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21 Cards in this Set

  • Front
  • Back

Three pairs of kidneys develop in human embryos:

1. The pronephroi (never function)

2. The mesonephroi (well developed, function briefly)

3. The metanephroi (permanent kidneys)

The pronephroi (never function) :

- appear early in 4th week

Represented by cell clusters in neck region Pronephric ducts run caudally into the cloaca (superior/ventral part of cloaca contributes to the bladder)

degenerate leaving pronephric ducts thatserve the next set of kidneys

The second pair of kidneys, the mesonephroi, developcaudal to the pronephroi in the fifth week and functionuntil about the 12th week


- is well developedand functions briefly during the early period.

- Large, elongated excretory organsappear late in the fourth week, caudal to the pronephoi. Consists of 40glomeruli with mesonephric tubules that open into the mesonephric ducts openingto cloaca. - It create urine in week 6 to 10until permanent kidneys function start.

- generates end of 3 months, theirtubules become the efferent ductules of the testes.

Metanephroi (primordium of permanent kidneys)

- begin to develop early week 5

- These final kidney organs actually begins development in the pelvic bowl as a diverticulum off the mesonephric duct called the ureteric bud- When degenerate, they also leave behind their tubules that become the male testicular efferent ductules

- The ureteric bud (one each side of cloaca) give rise to the ureter, the renal pelvis with all its calices and collecting tubules

- As the ureteric bud grows it penetrates a mass of cells (metanephrogenic blastema) developed from the nephrogenic cord and induces these cells to form the nephrons

· Permanentkidneys develop from two sources:

- uteric bud

- metanephrogenic blastemal

Give the definition of the uteric bud:

- diverticulum near the entrance into the cloaca. The primordium of the ureter, renal pelvis, calices and collecting tubules.

Give the definition of metanephrogenic blastemal

mass of cells derived from the nephrogenic cord that forms the nephrons.

Brieflydescribe the process of formation of the final (metanephric) kidneys:

1. The stalk of the ureteric budbecomes the ureter, and the cranial part of the diverticulum undergoesrepetitive branching.

2. Branches differentiate into thecollecting tubules of the metanephros.

3. The straight collecting tubulesundergo repeated branching, forming successive generations of collectingtubules.

4. 1st generations oftubules: major galices.

5. 2nd generations oftubules: minor galices.

6. End of each arched collectingtubule induce clusters in mesenchymal cells in the metaphrogenic blasterma toform small metanephric vesicles that are invaginated by glomureli.

7. The renal corpsuscle and itsproximal convoluted tubule, the nephron loop and the distal convoluted tubuleconstitute a nephron.

8. The collecting tubules becomeconfluent, forming a uriniferous tubule.

9. Branching the metanephricdiverticulum depends on an inductive signal from the metanephric mesoderm.

10. The fetal kidneys are subdividedinto lobes. Dissappears during infancy as nephrons increase in size.eat

Briefly describe the changes in kidney position:

- Developing metanephric kidneys lieclose to each other in the pelvis.

- As the pelvis and abdomen grow, thekidney relocate to the abdomen and move farther apart.

- Attain their vertebral position oneither side of the vertebral column by the ninth week.

- Associated with growth of theembryo body caudal to the kidney.

- 9th week, kidney come incontact with the suprarenal glands.

Explain the changes in blood supply of kidneys:

- Renal arteries are branches of thecommon iliac arteries.

- Kidneys receive blood from the distalend of the aorta.

- Most of cranial branches: renalarteries from abdominal aorta..&w

The cloaca becomes divided:

the urorectal septum into

Dorsal rectum

Ventral urogenital sinus

Note: Urogenital sinus forms bladder, urethra, penis or clitoris

Give the position, its epithelium origin, wall layer of the bladder within the embryo:

is continuous with allantois (an outpouching ofumbilical vesicle growing into connecting stalk and involved in earlyblood formation)

Allantois constricts to form the urachus or median umbilical ligamentof the bladder (distinct from the medial umbilical ligaments of thebladder that are derived from the umbilical arteries)

Epithelium derived from endoderm of urogenital sinus

Outer layers of the wall form from splanchnic mesenchyme

The trigone is from residual mesonephric duct tissue

Explain the bladder development:

- Cloaca divided by a septuminto urogenital sinus andrectum

• Absorption of mesonephricducts contributes to trigone

• Development of urogenitalsinus into urinary bladder,urethra (allantois becomesurachus, a fibrous cord)

• Changes in location andelongation of ureters

What are the three sources of the gonads (testes and ovaries) ?

mesothelium (mesodermal epithelium) lining the posteriorabdominal wall

underlying mesenchyme

primordial germ cells

Germ cells

originate from wall of umbilical vesicle

migrate into gonadal cords via dorsal mesentery

Differentiate into oocytes or sperm

How do theindifferent gonads develop?

develop during week 5

form from gonadal ridges that produce finger-likegonadal cords that grow into underlying mesenchyme

consist of external cortex and inner medulla In females (XX) cortex differentiates into ovary andmedulla region regresses

In males (XY) medulla differentiates into testis andcortex regresses

External Genitalia:

Distinguishable in the 12th week, yet first begins in thefourth week in both sexes with an external genitalswelling (genital tubercle)

On each side of the cloacal membrane, labioscrotalswellings and urogenital folds form, which then developinto sexual characteristics

In the 6th week the cloacal membrane divides into aventral urogenital membrane and dorsal analmembrane

How are the inguinal canals developped?

 develop during the indifferentphase, yet are there for the purpose of guidingthe descent of the testes

 There are two rings: a deep inguinal ring and asuperficial inguinal ring

 A ligament (the gubernaculum) forms obliquelyfrom the gonad to the anterior body wall, overthe pubis and down to the labioscrotalswellings

- Invagination along gubernaculum ligament route creates theinguinal canal, pulling the abdominal wall tissues along with it


During descent, fascial extensions of the abdominal wall ensheath the testes:

What are the fascial extensions?

1.- Transversalis fascia = internal spermatic fascia

2.- Internal oblique muscle and fascia = cremasteric

3. muscle and fascia

4.- External oblique fascia = external spermatic fascia

Which structures passes through the inguinal canal in females?

- the round ligament of the uterus + the ilioinguinal nerve.

Which structures passes through the inguinal canal in males?

- the spermatic cord and its coverings + the ilioinguinal nerve.