonly 12-18yrolds.
What are the 4 testicular changes at puberty
- Seminiferous tubules develop a lumen
- Germ cells (spermatogonia) begin to proliferate again
- Synthetic activity of leydig and sertoli cells increases sharply
- Beginning of spermatogenesis
What are the phases of spermatogenesis starting from spermatogonia
- spermatogonium under go mitosis 3x at the basal compartment
adluminal compartment: - These differentiate into 1’ spermatocytes which undergo meiosis 1 to become 2’ spermatocyte (2n but mixed)
- 2’ spermatocyte undergoes meiosis 2 to become spermatids (n)
- Spermatids undergo cytodifferentiation (spermiogenesis) to get the right shape and become Spermatozoa which enter the lumen. This requires androgens
Describe the structure of a sperm/spermatozoa after spermiogenesis -3 points
- It goes from round to head, midpiece and tail by shedding cytoplasm - called residual body eaten by Sertoli cells
- head contains condensed heterochromatic DNA and is covered by the acrosome: compartment filled with enzymes required for egg penetration
- Midpiece is packed with mitochondria to produce energy for swimming
Explain how there is constant production of finished sperm every day when it takes 64 days for a finished sperm to be produced from a spermatogonium (spermatogenesis)
In a cross section of a tubule there is a synchronisation of sperm development called the cycle of seminiferous epithelium (cells connected by cytoplasmic bridges to move together at same rate)- a new spermatogonium enters the cycle after mitotic division every 16 days.
However each segment of the seminiferous tubule contains a different stage of spermatogenic development that is either ahead or behind the consecutive segments - leading to synchronisation along the length of the tubule = spermatogenic wave
What is the role of Sertoli cells and why are they important. What is the action of FSH on sertoli cell
They organise the timing and placing of spermatogenesis, able to communicate with each other, spermatocytes and spermatids.
- Nourish spermatocytes
- Resorb excess cytoplasm
- Produce seminiferous tubule fluid for moving sperm
- Maintain Blood-testis barrier and spermatogonial stem cell niche
- Help promote tolerance of non self tissue implants if co transplanted as immune privileged
FSH acts on sertoli cells to
- upregulate androgen receptor expression on sertoli cells to support spermatogenesis
- produce androgen binding protein. 80% to sequester testosterone in the tubule lumen for spermatogenesis, 20% in the interstitium to carry testosterone in systemic circulation
Describe the path of sperm from seminiferous tubules to ejaculation including where each component of semen is added and specific things happening in each part
- Seminiferous tubules
- Rete testis
- Epididymis : 10-14 days getting concentrated 100x. high SA for fluid reabsorption by stereocillia. sperm get motility ability.
- Vas Deferens: inner + outer longitudinal, middle circular muscular wall for peristaltic contraction during ejac. At the Ampulla before prostate, major sperm storage up to 1 month after which they are reabsorbed by body after degeneration.
- Seminal vesicles: joins vd to form ejaculatory duct– secrete alkaline fluid containing fructose and semenogelin for semen clotting
- Prostate gland: sperm is mixed with seminal vesicle and prostatic fluids
- Urethra through the penis: inside the corpus spongiosum, underneath two corpus cavernosa,
What is the function of fluid in the seminiferous tubules-> upper epididymis, and what cells produce fluid (2)
- movement of sperm due to fluid pressure- taking 6 days: testis and cilliated efferent duct cells secretion
- Maturation of sperm; nutrient and hormone rich secretion from sertoli + epididymis epithelium
