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ANSC4045 - week 3

farm animal repro - pituitary and reproductive embryogenesis

TermDefinition
three germ layers 1. endoderm (innermost) 2. mesoderm (middle) 3. ectoderm (outermost)
relative time of formation of three germ layers • before embryonic attachment to the uterus
exact time of formation of three germ layers • bovines: 7 days after fertilization • humansL 5 - 6 days after fertilization
destiny of endoderm • digestive system incl. liver + pancreas • respiratory system • majority of endocrine system - most glands
destiny of mesoderm • muscle, skeleton, cardiovascular system, urinary system • majority of reproductive system - gonads; uterus, cervix, part of vagina; epididymus, ductus deferens; accessory glands
destiny of ectoderm • nervous system - hypothalamus, both pituitary lobes • skin, hair, nails, sweat glands incl. mammary • nasal + oral cavities • rest of reproductive tract - vestibule of vagina, penis, clitoris
development of adenohypophysis • originates from Rathke's pouch - diverticulum from tissue in the roof of the mouth
development of neurohypophysis • originates from diverticulum in the floor of the brain • axons + nerve terminals from the hypothalamus
regression of Rathke's pouch • occurs when cells forming the adeno- + neurohypophysis successfully migrate to adjacent positions
sella turcica • depression in the sphenoid bone that supports and protects the hyopophysis
most important hormones in animal reproduction • follicle stimulating (FSH) and luteinizing (LH) • produced by the adenohypophysis
difference between adeno- and neurohypophysis • dual embryonic origin --> two lobes with entirely different functions • adeno: specialized epithelium secretes glycoprotein hormones • neuro: houses terminal ends of neural cells from the hypothalamus
timing of sexual differentiation • genetic sex is determined at syngamy/fertilization but won't be expressed in M/F gametes until about 40 days of development
primordial germ cell formation + migration • cells form in early first trimester from base of hindgut then migrate to genital/gonadal ridge • cells multiply during migration and form bipotential gonad at arrival to the ridge; cells that don't make it degenerate
primitive sex cords • once germ cells arrive at genital ridge, local connective tissue forms primitive sex cords in close proximity to developing renal system • two duct systems - mesonephric/Wolffian, paramesonephric/Mullerian - can develop into either sex
six main events in embryological reproductive development 1. migration of primordial germ cells from yolk sac 2. development of sex cords + kidney structures 3. sex evident from structures 4. development of M vs. F gonads 5. formation of broad ligament 6. testicular descent
sex-determining region on the Y chromosome (SRY) • when expressed, primitive gonads produce SRY protein, causing male reproductive development
anti-Mullerian hormone (AMH) • after SRY is expressed and male reproductive development begins, Sertoli cells secrete AMH • AMH stimulates differentiation of Leydig cells which begin to secrete testosterone
effect of simultaneous AMH + testosterone production • degeneration of Mullerian duct system • development of male duct system, penis, scrotum, male accessory glands
main events in male embryological reproductive development 1. SRY --> testicular development --> Sertoli cells secrete AMH 2. simultaneous differentiation of Leydig cells + degeneration of Mullerian ducts 3. Leydig cells produce testosterone + DHT --> development of male ducts, accessory glands, penis, scrotum
main events in female embryological reproductive development 1. no SRY --> primitive follicular cells, ovarian development 2. no AMH --> Mullerian ducts become oviducts, uterus, cervix, anterior vagina
mesonephros • early embryonic kidney • part of the male reproductive tract is derived from this
mesonephric tubules • from within the mesonephros • penetrate into the primitive gonad and connect to the primitive sex cords by the rete testis, becoming the efferent ducts
rete testis • tubules connecting the seminiferous tubules to the efferent ducts
three phases of testicular descent 1. transabdominal (I): growth + elongation of the fetus away from the testes 2. transabdominal (II): rapid growth of the extra-abdominal gubernaculum 3. inguinal-scrotal: shrinkage of gubernaculum within the scrotum
transabdominal phase of testicular descent • growing gubernaculum fuses with peritoneum
inguinal-scrotal phase of testicular descent • rapid growth of gubernaculum through the inguinal canal • gubernaculum shrinks, pulling testis through inguinal ring • gubernaculum regresses to a small knot, attaching testis to scrotum
time frame of testicular descent • bull + ram: mid gestation • boar + human: last quarter of gestation • stallion: just before or after birth
cryptorchidism • failure of one or both testes to fully descend • bilateral --> sterility due to body heat being too warm for spermatogenesis • still produce normal testosterone for secondary sex characteristics and normal behavior
inguinal herniation • herniation of intestine through the inguinal canal and into the scrotum • swine: 1 in 200 males, usually repaired during castration
formation of primordial follicles • sex cords fragment into cellular clusters, each enclosing a primordial germ cell
Mullerian ducts • develop into the oviducts, uterus, cervix, cranial vagina • uterus, vagina, and cervix form from two fused ducts
Wolffian ducts • develop into the epididymis, testes, ductus deferens, and seminiferous tubules
bovine Freemartinism • occurs in a female calf born twin to a male calf • various degrees of masculinization; incomplete development of female tract; may form ovotestis • mosaic animals with both male and female cells; usually culled
mechanics of bovine Freemartinism • extraembryonic membranes of two twins fuse --> common chorion --> common blood supply day ~39 • testes develop first --> AMH + testosterone + male primordial germ cells distributed to both twins before female characteristics
Created by: junoreg
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