2.72B: Understand How the Kidney Carries Out its Roles of Excretion and Osmoregulation

EXCRETION: Removal of waste products of metabolism from the body

OSMOREGULATION: Control of the Water balance of the blood, tissue or cytoplasm of a living organism

KIDNEY AND EXCRETION:

ROLE OF KIDNEY IN EXCRETION

Diagram showing the Role and Structure of Kidney for Excretion

PROCESS: Renal Artery transports Oxygenated blood to the Glomerulus within Bowman's Capsule under high pressure High hydrostatic pressure is due to the wider afferent arteriole transporting blood to the Bowman's Capsule, and narrow efferent arteriole transporting blood out of Capsule Blood is therefore filtered at high pressure to produce Glomerular Filtrate composed of Water, Glucose, Salts and Urea However, as Proteins and Red blood cells are too large to be filtered through base membrane - material between Glomerulus and Bowman's Capsule, they will remain in blood Glomerular Filtrate enters the Proximal Convoluted Tubule (PCT), where all Glucose is reabsorbed into surrounding capillaries - selective reabsorption Remaining filtrate flows through the Collecting Duct, where Water is reabsorbed into the blood depending on levels of ADH secreted by Pituitary gland (ADH is produced by Hypothalamus and stored in Pituitary gland for secretion) Remaining filtrate composed of excess Water, Salts and Urea will form Urine, which is transported via the Ureter to the Bladder to be stored for Excretion

ROLE OF KIDNEY IN OSMOREGULATION

LOW LEVELS OF WATER	HIGH LEVELS OF WATER
Diagram Showing Osmoregulation when Water Levels in the Body is Low	Diagram Showing Osmoregulation when Water Levels in the Body is High
Hypothalamus detects low levels of Water in body, stimulating Pituitary gland to secrete more ADH Increase in ADH causes membrane of Collecting Duct to become more permeable with the increase in pores, therefore increasing the reabsorption of Water into blood capillaries via Osmosis As more Water is reabsorbed, Water levels in the body is regulated and returned to normal As a result, volume of Urine will decrease and become more concentrated	Hypothalamus detects high levels of water in body, stimulating Pituitary gland to secrete less ADH Decrease in ADH causes membrane of Collecting Duct to become less permeable with the decrease in pores, therefore preventing the reabsorption of Water into blood capillaries As less Water is reabsorbed, Water levels in the body is regulated and returned to normal As a result, volume of urine will increase and become less concentrated (more diluted)