Modes of nutrition
1.
Heterotrophic nutrition
2.
Autotrophic nutrition
Depends on: - energy source
- carbon source
2007 Heterotrophic Nutrition
Mode of Nutrition
Autotrophic
Carbon Source
P. 1
Heterotrophic
Energy
Source
Phototrophic use light energy use CO
2
(inorganic) to build up their food (organic substance)
Photoautotrophic
(Photosynthetic) e.g. all green plants, blue-green bacteria

Producers: transforming solar energy into biomass / organic compounds use organic source of C
(cannot build up their own food)
Photoheterotrophic few organism e.g. some purple non-sulphur bacteria
Chemotrophic use chemical energy released from reactions / oxidation
Chemoautotrophic
(Chemosynthetic) a few bacteria, e.g. Nitrifying bacteria and some other nitrogen cycle bacteria

aids recycling of nutrients between environment and biomass
Chemoheterotrophic all animals and fungi, most bacteria, some plants e.g. dodder (parasitic)

comsumers of various trophic levels (Holozoic animals, detritivores included, and parasites)
decomposers (saprophytic bacteria and fungi) that acquire energy through decomposition and recycle nutrients to producers and
the environment.)
Decomposer = a heterotrophic organism which feeds on dead organic matter; being a saprophyte or saprozoite.
∴ nitrifying bacteria oxidize inorganic nitrogen compounds (e.g. ammonium compound / nitrite) into nitrate, thus they are not decomposer.
1

2007 Heterotrophic Nutrition P. 2
How do the differences in energy acquisition amongst living organisms determine their ecological roles?
(94-II-1, 95-II-5, 2001-II-6)

- energy cannot be recycled in Ecosystem:
-- solar energy captured by photoautotrophic producers into chemical energy (biomass).
-- chemical energy released by oxidation of inorganic substances such as ammonium compound / nitrite is converted into chemical energy of organic biomass
-- energy (biomass) flow from producers to heterotrophic consumers through food chains
(Predator-prey relationship, parasite-host relationship)
-- energy loss to environment as heat at each trophic level and is not available to living organisms again.

- nutrients can be recycled in Ecosystem:
-- nutrients and inorganic carbon (CO
2
) absorbed by photo-autotrophic producers , green plants and chemoautotrophic nitrifying bacteria for the synthesis of organic food.
-- organic food (in tissues) flow from producers to chemo-heterotrophic consumers through food chains
-- recycle of locked nutrients / organic substance (food remains, undigested / egested, excreted materials and dead bodies into inorganic substance by chemo-heterotrophic decomposers for growth of producers
-- chemo-autotrophic nitrifying bacteria convert nitrogen compounds into nitrate for plants
(revision)
Ecosystem has its energy and nutrients input, output and conversion. Organisms of an ecosystem are linked by their energy and nutrient relationships.
Direction
flow of energy:
flow of nutrients:
Input from:
Sun
Soil, air and water bodies t hrough producers consumers :
Energy flow,
Nutrient flow
and
Energy lost as radiation to space
Decomposer
* - Ultimate source of energy for all life form on earth is radiation of sun (solar energy)
- utilizing the fixed energy (in form of chemical energy) in assimilated tissues and stored food.
- most energy flow is unidirectional (dissipated as heat during respiration) so continuous supply of energy from sun is essential
- while chemical matter can be recirculated
2

2007 Heterotrophic Nutrition P. 3
[HKALE 94 II]
1. (c) Using an annotated flow chart, illustrate how energy flows and carbon is cycled through photoautotrophic and chemoheterotrophic organisms. Indicate the roles of respiration and photosynthesis in the flow chart. (10 marks)
(c)
- route of energy flow showing loss at each level
- route of carbon showing recycling
- annotations ( marks indicated in brackets in the above flowchart )
- respiration ( suitably put in thee flowchart )
- death and consumption/feeding ( suitably put in the flowchart )
2
2
5
1
1
Note: - route of carbon should include autotrophs, animals and decomposers.
3

2007 Heterotrophic Nutrition
Heterotrophic Nutrition
P. 4
Heterotrophs
= organisms that must obtain their energy and nourishment form the organic molecules manufactured by other organisms.
Three types of heterotrophic nutrition:
1.
Saprophytic Nutrition,
2.
Parasitic Nutrition and
3.
Holozoic Nutrition
1. Saprophytic nutrition
Organisms feeding on soluble organic compounds obtained form dead animals and plants.
Example: Bread moulds (e.g.
Mucor and Rhizopus)
Feeding hyphae
Adaptive feature of bread mould
[89-II-7b]
Mycelium consists of a mass of delicate braching hyphae which penetrate into substratum
Braching rhizoid-like hyphae
To increase the
Significance surface area to volume ratio contact with food (substratum)
for
Secrete enzyme extracellurlarly to digest food into simple, soluble and absorbable form, then the digested food is being absorbed by diffusion through the surface of rhizoids..
Thin cell wall of hyphae Facilitates the secretion of digestive enzymes and absorption of the digested food.
* absorbed simple substances are assimilated by the saprotroph.
( anchorage provided by rhizoids and spore formation for reproduction is not related to its adaptation for nutrition)
4

2007 Heterotrophic Nutrition P. 5
Advantages of various saprophytes to human being
✌ recycle nutrients such as carbon and nitrogen and so maintain atmospheric composition and soil fertility (as decomposer)
✌ source of food e.g. mushrooms
✌ baking bread and brewing wines and beers using yeasts
✌ manufacture of foods e.g. cheese
✌ production of antibiotics e.g. penicillin
✌ aerobic decomposition of sewage
✌ involves in biotechnological processes, e.g. production of hormones, vitamins, enzymes, fuels.
5

