Bascis of Respiratory and Digestive Systems

BASCIS OF RESPIRAT ORY AND DIGEST IVE SYSTEMS Mitochondrion • • • Requires pyruvic acid (made from glucose in cytoplasm), free fatty acids or amino acids, oxygen Makes ATP (energy) and waste product CO2 E.g. gastric parietal cell: task is to secrete hydrochloric acid, in doing so concentrates H+ a millionfold, contains many mitochondria to generated energy required Advantages of single cell: easier O2 diffusion and CO2 removal, absorbs small molecules from environment, ingests food by engulfing a smaller creature and digesting them in an internal vacuole. Challenges of being multicellular: many cells are a great distance from air and food, need a mechanism for O2 intake and CO2 excretion, need a mechanism for ingesting food, need a circulatory system for transport. Respiratory system: bellow mechanism sucks air in and expels it with waste gases – diffusing chambers (alveoli) with thin membranes (close to small blood vessels) → gaseous transport Bellow mechanism • • During inspiration, the volume of the chest cavity actively increases: o Elevation of ribs o Contraction (downward flattening) of diaphragm During expiration, the volume of the chest cavity passively decreases: o Relaxation (upward bulging) of diaphragm < 50% o Ribs return to normal position ▪ Surface tension of water-air interface (> 50%) – walls of alveoli are attracted to each other because of cohesive H2O forces Cells of the alveolus (functional unit of lung) • • • • • Type 1: thin, squamous cells that form most of wall of alveolus, O2 diffuses across Type 2: secrete surfactant Macrophages: enter alveoli from blood Fibroblast: found in interstitium Capillary (squamous) endothelial cells: carry blood around periphery of each alveolus Surface tension • • Cohesive forces mean that water molecules on the surface adhere to those next to them and below them (resultant vector is downward) Surface molecules dives into bulk fluid → molecules at surface develop opposing forces Surfactant • • • Secreted by type 2 cell Decreases surface tension by decreasing density of water-molecules at air-water interface o Hydrophobic tail pulls the surfactant molecule upward (away from water) → resultant vector is minimal → alveoli don’t collapse o Decreased cohesion of H2O → easier diffusion of O2 → decreases work of breathing Disease: hyaline membrane disease (not enough surfactant) → alveoli are full of inflammatory cells and exudate (mass of cells and fluid that has seeped out of blood vessels) → little room for air Pseudostratified columnar – tracheal epithelial cells → epiglottis closes when swallowing (no food in lungs) Digestive system • • • • • Key functions: digestion and absorption (primarily small intestine) o Enterocyte: cell of intestinal lining → epithelium cell type is simple columnar cells o Villi: small tissue projections (SA) Oesophagus: transports food Stomach: homogenises food, sterilises it (gastric pH 1-2 due to HCl) Pancreas: secreting important digestive enzymes Colon: absorbs remaining water Digestion and absorption • • • Large molecules cannot diffuse across intestinal cells to reach bloodstream Digested in lumen of intestine to smaller molecules (can be absorbed) Exceptions: glucose, some small fats Carbohydrates • • Intake: starches (long chains of glucose) and some simple sugars Digestion: pancreatic enzymes produce simple sugars – glucose, galactose and fructose → actively absorbed across enterocytes into bloodstream Fats • Intake: mainly triglycerides and cholesterol • Digestion: pancreatic enzymes and bile acids from bile produces smaller fats that can diffuse across enterocytes and into the lymph channels (lacteals), and some directly into bloodstream Proteins • • Intake: mostly large protein molecules Digestion: pancreatic enzymes → amino acids and small peptides → actively absorbed across enterocytes into bloodstream