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Heterotrophic Nutrition
Nutrition is the process of acquiring energy and materials for cell metabolism,
including the maintenance and repair of cells and growth
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g
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g
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g
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g
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Holozoic: complex food is taken into a digestive system and broken down into
small pieces to be absorbed
2
...
Parasitic: obtain food from other organisms (host)
Digestion: reducing large complex molecules into smaller ones
Absorption: taking in soluble molecules from the region of digestion
Assimilation: using the absorbed nutrient for a particular purpose


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Saprophytic nutrition
Saprophytes feed on dead decaying matter (e
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mucor, Rhizopus and yeast)
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Then they absorb the
soluble products and assimilate it (they decompose the dead)
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Ingestion: taking in of food
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Ingestive eaters: use a mouth to ingest food

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Filter feeders: collect small organisms from water (e
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oysters and
mussels)

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Substrate feeders: eat the material they burrow through (e
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earthworms, termites)

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Fluid feeders: pierce the body and withdraw fluids (hummingbirds)

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Microphagous feeders: relatively small particles (e
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earthworms, filter
feeders)

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Macrophagous feeders: relatively large particles (e
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hydra, sea
anemones, sharks)

2
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Absorption: uptake of soluble molecules from the gut into tissues
4
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Egestion: elimination of indigested waste food material
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In humans, digestion and absorption occur in the alimentary canal / gut
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Accessory
organs are connected to the main system by a series of ducts

Layer
Mucosa

Structure

Functions

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Absorbing & secreting layer, secretes

2
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Muscularis mucosa

enzymes, hormones, prevents digestion
of the gut wall, epithelial cells have a
‘brush border’ of microvilli to increase SA
2
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Layer of smooth muscle that help to
produce

fold

of

the

mucosa

and

submucosa
Submucosa

1
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Mucus secreting glands which secrete

2
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Meissner’s

1
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Mass of nerve tissue which controls

Plexus

secretion from glands

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between submucosa &
circular

muscles

of

muscularis externa
Muscularis
Externa

1
...
Control

2
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Shorten the gut when they contract &

3
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Between the circular &
longitudinal,

1
...
Controls peristalsis, sympathetic nerves
cause the gut muscles to relax and the
sphincters

to

close,

parasympathetic

nerves stimulate the gut wall to contract
and sphincters to open
Serosa

1
...
Mesenteries support and suspend the

2
...
Lines of abdominal cavity and froms the

of

stomach and intestines from the body
wall

containing

blood

vessels

and lymph vessels
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The
muscular tongue mixes and moistens the food with saliva
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The eye
and the olfactory receptors stimulate salivary glands in the mouth to secrete saliva
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It also contains mucus and
various mineral salts including Cl- which speeds up the enzyme activity
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Lysozyme kills
bacteria by breaking down their cell walls
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To prevent the food from
entering the trachea, the larynx closes, the soft palate is pulled up and the epiglottis
covers the entrance of the trachea
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They
masticate food into small pieces
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Humans have two sets, deciduous and these
are replaced by the permanent teeth
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The
arrangement is expressed as the dental formula
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The entry of food in to the
oesophagus stretches the muscles of the gut
...

When the bolus reaches the end of the oesophagus it passes through the cardiac
sphincter, into the stomach
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The stomach
It stores food temporarily, releasing food slowly into the rest of the gut
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The stomach is dotted with gastric pits which lead to gastric glands
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There are two specialised types of cell in gastric glands:
1
...

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2
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Pepsin hydrolyses proteins into smaller polypeptides
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Rennin coagulates casein into the insoluble calcium salt of casein
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The stomach also secretes the hormone gastrin
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The slow introduction of food into the small intestine enables it to work on a little
material at a time
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It has three parts; the duodenum, jejunum and
ileum
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These villi have microvilli
to further increase the SA for absorption
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In these crypts:
-

New epithelial cels are made

-

Some secrete intestinal juice, a slight alkaline fluid and mucus

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There are paneth cells which secrete lysozyme

Throughout the small intestine, goblet cells secrete mucus which lubricates the food
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Digestion in the small intestine
The liver and pancreas – provide many enzymes and secretions
The liver synthesises bile from cholesterol which is stored in the gall bladder until it
is needed to assist to fat digestion
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It contains bile
salts which act as a natural detergent, emulsifying large fat globules into smaller
droplets, increasing SA on which lipase can act (emulsification) – mechanical
digestion
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Trypsinogen is activated to trypsin by an
enzyme called enterokinase
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The small intestine also contains enzymes
bound to the cell surface membranes of
the microvilli
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Monosaccharides, dipeptides and amino
acids are absorbed either by diffusion or
active transport
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The lipid molecules are coated with
proteins called chylomicrons
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Inorganic salts, vitamins and water are absorbed in the small intestine
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The large intestine (colon)
The sphincter muscle between the ileum and the caecum opens and closes to allow
small amounts of material into the intestine
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Epithelial cells secrete mucus which lubricates the solidifying undigested food
remains (faeces)
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The appendix with no known function
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They have a diastema, which provides space for
the tongue to manipulate the cropped grass
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The jaw joint is very loose and
allows forward, backward and sideways movement
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Ruminant stomach
Most herbivores do not produce cellulase to break down cellulose
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A ruminant is an animal in which the ‘stomach’ has several chambers to maximise
the benefits of their endosymbiotic microorganisms
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The acid is absorbed
and used as a major source of energy in respiration
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The food is regurgitated and thoroughly re-chewed, the food undergoes further
fermentation
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Smaller herbivores have a caecum branching off the large intestine
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They produce two types: pure waste discarded) and one
consisting mostly of caecal material, which they re-ingest
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They need long canines to grip and kill prey and carnassials teeth to scrap flesh
off bones
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