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
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
Elimination (egestion)
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
•
Phagotrophs - those (majority) take in solid food
•
Microphagous - phagotrophs taking in very small particles,
•
e.g. by filter feeding mechanism
•
Macrophagous - phagotrophs taking in relatively large particles,
e.g.
most animals
Clam (mussel)
See Figure 1:
Diet
•
In
mammals carbohydrates and fats are needed in relatively large quantities as
energy source, and
•
proteins for
growth and repair.
•
Vitamins
and minerals are required in much smaller quantities for a variety of specific
functions.
•
Water
is a vital constituent of the diet and
•
roughage
is necessary for preventing constipation.
Carbohydrates and fats (energy requirements)
v The energy required by an organism
varies with age, sex, size and activity.
v Ideally 2/3 from carbohydrates and
1/3 from fats.
v A high intake of fats, especially
saturated fats, is a contributory factor in causing heart disease.
Proteins
v Main function: as a source of amino
acids which are used to synthesized new proteins
v Plants are able to synthesize all
their own amino acids but animals are more limited.
v Thus man requires essential amino
acids in the diet.
v Although plant food contains
proportionately fewer proteins, a properly balanced diet can nevertheless
provide all the essential amino acids.
Vitamins - group of
organic compounds with the following features:
1. no energy value
2. essential in very small quantities for maintenance of good health
3. not structural materials in body
4. work as cofactors in enzymatic reactions
Two groups of
vitamins:
A.
Fat
soluble vitamins and
B.
Water
soluble vitamins
VITAMIN SOURCES DEFICIENCY
A MILK,
CARROT, SOURCES DRY
SKIN, POOR VISION
B1 CEREALS,YEAST,
LIVER BERI BERI
B2 MILK,
LIVER , VEGETABLE SORE
THROAT
C FRUITS,
VEGETABLES SCURVY
D EGG-YOLK,
COD-LIVER OIL RICKETS
E BUTTER,
PEANUT, EGG YOLK ANAEMIA
K FISH,
LIVER, VEGETABLES INABILITY
OF THE BLOOD TO CLOT
Too much vitamins, e.g. vitamin A, may be harmful to our body
**Vitamins B & C are water
soluble; others fat soluble
**Vitamin C could be destroyed by prolonged heating; tested by
decolorizing deep blue colour of DCPIP; and vitamin C has relatively larger daily requirement than other
vitamins
Minerals
v needed to regulate the metabolism of
the body
v essential for health
v needed in small amounts
MINERAL SOURCE FUNCTION/DEFICIENCY DISEASES
1. CALCIUM & PHOSPHORUS CHEESE,
MILK, VEGETABLE BONES& TEETH FORMATION/BLOOD CLOTTING
2. IRON LIVER,
EGG, BEEF FORMS
HAEMOGLOBIN/ ANAEMIA
3. IODINE SEA
FOOD THYROXINE
FORMATION/ GOITRE
4. SODIUM & POTASSIUM TABLE
SALT & VEGETABLES ANION &
CATION BALANCE,
/MUSCLE CONTRACTION
5. CHLORINE TABLE
SALT ANION
& CATION BALANCE / FORMS HCL
Water
ü - makes up about 75% of body weight
ü - importance:
ü as a solvent;
ü for transport;
ü as a reaction medium;
ü as a reactant;
ü dilutes wastes & poisons;
ü forms urine
Roughage/Dietary fibre
ü - consists of cellulose
ü - indigestible because
ü - human body has no enzyme for its
digestion
ü - stimulate peristalsis;
ü - absence will lead constipation
Milk
Milk is a balanced diet for growth and development of young mammals, but
it cannot sustain healthy development indefinitely because:
1. It contains little if any iron - new born baby has Fe accumulated
from mother, but store becomes deficient in later life
2. It contains no roughage - constipation results with its long-term
absence from diet
3. It contains a high proportion of fat
- ideal for young and actively growing organisms, but as energy demand
decreases, more fat deposits around the body would increase risk of heart
disease
•
Food
additives – examples:
- colourings,
- preservative,
- antioxidants,
- texture enhancers,
- synthetic flavourings,
- flavour enhancers and
sweeteners
Feeding mechanisms
A. Small-particle feeders – microscopic food, e.g. bacteria, unicellular
algae or small invertebrate larvae, etc., are eaten by unicellular organisms
like amoeba, paramecium
B. Filter feeding mechanism: microscopic foods are removed from the
surrounding water by some form of filtration mechanism, e.g. mussel
See Figure 2 and 3
C. Large-particle feeders - involving ingestion of particles which are
relatively large, e.g. most mammals
D. Fluid
and soft-tissue feeders - a mechanism to pierce their 'host' in some way and
then use a specialized suction apparatus for drawing food into their bodies, e.g. mosquito
See Figure 4, 5 and 6
Teeth and dentition in
man
•
The structure of the tooth
•
Enamel - non-living substance containing 97% calcium salt & 3% organic
matter; cement forms the root of enamel; fibres attach to jawbone for anchorage forming periodontal membrane
•
dentine -
hard but softer than enamel; with
channels of living cytoplasm from pulp cavity
•
pulp cavity - contains living cells with blood
vessels (supply food & O2) and nerves (sensation)
TYPES OF TEETH
See figure 7:
Types of teeth
•
Incisors
- at the front; chisel-like for biting & cutting
•
Canines
- pointed, curved & long for tearing flesh; in carnivores, they are well developed for
killing preys
Premolars - with one or two cusps for grinding & crushing food
Molars - have 4 cusps for grinding & crushing food
Wisdom teeth - last 4 molars; grow after the age of 20
Milk Teeth and Permanent Teeth
•
-
man is diphyodont: two sets of teeth
1.
Milk teeth - appear in babies; totally 20 in man
2.
Permanent teeth - replace milk teeth in later years;
cannot replaced if damaged; totally 32 in man
TOOTH DECAY
See Figure 8:
Dental decay (dental caries)
•
Cause
of tooth decay - results from a chemical reaction between bacteria &
food debris in mouth; bacteria forms a sticky, invisible film (plaque) reacting
with sugars to produce an acid which dissolves enamel, dentine & pulp
cavity
¾®
toothache ¾® more serious ¾®
periodontal disease ¾® teeth falling off
Calculus: hard deposits due to interaction of plaque & salts in
saliva
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
See Diagram A:
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
See Diagram B:
*
*Carboxypeptidase liberates Exopeptidases
acts on Aminopeptidase
breaks
terminal amino acids terminal
amino acids terminal
amino acids with –NH2 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 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
Digestion in Humans
A. 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
See Figure 9 and 10:
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
•
5. Taste buds allow food to be
selected.
The thoroughly chewed
food (bolus) is passed to the back of the mouth for swallowing.
Swallowing and
peristalsis
- pharynx leads to both
trachea & oesophagus
When swallowing food,
epiglottis closes entrance to trachea to prevent food going into lungs
See Figure 11 and 12:
Peristalsis - longitudinal & circular
muscles contract & relax alternately to drive food down oesophagus, small
intestine, large intestine & out of the anus as faeces
See Figure 13 and 14
and 15:
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:
1.
Gives an acid pH
to kill bacteria and activates enzymes in the stomach (pepsinogen &
prorennin);
Initiates the hydrolysis of sucrose & nucleoproteins
See Figure 16A B and C:
2. Pepsinogen - secreted by the zymogen (chief cells) in an inactive
form to pepsin
3. 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 produce 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.
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
global spread of obesity has been fueled in large part by the growing
availability and popularity of the Western-style diet, which is
characterized by foods with high contents of sugars, salt, and fat —
particularly from processed foods and red meat.