Spermatogenesis Flashcards
What is Spermatogenesis?
formation of haploid sperm from primordial germ cells in the seminiferous tubules of testes
What is the Site of sperm production?
seminiferous tubules
What is the Site of sperm storage?
epididymis
Why do testes lie outside the body?
1.5-2ºC below body temperature for sperm development because overheating reduces sperm count
Describe the Sperm pathway structures.
Seminiferous tubules >rete testis >efferent ductules >epididymis >vas deferens
What lines the seminiferous tubules?
Sertoli cells
What are Spermatogonia?
diploid primary germ cells in basement membrane of seminiferous tubules which give rise to spermatocytes by mitosis
What is the Fate of spermatogonia?
a) Commit to becoming sperm and undergo two meiotic divisions (after becoming primary spermatocytes) to become mature sperm
b) Divide by mitosis and replenish themselves
What initiates sperm production?
testosterone
How do sertoli cells control spermatogenesis?
There are tight junctions between Sertoli cells in seminiferous tubule walls which form the Adluminal compartment.
> Sertoli cells secrete growth factors, hormones, signalling molecules into Adluminal compartment to control environment in which sperm are developing
Outline the Development of sperm in seminiferous tubule.
Spermatogonia in basement membrane
-mature between Sertoli cells, moving slowly towards the central lumen where they finish development, and then to the epididymis for storage
What do the regions between seminiferous tubules contain?
Leydig cells, blood vessels, lymphatics, interstitial fluid
What are Leydig cells?
A cell that produces testosterone and other androgens and is located between the seminiferous tubules of the testes.
Describe the Sperm Stages during Spermatogenesis.
1) Spermatogonia (diploid)
- type Ad spermatogonia divide mitotically to produce more type Ad spermatogonia, maintaining population of spermatogonia
- or divide mitotically to produce type Ap spermatogonia, which then differentiate to type B spermatogonia and subsequently primary spermatocytes (which then undergo meiosis)
2) Primary Spermatocytes (46XY diploid)
- move into adluminal compartment & duplicate their DNA producing identical sister chromatids
- crossing over between non-sister chromatids
- undergo meiosis I to produce secondary spermatocytes
3) Secondary Spermatocytes (23X+23Y)
- haploid number of chromosomes arranged as chromatids
- undergo meiosis II to produce 4 haploid spermatids
4) Spermatids
- round spermatids differentiate to elongated spermatids
5) Spermatozoa
- mature sperm extrude into lumen of seminiferous tubule
Define Spermiogenesis.
differentiation of spermatids into spermatozoa (elongation, loss of cytoplasm and movement of cellular contents)
Describe the process of Steroid Production in Testes.
LH stimulates Leydig cells to produce testosterone and androgens
-testosterone can cross over into seminiferous tubules to stimulate Sertoli cell function and control spermatogenesis
FSH stimulates Sertoli cells to produce oestrogens from androgens
-Sertoli cells die without FSH
How do anabolic steroids affect the male HPG axis?
more steroids (testosterone) causes more negative feedback
>less FSH/LH released from pituitary
>Sertoli cells need FSH to survive, therefore there is Sertoli cell death and testicular atrophy
What are the Effect of parasympathetic nervous system on male gonads?
- constricts venous drainage from penis
- vasodilation of arterial blood flow to penis
- penis becomes full of blood
- hydrostatic pressure causes penis to be ERECT
What are the Effect of sympathetic nervous system on male gonads?
-causes smooth muscle contractions for sperm movement into epididymis, vas deferens, glands and urethra for EJACULATION
What are the Effect of somatic nervous system on male gonads?
some somatic nervous control in synergy with sympathetic nervous control during ejaculation, causing for expulsion of glandular secretions/sperm and evacuation from urethra
*perineal branch of pudendal nerve from S2-S4
What is Seminal fluid (Semen)?
sperm cells and secretions of seminal vesicles, prostate gland, and bulbourethral glands
Describe the Secretions of seminal vesicles.
- comprise 50-70% of ejaculate
- proteins, enzymes, fructose, prostaglandins, vitamin C
- high fructose provides energy source
- high pH (alkaline) protects against acidic environment in vagina
Describe the Secretions of prostate gland.
- comprise 30% of ejaculate
- milky/white fluid with <1% protein content including proteolytic enzymes, prostatic acid phosphatase and prostate-specific antigen involved in liquefaction after initial viscous sperm deposits near cervix
- high zinc concentration is antibacterial
Describe the Secretions of bulbourethral gland.
-clear viscous secretion high in salt [Na+] known as pre-ejaculate which lubricates the urethra for spermatozoa to pass through, neutralising any traces of acidic urine
Describe the Structure of sperm.
- no cytoplasm
- smallest cell in the body
- only provides DNA
- acrosome (invaginated membrane) containing digestive enzymes
- mitochondrial sheath- contains a lot of mitochondria for energy
- axoneme- microtubule based cytoskeleton in flagella
