Urogenital system

The urogenital system can be divided into

two entirely different components: the

urinary system and the genital system.

Two embryonic structures that play an

important role in the development of the

urogenital system are the intermediate

mesoderm and the cloaca.

We know that the mesoderm( or intra-

embryonic mesoderm is subdivided into:

(a) paraxial mesoderm

(b) an intermediate mesoderm;

(c) lateral mesoderm

The development of Urinary System

KIDNEY SYSTEMS

Kidney has passed three stages of evolution in a cranial to caudal sequence.

Pronephros

mesonephros

metanephros.

Pronephros

At the beginning of the fourth week, the pronephros is represented by 7 to 10 solid cell groups in the cervical region of nephrogenic cord.

These groups form vestigial excretory units, which are made up of pronephric tubules and a single desending pronephric duct. The human pronephros have no-function and disappear by the end of the fourth week.

But pronephric duct ending in the cloaca, however, persists. Then it become to mesonephric ducts after development of mesonephros.

• The mesonephros consist of a series of

excretory tubules that develop in the

thoracolumlar region. These tubules

(mesonephric tubules ) drain into the

nephric duct which may now are called the

mesonepheric duct.

Mesonephros

Mesonephros

mesonephric tubules( S-shaped )-Bowman’s C+Cap

mesonepheric duct

Cloaca

In the middle of the second month the

mesonephros forms a large ovoid organ on

each side of the midline. Since the

developing gonad is on its medial side, the

ridge formed by both organs is known as

the urogenital ridge.

the urogenital ridge

• Most of the mesonepheric tubules

disappear, but most part of them are

modified and take part in forming the duct

system of the testis. but they disappear in

the female.

• The metanephros, or permanent kidney,

appears in the fifth week. It arises from two

distinct sources. the metanephric blastema

and the ureteric bud

Metanephros

• The excretory dubules (or nephrons ) are

derived from the lower part of the

nephrogenic cord.This part is the

metanephros, the cells of which form the

metanephric blastema.

• The collecting part of the kidney is

derived from a diverticulum called the

ureteric bud which arises from the

lower part of the mesonephric duct

where it close to its entrance to the

cloaca.

The bud penetrates the metanephric tissue,

which cover the distal end of the bud as a

cap. Subsequently the bud grows and dilates

to form ampulla.The ampulla divides

repeatdly. The first three to five generations

of branches fuse to from the pelvis of the

kidney.the next divisions become the major

calyces while further divisions form the

minor calyces and collecting tubules.

The ureteric bud gives rise to the ureter, the

renal pelvis, the major and minor calyces,

and approximately 1 million to 3 million

collecting tubules.

Each newly formed collecting tubule is

covered at its distal end by a metanephric

tissue cap. Under the inductive influence of

the tubule, cells of the tissue cap form the

nephron.

• A solid clump of cells is converted into a

vesicle which soon becomes pear shaped

and opens into the ampulla. The visicle now

becomes an S-shapd tube. Its distal end

comes to be invaginated by a tuft of

capillaries which form a glomerulus.The

various parts of the nephron are derived

from this S-shaped tube.

• Capillaries grow into the pocket at one end

of the S and differentiate into glomeruli.

These tubules, together with their

glomeruli, form nephrons, or excretory

units.

Back to 58

• POSITION OF THE KIDNEY

The kidney, initially in the pelvic region,

later shifts to a more cranial position in the

abdomen. This ascent of the kidney is

caused by diminution of body curvature and

by growth of the body in the lumbar and

sacral regions.

• BLADDER AND URETHRA

Urinary bladder and urether are derived from the cloaca.

cloaca urorectal septum

urogenital sinus

Primitive rectum

•Between the two, the tip of the urorectal septum forms the perineal body.

Cloacal

Membrane

urorectal septum

urogenital membrane

anal membrane

The Vessico urethral canal

The phallic part

urinary bladder

The pelvic part

Derivatives of two parts of Primitive urogenital sinus

Primitive urethra

Definitive UGS

The prostatic and membranous parts of the urethra in male

Urethra in female

The phallic part

urinary bladder

The pelvic part

Derivatives of two parts of Primitive urogenital sinus

Penile urthra in male

Vestibule in female

Primitive urethra

urinary bladder

The upper and largest part is the urinary

bladder.Initially the bladder is continuous

with the allantois, but when the lumen of

the allantois is obliterated, a thick fibrous

cord, the urachus, remains and

connects the apex of the bladder with the

umbilicus. In the adult, it is known as the

median umbilical ligament.

During differentiation of the cloaca, the caudal portions of the mesonephric

ducts are absorbed into the wall of the urinary bladder. Consequently, the ureters, initially outgrowths from the mesonephric ducts, enter the bladder separately.

As a result of ascent of the kidneys, the

orifices of the ureters move farther

cranially; those of the mesonephric ducts

move close together to enter the prostatic

urethra and in the male become the

ejaculatory ducts.

• Anomalies of kidneys: 1. Agenesis

2. Duplication:

3. Anomalies of shape:Horseshoe kidney

4. Abnormal of position:

5. Congenital polycystic kindney:

• Congenital polycystic kindney:

• Failure of the excretory tubules of the

metanephros to establish contact with the

collecting tubules, leads to the formation of

cysts. Isolated cysts are commonly seen,but

sometimes the whole kidney is a mass of

such cysts.The cysts press upon normal

renal tissue and destroy it.

Back to 57

Back to 57