Excretion of waste products
• Blood enters kidneys through the renal artery and passes through capillaries in the
cortex (outer layer) of the kidneys
• ULTRAFILTRATION: blood passes through capillaries in the cortes and substances are
ltered out into long tubules that surround the capillaries
• SELECTIVE REABSORPTION: useful substances such as glucose and water are
reabsorbed
• The remaining unwanted substances pass along to the bladder and are excreted as
urine
The renal system is split into:
• Renal artery: oxygenated blood
• Renal vein: deoxygenated blood
The long tubules along with the bundles of capillaries where the blood is ltered are the
nephrons . These are located in the cortex of the kidney with their loops of henle in the
medulla
1)ULTRAFILTRATION
• Blood from renal artery enters via the a erent arteriole in the cortex of the kidney
• Each arteriole splits into glomerulus (bundle of capillaries looped inside Bowmans
capsule)
• E erent arteriole takes ltered blood away from glomerulus
• E erent arteriole is smaller in diameter than a erent arteriole —-> this result in the blood
in the glomerulus being under high pressure
• This high pressure forces liquid and small molecules in the blood out of the capillary
and into the bowman’s capsule
• The liquid and small molecules pass through three layers to get into the Bowmans
capsule and enter the nephron tubules- the capillary endothelium, the basement
membrane and the epithelium of the Bowmans capsule
• Larger molecules such as proteins and blood cells can’t pass through so stay in the
blood.
• The substances that enter the Bowmans capsule are known as the glomerular ltrate
• The glomerular ltrate passes along the rest of the nephron and useful substances are
reabsorbed along the way
• The ltrate then ows through the collecting duct and passes out of the kidney along
the ureter
Adaptions for e cient ultra ltration:
1. Large gaps in capillary endothelium
2. Basement membrane —-> ne lter which prevents movement of large molecules
Ultra ltration is selective on size, large molecules such as red blood cells, platelets and
plasma proteins stay in the blood but urea, glucose, amino acids, ions and water are
removed (useful substances removed will later be reabsorbed via selective reabsorption)
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