Download Kidney

Excretion
• Purpose: - Maintain Homeostasis
– Keeping the “status quo” externally and internally
• Function: Rids body of metabolic wastes
– Salts, Carbon Dioxide, Urea
• Excretory Organs
– Skin – water and salts
– Lungs – CO2
– Kidneys and associated organs - Urea
The Excretory System ((Liquid/salts)
• Kidneys (2, lower back)
– Filtration system  urine
• Ureters
– Tubes carrying urine from kidneys to bladder
• Urinary bladder
– Saclike organ where urine is stored
• Urethra
– Tubes from which urine is released from the body
Excretory System
Vein
Kidney (Cross Section)
Cortex
Medulla
Kidney
Ureter
Urinary bladder
Urethra
Artery
Kidney
Nephron
Bowman’s
capsule
Cortex
Capillaries
Glomerulus
Medulla
Renal artery
Renal vein
Ureter
Collecting
duct
Vein
To the bladder
Artery
Loop of Henle
To the ureter
Structure of Kidney
• Renal Cortex
– outer portion
• Renal Medulla
– Inner portion (loop of Henley)
• Nephrons
– Straddle the cortex and medulla
– Functional unit of kidneys; filters blood
• Flow
– Blood enters arteriole  capillaries (filtration) 
waste products accumulate in collecting duct 
Duct joins ureter
Function of Kidney
• Purification of blood
• Three processes:
– Filtration,
– Reabsorption
– Secretion
Filtration
Most filtration occurs in
the glomerulus. Blood
pressure forces water,
salt, glucose, amino
acids, and urea into
Bowman’s capsule.
Proteins and blood
cells are too large to
cross the membrane;
they remain in the
blood. The fluid that
enters the renal tubules
is called the filtrate.
Reabsorption
As the filtrate flows
through the renal
tubule, most of the
water and nutrients
are reabsorbed into
the blood. The
concentrated fluid that
remains is called
urine.
Secretion
Substances such as
hydrogen ions are
transferred from the
blood to the filtrate.
Nephron
• Bowman’s capsule
– Found in Cortex
– Contains glomerulus (capillary bed) and collecting
duct
– Filters the blood (extracts waste products)
• Renal tubes
– Reabsorb essential nutrients (glucose and aa)
– Secrete H+
• Loop of Henle
– Found in medulla
– Water conservation (reabsorb)
Result:
• Purified blood returned to circulatory
system
• Urine is collected in the bladder
– Released through the urethra
Kidneys
• Regulate water and waste content of blood
– Blood volume, pH, waste products
– Really controlled by blood levels
• What happens when you drink more
water?
• What happens if you eat salty food?
Dialysis
• Artificial cleansing of the blood