1. Describe the process of swallowing in man.
Answer: Swallowing, or deglutition, is a complex process that moves food from the mouth to the stomach. It involves both voluntary and involuntary actions and can be divided into three phases.
1. Oral (Voluntary) Phase:
Food is chewed and mixed with saliva to form a bolus. The tongue pushes the bolus against the hard palate and then moves it to the back of the mouth. This initiates the swallowing reflex.
2. Pharyngeal (Involuntary) Phase:
The bolus enters the pharynx. The soft palate rises to close off the nasopharynx, preventing food from entering the nasal cavity. The epiglottis folds down to cover the larynx, preventing food from entering the trachea (windpipe). The upper esophageal sphincter relaxes, allowing the bolus to enter the esophagus. Breathing is temporarily inhibited.
3. Esophageal (Involuntary) Phase:
The bolus is moved down the esophagus by peristalsis, a wave-like contraction of the esophageal muscles. The lower esophageal sphincter (cardiac sphincter) relaxes as the bolus approaches the stomach, allowing it to enter. Gravity also assists in the movement of food, especially when sitting or standing.
Regulation:
The swallowing reflex is controlled by the swallowing center in the medulla oblongata. It coordinates the muscles involved in swallowing and inhibits respiration.
In summary, swallowing is a coordinated process involving voluntary and involuntary phases, ensuring that food is safely transported from the mouth to the stomach while preventing entry into the airway. It is essential for digestion and nutrition.
2. Describe the human stomach with diagram.
Answer: The human stomach is a muscular, J-shaped organ located in the upper left part of the abdominal cavity. It is a key component of the digestive system, responsible for storing food, mixing it with gastric juices, and initiating protein digestion.
Structure:
Cardia: The upper part where the esophagus enters. It contains the cardiac sphincter, which prevents backflow. Fundus: The dome-shaped upper region. Body: The central, largest region. Pyloric Antrum: The lower region that connects to the duodenum. Pyloric Sphincter: A muscular valve that regulates the passage of chyme into the duodenum.
Layers of the Stomach Wall:
Mucosa: The innermost layer, lined with simple columnar epithelium. It contains gastric pits and glands (parietal, chief, mucous, and G cells). Submucosa: Connective tissue with blood vessels and nerves. Muscularis: Three layers of smooth muscle (longitudinal, circular, oblique) that allow for churning and mixing. Serosa: The outermost serous membrane.
Diagram Description: (A diagram would show the J-shaped stomach with labels: esophagus, cardia, fundus, body, pyloric antrum, pyloric sphincter, duodenum, rugae, and layers of the wall.)
Functions:
Storage: Holds food temporarily. Mechanical Digestion: Churns food with gastric juices to form chyme. Chemical Digestion: HCl denatures proteins and activates pepsinogen; pepsin digests proteins.
Protection: Mucus protects the lining. Regulation: Hormones (gastrin) and nerve signals regulate gastric secretion and motility.
In summary, the stomach is a vital organ that prepares food for further digestion and absorption in the small intestine.
3. Describe the structure of human small intestine.
Answer: The small intestine is a long, coiled tube that is the primary site for the digestion and absorption of nutrients. It is approximately 6-7 meters long and is divided into three sections: the duodenum, jejunum, and ileum.
Structure:
Duodenum: The first and shortest section (about 25 cm). It receives chyme from the stomach, bile from the liver, and pancreatic juice from the pancreas. Most chemical digestion occurs here. Jejunum: The middle section (about 2.5 meters). It is the primary site for absorption of nutrients. Ileum: The final and longest section (about 3.5 meters). It absorbs remaining nutrients, especially vitamin B12 and bile salts.
Wall Structure:
Mucosa: The inner lining has finger-like projections called villi, which greatly increase the surface area for absorption. Each villus contains a network of capillaries and a lacteal (lymph vessel). Epithelial Cells: The mucosa is covered with simple columnar epithelium, which has microvilli (brush border) on the apical surface, further increasing surface area. Submucosa: Connective tissue containing blood vessels, lymph vessels, and nerves. Muscularis: Two layers of smooth muscle (circular and longitudinal) that perform peristalsis and segmentation. Serosa: The outer serous membrane.
