Summary
Summary Life science notes on the excretory system
Notes/summary of the excretory system based off of both IEB textbooks and extra notes taken in class
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ExcretionDefinitions
Excretion: removal of metabolic wastes from the body
Egestion: removal of undigested substances (not products of
metabolism and were never inside a cell)
Secretion: release of harmful substances that are produced by
cells for important function (e.g. Digestive juices)
Basics
Metabolism: sum total of chemical reactions that occur in cell
During metabolism waste products such as CO2, excess water, salts
and nitrogenous wastes are formed.
If not removed it will poison the cells and inhibit normal functioning
if allowed to accumulate.
Metabolic waste products diffuse out cells via tissue fluid that
surrounds them to the blood in blood vessels
Waste products are transported in the blood to several excretory
organs that remove from blood stream and release out body
Different excretory organs
Lungs
Excrete CO2, water vapour and heat
Kidneys and bladder
Kidneys excrete urine and bladder stores it
Urine: water, mineral salts and nitrogenous waste (urea and uric
acid)
Liver and gut
Liver excretes urea and bile pigments
Transported in blood to kidneys and excreted
Bile pigments pass into guts and excrete as bile salts in faeces
Skin
Sweat via sweat glands
Consist of: excess water, salts and small amount of urea
Metabolic waste products and their origin
CO2: product of cellular respiration
, Excess water: product of cellular respiration and intake of fluids and
food
Urea: in liver from deamination (when nitrogen is removed from
amino acid and converted to ammonia) of excess amino acids
Uric acid: product of metabolism of nucleic acids
Creatine: creatinine phosphate in cells
Bile pigments: in liver during breakdown of haemoglobin
Structure of urinary system
Two kidneys, two ureters, the bladder and the urethra
Blood vessels: renal arteries and renal veins
Kidneys: in abdominal cavity on either side of vertebral column
below diaphragm
Kidneys receive oxygenated blood rich in metabolic waste from renal
arteries
Deoxygenated blood purified is transported away from kidneys via
renal veins
The ureters extend from kidneys and opens separately to bladder
Bladder is a thin walled muscular sac
Urethra transports urine from bladder to exterior
Sphincter at base of bladder controls flow of urine
Structure of kidney
External
Kidney is a dark red bean shaped organ and concaved side faces
vertebral column
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