Homeostasis and Excretion

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HOMEOSTASIS:

Maintenance of a constant and stable internal environment

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THE URINARY SYSTEM:

Two kidneys at back of abdominal cavity

Excrete waste nitrogen as urea

Eliminate excess salts

Osmoregulate to maintain water content of blood

Blood supplied to kidney through renal artery

From aorta so blood enter at high pressure

Blood filtered and passes out through renal vein to vena cava

Urine passes out through ureters and stored in bladder

Bladder has tube leading to outside called urethra

Wall of urethra has sphincters, 2 ring-like muscles which contract to hold back urine

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THE KIDNEYS:

ULTRAFILITRATION:

Arterioles branch into network of capillaries in glomerulus

Small molecules E.G. water, sugar, amino acids, vitamins, minerals, urea pass into Bowman’s capsule through selectively permeable membrane from glomerulus to form the glomerular filtrate

Larger substances E.G. RBC, WBC, proteins, platelets, too large to be filtered or pass through membrane

SELECTIVE REABSORPTION:

Efferent wraps around proximal convoluted tubule

Some substances diffuse back into blood stream

Since higher glucose in tube than blood, half diffused back into bloodstream

Then, through active transport, most substances go back into the blood, except for urea

Osmosis also takes place

SECRETION:

Excessive quantities of certain dissolved substances secreted in distal convoluted tubule E.G. creatinine, hydrogen and potassium ions, some hormones and drugs

Blood pH level maintained

If body needs water reabsorbed back into blood from collecting duct

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CONTROL OF THE BODY’S WATER CONTENT:

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CONTROL OF BODY TEMPERATURE: