IB Biology Topic 6: Human Physiology

IB Biology Topic 6: Human Physiology Topic 6.1: Human physiology – Digestion and absorption The structure of the wall of the small intestine allows it to move, digest and absorb food. • Understanding: The contraction of circular and longitudinal muscle of the small intestine mixes the food with enzymes and moves it along the gut.  Smooth muscles: muscles that exerts continuous moderate force that consists of relatively short cells not elongated fibres  Circular muscle: constricts the gut to prevent it from being pushed back towards the mouth  Longitudinal muscle: moves the food along the gut  Peristalsis: wave of muscle contraction that occurs in one direction  Function: churns the semi-digested food with the enzyme for digestion  Purpose: moves the food along the gut to initiate digestion process  Food moves very slowly in the intestine via peristalsis to allow time for digestion • Understanding: The pancreas secretes enzymes into the lumen of the small intestine.  Function of the pancreas:  Secretion of hormone: insulin and glucagon  Secretion of digestive enzymes: amylase (starch), lipase (lipids), proteases (proteins)  Secretion of digestive enzymes is controlled by hormones secreted by the stomach  Ducts within pancreas merge into larger ducts to form one large pancreatic duct for secretion • Understanding: Enzymes digest most macromolecules in food into monomers in the small intestine.  The wall of the small intestine produce enzymes (both immobilized enzymes and as intestinal juice)  Types of enzymes produced by intestine: nuclease, maltase (maltose), lactase (lactose), sucrase (sucrose)  Substance that cannot be digested: cellulose • Understanding: Villi increase the surface area of epithelium over which absorption is carried out.  Absorption: process of taking substance into cells and the blood  Assimilation: conversion of nutrients into solid or liquid parts of the organism  Digested materials need to be absorbed to be used in cell processes  Rate of absorption is proportional to the surface area of the epithelium  Villi: small finger-like projection of the mucosa on the inside in intestinal wall  Surface area: increases surface area of the absorption surface (by about a factor of 10)  Size: between 0.5mm and 1.5mm long • Understanding: Villi absorb monomers formed by digestion as well as mineral ions and vitamins.  Absorbed products of digestion by t he villi:  Monosaccharides: glucose, fructose, galactose  Amino acids: broken down from twenty; any of the twenty  Lipids: fatty acids, glycerides and glycerol  Nucleic bases: from digestion of nucleotides  Absorbed products required by the body by the villi:  Mineral ions: calcium, potassium, sodium etc.  Vitamins: ascorbic acid (vitamin C) etc. • Understanding: Different methods of membrane transport are required to absorb different nutrients. Molecule Transport mechanism Transported Monoglyceride Simple diffusion Lacteal (units forms triglyceride in epithelial cells and is transported) Long chain fatty acid Short chain fatty acids Simple diffusion Blood capillary Glucose and galactose Secondary active transport (facilitated coupled with active building of sodium gradient) Blood capillary Amino acids Secondary active transport (facilitated transport coupled with active building of sodium gradient) Dipeptides and tripeptides Active transport (facilitated transport coupled with active building of hydrogen gradient) Fructose Facilitated diffusion  Lipoprotein complex: forms in the epithelium when phospholipids and proteins covers reformed triglyceride and cholesterol • Application: Processes occurring in the small intestine that result in the digestion of starch and transport of the products of digestion to the liver.  Starch: a long chain of α-glucose molecules that consists of 1,4 bonds and 1,6 bonds (specific in amylopectin) Enzyme Target bond Target reactant Product Amylase 1,4 α-glucose bonds Starch (chain of at least four α-glucose molecules) Maltase, maltotriase, dextrinase Maltase 1,4 α-glucose bonds Maltose (fragment two α-glucose) α-glucose Maltotriase 1,4 α-glucose bonds Maltotriose (fragment of three α-glucose) α-glucose Dextrinase 1,6 α-glucose bonds Dextrin (fragment of amylopectin containing 1,6 bonds) α-glucose  Process of glucose transport and storage in liver:  Villus epithelium: glucose is absorbed into villus epithelium by co-transport with sodium ions  Blood capillary: glucose enters the porous blood capillary through diffusion  Venules: glucose in blood capillary flows through to the venules in the sub-mucosa  Hepatic portal vein: venules then flows to the hepatic portal vein to the liver  Liver: excess glucose is absorbed and stored by glycogen or vice versa • Application: Use of dialysis tubing to model absorption of digested food in the intestine.  Dialysis tube: semi-permeable tube that allows molecules of smaller size than the pore to pass through  Method of observation in function of intestine through dialysis tubes:  Dialysis tube filling: dialysis tube is filled with solution of starch and glucose  Dialysis tube immersion: dialysis tube is then immersed into a beaker of distilled water  Observation and record: after one hour, only glucose is present in water • Skill: Production of an annotated diagram of the digestive system. Structure Function Mouth Control of eating and swallowing; mechanical digestion of food and initiating chemical digestion by mixing food with saliva Esophagus Movement of food from mouth to stomach through peristalsis Stomach Killing of foreign bacteria by mixing with water and acid and initial stage of protein digestion Pancreas Secretion of enzymes (amylase, protease, lipases) Liver Secretion of surfactants bile to digest lipids and for neutralization Gall bladder Storage and regulation of bile release