13. Excretion in humans

• Excretion in humans:

  • urea is formed in the liver from excess amino acids
  • carbon dioxide is excreted through the lungs
  • kidneys excrete urea (toxic), excess water & salts
  • volume & concentration of urine is affected by water intake, temperature & exercise
• Kidney/bladder diagram:

  A) kidney

  B) ureter

  C) bladder

  D) urethra

  
• Function of liver:

  • assimilation of amino acids by converting them to proteins, including plasma protein (e.g. fibrinogen)
• Deamination - the removal of the nitrogen-containing part of amino acids to form urea
• Structure of kidney:

  • cortex: contains Bowman's capsules & coiled tubules
  • medulla: has loop of Henle and collecting ducts
  • ureter: carries urine from the kidney to the bladder

  
• Structure and function of nephron:

  • glomerulus: blood pressure forces fluid (small molecules) from the blood into the capsule - protein too big to be filtered out (ultrafiltration)
  • proximal/distal convoluted tubule: selective reabsorption of salt, water & glucose (active transport) out of the nephron
  • loop of Henle: permeable to water but not salt, water drawn out by osmosis due to low water potential outside nephron
  • collecting duct: filtrate becomes urine

  A) filtrate

  B) glomerulus

  C) bowman's capsule

  D) proximal tubule

  E) loop of Henle

  F) distal convoluted tubule

  G) collecting duct

  H) bladder

  
• Dialysis - unable to maintain salt balance, the maintenance of glucose concentration & the removal of urea in the body

  • helps the body of toxic waste products from the blood using dialysate (fluid)
  • (v): widely available & help extend the lives of those with kindey failure
  • (x): time consuming & need regular visits to a clinic

  Transplant:

  • (v): offer better quality of life & longer lifespan compared to dialysis
  • (x): availability of suitable donor; could risk infections, complications