Spermatogenesis Flashcards
What is the role of the testes?
- Produce Sperm
- Store sperm
- Produce hormones which regulate spermatogenesis
Approximately How much Sperm is produced each second?
- Approximately 1500 produced per second
- Around 5.5 million in an hour
- Estimated to be around 130 million sperm per day
Where are the testes located?
- Lie in the scrotum outside the body cavity
What is the optimum temperature for sperm production?
1.5°c to 2.5°c below body temperature
What happens if the temperature exceeds the optimum?
Overheating of testes reduces sperm count
What is the normal volume of the testes?
- Normal volume of testes approximately 15-25ml
- Measured by orchidometer
- Well vascularised and well innervated
How are the testi’s arranged?
- Testi’s are 90% seminiferous tubules
- Which is the site of spermatogenesis
How long are these tubules?
How are these tubules structured?
- 600 meters long in each testi
- Tubules are tightly coiled
Where do these tubules lead to?
All lead to the epididymis and ultimately vas deferens
What is the vas deferens?
The vas deferens, also known as the ductus, is a tube through which spermatozoa travel through
Where are primary germ cells or spermatogonia found?
On the basement membrane
What are the walls of the tubules made up off in the cross section of the seminiferous tubule?
Walls of tubules made up of tall columnar endothelial cells called Sertoli cells
Where are Adluminal compartments formed?
Tight junctions between these Sertoli cells form Adluminal compartments
What is the advantage of the formation of Adluminal compartments?
Allows specific enclosed environment for spermatogenesis which is filled with secretions from Sertoli cells
What are the spaces between the seminiferous tubules filled with?
Filled with
- Blood
- Lymphatic vessels
- Leydig cells
- Interstitial fluid
Describe the steps that occur in meiosis (PART 1)
- During interphase, (S-phase) each chromosome is duplicated
- The replicated chromosomes stay attached to the originals forming two pairs of sister chromatids (tetrads) for each chromosome
- Tetrads align at the metaphase plate and crossing over occurs. The sister chromatids move to the opposite poles of the cell
Describe the steps that occur in meiosis (PART 2)
- After the meiosis I division, There is one sister chromatid pair in each cell. They are no longer identical due to crossing over
- MII (Meiosis 2) is another cycle of cell division in which the sister chromatids separate to give a single unique chromosome in each daughter cell
What are the different sperm stages during spermatogenesis?
Spermatogonia -> Primary spermatocytes -> Secondary spermatocytes -> Spermatids -> Spermatozoa
Describe the Spermatogonia stage
Germ cell is on the basement membrane
- Capable of mitotic or meiotic division to produce primary spermatocytes or more spermatogonia
- They are diploid
Describe the Primary Spermatocytes stage
- They move into the Adluminal compartment
- Duplicate their DNA to produce sister chromatids which exchange genetic material before entering meiosis 1
- They are 46 XY diploid
Describe the Secondary Spermatocytes stage
- Secondary Spermatocytes have undergone meiosis 1 to give 23X + 23Y haploid number of chromosomes
- Arranged as sister chromatids
Describe the Spermatids stage
- Meiosis 2 occurs to give 4 haploid spermatids
- Round Spermatid to elongated spermatid differentiation
Describe the Spermatozoa stage
Mature sperm extruded into the lumen
How long does the process of Spermatogenesis last?
New cycle every 16 days
Entire process takes approximately 74 days
In SHORT, briefly describe the spermatogenesis process
- Mitotic proliferation of spermatogonia
- Meiosis and development of spermatocytes
- Spermiogenesis, elongation, loss of cytoplasm, movement of cellular contents
What type of cell division occurs from Spermatogonium?
- Each cell division from the spermatogonium to a spermatid is incomplete
- The cells remain connected to one another by cytoplasmic bridges
- Forming a synctium allowing synchronous development
- Syncytia at various stages of development throughout seminiferous tubule giving continuous supply
Compare Oogonia against Spermatogonia
Oogonia
- Oogonia all laid down in Foetus
- Begin meiosis to make oocyte before birth
- Cannot make more Oogonia by mitosis
- Limited supply
Compare Oogonia against Spermatogonia
Spermatogonia
- Spermatogonia laid down in foetus
- Begin meiosis to make spermatocyte after puberty OR
- Divide mitotically to make more spermatogonia
- Lifetime supply
How do Gonadotrophins act on the testis? (PART 1)
- Leydig cells contain LH receptors and primarily convert cholesterol to Androgens
- Intra-testicular testosterone levels are 100x those in plasma
- Andrigens cross over to and stimulate Sertoli cell function and thereby control spermatogenesis
How do Gonadotrophins act on the testis? (PART 2)
- Sertoli cells contain FSH receptors and converts androgen to oestrogen
- FSH establishes a quantitatively normal Sertoli cell population
- Whereas Androgen initiates and mainatians sperm production
What interferes with negative feedback?
Anabolic steroids
How does Anabolic steroids interfere with the negative feedback system?
Reduce FSH/LH from pituitary leading to testicular atrophy
How is an erection triggered?
- Vasodilation of the corpus cavernosum
- Partial constriction of the venous return
- Autonomic nervous system causes co-ordinated smooth muscle contractions of vas deferens, glands and urethra
What part of the penis does the parasympathetic nervous system control?
The Erection
What part of the penis does the sympathetic nervous system control?
movement of sperm into epididymis, vas deferens, penile urethra (emission)
What part of the penis does the somatic nervous system control?
Expulsion of the glandular secretions
& evacuation of urethra
What does the dilation of the cavernosal arteries cause? (during erection)
- It engorges corporal tissue with blood
- Which causes corporal tissue to swell
- Causes the penis to become erect
What happens to The ischiocavernosus and bulbospongiosus muscles during erection?
They compress the veins of the corpora cavernosa restricting venous drainage
Describe the contents of the Ejaculation
- Normal ejaculate volume is 1.5 - 6 ml
- Initial portion of the ejaculate is the most sperm rich
Out of all the sperm released, How much of it gets close to the egg cell?
- Around 120 million or more sperm gets released in the average ejaculate
- Only around 120,000 sperm get near to the egg cell
What does the seminal fluid consist of?
Consists of secretions from seminal vesicles, prostate, bulbo-urethral gland combined with epididymal fluid
In the Seminal fluid, Describe the bulbo urethral gland
- Produces a clear viscous secretion high in salt known as pre-ejaculate
- This fluid helps to lubricate the urethra for spermatozoa to pass through neutralising traces of acidic urine
In the Seminal fluid, Describe the seminal vesicles
- Secretions comprise 50-70% of the ejaculate
- Contains proteins, enzymes, fructose, mucus, vitamin C and prostaglandins
- High fructose concentrations provide energy source
- High pH protects against acidic environment in vagina
In the Seminal fluid, Describe the prostate
- Secretes milky or white fluid roughly 30% of the seminal fluid
- Protein content is less than 1% and includes proteolytic enzymes, prostatic acid and prostate specific enzymes which are involved in liquefaction
- High zinc concentration 500-1000 times that in the blood is antibacterial
Analyse the Semen’s contents
Volume = 1.4 - 6.0 ml
Appearance = Grey - opalescent
Liquefaction = <30 minutes
Sperm concentration = > 16 million ml
