Physiology Of Digestive system

                        How digestion of Foods occur

The Digestion begins when food is taken in through the mouth, mixed with saliva and chewed. Structure in the oral cavity work together to break down foods into a small mass called bolus.

During the process of swallowing, the tongue rises to the roof of the mouth directing the bolus out of the oral cavity. The bolus then passes from the oropharynx to the pharynx and into the esophagus.

Involuntary muscular contraction called peristaltic waves, moves the bolus down the esophagus and into the stomach.

 Peristaltic waves continue the Mechanical breakdown of food in the stomach. Digested food mixed with digestive enzyme and acids secreted by stomach is called chyme.

Enzyme in small intestine further do the chemical process.

A small amount of nutrient absorption occurs in the stomach but most absorption occurs as chyme travels through the section of the small intestine. The wall of the small intestine are lined with structure that absorb nutrient from chime and then pass these nutrient into blood stream. Some absorption continue in the large intestine. As indigestible waste moves through the structure of the large intestine it is compacted. The elimination of indigestible waste completes the digestive process.

Mechanical digestion

Chewing and swallowing:

Digestion begins in the oral cavity where the salivary glands teeth and the tongue work to break down food into the small masses that can be swallowed.

The movement of the jaw enables the teeth to grind food. Saliva secreted by salivary glands aids the mechanical and chemical process of digestion.

The tongue manipulates the chewed food into a small mass then moves it into the oropharynx. The next stapes are involuntary: the bolus passes through the pharynx, the epiglottis closes off the trachea and peristaltic waves move the bolus into the stomach.

 

Function of epiglottis and larynx during swallowing:

During swallowing the epiglottis prevent checking by folding down to close off the larynx and trachea. This prevent the bolus from passing into esophagus instead of the lower airways.

Peristalsis

The autonomic nervous system control contraction of the alimentary canal, then move swallowed food down the esophagus churn the stomach and move chymes through the small intestine and large intestine.

The alimentary canal is single continues tube that include the oral cavity esophagus stomach and intestine.

The tissue layer that forms the wall of tube include layers of smooth muscle. The contraction and relaxation of these muscle is called peristalsis.

One peristaltic wave cause enough to move a bolus down the esophagus and into the stomach. In the intestine the wave are smaller and more regular. As one section of the intestine contracts the section in front relaxes. This occurs in the rhythmic wave like patterns that create the peristalsis that propels substances forward.

Chemical digestion

Chemical digestion involves the breaking of covalent chemical bonds in organic molecules by digestive enzymes.

Carbohydrates are broken down into Glucose, proteins are broken down into amino acids, and fats are broken down into fatty acids and glycerol.

Digestion of carbohydrates:

Carbohydrate digestion begins in the oral cavity with the partial digestion of starches by
salivary amylase. About 30 percent of starch is hydrolyzed here by salivary amylase into a disaccharide called maltose.

A minor amount of digestion occurs in the stomach through the action of gastric amylase and gelatinase. Carbohydrate digestion is continued in the intestine by pancreatic and intestinal amylase. A series of disaccharides enzymes that are released by intestinal epithelium digest disaccharides into monosaccharides.

 

Digestion of Proteins

Digestion of proteins into single amino acids, dipeptides, and tripeptides is carried out by a variety of peptidases enzyme in both the stomach and the small intestine.

Digestion of proteins begins in the stomach with pepsin which is secreted by oxyntic glands. Pancreatic digestive enzymes perform the majority of protein digestion. The major proteolytic enzymes include trypsin, chymotrypsin, elastase, and carboxypeptidase. These enzymes digest proteins to short chains of a few amino acids.

The final stage of protein digestion occurs on the brush border of the small intestine epithelium. Here, membrane-bound peptidases complete digestion of oligopeptides to either single amino acids or dipeptides and tripeptides.

Digestion of Lipids

The major dietary lipids include triglycerides, phospholipids, cholesterol, steroids, and fat-soluble vitamins.

The first step in lipid digestion is emulsification, which is the transformation of large lipid droplets into much smaller droplets. Emulsification is accomplished by bile salts secreted by the liver and stored in the gallbladder.

The primary location for lipid digestion is the small intestine where strong emulsifiers synthesized by the liver are present together with strong lipid-digesting enzymes synthesized by the pancreas.

Pancreatic Lipase digests triglycerides into components fatty acids and 2-monoglycerides

Pancreatic Cholesterol Esterase digests cholesterol esters into component cholesterol and fatty acid

Pancreatic Phospholipase  digests phospholipids into their component head groups and fatty acid

Absorption

Mechanical and chemical digestion in the stomach results in chymes. periliastic wave propel chymes through the pyloric sphincter into the duodenum of the small intestine. Finger like projection called villi line the interior wall of the small intestine.

Most absorption of nutrient from ingested food occurs through these. In the small intestine nutrient in the chymes are further broken down by secretion from organs.

Inside each villus there are lacteals of the lymphatic system that fatty acid pass into, and capillary beds of the circulatory system into which other nutrient pass. Water and other substance from chymes that are not absorbed move into the large intestine for further absorption, digestion or elimination.