Download DIGESTIVE SYSTEM:

Digestive System:

The function of the digestive system is to break down large food particles into smaller
ones that can be absorbed into the membranes of cells.

Nature of Digestive System:
 Incomplete Digestive System—one opening
 Complete Digestive System—two openings allowing food to move in one
direction; from mouth to anus

Two main groups of organs comprise the digestive system.
1. The first group is made up of the organs of the gastrointestinal (GI) tract, also
known as the alimentary canal.
 This is a tube that extends from mouth to anus and is open at each end.
2. The second group is made up of accessory organs such as the teeth, tongue, and
glands that line the GI tract.
 These aid in the mechanical and chemical breakdown of foods.
Process of Digestion

The process or digestion begins when food enters the digestive system at the oral
cavity (mouth). Here the food is broken down mechanically and moistened with
secretions.

It is shaped into a football known as a bolus by the tongue, and then enters the next
part of the GI tract, the pharynx, which starts at the rear of the mouth.

The organ that transports food to the stomach is the muscular esophagus.

This tube passes through the thoracic cavity and pierces the diaphragm before
entering the pouch-like stomach. Here food mixes with acid and protein-digesting
enzymes.

Passing from the stomach, food enters the twenty-foot long small intestine.

A great portion of the abdominal cavity is taken up by the numerous folds and twists
of this organ, and the main processes of digestion and absorption occur here.

At the lower left portion of the plate (the anatomical right), the small intestine leads
into the large intestine (colon).

This tube can be seen ascending along the anatomical right side, passing along the
midline, then turning and descending.

Undigested material is dehydrated and compacted in this organ.

Prior to defecation, indigestible waste is stored in the rectum.

After a certain amount of feces has accumulated, it passes through the anus.

Three sets of salivary glands supply enzymes that digest carbohydrate in the oral
cavity.
1. In the abdominal cavity, the liver secretes bile that participates in fat
digestion, and the liver processes some of the products of digestion before
sending them to the tissue cells.
2. Beneath the liver is the gallbladder. Bile from the liver is stored here
(gallbladder) before it is delivered to the intestine.
3. An important contributor of enzymes to the digestive process is the pancreas.

Exocrine cells of this gland deliver their secretions into the first part of the small
intestine--

Present in salivary secretion is the enzyme salivary amylase. This enzyme breaks
down starch through the process of hydrolysis, producing the disaccharide maltose.

The next digestive enzymes encountered by the food are present in the stomach.

The stomach contains gastric juice, which has a pH 2, and this gastric juice contains
the enzyme pepsin, which breaks down proteins.

Chemical breakdown of food continues in the small intestine, where pancreatic
enzymes continue to hydrolyze starch, proteins and other materials
1. Amylase
2. Trypsin
3. Chymotrypsin
4. Carboxypeptidase
5. Aminopeptidase
DIGESTION AND HUMAN NUTRITION

Nature of Digestive System:
A. Incomplete Digestive System—one opening
B. Complete Digestive System—two openings allowing food to move in one
direction; from mouth to anus
1. Mechanical processing and motility—breaking down, mixing, transport
of nutrients
2. Secretion—enzymes and fluids
3. Digestion—food material
4. Absorption—digested nutrients into blood and lymph
5. Elimination—undigested and unabsorbed residues

Human Digestive System:
A. Humans have a Complete Digestive System
B. 6-9 meters in length-comprising mouth, pharynx, esophagus, stomach, small
intestine, colon (large intestine), rectum, and anus

Mechanical Breakdown of food;
A. Food mixes with saliva
B. Teeth chew the food---Enamel coat, dentin core, inner pulp
1. Incisor—bite off chunks
2. Canines—tear
3. Premolar/molars—grind food
Example: teeth—correlated with food source
C. Tongue function—position food, taste food, swallowing
Example: hot peppers (red meat)
D. Saliva function—neutralize acid, lubricate food

Digestion—move from stomach to small intestine
A. Muscular walls that mix, grind, and move the food along in the lumen
B. Digestive enzymes will chemically break down food into small molecules to
be absorbed
C. Stomach
1. Muscular sac stores, mixes food, and degrades food
2. Gastric fluid—HCl, pepsinogens, mucus
3. Helicobacter bacteria, E. coli. (sometimes)
Example: imbalance in mucus and bicarbonate ions
(stomach lining)—ulcers
D. Small Intestine
1. Digestion is completed
2. Enzyme secretion from pancreas and liver—nutrients are absorbed into
internal environment
3. Monosaccharides, fatty acids, amino acids, nucleotides
4. Bicarbonate neutralize HCl in stomach

Role of Bile Salts in Fat Digestion:
A. Depend on more than one enzyme action
B. Speed up fat digestion
C. Bile—secreted continuously by liver
D. Fat
1. Insoluble in water
2. Aggregate into large globules
3. Bile salts bind to fat help cause them to stay separated

Large Intestine (colon)
A. Colon stores and concentrates feces—undigested and unabsorbed—material,
water, and bacteria
B. Colon leads to the rectum (feces storage) that opens to the outside through the
anus
C. Bulk (fiber and other undigested material)—important in moving material in
feces through the colon at proper speed

Human Nutrient Requirement
A. Carbohydrates: 60% (beans, fruits, cereal, peas, bread, rice, legume)
B. Fats/lipids: 20-25%
C. Proteins: 12-15%
D. Vitamins and minerals