Spermatogenesis and Spermiogenesis Flashcards
What are found in between the seminiferous tubules?
Peritubular compartments (leydig cells found here)
What are the 2 major compartments of the testes?
- Seminiferous tubules
- Interstitial spaces
Why are the seminiferous tubules and interstial spaces seperate?
Create a blood-testis barrier
- Prevents immune reaction to spermatozoa
- Separates fluids of different composition
What do the interstitial spaces contain?
- Leydig cells
- Blood and lymph vessels
Where is the blood-testis barrier made?
Formed through interactions between tight junctions, zonular junctions and filament bundles between neighbouring sertoli cells, spermatogonia reside on one side of the blood-testis barrier, as development procedes it travels through it
What are the 3 stages to produce a mature spermatozoa?
- Mitotic proliferation
- Meiotic divisions
- Cell modeling (spermiogenesis)
What are the undifferentiated germ cells called which spermatozoa are derived from?
Primordial germ cells
What are the names of all the cells from primordial germ cell to spermatozoa?
- Primordial germ cell
- Spermatogonia
- Primary spermatocyte
- Secondary spermatocyte
- Spermatid
- Spermatozoa
What does the primary spermatocyte do?
Enters meiosis 1
How long is the spermatogenic cycle?
~ 74 days (from 1st mitotic division to release of spermatozoa)
How many days does it usually take to initiate spermatogenesis?
16 days (occurs in waves)
How long does it take for the spermatogonium to develop into the primary spermatocyte?
25 days
How long does the meiotic division 1 take (primary to secondary spermatocyte)?
9 days
How long does it take for the secondary spermatocyte to develop into a spermatozoa?
21 days
What is spermiogenesis?
Process that remodells the spermatid into the spermatozoa, during this period where the sperm develops the machinary required for sperm motility
How much sperm is made in 1 day roughly?
200 million
What structures surround the middle piece?
Sheathes of ring shaped mitochondria
What is the acrosome fprmed by?
The golgi
What does fluid secreted by sertoli cells do?
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 perstaltic muscle contractions
Why would ejaculated sperm not fertilize an oocyte in vitro immediately?
- Need to undergo capacitation (normally occurs in reproductive tract (2-6h)
- Glycoprotein coat gained in the epidymis is stripped
- Head then aquires the capacity to initiate the acrosome reaction
- Hyperactivation (increased flagellar beats)
What percentage of sperm show normal morphology under a microscope?
~ 4 - 14%
If normal morphology drops below what level does fertilisation rates obtained with IVF reduced?
4%
Infertility in men is primarily diagnosed by semen analysis comprising of what?
- Determination of sperm concentration/total count
- Motility
- Morphology
What level of sperm count would make a man sub-fertile?
Below 15 million
What is oligozoospermia?
Reduced sperm count (< 15 million/ml)
What is azoospermia?
Absence of sperm in ejaculate
What is asthenozoospermia?
Reduced sperm motility (<50% moving)
What is teratozoospermia?
Reduced percentage of sperm with normal morphology
What is antisperm antibodies?
Abnormal immune response to sperm (combinations of these abnormalities afre common)
What cells in the testicles does mumps affect?
Sertoli cells
How much lower is the temperature of the scrotum in relation to the rest of the body?
2-3 degrees lower
What stimulates the anterior pituitary gonadotropins?
Pulsatile secretion of Gonadotropin-releasing hormone (GnRH) from the hypothalamus
What are the pituitary gonadotrophins?
- Lutenizing hormone (LH)
- Follicle stimulating hormone (FSH)
- They control testicular function
What cells have LH receptors?
Leydig cells (stimulate synthesis and secretion of testosterone)
What happens to testosterone if LH secretion is low?
Testosterone is low (spermatogenesis halts)
What does FSH do?
Acts on Sertoli cells and maximises sperm production
WHat are the functions of FSH on Sertoli cells?
- Increased RNA and protein synthesis
- Increased energy metabolism
- Increased inhibin secretion
- Increased cAMP
- Increased ABP secretion
- Increased fluid secretion
- Increased androgen receptors
- Increased FSH receptors
What is more important for sperm production FSH or LH?
LH
What can testosterone be converted into?
Dihydrotestosterone or estrogens
What are estrognes made by?
Sertoli and Leydig cells
What is are inhibins produced by?
Peptide hormone released by Sertoli cells (feedback loop to control hormone levels)
WHat is oxytocin (peptide hormone) produced by?
Leydig cells
What does oxytocin do?
Contraction of Smooth muscle of the genital tract
Where will spermatogenesis fail if testosterone is blocked?
When primary spermatocyetes enter meiotic prophase
What will happen if blood testosterone is low?
Fewer stem cells will begin cell division but the whole process will still take 74 days
Where does testosterone act on to negatively feedback?
Hypothalamus and anterior pituitary
What perecentage of infertile men are actually provided a causal diagnosis?
~ 28%
What are the causes of male infertility that can often be diagnosed?
- Gonadotoxic chemo or radio therapy (10%)
- Testosterone abuse or other chronic diseases (e.g diabetes) (14%)
- Genetic disorders (Klinfelter, Karyotype 47, XXY or microdeletions on the Y chromosome) (4%)
What is thought to be one of the causes of congenital hypogonadotrpic hypogonadism?
Mutated genes involved in the migration and function of GnRH neurons or their upstream regulators, can include anosmia
