Mahatma Jyotiba Fule College of Veterinary Science and

Animal Husbandry, Chomu (RAJ.)

PRESENTED BY:

Dr. Lakshmi kant

2019-2020

Assistant professor

DEPARTMENT OF VETERINARY ANATOMY AND HISTOLOGYCOLLEGE OF VETERINARY SCIENCE & ANIMAL HUSBANDRY, CHOMU

(RAJ.)

Development of Reproductive

System

ORGANOGENESIS

Development of Reproductive System

• Urinary and genital systems are closely associated.

• Both develop from inter-mediate mesoderm.

• At first a bulging appears on the abdominal wall atthe lateral aspect of dorsal mesentery of the gutwhich extends from cervical region to sacral regionof the embryo.

• These linear bulging on either side are called the uro-genital ridge.

• This uro-genital ridge is divided in to two parts-

• The medial part is genital ridge and it develops the gonads.

• The lateral part is nephrogenic ridge it develops the urinarysystem.

Development of gonads

(testes and ovaries)

The gonads develops

from

• The celomic epithelium

(mesodermal

epithelium) lining the

posterior abdominal

wall.

• The underlying

mesenchyme

(embryonic connective

tissue).

• The primordial germ

cells.

Indifferent gonads

• During the 5th week a

thickened area of

mesothelium

develops on the

medial side of the

mesonephros: a pair

of gonadal (genital)

ridges.

• Finger-like epithelial

cords (gonadal

cords) grow into the

underlying

mesenchyme.

• The indifferent gonad

now consists of an

external cortex and an

internal medulla.

• If the embryo is XX:

cortex will differentiate

into an ovary, medulla

regress

• If the embryo is XY

medulla differentiates

into a testis, cortex

regress except for

vestigial remnants.

Primordial germ cells

• Large spherical sex cells

are visible early in the 4th

week among the endodermal

cells of the dorsal wall of

hind gut near the origin of

the allantois.

• Thus the primordial germ

cells migrate along the dorsal

mesentery of the hindgut to

the gonadal ridges.

• During 6th week primordial

germ cells enter the

underlying mesenchyme and

are incorporated in the

gonadal cords.

Sex determination

• Chromosomal and genetic sex is established at

fertilization.

• The type of gonads that develop is determined by

the sex chromosome complex of the embryo (XX

or XY).

• Before 7th week gonads of both sexes are

identical (indifferent gonads).

• Male phenotype requires Y chromosome (SRY-

sex determining region on Y gene) for a testis

determining factor-TDF.

• Female phenotype requires two X chromosomes.

• The testis determining effect of Y chromosomedifferentiate the cords of medulla of indifferentgonads into primordia of seminiferous tubules andregression of cortex.

• Absence of a Y chromosome (XX sex chrom) resultsin the formation of the ovary by the cortex andmedulla will regress.

• Types of present gonads determines the type of sexualdifferentiation of the genital ducts and externalgenitalia.

• In male embryo testosterone produced by the fetaltestes determines maleness.

• In female embryo primary sexual differentiation doesnot depend on hormones; it occurs even if the ovariesare absent (depending possibly on an autosomalgene).

Development of testes

• TDF induces the gonadal cords (seminiferous cords)

to condense and extend into the medulla of the

indifferent gonad; where they branch and

anastamose to form the rete testis.

• A dense layer of fibrous CT (tunica albuginea)

separates the testis cords from the surface epithelium

• In the 4th month testis cords become horse-shoe

shaped; their extremities are continous with those

of the rete testis.

• Sertoli derived from the surface epithelium of the

gland.

Development of testes

• Interstitial cells of Leydig

derived from the original

mesenchyme of the gonadal

ridge begin development

shortly after onset of

differention of these cords.

• Leydig cells lie between the

testis cords and begin

testosterone production by 8th

week of gestation.

• Now the testis is able to

influence sexual differentiation

of the genital ducts and external

genitalia.

Development of testes

• Testis cords remain soliduntill puberty; when they arecanalyzed formingseminiferous tubules.

• Now they join rete testistubules, which in turn enterthe ductuli efferentes whichare the remaining parts ofthe excretory tubules of themesonephric system.

