Digestive System PDF

**[Digestive system ]** **[Learning outcomes ]** **1. Describe the Organs of the Digestive System** - **Mouth**: The entry point where food is ingested. Teeth, tongue, and salivary glands work together to chew and mix food with saliva, beginning the process of digestion. - **Pharynx...

**[Digestive system ]** **[Learning outcomes ]** **1. Describe the Organs of the Digestive System** - **Mouth**: The entry point where food is ingested. Teeth, tongue, and salivary glands work together to chew and mix food with saliva, beginning the process of digestion. - **Pharynx and Esophagus**: The pharynx connects the mouth to the esophagus, guiding food down. The esophagus is a muscular tube that transports food to the stomach using rhythmic contractions known as peristalsis. - **Stomach**: A muscular, J-shaped organ that churns food and mixes it with gastric juice. Its acidic environment aids in protein digestion and kills pathogens. - **Small Intestine**: Comprised of the duodenum, jejunum, and ileum, it is the primary site for digestion and nutrient absorption. - **Large Intestine**: Includes the cecum, colon, rectum, and anus. It absorbs water and electrolytes, forming and storing feces before excretion. - **Accessory Organs**: - **Liver**: Produces bile to emulsify fats, processes nutrients absorbed from the small intestine, and detoxifies chemicals. - **Gallbladder**: Stores and concentrates bile, releasing it into the small intestine as needed. - **Pancreas**: Produces digestive enzymes (like lipase, amylase, and proteases) and bicarbonate to neutralize stomach acid in the small intestine. **2. Explain the Functions of the Major Organs of Digestion** - **Mouth**: Initiates mechanical digestion through chewing and starts carbohydrate digestion with salivary amylase. - **Stomach**: Secretes gastric juice containing hydrochloric acid (HCl) and pepsinogen (activated to pepsin in the acidic environment) to begin protein digestion. - **Small Intestine**: Completes chemical digestion with the help of enzymes and absorbs nutrients into the bloodstream via villi and microvilli. - **Large Intestine**: Absorbs water and salts from the remaining indigestible food, converting it into feces for excretion. - **Liver**: Processes and stores nutrients, synthesizes bile for fat emulsification, and detoxifies the blood. - **Gallbladder**: Stores bile and releases it when fat enters the small intestine. - **Pancreas**: Secretes enzymes (amylase, protease, and lipase) for digesting carbohydrates, proteins, and fats, as well as bicarbonate to neutralize acidic chyme from the stomach. **3. Describe the Types of Tissue and Linings Associated with Digestive Organs** - **Mucosa**: Innermost layer lining the alimentary canal, containing glandular epithelial cells that secrete digestive enzymes, mucus, and hormones. - **Submucosa**: Layer of connective tissue containing blood vessels, lymphatics, and nerves that support nutrient absorption and transport. - **Muscularis Externa**: Contains layers of smooth muscle that facilitate peristalsis and segmentation. It has two main layers: inner circular and outer longitudinal muscle layers, with a third oblique layer in the stomach. - **Serosa (Adventitia)**: The outermost layer, composed of connective tissue, reduces friction between digestive organs and surrounding structures. **4. List the Functions of Gastric Juice** - **Protein Digestion**: Gastric juice contains pepsinogen, which is activated to pepsin in the acidic environment, breaking down proteins into peptides. - **Acidic Environment**: Hydrochloric acid (HCl) creates a low pH, denaturing proteins and killing bacteria in food. - **Intrinsic Factor Production**: Secreted by the stomach, intrinsic factor is essential for vitamin B12 absorption in the small intestine. - **Mucus Secretion**: Protects the stomach lining from being digested by its own acidic contents and enzymes. **5. Summarize the Chemical Digestion of Food** - **Carbohydrates**: Salivary amylase in the mouth starts breaking down starches into maltose. In the small intestine, pancreatic amylase continues this process, breaking polysaccharides down into disaccharides and monosaccharides for absorption. - **Proteins**: Pepsin in the stomach initiates protein digestion, breaking proteins into smaller peptides. In the small intestine, pancreatic proteases (trypsin and chymotrypsin) further break down peptides into amino acids. - **Fats**: Bile from the liver emulsifies fats in the small intestine, breaking them into smaller droplets. Pancreatic lipase then digests triglycerides into fatty acids and glycerol, making them easier to absorb. - **Nucleic Acids**: Pancreatic nucleases digest nucleic acids (DNA and RNA) into nucleotides, which are further broken down and absorbed in the small intestine. **1. Component Parts of the Alimentary Canal** - **Mouth**: Begins mechanical and chemical digestion; teeth chew food, and salivary