PY 105 Chapter Notes - Chapter 12: Nephron, Renal Vein, Renal Artery
The Excretory System Overview
• Excretion is the disposal o waste products
• Liver
o Responsible for excreting many wastes by chemically modifying them and releasing them
into bile
o Deals with hydrophobic or large waste products which cannot be filtered out by the kidneys
o Old heme units are broken down into bilirubin which is then tagged with a molecule called
glucuronate; the resulting bilirubin glucuronate is excreted with bile
o Synthesizes urea and releases it into the bloodstream
o Urea is a carrier of excess nitrogen resulting from protein breakdown
o Excess nitrogen must be converted into urea because free ammonia is toxic
• Colon
o The large intestine reabsorbs water and ions from feces
• Skin
o Produces sweat, which contains water, ions and urea
o Sweat is similar to urine
o The excretory role of the skin is secondary
• Kidneys
o Excretion of hydrophilic wastes
o Excretes urea, sodium, bicarbonate and water
o Sensitive regulator that must keep concentrations at optimum levels
• Homeostatic role of the kidneys
o Homeostasis - constancy of physiological variables
Excretory and Homeostatic Roles of the Kidney
1. Excretion of hydrophilic wastes
2. Maintenance of constant solute concentration and constant pH
3. Maintenance of constant fluid volume (important for BP and cardiac output)
• Filtration - passage of pressurized blood over a filter. Cells and proteins remain in the blood, while
water and small molecules are squeezes out into the renal tubules. Water, waste products and
useful small molecules like glucose are filtered into the renal tubule. The fluid in the tubule is
called filtrate and will eventually be made into urine
• Selective reabsorption - take back useful items (glucose, water, amino acids), while leaving wastes
and some water in the tubule
• Secretion - the addition of substances to the filtrate. Secretion can increase the rate at which
substances ae eliminated from the blood
• Last step is concentration and dilution - selective reabsorption of water
Anatomy and Function of the Urinary System
• Each kidney is a filtration system that removes unwanted materials from the blood and passes
them to the bladder for storage and eventual elimination
• Blood enters the kidney from a large renal artery
• Purified blood is returned to the circulatory system by the large renal vein, which empties into the
inferior vena cava
• Urine leaves the kidney in a ureter, which empties into the urinary bladder
• The bladder is a muscular organ which stretches as it fills with urine
• When it is full, a signal of urgency is sent to the brain
• There are two sphincters controlling release of urine: an internal sphincter made of smooth
(involuntary) muscle and an external sphincter made of skeletal (voluntary) muscle
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Document Summary
The excretory system overview: excretion is the disposal o waste products. Excretory and homeostatic roles of the kidney: excretion of hydrophilic wastes, maintenance of constant solute concentration and constant ph, maintenance of constant fluid volume (important for bp and cardiac output) Filtration - passage of pressurized blood over a filter. Cells and proteins remain in the blood, while water and small molecules are squeezes out into the renal tubules. Water, waste products and useful small molecules like glucose are filtered into the renal tubule. The fluid in the tubule is called filtrate and will eventually be made into urine. Selective reabsorption - take back useful items (glucose, water, amino acids), while leaving wastes and some water in the tubule. Secretion - the addition of substances to the filtrate. Secretion can increase the rate at which substances ae eliminated from the blood. Last step is concentration and dilution - selective reabsorption of water.
