Spermatogenesis Flashcards
What is the function of the testes?
- To produce sperm and store it
- To produce hormones which regulate spermatogenesis
- Sperm production
Why is the scrotum outside of the body cavity?
- For the optimum temperature for sperm production is 1.5-2.5 degrees below body.
What happens if there is overheating of the testes?
Reduces sperm count
What is the normal volume of the testes and how is this measured?
15-25 ml and measured by an orchidometer
What percentage of the testis is seminiferous tubules and what is the function of these tubules?
95%, and the site of spermatogenesis
How long are the seminiferous tubules in the testes?
600 m long
Where do the tubules in the testis lead to?
the epididymis and ultimately the vas deferens
Where are the spermatogonia located?
On the basememnt membrane
What are the walls of the seminiferous tubule made of?
tall columnar endothelial cells called sertoli cells
What are the tight junctions between the seminiferous tubules and what is their function?
Adluminal compartments for a specific enclosed environment for spermatogenesis that is filled with secretions from sertoli cells.
What is filled between the tubules?
Blood and lymphatic vessels, Leydig cells and interstitial fluid
Summarise Meiosis
- S-phase the chromosomes are replicated and stay attached to the originals forming identical sister chromatids.
- Homologous chromosomes group together in pairs ab=nd exchange genetic material that gives rise to new chromosomes a mixture of maternal and paternal genes.
- Sister chromatids remain attached and may differ from one another if cross over.
- Cell division creates two haploid daughther cells, but each chromosome is two sister chromatids and are no longer identical due to crossing-over.
- Sister chromatids separate as cell divides giving haploid gametes.
What is spermatogonia?
Germ cell on basement membrane, capable of mitotic or meiotic division to produce primary spermatocytes or more spermatogonia by mitosis. They are diploid.
What are primary spermatocytes?
They move into the adluminal compartment and duplicate their DNA to produce sister chromatids which exchange genetic material before entering meiosis I. They are 46XY diploid.
What are secondary spermatocytes?
Have undergone meiosis I to give 23X to 23Y haploid number of chromosomes arranged as sister chromatids.
What are spermatids?
Meiosis II occurs to give 4 haploid spermatids. Round spermatid to elongated spermatid differentiation
What is spermatozoa?
Mature sperm extruded into the lumen
How often does a new spermatogenesis cycle occur?
Every 16 days
How long does spermatogenesis take?
74 days
What allows for the synchronous development of sperm?
A syncytium - formed from the cells remaining connected to one another by cytoplasmic bridges.
What is the difference between oogonia and spermatogonia?
- Spermatogonia and oogonia is laid down in foetus.
- Spermatogonia begins to make spermatocyte after puberty or divide mitotically to make more spermatogonia whereas oogonia begin meiosis after birth and cannot make more mitotically.
- There is a lifetime supply of spermatogonia whereas a limited supply of oogonia.
Describe the feedback mechanism of spermatogensis hormones
Hypothalamus releases GnRH into the pituitary this releases LH/FSH to the testis. This then produces testosterone/DHT which acts in a negative feedback manner.
What is the primary role of Leydig cells?
They contain LH receptors and primarily convert cholesterol into androgens.
How do androgens control spermatogenesis?
They cross-over to and stimulate sertoli cell function.
What is the function of sertoli cells?
They contain FSH receptors and convert androgens to oestrogen.
What does FSH do?
It establishes a quantitatively normal Sertoli cell population.
What do the androgens do?
They initiate and maintain sperm production.
What can interfere with negative feedback?
Taking anabolic steroids will reduce FSH/LH from pituitary leading to testicular atrophy.
What causes erection and ejaculation?
- 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.
Which system controls erection?
Parasympathetic
What does the sympathetic nervous system control?
Movement of sperm into epididymis, vas deferens, penile urethra (emission)
What does the somatic nervous system do?
- Explusion of the glandular secretions
- Evacuation of urethra
What nerves control the somatic nervous system in the penis?
The perineal branch of the pudendal nerve from nerve roots S2-S4.
How much sperm is produced per day on average?
300 million
3500 per second
What is the volume of ejaculate?
1.5 ml to 6 ml
Around 1/3 or just over a teaspoon full
How much sperm is lost before reaching the ampulla of the uterine tube?
99.9% - the first portion of the ejaculate is the most sperm rich.
What does the seminal fluid contain?
It contains seminal vesicles, prostate, bulbo-urethral gland combined with epididymal fluid.
What is the function of the bulbo-urethral gland?
- Produces a clear viscous secretion high in salt - known as pre-ejaculate.
- This helps to lubricate the urethra for spermatozoa to pass through, neutralising traces of acidic urine.
What is the composition of the seminal vesicle secretion?
- Contains proteins, enzymes, fructose, mucus, vitamin C and prostaglandins.
What is the function of the fructose in the seminal secretions?
Provide energy source
What does the high pH in the seminal secretion do?
It protects against acidic environment in the vagina.
What is the function of the prostate?
It secretes milky or white fluid roughly 30% of the seminal fluid.
What is the protein content of the prostate secretions?
Less than 1% and includes proteolytic enzymes, prostatic acid phosphatase and prostate-specific antigen.
What do prostate-specific antigen do?
It is involved in liquefaction.
What element is in prostate fluid that is useful?
A high zinc concentration (500-1000 times more than blood) for antibacterial purposes.
Structure of spermatozoon
Head - containing acrosome, nucleus and connecting piece.
Sperm Tail - Midpiece, Principal Piece and End piece
Midpiece - contains the mitochondrial sheath.
It is all surrounded by a plasma membrane.
