ASCI 341- Embryogenesis of Pituitary Gland

Differentiation

Process whereby a primitive group of unspecialized cells develop into functional, recognizable group of cells that have a common function

Embryonic germ layers (formed for first step of differentiation)

Endoderm (inner layer) guts lungs, liver

Mesoderm = muscle, skeleton, cardiovascular repro system

Ectoderm = nervous system, skin, hair

Mammals Sex

Chromosomal = XY (male) AND XX (female)

Gonadal Testis = Male, Ovary = Female (determination happens early on in the embryonogenesis/gestation)

Phenotypic sex= voice, breasts, fat deposition, hair patterns, other characterisitics

Behavioral Sex= Sex of the Brain

1st trimester

migration of primoridal germ cells from yolk sac, sex cords develop in gonad, paramesonephric ducts develop

sex evident from features

2nd trimester

development of male/female ducts, oviduct/testes

formation of broad ligament (half in 1st half in second for male/female ducts)

3rd trimester

testicular descent (before partiution) sooner for bull and ram (more like 2nd trimester) very late for colt

Formation of anterior and posterior pituitary glands

Diverticulum = sac/pouch diverting from a main tube, channel, or cavity

Infundibulum = diverticulum of the brain floor

Rathke’s Pouch = diverticulum of the stomodeal roof/embryonic mouth)

near third ventricle (where hypothalamus is located)

peak is developed

eventually rathke’s pouch loses contact (regressing stalk)

Developing sphenoid bone (part of the cranium)

Mature structures:

posterior lobe and anterior lobe of pituitary, sella turnica = cavity, developing sphenoid bone around pituitary , all over roof of pharynx

Posterior pituitary (neurohypophysis)

neural tissue, derived from infundibulum (back of brain)

Anterior pituitary adenohypophysis

glandular tissue, derived from rathke’s pouch (front of brain

Primordial Germ Cells (PGCs)

Migrate from:

Yok sac (portion of placenta, only around for first 15% of gestation)——midgut—-mesentary—-gondal ridge

-ameboid movement

-chemotactic signal (movement towards the signal)

-when arriving at gonadal ridge:

stimulate proliferation of connective tissue

form primitive sex cords

cause gonadal ridge to enlarge and push against kidneys (testes forming near kidneys before dropping)

undergo mitosis to increase in numbers

(GONADAL SEX IS NOT DETERMINED YET)

Pronephros

Nonfunctional remnant of kidney formation in lower animals

Mesonephros

Functional bilateral pair of intermediate kidneys

produce urine, drains by mesonephric pair of ducts (1st 15% of gestation)

Metanephros

FINAL Adult form

Develop functional nephrons

1st 30-35% of gestation

Sexually indifferent stage

Mesonephric wolffian ducts in male

paramesonephric mullerian ducts in female

Key of Sex Determination for Males

Y chromosome or SRY gene (leads to testis formation)

-Sertoli cells (in testis) secrete anti-millerian hormone——related to paramesonephric duct, will degenerate it(AMH) and dihydrotestosterone (DHT= stronger testosterone, inhibit female reproductive system)

^govern spermatogenesis

AMH + testosterone degenerate paramesonephric duct

Desert Hedgehog (DHH) gene (transcription factor) differentation of fetal leydig cells = testosterone and dihydrotestosterone= male duct system

DHT = development of penis, scrotum, and accessory sex glands

Female Sex Determination

No SRY

Ovaries develop

NO AMH

Paramesonephric ducts = oviducts, uterus, cervix, and part of vagina

Will eventually form female tract

Male Development of Reproductive Tract (stage 1)

No interconnected tubes

Paramesonephric duct

Mesonephric tubules = future efferent ducts, from mesonephric duct

Rete tubules form close to mesonephric tubules

Undifferentiatied sex cords will be gonad (testis)

tunica albuginea around sex cords

Male tract development (Stage 2)

Epithelial cords shape from sex cords, future seminerferous tubules

Rete testis now connected to mesonephric tubules and epithelial cords

Mesonephric duct is forming off of rete tubules

Paramesonephric still present

Male tract development stage 3

100s seminiferous tubules formed

rete tubules formed complex interconnections

Mesonephric tubules = efferent ducts (6-12)

mesonephric duct = ductus deferens, also forms epididymis

Remembering primitive versus mature

Testicular descent

Gubernaculum= connective tissue

organ (ligament) that attaches to the ventral pole of the testis and extends to inguinal region of developing fetus

What controls gubernaculum growth? Decendin = insul3

Gubernaculum

grows after fusion of perioteneum and gubernaculum

enters in inguinal canal in viceral vaginal tunic, vaginal cavity, parietal vaginal tunic, pulling visceral growth

FINAL DESCENT = regression of the gubernaculum

^testis continues to move downwards

regresses until it forms a little knot at the bottom to anchors testis to bottom

(stallions anchoring hasn’t happened until after birth)

