Human Anatomy, 3rd editionPrentice Hall, © 2001

Human AnatomyChapter 26

The Urinary System

Human Anatomy, 3rd editionPrentice Hall, © 2001

Introduction– Cellular metabolism produces wastes

• CO2

• Urea

• Ammonia

– Kidneys rid the body of most nitrogenous wastes

– Kidneys regulate the chemical make-up of blood

Human Anatomy, 3rd editionPrentice Hall, © 2001

General Functions– Serves as a blood filter– Toxins, metabolic wastes leave the body in

urine

– H2O, glucose, and amino acids are returned to blood

Human Anatomy, 3rd editionPrentice Hall, © 2001

Organs of the Urinary System– Kidneys (paired)

• Perform filtering functions and manufacture urine

– Ureters (paired)• Transport urine

– Urinary bladder (single)• Stores urine

– Urethra (single)• Transports urine

Human Anatomy, 3rd editionPrentice Hall, © 2001

The Urinary System

Human Anatomy, 3rd editionPrentice Hall, © 2001

Location of Kidneys– Lie against the dorsal body wall– Beneath the parietal peritoneum– In the superior lumbar region

• Protected by the lower part of the rib cage

Human Anatomy, 3rd editionPrentice Hall, © 2001

Location of the Kidneys

Human Anatomy, 3rd editionPrentice Hall, © 2001

External Structure of the Kidney– Hilus– Renal capsule– Renal artery– Renal vein– Ureter

Human Anatomy, 3rd editionPrentice Hall, © 2001

Internal Structure of the Kidney– Renal cortex– Renal medulla

• Renal pyramids

• Renal papilla

– Renal pelvis– Calyces

Human Anatomy, 3rd editionPrentice Hall, © 2001

Structure of the Kidney

Human Anatomy, 3rd editionPrentice Hall, © 2001

Blood Supply of the Kidney– Approximately ¼ of the total blood supply of

the body passes through the kidneys each minute

– Renal artery branches inside the kidney• Supplies the pyramids and the cortex

– Venous blood leaves the cortex and medulla• Small veins join the renal vein

Human Anatomy, 3rd editionPrentice Hall, © 2001

Blood Supply of the Kidney

Human Anatomy, 3rd editionPrentice Hall, © 2001

Blood Supply of the Kidney

Human Anatomy, 3rd editionPrentice Hall, © 2001

Nephrons and Urine Formation– Nephrons form the urine product

• Filtration

• Reabsorption

• Secretion

– Each kidney contains about 1 million nephrons

Human Anatomy, 3rd editionPrentice Hall, © 2001

Structure of a Nephron– 2 main structures

• Glomerulus – a knot of capillaries

• Renal tubule– Bowman’s capsule surrounds the glomerulus

– Proximal convoluted tubule

– Henle’s Loop

– Distal convoluted tubule

– Renal tubule enters collecting duct• Receives urine from nephrons

• Delivers final urine product into the calyces

Human Anatomy, 3rd editionPrentice Hall, © 2001

A Renal Corpuscle

Human Anatomy, 3rd editionPrentice Hall, © 2001

Renal Corpuscles

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A Typical Nephron

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A Typical Nephron

Human Anatomy, 3rd editionPrentice Hall, © 2001

Blood Supply of the Nephron

Human Anatomy, 3rd editionPrentice Hall, © 2001

Urine Formation– Filtration

• Blood in afferent arteriole is under high pressure• Glomerulus acts as a filter• Filtrate = the substance that is filtered from the blood into the

renal tubule• Blood leaves the glomerulus through the efferent arteriole

– Reabsorption• Filtrate contains useful substances (as well as wastes) which

are returned to the blood• Most depends on active transport

– Transported into peritubular capillaries– Most occurs in the proximal convoluted tubule

– Secretion• Substances move from cells or blood (peritubular capillaries)

into the filtrate• Important in controlling pH of blood

Human Anatomy, 3rd editionPrentice Hall, © 2001

Control of Blood Composition

– Excretion of nitrogen-containing compounds• Urea

• Uric acid

– Water and electrolyte balance• Regulated by hormones

Human Anatomy, 3rd editionPrentice Hall, © 2001

Summary of Urine Flow– Kidneys produce urine

• Filtration

• Reabsorption

• Secretion

– Ureters– Bladder– Urethra