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
Hormonal Regulation of Exocrine Testis:
Expression of FSHR and (Less) LHR in sertoli cells causes:
Proliferation and differentiation of sertoli and germ cells
Hormonal Regulation of Exocrine Testis:
Androgen and oestrogen work locally on __ and __ cells.
Germ and sertoli cells
What horone is a marker for successful completion of spermiogenesis and why?
Inhibin. Inhibin made by sertoli cells inhibits FSH secretion by reducing anterior pituitary sensitivity to GnRH. Failure to complete spermiogenisis in man corrrelates with increased FSH and decreased inhibin.
FSH-induced Function of Seminiferous Tubules:
FSH stimulates the secretion of ____ by sertoli cells.
Androgen binding protein (ABP)
FSH-induced Function of Seminiferous Tubules:
Androgen-ABP complex binds to ___ and stimulates ___.
Androgen-ABP complex binds to Germ cells and stimulates Spermatogenesis.
What 3 factors acting on GnRH release can lead to hypoandrogenism
Acute and chronic illness, Opiods, Hypoprolactinaemia
What 3 factors acting on testosterone secretion can cause hypoandrogenism in men?
Corticosteroids, fasting, opioids
Interaction between Endocrine and Exocrine Testis:
How many ml of Testosterone is produced by men daily?
4-10ml
How does androgen get from the Leydig cells to the sertoli cells?
Passes through the baseent membrane and cellular barriers into sertoli cells.
Where is testosterone converted into dihydrotestosterone?
Sertoli cells.
Spermatogenesis is driven by which androgen?
DHT
Where does spermatogenisis take place?
In intercellular space within sertoli cell territory (Sustentacular cells)
What is the function of Sertoli cells in spermatogenesis?
- support, protect, nourish and fix germ cells and allow intercellular communication
- form hormones and other peptides:
– oestrogen – inhibin – activin
• form blood-testis barriers
What are the 3 types of intimate associations, with all cells of the spermatogenic lineage, that sertoli cells engage in?
- Primary spermatocytes communicate and recieve material from SCs via gap junctional complexes
- Spermatocytes and spermtids form ectoplasmic specialisations with SCs which anchor, then release the cells (Lost at spermiation)
- Tubulobulbar complexes through which SC removes material (phagocytic) from spermatids during cytoplasmic condensation.
Sertoli cells show changes in morphology & biochemistry in concert with spermatogenic cycle. How so?
Volume, lipid content, nuclear morphology, number and distribution of lysosomes vary cyclically
Synthesis & output of proteins e.g. ABP, transferrin, plasminogen activator vary cyclically
How long does spermatogenesis take?
65-75 days
How many sperm/gram of testis tissue/ second are produced?
300-600
How many meitoc divisions are involved in spermatogenesis
2 in addition to mitosis
What are the start and end products of spermatogenesis?
Spermatogonium to sperm
What are the starting and end products of spermiogenesis
Spermatid to elongated sperm (cytodifferentiation)
What stage of prophase 1 does crossing over occur?
Pachytene
What stage of Prophase 1 does the synaptonemal complex align non-sister chromatids homologous chromosomes?
Zygotene
What is thename of nuclear divisions?
Karyokinesis
Does type A or type B spermatogonium remain at basal membrane of seminiferous tubule?
A
What 2 ways do spermatocytes exchange genetic information during meiosis?
Random assortment and crossing over
What is spermiogenesis?
Cytoplasmic remodellling and shape changing from round to elongated.
What are 5 key features of spermiogenesis?
- Acrosom formation
- Formation of tail from centrioles
- Migration of cytoplasmic contents
- Removal of excess cytoplasm
- Condensation of the nucleus
On avaerage, what is the concentration of sperm/ml in ejaculate?
100million/ml
What semen composition determins male infertility?
One or more of:
<20million sperm/ml
<60% sperm motility
>20% abnormal sperm morpholgy
When does capacitation of sperm occur?
Exposure of sperm to female tract
How long may sperm survive post-ejaculation?
24-72hrs
What is the pH of semen?
pH: 7.3-7.5
What is seminal fluid composed of?
fructose, citrate
- prostaglandins
- fibrinogen
- enzymes – proteases, vesiculase
- fibrinolysin
- PSA (prostate specific antigen)
- seminal plasmin
What are the 4 general phases of sexual response and sperm delivery?
- Sexual Arousal: Excitement erection, lubrication
- Seminal emission: Propulsatile ejaculation, orgasm
- Resolution: dissipated sexual arousal
- Refractory: inability to restart sexual arousal
Is an erection a sympathetic or parasympathetic outcome?
Parasympathetic
What are the two types of stimuli for sexual arousal?
Psychogenic: sexual and erotic thoughts
Somatogenic: mixture of objects, people, activities, tactile
What mechanism is activated by a spinal reflex initiated by stimulation of mechanoreceptors on glans penis?
Corporal Veno-Occlusive mechanism
What occurs during the corporal veno-occlusive mechanism?
Parasympathetic stimuation=
Relaxation of arterial smooth muscle= vasodilation of penile arterioles (Can be done using Ach or NO).
Engorgement of erectile tissue with blood results in hardening of penis and compression of the veins against the nondistensible tunica albuginia.
How is an erection inhibited?
Sympathetic induced inhibition=
Contraction of arterioal smoooth muscle cells leading to vasoconstriction of arteries =reduced blood flow to penis.
What is the enzyme that degenerates cGMP-> GMP?
PDE5
What is the other name for sidenifil citrate?
Viagra
How does sildenafil citrate cause an erection?
It inhibits PDE5 enzyme thus cGMP isnt degraded. More cGMP can activate cGMP-specific protein kinase = more vasodilation of arteries in penis.
What sympathetic nerve levels are involved in orgasm?
T10-L2
What happens to the urinary sphincter during orgasm?
It closes due to sympathetic stimulation of the smooth muscle.
Somatic contraction of which 2 muscle causes propulsative ejaculation?
Bulbospongiosus
Ischiocavernosus
Somatic (s2-s4) nervous system + ____ = rhythmic contactions of bulbospongiosus and ischiocavernosus
oxytocin
>90% of volume of ejaculated semen is from the
Accessory glands
What are the functions of these components to semen?
- fructose, citrate
- prostaglandins
- fibrinogen
- enzymes
- seminal plasmin
- fibrinolysin
- fructose, citrate - energy source
- prostaglandins - sperm motility, uterine contractions
- fibrinogen – coagulation
- enzymes – proteases, vesiculase - converts fibrinogen to fibrin after ejaculation
- seminal plasmin – antibiotic
- fibrinolysin for liquefaction
What is the speed of spermafter ejaculation?
1 to 3 mm/min
What is removed from the head of sperm during capacitation?
cholesterol • proteins and • glycoconjugate (decapacitation factor)
