BY4 - Homestasis

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  • BY4 - Homeostasis
    • Ultrafiltration
      • Takes place in the cortex of the kidney
        • It involves the glomerulus and Bowman's capsule
      • Basement membrane of the glomerulus forms a selective barrier between the blood and the nephron
        • 'Molecular Sieve'
          • How is this created?
            • Endothelium in the glomerulus contains pores, as does the basement membrane, forming the glomerulus wall
            • Walls of the Bowman's capsule consists of epithelium cells called PODOCYTES.
              • Filtration takes place between podocytes
        • The sieve allows smaller molecules through and enter the Bowman's capsule
          • E.G. Urea, amino acids, glucose, water, NaCl etc.
          • Larger molecules remain in the blood
            • E.G. Red blood cells and plasma proteins
      • Hydrostatic pressure of the blood is HIGH in the renal artery
        • Pressure is even higher in the glomerulus because of the differences between the diameter of the afferent arteriole and the efferent arteriole
          • Afferent is wider than the efferent
        • The higher pressure is also because of plasma proteins
        • The pressure in the glomerulus capillary forces small molecules out into the bowman's capsule
    • Selective Reabsorption
      • Takes place in the Proximal Convoluted Tubule
        • It is the process by which useful products are reabsorbed back into the blood as the filtrate flows along the nephron
          • Glucose and amino acids are completely reabsorbed in the PCT
            • Most of the water is reabsorbed
              • Some is collected from the Loop of Henle and the Collecting Duct
      • Adaptations of the Proximal Convoluted Tubule
        • Microvilli
          • Provides a large surface area
        • Numerous Mitachondria
          • ATP for active transport
        • Closeness of blood capillaries
          • Short diffusion pathway
        • Basal Channels
          • Pathway
        • To maximise reabsorption
      • Sodium and chloride ions, glucose, vitamins and amino acids are reabsorbed in the PCT
        • Water potential in the filtrate rises
          • Water moves from the filtrate and into the blood by osmosis (high to low)
        • Concentration of urea in the filtrate increases as it becomes a concentrated solution


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