Removal of materials from blood Chapter 23

Role of lungs CO2 produced by cells is transported to the lungs Pulmonary capillaries lie close to alveoli Plasma has CO2 dissolved in it as bicarbonate (HCO3-) In pulmonary circulation HCO3- enter red blood cells to form carbonic acid Carbonic acid converted to CO2 & H2O by an enzyme CO2 diffuses from blood to alveoli by diffusion CO2 then excreted

Role of liver Conserves useful substances: Regulates glucose levels Synthesises plasma proteins Detoxifies toxic materials: Chemical alteration e.g drugs - Excreted in bile or by kidneys Chemical breakdown - H2O2 into Water & Oxygen - by Catalase - Alcohol into acetyl CoA (Excess = cirrhosis) Conjugation (Chemical Attachment) - Unwanted substances attached to glycine - recognised as waste by the kidneys Uptake by macrophages - Removal of foreign particles

Bilirubin Red blood cells broken down by macrophage - in liver, spleen, & bone marrow Breakdown releases haemoglobin - converted into bilirubin - gives plasma it’s yellow colour Liver removes it and conjugates it to another substance Then joins onto bile (conjugation) = bile pigment In gut, bacteria breakdown bilirubin into a brown pigment – into faeces Jaundice caused by bilirubin build up: - Liver disease preventing bilirubin absorption - Bile duct blockage preventing release into intestine - Very high red blood cell death

Production of urea Excess amino acids undergo deamination in liver cells Ammonia and organic acid formed Organic acid enters Kreb’s cycle Ammonia (v toxic) enters ornithine cycle: Controlled by enzymes in liver cells Ammonia + CO2 Urea + Water Urea leaves via hepatic vein - removed from blood by kidneys

Kidney Structure

Role of Kidneys - Ultrafiltration Glomerulus wall has large pores Wall attached to basement membrane – permeable but with small pores Small molecules allowed through - not plasma proteins Bowman’s capsule has cytoplasmic projections – allow rapid passage of filtrate High pressure maintained by: - Existing pressure from renal artery supply - ‘Bottle-neck’ effect – blood squeezed through glomeruli - Total volume of 1500 litres of blood/day - 180 litres of glomerular filtrate produced - However only 1-2 litres of urine

Role of kidneys - Reabsorption 99% of water is reabsorbed Concs of other substances vary little from arterial blood to glomerular filtate But vary greatly between filtrate and urine Proximal Convoluted Tubule (PCT): Glucose (& amino acids) are reabsorbed by PCT epithelial cells Epithelial cells are suitable because: - Cells have microvilli - Cells have mitochondria (active transport) - Cells have carrier molecules Virtually all glucose reabsorbed (exception – diabetes) Salt (sodium & chloride ions) are actively pumped back into blood Water is absorbed by osmosis (85%)

Role of kidneys – Reabsorption 2 Loop of Henle: Water reabsorbed by osmosis in descending limb Sodium & Chloride ions pumped back into tissue fluid in ascending limb Water not reabsorbed in ascending limb (wall impermeable) Therefore low water conc in surrounding medulla Distal Convoluted Tubule (DCT): Sodium Chloride reabsorbed Water reabsorbed Collecting Duct: Large level of water reabsorption by osmosis if required Reabsorption controlled by levels of ADH Any remaining filtrate – released in urine (nitrogenous excretion)

ADH