Mammalian Nutrition OCR Mammalian Physiology and Behaviour A2 Revision

Mammalian Nutrition Heterotrophic nutrition Mechanical and chemical digestion Enzymes – sites of production and action Microscope analysis of stomach, ileum and colon. Structure and function of stomach Structure and function of pancreas Ileum and colon in absorption Nervous and hormonal control of digestion Specialisations of herbivores and carnivores.

Balanced Diet oMacronutrients – fats, proteins and carbohydrates oEssential amino acids oEssential fatty acids – linolenic acid and linoleic acid oMicronutrients – vitamins and minerals oWater oFibre Heterotroph or Autotroph

Heterotrophic Nutrition There are four main stages involved in the processing of food in the gut of a mammal. Ingestion oFood is taken into the mouth and mechanically broken down and crushed by the teeth. Digestion oLarge insoluble molecules are broken down into smaller soluble molecules by the action of digestive enzymes. oHydrolysis reactions. Absorption oProducts of digestion are absorbed through the gut wall. Egestion oElimination of undigested food, dead cells and bacteria as faeces.

The Digestive System The digestive system is made up of the alimentary canal and digestive organs. Serosa submucosa Muscularis mucosa Longitudinal muscles Circular muscles mesentery lumen Glands outside the gut Glands in submucosa Glands of connective tissue of mucosa Glands of epithelium mucosa

The digestive system

Enzymes and Digestion Carbohydrate digestion Saliva contains amylase which hydrolyses some starch to maltose. Pancreatic juice contains amylase In small intestine oMaltase hydrolyse maltose to glucose oSucrase hydrolyse sucrose to glucose and fructose oLactase hydrolyse lactose to glucose and galactose

Enzymes and Digestion Protein Digestion Endopeptidases and exopeptidases Stomach pepsin (pepsinogen) Duodenum trypsin (trypsinogen), chymotrypsin Carboxypeptidase Ileumpeptidase

Enzymes and Digestion Lipid digestion Stomach lipase Duodenum and ileum lipase (pancreatic juice) bile emulsification

Mouth and Oesophagus Mastication Saliva – mucus and amylase Bolus Peristalsis

Stomach Cardiac and Pyloric sphincters Digestion in stomach oGastric pits Oxyntic (parietal) cells – hydrochloric acid Chief cells – pepsinogen Goblet cells – alkaline mucus Absorption in stomach oSmall lipid soluble molecules e.g. aspirin, alcohol

MICROSCOPIC FEATURES OF BOVINE STOMACH. Epithelium, Muscularis mucosa, submucosa, muscularis externa and Serosa. This region of the stomach consists gastric glands which contain parietal and chief cells

Gastric Gland

Liver and pancreas Liver oBile secreted into gall bladder Pancreas (exocrine function) oSecrete pancreatic juice Trypsinogen, chymotrypsinogen and enterokinase, carboxypeptidase Lipase Amylase Hydrogencarbonate ions

Small Intestine - Structure Duodenum oPancreatic duct and bile duct open here Ileum oVilli microvilli (brushborder) Large surface area Blood capillaries Lacteals oCrypts of Lieberkuhn Goblet and paneth cells

Structure of the Small Intestine

Small Intestine - digestion Designed so that the products of digestion are concentrated next to the cells that will absorb them. Proteins (trypsin, chymotrypsin, carboxypeptidase) Lipids Starch (amylase) Plasma membrane of epithelial cells contain enzymes (exopeptidases and carbohydrases)

Small Intestine - Absorption Final products of digestion are absorbed across the plasma membrane of epithelial cells in the villi. Blood capillaries oAmino acids - active transport oMonosaccharides - cotransport – glucose with sodium ions Lacteals oFatty acids and glycerol are lipid soluble (micelles) oForm chylomicron Water – osmosis (wpg) Inorganic ions – facilitated diffusion or active transport) Vitamins (a, d and e) – fat soluble, diffusion

Large Intestine Colon, caecum, appendix, rectum Columnar epithelium with microvilli and goblet cells Function to absorb inorganic ions and water Indigestible material, mucus and cells pass into rectum and then out through anus.

structure of the colon

Control of Digestion Coordinated by both nervous and endocrine working together Buccal cavity oSecretion of saliva – autonomic response along vagus nerve oConditioned reflex Stomach oSecretion of gastric juice – conditioned reflex oGastrin released Pancreas oPancreatic juice oCholecystokinin (causes gall bladder to contract) Small intestine oSecretin

Digestion in Carnivores Concentrated food sources Adaptations oSharp incisors oLong pointed canines oWell developed jaw muscles oShort alimentary canal oCarnassial teeth

Digestion in Herbivores Food surrounded by cellulose cell walls Adaptations oDiastema oMolars with ridges and cusps oIncisors and horny pad oContinual teeth growth oRumen, reticulum, omasum, abomasum o“Chewing the cud”