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Excretion, :, Labelled Diagram, Labelled Diagram, Labelled Diagram, image,…

- - - - Filtration takes place in the glomerulus
      - This is the first step in urine production
      - Blood enters through the afferent arteriole containing waste products
      - Filtration occurs by small molecules eing forced out of the plasma and into the Bowman’s Capsule
      - Here it forms a dilute solution called the Glomerular filtrate
  - - - Filtration means that water and small molecules pass from the blood into the nephron
      - This occurs under high pressure from the afferent arteriole (wide vessel)
      - Large substances such as white blood cells, platelets and proteins do not enter the glomerular filtrate
  - - - The most useful substances e.g. water, salts, glucose are then reabsorbed back into the blood
      - This happens in the rest of the nephron
        
        Most of the water is reabsorbed by osmosis in the proximal convoluted tube
        
        This is aided by the tube being thin-walled (only one cell thick) and it being long (14 mm)
        
        A small amount of water is also reabsorbed in the descending (downward) Loop of Henle
        
        The ascending (upward) Loop of Henle absorbs salts and water by osmosis
      - Urine production
        
        About 99% of the glomerular filtrate is reabsorbed, leaving about 1.5 litres of urine to be excreted in a normal day
  - - - The distal convoluted tube is involved in the precise control of water, salt and pH balance in the blood. This is controlled by secretion
      - Some water and salts are re-absorbed here
      - A small amount of water is reabsorbed from the filtrate in the collecting duct
      - The liquid passing from the collecting duct is urine and flows into the pelvis of the kidneys and then into the bladder through the ureters
- - - - Vasoconstriction: The skin contracts when cold
      - Piloerection: Body hair traps heat
      - Sweat cools body down
  - - - Sun exposure causes an increase in melanin production i.e. a sun tan/freckles
        
        Melanin protects the skin against the harmful UV rays from the sun
        
        The granular layer contains melanin, a pigment that gives colour to hair, skin and eyes, freckles are very concentrated melanin
        
        Inner layer contains living granular cells
        
        Dead, full of waterproof keratin
    - - Contains a strong protein called collagen
      - Has many blood vessels, sweat glands, sebaceous glands and nerve receptors
      - The subcutaneous layer contains fat in adipose tissue
      - The subcutaneous layer contains fat in adipose tissue
- - - - Ureters connect the kidney to the bladder
      - The bladder stores urine
        
        Sphincter muscle controls the release of urine
      - Renal vein carries blood away from the kidney
      - Renal artery carries blood to the kidney
- - - - To maintain fluid balance, a constant temperature and chemical composition
      - To maintain composition of an organism's fluids,including fluid balance and chemistry. by preventing the accumulation of poisonous wastes which might interfere with metabolism.
      - Controlling osmosis (salt/water balance)
      - Regulating body temperature
- - - - Affects the distal convoluted tubule and the collecting duct
      - Causes more water to be re-absorbed from the nephron
      - Blood plasma too concentrated/body is dehydrated:
        
        Pituitary gland releases ADH and it travels to the kidneys
        
        Causes the walls of the distal convoluted tube and collecting duct to become more permeable to water
        
        More water is reabsorbed from the nephron
        
        Results in a reduced salt concentration of plasma
        
        A reduced volume of urine
      - Blood plasma concentration normal/ too dilute
        
        ADH is not released
        
        The distal tubes and collecting ducts are impermeable to water
        
        Little water is re-absorbed
        
        The concentration of blood plasma remains unchanged
        
        Large volume of urine is produced