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F214 Communication, Homeostasis and Energy

Module 2 Excretion

4.2.1 Excretion

a. Define the term excretion

Excretion-The removal of metabolic waste from the body which are by products
or unwanted substances from cell processes.

b. Explain the importance of removing metabolic wastes, including carbon dioxide
and nitrogenous waste from the body…

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Hepatic portal vein
o This carries oxygenated blood to the liver.
o The blood is rich in the products of digestion some of which may be toxic
Hepatic vein
o This is where blood leaves the liver which then re-joins the vena cava.
Bile duct
o Bile is secreted…

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d. Describe the formation of urea in the liver including an outline of the
ornithine cycle

o Amino acid + O2 Keto acid + ammonia
Ornithine cycle
o 2NH3 + CO2 CO(NH2)2 + H2O
o Ammonia + carbon dioxide Urea + water

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e. Describe the roles of the liver in detoxification

Liver cells contain enzymes that make toxic molecules less toxic.
o E.g. Catalase which converts hydrogen peroxide to oxygen and water.
Detoxification of alcohol
o Ethanol contains chemical potential energy that can be used in respiration.
o It is broken down…

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h. Describe and explain the production of urine, with reference to the processes
of ultrafiltration and selective reabsorption

1. Blood flows into the glomerulus from the afferent arteriole which is
wider than the efferent arteriole which carries the blood away from the
2. This means that the blood…

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Loss of water by osmosis to the surrounding tissue fluid.
Diffusion of sodium and chloride ions into the tubule from the
surrounding tissue.
The lower down the descending limb the lower the water potential.
o In the ascending limb
At the base the sodium ions diffuse out.
Higher up the…

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o Also, the body is unable to regulate the levels of water and salts in the
o It removes wastes, excess fluid and salt from the body by passing the
blood over a partially permeable dialysis membrane which allows
exchanges between the blood and dialysis fluid.
o Because…

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o The hCG antibody complex moves up the stick and attaches to a band of
immobilised enzymes forming a blue line.
Anabolic steroid testing
o Anabolic steroids increase protein synthesis in cells resulting in a
build-up of cell tissue especially in muscles.
o They have a half-life of about 16…


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