1. the intermediate mesoderm

2. mesothelium lining of the abdominal cavity

3. endoderm of urogenital sinus

1. Nephrogenic cord or ridge

2. gonadal or genital ridge

Pronephroi

1. Transitory,nonfunctional structures appear in human embryos in 4th week

2. Represented by a few cells clusters and tubular structures in neck region.

3. Pronephric ducts run caudally and open in cloaca.

4. The pronephroi will soon degenerate but most of the ducts persist and are utilized by the next set of kidneys.

Mesenophroi

1. Appear late in the 4th week and are located caudal to the pronephroi

2. Function as interim kidneys until permanent kidneys form.

3. They degenerate towards the end of the 1st trimester but function unitl the permanent kidneys develop

4. Degenerates end of 1st trimester but tubules become the efferent ductules of testes

5. Mesonphric ducts have serveral adult derivatives in male (Wolffian duct)

1. Glomeruli and mesonephric tubules

2. Tubules open into mesonephric ducts( originally pronephric duct)

Metanephroi- begins to develop early in th 5th week and start to function about 4 weeks later and continue to function throughout fetal life

1.They are funtional by week 11-13 and excrete urine in the amiontic fluid. 

2. This excretion continues during the fetal life  and the fetus swallows this urine mixed in the amniotic fluid. It is then absorbed in the stomach and duodenum to the blood for transport to the placenta and disposal.

1. Mesodermally from the metanephric diverticulum or uretic bud

a. Its stalk gives rise to the ureter

b.Its cranial end to the renal pelvis and collecting duct system

c. The ureteric bud elongates and branches (up to 14 or 15 times)

2. Metanephric mass or cap (metaphric blastema)

a. The metanephric cap gives rise to the primitve S-shaped renal tubules which are critical to nephron formation

b. The S-shaped renal tubules differentiated into the connecting tubule, distal convuluted tubule, loop of henle,proximal convoluted tubule, and Bowman's capsule.

c. Tufts of capillaries protrude into Bowman's capsule.

d. Nephron formation is complete at birth but functionall maturation of nephrons continues throughout infancy.

1. its first 4 generations of tubules enlarge and become confluent to form major cavities

2. its second 4 generations coalesce to form to minor calyxes

3. the remaining generations of tubules form the collecting ducts

The metanephric diverticulum or ureteric bud penetrates the metanephric mesoderm in the caudal part of the nephrogenic cord and stimulates the its formation

(Metanephric blastema)

(mestanephrenic vesicles)

1. nephron- metanephric mass of intermediate mesoderm

2. collecting system-metanephric diverticulum

1. Intially the metanephric kidneys lie close to each other in pelvis ventral to sacrum.

2. As abdomen and pelvis grows, the kidneys gradually come to lie in abdomen and move farther apart

3. When kidneys come in contact with suprarenal gland (adrenal gland), in the 9th week, the asent stops.

4. Eventually they are retroperitoneal in the posterior abdominal wall.

5. Intially hilum faces ventrally but as kidneys asends, it rotates medially almost 90 degress

6. by 9th week the hilum is anteromedial

1. As the kidneys ascend from the pelvis , they recieve their blood supply from vessels that are close to them.

2. Intially  the renal arteries are branches of the common iliac arteries.

3.Asend- recieve blood supply from the distal end of aorta

4. When they reach a higher level, they recieve new branches from aorta.

5. Normally the caudal branches undergo involution and disappear.

6. The kidneys recieve their most cranial arterial branched from the abdominal aorta. These branches become permanent renal arteries

urorectal septum

Dorsal rectum and ventral urogenital sinus

1 Cranial vesicle part that forms most of the bladder and is continous with the allantois

2 Middle vesicle part that become the urethra in bladder neck and prostatic part of the urethra in males and entire urethra in females

3 Caudal phallic part that grows toward genital tubercle

Urogenital sinus (endoderm)

the surrounding splanchnic mesenchyme (mesoderm)

allantois

1. The allantois constricts to become the urachus

2. Adults -median umbilical ligament