8. Spermatogenesis Flashcards
What are the two major compartments of the testes?
Seminiferous tubules
- Developing germ cells
- Sertoli cells
Interstitial spaces
- Leydig cells (synthesise androgens)
- Blood and lymph vessels
Both compartments are separate, “blood-testis barrier”
Role of “blood-testis barrier”?
Prevents immune reaction to spermatozoa
Separates fluids of different composition
What is spermatogenesis?
Production fo mature spermatozoa from undifferentiated germ cells (primordial germ cell) occurs in three stages;
- Mitotic proliferation
- Meiotic (reduction) division
- Cell modelling (spermatogenesis)
First mitotic division to release spermatozoa…
after 74 days
Spermatogenesis occurs in waves, initiated every ___ days…
16 days
Structure of sperm
Flagella: End piece, principal piece, middle piece and head (covered by acrosome)
Sperm maturation at the end of differentiation, what happens?
- Cytoplasmic links are broken
- Spermatozoa released into tubule lumen
- Sperm virtually immobile
Role of Sertoli cells at sperm maturation stage>
Fluid secreted by Sertoli cells flushes developing spermatozoa from seminiferous tubules, through the rete testis into the epididymis:
– Capacity for motility by the time they reach the tail of the epididymis
– Motility is suppressed by epididymal fluid
What is capacitation?
If ejaculated spermatozoa are placed with oocytes in vitro fertilization does not occur immediately.
They need to undergo the process known as capacitation:
- Normally occurs in the female reproductive tract (2-6h)
Process: Glycoprotein coat gained in epididymis is stripped. Results in two changes:
- Hyperactivation (increased flagellar beats)
- Head acquires the capacity to initiate the acrosome reaction
Sperm quality?
Poor
30% show morphological abnormalities
Normal and sub fertile sperm count?
Normal: 50-150 x 10^6/ml
Sub-fertile: Less than 20 x 10^6/ml
What is oligozoospermia?
Less than 20 x 10^6/ml sperm count
What is azoospermia?
Absence of sperm in ejaculate
What is asthenozoospermia?
Low sperm motility (<50% moving)
What is teratozoospermia?
High proportion of abnormally-shaped sperm
What is antiserum antibodies?
Abnormal immune response to sperm
What hormones are produced by the testes?
- Testosterone (steroid) by Leydig cells
• In some tissues do not exert direct effects, but are converted to dihydrotestoterone or oestrogens - Oestrogens (steroid) by Sertoli and Leydig cells
- Inhibits (polypeptides) by Sertoli cells
- Feedback loop to control hormone levels - Oxytocin (polypeptide) by Leydig cells
- Contraction of smooth muscle of the genital tract
Role of testosterone in spermatogenesis?
– If production prevented spermatogenesis ceases
– Blocked when primary spermatocytes enter meiotic prophase
if blood levels are low then fewer stem cells will begin division but whole process will still take 74 days
Role of pituitary glands and hypothalamus in spermatogenesis?
Ant pituitary controls testicular function by secreting the gonadotrophin from the gonadotroph cells
Pituitary gonadotrophs in turn are controlled by the hypothalamus, which secretes gonadotrophin-releasing hormone (GnRH)
Secretion of hormones by the hypothalamus, anterior pituitary and testes are regulated by complex feedback loops
Blood supply between hypothalamus and pituitary glands
The hypophyseal portal system is a system of blood vessels in the brain that connects the hypothalamus with the anterior pituitary. Its main function is the transport and exchange of hormones to allow a fast communication between both glands.
Hormone production in the pituitary gland that influence spermatogenesis?
- Ant pituitary
-Gonadotrophs
Basophili cells secrete LH and FSH
Most cells secrete one or there, or both
-Lactotrophs
Acidphilic cells secrete prolactin
Post pituitary
-Neurosecretory neurones
Secrete arginine vasopressin and oxytocin
Control of gonadotrophin secretion
LH and FSH secretions controlled by GnRH secreted by the hypothalamus
GnRH is released into the portal blood in pulses every hour
GnRH must be pulsatile or it is ineffective
High GnRH pulse amplitude and frequency preferentially stimulates LH synthesis and secretion
Low GnRH pulse amplitude and frequency stimulates FSH synthesis and secretion
Functions of LH and FSH in spermatogenesis
Leydig cells in the tests have receptors for LH. Stimulates synthesis and secretion of testosterone
If LH secretion is too low, testosterone is low and spermatogenesis helps.
All 3 hormones essential for process to resumes
FSH is required for max sperm production, acts on Sertoli cells
Function of FSH on Sertoli cells
- Increase RNA and protein synthesis
- Increase energy metabolism
- Increase inhibin secretion (reduces FSH secretion from ant pituitary)
- Increase cyclic AMP
- Increase ABP secretion
- Increase fluid secretion
- Increased androgen receptor expression –> Increase FSH receptors
