Human Digestive System
The digestive tract is a series of hollow organs through which food passes: mouth, pharynx, esophagus, stomach, small intestine. Each portion is specialized for one or more aspect of the three major functions of the digestive system the secretion, digestion, and absorption. Accessory organs such as salivary glands, liver, gallbladder and pancreas have duct that lead into the digestive tract and thus support digestive function.
Digestion is defined as the mechanical and chemical breaking down of food into smaller components, to a form that can be absorbed and utilized by the cells of the body. The two phase of digestion are mechanical and chemical or enzymatic. The former involves the movement of organs while the latter involvesthe actions of enzymes in the process of digestion. These enzymes produced by the body cell and released catalyze specific chemical reaction.
Mouth the beginning of the one-way human digestive tract. Mouth does not only serve as the entrance of food but is also functioning in digestive process. It features teeth and tongue that are both accessory organs of digestion as well as saliva. The teeth are responsible for tearing, biting and churning of food. Tongue is responsible for determining taste of the food, mixing them and pulling bolus down the esophagus in the process of swallowing or deglutition. The salivary glands release saliva that lubricates the food for easy swallowing and pass to esophagus and it contains the salivary amylase that is responsible for breakdown of carbohydrates. Saliva is a watery solution containing mucus, mineral ions and digestive enzymes. The enzyme is secreted by the salivary glands are parotid glands, submandibular glands and sublingual glands. Parotid glands are secretes a serous solution that flows through a parotid duct leading to the cheek wall across from the second upper molar. Submandibular glands are produce mostly serous fluid and mucous fluid. Sublingual glands produce mostly mucous fluid.
Esophagus is a long muscular tube approximately 2.5 cm connecting the pharynx to the stomach. It is the vital component of human digestive system without it there would be no way of food and liquids to make their way to our stomach. The top of the esophagus attached to the pharynx, which is the anatomical term for our throat and it also the common chamber between the upper respiratory tract and digestive tract. The esophagus is a unique organ which is the upper part is under voluntary control
while the muscles of the lower end are involuntary. Upper esophageal sphincter refers to the superior portion of the esophagus. Lower esophageal sphincter, it consists of striated muscle and yet, is not under conscious control. Peristaltic movement is initiated by circular smooth muscles contracting behind the chewed material to prevent it from moving back into the mouth, followed by a contraction of longitudinal smooth muscles which pushes the digested food forward.
Stomach is an enlargement of the digestive tract just inferior to the diaphragm at the end of esophagus. A human stomach is a muscular, elastic, pear-shaped bag, lying crosswise in the abdominal cavity beneath the diaphragm. Food goes to the stomach via the esophagus. The food in this are becomes a semi-solid, soapy mixture called chime. The stomach composed of four layers of tissues. The inner most layer is the mucosa where stomach acid and digestive juices are made. Next layer is the sub mucosa which is surrounded by the muscularis, a layer of muscle that moves and mixes the stomach content. The next layer is serosa which is the covering of the stomach. The stomach walls particularly the mucosa secretes gastric juices. This is strong acidic liquid, PH 1 to 3 in humans which is close being colorless. Its main components are digestive enzyme pepsin which initiates the breakdown of proteins and rennin, hydrochloric acid and mucus. A...
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