The Excretory System Aorta Renal Artery Right Kidney Renal Vein Vena cava Ureter Bladder Sphincter Muscle Urethra

The kidney Renal Capsule Cortex; dark red, full of blood vessels, where ultrafiltration takes place Medulla; pink, fewer blood vessels Pyramid; urine drains from these into the pelvis Ureter; urine flows from the kidney to the bladder down this tube Nephron; filtering tubes Pelvis

Role of the Kidney All small molecules are removed from the blood Most are then returned to the blood before it leaves the kidneys Any that are not needed or any surplus become part of the urine. The urine passes from the kidneys to the bladder where it is stored until full

Nephrons There are about one million of these microscopic tubes in each kidney The blood is filtered in these Nephron

A Nephron Afferent Arteriole Glomerulus Efferent Arteriole Renal vein Bowman’s capsule Second coiled tubule First coiled tubule Collecting Duct Descending Loop Ascending Loop Loop of Henle A Nephron

Ultrafiltration The high pressure in the Glomerulus forces small molecules out of the blood into the Bowman’s capsule, e.g amino acids, glucose, water The ultrafiltrate is formed Ultrafiltration occurs in the glomerulus forming ultrafiltrate in the bowman’s capsule

Selective Reabsorption First coiled tubule 70% of water, all glucose, some salts and some amino acids are reabsorbed back into the capillaries surrounding the tubule Loop of Henle Some water is reabsorbed Second coiled tubule Some water (affected by ADH) and some salts are reabsorbed Collecting Duct Some water is reabsorbed (affected by ADH)

Reabsorption of water occurs in the collecting duct Selective Reabsorption in the first coiled tubule Reabsorption of water in the Loop of Henle by osmosis Some water and some salts are reabsorbed in the second coiled tubule Osmosis: water moves from a high concentration of water to a low concentration

Osmoregulation; regulation of the concentration of water and salt concentration in the blood * *Makes cells in collecting duct and second coiled tubule more permeable to water

INTAKE cm3 OUTPUT cm3 Food 800 Sweat 600 Drink 1500 Breath 400 BALANCE OF WATER INTAKE cm3 OUTPUT cm3 Food 800 Sweat 600 Drink 1500 Breath 400 Metabolism 350 Faeces 100 Urine 1500 TOTAL 2600 TOTAL 2600