See more from our free eBook library. Study: Immune system promotes digestive health from Science Daily. Propulsion and Peristalsis. Accessory Organs.
Common Diseases and Disorders. When you select "Subscribe" you will start receiving our email newsletter. Use the links at the bottom of any email to manage the type of emails you receive or to unsubscribe. See our privacy policy for additional details. Learn Site. Villi That Line the Walls of the Small Intestine Absorb Nutrients Villi that line the walls of the small intestine absorb nutrients into capillaries of the circulatory system and lacteals of the lymphatic system.
The Large Intestine Completes Absorption and Compacts Waste Chyme passes from the small intestine through the ileocecal valve and into the cecum of the large intestine.
Defecation Eliminates Waste From the Body The body expels waste products from digestion through the rectum and anus. These contractions isolate small sections of the intestine, moving their contents back and forth while continuously subdividing, breaking up, and mixing the contents. By moving food back and forth in the intestinal lumen, segmentation mixes food with digestive juices and facilitates absorption.
In chemical digestion , starting in the mouth, digestive secretions break down complex food molecules into their chemical building blocks for example, proteins into separate amino acids. These secretions vary in composition, but typically contain water, various enzymes, acids, and salts.
The process is completed in the small intestine. Food that has been broken down is of no value to the body unless it enters the bloodstream and its nutrients are put to work. This occurs through the process of absorption , which takes place primarily within the small intestine. There, most nutrients are absorbed from the lumen of the alimentary canal into the bloodstream through the epithelial cells that make up the mucosa. Lipids are absorbed into lacteals and are transported via the lymphatic vessels to the bloodstream the subclavian veins near the heart.
The details of these processes will be discussed later. In defecation , the final step in digestion, undigested materials are removed from the body as feces.
Age-related changes in the digestive system begin in the mouth and can affect virtually every aspect of the digestive system. Swallowing can be difficult, and ingested food moves slowly through the alimentary canal because of reduced strength and tone of muscular tissue. Neurosensory feedback is also dampened, slowing the transmission of messages that stimulate the release of enzymes and hormones.
Pathologies that affect the digestive organs—such as hiatal hernia, gastritis, and peptic ulcer disease—can occur at greater frequencies as you age. Problems in the small intestine may include duodenal ulcers, maldigestion, and malabsorption. Problems in the large intestine include hemorrhoids, diverticular disease, and constipation.
Conditions that affect the function of accessory organs—and their abilities to deliver pancreatic enzymes and bile to the small intestine—include jaundice, acute pancreatitis, cirrhosis, and gallstones. In some cases, a single organ is in charge of a digestive process.
For example, ingestion occurs only in the mouth and defecation only in the anus. However, most digestive processes involve the interaction of several organs and occur gradually as food moves through the alimentary canal Figure 2. Figure 2. The digestive processes are ingestion, propulsion, mechanical digestion, chemical digestion, absorption, and defecation.
Some chemical digestion occurs in the mouth. Some absorption can occur in the mouth and stomach, for example, alcohol and aspirin. Neural and endocrine regulatory mechanisms work to maintain the optimal conditions in the lumen needed for digestion and absorption. These regulatory mechanisms, which stimulate digestive activity through mechanical and chemical activity, are controlled both extrinsically and intrinsically.
The walls of the alimentary canal contain a variety of sensors that help regulate digestive functions. These include mechanoreceptors, chemoreceptors, and osmoreceptors, which are capable of detecting mechanical, chemical, and osmotic stimuli, respectively.
Stimulation of these receptors provokes an appropriate reflex that furthers the process of digestion. This may entail sending a message that activates the glands that secrete digestive juices into the lumen, or it may mean the stimulation of muscles within the alimentary canal, thereby activating peristalsis and segmentation that move food along the intestinal tract. The walls of the entire alimentary canal are embedded with nerve plexuses that interact with the central nervous system and other nerve plexuses—either within the same digestive organ or in different ones.
Bile is stored in the gallbladder until it is needed. The pancreas makes enzymes that help digest proteins, fats, and carbs. It also makes a substance that neutralizes stomach acid. These enzymes and bile travel through special pathways called ducts into the small intestine, where they help to break down food. The liver also helps process nutrients in the bloodstream. From the small intestine, undigested food and some water travels to the large intestine through a muscular ring or valve that prevents food from returning to the small intestine.
By the time food reaches the large intestine, the work of absorbing nutrients is nearly finished. The large intestine's main job is to remove water from the undigested matter and form solid waste poop to be excreted.
Reviewed by: Larissa Hirsch, MD. Larger text size Large text size Regular text size. What Is the Digestive System? Almost all animals have a tube-type digestive system in which food: enters the mouth passes through a long tube exits the body as feces poop through the anus Along the way, food is broken down into tiny molecules so that the body can absorb nutrients it needs: Protein must be broken down into amino acids.
Starches break down into simple sugars. Fats break down into into fatty acids and glycerol. The waste parts of food that the body can't use are what leave the body as feces. How Does Digestion Work? The small intestine is made up of three parts: the duodenum pronounced: due-uh-DEE-num , the C-shaped first part the jejunum pronounced: jih-JU-num , the coiled midsection the ileum pronounced: IH-lee-um , the final section that leads into the large intestine The inner wall of the small intestine is covered with millions of microscopic, finger-like projections called villi pronounced: VIH-lie.
The large intestine has three parts: The cecum pronounced: SEE-kum is the beginning of the large intestine.
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