Renal Anatomy Development

Question 1

Where does the urinary and reproductive system originate from?

Answer 1

• Paraxial mesoderm gives rise to somites
  -between the somites and lateral plate mesoderm lies the intermediate mesoderm
  >intermediate mesoderm gives rise to urinary and reproductive system

Question 2

What induces kidney formation?

Answer 2

-paraxial mesoderm induces kidney-forming ability of the intermediate mesoderm. This induction leads to expression of transcription factors in the intermediate mesoderm that drive nephric tubule development

Question 3

Urinary system development complexity

Answer 3

-developmental complexity of kidney and its functional efficiency is vastly increased from lower animal forms to higher animal forms

Question 4

Urinary system development

Answer 4

-develops in an organized fashion of “generations” of nephric tubules
1.Pronephros- less complex, form in cervical region
2. Mesonephros- develop in thoraco-lumbar region
3.Metanephros- most functionally capable structure; develop in sacral region
**first and second generations are relatively short lived; each replaced by the next through atrophy

Question 5

Holonephros

Answer 5

-term including pronephros, mesonephros, metanephros

Question 6

Pronephros development

Answer 6

-occurs at time of somite presence
1.Cells of intermediate mesoderm in cervical region give rise to inner visceral layer and outer parietal layer, and a nephrocele cavity between them
2.Cords of cells called nephrotomes grow out from parietal (dorsal) wall and form pronephric tubules
3. The distal end of each tubule grows and extends laterally then moves caudally to fuse with same region of growing cells of the tubule right behind it resulting in the pronephric duct
4.Pronephric duct grows toward the cloaca and becomes canalised (forms a canal or lumen)

Question 7

Pronephros glomeruli development

Answer 7

-The first glomeruli to form during development of this system starts as tufts of capillaries branching from dorsal aorta in pronephros
>the tufts push and invaginate into wall of pronephric tubule to form internal glomeruli (in higher vertebrates)
>the invaginated epithelium around the glomerulus becomes the Bowman’s capsule

Question 8

Pronephric tubule connections

Answer 8

-lumen of pronephric tubule is continuous with nephrocele which opens into coelomic cavity via nephrostome

Question 9

Function of pronephros

Answer 9

-early excretory organ
-internal glomerular filtration produces a filtrate that moves to the pronephric tubule
>water and electrolytes are re-absorbed and waste products move to pronephric duct then cloaca

Question 10

Mesonephros development

Answer 10

-occurs around the post-somite stage
1. a column of tissue called urogenital ridge grows from the proliferation of intermediate mesoderm in the thoraco-lumbar region and projects into peritoneal cavity
2. The pronephric duct in early mesonephros development still extends to the cloaca but also induces mesonephric tissue to from nephric vesicle and then mesonephric tubule
3.A peri-tubular capillary network forms around each mesonephric tubule

Question 11

Mesonephros glomerular development

Answer 11

-Glomerular tufts from dorsal aortae push into invaginating mesonephic tubule epithelia to form Bowman’s capsule but this is more intimate than pronephros, and forms the Renal corpuscle
**therefore better blood filtration system for more developed fetus

Question 12

Purpose of peri-tubular capillary network in mesonephros

Answer 12

-greater reabsorption capability of water and electrolytes

Question 13

Size difference between pronephros and mesonephros

Answer 13

-Mesonephros is larger in size and projects into abdominal cavity (obvious in pigs, less in horses, ruminants, carnivores; poorly developed in primates and rodents)
>pronephros: one tubule at level of each somite
>mesonephros: multiple mesonephric tubules at each somite

Question 14

Metanephros development

Answer 14

• occurs in the sacral region of embryo
  -Arise from:
  1.Outgrowth of mesonephric duct called ureteric bud
  2. Region of urinary ridge called metanephric mass or blastema

Question 15

Ureteric bud role in metanephros development

Answer 15

1.Dilated or widened portion of ureteric buds give rise to pelvis of kidney and undergoes branching to produce collecting ducts of kidney
2. The collecting ducts induce metanephric tissue to give rise to metanephric tubules

Question 16

Kidney arrangement in different mammals

Answer 16

-the final kidney arrangement depends on the way in which the ureteric buds develop
Eg. unilobar vs. multilobar kidneys

Question 17

Metanephric blastema or mass

Answer 17

-composed of mesenchyme and is needed for ureteric bud formation
-BUT ureteric bud is also needed for survival of metanephric mesenchyme. Without it mesenchyme dies

Question 18

Retinoic acid (RA) and Glial-derived neurotrophic factor (GDNF)

Answer 18

-secreted by mesenchyme
-participates in ureteric bud branching and kidney development
-GDNF
>one copy will result in a smaller ureteric bud and poorly developed kidney
>no copies will result in no kidney/branching

Question 19

Vascular endothelial growth factor (VEGF)

Answer 19

-secreted by podocytes which stimulate branching of the renal artery and formation of the vasculature

Question 20

Metanephros position

Answer 20

-Position of metanephros changes from pelvic to the lumbar region. The definitive kidney will then occupy a position dorsal to the degenerating mesonephros
>right kidney in domestic animals migrates more caudally (except in pigs) than left kidney

Question 21

Kidney organization

Answer 21

1.outer cortical region
2.Inner medullary regions

Question 22

Cortex components

Answer 22

-renal corpuscles
-proximal convoluted tubules
-distal convoluted tubules

Question 23

Medulla components

Answer 23

-loops of Henle
-collecting ducts

Question 24

Medullary pyramid

Answer 24

-due to the conical arrangement of the loops of Henle and collecting ducts
-the base of the pyramid covered by the cortex of the kidney and the apex is a papilla projecting into the pelvis of kidney

Question 25

Renal lobe

Answer 25

-a medullary pyramid with cortical covering
>different species might have fused pyramids

Question 26

Newer nephron vs. older nephron locations

Answer 26

-newer nephrons in cortex
-older nephrons in medulla

Question 27

Cloaca

Answer 27

-caudal end of hindgut and the allantois
-endodermally lined chamber that is closed by cloacal or anal membrane

Question 28

Partitioning of the cloaca

Answer 28

-Urorectal septum (mesodermal tissue) is found between the hindgut and the base of allantois. As development continues, the septum will grow toward cloacal membrane dividing the cloaca into the rectum with anal membrane and urogenital sinus with urogenital membrane

Question 29

Perineal body

Answer 29

-site of muscles in the pelvic floor

Question 30

Bladder development

Answer 30

-bladder develops from the pelvic region of the urogenital sinus (after cloacal partitioning), and the caudal part forms the urethra
- distal end of allantois relative to bladder forms the urachus

Question 31

Male bladder

Answer 31

-As the male bladder grows, it incorporates the terminal parts of the mesonephric and ureteric ducts. Each duct develops its own separate openings into the developing bladder
>initially, mesonephric ducts are anterior to ureteric buds but positions change and the ureteric buds open into bladder laterally and anterior to the mesonephric ducts
>results in trigone (triangular area in dorsal wall of the bladder) which marks the region of the mesonephric duct and ureteric bud incorporation

Question 32

Female Bladder