enzymes begin to break down carbohydrates. - **Pharynx**: Pathway for food to move from the mouth to the esophagus; involved in swallowing. - **Esophagus**: A muscular tube that transports food from the pharynx to the stomach using peristalsis. - **Stomach**: Secretes gastric juices for protein digestion and churns food into a semi-liquid form called chyme. - **Small Intestine**: Primary site of nutrient absorption; divided into the duodenum, jejunum, and ileum. - **Large Intestine (Colon)**: Absorbs water and salts; forms and stores feces. - **Rectum and Anus**: Control the release of feces from the body. **2. Five Activities in the Alimentary Canal** - **Ingestion**: Taking food into the mouth. - **Propulsion**: Moving food through the canal, mainly by peristalsis. - **Mechanical Digestion**: Physically breaking down food via chewing, stomach churning, and segmentation in the intestines. - **Chemical Digestion**: Enzymatic breakdown of food into absorbable molecules. - **Absorption**: Uptake of nutrients into the bloodstream or lymphatic system, mainly occurring in the small intestine. **3. What is Formed During Mastication, Ready for Swallowing?** - **Bolus**: A soft, rounded mass of chewed food mixed with saliva, making it easier to swallow. **4. What Assists the Formation of the Bolus?** - **Saliva**: Secreted by salivary glands, it moistens food and contains enzymes like amylase, which begins carbohydrate digestion. **5. What Needs to be Closed Off Before Swallowing Takes Place?** - **Epiglottis**: This flap closes over the trachea to prevent food from entering the airway. **6. Function of Smooth Muscle in the Wall of the Esophagus** - **Peristalsis**: Rhythmic contractions of smooth muscle push the bolus down toward the stomach. **7. What is the Food Called Within the Stomach?** - **Chyme**: A semi-liquid mixture of partially digested food and gastric juices. **8. Names and Details of Both Stomach Sphincters** - **Lower Esophageal (Cardiac) Sphincter**: Controls food entry from the esophagus to the stomach and prevents acid reflux. - **Pyloric Sphincter**: Regulates the passage of chyme from the stomach into the small intestine. **9. pH Environment of the Stomach** - **Highly Acidic (pH 1.5-3.5)**: The acidic environment, due to hydrochloric acid (HCl), helps break down food and kills bacteria. **10. Parts of the Small Intestine and Details** - **Duodenum**: First section where most chemical digestion occurs; receives bile and pancreatic enzymes. - **Jejunum**: Middle section, where a significant portion of nutrient absorption occurs. - **Ileum**: Final section that absorbs remaining nutrients, especially vitamin B12 and bile salts. **11. Two Ducts Entering the Small Intestine and Their Functions** - **Bile Duct**: Carries bile from the gallbladder and liver to the duodenum for fat digestion. - **Pancreatic Duct**: Delivers digestive enzymes and bicarbonate from the pancreas to the duodenum, aiding in chemical digestion. **12. Major Function of the Small Intestine Apart from Digestion** - **Absorption**: The small intestine absorbs nutrients into the bloodstream through villi and microvilli, increasing surface area. **13. Accessory Organs of the Digestive System** - **Liver**: Produces bile, processes nutrients, detoxifies, and regulates metabolism. - **Gallbladder**: Stores and concentrates bile produced by the liver, releasing it when needed for fat digestion. - **Pancreas**: Produces digestive enzymes and bicarbonate to neutralize stomach acid in the small intestine. **14. Hormone Stimulating Release of Bile from the Gallbladder** - **Cholecystokinin (CCK)**: This hormone is released when fats enter the small intestine, signaling the gallbladder to release bile. **15. Function of Bile Salts and Phospholipids in Bile** - **Emulsification of Fats**: Bile salts and phospholipids break down large fat droplets into smaller ones, allowing enzymes like lipase to act more effectively on fats. **16. What is Absorbed in the Large Intestine?** - **Water and Electrolytes**: The large intestine absorbs remaining water and minerals, like sodium and potassium, to help form solid stool. **17. Reason for Gas Production in the Large Intestine** - **Bacterial Fermentation**: Gut bacteria ferment undigested carbohydrates, producing gases such as methane, hydrogen, and carbon dioxide. **18. Enzymes Helping Digestion in the Stomach** - **Pepsin**: The main digestive enzyme in the stomach, activated by the acidic environment, breaks down proteins into smaller peptides. **19. Enzymes Helping Digest Protein** - **Proteases**: Including pepsin (stomach), trypsin, and chymotrypsin (from the pancreas, active in the small intestine), these enzymes break down proteins into amino acids. **20. Enzymes Helping Digest Lipids** - **Lipase**: Primarily pancreatic lipase, which breaks down triglycerides into fatty acids and monoglycerides after bile emulsifies fats, aiding in fat digestion and absorption.