Gastrointestinal Physiology Quiz

Gastrointestinal (GIT) Physiology

• The digestive system is responsible for the breakdown of food into absorbable components.
• The digestive system has four main functions: motility (movement of food), secretion (release of digestive juices), digestion (breakdown of food), and absorption (uptake of nutrients).
• The digestive system includes organs like the mouth, pharynx, esophagus, stomach, small intestine, and large intestine. Accessory organs include the salivary glands, liver, gallbladder, and pancreas.

Parts of the Digestive System

• Mouth: Mechanical digestion begins here by chewing, while saliva contains enzymes including amylase to initiate starch digestion.
• Pharynx: The throat, a passageway for air and food.
• Esophagus: Transports food from the pharynx to the stomach.
• Stomach: Holds and mixes food with gastric juices (HCl, pepsin). Proteins are digested here.
• Small Intestine: The primary site of digestion and absorption of nutrients.
• Large Intestine: Absorbs water and electrolytes and forms feces.
• Accessory organs: Salivary glands, liver, gallbladder, and pancreas contribute juices that aid digestion in the small intestine.

Digestive System Summary of Functions

• Oral Cavity & Esophagus: Motility: swallowing and chewing. Secretion: saliva (amylase). Digestion: minimal carbohydrate and fat. Absorption: none.
• Stomach: Motility: peristaltic mixing and propulsion. Secretion: HCI, pepsinogen, mucus, gastrin. Digestion: proteins, fats. Absorption: lipid-soluble substances.
• Small Intestine: Motility: mixing (segmentation), propulsion. Secretion: enzymes (pancreas, liver, intestine), HCO3-. Digestion: carbohydrates, fats, protein, nucleic acids. Absorption: nutrients.
• Large Intestine: Motility: segmental mixing, mass movement. Secretion: mucus. Digestion: limited (by bacteria). Absorption: water, mineral, vitamins.

Functional Anatomy of GIT Wall

• Mucosa: Secretes, absorbs, protects.
• Submucosa: Blood vessels and lymphatics, allows GIT wall stretch.
• Muscularis: Motility is possible due to longitudinal and circular muscle layers.
• Serosa: Attachment, lubrication; prevents friction.

Structure of GI

• The GI tract has a layered structure with a lumen (central cavity) surrounded by mucosa, submucosa, muscularis externa, and serosa. These layers support secretion, absorption, and motility.
• Specialized cells in each layer support these functions.

Stomach Functions

• Motility: Storage and emptying of food, with emptying speed variable among food types.
• Secretion: Secrete gastric juice with pepsin, HCI and other components.

The Stomach: Gastric Glands

• The stomach contains gastric glands responsible for producing gastric juice.
• Specialized cells in the gastric glands include parietal cells (HCl), chief cells (pepsin), mucous cells, enterochromaffin-like cells (histamine), and G cells (gastrin).

Secretion of Gastric Glands

• Different cells in the gastric glands are stimulated by different factors to produce various components of gastric juice.

Control of Gastric Secretion

• Gastric secretion is controlled by the cephalic (before food), gastric (during food), and intestinal (after food) phases, influenced by nerves, hormones, and other factors.

Gastric Acid Secretion

• Parietal cells actively secrete HCI, playing a major role in protein digestion, killing bacteria and activation of pepsinogen.

Mechanism of Gastric Acid Secretion

• Carbonic anhydrase catalyzes the reaction of CO2 and water to form carbonic acid, disassociating into hydrogen ions and bicarbonate ions, which are exchanged for chloride in the lumen.

Gastric Acid Protection

• Strong acid in the stomach is contained due to the epithelial cells, tight junctions, and mucus lining. In addition, there is a high turnover rate to replace cells damaged by the acid.

Peptic Ulcer

• Peptic ulcers are caused by injury to the stomach wall, most commonly from bacteria like Helicobacter pylori or drugs.

Drug Treatment of Peptic Ulcer

• Drug treatments include H2-histamine receptor blockers, proton pump inhibitors, and antibiotics. These drugs aim to reduce acid secretion and treat infection.

Stomach Absorption

• The stomach does not readily absorb much. Alcohol and aspirin, being relatively weak acids, can be absorbed in small quantities.

Pancreatic Juice and Bile

• The pancreas has endocrine and exocrine functions. Endocrine secretions include hormones like insulin and glucagon while exocrine secretions are pancreatic juice rich in enzymes.
• Pancreatic juice is rich in enzymes for digesting carbohydrates, proteins, fats, and nucleic acids. Pancreatic juice also contains bicarbonate, which neutralizes acidic chyme from the stomach.

Pancreatic Enzymes

• The pancreas produces various enzymes, each specific for a different macromolecule, and must be activated in the duodenum by enterokinase or other specific enzymes.

Phases of Pancreatic Secretion

• The pancreas' secretion is influenced by different phases (cephalic, gastric, and intestinal), triggered by factors like nerves and hormones in the duodenum. The intestinal phase is largely responsible for the secretion.

Hormonal Control of Pancreatic Juice

• Two major hormones, Secretin and Cholecystokinin (CCK), regulate pancreatic secretion. Secretin stimulates bicarbonate production in the pancreatic duct cells. Cholecystokinin (CCK) stimulates enzyme secretion in the acinar cells.

Liver Functions

• The liver secretes bile, processes nutrients, synthesizes proteins and clotting factors, filters blood, and excretes metabolites and drugs.

Bile

• Bile is produced by the liver, stored in the gallbladder, and released into the duodenum to emulsify fats and enhance lipid digestion and absorption.

Control of Bile Secretion

• Bile secretion is regulated by bile salts (enterohepatic circulation), secretin (acidic chyme), and vagal stimulation.

Test your knowledge on the functions of the digestive system and the anatomical structure of the gastrointestinal tract. This quiz covers topics such as the movement of food, nervous regulation, and the roles of various enzymes and muscle layers involved in digestion.