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
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Macronutrients – fats, proteins and carbohydrates
Essential amino acids
Essential fatty acids – linolenic acid and linoleic acid
Micronutrients – vitamins and minerals
Water
Fibre
Heterotroph or Autotroph
Heterotrophic Nutrition
There are four main stages involved in the processing of food in
the gut of a mammal.
Ingestion
o Food is taken into the mouth and mechanically broken down
and crushed by the teeth.
Digestion
o Large insoluble molecules are broken down into smaller
soluble molecules by the action of digestive enzymes.
o Hydrolysis reactions.
Absorption
o Products of digestion are absorbed through the gut wall.
Egestion
o Elimination 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.
Muscularis mucosa
Longitudinal muscles
Circular muscles
Serosa
mesentery
lumen
submucosa
mucosa
Glands of epithelium
Glands of connective
tissue of mucosa
Glands
outside
the gut
Glands in submucosa
The digestive system
Enzymes and Digestion
Carbohydrate digestion
Saliva contains amylase which hydrolyses some starch to
maltose.
Pancreatic juice contains amylase
In small intestine
o Maltase hydrolyse maltose to glucose
o Sucrase hydrolyse sucrose to glucose and fructose
o Lactase hydrolyse lactose to glucose and galactose
Enzymes and Digestion
Protein Digestion
Endopeptidases and exopeptidases
Stomach
pepsin (pepsinogen)
Duodenum trypsin (trypsinogen), chymotrypsin
Carboxypeptidase
Ileum
peptidase
Enzymes and Digestion
Lipid digestion
Stomach
Duodenum and ileum
lipase
lipase (pancreatic juice)
bile
emulsification
Mouth and Oesophagus
Mastication
Saliva – mucus and amylase
Bolus
Peristalsis
Stomach
Cardiac and Pyloric sphincters
Digestion in stomach
o Gastric pits
• Oxyntic (parietal) cells – hydrochloric acid
• Chief cells – pepsinogen
• Goblet cells – alkaline mucus
Absorption in stomach
o Small 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
o Bile secreted into gall bladder
Pancreas (exocrine function)
o Secrete pancreatic juice
• Trypsinogen, chymotrypsinogen and enterokinase,
carboxypeptidase
• Lipase
• Amylase
• Hydrogencarbonate ions
Small Intestine - Structure
Duodenum
o Pancreatic duct and bile duct open here
Ileum
o Villi
• microvilli (brushborder)
• Large surface area
• Blood capillaries
• Lacteals
o Crypts 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
o Amino acids - active transport
o Monosaccharides - cotransport – glucose with sodium
ions
Lacteals
o Fatty acids and glycerol are lipid soluble (micelles)
o Form 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
o Secretion of saliva – autonomic response along vagus
nerve
o Conditioned reflex
Stomach
o Secretion of gastric juice – conditioned reflex
o Gastrin released
Pancreas
o Pancreatic juice
o Cholecystokinin (causes gall bladder to contract)
Small intestine
o Secretin
Digestion in Carnivores
Concentrated food sources
Adaptations
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Sharp incisors
Long pointed canines
Well developed jaw muscles
Short alimentary canal
Carnassial teeth
Digestion in Herbivores
Food surrounded by cellulose cell walls
Adaptations
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Diastema
Molars with ridges and cusps
Incisors and horny pad
Continual teeth growth
Rumen, reticulum, omasum, abomasum
“Chewing the cud”