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Tenth edition Campbell biology textbook p 897

The main stages of food processing are ingestion, digestion, absorption, and
elimination
The first stage, ingestion, is the act of eating or feeding
...
Mechanical digestion, such as chewing breaks food into smaller pieces,
increasing the surface area available for chemical processes
...

A cell makes a macromolecule or fat by linking together smaller components; it does so
by removing a molecule of water for each new covalent bond formed
...
This
splitting process is called enzymatic hydrolysis
...

In the third stage, absorption, the animal’s cells take up (absorb) small molecules such as
amino acids and simple sugars
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Organs specialised for sequential stages of food processing form
the mammalian digestive system
The oral cavity, Pharynx and Esophagus
Ingestion and the initial steps of digestion occur in the mouth or oral cavity
...
Meanwhile, the salivary glands deliver
saliva through ducts to the oral cavity
...

The enzyme amylase, found in saliva, hydrolyses starch (a glucose polymer from plants)
and glycogen (a glucose polymer from animals) into smaller polysaccharides and the
disaccharide maltose
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When food arrives at the oral cavity, the tounge plays a critical role in distinguishing
which foods should be processed further
...
During swallowing, the tounge
provides further help, pushing the bolus to the back of the oral cavity and into the
pharynx
...
The trachea leads to the lungs, whereas the oesophagus connects to the
stomach
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Swallowing must be carefully choreographed to keep
food and liquids from entering the trachea and causing choking, a blockage of the
trachea
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The stomach secretes a digestive fluid called gastric juice and
mixes it with the food through a churning action
...

Chemical digestion in the stomach
The concentration of HCl is so high that the pH of gastric juice is 2
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This low pH
denatures proteins in food, increasing exposure of their peptide bonds
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Unlike most enzymes, pepsin works best in a very
acidic environment
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Further digestion to individual amino acids occurs in the small intestine
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The sphincter between
the oesophagus and the stomach normally opens only when a bolus arrives
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The resulting irritation of the oesophagus is commonly
called “heartburn”
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The sphincter located where the stomach opens to
the small intestine helps regulate passage into the small intestine, allowing one squirt of
chyme at a time
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The small intestine is the alimentary canal’s longest compartment - over 6m
long in humans! Its name refers to its small diameter, compared with that of the large
intestine
...
It
is here that chyme from stomach mixes with digestive juices from the pancreas, liver, and
gallbladder, as well as from gland cells of the intestinal wall itself
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The bicarbonate neutralises the acidity of chyme
and acts as a buffer
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Bile contains bile salts, which
act as emulsifiers (detergents) that aid in digestion and absorption of lipids
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Secretions of the small intestine
The epithelial lining of the duodenum is the source of several digestive enzymes
...
Most digestion is completed in the duodenum
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Absorption in the small intestine
To reach body tissues, nutrients in the lumen must first be absorbed across the lining of
the alimentary canal
...
Large folds in the lining encircle the intestine and are studded with
fingerlike projections called villi
...

From there, fructose exits the basal surface and is absorbed into microscopic blood
vessels, or capillaries, at the core of each villus
...
The capillaries and veins that carry
nutrient-rich blood away from the villi converge into the hepatic portal vein, a blood
bessel that leads directly to the liver
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Hydrolysis of fats by lipase in the small intestine generates fatty acid joined to
glycerol) These products are absorbed by epithelial cells and recombined into
triglycerides
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Being water soluble, chylomicrons can dissolve in the
blood and travel via the circulatory system
...
Lacteals are part of
the vertebrate lympathic system, which is a network of vessels filled with a clear fluid

called lymph
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Processing in the large intestine
The alimentary canal ends with the large intestine, which includes the colon, cecum and
rectum
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One
arm of the T is the 1
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The other arm
is a pouch called the cecum
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Compared with any other
mammals, humans have a small cecum
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The colon completes the reabsorption of water that began in the small intestine
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It takes approximately 12-24 hours for
material to travel the length of the colon
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Although it provides no caloric
value (energy) to humans, finer helps move food along the alimentary canal
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As byproducts of their metabolism, many colon bacteria generate gases, including methane and
hydrogen sulphide, the latter of which has an offensive door
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The terminal portion of the large intestine is the rectum, where the feces are stored until
they can be eliminated
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1) controls blood glucose levels
2) involved in inter conversation/distribution of nutrients
3) carries out deamination (resulting in urea)
4) carries out detoxification
5) stores iron and certain vitamins
6)produces bile - which is stored in gall bladder and secreted to duodenum via bile duct
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- a juvenile or “milk” dentition which is deciduous (i
...
falls out)
- a permanent dentition
A tooth from the permanent dentition set is not replaced if it is damaged or lost
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This type of dentition is referred to as heterodont dentition - teeth are different
in shape and function
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Teeth are named from the anterior (front) to the posterior (back) on the jaw as:
Incisors - for cutting, grasping and gnawing
Canines - for piercing
Premolars - for shearing and slicing
Molars - for crushing and grinding
Adaptations for different diets
mammals are divided into
- Insectivores: usually small mammals - feed on insects and variety of small
invertebrates such as worms and grubs
...

- Herbivores: feed on vegetation

further divided into browsers (eating leaves), grazers (eating grasses), gnawers (such
as rodents and rabbits)
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- Carnivores: (flesh-eaters) that live mainly on herbivores
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- Omnivores: feed on both plants and animals and are adapted for chewing a variety of
foods
Has a versatile dentition for a varied diet
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The microorganisms break down the cellulose walls of the ingested plant material,
allowing the host’s digestive enzymes access to the nutrients within the plant cells
...

- For example, ruminants such as cows, goats, sheep and giraffe, have a four-chambered
stomach, with the bacteria inhabiting the first two chambers
...

2) Periodically, the cow regurgitates and riches “cud” from the reticulum, further
breaking down fibres and thereby enhancing microbial action
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In this way, the
cow obtains significant nutrients from both the grass and the mutualistic microorganism,
which maintain a stable population in the rumen,
While other herbivores such as horses, rabbits, elephants, rodents, koalas have ab
enlarged caecum - site of bacterial fermentation
(caecum is a dead-end pouch at the junction of the small and large intestine)
...
The
reason for this is that the carnivore’s diet of meat us high in protein and is more easily
digested than the high finer diet of the herbivores
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Consequently, meat
doesn’t need to remain in the digestive tract as long
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In addition, since no fermentation chamber is required, carnivores either lack a caecum,
or if present it is vestigial*
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e
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