2. Parasitic nutrition
- Parasites:
2007 Heterotrophic Nutrition P. 6
= Organism which feed on complex organic food derived from other living organism by living in or on its host
-- They are usually harmful to their host.
- types of parasitism: i. Endoparasites
Ectoparasites ii Facultative parasites
Obligate parasites
What are the main advantages of a parasitic mode of life?
1.
food available in a readily usable form
2.
parasites need not maintain a complex digestive system; a relatively constant supply of food, digestive system is degenerated.
3.
parasites is buffered to some degree from the external environment, live in a homeostatically controlled environment
4.
parasite is afforded protection from predators; degenerate sensory system
5.
Reproductive system is especially well developed
Problem faced and adaptation used by parasites e.g. Tapeworm (Taenia solium)
Tapeworm ( Taenia solium )
- Two hosts involved in life cycle
- adult stage live in primary host (man)
- immature stage live inside secondary host (e.g. pig or ox)
- Show different response in a day
- day time (1200-1600)
- move to posterior region of gut where digestive actions are less active.
- night time
- move towards the anterior part of gut where is less active (digestive action)
- more digested nutrient are available
1.
Access to host tissue (Adaptation: a, b and g)
❀ attachment to host tissue
❀ the body of host are often lined / equipped with a protective layer / mechanism against invading organisms
2.
Feeding (Adaptation: d)
❀ the parasites must be able to derived nutrients form their hosts but at the same time not to kill hosts to deprive themselves of food
3.
Reproduction and transmission (Adaptation: f, g)
❀ parasites must be able to reproduce transmission; able to spread offspring
❀ offspring must be able to find a suitable habitat / host to develop
4.
Protection against host reactions / adapt to adverse condition in the host (Adaptation: c, e)
❀ small intestine has enzyme that is able to digest parasites
6

2007 Heterotrophic Nutrition P. 7
Problems to parasitic mode of life a.
Attachment to the host
Adaptation to parasitic mode of life in tapeworm ( Taenia solium)
Special features Adaptations
Scolex with hooks and suckers
Elongated body
Attach it firmly to the intestinal wall of the host to prevent it to be removed away during peristalsis
Fit the course of the intestine. b.
Fitting itself inside the host c.
Shortage of oxygen d.
Obtaining nutrients efficiently e.
Host reaction f. Reproduction g. Transmission
(through a second host) h. Others
Anaerobic respiration i.
Live in small intestine. ii.
Elongated, flattened body dorsoventrally iii.
digestive system is degenerated
Cover the strobila (body) with mucus i.
Continuous production of new proglottids behind the neck. ii.
The adult is a hermaphrodite iii.
Each proglottid produces a large number of eggs i.
Embryo (hexacanth embryo) is enclosed by an egg shell ii.
Embryo bears hooks
Degeneration of i.
locomotory system. ii. sense organs
Produce energy inside the small intestine
Bath in a medium of digested food which is immediately available
Increase the surface area to volume ratio for absorption of the digested food by diffusion and active transport through the body surface
No need to digest food.
Protect it against the digestive juices of the host.
Keep a large number of reproductive units.
Avoids the trouble of finding a mate inside the host
Increase the chance to infect the secondary host
Protect it against the adverse conditions in soil and faeces to increase the chance of getting in touch with the pig’s food and infect the latter.
Penetrate into pork (and develop as a bladder worm ) , as pork is a favourite food of man that increases the chance of infecting man.
No need to find food which can easily be absorbed form its surroundings.
No great change of stimuli in the relatively stable environment of the small intestine.
7

2007 Heterotrophic Nutrition P. 8
Compare and contrast saprophyte with parasite.
Similarity
★ are heterotrophic ★ absorb soluble food ★ produce large no. of offspring
Differences
Parasites
Energy derived from living organisms
Very specific to host
Very specialized and highly adapted means of obtaining their food have simple digestive systems where they are present
Saprophytes
Energy derived from dead organisms
Use a variety of food sources
Simple methods of nutrition no digestive system is needed for digestion outside body.
8

3. Holozoic nutrition\
2007 Heterotrophic Nutrition P. 9
Organism obtains energy from the consumption of complex organic food which is digested within their bodies into simple molecules. Digested substances are then absorbed and be assimilated.
The main processes of nutrition (Five Stages)
Ingestion Food is taken into the alimentary canal through the mouth
Digestion
Absorption
Assimilation
Egestion
Food is gradually broken down into smaller simpler, diffusible and absorbable molecules that can be absorbed by the body i. physical digestion
(breaking up of food into pieces by mechanical actions) ii. chemical digestion
(breaking up food substances into smaller, simpler molecules by chemical means in the presence of enzymes)
Uptake of small, simple and soluble molecules ( digested products ) through the epithelium of the alimentary canal into the bloodstream the conversion of the absorbed food into the body materials of the animal
(The absorbed food is transported via blood to body cells for various purposes, ) e.g. building up new tissues
The removal indigested and unabsorbed materials from the body as faeces
(reference)
Holozic organisms can be classified according to the type of food ingested.
Herbivores: VS Carnivores: VS Omnivores:
Liquid feeders VS Phagotrophs
Macrophageous feeders VS Microphagous feeders (mussels)
* insectivorous plants (e.g. Pitcher-plants) are partly holozoic. various structure of mouth parts / feeding mechanisms of organisms and their way to obtain food are related to the different in their food habits
9

