Summary Life science notes on the excretory system

Excretion
Definitions

 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