The Urinary System
Chapter 15
Human Anatomy, 3rd edition
Prentice 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 edition
Prentice 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 edition
Prentice 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 edition
Prentice Hall, © 2001
The Urinary System
Human Anatomy, 3rd edition
Prentice 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 edition
Prentice Hall, © 2001
The Urinary System
Human Anatomy, 3rd edition
Prentice Hall, © 2001
External Structure of the Kidney
– Renal capsule
• Connective tissue
– Renal artery
• Blood (oxygenated) to the kidney
– Renal vein
• Receives blood from kidney
– Ureter
• Drains urine
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Internal Structure of the Kidney
– Renal cortex
– Renal medulla
• Renal pyramids
– Renal pelvis
• Continuous with ureter
– Calyces
• Extensions of the pelvis
• Function – collect urine
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Structure of the Kidney
Human Anatomy, 3rd edition
Prentice 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 edition
Prentice Hall, © 2001
Blood Supply of the Kidney
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Nephrons and Urine Formation
– Nephrons form the urine product
• Filtration
• Reabsorption
• Secretion
– Each kidney contains about 1 million nephrons
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Structure of a Nephron
– 2 main structures
• Glomerulus – a knot of capillaries
• Renal tubule (about 2 inches long)
–
–
–
–
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 edition
Prentice Hall, © 2001
A Typical Nephron
Human Anatomy, 3rd edition
Prentice Hall, © 2001
A Typical Nephron
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Renal Corpuscles
Human Anatomy, 3rd edition
Prentice Hall, © 2001
A Renal Corpuscle
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Blood Supply of the Nephron
Human Anatomy, 3rd edition
Prentice 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 which are returned to the
blood
• Most occurs in the proximal convoluted tubules
– Secretion
• Substances move from blood (capillaries) into the filtrate
• Important in controlling pH of blood
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Control of Blood Composition by Kidneys
– Excretion of nitrogen-containing compounds
• Urea
• Uric acid
– Water and electrolyte balance
• Regulated by hormones
– ADH – increases water reabsorption
– Aldosterone – increases sodium reabsorption
» Second effect of aldosterone – increase water
reabsorption.
– Acid-base balance of blood
» Blood pH must be 7.35 – 7.45 (very narrow range)
» Tubule cells secrete whatever is necessary into filtrate
» Urine pH = 4.5 – 8.0
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Summary of Urine Flow
– Kidneys produce urine
• Filtration
• Reabsorption (active transport)
• Secretion
– Ureters
– Bladder
– Urethra
Human Anatomy, 3rd edition
Prentice Hall, © 2001