Control of testicular function and sperm physiology Flashcards
What is the function of the testicles?
- production of sperm
- secretion of androgens
What is the length of the seminiferous tubules ?
500m
Describe the structure and function of the seminiferous tubules
A.) spermatogonial stem cells for sperm production
B.) sertoli cells: support,nutrition, protection,secretory,excretory
Describe the characteristics of spermatogenesis
- starts at puberty
- Maintains species
- Mitosis followed by meiosis
- 120million sperm/day or 1500/sec
- whole cycle takes 72days
What is spermiogenesis?
- final stage of spermatogenesis, which sees the maturation of spermatids into mature, motile spermatozoa.
- Repackaging
What is the function of the sertoli cells?
- Provide structural support
- create two compartments
- Provide nutrients for mature sperm
- Eliminate degenerate germ cells
- Secrete inhibin, ABP, AMH and growth factors.
What is the function of the Leydig cells?
Secrete androgens (C19), mainly testosterone
What are the actions of testosterone?
- Male hormone, anabolic (bone&muscle mass)
- Primary and secondary sexual characteristics
- Libido and sexual behaviour
- Stimulates sertoli cells and spermatogenesis
What are the two compartments of the seminiferous tubule?
1.)adluminal compartment, near the lumen of the seminiferous tubule
2.)Interstitial compartment,the basal spermatogonal cell and the interstital cells of Leydig
They are separated by the blood-testicular barrier
What makes up the blood-testicular barrier?
The intracellular junctions of the sertolli cells.
Describe the Hypothalamic-Pituitary-Gonadal axis
Hypothalamus releases GnRH which stimulates the pituitary to release LH&FSH which stimulate the testes to release testosterone.
Describe the role of testosterone in the feedback loop.
Takes part in negative feedback. Testosterone feeds back to the hypothalamus to reduce the release of GnRH& also on the pituitary to reduce the release of FSH& LH (thus directly and indirectly)
Which cells do FSH & LH act on?
the FSH acts on the Sertoli cell while LH acts on the Leydig cell. Testosterone also acts on the Sertoli cell.
What is testosterone aromatised into?
Estradiol.
What is testosterone reduced to?
DHT
Where are FSH receptors located?
On the surface of the Leydig & Sertoli cells.
Describe the role of the Sertoli cells and testosterone in negative feedback of the FSH &LH
- The Sertoli cells produce INHIBIN which inhibits FSH.
- The testosterone inhibits the LH production.
Describe the different elements of sperm transport.
- Ejaculation: deposition of sperm in vagina(acidic)
- Cervix: mucous barrier and crypts act as sperm reservoirs-motility is important
- Uterus and tubes: mild contraction to propel the sperm towards the egg
- Ampullary portion of the tube: fertilization
What is sperm capacitation?
Refers to the physiological changes spermatozoa must undergo in order to have the ability to penetrate and fertilize an egg.
- “switching on” of sperm- HYPERACTIVE
- Takes about 4 hours after ejaculation
- cholesterol loss and calcium influx
Outline the acrosome reaction.
- Triggered by contact with oocyte
- Interaction with ZP3 protein on oocyte membrane
- Leads to exposure of hyaluronidase and acrosin enzymes
- Facilitates oocyte penetration
Outline Oocyte activation.
- Release of cortical granules. This acts as a block to polyspermic penetration
- Resumption of meiosis
- Formation of the male and female pronuclei (fertilisation)
Which factors affect sperm production?
- Recreational anabolics abuse
- Environment
- Non-hormonal factors: e.g vasectomy= the male vas deferens are cut and tied or sealed so as to prevent sperm from entering into the urethra
- Heat exposure( optimum temp. for testes is 35 degrees Celsius which is why they are located outside the body)
- Radiation
- Air pollution
- Food chain pollution
- stress &reduced sexual activity may also play a role
Outline the mechanism of factors causing infertility
- A factor( such as smoking,drugs, varicocele or cancer) causes oxidative stress( oxygen,hydrogen peroxide or hydroxide)
- This then causes protein damage, lipid peroxidation,bio-membrane damage or DNA damage, which ultimately leads to sperm damage and thus infertility.
At which level can there be disturbance in regulation of testicular function?
- Genetic level
- Hypothalamic level
- Pituitary level
- Target tissue level
What is the presentation of Klinefelter syndrome?
47 XXY
- Taller than average height
- reduced facial and body hair
- gynaecomastia
- Osteoporosis
- Feminine fat distribution
- Small testes( testicular atrophy)
- May cause delayed puberty
What is Kallman syndrome?
- is a genetic disorder that prevents a person from starting or fully completing puberty
- a form of a group of conditions termed hypogonadotropic hypogonadism
- More common in men
- infertility
- affected at the olfactory bulb& tract
- These patients have no sense of smell or a reduced sense of smell because those nuclei develop next to the olfactory bulb
- Due to lack of development of the hypothalamic nuclei that are responsible for producing GnRH
- can be treated with HRT
What is androgen insensitivity syndrome?
- Partial or complete inability of the cell to respond to androgens
- genetically a man, phenotypically a woman
- There could be target tissue level abnormality i.e normal testosterone production from testicle but tissue not respond effectively, it may lack receptors
- 46 XY but phenotypically female because the target tissue can’t respond to the testosterone
What does testicular function ultimately depend on?
The delicate interaction between the two testicular compartments.
What is the function of the pampiform venous plexus
contains cooler venous blood to absorb heat from arterial blood in the testes.
-so regulates temp. of the testes
