Excretion – Section 39.3. Excretion n Process that rids the body of substances: –toxic chemicals...
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Transcript of Excretion – Section 39.3. Excretion n Process that rids the body of substances: –toxic chemicals...
Excretion
Process that rids the body of substances:– toxic chemicals– excess water– salts– carbon dioxide
Maintains osmotic (water) and pH balance
Excretion
Lungs
– Excrete CO2 and water vapor in exhaled air
Kidneys– Excretes nitrogen wastes,
salts, water, and other substances in urine
Skin– Excretes water, salts,
small amounts of nitrogen wastes, and other substances in sweat
Excretion
Urea
– Main nitrogenous waste of body
– Produced in liver from ammonia (NH3
– Formed during metabolism of proteins and nucleic acids
The Kidneys
Maintains balance of salt, water, minerals, vitamins, pH, and volume of blood
Each Kidney composed of ~ 1 million microscopic units called a nephron that filter the blood
Three phases occur as blood flows through a nephron:– Filtration– Reabsorption– Secretion
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Filtration
Occurs in Bowman’s capsule where there is a network of arteries called a glomerulus
Blood pressure inside the capillaries forces fluid containing water, salt, glucose, amino acids, and urea into the hollow interior of Bowman’s capsule.
This fluid is called filtrate. Blood cells, proteins, and
other molecules too large to cross the membrane remain in the blood.
Reabsorption
Filtrate passes from the Bowman’s capsule into the renal tubules.
As the filtrate passes through the renal tubules useful molecules; glucose, ions, and some water, is reabsorbed.
These substances reenter the bloodstream through capillaries that wrap around the tubule
About 99% of water is returned to blood by osmosis
Secretion
When substances pass from the blood into the filtrate Eliminate toxic substances from blood
Some Interesting Facts!
Blood passes through kidneys 300 times a day.
Nephrons clean all your blood in 45 minutes
Every day the nephrons send about six cups of urine to the bladder
Urine Formation
Filtrate contained in nephron is urine
Formed from the water, urea, and salts that are left after the absorption and secretion processes
Urine leaves the kidneys through the ureters and travels to the urinary bladder
Urinary bladder stores urine and expands as more urine enters
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Excretion
Stretch receptors send nerve impulses to spinal cord
Spinal cord returns impulses to bladder and urethra simultaneously
Impulses cause contractions of bladder’s muscular wall and relaxes muscle of urethra
Urine is emptied through the urethra
Review Questions
1. Identify how the carbon dioxide in your body is produced and excreted.
2. Relate the following terms to the formation of urine: filtration, reabsorption, and secretion.
3. Summarize how urine is stored and eliminated from the body.
4. Concept Generalization: circulatory system, respiratory system, and excretory system