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Reproductive Physiology of the Male (Puberty (Factors affecting age of…
Reproductive Physiology of the Male
Functional anatomy
Neuroendocrine
Hypothalamus
Adenohypophysis
Genital system
Testes
suspended within scrotum by spermatic cord and external cremaster muscle
Located outside abdomen for lower temp
temp must be 2-6 degree lower than body temp, as elevated temp reduces numbers of live normal spermatozoa
Thermoregulation
pendulous scrotal sac
regulate through conduction, convection and evaporation
testicular vasculature
highly coiled and convoluted
reduces mean blood pressure
form venous pampiniform plexus network surrounding testicular artery
allow counter current heat transfer from high heat (artery) to low heat (vein)
dartos and cremaster muscles
control surface area of scrotum
move testes closer or father from abdomen
scrotal skin
thin, lack of hair/fur and fat
Have sebaceous gland and sweat gland
allow evaporation
Extensive blood and lymphatic system
facilitate heat loss through radiation of heat to the environment from blood vessels
has thermoreceptors
Leydig cells
secretes testosterone, bath seminiferous tubules in fluid rich in testosterone
Seminiferous tubles
has 2 compartments
basal
mitosis of spermtogonia
adluminal
meiosis of spermatocytes
has Sertoli cells
provide nourishment to developing spermatocytes
Rete testis
connects testis to epididymis, carrying spermatozoa and fluid
Epididymis
consists of head, body and tail
conduit for spermatozoa, allowing them to mature here to be capable of fertilization
Vas Deferens
in some species, have ampullae, which act as storage, basically a modified end of epididymis, closely related to ampulla gland?
Accessory sex glands
ampullary glands
seminal vesicles
prostate gland
bulbourethral gland
Penis
copulatory organ
Transfer of spermatozoa
Emission is the release of spermatozoa and accessory gland fluids into the pelvic urethra as a result of sympathetically mediated thoracolumbar reflex contraction of the smooth muscle in the ductus deferens and accessory glands
Ejaculation is the forceful expulsion of semen from the urethra and is prompted by a parasympathetically mediated sacral reflex that induces rhythmic contractions of the bulbospongiosus, ischiocavernosus, and urethralis muscles
After ejaculation, a sacral sympathetically mediated increase in the smooth muscle tone of the cavernous spaces increases the outflow of blood, and contraction of the retractor penis muscle withdraws the penis into the prepuce
Spermatogenesis
has 3 events:
Spermatocytogenesis
has 2 functions:
mitosis of type A spermatogonia that are still uncomitted to immediate spermatozoa production, increase stem cell population
conversion of type A to type B spermatogonia that will undergo mitosis to produce primary spermatocytes that are ready to undergo meiosis for spermatozoa production
Meiosis
production of haploid germ cells, spermatids
Spermiogenesis
spermatids undergo several transformation to before released as spermatozoa
formation of acrosome
condensation and elongation of nucleus
formation of flagellum
extensive shedding of cytoplasm
after spermiogenesis, is called spermatozoon, consists of:
Head
contain genetic information for fusion with oocyte
covered by acrosome that contains hydrolytic enzyme to enable penetration of oocyte
Middle piece
contains mitochondria to generate energy for movement
Tails
for movement
from spermatogenesis to maturation takes 60-70 days in ram
Testicular size (measured via scrotal circumference since can measure size of testes) affects daily sperm production where bigger means more
Hypothalamic-pituitary-testicular axis
Hypothalamus
Adenohypophysis
Testes
Leydig cells
Binding of LH
Stimulates conversion of cholestrol to testosterone (a type of androgen)
Testoterone
Diffuse to blood and lymph and bind to androgen binding protein (ABP) synthesized by Sertoli cells
Also bind to Sertoli cells
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high conc of testosterone important for normal spermatogenesis to occur
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inhibit LH synthesis through negative feedback on hypothalamus or adenohypophysis
Sertoli cells
Binding of FSH and testosterone
Synthesize
ABP
Synthesize
inhibin
stimulate steroid production of Leydig cells
potent inhibitor of FSH from pituitary
Synthesize
estrogen
inhibit LH synthesis throught negative feedback on hypothalamus or adenohypophysis
Synthesize transferin
involved in nutrients transfer to germ cell
release FSH and LH
LH binds to receptor on Leydig cells
FSH binds to receptor on Sertoli cells
Secretes GnRH in pulsatile manner
Affect gonadotropic cells of adenohypophysis
Puberty
In male, is defined by ability to produce sufficient sperm to impregnate a female
ejaculate contains 50x10^6 with 10% or more motile spermatozoa
Onset theorized to occur when hypothalamus became desensitized to feedback inhibition of gonadal steroids which allow increased release of GnRH from hypothalamus and increased respond of adenohypophysis to GnRH
Factors affecting age of puberty
Breed
Energy intake
Season of birth
not related to sexual maturity as it could be years later after onset of puberty
Anabolic steroids
androgen derivatives that exert negative feedback to the hypothalamic-pituitary-testicular axis
effects
positive
administration improve athletic performance
negative
use during pre or peripuberty may hinder puberty
impair testicular endocrine function
reduce seminal quality
reduce daily sperm output
reduce testicular size
impairment of spermatogenesis