2007 Heterotrophic Nutrition
I. Ingestion and Swallowing
Mastication
P. 10
Food is chewed by teeth and mixed with saliva in the mouth
Swallowing
Process [swallowing is initially a voluntary action, but once begun it continues involuntarily to its completion. It is a reflex action controlled by the swallowing center in medulla oblongata (and the lower portion of the pons) of the brain]
The tongue rolls the food into a soft bolus which is ready to be swallowed
The tongue rises upwards and backwards and forces the food bolus to enter the pharynx
The soft palate moves up to prevent the food from entering the nasal cavity
The larynx moves up so that the glottis is covered by the epiglottis
The food bolus then passes along the oesophasgus to the stomach
10

2007 Heterotrophic Nutrition P. 11
(reference and revision)
Mastication
- cut solid food into smaller pieces by teeth

- facilitate swallowing
- increase surface area for enzymatic reaction
- can be considered as physical digestion
Structure
The structure of a Mammalian tooth (through the longitudinal section)
Feature
External structure
Crown
Neck
Root
Enamel
Dentine
The visible part that is exposed above the gum
A narrow region between the root and the crown, surrounded by the gum
The part that is embedded in the jaw bone
( the cavity in the jaw bone in which a tooth embeds is called a socket)
The outermost, hardest layer of the crown
A non-living layer, the hardest substance of the body , contains calcium salts
Forms a hard biting surface and protects the tooth from mechanical damage
The middle layer of the tooth, makes up most of a tooth
A bone-like substance, softer than enamel
Internal structure
Has fine channels of living cytoplasm running through
Pulp cavity The cavity at the center of the tooth filled with pulp (a soft connective tissues)
Contains blood vessels to supply nutrients and oxygen
Contains nerves responsible for the sensations of temperature, pressure and pain
Cement A thin calcified connective tissue layer of substance covering the dentine in the root
Attached to the periodontal membrane and allows to fix the tooth on jaw bone
Periodontal membrane
A strong fibrous membrane, fix the cement firmly to the jaw bone
Allows the tooth to move slightly and absorb the shock when biting hard food materials
(this reduces the risk of tooth breaking when hard food is chewed)
Root canals : - narrow extensions of the pulp cavity
---> through them, blood vessels and nerves reach the pulp cavity
- widely open in herbivores for continuous growth of the tooth (i.e. with open root)
11

2007 Heterotrophic Nutrition P. 12
(reference)
Type and function of mammalian teeth most mammals have different types of teeth (i.e. heterodont)
Type of teeth
Incisor
Canine
Premolar
Location
At the front of the jaw
Beside the incisors
At the sides of the jaws
Feature
Sharp and chisel-like shaped
(with a sharp cutting edge) may be pointed in carnivores
Sharp and pointed
curve backward
may be unspecialized or absent in herbivores or omnivores
Large and flattened top with cusps (pointed elevations)
or with ridges on flat surfaces in herbivores
Function for biting and Cutting food into small pieces
Piercing and tearing food
(grip the prey tightly or killing prey)
Crushing bones, tearing flesh / grinding vegetations
Molar At the back of the jaws, behind premolars
Similar to premolars, but are larger in size
Crushing and grinding food
( Premolars differ from molars in that the molars are present only in the permanent dentition, but not in the milk dentition)
Dentition and dental formula
Dentition
The number and arrangement of different types of teeth in a mammal
-- can be shown by dental formula
Dental formula Shows the number and types of teeth on one side of the upper and lower jaws
Dentition of man: diphyodont (i.e. two sets of teeth), wisdom teeth (the last 4 molars) usually grow after the age of 20
12

2007 Heterotrophic Nutrition P. 13
Tooth decay
Periodontal disease
(reference )
Cause
Consumed a lot of candies, sugary snacks and sugary drinks
Tooth problems
Process
Formation of invisible, sticky plaque on the tooth surface
Bacteria in the plaque feed on the food trapped on or between the teeth
Bacteria breaks down sugars and produces acids that dissolve away the enamel to form small holes
The acids will eventually attack the dentine and pulp cavity and casue pain
The accumulation of the plaque in the neck region of the teeth
The accumulated plaque will gradually change into calculus
Bacteria will produce toxins around the gum and cause inflammation
The disease may spread to the roots and the tooth may become loosen and may finally fall out
Method
Have a balanced diet to obtain enough calcium, phosphate and vitamin D
Avoid too much sugary foods
Oral health
Purpose
Necessary for maintaining healthy teeth
Prevent sugars from broken down to acids by bacteria
Clean your teeth with toothpaste containing fluoride Strengthen the teeth and prevent tooth decay
Brush your teeth after meal or at least twice a day
Brush your teeth in a correct way
Choose a toothbrush that is not too hard and not too soft
Develop the habit of using dental floss after meal
Have regular dental check-up
Effectively remove the plaque on teeth surfaces and food debris trapped between teeth
Help to identify any signs of tooth problems and allow to save the tooth
13

2007 Heterotrophic Nutrition P. 14
The dentition and the jaw movements closely related to the mammals’ diet and methods of feeding.
Comparison between the dentition between a carnivore, herbivore and omnivore (1985-I-2, 1992-II-1a)
Example Dog (carnivorous dentition) Rabbit (herbivorous dentition)
1. Diet Carnivorous
2. Incisor ❀ small and pointed for holding prey, cutting and nipping off tearing away flesh near bone surface
3. Canine ❀ Long, shape and tearing flesh. pointed for killing prey and
❀ curved backwards to grip for holding the prey more firmly to prevent its escape.
Herbivorous
✞ sharp cutting edges for cropping of vegetation
✞ chisel-shaped for gnawing
✞ incisors in upper jaw may be replaced by a horny pad (e.g. in sheep) to facilitate biting off vegetation when lower incisors press against the pad.
Either:
✞ absent (e.g. rabbit) and leaving a space between incisors and premolars (called diastema)
 to provide a space to facilitate manipulation of plant matter or
✞ reduce and unspecialized – looked like the incisor
(as in the lower jaw of sheep)
✞ large flattened and parallel ridges on surfaces

for grinding vegetations.
4. Premolar
& molar
❀ With s harpe ridges ( cusps ) for tearing flesh and crushing bones.
❀ The last upper premolar and the first lower molar are especially enlarged with sharp edges and They are known as carnassial teeth . They fit nicely into each other.

- slicing flesh from bones
- cracking bones open for the bone marrow.
5. Growth ❀ growth of tooth stops at a certain stage due to closure of pulp canal.
6. Jaw movements
❀ up and down ‘ vertical biting’ jaw movement

to facilitate the shearing action of the cheek teeth.
(scissor-like)
✞ teeth subjects to continual wear, pulp canal retains opening (open root) and grow throughout life/ continuous growth
✞ backwards and forwards or sideways as well as up and down a facilitate the grinding action.
Man (omnivorous dentition)
Omnivorous
☭ flat with sharp edges for cutting and biting food.
☭ slightly pointed (but are not elongated) for assisting the general chewing action
(grinding vegetables and tearing flesh) .
☭ rounded cusps to provides efficient chewing, crushing and grinding food.
☭ growth of tooth stops at a certain stage due to closure of pulp canal .
☭ up and down and considerable sideways movement
14

2007 Heterotrophic Nutrition P. 15
15

2007 Heterotrophic Nutrition P. 16
II.
Digestion
- breaking down large and complex food molecules to chemically smaller, simpler, soluble and diffusible molecules by actions of digestive enzymes
---> - small size facilitate nutrients pass across the intestine wall into bloodstream
- soluble form facilitate transport in blood to tissue
- facilitated by mechanical actions to break solid food into smaller pieces
---> increase surface area for digestive enzymes to act on
(since digestive enzymes act only on the surfaces of food particles, the rate of digestion is absolutely dependent on the total surface area exposed to the digestive secretions.)
Table 10: Types of human digestion
Action
Mechanical digestion
Chemical digestion
Chewing action of the teeth
Churning action by rhythmical contraction of the stomach into a creamy semi-fluid ‘chyme’ peristaltic contractions of gut walls along the alimentary canal emulsification of lipid by bile salt
Involves secretion of digestive enzymes from salivary glands, gastric glands, pancreas and intestinal glands
Carbohydrases: digest carbohydrates into simple sugars
Lipases: digest fats into fatty acids and glycerol
Proteases: digest proteins into amino acids
16

2007 Heterotrophic Nutrition P. 17
The digestion of carbohydrates, proteins and lipids in various parts of the alimentary canal
---- the functions of carbohydrase, amylase, protease and lipase.
Substrates for digestion
Carbohydrates Cellulose
Starch
Digestive enzymes involved
(digestive juice – site of digestion - condition)
Nil
Amylase
(saliva – mouth - slightly alkaline, pH~7.5)
(pancreatic juice – duodenum - alkaline)
Others carbohydrates
(maltose, sucrose, lactose)
Various type of carbohydrase
(intestinal juice – in epithelial cells of small intestine - alkaline)
Protein Proteins
Peptides
Proteases
(gastric juice – stomach – acidic, pH ~ 0.8)
(pancreatic juice – duodenum - alkaline)
Peptidases
(pancreatic juice – duodenum - alkaline)
(intestinal juice – small intestine – alkaline, pH 7.5 to 8.0)
Action
Nil
Starch  maltose
( glycogen and most carbohydrate except cellulose
 disaccharides and a few trisaccharides)
Disaccharides
Protein

Peptides

monosaccharides
peptides (+ amino acids)

amino acids
Lipids Lipids Lipase
(pancreatic juice – duodenum- alkaline)
(intestinal juice – small intestine - alkaline)
* Bile contains no enzyme! Bile salts (/ bile acids) act as emulsifying agents to lower surface tension of fats into oil droplets and forming micelles ( without the presence of bile salts, up to 40% of the ingested lipids are lost into the feces).
This is a physical process and lipid molecules are chemically unchanged..
Lipids  fatty acids + monoglycerides + glycerol
Bile salts
* insoluble fatty acid ----------------- > soluble soaps
(can’t be absorbed directly) (can be absorbed)
with 94% of bile salts reabsorbed into blood from small intestine
bolus = a rounded mass; lump of chewed food.
chyme = the partially digested food after leaving the stomach
chyle = the milky fluid that after digestion of the food. It is readily to be absorbed into blood. / or
= lymph containing globules of emulsified fat, found in the lacteals during digestion.
17

2007 Heterotrophic Nutrition P. 18
Sources and actions of digestive secretions (name of individual enzymes are not required)
Site of action
Mouth
Source
3 pairs of Salivary glands
Secretion
Saliva (slightly alkaline)
- about 1.5 L by man per day
Constituents
Salivary amylase
Lysozyme
Mucus (water + mucin)
Salts hydrogencarbonate
Stomach Gastric glands at
‘gastric pit’of stomach wall
Duodenum
(main site of digestion in gut)
Liver (secretion) gall bladder (storage)
- via bile duct
Pancreas
- via pancreatic duct
Gastric juice
(acidic)
Bile (alkaline)
- no enzyme
Pancreatic juice
(alkaline)
HCl (pH ~ 0.8)
[by parietal (oxyntic) cells]
Mucus [by moucous neck cells, no goblet cells]
Protease (pepsinogen
 pepsin)
[by chief (peptic) cells]
Sodium bicarbonate
Bile salts
Bile pigments
Sodium bicarbonate
Amylase
Protease (trypsin)
Peptidase
Lipase
Nuclease
Consequence
Starch

maltose
Attack bacterial cell wall
Lubrication of food mass/ stick bolus
maintain correct pH
buffer action provides almost neutral (pH about 7.5) medium for the action of salivary amylase
prevent tooth decay (enamel may dissolved by acid)
provides acidic medium fro the activities of protease
non-enzymatic hydrolysis of food
loosens fibrous and cellular components of tissue
sterilizing effect ( kills germs / inhibits bacterial growth)
stops the action of salivary amylase
activate protease [pepsinogen

pepsin]
further stimulation of gastic juice secretion
Protection of stomach lining against the action of protease (avoid self-digestion) and mechanical damage
Lubricate the food
Protein

peptides
Neutralization of stomach acid and stop action of pepsin on chyme
Provide alkaline condition for pancreatic and intestinal enzymes
Slow down growth of bacteria which can resist acidic condition.
Emulsification, formation of micelles [  increase S.A. to volume ratio for action of lipase in small intestine and hence increase the efficiency of lipid digestion]
Activates pancreatic lipase
Facilitate absorption of insoluble fatty acid
Breakdown product of haemoglobin for excretion
Neutralization of stomach acid and stop action of pepsin
Provide alkaline condition for pancreatic and intestinal enzymes
Starch  maltose
Protein  peptides + amino acids
Peptides

amino acids
Fat

fatty acids + glycerol +monoglycerides
Nucleic acids  nucleotides
18

2007 Heterotrophic Nutrition P. 19
Site of action
Small intestine
duodenum
jejunum
ileum
Source Secretion
Wall of small intestine Intestinal juice
(alkaline, pH 7.5 to
8.0 )
[contains a variety of digestive enzymes secreted by crypts of
Lieberkuhn from duodenum to ileum]
Constituents
Carbohydrases:
maltase
sucrase
lactase
Aminopeptidase
Nucleotidase
Lipase
Alkaline mucus
[by Brunner’s glands in sub-mucosa]
(pH 7 to 8)
[by goblet cells among the simple columnar epithelial cells and Brunner’s glands in sub-mucosa in duodenum but absent in jejunum and ileum]
* the lining of the whole alimentary canal is coated by mucus i.
- as a lubricant to aids peristalsis;
- protected from mechanical damage; or / and
- prevent self-digestion of alimentary wall by digestive enzymes (protease and lipase)
Consequence
Maltose  glucouse
Sucrose  glucose + fructose
Lactose  galactose + glucose
Peptides

amino acids
Nucleotides

pentose + phosphoric acid + organic N- bases
Fat  fatty acids + glycerol + monoglycerides
- lubrication of food mass
- protection of intestinal lining against the acidic chime from stomach and the action of activated enzymes
- Provide alkaline condition for pancreatic and intestinal enzymes
* mucus contain a globular protein to which short-chain polysaccharides are added before mucus is secreted, making a glycoprotein. When secreted, if they come into contact with water, glycoproteins swell up (imbibition) to become sticky and gel-like. ( * mucin = a slimy protein)
19

2007 Heterotrophic Nutrition P. 20
III.
Absorption
Absorption of digested products through the gastrointestinal mucosa by - osmosis (water)
Water is transported by osmosis from dilute chyme into intestinal mucosa into blood of villi
(conversely, from the plasma into the chyme when hyperosmotic solutions are discharged from the stomach into the duodenum)
- simple diffusion
- facilitated diffusion
- active transport
Digestion results in the formation of relatively small, soluble molecules which, provided there is a concentration gradient, could be absorbed into the body through the intestinal wall by diffusion. This, however, would be slow and wasteful and in any case, if the epithelial lining were permeable to molecules such as glucose, it could just as easily result in it diffusing out of the body when the concentration in the intestines was too low. For these reasons most substances are absorbed with the aids of active transport which only allows inward movement.
For example:
- glucose and amino acid absorption appear to be linked to the active transport of sodium ions across the membranes of epithelial cells microvilli; then carrier protein transports glucose out of the cell (higher concentration) by facilitated diffusion then into blood capillaries (lower concentration). Thus blood flow in the capillary remove the glucose constantly for maintaining the glucose concentration gradient within the cell.
- pinocytosis
- and possibly solvent drag
(i.e. any time a solvent is absorbed because of physical absorptive forces, the flow of the solvent will ‘ drag ‘ dissolved substances along with the solvent.)
* calcium ion absorption requires the presence of vitamin D.
20

2007 Heterotrophic Nutrition P. 21
21

2007 Heterotrophic Nutrition P. 22 before intestine: there is very little absorption
Stomach
(or even in buccal cavity)
A small quantity of simple food substances. e.g. water, minerals, alcohol and simple sugars, are absorbed into blood.
Small intestine:
Absorption of the digested food substances in the stomach and intestine
Food substances absorbed ( water moves by osmosis)
Duodenum & esp.
Ileum
- occurs mainly by combination of diffusion and active transport
into blood vessels via capillaries of villi:
-- amino acids, monosaccharides, water soluble vitamins (vitamin B complex and C), mineral salts, most water, and some triglycerides *(medium-chain triglycerides)
(MCT is rapidly absorbed from the small intestine, intact or following hydrolysis, into the portal circulation. From there, it is transported to the liver.)
-- via hepatic portal vein to liver

for detoxification and homeostatic regulation before it passes to other organs where fluctuation in blood composition could be damaging
- into lymph vessel via lacteal of villi:
-- most glycerol + fatty acids + monoglycerides
(diffuse and be absorbed in form of ' bile-salt micelles 膠團 / 分子團 ' across the lipid bilayer of columnar epithelial cells plasma membrane and be resynthesized into triglycerides molecules (in smooth ER) which is packed with cholesterol and phospholipids and become coated with protein

as 'chylomicrons 乳糜微滴 ' in the epithelial cell of intestinal mucosa and are expelled by exocytosis to pass into lacteal flowing upward through the thoracic lymph duct to empty into the circulatory ) The protein coat keeps the fat in suspension during transport
-- fat soluble vitamins (vitamin A, D, E and K)
(absorption also facilitated by combination with bile salts)
-- chylomicrons are transported via: lacteal

main lymphatic ducts

thoracic duct

left subclavian vein

superior (/anterior) vena cava

heart

circulation some undigested oil droplets pass directly into the epithelial cells of villi by the process called pinocytosis.
22

2007 Heterotrophic Nutrition P. 23
Large intestine
(absorbing colon: the proximal one half of the colon; the distal colon functions principally for storage and is therefore called the storage colon)
The remaining water and some minerals from the waste materials are absorbed at a very low rate: i. water and mineral salts
- the remainder is absorbed and carried back into blood
- excess are passed out of the body with indigested materials as faeces ii. others
- some bacteria in colon produce vitamin B and vitamin K as by-products of their metabolisms and absorbed by host
- malfunction of large intestine

- diarrhoea
- constipation
* MCT is rapidly absorbed from the small intestine, intact or following hydrolysis, into the portal circulation. From there, it is transported to the liver. While long-chain triglycerides are first hydrolyzed in the small intestine to long-chain fatty acids. They are in turen re-esterified in the mucosal cells of the small intestine to long- chain triglyerides, which are then carried by chylomicrons and transported via the lymphatic system to the systemic circulation.
Since MCT, in contrast with long-chian fatty acids, does not require pancreatic enzymes or bile salts for digestion and absorption, MCT is better handled in those with malabsorption syndromes than are the long-chain fatty acids. These syndromes include pancreatic disorders, hepatic disorders, gastrointestinal disorders and disorders of the lymph system.
Fig.
23

2007 Heterotrophic Nutrition P. 24
Process of absorption
Minerals Vitamins Simple sugars Amino Acids Vitamins Glycerol & Fatty Acids
(B complex & C) (A,D,E,K)
Water soluble Fat soluble
Passing through epithelium of villi in ileum by diffusion or active transport
Some Most
Blood capillaries in villi Epithelial cells of villi (Recombining into fats)
Hepatic portal vein Lacteals
Liver Lymphatic system
Hepatic vein Thoracic duct
Left subclavian veins
Vena cava and blood circulation
24

2007 Heterotrophic Nutrition P. 25
IV. Assimilation and fate of absorbed food subtances
Ingested food
Carbohydrates Glucose and other monosaccharides
(starch, glycogen, Blood glucose Oxidized to liberate energy for various cellular activities sucrose, lactose, promoted by insulin, excess glucose is converted to glycogen for storage (in liver and muscle) maltose, etc.) Converted to fat s and stored under skin for storage if too much (storage of glycogen inside liver has reached the maximum) glycogen inside liver
glucose can be used to synthesis of other macromolecules such as fat and protein .
Lipids Glycerol and fatty acids
(fats and oils) triglycerides resynthesized in epithelium of villi
Oxidized to liberate energy (respiratory substrate) for various cellular activities
Synthesized into fat for storage ( in adipose tissues) and deposited under the skin and around internal , or other structural (e.g. phospholipid in membranes) and functional lipids (e.g. steroids)
Secreted out as oil from sebaceous glands
Proteins Amino acids Proteins
Protoplasm (for growth and repair)
Structural proteins (muscles, connective tissues, hairs, nails)
Functional proteins (enzymes, hormones, antibodies, haemoglobin )
Deaminated in liver (excess a.a. are not stored in body)
Carbon skeleton (keto acid)
Convert into glucose and be oxidized to liberate energy + H
2
O + CO
2
,
( Dietary protein Vs protein in our body act as energy source for respiration when under prolonged starvation)
Converted to glycogen or fat for storage
Amino group (-NH2)- Ammonia (which is poisonous and is converted to urea and be excreted by kidneys)
25

2007 Heterotrophic Nutrition P. 26
The composition of human digestive system
Alimentary canal
Components
Mouth (with teeth)

pharynx

oesophagus

stomach

small intestine (duodenum and ileum)

large intestine (colon, rectum, caecum and appendix)

anus
Glands Salivary glands, gastric glands, intestinal glands, pancreas and liver
26

2007 Heterotrophic Nutrition P. 27
The general plan of mammalian alimentary canal (e.g. ileum) and their associated glands (e.g. salivary glands, liver, pancreas)
1. Histology of alimentary canal
- the transverse section of the gut c onsists of the following layers: a. Mucosa
- the innermost layer of alimentary canal i. Epithelium
- the innermost layer
- columnar epithelial cells
- thin
- often equipped with microvilli in small intestine
- all the glands of the digestive system develop from this epithelium ii. Lamina propria
- beneath epithelium
- a layer of loose connective tissues which supports the epithelium
- contains blood vessels, lymphatic vessels, and may contain lymph nodes
- in most regions this layer accommodates glands [e.g. Crypt of Lieberkühn in small intestine (duodenum, jejunum and ileum), gastric gland in stomach] iii. Muscularis mucosa
- the outermost layer of mucosa
- a thin layer of smooth muscle b Submucosa
- a layer of connective tissues (largely composed of collagenous fibres but elastic fibres are also present)
- accommodates blood vessels, lymphatic vessels and nerves
- glands occur in the regions of oesophagus (mucus glands) and duodenum (Brunner's glands) c. Muscularis externa
- inner circular and outer longitudinal muscle layers
- Auerbach's plexus lies between the layers and co-ordinate movement of the two layers
----> peristaltic activity d. Serosa
- a layer of fibrous connective tissue
- continuous with the mesenteries supporting the gut e.
Peritoneum (serous membrane cover the abdominal cavity)
- cover the outer surface of the gut and lines the abdominal cavity
- constitutes the mesenteries which suspend and support the digestive organs in abdominal cavity
- help to reduce friction between organs
(* mesenteries --- a double layer of peritoneum attaching the stomach, small intestine, pancreas, spleen and other abdominal organs to the posterior wall of the abdomen contains blodd and laymph vessels and nerves.)
27

