Digestive System

The digestive system consists of the organs involved in ingestion, digestion and absorption of food. Thus it is composed of the digestive tract from the mouth to the anus, and its associated glands and organs (salivary glands, liver, gall bladder and pancreas). Other roles of the organs of the digestive system include the metabolic functions of the liver and the endocrine functions of the pancreas.

The digestive system. Source: Wikimedia Commons.

Other Names

Synonyms

• Alimentary System
• Digestive Apparatus
• Gastrointestinal System

Related terms

• Alimentary Canal, Tract or Tube
• Digestive Tract or Tube
• Gastrointestinal Tract or Tube

Description

The alimentary system is composed of the digestive tract from the mouth to the anus, and glands and organs associated with the digestive tract.

Digestive Tract

The digestive tract has the following parts:

• Oral cavity
  
• Fauces
  
• Pharynx
  
• Alimentary canal
  
  • Esophagus
    
  • Stomach
    
  • Small intestine
    
    • Duodenum
      
    • Jejunum
      
    • Ileum
      
  • Large intestine
    
    • Cecum
      
    • Colon
      
    • Rectum
      
    • Anal canal
      

Associated Glands and Organs

The digestive system includes the following glands and organs, which are connected to the digestive tract by ducts:

• Salivary glands (Glands of mouth)
  
  • Parotid glands
    
  • Sublingual glands
    
  • Submandibular glands
    
  • Minor Salivary Glands
    
• Liver
  
• Gall Bladder
  
• Pancreas
  

Role of the Digestive System in the Body

Digestion is necessary for the body to take in nutrients from food and to absorb water.

Below are the chief functions of the digestive system:

• Ingestion, digestion and absorption of food
  
• Synthesis, interconversion, degradation and release of metabolites by the liver
  
• Synthesis of blood plasma constituents in the liver
  
• Detoxification of various chemicals by biotransformation in the liver
  
• Excretion of waste products (e.g., cholesterol and bilirubin diglucuronide) in bile by the liver
  
• Synthesis and secretion of hormones (e.g., glucagon and insulinby the pancreatic islets of Langerhans)
  

(Synthesis and secretion of hormones is a function of some organs included in the anatomist's digestive system; however, physiologists would include these functions, and the relevant tissues and cells, in the Endocrine System.)

How the Digestive System Works

Digestion begins at the mouth, where food is broken down by chewing and by chemical reactions by substances contained in saliva. Food continues to be broken down by digestive enzymes as it passes down the esophagus into the stomach. Absorption begins in the stomach and is greatest in the small and large intestines. Waste materials pass through the colon to the rectum and are released through the anus.

Ingestion

Food is taken in by the mouth. The tongue and teeth help chew the food. Salivary glands secrete enzymes that help begin digestion here. Food is swallowed and passes through the pharynx and the esophagus into the stomach.

Digestion

Digestion begins in the mouth and continues in the stomach, where enzymes such as pepsin help break food down. Food passes into the duodenum, where secretions from the pancreas and liver begin to work. The pancreas secretes digestive enzymes such as pancrease and lipase and the liver secretes bile, which is stored in the gall bladder.

Digestive hormones such as secretin, cholecystokinin, and gastrin help regulate digestion.

Absorption

Nutrients are absorbed throughout the digestive tract. Different compounds are absorbed in different places. For example, alcohol is absorbed in the stomach and vitamin B12 is absorbed in the cecum.

Elimination

Waste matter passes through the colon into the rectum. This matter passes through the anus as stool, also known as feces.

Diseases of the Digestive System

Conditions

Diseases of the digestive system include the following:

• Appendicitis
• Celiac Disease
• Crohn Disease
• Diabetes Mellitus
• Gastroesophageal Reflux Disease
• Irritable Bowel Syndrome
• Pancreatitis
• Peptic Ulcer Disease

Symptoms

Symptoms of diseases in the digestive system include:

• Abdominal Pain
• Constipation
• Diarrhea
• Nausea

Procedures

Many procedures have been developed to diagnose and treat diseases of the digestive sytem:

• Colonoscopy
• Esophagogastroduodenoscopy (EGD)
• Fecal Occult Blood Test
• Sigmoidoscopy

Surgery

Surgeries that are performed on the digestive system include the following:

• Gastric Banding
• Nissen Fundoplication

Radiographic studies

• Barium Enema
• Virtual Colonoscopy

Related Professions

• A gastroenterologist is a medical doctor (MD) who has completed a residency in internal medicine followed by specialized training in disorders of the digestive system.
• A general surgeon is a surgeon trained to treat a variety of diseases, including those of the stomach, small and large intestines, liver, gall bladder, and pancreas.
• A dentist is a doctor of dental surgery trained to treat diseases of the teeth and oral cavity.
• An oral surgeon is a dentist trained to treat diseases of the oral and maxillofacial regions.

History

Surgeon William Beaumont is famous for experiments he conducted on Alexis St. Martin, a victim of a gunshot wound to the stomach, who developed a fistula, or connection between the stomach and the skin. Beaumont would tie food to a piece of string and pass it through the fistula into the stomach and later remove it and observe the digestion that had occurred.^[1]

Research

The Director of the NIH, Dr. Elias A. Zerhouni, has established a National Commission on Digestive Diseases based on the mutual interest in advancing digestive diseases research shared by the NIH and the Congress.^[2]

References

1. ↑ Wikipedia. William Beaumont.
2. ↑ National Institute of Diabetes and Digestive and Kidney Diseases Web site. Research: Digestive Diseases.

External Links

American Gastroenterological Association

American College of Gastroenterology

National Institute of Diabetes and Digestive and Kidney Diseases