Definition: The breakdown of large food molecules or complex food molecules into smaller food molecules or simple food molecules is called digestion.
The passage of these molecules (digestive molecules) into blood and lymph is called absorption.
The digestion and absorption is in our body the organ is perform is called digestive system. The digestive system is composed by two main groups.
- GIT (Gastro Intestinal Tract)
- Accessory Digestive Organ
- The GIT is continuous tube which start from mouth to the anus.
- The accessory digestive organs include teeth, tongue, salivary gland, liver, gall bladder and pancreas.
- GIT includes mouth, nasopharynx, oesophagus stomach, small intestine (Duodenum, Jujjaunm, Illeum) and large intestinal (Ciecum, colou , rectum, anus canal ) and anus.
Digestion include six basic process:
- Ingestion, secretion, mixing, propulsion, mechanical and chemical digestion, absorption and defecation.
- Mechanical digestion consists of mastication and moment of the Gastro intestinal tract. That aid chemical digestion.
- Chemical digestion each a series of hydrolysis reactions that break down carbohydrates, lipids, proteins and nucleic acids in food into smaller molecules that are utilize by body cells.
Layers of the Gastro Intestinal Tract:
- The basic arrangement of layers in Gastro Intestinal Tract from deep to superficial is mucosa, submucosa , muscular and serosa.
- Associated with the lamnia propria of the mucosa are extensive patches of lymphatic tissue cold mucosa associated lymphatic tissue.
- The mouth is found or formed by check, hard and soft plate, lips, and tongue.
- The vestibule is space bounded by checks and lips externally and internally by teeth and gums.
- The oral cavity proper extends from vestibule to faces.
- The tongue together with its associated muscles form the flower of oral cavity. It is composed of skeletal muscle covered with mucous membrane.
- The upper surface and sides of the tongue are covered with papillae, some of which contain taste buds.
- The major portion of saliva by major salivary gland which lies outside the mouth and pour their contact into duct that empty into oral cavity.
These are three pairs of major salivary glands.
- Parotid gland
- Submandibular gland
- Sublingual gland
- Saliva lubricates foods and start the chemical digestion of carbohydrates.
- Salivation is controlled by nervous system.
- The teeth project into the mouth and are adapted for mechanical digestion.
- A typical tooth consists of three parts.
- Crown (b) Root (c) Neck
- Teeth are composed primary of dentitions
- Deciduous (b) permanent
- Through mastication food is mixed into saliva and shaped into a soft, fleibles mass called a bolus.
- Salivary amylase begins the digestion of starch and sublingual lipase begin the digestion of lipids.
By this part the food are swallowing moves a bowls from the mouth to stomach.
Swallowing consists of two voluntary stages.
- Pharyngeal step
- Esophageal step
- The esophagus is collapsible , muscular tube that connect the pharynx to stomach.
- It possess food as a bolus from pharynx to stomach.
- It contain an upper and lower esophageal sphincter.