Male Physiology Flashcards
What controls the secretion of testestosteron from fetal testes?
Fetal hCG
What does testosterone act on in the male fetus?
Testis
Duct system
External genitalia
Accessory Organs
CNS, hypothalamus development and GnRH release
What does GnRH-induced LH stimulae in male fetal periods/
Leydig cell development- androgen
Why does fetal hCG control fetal testosterone release?
HPG Axis not fully developed until hypothalamus is capable of secreting GnRH
What happens to fetal Leydig cells duing juvenile period?
They degenerate and decrease androgen levels
When does the Hypothalamus-pituitary-testes axis fully develop?
Puberty
How do undifferentiated interstitial cells become Leydig cells? When does this occur?
Expression of LH Receptors
Puberty
At puberty in males, increased sensitivity of LHR of Leydig cells =
Increased testosterone production
Inreased sensitivity of FSHR of sertoli cells during male puberty =
Proliferation of sertoli cells and germ cells = sperm formation
What compartmen of the testes is vascular?
Interstitial compartment containing Leydig cells
What is the site of hormone formation in the testes?
INterstitial Leydig cells
What cells make up 20% of fetal, newborn and adult testes?
Leydig cells
What are some steroidogenic features of mature Leydig cells?
- Numerous mitochondria with vesicular/tubular cristae
- Abundant sER
- Numerous lipid droplets
What is the precursor molecule for all steroids?
Cholesterol
What is the enzyme that converts Testosterone to DHT?
5-alpha reductase
What is the enzyme that converts testosteron to estradiol?
Aromatase
What kind of receptor does testosterone act via?
Intracellular/Intranuclear receptor
In which tissues is testosterone converted into oestrogen?
Locally and in adipose tissue
What proteins does testosterone bind to?
Steroid-binding globulin (SBG) also known as Androgen Binding Protein(ABP) and albumin
Can testosterone bound to SBG exert androgenic effect? What about Albumin?
No, too tightly bound to exert change. Weakly bound to albumin so it is more available to exert change.
What is considered bioavailable testosterone?
Testosterone that is unbound + testosterone bound to albumin
What are the three androgens in order of potency?
Androstenedione -> Testosteron -> Dihydrotestosterone
What ligament is the testes suspended by before testicular descent? What receptors does it have?
Supsensory cranial ligament. It has androgen receptors.
What causes the descent of the testes?
Androgen stiulated rhythmic contractions of the gubernaculum via genitofemoral nerve.
What is the avascular compartment of the testis?
Seminiferous tubules
How long is the seminiferous tubules?
200m long
What is contained within the lamina propria surrounding the seminiferous tubules?
Undifferentiated fibroblast-like cells
Peritubular myoid cells, smooth muscle cells
Extracellular matrix, collagen
What is a histological featur of a leydig cell?
They have pale cytoplasm due to cholesterol lipid droplets.
What are histlogical feature of a sertoli cell?
Simple columnar-like extending from basement membrane to lumen. Have pale nucleus but a very dark densly basophilic nucleolus.
What makes up the Blood-testes barrier?
Multiple layers of gap and tight junctions between sertoli cells.
What is separated by the Blood-Testis Barrier and why?
The basal (Diploid Spermatogonia) and adluminal (Haploid spermatogonia) compartments of the seminiferous tubules are separated. Preventsmixing of intratubular fluid with intertubular fluid. Prevents leaking of sperm into interstitial fluid w/ blood and lymph. Immune system develops @6month, sperm develops at approx 12yr, sperm has not developed ‘self-antigen’ therefore sperm is attacked by immune system.
Why are those with sertoli-cell only syndrome infertile?
PGCs dont make it to genital ridge therefore there is no sperm production
What cells in the testis convert Leydig cell induced androgen to oestrogen?
Sertoli cells