Final: vaginal cavity, visceral vaginal tunic, testes can still move for thermoregulation (closer or further away from body cavity)

What triggers growth of gubernaculum

gubernacular cells need MW testicular extract for significant growth (molecular weight proteins)

cryotiorchidism

bilateral sterile animal

inguinal hernia example below:

invasion of other organs from improper closure of peritoneum and inguinal ring, now intestines can drop down into female cavity

female development (stage 1)

paramesonephric duct development

First stage

future infundibulum

regressing tubules (not making connections)

epithelial cords

coelomic epithelium (future cortex)

paramesonephric duct/mullerian duct

Mesonephric duct still currently exists

female development stage 2

-regressing mesonephric

-regressing epithelial cords

-future ovarian cortex

-paramesonephric duct

-regressing mesonephric

-future infundibulum

female development 3 (first 40% of gestation)

regressing mesonephric, regressing epithelial, paramesonephric = future uterus + oviduct, regressing mesonephric, future infundibulum, primative follicles (no penetration, within cortex)

^Cells in clusters = cell syncitium

Cell synsitium

connections between germ cells/follicles, extracellular connections for similar developmental rates, look like o=chem chair/triangular structure

Stage 4 femal edevelopment

primordial follicles present! Remanants of mesonephric, ovarian medulla + cortex formed

Still paramesonephric for future oviduct/uterus, and future infundibulum

Regressing mesonephric duct

(in mare, there is still the inverted ovary that is forming)

total female development 1

cranial urogenital sinus = future bladder

fused paramesonephric ducts = cervix + uterine body (simplex, duplex, etc. formation = amount of fusion)

bud from urogenital sinus

caudal urogenital sinus = future vestibule

total female development 2

fused paramesonephric = cervix + uterine body

still have bud from urogenital sinus

total female development 3

uterine horn, uterine body, cervix, future bladder, cranial vagina, future urethra, vestibule, rectum

uterine horn, cervix, cranial = from paramesonephric, from mesoderm

Bladder + vestibule = ectoderm

cross section of female embryo 1

neural tube, notochord, aorta, regressing mesonephric, paramesonephric (oviduct future) gonad, gut

Gonads moving ventrally in wing like motion

ovary and paramesonephric still have distance from each other

(more anterior view)

cross section of female 2, more posterior

genital fold, regressing mesonephric duct, paramesonephric duct (future oviduct) more migration closer together

Gonads present

cross section of female embryo 3, even more posterior

remanant of mesonephric= gartners ducts

geneital fold = future broad ligament, connective tissue

periotenum = fused together (specifically talking about mesometrium of broad ligament)

Paramesonephric duct (future uterus)

chromosomal sex (heterogametic)

Mammals = Male = XY, Female = XX

Birds/Reptiles = Male = ZZ Female = ZW

Some lizards/tortoises have NO heteromorphic pair (determined by temperature and steroids)

in Mammals = one x is inactivated = barr body in somatic cells

XXY Klinefelter’s syndrome -= sterile, testicular hypoplasia

XO= turner’s syndrome = sterile, inactive ovaries

Hermaphrodites

Cogenital malformation in sexual development

True hermaphrodite

male psuedohermaphrodite

female psuedohermaphrodite

true in swine = ovatestis with epididymis on the end of uterine horn

Female pseudohermaphrodite (freemartin)

heifer born twin to a bull

-membranes of placental units fuse to occupy same cotyledon (interact with caruncles)

-common blood supply for male and female fetus

-AMH from male inhibits development of repro tract in female fetus

(male tract happens a little bit before female in development)

-ovaries cease growing = decrease in germ cells + NO ESTROGEN

-Infantile repro tract remains

-Produce testosterone and androstenedione (have male characteristics)

Gene defect in men

5 alpha reductase deficiency (dominican republic)

testosterone (enzyme 5 alpha reductase) 5 alpha dihydrotestosterone

XY men have external female genitalia and internal testis (as children), testes will eventually drops

can also be caused by a lack of androgen receptor

Testicular feminization

Gene defect in Women

Congenital Adrenal Hyperplasia

ACTH stimulates adrenal to produce cortisol but lack of enzyme for conversion of progesterone to cortisol increases high concentrations of testosterone causing masculinization

Exceptions to the rules

Three mammals where sex differentiation is unconventional and appears to be different from other mammals

-Spotted Hyenas

-Elephants

-Tammar Wallabies

Spotted Hyenas

reproductive tract is external (clitoris of the female looks more like glans penis), no external vagina

Elephant

layout of female repro tract,  and orientation of male tract

female orientation looks more like male orientation

Tamir Wallabees

5 days before birth (day 22) STILL INDIFFERENT gonadal ridge

Day 9 postpartuition can see sex differentiation between scrotum and mammary gland pouch

-both have genital tubercle

(as a marsupial)