[candi]

Mouth:
1- Analysis of material before swalling.
2- Mechanical processing by the teeth, tongue and platal surface.
3- Lubrication.
4- Limited digestion
As food is passed into the mouth, it is masticated by the teeth and tongue (process referred to
as mastication)
The teeth: Crush large pieces of food into smaller ones.
Taste buds: Detect one or a combination of four taste sweet, salty, bitter and sour.
The tongue: Taste food, move food around the mouth, facilitating chewing and swallowing.

Salivary gland:
Three pairs of gland produce saliva.
The amount of saliva produced is 1-1.5 liter/daily
The rate of secretion is controlled by:
1- Nerve impulses and the stimuli for secretion are psychic (sight, smell, taste and thought of food.
2- Mechanical: chew of food.
3- Chemical: stimulation of taste buds.
Saliva contains:
Functions of Saliva: The functions of saliva are as follows:
It moistens dry food and facilitates swallowing by a lubricating action of Mucin (mucoprptein).
It contains an a-amylase ( Ptyaline): which rapidly digests d starch into maltos, isomaltose and dextrine. The digestion of starch begins in the mouth.
Since, food remains the mouth for too short a period, very little digestion takes place in the mouth.
Saliva also contain inorganic ions such as Ca ion help to stabilize the amylase and cl ion increase the activity of amylase.
Saliva contains buffering substances, viz., bicarbonate, phosphates and mucin.
It keeps the mouth at a neutral pH and thus protects the teeth from decalcification. It keeps the mouth and teeth clean.
Pharynx:
A short tube that is shared by both digestive and respiratory system. The food passes through the pharynx. To prevent choke the epiglottis closes off.
Esophagus: Passers food from the mouth to the stomach
Bolus: A portion with respect to food, the amount swallowed at one time.
Bolos: Lump.
Bolus: Rounded mass of food formed in the mouth and ready to be swallowed.
The Stomach:

The stomach has the thickest walls and strongest muscles of all the GI tract organs.
Gastric glands secrete Gastric juice, a thin light colored fluid which is strongly acidic. It contain water, enzymes and Hydrochloric acid.
Normal adults secrete from 1500 to 2500 ml/day.
The concentration of HCI is about 0.45 per cent in the gastric juice of normal
individuals.
Functions of HCl : (1) It provides-the optimal pH (2 to 3) for digestion of proteins by pepsin
(2) It converts inactive pepsinogen into active pepsin
(3) It denatures food proteins, thus making them more readily digestible
(4) It helps in the absorption of iron by converting food iron into inorganic form and by reducing
ferric iron to ferrou form
(5) It stimulates duodenum to secrete secretin
(6) It helps to some extent to hydrolyse (inversion) sucrose to glucose and fructose
(7) It has a germicidal effect on microorganisms and hence prevents the growth of microorganisms
In the stomach.

Mucin: A glycoprotein, a thick slippery, white substances that coat the cells of the stomach protect them from the acidity of gastric juice, enzymes and disease causing bacteria.
Intrinsic factor: Mucoprptein, essential for absorption of vitamin B12.
Enzymes:
Pepsin: Pepsinogen is converted into active pepsin by the HCI.
Pepsin converts food proteins mainly into a mixture of polypeptides.

Rennin: This enzymes occurs in small amounts in the stomach of infants and not of adult human beings. It hydrolyses casein to paracasein and a peptide, Para casein, in the presence of calcium ions, forms a thick curd of'Ca- caseinate.
Gastric Lipase: Hydrolysis of fat to free fatty acids and glycerol.

Chyme: (KIME): the semi liquid mass of partly digested food expelled by the stomach into the duodenum.
chymos » juice
The small Intestine:
The stomach empties into the small intestine, which is coiled below it in the abdomen.
A 10 foot length of small diameter intestine that is the major site of digestion of food and absorption of nutrients.
The small intestine is divided into three sections:
Duodenum: (doo-oh-DEEN-um, doo-Ofrlr-nurn): the top portion of the small intestine (about "12 fingers' breadth" long in ancient terminology).
duodecim = twelve

jejunum: (je-jOON-um): the first two-fifths of the small intestine beyond the duodenum.
Ileum: (ILL-ee-um): the last segment of the small int
Three types of secretion are secreted into the small intestines:
Bile, Pancreatic
juice and Intestinal juice.
Bile:
An exocrine secretion, flows into the duodenum. The liver synthesis bile, it is concentrated and stored in the gallbladder and released into the small intestine when needed.
Bile is not enzyme, it is an emulsifier that bring fat into suspension in water.
About 300 to 1200 ml of bile are formed daily in adult human.
Pancreatic Juice:
Pancreas: An organ with two main functions:
Endocrine function (endo means into the blood). The islets of langerhanse present in the pancreas secretes hormones into the blood that help to maintain glucose homeostasis.
An exocrine function (exo means out, into a body cavity or onto the skin surface), produce the pancreatic juice which contain digestive enzyme which release
through a duct into the small intestine.
Pancreatic juice secreted in adult human may range from 600-800 ml/day.


The pancreatic juice contains enzymes that act on all three energy nutrients.
1-?-amylase Pancreatic amylase (amylopsin). It is an endoamylase. Its action on starch is similar to that of salivary amylase. Its hydrolyze starch and dextrin to form dextrin and maltose
2-Trypsin (activated trypsinogen) hydrolyzes protein and polypeptide to peptides and amino acids.

3-Chyymotrypsin(activated chymotrypsinogen) hydrolyzes protein and polypeptide to peptides and amino acids.
4-Carboxypolypeptidase hydrolyze polypeptides (carboxyl end) to form amino acids.

5-Lipase hydrolyze fat to form simple glycerides, fatty acids and glycerol.


6-Cholesterol esterase hydrolyze cholesterol ester to cholesterol and fatty acids
7-Ribonuclease hydrolyzes ribonucleic acids to form mononucleotides.

8-dioxyribonuclease hydrolyzes deoxyribonucleic acids to form mononucleotides.

9-Elastase hydrolyzes fibrous protein to form peptides and amino acids.
10- Collagenase and Elastase: Pancreatic juice contains collagenase a elastase which hydrolyse collagen and elastin present in. meat and fish.
In addition to enzymes, the pancreatic juice contains sodium bicarbonate, which is basic or alkaline the opposite of the stomach's acid. The pancreatic juice thus neutralizes the acidic chyme arriving in the small intestine from the stomach
Intestinal Juice:
The intestinal juice is an alkaline fluid secreted by the small intestines contains mucus, sodium bicarbonate, enterokinase and erepsin. The quantity of intestinal juice secreted in an adult may vary from 2000 to 3000 ml per day
Many important enzymes are present in the intestinal mucosa These include peptidases, disaccharidases, nucleinases, phosphatases, phospholipases
The large intestine:

The small intestine empties into the large intestine (also called colon), it's about 3.5 ft long. Its segments are cecum, the ascending colon, the descending colon, the transverse colon and sigmoid colon. Sigmoid (sigma from Gerek)

Sigmoid=shaped like the letter S.
Function of large intestine:

The colon mixes the intestinal con tents, absorb water and salt and form stools.
Incubator for harmless bacteria. Intestinal bacteria ferment some fibers s producing water, gas and small frahment of fat that provide energy for colon. Some fat, cholesterol and minerals are bind to fiber and are excreted.
Some vitamins such as vitamin K and B complex are synthesis by
intestinal bacteria.
Control Secretions:
Two system coordinate all the digestion and absorption:
1) The nervous system.
2) The hormonal system.