2IntroductionHeterotrophic nutrition consumes complex organic food material which originates from autotrophic organisms.There are several forms of heterotrophic nutrition:1. Saprophytic nutrition2. Parasitic nutrition3. Holozoic nutrition
31. Saprophytic nutrition – involves the consumption of complex organic food from the bodies of dead organisms.The food is either in soluble form or digested externally into simple molecules to diffuse into the organism,e.g bacteria and fungi
42. Parasitism:some organisms live on or inside other organisms, obtaining benefits from them and causing harm.Organisms have simple digestive system and food is often soluble forms,e.g.Tapeworm (parasite) obtain digested food (benefit) from man (host)rostellumhooksuckerimmature proglottis
53. Holozoic nutrition – involves the consumption of complex (solid) food which is broken down inside the organism into simple molecules which are then absorbed,e.g. most animals
615.1 Holozoic NutritionHolozoic organisms obtain their energy from the consumption of complex organic food which is digested within their bodies.It involves:1. Obtaining food (ingestion)2. Ingestion3. Physical (mechanical) digestion4. Chemical digestion5. Absorption6. Assimilation7. Elimination (egestion)
7According to the type of food ingested, holozoic organisms are classified into: Herbivores - those feed on plant materialCarnivores - those feed on other animalsOmnivores - those feed on both plants andanimalsFluid feeders - those consume liquidmaterials
8Teeth and dentition in man The structure of the tooth
12Adaptations to particular diets Skull of deerAdaptations to particular dietsHerbivorous adaptations of mammals, e.g. deerA horny pad replaces the upper incisors & caninesDiastema - a gap to separate newly nibbled food from those chewing at the back
13Dental formula of a sheep : 0033 31233. Cheek teeth with ridged surfaces because of differential wearing of enamel and dentine
144. Jaws can move vertically & laterally - for more efficient grinding by teeth5. Teeth have open roots- teeth grow continuously throughout life to replace wearing by constant grinding activity6. Stomach is divided into a number of chambers with micro-organisms to secreted cellulase for the digestion of cellulose (ruminants).Regurgitation of food from stomach to mouth before passing into the remaining stomach compartments7. The alimentary canal is relatively long becausethe digestion of plant material is difficult
1515.3 Principles of Digestion Mechanical breakdown of food has the effect of giving the food a large surface area which aids later digestion.The food must be made small enough to pass through cell membranes. Thus chemical digestion with the aid of enzymes occurs.amylase - breaks down starch into maltose
16peptidases – break down peptides into amino acids endopeptidases – break down peptide bonds in the middle of peptides
17Endopeptidases hydrolyse peptide bonds at points along the protein COOHNH2Exopeptidases acts on terminal amino acidsCarboxypeptidase liberates terminal amino acidsAminopeptidase breaks terminal amino acids with –NH2 group
18exopeptidases – break down peptide bonds on terminal amino acids aminopeptidases – break down amino acids with a free amino (-NH2) groupcarboxypeptidases – break down amino acids with a free carboxyl (-COOH) grouplipase - breaks down fats into fatty acids and glycerol
19The food vacuoles of protozoans represent the simplest form of digestive system: Advantages:allows the organism to achieve the optimum concentration of enzymes in a small space within the vacuoleDisadvantages:1 The organism is restricted to food small enough to be ingested by phagocytosis2 All enzymes operate within the vacuole without specialization of certain regions3 Acidic and alkaline phases must be taken within the same vacuole at separate times
2015.4 Digestion in HumansDigestion in the mouthMechanical digestion of food begins in the buccal cavity. The tongue manipulates the food during chewing with saliva produced from 3 pairs of salivary glands.
24Saliva contains:1. Water – over 99%2. Salivary amylase – enzyme3. Mineral salts– maintain optimum pH for amylase4. Mucin– bind food particles together andlubricates food for swallowingTaste buds allow food to be selected.The thoroughly chewed food (bolus) is passed to the back of the mouth for swallowing.
2515.4.2 Swallowing and peristalsis - pharynx leads to both trachea & oesophagus- when swallowing food, epiglottis closes entrance to trachea to prevent food going into lungs
2915.4.3 Digestion in the stomach The stomach is a muscular sac with a folded inner layer (gastric mucosa) with holes (gastric pits) lined with secretory cells which secrete gastric juice:1. Water - the bulk of the secretion2. Hydrochloric acid - secreted by the oxyntic cellsFunctions:Gives an acid pH to kill bacteria and activates enzymes in the stomach (pepsinogen & prorennin);Initiates the hydrolysis of sucrose & nucleoproteins
333. Pepsinogen - secreted by the zymogen (chief cells) in an inactive form to pepsin It is activated by HCl4. Prorennin - secreted by zymogen cells; activated by HCl to rennin to coagulate milk by converting caseinogen (soluble protein in milk) to casein (insoluble)5. Mucus - secreted by goblet cells to produced a protective layer to prevent autodigestion of the gastric mucosa (thus preventing ulcer)It also lubricates food in the stomach
34What is peptic ulcer?It is a disease in which a hole has been made in the mucous membrane lining the stomach or duodenum.Causes: too much HClbecause of nervous tension, irregular meals, smoking, alcohols, lack of sleeps, etc.Cure: antacids
35The churning and mixing action of the muscular stomach wall changes the bolus of food into a creamy fluid (chyme).The chyme from any one meal takes 3-4 hours to be released little by little into the duodenum.This provides a continuous supply of food for absorption throughout the period between meals.
3615.4.4 Digestion in the small intestine Duodenum: for digestionIleum: chiefly for absorptionThe walls of the small intestine are folded with villi which contain fibres of smooth muscle.These muscles regularly contract and relax to mix food and enzymes so as to facilitate absorption.The digestive juices of the small intestines are: