Spermatogenesis Flashcards
Testes have two major compartments:
Seminiferous tubules
Interstitial spaces
Seminiferous tubules
- ~250 m total length
- Developing germ cells
- Sertoli cells
Interstitial spaces
- Leydig cells (synthesize androgens)
* Blood and lymph vessels
what separates the two compartments
“Blood-testis barrier”
• Prevents immune reaction to spermatozoa
• Separates fluids of different composition
Spermatogenesis
Production of mature spermatozoa from undifferentiated germ
cells (primodial germ cell)
what re the three stages of spermatogenesis
1) Mitotic proliferation
2) Meiotic divisions
3) Cell modeling (spermiogenesis)
The Spermatogenic cycle is
~74 days (from 1st mitotic division to release of spermatozoa)
when is spermatogenesis initiated
every 16 days and occurs waves
Rate of each developmental stages is not uniform:
- Spermatogonium > 1 ̊ spermatocytes = 25 days
- Meiotic division 1 > 2 ̊ spermatocytes = 9 days
- Development > spermatids = 19 days
- Differentiation > spermatozoa = 21 days
At end of differentiation: in spermiation
- Cytoplasmic links are broken
- Spermatozoa released into tubule lumen
- Sperm virtually immobile
what flushes spermatozoa from seminiferous tubules, through the rete testis into the epididymis:
Fluid secreted by Sertoli cells
what happens when the fluid flushes 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
- Instead movement through reproductive tract is aided by peristaltic muscle contractions
capacitation:
- Normally occurs in the female reproductive tract (2-6h)
Glycoprotein coat gained in the epididymis is stripped
what changes occur in capacitation
- Head acquires the capacity to initiate the acrosome reaction
- Hyperactivation (increased flagellar beats)
Infertility in men is primarily diagnosed by semen analysis comprising of:
- Determination of sperm concentration/total count
- Motility
- Morphology
Oligozoospermia
• Reduced sperm count (< 15 million/ml)
Azoospermia
• Absence of sperm in the ejaculate
Asthenozoospermia
• Reduced sperm motility (< 40% moving)
Teratozoospermia
• Reduced percentage of sperm with normal morphology
Anti-sperm antibodies
• Abnormal immune response to sperm
–
where are the hormones released from
Hormones released by the hypothalamus, pituitary and testes are regulated by complex feedforward and feedback loops
Hypothalamic secretion of Gonadotrophin-releasing hormone (GnRH) stimulates
the release of gonadotropins from ant. Pit.
Pituitary gonadotrophins, luteinizing hormone (LH) and follicle stimulating hormone (FSH) control what
control testicular functions
High GnRH pulse amplitude and frequency preferentially stimulates
LH synthesis and secretion whereas low GnRH pulse frequency stimulates FSH synthesis and secretion
1)
Anterior pituitary
Gonadotrophs – Secrete LH and FSH (glycoproteins) – Most cells secrete one or other, but some secrete both Lactotrophs – Secrete prolactin (protein)
Posterior pituitary
Neurosecretory neurones
– Secrete arginine vasopressin (AVP) andoxytocin (peptides)
Leydig cells
in the testes have receptors for LH
– stimulates synthesis and secretion of testosterone
If LH secretion is too low
testosterone is low
– spermatogenesis halts
FSH is required for
FSH is required for maximum sperm production – acts on Sertoli cells
Testosterone (steroid) by Leydig cells
• In some tissues do not exert direct effects, but are converted to dihydrotestoterone or estrogens
2) Estrogens (steroid)
) by Sertoli and Leydig cells
3) Inhibins (peptide hormone)
by Sertoli cells
• feedback loop to control hormone levels
4) Oxytocin (peptide hormone)
by Leydig cells
• contraction of smooth muscle of the genital tract
Role of testosterone
– If production prevented spermatogenesis ceases
– Blocked when primary spermatocytes enter meiotic prophase
If blood [testosterone] is low
hen fewer stem cells will begin cell division but the whole process will still take 74 days.
