Digestion and absorption of food take place in gastrointestinal tract that represent a tube beginning in the mouth cavity and ending in rectum. The digestive tube is divided into different part each of which fulfill a specific function. Digestive system begins with oral cavity, then follows pharynx, esophagus, stomach, small and large intestine. The wall of the digestive tube consists of four different layers: mucosa, submucosa, muscular layer and serous membrane.
Oral cavity includes teeth, tongue and salivary glands. In the mouth food is undergone mechanical grinding by teeth. Tongue is a muscular organ that is covered by a wide variety of taste and temperature receptors. Tongue participate in formation of food bolus. Salivary gland produce saliva that moistens food bolus and contains enzyme (alpha-amylase) that breaks down starch into polysaccharides.
The pharynx has a funnel-shaped form, connects the mouth cavity and esophagus. It consists of three main parts: nasopharynx, oropharynx and larynx. The pharynx participates in swallowing of food bolus.
Esophagus is the upper part of the alimentary canal, represents 25 cm tube consisting from striated and smooth muscles. The tube is covered by pavement epithelium. . The esophagus carries food into the stomach.
Stomach is the extended part of the gastointestinal tract. The stomach walls consist of smooth muscle tissue and are covered by glandular epithelium. Stomach glands produce gastric juice. The main function of the stomach is digestion.
Digestive gland: liver and pancreas. The liver produces bile, which participates in digestion. Pancreas produced enzymes that break down proteins, fats and carbohydrates. It also produces hormones insulin that controls sugar blood levels.
Intestine begins the duodenum. The duodenum precedes the jejunum and ileum and is the shortest part of the small intestine, where most chemical digestion takes place.
Small intestine is the longest part of the digestive system. The mucous membrane forms the villi consisting from blood and lymphatic capillaries. The process of absorption take place through these villi.
The large intestine has a length of 1,5 m, it produces mucus contains bacteria decomposing cellulose. Gastrointestinal tract ends with rectum and anus through which undigested food is eliminated.