Gastrointestinal System Physiology PDF

# Physiology and Pathophysiology of Gastrointestinal System ## Presented by: Dr. Noha Fawzy Lecturer of pharmacology and toxicology Faculty of pharmacy MTI University ## Gastrointestinal System Diagram This diagram shows the following parts of the Gastrointestinal System: - **Oral Cavity** -...

# Physiology and Pathophysiology of Gastrointestinal System ## Presented by: Dr. Noha Fawzy Lecturer of pharmacology and toxicology Faculty of pharmacy MTI University ## Gastrointestinal System Diagram This diagram shows the following parts of the Gastrointestinal System: - **Oral Cavity** - **Salivary Glands** - **Pharynx** - **Esophagus** - **Liver** - **Gall Bladder** - **Stomach** - **Spleen** - **Pancreas** - **Large Intestine** - **Small Intestine** ## Physiology of Gastrointestinal Tract The main functions of the Gastrointestinal tract are to **digest** and **absorb** ingested nutrients, and to excrete waste products of digestion. ### Digestion: Includes both **mechanical** and **chemical** processes. 1. **Mechanical Digestion:** - A purely physical process that does not change the chemical nature of the food. - Only makes the food smaller. 2. **Chemical Digestion:** - Digestive secretions break down food macromolecules into their chemical building blocks. - For example, proteins into amino acids, fats to fatty acid and glycerol. - This step is very important as it is difficult for macromolecules to pass through membranes during absorption. ### Mechanical Breakdown of Food: 1. **Mouth** - Only carbohydrates - Here digestive processes begin - **Mechanical Digestion:** - **Mastication:** or chewing - Break food into smaller bits and mix food with saliva. - Contains mucus and H₂O to moisten food and lubricate the esophagus. - Neutralizes food to become a soft mass called a bolus. - Contains bacteriolytic enzymes for antimicrobial action. - **Chemical Digestion:** - **Ptyalin:** (salivary amylase) breaks down polysaccharides (starches) into disaccharides. 2. **Stomach** - Only protein. - Once the bolus is propelled to the stomach through the esophagus. - **Mechanical Digestion:** - **Churning:** of food in the stomach serves to further break it smaller besides mixing food with gastric juice. - Gastric juice is secreted by the parietal cells of the stomach mucosa. - Food becomes a thick material called chyme. - **Gastrin Hormone:** - This is done under the control of the Gastrin hormone. - Secretion by specialized epithelial cells called endocrinocytes, located in the mucosal epithelium of the stomach. ## Mixing and Emptying Actions: - This diagram shows that the **pyloric sphincter** is contracted when the food enters the stomach. - Once the food is mixed and churned into chyme, the **pyloric sphincter** relaxes and sends chyme to the duodenum. ## Gastric Juice Components & their Functions: 1. **Hydrochloric Acid:** - Makes gastric juice. - Highly acidic. - Activating pepsinogen. - Antimicrobial activity. - Aids in iron absorption through activating ferric reductase to convert ferric to absorbable ferrous that is absorbed from the duodenum. - This process is also activated by Vitamin C. - Inhibited by antacid drugs and tannins. 2. **Pepsinogen** - Activated to pepsin. - Begins the digestion of proteins to polypeptides. 3. **Intrinsic Factor** - Binds with Vitamin B₁₂ to form a complex (resistant to acidity). - In the intestine, this complex degrades and Vitamin B₁₂ is absorbed from the small intestine. ## Only alcohols and aspirin are absorbed through the stomach lining to bloodstream. ## Protection of the Stomach wall from Acidity: - The stomach wall is protected from acidity by the secretion of **prostaglandins** which: - Secret insoluble mucus that acts as a protective barrier. - Secret buffer which neutralizes acidity near cell lining. - Improve gastric mucosal blood flow. ## Chyme is passed through the **pyloric sphincter** into the small intestine. ## Function of Pepsins - This diagram shows how **pepsinogen**, in acidic conditions, is converted to **pepsin** through the action of **HCL**. - **Pepsin** then breaks down **proteins** into **polypeptides**. ## Small Intestine: - Here digestion is completed and absorption takes place. - **Secretin**: is secreted from the duodenal mucosa for: - Inhibiting gastric juice secretion and stomach motility. - Increasing secretion of bicarbonate ions to neutralize the acidity of chyme and make the medium alkaline by which pancreatic enzymes are activated. - Stimulating mechanical