1. Heterotrophic Nutrition
Chapter 15
Heterotrophic Nutrition

2. Introduction
Heterotrophic nutrition consumes complex organic food material which originates from autotrophic organisms.
There are several forms of heterotrophic nutrition:
1.   Saprophytic nutrition
2.   Parasitic nutrition
3.   Holozoic nutrition

3. 1. 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

4. 2. 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)
rostellum
hook
sucker
immature proglottis

5. 3. 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

6. 15.1 Holozoic Nutrition
Holozoic organisms obtain their energy from the consumption of complex organic food which is digested within their bodies.
It involves:
1. Obtaining food (ingestion)
2. Ingestion
3. Physical (mechanical) digestion
4. Chemical digestion
5. Absorption
6. Assimilation
7. Elimination (egestion)

7. According to the type of food ingested, holozoic organisms are classified into:
Herbivores - those feed on plant material
Carnivores - those feed on other animals
Omnivores - those feed on both plants and
animals
Fluid feeders - those consume liquid
materials

8. Teeth and dentition in man
The structure of the tooth

9. Types of teeth

10. Milk Teeth and Permanent Teeth
- appear in babies;
- totally 20 in man
Permanent teeth
- replace milk teeth in later years;
- cannot replaced if damaged;
- totally 32 in man

11. Tooth decay

12. Adaptations to particular diets
Skull of deer
Adaptations to particular diets
Herbivorous adaptations of mammals, e.g. deer
A horny pad replaces the upper incisors & canines
Diastema - a gap to separate newly nibbled food from those chewing at the back

13. Dental formula of a sheep : 0033
3123
3. Cheek teeth with ridged surfaces because of differential wearing of enamel and dentine

14. 4. Jaws can move vertically & laterally
- for more efficient grinding by teeth
5. Teeth have open roots
- teeth grow continuously throughout life to replace wearing by constant grinding activity
6. 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 compartments
7. The alimentary canal is relatively long because
the digestion of plant material is difficult

15. 15.3 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

16. peptidases – break down peptides into amino acids
endopeptidases – break down peptide bonds in the middle of peptides

17. Endopeptidases hydrolyse peptide bonds at points along the protein
COOH
NH2
Exopeptidases acts on terminal amino acids
Carboxypeptidase liberates terminal amino acids
Aminopeptidase breaks terminal amino acids with –NH2 group

18. exopeptidases – break down peptide bonds on terminal amino acids
aminopeptidases – break down amino acids with a free amino (-NH2) group
carboxypeptidases – break down amino acids with a free carboxyl (-COOH) group
lipase - breaks down fats into fatty acids and glycerol

19. The 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 vacuole
Disadvantages:
1 The organism is restricted to food small enough to be ingested by phagocytosis
2 All enzymes operate within the vacuole without specialization of certain regions
3 Acidic and alkaline phases must be taken within the same vacuole at separate times

20. 15.4 Digestion in Humans
Digestion in the mouth
Mechanical digestion of food begins in the buccal cavity. The tongue manipulates the food during chewing with saliva produced from 3 pairs of salivary glands.

21. The human digestive system

23. Digestive System of the Rabbit

24. Saliva contains:
1. Water – over 99%
2. Salivary amylase – enzyme
3. Mineral salts
– maintain optimum pH for amylase
4. Mucin
– bind food particles together and
lubricates food for swallowing
Taste buds allow food to be selected.
The thoroughly chewed food (bolus) is passed to the back of the mouth for swallowing.

25. 15.4.2 Swallowing and peristalsis
- pharynx leads to both trachea & oesophagus
- when swallowing food, epiglottis closes entrance to trachea to prevent food going into lungs

27. Peristalsis - longitudinal & circular muscles contract & relax alternately to drive food down oesophagus, small intestine, large intestine & out of the anus as faeces

28. Gastric mucosa of stomach

29. 15.4.3 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 secretion
2. Hydrochloric acid - secreted by the oxyntic cells
Functions:
Gives an acid pH to kill bacteria and activates enzymes in the stomach (pepsinogen & prorennin);
Initiates the hydrolysis of sucrose & nucleoproteins

33. 3. Pepsinogen - secreted by the zymogen (chief cells) in an inactive form to pepsin
It is activated by HCl
4. 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

34. What 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 HCl
because of nervous tension, irregular meals, smoking, alcohols, lack of sleeps, etc.
Cure: antacids

35. The 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.

36. 15.4.4 Digestion in the small intestine
Duodenum: for digestion
Ileum: chiefly for absorption
The 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: