Excretion

Unit 1 Module 2

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Excretion

  • the removal of metabolic waste from the body
  • metabolic waste consists of waste products that may be toxic or in excess from reactions in cells
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Carbon Dioxide

  • reduction of oxygen transport
  • majority of CO2 is carried in the blood as HCO3- ions
  • formation of HCO3- also forms H+ which produces HHb
  • competes with O2 for space, reducing oxygen transport
  • CO2 combines directly with Hb to form carbaminohaemoglobin
  • has a lower affinity for oxygen than Hb
  • respiratory acidosis
  • CO2 + H2O  →  H+ + HCO3-
  • Hb acts as a buffer, takes up H+, resists change in pH
  • medulla oblangata detects small pH change, increases breathing rate: remove excess CO2
  • ff blood pH drops below 7.35, it results in difficult breathing 
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Nitrogenous compounds

  • the body cannot store proteins/ amino acids
  • amino acids contain equivalent energy to carbohydrates
  • would be wasteful to excrete
  • transported to the liver
  • deamination removes ammonia, produces keto acid
  • ammonia is converted to urea, transported to the kidneys for excretion
  • keto acid can be used directly in respiration to release energy
  • keto acid can also be converted to carbohydrate or fat for storage
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Ultrafiltration

  • afferent arteriole → glomerulus → efferent arteriole
  • diameter of afferent is larger than efferent arteriole
  • increased pressure; bottleneck effect
  • pressure difference pushes fluid from the glomerulus to lumen of Bowman's capsule
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Bowman's capsule

Endothelum

  • narrow gaps between cells
  • blood plasma and its solutes can pass through

Basement membrane

  • fine mesh of collagen fibres and glycoproteins
  • prevents passage of molecules with Mr > 69000
  • ensures most proteins remain in the glomerulus

Epithelium

  • podocytes
  • finger-like projections called major processes
  • ensures there are gaps between cells
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Bowman's capsule 2

(http://img10.imageshack.us/img10/2048/glomerulusandbowman.png)

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