Urinary System Development

Kidneys

Filters blood and removes waste + maintain water and electrolyte balance

Ureters

Transport urine (filtered waste) out of the kidneys to bladder

Bladder

Stores urine

Urethra

Transports urine outside the body

Renal Capsule

Tough outer covering

Renal Cortex

The outer region containing most nephron structures; excludes Loop of Henle

Renal Medulla

Inner region containing loop of Henle

Calyxes

Structures that collect urine and funnel it towards ureter

Renal Lobes

Each lobe consists of renal pyramid (wedge of medulla) and its surrounding renal cortex; can have up to 18 lobes and 1.5 million nephrons (all formed before birth)

Blood supply

Kidneys receive blood from renal arteries, which branch off the abdominal aorta

Nephron

Functional unit of kidney that filters blood; located in both cortex and medulla layers

Glomerulus

Network of capillaries where blood filtration begins

Bowman’s capsule

Sac that surrounds glomerulus

System of tubules

Includes proximal convoluted tubule, loop of Henle, distal convoluted tubule and collecting tube; network of blood vessels that wrap around nephron, facilitate reabsorption of solutes back into blood

Original of Urinary System

Intermediate mesoderm

Pronephros

“Primitive homolog of kidney”: forms around day 22, degenerates cranial as mesonephric tubes are induced caudally

Mesonephros

Temporary structure before metanephros; formed of mesonephric tubules and mesonephric duct → degreases as metaneohros becomes functional

Metanephros

“Final version of kidney”; forms around day 28 when ureteric bud sprouts from caudal nephric duct near cloaca

Metanephric Mesenchyme role

Induces ureteric bud to elongate and branch

Ureteric Bud role

Form cellular aggregates; differentiate into tubules of nephron

Mesenchymal to Epithelial Transformation

Mesenchymal cells condense around tip of ureteric bud → creates renal vesicles

Cells within renal vesicles undergo MET → become podocytes of Bowman’s capsule + proximal/distal convoluted tubules and loop of Henle

Kidney Migration + Rotation

Between 6-9 weeks, kidneys migrate from pelvic to abdominal region thru cranial, dorsal and lateral migration + 90° rotation → take over production of amniotic fluid at 4 months

Minor defects

Usually asymptomatic; may be prone to kidney stones or tract infections later in life

Moderate defects

can also be asymptomatic; increased workload on functional kidney may eventually cause damage

Severe defects

Impair kidney function and lead to progressive damage, results in toxic fluid buildup and can lead to end stage renal disease and death