digestion. ## Mechanical Digestion in the Small Intestine: - **Segmentation:** breaks up chyme further mixes it with digestive juices and facilitates absorption. ## Cholecystokinin (CCK) hormone - Secreted from duodenal mucosa. - Controls **segmentation**. - Completes digestion of carbohydrates, proteins (started in mouth and stomach), and fats. - Stimulates the secretion of pancreatic enzymes. - Release of bile made by the liver from the gall bladder. ## Chemical Digestion - Duodenum receives **Pancreatic Enzymes** from the pancreas. - Examples of these enzymes include: - **Trypsinogen** - **Chemotrypsinogen** - **Amylase** ## Functions of Pancreatic Juice Enzymes: - **Pancreatic Amylase**: breaks down disaccharides into monosaccharides. - **Pancreatic Lipase**: breaks down fats into glycerol + fatty acids. - **Trypsinogen**: breaks down polypeptides into smaller polypeptides. - **Chymotrypsinogen**: breaks down smaller polypeptides into amino acids. ## Digestion of Fats: - This process is acted through these two steps: - **Secretion of Bile:** - Non-enzymatic juice composed of bile salts that emulsify fats. - Bile pigment (bilirubin) gives it a yellowish-green color. - **Secretion of Pancreatic Lipase:** - Acts on emulsified fats. - Converts them into fatty acids and glycerol. ## Along with water and electrolytes, these nutrients are absorbed through the intestinal mucosa into the bloodstream for use by the body. ## Regulation of Gastrointestinal Tract ### 1. CNS Control (Long Reflexes) - Digestion under control of CNS is stimulated in response to two stimuli. 1. **First Stimuli:** Outside the digestive system, such as sight, smell, and taste of food. - This initiates long reflexes which begin with a sensory neuron delivering a signal to the medulla oblongata. - This signals muscular contractions and secretions by transmitting the impulse to mechanoreceptors and chemoreceptors in the walls of the alimentary canal. 2. **Second Stimuli:** The expansion of GIT with entrance of food. - This stimulates mechanoreceptors and chemoreceptors, sending afferent impulses to CNS to continue the digestive signaling and cause the enteric nervous system to secrete hormones such as: - Gastrin - Secretin - CCK ### 2. Enteric Nervous System (Short Reflexes) - This is an intrinsic nerve plexus within the alimentary canal wall. - Sends impulses in response to expansion of GIT with food. - Regulates the motor functions of the system in addition to the secretion of gastrointestinal enzymes under hormonal control. - Although the enteric nervous system (ENS) normally communicates with the central nervous system (CNS), it is capable of operating independently of the brain and spinal cord. - For this reason, the Enteric Nervous System is often called a "second brain". ## Summary of Hormonal Control of Digestive Secretions - This diagram shows how the following hormones regulate digestive secretions: - **Secretin**: - Secreted in response to acid food in the duodenum. - Inhibits stomach motility and increases bicarbonate secretion. - **CCK**: - Secreted in response to fatty foods in the duodenum. - Increases enzyme flow and increases bicarbonate secretion. - **Gastrin**: - Secreted in response to food in the lower stomach, and increases stomach motility and increases acid production. ## Gastrointestinal Disorders ### Peptic Ulcer - A peptic ulcer is a lesion in the mucosal membrane of the upper GI tract (stomach, duodenum). #### Causes of Peptic Ulcers: 1. **Helicobacter pylori:** - This bacterial infection is the cause of 90% of peptic ulcers. - It releases a toxin that destroys the stomach's mucus coat, reducing the epithelium's resistance to acid digestion and causing gastritis and ulcer disease. 2. **Nonsteroidal Anti-Inflammatory Drugs (NSAIDs):** - These drugs work by inhibiting COX1, which produces prostaglandins in the stomach. - Prostaglandins protect the stomach wall during digestion. - Inhibition of prostaglandins leads to: - Inhibition of the insoluble mucus. - Inhibition of HCO₃ which neutralizes acidity. - Decreased blood flow. ### Complications of Peptic Ulcer: 1. **Erosion of the mucosa:** - Can cause gastrointestinal hemorrhage, which can progress to hypovolemic shock. 2. **Obstruction of the pylorus:** - Due to inflammation and edema. ### Signs & Symptoms of Peptic Ulcer: - Loss of weight and appetite. - Abdominal pain which is increased by eating, heartburn, and indigestion. - Feeling of abdominal fullness. - Anemia, caused by blood loss, so gives pale skin.