VBMS 325 pregnacy and sex determination

placenta

• interface comprised of fetal and maternal tissue

• chorion and allantois

• chorion and yolk sac

• endometrium/decidua

chorionic villi

projections on the surface of chorion that intimately interact with maternal tissue

diffuse placenta

chorionic villi located over the entire uterine luminal epithelium (pig, horse)

cotyledonary placenta

vascularized chorionic villous trophoblasts formin cotyledons and uterine endometrial structures termed caruncles coming together (called placentomes)

zonary placenta

an invasive band of chorion surrounds the middle of the fetus (dog&cat)

discoid placenta

a disc like structure of chorion interacting with maternal tissue (higher primates and rodents)

placental function during pregnancy

• transfer oxygen and carbon dioxide

• fetal nutrition

• excretory functions

• hormone/enzyme production

• immunological functions

marked placental growth

must occur prior to significant fetal growth

progesterone during gestation

• placentae produce steroids like estrogen and progesterone

• early in pregnancy- stimulates endometrial growth and gland development and secretions

• progesterone block inhibiting uterine contractions

estrogens/estadiol during gestation

• stims endomerial growth early in pregnacy

• an important product of placenta during last part of pregancy

• peck of estradiol close to parturition (promotes labour)

myometrial contractile activation

• increase in gap junctions production and communication just prior to and during labour

• coordianted and forcefull contractions

glucocorticoids

• a class of steriod hormones produced by the adrenal glands

• produced on demand, diffuses out of cells and into blood to be transported by carrier called corticosteroid binding globulin (CBG)

fetal cortisol actions

• mediates maternal energy demands (frees up plasma glucose for fetus)

• triggers maturation of fetal organs

• can regulate intreuterine prostaglandins synthesis

• initiates parturition

growth of conceptus

distends uterus and stimulates expression of CAPs that aid parturition; GJ proteins,oxytocin receptors, prostaglandin receptor

key players of parturition

• the fetus

• fetoplacental unit

• uterine musculature (ripens cervix, coordinated contractile muscle)

parturition phase 0

quiescence

• 95% of gestation marked by myometrial quiescence and non-dilated cervix

parturition phase 1

activation

• softening of cervix, myometrium becoming prepared for contractions with increased CAPs (gap junctions, PG receptors) and uterotrophic factors (E2,PGs)

parturition phase 2

stimulation

• increased contractility. large surges in PG oxytocin release, dilatation of cervix, delivery of the fetuses

parturition phase 3

involution

• afterborth delivered. uterus and cervix begin to be remoldeled back to non-pregnant stage

ferguson’s reflex

• uterine contractions force fetus toward cervix and vagina

• stims pressure sensitive neurons in cervix that synapse with neurons in hypothalamus

• leads to increased oxytocin secretion and cycle of greater contractions with greater pressure on cervix

oxytocin

• hormone produced by hypothalamus but released from posterior pituitary

• powerful muscle stimulant

• induces labour

preg tests

• transrectal palpation

• hormone measurement

• ultrasonography

female reproductive functions

• production of ova (oogenesis) and ovulation

• reception of sperm

• transport of sperm and ovum to site of fertilization

• nourishment of development fetus

• parturition or laying eggs

• nourishment of offspring

female repro organs

• oviducts

• uterus (shell gland)

• vagina

• external genitalia (vulva)

male repro functions and organs

• production of sperm

• delivery of sperm

• testes

• scrotum

• vasa efferentia, epididymis, ductus deferens, ejaculatory duct, urethra

• accessory sex glands: seminal vesicle, prostate galnd, bulbourethral gland

• penis or hemipenis

sexual dimorphism

trait that differentiate members of same species by sex

• ornamentation

• coloration

• size

• behaviour

sex differences

significant differences in the averages of phenotype between males and female

• height, sex, hormone levels, immune cell composotion

sex of an animal

defined as its ability to produce a particular type of gamete along woth any associated phenotypic traits

intersex individuals

animals born with varying presentation of male and female genitalia

sex determination

process where an organism begins the development of ovaries or testes from the embryonic gonad through hormone production

mammals and frogs genotypic sex

males heterogametic xy and females homogametic xx

birds and urodele amphibians genotypic sex

male homogametic ZZ and females heterogametic ZW

insects genotypic sex

males have 1 sex chromosome XO, females have two XX

environmental sex determination

reptiles like crocodiles, lizards, turtles, some fish

• sex determination depends on external factors like temp

• sex chromosome are absent

primodial germ cells

• displaced to definitive yolk sac and part of allantois

• give rise to oogonia and spermatogonia

PGC migration

PGC migrate as a group from base of allantois and yolk sac into hindgut

somatic cells

located around PGC and secrete chemoattractants and survial factors to maintain PGC viability during migration

membrane adhesion proteins

keep PGCs grouped together during migration

membrane receptors

promote interaction with extracellular environment for migration to proceed

PGC outside of gonadal/genital ridge

normally die

gonaldal ridge

• bipotential gonad

• time of development it can differentite along different paths (ovary or testes)

• forms near embryonic kidneys

primitive sex cords

compact strands of tissue that incorporate PGCs (seminiferous tubles in males)

SRY

sex determining region of Y chromosome, stimulates production of testis-determing factor (TDF) by primodial germ and gondal cells

lack of SRY gene

fetus develops ovaries

dihydrotestosterone

stims develoment of male repro tract and external genitalia

wolffian ducts

• develop into male repro tract

mullerian ducts

regress due to anti-mullerian hormone secreted byb developing testes

presenc of DHT and testosterone

• develop penis

• urethral fold

• genital (scrotal) swelling

• prepuce

• scrotum

absence of DHT and testosterone

• developing clitoris

• urethral fold

• genital swelling

• glans clitoris

• labia minora

• vagina

epigenetic regulation

altering gene expression and phenotype without altering DNA sequence

ESD developmental window

during which environment influences sex is long

DSDs: sex reversal

• high frequency in pigs and goat

• polled intersex syndrome (deletion within a chromosome)

turner syndrome

• gondal dysgenesis

• X chromosomme is present XO no Yo

• hypoplastic ovary

• small uterus

• underdeveloped genitali

Klinefelter’s syndrome

• XXY

• male deteriming genes influencing development

• individual develops phenotypically male

parthenogenesis

• unisexual reproduction

• repro occurs in absence of males

parthenogenesis: obligate

repro exclusively through asexual means

• requires doubling of chromsome in egg-producing cells prior to meiosis

parthenogenesis: facultative

repro in sexually reproducing species that sometimes utilizes asexual meas

• can be due to stress,captivity

• diploid chromsome complement of egg restored by failure of second meiotic division or fushion of second polar boy with egg nucleus