1. The functions of the digestive system include:
- Ingestion: The process of taking in food through the mouth.
- Digestion: The breakdown of food into smaller molecules that can be absorbed by the body.
- Absorption: The process by which nutrients are taken up into the bloodstream from the digestive tract.
- Motility: The movement of food through the digestive tract, which includes swallowing, peristalsis, and segmentation.
- Secretion: The release of digestive enzymes, acids, and other substances necessary for digestion.
- Elimination: The removal of undigested waste products from the body through defecation.
2. The digestive system is divided into two main parts: the gastrointestinal tract (alimentary canal) and the accessory organs.
The organs in the gastrointestinal tract are:
- Mouth: The site of ingestion and initial mechanical and chemical digestion.
- Esophagus: Transports food from the mouth to the stomach.
- Stomach: Stores and mixes food, secretes digestive enzymes and acids.
- Small Intestine: Consists of three regions - duodenum, jejunum, and ileum - where most digestion and absorption occur.
- Large Intestine: Consists of the cecum, colon, rectum, and anus, and is responsible for reabsorbing water and forming feces.
The accessory organs include:
- Salivary Glands: Produce saliva, which contains enzymes that begin the digestion of carbohydrates.
- Liver: Produces bile, which aids in the digestion and absorption of fats.
- Gallbladder: Stores and concentrates bile produced by the liver, releasing it into the small intestine.
- Pancreas: Produces digestive enzymes and hormones, such as insulin, that regulate blood sugar levels.
3. Mechanical digestion involves the physical breakdown of food into smaller pieces. This includes actions like chewing, mixing food with saliva, and the muscular contractions of the stomach and intestines that help break down food into smaller particles.
Chemical digestion involves the breakdown of complex molecules into smaller, simpler molecules through the action of digestive enzymes. These enzymes break down carbohydrates, proteins, and fats into their respective building blocks, such as glucose, amino acids, and fatty acids.
4. The structural layers of the alimentary tube (gastrointestinal tract) include:
- Mucosa: The innermost layer lining the lumen of the tube. It contains epithelial cells specialized for absorption and secretion, as well as glands that secrete mucus and digestive enzymes.
- Submucosa: A layer of connective tissue that contains blood vessels, lymphatic vessels, and nerves. It provides support and nourishment to the mucosa.
- Muscularis Externa: Consists of two layers of smooth muscle - circular and longitudinal - that are responsible for the movement of food through the digestive tract.
- Serosa (or adventitia): The outermost layer that serves as a protective covering. It is composed of connective tissue and in some areas is covered by a serous membrane called the peritoneum.
5. The three pairs of major salivary glands are:
- Parotid Glands: Located in front of the ears, they produce saliva that contains digestive enzymes, mainly amylase, which begins the digestion of carbohydrates.
- Submandibular Glands: Located beneath the lower jaw, they produce saliva that is rich in both mucus and enzymes.
- Sublingual Glands: Located beneath the tongue, they produce saliva that is mainly mucus and helps lubricate food for swallowing.
6. The regions of the large intestine are:
- Cecum: The first part of the large intestine, which receives undigested material from the small intestine.
- Colon: Divided into several regions including the ascending, transverse, descending, and sigmoid colon. It absorbs water and electrolytes from the undigested material, forming feces.
- Rectum: The terminal part of the large intestine, where feces are stored before elimination.
- Anus: The external opening at the end of the digestive tract, through which feces are expelled.
7. The main structures of the stomach include:
- Cardiac Sphincter (Lower Esophageal Sphincter): Located between the esophagus and the stomach, it prevents the backflow of stomach contents into the esophagus.
- Fundus: The upper part of the stomach that stores swallowed food and gases.
- Body: The main central part of the stomach where most of the digestion and mixing of food occur.
- Pylorus: The lower part of the stomach that connects to the small intestine. It contains the pyloric sphincter, which regulates the release of food into the small intestine.
8. The small intestine is responsible for the majority of digestion and absorption of nutrients. Its main functions include:
- Digestion: Enzymes from the pancreas and intestinal cells break down proteins, carbohydrates, and fats into their smaller building blocks.
- Absorption: The lining of the small intestine contains finger-like projections called villi, which increase the surface area for absorption. Nutrients are absorbed into the bloodstream through the villi and transported to the body's cells.
- Secretion: The small intestine secretes digestive enzymes and hormones that aid in digestion and regulate its functions.
9. The three regions of the small intestine are:
- Duodenum: The first and shortest part of the small intestine, where bile from the liver and enzymes from the pancreas are secreted to aid in digestion.
- Jejunum: The middle part of the small intestine, where most of the absorption of nutrients occurs.
- Ileum: The final part of the small intestine, which connects to the large intestine. It further absorbs nutrients and vitamins, as well as reabsorbs bile salts.
10. The main function of the large intestine is to reabsorb water and electrolytes from undigested material, forming solid feces. It also houses beneficial bacteria that aid in the production of vitamins and the breakdown of certain substances. The large intestine also helps propel feces toward the rectum for elimination through muscular contractions known as peristalsis.
