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Parts of the Human Digestive System

                                                                                                             The Mouth  

gafacom image of the parts of the digestive system and their functionsThe first part of the digestive system is the mouth, the entry point of food. The smell and sight of food, stimulates your salivary glands to secrete fluid called saliva, consisting of water and enzymes.
 The purpose of the saliva is to lubricate the food for swallowing, dissolve water soluble food particles, and start chemical digestion of carbohydrates (starch) into smaller molecules. Amylase is the enzyme secreted. The pH of the mouth is 7. 

Salivary glands – are glands in the mouth that produces saliva to begin the chemical digestion of food. 
 
Saliva – is a watery secretion in the mouth that begins the digestive process. 
 
Mechanical digestion also begins here. The teeth and tongue are responsible for the breaking of large food particles into smaller food particles, while increasing surface area for faster chemical digestion. 

Each parotid gland and sub-mandibular gland release saliva into the mouth through the parotid duct and the sub-mandibular duct. The sublingual glands release saliva into the mouth through many smaller ducts.                    

The Esophagus  

The esophagus is a tube connecting the mouth to the stomach running through the Thoracic cavity. Your teeth and tongue move food around in the mouth turning the food into a mushy bolus. The tongue moves the bolus to the back of the throat for swallowing. The bolus enters the esophagus.  
 
The esophagus lies behind your windpipe (Trachea).  The trachea has as an epiglottis which prevents food from entering the windpipe, moving the food to the esophagus while swallowing. This prevents food from entering the windpipe and choking. Food travels down the esophagus, through a series of rhythmic contractions (wave-like) called peristalsis. The lining of the esophagus secretes mucus, lubricating to support the movement of food. 
 
When the bolus reaches the stomach, it must pass through a muscular ringed valve called the esophageal sphincter (Cardiac Sphincter). The role of the sphincter is to prevent stomach acids from back flowing into the esophagus creating a burning feeling known as heart burn. 



Peristalsis moves food through the esophagus by means of muscular contractions. When you vomit, or ‘throw up’ your stomach contents, the contractions of the esophagus are reversed. Similarly, small amounts of acidic liquid can escape from the stomach and move up the esophagus into your throat. This id experienced as a burning sensation in the throat or chest, commonly called heartburn or acid reflux.

The Stomach 

The stomach is a muscular J-shaped organ found in the abdominal cavity. Food is temporarily stored in the stomach. The stomach is a muscular organ (three layers of muscle fibres) which performs mechanical digestion by churning the bolus and mixing it with the gastric juices (HCl, salts, enzymes, water and mucus) secreted by the lining of the stomach. The bolus is now called Chyme. 
 
Gastric Juices – are a mixture of hydrochloric acid, salts, enzymes, water and mucus that is produced by glands in the stomach to help digest food. 
 
The environment of the stomach is very acidic. HCl is secreted to kill any microbes that are found in the bolus, creating a pH of 2. Mucus prevents the stomach from digesting itself. 
 
Pepsin is also secreted. This enzyme is responsible for initiating the breakdown of proteins found in the food. Pepsin hydrolyzes proteins to yield polypeptides. Since the pH is 2, the enzyme from the salivary glands stops breaking down carbohydrates. 

Folds in the stomach wall allow it to expand and contract as it fills with food and then empties its contents into the small intestine.  
  
The stomach does not digest itself because of three protective mechanisms. First the stomach only secretes small amounts of gastric juices until food is present. Second the secretion of mucus coats the lining of the stomach protecting it from the gastric juices. The third mechanism is the digestive enzyme pepsin is secreted in an inactive protein called pepsinogen. Pepsinogen is converted to pepsin in the increased presence of hydrochloric acid (pH 1). 
  
The chyme moves from the stomach to the small intestine. It passes through a muscular ringed sphincter called the pyloric sphincter. 
 
Chyme – is a thick liquid produced in the stomach and made of digested food combined with gastric juice. 
 
Pepsin – is an enzyme in gastric juice that helps break down proteins into polypeptides. 

The Small Intestine 

The small intestine is responsible for the complete digestion of all macromolecules and the absorption of their component molecules (glucose, glycerol, fatty acids, amino acids and nucleotides). The process of absorption allows the component molecules to be diffused into the surrounding intestinal cells and then into the circulatory system for transport to all the cells in the body. 
  


Parts of the Human Digestive System Parts of the Human Digestive System Reviewed by gafacom on June 03, 2019 Rating: 5

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