• They link the rete testis andthe mesonephric or wolffianduct which becomes ductusdefferens.

• In female gonadal development occurs

slowly.

• In XX embryo primitive sex cords

dissociate into irregular cell clusters

containing groups of primitive germ cells

in the medullary part of ovary.

• Later they disappear and are replaced by a

vascular stroma thet forms the ovarian

medulla.

Development of ovaries

• Surface epithelium of

the female gonad

(unlike that of the

male) continues to

proliferate giving rise

to a second generation

of cords (cortical

cords) in the 7th week.

• Cortical cords penetrate

the underlying

mesenchyme but

remain close to the

surface.

• In the 4th month

cortical cords split into

isolated cell clusters

with each surrounding

one or more primitive

germ cells.

• Germ cells develop into

oogonia, surrounding

epithelial cells,

descendants of the

surface epithelium form

follicular cells.

Genital duct development in male

• Mesonephros regress; a few excretory tubules (epigenital

tubules) establish contact with cords of the rete testis and

finally form efferent ductules of the testis.

• Excretory tubules along the caudal pole of the testis

(paragenital tubules) do not join the cords of the rete testis;

their vestiges are named paradidymis.

• Mesonephric ducts persist and form the main genital

ducts except for the most cranial portion (appendix

epididymis).

• İmmediately below the entrance of the efferent

ductules, mesonephric duct elongate and become

highly convoluted forming the ductus epididymis.

• Mesonephric ducts obtain a thick muscular coat and

form ductus deferens (from the tail of the

epididymis to the outbudding of the seminal vesicle).

• The region of the ducts beyond the seminal vesicles

is the ejaculatorius duct.

Development of male genital glands• A lateral outgrowth from the

caudal end of each mesonephric

duct gives rise to seminal

vesicle/gland.

• Multiple endodermal outgrowths

arising from the prostatic part of

urethra grow into the surrounding

mesenchyme and differentiate

into prostate glandular

epithelium; mesenchyme

differntiate into prostatic stroma.

• Bulbourethral glands develop

from paired outhgrowths from the

spongy part of urethra.

Genital duct development in female

• Paramesonephric ducts

(Mularian Duct) develops into

the main genital ducts -

• Initially 3 parts can be

recognized in each duct:

Cranial vertical portion that

opens into the abdominal cavity

develops into uterine tube.

Horizontal part that crosses

the mesonephric duct develops

into uterine horn.

Caudal vertical part that fuses

with its partner from the

opposite side fuse to form

uterine canal.

Genital duct development in female

• Second part of the paramesonephric ducts move medio-

caudally; urogenital ridges gradually come to lie in a

transvers plane.

• The ducts fuse in the midline; a broad transverse pelvic

fold (broad ligament of uterus) is established.

• The uterine tube lies in its upper border and the ovary lies

on its posterior surface.

• Uterus and broad ligament divide the pelvic cavity into

rectal genital pouch and the vesico-genital pouch.

• Fused paramesonephric ducts differentiate into body and

cervix of the uterus.

• They are surrounded by a layer of mesenchyme that forms

the myometrium and the perimetrium.

Genital duct development in female

Development of vagina

• The solid tip of the

paramesonephric ducts reaches

the urogenital sinus; two solid

evaginations (sinovaginal

bulbs) grow out from the pelvic

part of the sinus.

• Sinovaginal bulbs proliferate

and form a solid vaginal plate.

• Proliferation continues at the

cranial end of the plate;

increasing the distance between

the uterus and the urogenital

sinus.

• By the 5th month vaginal

outgrowth is entirely

canalized. Vaginal fornices

(wing-like expansions of the

vagina around the end of

uterus) are of para-

mesonephric origin.

• So the vagina has two origines:

–upper portion derived from the

uterine canal.

–lower portion derived from the

urogenital sinus.

• Lumen of the vagina remains

separated from that of the

urogenital sinus by a thin tissue

plate; the hymen.

• Hymen consists of epithelial

lining of the sinus and a thin layer

of vaginal cells. It usualy

develops an opening during

perinatal life.

Remnants of the ducts in female

• Mesonephric duct disappear except for a small a

small caudal portion in the wall of uterus or

vagina it is known as Gartner’s canal.