Saturday, January 4, 2014

What are the components of the human digestive system?

What are the components of the human digestive system?
Humans have a complete digestive system. Swallowing forces food and water from the mouth into the pharynx. Food continues through an esophagus to the stomach. Food processing starts in the mouth. Most digestion and absorption occurs in the small intestine. The colon absorbs most of the remaining water and ions, which causes the wastes to compact. The rectum briefly stores the wastes before they are expelled through the anus.The liver and pancreas have an accessory role in digestion. They produce substances that are secreted into the small intestine.

Human Digestive system

 

The human alimentary canal: The alimentary canal begins at the mouth and the pharynx.
From here, food travels down a muscular tube called the esophagus and into the stomach. The stomach connects to the small intestine, which in turn connects to the large intestine. Some form of mechanical and chemical digestion breaks down food at every step along this tube and Nutrients are absorbed across the walls of both intestines. All products remaining after food travels through the large intestine are waste, which exit the body through the anus.
Saliva: Contains water, salt and an enzyme called salivary amylase. Salivary amylase breaks down starch into smaller sugars. Contains buffers, substances that neutralize acidic foods. Antibacterial substances that kill bacteria in the food. Also eases the passage of food through the pharynx and esophagus.
The Esophagus The esophagus shuttles food from the pharynx (part of mouth) to the stomach. The muscles surrounding the esophagus perform peristalsis, the rhythmic and stepwise contraction of muscle that forces food to move along the esophageal passage. Sphincter muscles at each end prevent backflow.
The Stomach A saclike organ. Inner surface is highly convoluted, allowing it to fold up when empty and expand when full. Digestion occurs in the stomach as gastric juice, is secreted by gastric glands located in the stomach lining. Gastric juice is an acidic mixture of enzymes and mucus. Gastric glands are composed of two types of cells: 
Parietal cells: secrete hydrochloric acid (HCl)
Chief cells: secrete pepsinogen, the precursor to the enzyme pepsin.
Protein digestion is initiated by the acidic environment of the stomach. The HCl, lowers the acidity of the gastric juice to a pH level of 2. Low pH levels are necessary for pepsinogen to be converted into the active digestive enzyme pepsin, which further breaks down food proteins. If chief cells were to secrete pepsin directly into the stomach, the pepsin would digest the cells themselves. Additionally, mucus lines the stomach walls and prevents it from being digested. A mixture of gastric acid and partially digested food called chyme passes out of the stomach.