Adaptations for Absorption:
Length: Provides a long path for digestion and absorption. Villi and Microvilli: Increase surface area. Rich Blood Supply: Capillaries absorb glucose and amino acids. Lacteals: Absorb fats.
In summary, the small intestine is highly adapted for its role in digestion and absorption, with its structure maximizing surface area and efficiency.
4. Explain the absorption of digested products from the small intestine lumen to the blood capillaries and lacteals of the villi.
Answer: The absorption of digested products occurs in the small intestine, specifically in the villi. The process involves different mechanisms for different nutrients.
1. Absorption of Carbohydrates:
Monosaccharides (glucose, fructose, galactose) are absorbed by active transport and facilitated diffusion into the epithelial cells of the villi. From the epithelial cells, they enter the blood capillaries in the villi by diffusion. They are then transported to the liver via the hepatic portal vein.
2. Absorption of Proteins:
Amino acids are absorbed by active transport into the epithelial cells. From there, they enter the blood capillaries and are transported to the liver.
3. Absorption of Fats:
Fatty acids and glycerol are absorbed by simple diffusion into the epithelial cells. Inside the epithelial cells, they are re-esterified into triglycerides and packaged into chylomicrons (lipoproteins). Chylomicrons are too large to enter blood capillaries, so they enter the lacteals (lymph vessels) in the villi by exocytosis. They travel through the lymphatic system and eventually enter the bloodstream via the thoracic duct.
4. Absorption of Water and Electrolytes:
Water is absorbed by osmosis. Electrolytes (sodium, potassium, chloride) are absorbed by active transport and diffusion.
5. Absorption of Vitamins:
Fat-soluble vitamins (A, D, E, K) are absorbed with fats into lacteals. Water-soluble vitamins (B, C) are absorbed by diffusion and active transport into blood capillaries.
In summary, the absorption of digested products involves specific transport mechanisms that move nutrients from the intestinal lumen into the blood or lymph for distribution throughout the body.
5. Describe the large intestine of man. What are the functions of large intestine?
Answer: The large intestine, also known as the colon, is the final section of the digestive tract. It is approximately 1.5 meters long and is wider than the small intestine. It extends from the cecum to the rectum.
Structure:
Cecum: A pouch at the beginning of the large intestine. It has the vermiform appendix attached. Colon: The main section, divided into four parts:
Ascending colon: Travels up the right side of the abdomen. Transverse colon: Crosses the abdomen horizontally. Descending colon: Travels down the left side. Sigmoid colon: An S-shaped curve that connects to the rectum.
Rectum: The final straight section that stores feces. Anal Canal: Ends at the anus, which has two sphincters (internal and external).
Functions of the Large Intestine:
Water and Electrolyte Absorption: Absorbs most of the remaining water and electrolytes from the indigestible food matter, forming solid feces. Vitamin Synthesis: Bacteria in the colon synthesize vitamin K and some B vitamins. Feces Formation and Storage: Forms and stores feces until defecation. Mucus Secretion: Secretes mucus to lubricate the feces and protect the lining. Bacterial Fermentation: Bacteria ferment undigested carbohydrates, producing gases and short-chain fatty acids.
In summary, the large intestine is crucial for water conservation, vitamin synthesis, and waste elimination. Its structure and functions are adapted to complete the digestive process.
6. What is bile? Describe the composition of bile. What is the role of constituents of bile?
Answer: Bile is a yellowish-green fluid produced by the liver and stored in the gallbladder. It is secreted into the duodenum to aid in the digestion and absorption of fats.
Composition of Bile:
Water: About 97%.
Bile Salts: Sodium glycocholate and sodium taurocholate. Bile Pigments: Bilirubin (yellow) and biliverdin (green), which are breakdown products of hemoglobin. Cholesterol: A sterol. Phospholipids: Lecithin. Electrolytes: Bicarbonate, chloride, sodium, potassium. Mucus: Lubricant.
