Download 2005 nutrition AlCh15a

Chapter 15
Heterotrophic
Nutrition
• Introduction
• Heterotrophic nutrition consumes complex
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organic food material which originates from
autotrophic organisms.
There are several forms of heterotrophic
nutrition:
1. Saprophytic nutrition
2. Parasitic nutrition
3. Holozoic nutrition
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
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
• 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
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)
• According to the type of food ingested,
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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
Teeth and dentition in man
The structure of the tooth
Types of teeth
• Milk Teeth and Permanent Teeth
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Milk teeth
- appear in babies;
- totally 20 in man
Permanent teeth
- replace milk teeth in later years;
- cannot replaced if damaged;
- totally 32 in man
Tooth decay
Skull of
deer
Adaptations to particular diets
Herbivorous adaptations of mammals, e.g. deer
1. A horny pad replaces the upper incisors &
canines
2. Diastema - a gap to separate newly nibbled
food from those chewing at the back
Dental formula of a sheep : 0033
3123
3. Cheek teeth with ridged surfaces because of
differential wearing of enamel and dentine
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
• 15.3 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
• peptidases – break down peptides into
amino acids
• endopeptidases – break down peptide bonds
in the middle of peptides
Endopeptidases hydrolyse peptide bonds at points along the protein
NH2
COOH
Carboxypeptidase
liberates terminal
amino acids
Exopeptidases acts on
terminal amino acids
Aminopeptidase
breaks terminal amino
acids with –NH group
• 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
The food vacuoles of protozoans represent the
simplest form of digestive system:
• Advantages:
• allows the organism to achieve the optimum
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concentration of enzymes in a small space within the
vacuole
Disadvantages:
The organism is restricted to food small enough to be
ingested by phagocytosis
All enzymes operate within the vacuole without
specialization of certain regions
Acidic and alkaline phases must be taken within the
same vacuole at separate times
• 15.4 Digestion in Humans
• 15.4.1 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.
The human
digestive
system
Digestive
System of
the Rabbit
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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.
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
Peristalsis - longitudinal & circular muscles
contract & relax alternately to drive food
down oesophagus, small intestine, large
intestine & out of the anus as faeces
Gastric mucosa of
stomach
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
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
• 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
• 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.
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: