BIOL 205 Study Guide - Final Guide: Gastrointestinal Tract, Gastric Acid, Pancreatic Juice
Course CodeBIOL 205
LECTURE 6: CAPTURE, INGESTION, DIGESTION AND ABSORPTION OF
FOOD IN ANIMALS
1) Nutritional requirements obtained from food
All animal obtain food by eating plants (directly) or by eating animals who eat plants (indirect)
complex food requirements
Types of food components obtained by animals:
- aa build proteins. Obtained during digestion
- Simple sugars (Glucose) used to obtain E or to store it as glycogen. Also needed to
synthetize other molecules
- Lipids synthetize cellular membrane or source of metabolic E
- Inorganics salts synthesis of nucleic acids + osmoregulation
- Vitamins to assure normal function
- Water essential solvent.
Not every chemical element = essential in animal nutrition. Biological evolution = continuity of
chemical evolution certain chemical elements were selected to build up prebiotics systems and
biological systems were built from it.
Animals require them in various proportions Some can be needed to some species and not to
Essential nutrients = nutrients that cannot be produced by the organism Vitamins and some aa.
2) Feeding methods
Unicellular organism take up food by surface absorption food has to be in molecular form. Is
produced by death and decay of other life form.
Unicellular fed by endocytosis.
If food taken in solid = phagocytosis
If food is dissolved =pinocytosis
Multicellular capture food in specific ways
Feeding methods of bird have to overcome certain difficulties: refractive index of water (apparent
position of prey is not the real one) + movement of the prey.
Possible neural mechanisms
3) Digestive system
Digestive system structural organs providing contained space for digestion + accessory digestive
system secreting enzymes
Some animals: Secluded groove long tube track opened at ends (one for ingestion and the other
one for expulsion of undigested stuff)
Those grooves not internal to organism. Food lies outside body of organism.
Tube like structure called digestive track/alimentary canal/gastrointestinal tract/ gut
Tube like nature Efficient design different regions of the tubes can be modified to carry out
temporal sequence of digestive steps as food passes through.
Digestive system digestive track +glands (putting biochemical digestive fluids) in gut.
Throughout length of alimentary canal cells secrete mucus that facilitate food movement
Vertebrate alimentary canal regions (4):
Head gut mouth part of the gut serves to detect/ingest and breakdown food into smaller parts .
Process increase total surface area of food particle rapid enzyme action.
In first part of it (mouth) : Saliva+mucus secreted . Mucus wets food for easy handling
Saliva has bicarbonate and amylase that degrades enzymes.
Digestion starts with mouth chewing
Foregut includes esophagus ( part of it can become crop in some invertebrates + grain eating
and fish-eating birds have a large one for storage )
Midgut stomach and small intestine. Part where both absorption and digestion happens.
In stomach cells secrete hydrochloric acid into lumen activates digestive enzymes
Small intestine digestion of protein = completed & digestion of fats and digestion of carbohydrate
continues . Acidity from Stomach=neutralized
Absorption of products from digestion takes place in small intestine
Hindgut Large intestine. Absorption of materials and water takes place before undigested
materials is expelled. Contains microbial community to try and digest cellulose and vitamins.
=Biochemical process by which macromolecules monomers constituents
Different parts of alimentary tract digest diff components of food.
Nature of digestive enzyme varies with part of digestive track.
Mouth food physically broken into pieces to increase total surface area for the action of enzymes.
several pairs of salivary glands that will secrete saliva (with amylases – starch degrading enzymes)
Saliva has 3 functions:
- Moisten food for easy chewing/swallowing
- Acts as solvent for food molecules bind to taste bud, facilitates perception of taste
- Contains amylase degrade starch into glucose
Also contains bicarbonate ions neutralize acids in foods.
In insects enzyme invertase that breaks down sucrose.
In some animals saliva has special functions (contains poisons and toxins and anti-coagulant)
Every day production of 1L of saliva.
Esophagus Muscular tube with sphincter at each end. Food enters it as soon as swallowed (is all
or none reflex)
Food =prevented from entering into nasal/trachea passages or re-entering mouth
Digestive process from mouth continues in esophagus. Cells on walls secrete mucus that helps
Sphincter (band of muscle tissue) controls passage from esophagus to stomach
Stomach As food enters carbohydrate digestions continues. Cells in stomach lining contains
secrete gastric juice that contains hydrochloric acid + pepsinogen + intrinsic factor essential for B12
vitamin. HCl produced by stomach lining converts pepsinogen to pepsin (active form)
Up to 3L of gastric juices produced daily, its pH=1,5=strong enough to kill a bacteria
Protein digestion begins here
Small intestine Partially digested food stomach small intestine
First u-shapped part= duodenum. Specialized cells in it secrete enzyme that participate in digestion/
activate other digestive enzyme
2 types of digestive secretions poured in:
- Pancreas secretes pancreatic juice by pancreatic duct. Contains unprocessed form of prot
degrading enzymes. (Contains lipase, amylase, nuclease, maltase ) +Bicarbonate
- Bile brought in by bile-duct. Produced by liver, store in gall bladder has bile fats (essential
for fat digestion)
Digestion of all fats primarily in small intestine
pH=7 to 8
Large intestine Digestion is already complete large intestine will maintain water and ionic
balance . Absorbs water & ion from undigested material before expelled by defecation
Total length of gut reflects digestibility of food that animal eats. Herbivore’s food takes longer
to be digested than carnivore’s Total length gut greater in herbivore.
Within particular group (bird) length related to type of food eaten (Ecomorphology)
Gut also contains ++ organisms: archae, bacteria, fungi, parasitic worms play essential role in
digestion= Mutualistic relation (both benefit)
Their role particularly important in herbivore bc cannot degrade cellulose (that is major part of
plant material) Some of the micro organisms produce cellulose and will help org to degrade
cellulose to glucose.
Can also produce Vitamins
Evolutionary conflict between organisms & food some plants now have defense mechanisms Ex :
tannins and thorns
5) Chemical reactor theory
Digestion system can be compared to a reactor (series of bulk reactions where reactant and catalyst
mixed and products removed according to time)
Food and enzymes mixed together and product = removed through absorption
Reactor will influence production efficiency: size/shape/patterns