LEC 17 - Structure and Function of the Kidney

Kidney functions

Regulates blood volume, removes wastes, controls electrolytes and pH, and releases erythropoietin.

Erythropoietin (EPO)

Hormone released by kidneys that stimulates red blood cell production.

Urinary system pathway

Kidneys → ureters → urinary bladder → urethra → outside of body.

Ureter

Tube that carries urine from kidneys to bladder.

Urinary bladder

Stores urine before elimination.

Urethra

Tube that carries urine out of the body.

Peristalsis

Rhythmic muscle contractions that move urine through the ureters.

Renal cortex

Outer region of the kidney containing many nephron structures.

Renal medulla

Inner kidney region where urine concentration occurs.

Renal pyramids

Structures in the medulla that contain collecting ducts and drain urine.

Renal pelvis

Area that collects urine before it enters the ureter.

Kidney stones

Crystals of minerals/waste that form in kidneys and may block urine flow.

Kidney stone risk factor

Dehydration increases risk because urine becomes more concentrated.

Micturition

Urination; emptying the bladder.

Detrusor muscle

Smooth muscle of the bladder that contracts to push urine out.

Internal urethral sphincter

Smooth muscle that automatically controls urine release.

External urethral sphincter

Skeletal muscle that allows voluntary control of urination.

Guarding reflex

Prevents involuntary bladder emptying.

Voiding reflex

Reflex that causes bladder contraction when full.

Stretch receptors

Detect bladder filling and send signals to the spinal cord.

Nephron

Functional unit of the kidney that produces urine.

Nephron function

Filters blood, reabsorbs needed substances, and removes wastes.

Renal corpuscle

Filtration area made of glomerulus and Bowman’s capsule.

Glomerulus

Capillary network where blood filtration begins.

Bowman’s capsule

Collects filtrate from the glomerulus.

Renal artery

Carries blood into the kidney.

Afferent arteriole

Carries blood into the glomerulus.

Efferent arteriole

Carries blood away from the glomerulus.

Peritubular capillaries

Receive substances reabsorbed from nephron tubules.

Renal vein

Carries filtered blood away from the kidney.

Juxtamedullary nephron

Nephron specialized for producing concentrated urine.

Cortical nephron

Nephron located mostly in the kidney cortex.

Glomerular filtration

Process where water and small molecules move from blood into Bowman’s capsule.

Filtrate

Fluid that enters the nephron after filtration.

Filtration barrier

Allows small molecules through but blocks blood cells and large proteins.

Fenestrated capillaries

Capillaries with pores allowing water and small solutes to pass.

Podocytes

Cells forming filtration slits that help prevent protein loss.

Proteinuria

Protein found in urine due to filtration barrier damage.

GFR (glomerular filtration rate)

Amount of filtrate produced by kidneys per minute.

Normal GFR

About 115–125 mL/min.

High GFR

Usually caused by increased filtration pressure.

Low GFR

May indicate reduced kidney function.

Net filtration pressure

Pressure that pushes fluid from blood into Bowman’s capsule.

Afferent arteriole dilation

Increases blood entering glomerulus and increases GFR.

Afferent arteriole constriction

Decreases blood entering glomerulus and decreases GFR.

Sympathetic effect on kidney

During stress, decreases kidney blood flow and urine formation.

Renal autoregulation

Kidney ability to maintain stable GFR despite blood pressure changes.

Myogenic mechanism

Arteriole smooth muscle responds to blood pressure changes to control GFR.

Tubuloglomerular feedback

Macula densa adjusts GFR by sensing sodium and water levels.

Macula densa

Cells in the distal tubule that detect NaCl levels.