male reproductive biology Flashcards
the bipotential gonad
has both wolffian and mullerian ducts
for males,
wolffian ducts differentiate epididymis, vas deferents
mullerian ducts regress (apoptosis)
for females ,
muller an ducts differentiate to oviducts, Fallopian tubes, uterus, cervix and upper vagina
wolffian ducts regress (apoptosis)
SRY controls
early testis differentiation
sertoli and leydig cells
sertoli cells secrete AMH - causes female reproductive structures to regress
leading cells secrete testosterone which induces differentiation of the wolffian duct system (epididymis, vas deference, sex accessory glands)
no-SRY gene
7-8 weeks - primitive gonad cortex develops not ovary (medullar regresses)
embryonic ovary does not secrete hormones
puberty is regulated by
HPG axis
adrenal cortex also secondarily involved
brain stimulates the hypothalamus to increase production of GnRH which stimulates anterior pituitary to increase LH and FSH to trigger gonads to produce sex hormones
ovaries produce oestrogen (oestradiol) and testes produce testosterone
FSH and LH also stimulate the development go oocytes and spermatozoa
hypothalamus in puberty
hypothalamus generates pulses of GnRH around 12th year of life
pulses of GnRH dependant on
pulses typically occur at night, due in part to gradual decrease in nocturnal melatonin secretion from pineal gland
also influences by nutritional status of body and growth rate
GH an IGF-1 stimulate reproductive function
leptin/ghrelin - metabolic hormones that determine size of fat stores
kisspeptin
patients with Kiss1 or KissR null mutations have hypogonadotrophic hypogonadism (HH) - pathological impubertism + infertility of CNS origin
a rise in the pulsatile release of kisspeptin in the median eminence takes place at puberty
exogenous administration of kisspeptins advances the onset of puberty and activates the pulsatile release of GnRH
testosterone is secreted by
leydig cells in response to LH
dehydrotestosterone
made from testosterone by 5a-reductase in some target cells
binds receptor stringer than testosterone
amplifies action of testosterone in some target tissues
systemic testosterone inhibits
GnRH and LH secretion
blood testes barrier
sertoli barrier
keeps testosterone in testes to prevent diffusion into blood and negative feedback
Sertoli cells secrete ABP
androgen binding protein
binds testosterone and keeps it at local high testosterone
testes
formed near kidneys - descend to scrotum
guided by gubernaculum through inguinal canal
undescended testes
crytorchidism - infertility
scrotum
sweat glands, pampiniform plexus, cremaster and darts muscles (increases in temperature causes cremaster and dartos to relax and the testes drop)
pampiniform plexus
warm blood comes down and looses heat to testicular blood rising back up
spermatogenesis
occurs in seminiferous tubules
epididymis
coiled tube which enlarges into vas deferens
vas deferens enters
prostate gland
content pass into ejaculatory duct and into the internal urethra
and urethra carries sperm away
germ cells in seminiferous tubules
spermatogenia
mature, proliferate and differentiate into spermatozoa
Sertoli cells
nourish and provide support for developing spermatozoa by providing local hormones, lipids and glycogen
create blood testis barrier
myofibroblasts
contractile
when sperm are in the seminiferous tubules they can’t move yet - must be mechanically moves out before they acquire motility
spermatogenesis
primordial germ cells migrate and become spermatogonia
spermatogonia
at puberty, spermatogonia mature, proliferate and differentiate into 1° spermatocyte
meiosis 1 into 2 x 2° spermatocytes
meiosis 2 into 4 x spermatids
differentiate into mature spermatozoa
1 spermatogonium
can make 512 sperm
spermatozoa
contain haploid genome
acrosome - large quantities of hyaluronidase and proteolytic enzymes to facilitate ovum penetration
minimal cytoplasm
tails - mitochondria-packed so lots of power
motile microtubules flagellate
epididymal sperm maturation
testicular spermatozoa are incapable of fertilising eggs (unless injected)
maturation achieved at distal corpus or cauda
acquire progressive motility
biochemical changes - increasing capacity for glycolysis, increase phospholipid FA content, activate CatSper (Ca trigger for acrosome reaction)
seminal vesicles
paired glands 65% of seminal fluid alkaline prostaglandins, fibrinogen and fructose semenogelin (prevents early sperm capacitance, limits motility)
semenogelin
gel slowing down the sperm so they can acquire motility without moving away
prostate
30% of seminal fluid
liquefying enzymes, fibrinolysis
PSA - serine protease - hydrolyses semenogelin (sperm motility inhibitor)
PSA
enzyme that gets rid of semenogelin
bulbourethral glands
paired glands 5% seminal fluid alkaline pre ejaculatory fluid make movement of ssperm easier
vasodilation in erection
increased arterial blood flow to corpora cavernosa
turgor compresses veins to limit loss of blood creating erection
corpus spongiosum
remains pliable in erection - prevents urethral occlusion
erection is controlled by
integrating centres (lumbar) activated by descending path (aroounsal) and afferents from genitalia
parasympathetic nerves in penis release
- ACh + VIP (co-transmitters) create vasodilation
- NANC fibres release nitric oxide for vasodilation
erection is sympathetic or parasympathetic
parasympathetic
emission
movement of semen through the urethra
vas deferens smooth muscle contraction move sperm forward
prostate, seminal vesicle smooth muscle contraction move prostatic and seminal fluid forward
mix in internal urethra (+ bulbourethral secretions)
ejaculation
propulsion, expulsion
rhythmical contraction of bulbospongiosus (skeletal muscle)
way finding of sperm
use chemotaxis (using sensing progesterone receptors) and thermotaxis (seek warmer environment)
capacitation of sperm
PSA degrades semenogelin
increase in motility, alkaline uterine/fallopian fluid alters membrane (increase in calcium permeability and CatSpur channels)
acrosome reaction
hyaluronidase and proteolytic enzymes digest proteins in ovum ECM
sperm reaches zona pellucida
sperm membrane binds receptor proteins, entire acrosome rapidly dissolves and releases enzymes
open penetrating pathway for the sperm to enter the ovum
sperm head and oocyte membranes fuse (cortical reaction) and deliver sperm genome
sperm membrane binds
ZP3 proteins
why does only 1 sperm enter the oocyte
sperm entry causes Ca2+ release which triggers cortical reaction
cortical reaction
cortical granules exocytosed into the periviteline space
cortical granules contain
proteases - that severe ZP3 receptors - any other bound sperms fall off and new sperm can’t bind
hyalin - forms a layer hardening the vitelline membrane making it impenetrable
hygroscopic mucopolysaccharides (GAGs) expand the vitelline space