Role of Constituents:
Bile Salts: Emulsify fats, breaking them into smaller droplets to increase surface area for lipase action. They also aid in the absorption of fats and fat-soluble vitamins. Bile Pigments: Bilirubin and biliverdin are waste products. They give feces its brown color. Cholesterol and Phospholipids: Help in emulsification and transport of fats. Bicarbonate: Neutralizes acidic chyme from the stomach, creating an alkaline environment for pancreatic enzymes. Mucus: Protects the duodenal lining.
In summary, bile is essential for fat digestion and absorption. Its constituents work together to emulsify fats, neutralize acid, and facilitate nutrient absorption.
7. How secretion of bile is related to the secretion of hormone secretin?
Answer: The secretion of bile is regulated by the hormone secretin, which is produced by the S cells in the duodenum.
Mechanism:
When acidic chyme from the stomach enters the duodenum, it stimulates the release of secretin into the bloodstream. Secretin acts on the pancreas to stimulate the secretion of bicarbonate-rich pancreatic juice, which neutralizes the acid. Secretin also stimulates the liver to secrete bile. It increases bile production and flow.
Additionally, another hormone, cholecystokinin (CCK), which is released in response to fats in the duodenum, stimulates the gallbladder to contract and release stored bile into the duodenum.
Relationship:
Secretin primarily stimulates the liver to produce and secrete bile. CCK stimulates the gallbladder to release bile. Both hormones work together to ensure that bile is available in the duodenum when needed for fat digestion.
In summary, secretin plays a key role in stimulating bile secretion from the liver, while CCK stimulates bile release from the gallbladder. This coordinated regulation ensures efficient fat digestion.
8. Write the functions of stomach of man.
Answer: The stomach performs several vital functions in the digestive system.
1. Storage: It acts as a reservoir for food, allowing for the consumption of large meals. The rugae (folds) allow it to expand.
2. Mechanical Digestion: It churns and mixes food with gastric juices through muscular contractions (segmentation and peristalsis), forming chyme.
3. Chemical Digestion:
Protein Digestion: HCl denatures proteins and activates pepsinogen to pepsin, which breaks proteins into peptides. Fat Digestion: Gastric lipase begins the digestion of fats (minor role).
4. Secretion of Gastric Juice: It secretes HCl, pepsinogen, mucus, and intrinsic factor.
5. Protection: Mucus protects the stomach lining from acid and enzymes. HCl kills bacteria.
6. Absorption: It absorbs a small amount of water, alcohol, and some drugs.
7. Regulation: It regulates the release of chyme into the duodenum via the pyloric sphincter.
8. Hormone Secretion: It secretes gastrin, which regulates gastric secretion and motility.
In summary, the stomach is essential for the storage, mechanical and chemical digestion of food, and regulation of the digestive process.
9. What is the structure of pancreas? Explain the functions of pancreas as an exocrine gland.
Answer: Structure of Pancreas: The pancreas is a soft, lobulated gland located behind the stomach. It has both exocrine and endocrine functions. The exocrine portion consists of clusters of acinar cells that secrete digestive enzymes into a system of ducts. These ducts converge to form the main pancreatic duct, which joins the common bile duct and empties into the duodenum. The endocrine portion consists of the islets of Langerhans, which secrete hormones (insulin and glucagon) into the blood.
Functions as an Exocrine Gland: The exocrine pancreas secretes pancreatic juice, which contains:
Digestive Enzymes:
Proteases: Trypsinogen, chymotrypsinogen, and procarboxypeptidase (activated in the duodenum). They digest proteins. Amylase: Digests starch into maltose.
Lipase: Digests fats into fatty acids and glycerol. Nucleases: Digest nucleic acids.
Bicarbonate: Neutralizes acidic chyme from the stomach, creating an alkaline environment for enzyme activity.
Regulation:
Secretin: Stimulates bicarbonate secretion. Cholecystokinin (CCK): Stimulates enzyme secretion.
In summary, the exocrine pancreas produces and secretes digestive enzymes and bicarbonate into the duodenum, playing a crucial role in the digestion of carbohydrates, proteins, and fats.
