Digestion and Absorption Digestion The process by which
Digestion and Absorption Digestion: The process by which food is broken down into absorbable units. Digestion: Take a part.
Absorption: The uptake of • nutrients by the cells of the small intestine for transport either the blood or lymph. Absorb: Suck in •
Gastrointestinal (GI) Tract: The digestive tract. The principal organs are the stomach and intestines. Gastro: Stomach. Intestinalis: Inttestine. Mastication: The process of chewing
The digestive System
Digestive Tract The Gastrointestinal tract (GI ): Is a • flexible muscular tube that extends from the mouth, through the esophagus, stomach , small intestine, large intestine and rectum to the anus. The inner space within the GI tract •
Functions of Digestive Ingestion • Mechanical processing • Digestion • Secretion • Absorption • Excretion •
Control of digestive system Movement of materials along the • digestive tract is controlled by: Neural mechanisms – Parasympathetic and local reflexes • Hormonal mechanisms – Enhance or inhibit smooth muscle • contraction
Movement of the Digestive Materials Visceral smooth muscle shows • rhythmic cycles of activity Pacemaker cells– Peristalsis • Waves that move a bolus– Segmentation • Churn and fragment a bolus–
Stages of Digestion in the Mouth: 1 - Analysis of material before swalling. 2 - Mechanical processing by the teeth, tongue and platal surface. Lubrication. Limited digestion.
e teeth: Crush large pieces of od into smaller ones. ste buds: Detect one or a ombination of four taste sweet, alty, bitter and sour. e tongue: Taste food, move food ound the mouth, facilitating
vary gland: ee pairs of gland produce saliva amount of saliva produced is 1 -1. 5 /daily.
The rate of secretion is controlled by: 1 impulses and the stimuli for secretion are psychic (sight, smell, taste and thought o 2 - Mechanical: chew of food. 3 - Chemical: stimulation of taste buds. Th of secretion is controlled by: 1 - Nerve im and the stimuli for secretion are psychic smell, taste and thought of food.
Saliva contain: Amylase (Ptyaline): which hydrolyze starch into maltos, isomaltose and dextrine. Mucin: It is a mucoprpteinact as a lubricant which facilitate the swalling of the food.
Saliva also contain inorganic ions such as Ca ion help to stabilise the amylase and cl ion increase the activity of amylase.
Pharynx: A short tube that is shared by both digestive and respiratory system. The food passes through the pharynx. To prevent choke the epiglottis closes off.
As food enters the duodenum, Threes sources o digestive j juices are secreted: The liver: secretes Bile. The pancreas: secretes pancreatic juices. Crypts: Tubular glands secrete intestinal juices
Digestion in the Small intestine The small is the organ of digestion and absorption. The small intestine is divided into three segments: The duodenum, the jejunum and the ileum.
The Stomach Figure
Digestion in the stomach
Esophagus: Passers food from the mouth to the stomach. Bolus: A portion with respect to food, the amount swallowed at one time. Bolos: Lump. Bolus: Rounded mass of food formed in the mouth and ready to be swallowed.
Bile: An exocrine secretion, flows into the duodenum. The liver synthesis bile, it is concentrated and stored in the gallbladder and released into the small intestine when needed.
ontrol Secretions: Two system coordinate all the digestion and absorption: 1)The nervous system. 2) The hormonal system.
The nervous system in response to the visual and chemical sense. Presence of food in the GI tract and emotions.
Gastrointestinal Hormones: Gastrin: It is a polypeptide. Release from mucosal cells in the antrum of the stomach. Stimulant for release: food in the stomach, peptides, amino acids, caffeine, beverage, alcohol and meat extract.
Organs affected: stomach, esophagus and entire GI tract. Functions: -Stimulate the secretion of Hcl by stomach. - Increase gastric antral motility. Increase lower esophageal sphincter tone.
When the PH falls below 3 a feedback mechanism cuts off Gastrin secretion and prevent excess acid formation.
Enterogastrone: It is a peptide hormone. Secreted from duodenal mucosa. Stimulant for release: present of fat food in the diet.
Functions: Prevent gastric activity by: - Inhibits gastric HCL secretion and pepsin. - Inhibits gastric motility. - Protect against the development of duodenal ulcer in some experimental animals
Secretin: It is polypeptide. Secreted by duodenal mucosa. Stimulant for release: acid chyme when enters the duodenum from the stomach
Organs affected: Pancreas: - Stimulates the pancreas to secrete bicarbonate rich juices into the small intestine. - Stimulates output of water. - Increase release of insulin and some pancreatic enzymes.
5 In duodenum: Decreases motility and increases mucus output.
Cholecystokinin (cck): A peptide hormone. Secreted from duodenal mucosa. Stimulant for release: fat or protein in the small intestine.
Organs affected: - pancreas: stimulates secretion of pancreatic enzymes. - Stomach: slow gastric emptying. - Colon: increase motility.
Gastric inhibitory polypeptide (GIP): Release from small intestine. Stimulant for release: Glucose and fat. Organs affected: Stomach and pancreas: Inhibits gastrin. Stimulate gastric acid secretion. Small intestine: inhibits motility.
Motilin: Release from stomach, small intestine and large intestine. Stimulant for release: biliary and pancreatic secretion. Organs affected: stomach small and large intestine: Promote gastric emptying and increase GI motility.
Somatostatin: Release from stomach, pancreas and upper small intestine. Stimulant for release: gastric and duodenal acidity, product of protein and fat digestion.
Organs affected: Stomach, pancreas, small intestine and gallbladder: - Inhibits release of gastrin, motilin and pancreatic secretion. - Decrease motility and contraction of GI tract.
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