2007 Heterotrophic Nutrition P. 28
28

2007 Heterotrophic Nutrition P. 29
29

2007 Heterotrophic Nutrition P. 30
30

Reference:
2007 Heterotrophic Nutrition P. 31
31

Reference:
2007 Heterotrophic Nutrition P. 32
32

2007 Heterotrophic Nutrition P. 33
Surface of gastric mucosa of stomach
33

2007 Heterotrophic Nutrition P. 34
Lining of ileum
34

2007 Heterotrophic Nutrition P. 35
35

2007 Heterotrophic Nutrition P. 36
36

2007 Heterotrophic Nutrition P. 37
The structure of the alimentary canal for the movement of food
Structure
Epithelium of alimentary canal produce mucus
Circular and longitudinal muscles
Function/Action
Acts as lubricant to faciliate the passsage of food
Protects the inner surafce from the action of digestive enzymes
The rhythmic contracton and relaxation of the muscles able to push food forward (peristalsis)
37

2007 Heterotrophic Nutrition P. 38
The structure of the ileum wall in relation to its functions -- (digestion and) absorption
Adaptive structure for digestion: (85-II-6)
the microvilli membranes of the columnar epithelium have digestive enzymes bound to them.
Glandular cells in the epithelial lining secrete digestive enzymes which digest food molecules as they pass through
The very large overall surface area of ileum means a very large surface area of enzymes available to digest the food.
Each villus contains muscle fibres. Contraction of these moves the villi and mixes up the gut contents. This increases the contact between the food and the enzymes on the microvilli membranes.
mucus secretion
 for the protection of epithelium from digestive juice
Adaptive structure for absorption: a. thin surface
- simple, thin (o ne-cell thick) epithelium of villi on intestinal wall with short distance for absorption of sugar, amino acids, vitamins, salts and water from intestine lumen b. great surface area
- very long and greatly folded muscular tube (increase length)
- intestinal walls are folded ( folds of Kerkring )
- numerous finger-like villi of intestinal mucosa
(villus contains micofilaments so as to move about to contact food)
- modified columnar epithelium cell with numerous brushborder / microvilli c. epithelial cells have many mitochondria to provide sufficient energy for active transport of digested food. e. nerve plexus, circular and longitudinal muscles involved with peristalsis

Brings the digested food into close contact with the villi for absorption f. movement of villi

increase the contact between the gut epithelium and the food molecules. g. rich of vessels for transport

Allows the absorbed food transport rapidly away from the site of absorption i. blood vessels (capillaries of villi) ii. lacteal (lymph vessel)
38

2007 Heterotrophic Nutrition P. 39
Characteristic features of different parts of alimentary canal for digestion
Mouth
Stomach
Liver
Small intestine
Characteristic feature
The cutting and grinding action of the teeth
Function
Breaks down large food particles into smaller pieces
Increases surface area of food substances for the action of digestive enzymes
Saliva passes into the mouth through salivary duct
Water in saliva moistens and softens the food
Mucus in saliva binds small food pieces together and lubricates the food during swallowing
A large muscular sac with the upper part connects to oesophagus and the lower part conncets to duodenum
The entrance is guarded by the cardiac sphincter
Storing food: fluid food usually stays much shorter than solid food
Controls the entrance of food from oesophagaus
Controls the exit of food to duodenum The exit is guarded by the pyloric sphincter
Thick layer of mucus to cover its inner surface
Protects against the action of the digestive juice and acid
Vigorous waves of peristaltic contractions (churning movement)
Produce bile
Food is constantly churned by peristalitic movement
Mixes the food thoroughly with the gastric juice to break down food mechanically
Bile, which is stored in gall bladder, responsibles to speed up the digestion of fats
Contains bile pigment which is the waste products formed from the breakdown of old red blood cells and gives the faeces a green or brown colour
Mixes the food with the digestive juices
The food is finally digested into simple molecules that are ready for absorption
39

2007 Heterotrophic Nutrition P. 40
2. Associated glands associated glands outside alimentary canal included:
- salivary glands (secretes saliva)
- liver (secretes bile)
- pancreas (secretes pancreatic juice and hormones) a.
Liver
- the largest organ in body
- just below diaphragm, reddish-brown in colour
- composed of numerous lobules roughly cylindrical in shape
- with a rich supply of blood: i. Hepatic artery - oxygenated blood
- from circulation
- Interlobular artery (interlobular branches of Hepatic artery) ii Hepatic portal vein - deoxygenated blood
- rich in nutrients
- from guts
- Interlobular vein
(interlobular branches of Hepatic portal vein

to blood space in lobules
( sinusoids ) which bath the liver cells, liver cells absorb useful substances and discard metabolic products / wastes into sinusoids
- blood from hepatic artery and hepatic portal vein drain into the liver.
Through branches of the vessels, blood flows into the lobular blood space (sinusoids) to the lobular central veins then to the hepatic vein, and eventually leave the liver. iii. Hepatic vein - deoxygenated blood
- from central vein of lobules
- metabolic products from liver e.g. urea
- to inferior (posteria) vena cava
- Bile duct
-- liver cells secrete bile into canaliculi and finally into
the bile duct
-- drains bile to gall bladder for temporary storage
- liver cells (hepatocytes)
-- structurally undifferentiated
-- have prominent cellular organelles adapted to its functions.
(e.g. mitochondria and prominent golgi apparatus)
- Kupffer cells
-- attaching to walls of sinusoid
-- phagocytic
-- destroy old red blood cells
-- remove bacteria and foreign particles from blood in liver
-- amoeboid movement
40

