T4: Sex Differentiation Flashcards
what are the seven sexual differentiation items
genetic, gonadal, internal genitalia, external genitalia, hypothalamic, secondary sex traits , psychological, behavioral
describe the differences for genetic sex
mammals
-male XY (heterogametic)
-female XX (homogametic)
birds
-males ZZ (homo)
-females ZW (hetero)
what is the difference with reptiles and genotype
have no heteromorphic pair, sex is determined by temperature
why can female cats be calico
-one of the X’s is inactivated (tortie)
-appears as the Barr body in the somatic cells of females
what are some abnormal gene types
XXY: sterile male, Klinefelter syndrome
XO “missing” : turners syndrome, sterile female
-happens around the time of oogenesis or spermatogenesis
What is the Sry gene
sry= sex-determining region of the Y chromosome
Sry is the gene on the Y chromosome responsible for male development
-production of TDF or SRY protein (which causes the indifferent gonad to be organized as a testes)
what can be used to accurately sex embryos
SRY gene
describe the male developing process
-XY, TDF, or SRY protein is present
-testes develop
-Sertoli cells secrete anti-Mullerian hormone (AMH)
-(degeneration of paramesonephric duct)
-AMH causes Leydig cells to differentiate to
1. testosterone- development of male duct system
2.Dihydrotesterone- development of penis, scrotum and accessory sex glands
describe the female developing process
-XX, no TDF
-ovaries develop, no AMH
-paramesonephric ducts become the oviducts, uterus, cervix, and part of the vagina
-complete female tract
what layer does the repro tract come from
mesoderm
describe the development of the gonads
- bipotential (undifferentiated gonad) develops from the gonadal *gential ridge
-PGCs (primordial germ cells) migrate to and inhabit gonadal ridge
-chemotactic agent (telopheron) stimulates movement to genital ridge
describe the development of the gonads part 2
-undifferentiated gonad will become either testis or ovary
-PGCs will become either spermatogonia or oogonia
describe the role of primordial germ cells
-wander in a amoeboid manner from the primary ectoderm into the yolk sac wall and collect near the base of the allantois and hindgut
PGCs vs somatic cells
-larger (12-20 microns)
-large round nuclei containing prominent nucleoli
-pseudopodia
-secrete lytic enzymes
-migrate by ameboid movement
-use telopheron to help migrate to the gonad
describe how the ducts develop for male and females
a starting conceptus has both male and female components
starting: gonad, mesonephros, Mullerian duct, wolffian duct, urogenital sinus
female: (mullerian duct) develops from the paramesonephric system
Male: (wolffian duct) develops from the mesonephric system
describe how the testis are formed
- SRY gene is expressed in cell precursors in XY gonad, sertoli cells differentiate, sex cords persist in development to organize a testis
- undifferentiated sex cords align with rete tubules
-mesonephric tubules have not interconnected with rete tubules
-surface of undifferentiated gonad covered with albuginea
-paramesonephric duct present but serves no function
describe how the testis formed part 2
-rete and mesonephric tubules now interconnected to provide continuity b/w undifferentiated sex cords now developing into epithelial cords
-epithelial cords will become seminiferous tubules
-paramesonephric duct regressing due to AMH produced by setoli cells of developing testis
describe how the testis are formed part 3
-seminiferous tubules are now formed
-Rete testis and efferent ducts continuous
-mesonephric duct becoming epididymis
-parames duct has regressed
describe how the female repro system develops
-paramesonephric and mesonephric ducts intact
-coelomic epithelium will become ovarian cortex
-remnants of mesonephric tubules do not make contact with rete tubules
describe how the female repro system develops pt 2
-rete testis have disappeared and paramesonphric duct continues to develop and enlarge
-sex cords regress but primitive germ cells do not
-primordial follicles begin to develop
-paramesonephric ducts continue to develop and mesonephric ducts continue to regress
escribe how the female repro system develops pt 3
-distinct clusters of follicles surrounded by a single layer of cells develop at periphery of ovary
-sex cords have completely disappeared
-ovary has distinct cortex (region containing primordial oocytes) and medulla
-mesonephric tubules and ducts have regressed
how do the testes drop (part one)
-before they lie retroperitoneal and are attached caudally to the gubernaculum
-cells of the peritoneum infiltrate the gubernaculum in the inguinal region and form a junction and form a junction w/ it
-allows vaginal process to form as the distal gubernaculum grows towards and into the scrotal region
-after the gubernaculum penetrates the inguinal ring, there is rapid growth.
-this growth is the force for mechanically pulling the testes into the inguinal canal
how do the testes drop (part two)
- once testes are in the inguinal canal, they are pulled through as gubernaculum regresses
-gubernaculum regresses pulling testes deeper into scrotum and causing encapsulation by visceral vaginal tunic
-inner (visceral) layer covers testis and outer (parietal) layer lines scrotum
what are the times of testicular decent for the species
bull: 1/2 gestation
Ram: 1/2 gestation
Boar: last 1/4 gestation
stallion: just before or just after birth
man: 7th month of gestation
what are the potential problems associated with testicular descent
-cryptochidism: failure of testicular descent, may be unilateral or bilateral
-scrotal hernia: passage of intestines into scrotum (often removed from herd)
what species are abnormalities common
-may occur in any species but is especially common in boars
what is going on in the first trimester
-migration of primordial germ cells from yolk sac
-sex cords develop in gonad, paramesonephric ducts develop
-sex evident from structures are visual
what happens in the second trimester (bull and ram)
-development of make ducts and testes or development of female ducts and ovaries
-formation of broad ligament
what happens in the 3rd trimester
-testicular descent
then parturition
