Kidney Physiology

What structures make up the urinary system?

Kidneys, ureters, bladder, urethra

How much blood do the kidneys filter per minute?

1.2 L/min

Where are the kidneys located?

Retroperitoneal, protected by ribs T12–L3

What is the hilum of the kidney?

Entry/exit point for blood vessels, nerves, and ureter

What are the main regions of the kidney?

Cortex (outer), medulla (inner), pyramids, calyces

What is the functional unit of the kidney?

The nephron

What are the main parts of a nephron?

: Glomerulus, proximal/distal convoluted tubules, loop of Henle, collecting duct

What is the function of the nephron?

Refines filtrate to maintain fluid and electrolyte balance

What is glomerular filtration?

Blood is filtered across glomerular capillaries into Bowman’s capsule

What is the ultrafiltrate?

Plasma-like fluid without proteins or cells

What restricts filtration at the glomerulus?

Filtration barrier: fenestrated endothelium, basement membrane, podocytes

What are podocytes?

Epithelial cells with foot processes that form filtration slits

What type of molecules are restricted from filtration?

Large (>3.6 nm) and negatively charged molecules (e.g., albumin)

What condition results from loss of barrier charge?

Proteinuria

What is GFR in a healthy adult?

~125 ml/min or ~180 L/day

What percentage of plasma entering the kidneys is filtered?

~20%

What happens to the rest of the fluid?

~99% is reabsorbed; <1% excreted

What pressures influence GFR?

• Hydrostatic pressure (glomerular & Bowman’s capsule)

• Colloid osmotic pressure

• Hydrostatic fluid pressure (resists filtration)

What is net filtration pressure like?

Quite low, but tightly regulated

What controls GFR?

• Net filtration pressure

• Renal blood flow & pressure

• Filtration coefficient

What can alter GFR?

Changes in afferent/efferent arteriole diameter or podocyte surface area

What makes up the filtration barrier?

• Fenestrated endothelium

• Basement membrane

• Podocyte foot processes (pedicels)