2007 Heterotrophic Nutrition P. 41
41

2007 Heterotrophic Nutrition P. 42
42

2007 Heterotrophic Nutrition P. 43
43

2007 Heterotrophic Nutrition P. 44
- Roles of liver (as the metabolic centre in the body) i. Regulatory functions
- Carbohydrate metabolism
-- blood sugar level insulin glucose too high blood --------------->

------> normal glucose level glycogen
(>90mg in 100ml blood) glucagon glucose too low blood -------------->

-----> normal glucose level glycogen
(<90mg in 100ml blood)
-- respiration glucose -------> energy + CO
2
- Protein metabolism ( deamination )
-- excess amino acids cannot be stored in body
-- deaminated by liver cells:
- remove of amine group (NH
2
) ---->ammonia (NH
3
)
- NH
3 is highly toxic and is conveted into urea
- residue (i.e. keto group) for carbohydrate metabolism and oxidized
- Lipid metabolism
-- excess carbohydrate -----> fat
-- remove lipid from blood by breaking down or modifying them ii. Production
-- heat:- high metabolic rate
- large size
- rich blood supply
---> involved in regulation of body temperature
-- bile: - with bile pigment (product of haemolglobin destruction)
- stored in gall bladder
- contain bile salts

-- emulsify fats
-- facilitate absorption of fat-soluble vitamins
(A, D, E, and K)
- alkaline

neutralize acidic chyme from stomach and provide an alkaline medium for the enzymes in the small intestine
-- cholesterol:
- a fat derivative
- as an important constituent of cell membrane
- made in liver when dietary requirement is inadequate
- excess cholesterol is excreted in bile
- gross excess may be precipitated as gall stones in bile duct and gall bladder
44

2007 Heterotrophic Nutrition P. 45
-- red blood cells:
- produced in liver only during foetal stage
- in adults, produced in bone marrow (however it depend on a kind of substance that is synthesized in liver, haematinic principle
) iii. Storage
-- blood:
- veins in liver have high power of expansion and contraction
---> serves as a blood reservoir to regulate blood volume in circulation
-- vitamins (A, D, B
12
)
-- a number of minerals (e.g. iron, copper)
-- glycogen iv. Elimination
-- haemoglobin:
- old RBC are destroyed by phagocytic Kupffer cells
- Hb is broken down by liver cells to green pigment, biliverdin
- biliverdin is then converted to brown pigment, bilirubin
- bilirubin combines with glucuronic acid to form bile pigment and eliminated in bile
-- sex hormone:
- some are modified chemically by liver cells
- some are excreted through kidney
- some are excreted in bile v. Detoxification
-- liver cells detoxify many poisonous substances by absorbing them and then changing them chemically. vi. Homeostasis
-- synthesizes certain plasma proteins (include fibrinogen, prothrombin and albumin)
-- regulation of body temperature vii. Defense
-- Kupffer cells are phagocytic which are able to remove invading bacteria
Fine structures of the hepatocytes in relationship to its function
Organelle Function
Mitochondria
Rough endoplasmic reticulum
Smooth endoplasmic reticulum
Golgi apparatus
Lysosome
Peroxisomes
Liver cells require a lot of energy to support its high level of metabolic activities
Liver cells require a lot of enzymes for catalyzing the various metabolic activities.
For liver cells detoxification function
To control the glucose metabolism
Liver cells secrete a lot of cellular products
Liver cells release enzymes to digest parts of the cells for detoxification for break down red blood cells
Exceptionally large which contain catalase and other enzymes responsible for detoxification
Site at which much of the ethanol that a person drinks is disposed
45

2007 Heterotrophic Nutrition P. 46 b.
Pancreas
- an elongated, whitish gland
- lies in loop formed by the duodenum and under surface of stomach
- a mixed gland with exocrine and endocrine tissues: exocrine gland: - acinar cells ---> pancreatic juice endocrine gland: - Islet of Langerhans - (

cells ) ---> insulin
- (

cells ) ---> glucagon
- insulin :
-- stimulated by high glucose level in blood
(e.g. after a meal )
---> - promotes the conversion of glucose to glycogen for storage in muscles and liver
- increase the absorption of blood glucose by cells, especially muscle cells
- facilitates glucose oxidation to yield energy and carbon dioxide
-- deficiency:
---> diabetes mellitus
--symptoms: - high blood sugar (hyperglycemia)
- sugar in urine (glycosuria)
- glucagon
---> increase in blood glucose level by:
- converting glycogen to glucose at liver
- decreasing glucose oxidation in cells
46

2007 Heterotrophic Nutrition P. 47
47

2007 Heterotrophic Nutrition P. 48
48

2007 Heterotrophic Nutrition P. 49
V. Egestion
-----> rectum be stored temporarily and normally the desire for defecation is initiated immediately by the mass movement feces forced into the rectum and elicit the defecation reflexes
-----> anus
relaxation of anal sphincters
----> outside body
(* much of the material making up the faeces is not the result of metabolic reactions within the body, faeces is said to be egested rather than excreted )
49