EXCRETORY SYSTEM
Introduction
Metabolism is the sum of all chemical reactions taking place inside the body (catabolic and anabolic)
All metabolic reactions produce waste products which must be removed from the body. Metabolic waste and toxic substances are removed through the process of excretion.
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Excretory Products:
- Heat
- Water (chemical reactions produce [condensation] or use water [hydrolisis]
- Salts
- Carbon dioxide
- Urea
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Organs involved
Liver - Excretes bile pigment via the intestine. Nitrogenous waste from the breakdown of protein in urea
Lungs - Waste products (water & carbon dioxide) through exhalation
Skin - Sweat glands
Kidney - Major urinary system organ
Liver
- Detoxifies blood
- Filters bacteria, alcohol, drugs, toxic substances
- Changes them into inactive or less toxic substances
- Excretes bile (made of worn out RBCs, bile salts & cholestrol)
- Forms urea (changes toxic material to urea, e.g. deamination of amino acids from worn out RBCs)
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Urea Blood Kidney Filtered Out
Lungs
Alveoli - Exchanges oxygen and carbon dioxide between air and blood via diffusion
- Capillaries line alveoli (single cell thick)
- Diffusion is very rapid
Skin
- Excretes 99% of water, mineral salts and urea
- Perspiration (evaporation, cooling process)
- Helps cool body. Heat escapes through millions of pores in skin surface
- Sweat glands
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Kidneys & Urinary System
- Kidneys are bean shaped
- Excretes waste and maintains homeostasis
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Kidneys - Process urine and regulate amount of water in the body
Ureters - Transports processed urine to bladder, narrow muscular tract
Bladder - Storage, muscular sac which can expand and contract
Uretha - Excreted out, narrow tube leading outside the body
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INSIDE THE KIDNEY
Nephrons
- Microscopic filters
- Millions present
- Tissues (modifiable)
- Filters waste and water from the blood
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Glomerulus
- Clump of capillaries present at the end of each nephron
- Network of coiled tubes
- Blood re-absorbs water if needed after waste is filtered (homeostasis & ADH hormone)
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Urine
- Pale yellow solution
- Urea, water, salts, toxins etc.
- a protein rich diet will result in more urea being present in the urine (urea is formed when excess amino acids are deaminated in the liver)
- Taking in more liquids or water rich food increases water potential of the urine
- A high intake of salty foods will result in excess salts being excreted in urine
*A person with diabetes excretes large amounts of glucose in his/her urine
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FAILURE OF HOMEOSTASIS
Bladder & Kidney Failure - Bacteria from colon/rectum in uretha
Kidney Stones - Crystallization of mineral salts and uric acid, block urine passage
Kidney disease - Long term diabetes, infection and chronic poisoning
Gout - Arthritis in which excess production of uric acid leads to crystals in joint
Common causes of kidney failure:
- High blood pressure
- Diabetes
- Alcohol abuse
- Severe accidents that physically damage the kidney
- Complications from undergoing major surgeries
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Patients with kidney failure may get a kidney transplant, but if not available, will undergo dialysis.
A dialysis machine mimics the functions of a kidney and helps to clean the patient's blood from metabollic waste products and toxins.
The patient needs to undergo dialysis 2-3 times a week, with each sessions lasting 3-5 hours.
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Dialysis Process:
1. Blood is drawn from the vein in patient's arm and is pumped through the tubing in the dialysis machine
2. The tubing is bathed in a specially controlled fluid (walls of tubing are partially permeable)
3. Small molecules, such as urea and metabollic waste diffuse out of the tubing into the dialysis fluid. Blood cells, platelets and other large molecules remain in the tubing.
4. The filtered blood is returned to a vein in the patients arm.
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Features of a Dialysis Machine:
- Contains the same concentration of essential substances as healthy blood (so that essential substances like glucose and amino acids do not diffuse into the dialysis fluid, and if there is low concentration of such substances in the blood, will diffuse into it)
- Dialysis fluid does not contain metabollic waste products (keeps a constant concentration gradient)
- Tubing in machine is narrow, long and coiled (increases SA:V and helps speed up the rate of exchange of substances between blood and fluid)
- The direction of blood flow is opposite to the flow of dialysis fluid (concentration gradient)
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