Overview of the Digestive System

The digestive system is a group of organs that work to gether to convert organic components into energy and nutrients to feed the entriee body. The esophagus, stomach, small intestine, large intestine, liver and panbcreas make up the digestive system. The digestive system would not be able to work without other organ systems. The circulatory system must transfer nutrients around the body and the respiratory must supply adequate gas exchange.  There are four components of digestion which are ingestion, digestion, absorption and egestion.  

1. Ingestion - the taking in of nutrients
2. Digestion - the breakdown of complex organic molecules into smaller components by enzymes
3. Absorption - the transport of digested nutrients  to the tissues of the body
4. Egestion - the removal of waste food materials from the body 

 

 

 

 

 

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Ingestion 

Physical digestion begins in the mouth when we chew on food. The front teeth called incisors are specialized for cutting. The canine teeth are the premolars which are specialized for grinding. The molars are designed for crushing the food. Saliva contains a digestive enzymes known as amylase which breaks down the starches into simpler carbohydrates. Salvia helps to lubricate the food so it can be swallowed, dissolves food particles, and makes it possible to taste. After food has been chewed it turns into bolus, which then travels down the esophagus to the stomach after being swallowed. The bolus stretches the walls of the esophagus, activating smooth muscles which create waves of rhythmic contractions known as peristalsis. The allows the food to travel down into the stomach. 

 

 

 

 

 

 

 

 

 

 

             Digestion 

The stomach is the initial spot for protein digestion and is the site for food storage. Chemical digestion occurs here.The movement of food to and from the stomach is regulated by cicular musciles called sphincters. The cardiac sphincter closes the opeing to the stomach , while its relaztion allows food to enter. The pyloric sphincter regulates the movement of foods and stomach acids to the small intestine. The stomach can hold 1.5 L of food. Within the stomach, millions of cells line the inner wall. These cells secrete stomach fluids known as gastric fluid which aid in digestion. Gastric fluid includes mucus, hydrochloric acid(HCI), pepsinogens, and other substances. Mucus provides a protective coating. Hydrochloric acid kills harmful substances that are ingested with food. HCI also converts pepsinogen into pepsin which is a protein-digesting enzyme. Pepsin breaks amino acid chains in proteins into shorter chains known as polypeptides. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Absorption 

Most absoprtion occurs in the small intestine, an area known as the duodenum. The other two components of the small intestine are called the jejunum and ileum. The small intestine is 7 m in length.  Prosecretin is converted to secretin when acid enters the small intestine. A signal is sent to the pancreas to release bicarbonate ions, which help neutrilize HCI and inactivate pepsin. Pancreas secretion plays a significant role in protein digestion. Lipases, a lipid digesting enzyme and amylase are screted by the pancreas. Disaccharidases are secreted by the small intestine which completes the digestion of carbohydrates. The liver produces a fluid called bile that contains bile salts which speeds up fat digestion. The liver stores glycogen and vitamins and also detoxifies many harmful substances. Chemical digestion is complete by the time food reaches the large intestine. The largest part of the stomach, known as the colon stores wastes long enough to reabsorb water out of the wastes. Inorganic salts, minerals and vitamines are absorbed with the water. Information is sent to the central nervous system to prompt a bowel movement when wate builds up in the large intestine. Villi are long fingerlike tubes which increases the surface area of the small intestine to ensure absorption. Microvilli are threadlike extension of the membrane that also help increase the surface for absorption. 





 

 

 

 

Egestion 

Elimination occurs here. 

 

 

 

 

 

 

 

 

The Importance of Digestion
 

1. Digestive systems enable the absorption of nutrients needed for growth, maintenance, and repair. The digestive system and other organ systems are interdependent. The four components of digestion are ingestion, digestion, absorption, and egestion.


2. In protozoa, digestion occurs in intracellular vacuoles.


3. Some simple organisms have a single gastrovascular cavity with one opening, which both stores food and digests it.


 4. Digestive tracts allow the separation of processes into different regions.