Excretion and Homeostatic control

• Waste

  • metabolic reactions create waste products and the removal of waste = excretion
  • carbon dioxide and nitrogenous waste
  • CO2 waste in the lungs
  • nitrogenous waste (urea) excess amino acids
  • excess amino acids cant be stored = ammonia + urea
• The Liver

  Function: glycogen storage, detoxification and formation of urea

  • receives oxygen through the hepatic artery
  • blood leaves through the hepatic vein
  • blood from the digestive system is from the hepatic portal vein
• what are liver cells called?

  Hepatocytes

  • have many mitochondria
  • large nuclei
  • prominent Golgi apparatus
  • enables a high metabolic rate
• structure and histology of the liver

  • blood delivered to liver through hepatic portal vein and hepatic artery mixes in sinusoids
  • hepatic artery is highly oxygenated and oxygen mix with the blood from the hepatic portal vein
• structure and histology of the liver (2)

  • to stop disease the liver has Kupffer cells in the sinusoids
  • Kupffer cells are macrophages = engulf + breakdown old blood +blood cells
  • hepatocytes produce bile using old blood +blood cells
  • bile is secreted into spaces called canaliculi - bile ducts - gall bladder where its stored
• the functions of liver

  • hepatocytes response to insulin glucose in blood converted to glycogen.
  • hepatocyte glucagon response glycogen back to glucose
  • detoxification = neutralisation + breakdown unwanted chemicals = alcohols + drugs + hormones + toxins
  • ornithine cycle (urea cycle) how urea is produced from ammonia - ready to go kidneys +excreted
  • deamination removing the amine group + ammonia acid removed
• Mammalian Kidney

  • excretion of nitrogenous waste + osmoregulation
  • osmoregulation = controlling the water potential of the blood
  • renal artery = blood to be filtered
  • renal vein = carries away filtered blood
• Cortex 


  dark outer layer that contains many capillary networks + carries blood from renal arteries to nephrons
• medulla 


  conatins the neuphrons
• pelvis 


  urine collects before leaving the kidney and travelling to the ureter
• what happens in the Bowmans (renal) capsule?

  Ultrafiltration occurs here
• Proximal convoluted tubule (PCT)?

  glucose is reabsorbed
• what happens in the loop of Henle?

  sodium ion are actively transported out of the ascending limb into the medulla to create a low water potential
• what happens in the descending limb?


  water moves out of the descending limb + out of the distal convoluted tubule and collecting duct by osmosis
• what happens in the collecting duct?


  the liquid remaining in collecting duct forms urine = water + dissolved salts +urea + other substance = hormones
• stages filtration + reabsorption

  1. glomerulus
  2. proximal convoluted tubule
  3. descending loop Henle
  4. Ascending loop of Henle
  5. distal tubule
  6. collecting duct
• what happens in the glomerulus ?


  filters small solutes from the blood
• what happens in proximal convoluted tubule?

  reabsorbs ions, water, nutrients (removes toxins + adjust filtrate pH)
• what happens descending loop of Henle?

  water passes from the filtrate into the interstitial fluid
• what happens in ascending loop Henle?

  reabsorbs sodium ion + chlorine ions from filtrate into the interstitial fluid
• what happens in the distal tubule?

  selectively secretes + absorbs different ions to maintain blood pH + electrolytes balance
• what happens in collecting duct?


  reabsorbs solutes + water (urine)
• ultrafiltration 


  blood enters through arterioles + splits smaller capillaries which make up the glomerulus

  • hydrostatic pressure of the blood
  • water + small molecules such as glucose + mineral ions are forced out + form glomerulus filtrate
• once fluid from capillary it passes through the basement membrane = sieve

  • The Bowmans capsule wall also has podocytes = additional filters
  • large proteins + blood cells too big = stay in blood
• selective reabsorption

  • occurs in the PCT = glomerulus filtrate is reabsorbed
  • conc of Na+ ions PCT cell is decreased as Na+ are actively transported out into blood in capillaries
  • conc gradient Na+ diffuse down gradient from lumen PCT in lining
  • e.g. co transport = transport Na+ + glucose
  • this how glucose is reabsorbed
• selective reabsorption

  
• • all of the sodium ion are actively transported out of the loop of Henle
  • due to their being a high conc of filtrate more water diffuses out of the DCT
• what happens in the hypothalamus?

  changes in the water potential of the blood are detected by osmoreceptors
• what does the hypothalamus do if the water potential is low?

  if the water potential is too low water osmoreceptors by osmosis + they shrivel

  • stimulates production of more ADH hormone

  if water potential too high water enters the osmoreceptors by osmosis

  • stimulates less ADH produced
• what is ADH (Antidiuretic hormone)?

  • complementary binds to receptors that only are located on target cells on DCT
  • activate adenyl cyclase to make cAMP
  • activates an enzyme which contain vesicles containing aquaporins
  • aquaporins = channel proteins allow water to transport across membrane
  • more permeable to water + more will leave to be reabsorbed
• what doe ADH cause?

  • increase on permeability of collected duct + distal convoluted tubule
  • more water to leave the nephron + reabsorbed into blood = urine more concentrated

  
• water potential of blood increases - detected by osmoreceptors in hypothalamus - hypothalamus releases less ADH - DCT + collecting duct walls become less permeable to water - less water is reabsorbed into the blood + more is lost in the urine - normal water potential of blood
• water potential blood decreases - detected by osmoreceptors in hypothalamus - hypothalamus releases more ADH which is then released into blood by pituitary gland - DCT + collecting duct walls become more permeable to water - more water is reabsorbed into blood less is lost in urine - normal water potential of blood
• how does a pregnancy tests work?

  monoclonal antibodies detect the presence of the human growth human which is produced by pregnant women.

  a monoclonal antibody is a single type of antibody that can be isolated + cloned
• urine diagnosis

  • (A) urine sample is test put in urine
  • (B) first mobile antibody a coloured dye attached
  • (C) second antibody complementary in shape to antigens is immobilised in test
  • (D) third antibody is immobilised + complementary is shape to the first antibody
• pregnancy tests

  
• Kidney Failure

  • kidney infections + high BP damage tubules, podocytes, epithelial cells + basement membranes
  • if kidney fails the blood is not filtered properly = build up of urea + mineral ions = imbalance
  • glomerular filtration rate is affected by kidney failure
• haemodialysis

  • involves a dialysis machine
  • blood enters machine and is filter
  • dialysis fluid allows the urea to diffuse out blood
• Peritoneal dialysis

  • peritoneum the abdomen as it acts as a natural dialysis membrane
  • dialysis fluid is introduced to the abdomen
  • urea + excess amino acid move out blood into tissue fluid then peritoneal membrane - into dialysis fluid
  • blood then filtered