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 due-uh-DEE-num , the C-shaped first part the jejunum jih-JU-num , the coiled midsection the ileum 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 VIH-lie.
The large intestine has three parts: The cecum SEE-kum is the beginning of the large intestine. The appendix , a small, hollow, finger-like pouch, hangs at the end of the cecum. Doctors believe the appendix is left over from a previous time in human evolution. It no longer appears to be useful to the digestive process. The colon extends from the cecum up the right side of the abdomen, across the upper abdomen, and then down the left side of the abdomen, finally connecting to the rectum.
The colon has three parts: the ascending colon and the transverse colon, which absorb fluids and salts; and the descending colon, which holds the resulting waste.
Bacteria in the colon help to digest the remaining food products. The rectum is where feces are stored until they leave the digestive system through the anus as a bowel movement. It takes hours for our bodies to fully digest food. Saliva also has an enzyme that begins to break down starches in your food. After you swallow, peristalsis pushes the food down your esophagus into your stomach. Glands in your stomach lining make stomach acid and enzymes that break down food. Muscles of your stomach mix the food with these digestive juices.
Your pancreas makes a digestive juice that has enzymes that break down carbohydrates, fats, and proteins. The pancreas delivers the digestive juice to the small intestine through small tubes called ducts. Your liver makes a digestive juice called bile that helps digest fats and some vitamins. Bile ducts carry bile from your liver to your gallbladder for storage, or to the small intestine for use.
Your gallbladder stores bile between meals. When you eat, your gallbladder squeezes bile through the bile ducts into your small intestine. Your small intestine makes digestive juice, which mixes with bile and pancreatic juice to complete the breakdown of proteins, carbohydrates, and fats.
Bacteria in your small intestine make some of the enzymes you need to digest carbohydrates. Your small intestine moves water from your bloodstream into your GI tract to help break down food. Your small intestine also absorbs water with other nutrients. In your large intestine, more water moves from your GI tract into your bloodstream. Bacteria in your large intestine help break down remaining nutrients and make vitamin K. Waste products of digestion, including parts of food that are still too large, become stool.
The small intestine absorbs most of the nutrients in your food, and your circulatory system passes them on to other parts of your body to store or use. Special cells help absorbed nutrients cross the intestinal lining into your bloodstream. Your blood carries simple sugars, amino acids, glycerol, and some vitamins and salts to the liver.
Your liver stores, processes, and delivers nutrients to the rest of your body when needed. The lymph system , a network of vessels that carry white blood cells and a fluid called lymph throughout your body to fight infection, absorbs fatty acids and vitamins. Your body uses sugars, amino acids, fatty acids, and glycerol to build substances you need for energy, growth, and cell repair. Your hormones and nerves work together to help control the digestive process.
Signals flow within your GI tract and back and forth from your GI tract to your brain. Study Findings. Metastatic Cancer Research. Intramural Research. Extramural Research.
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However, animals that have gastrointestinal tract carry out internal digestion which is a more efficient way of digesting of food. Single-cell organisms, such as Porifera, can directly take up the via phagocytosis or by endocytosis while in complex creatures specialized organs and tissues developed to carry out the process of digestion. Invertebrates , for example, Platyhelminthes flatworms , Ctenophora comb jellies , and Cnidaria coral, jellyfish, and sea anemones have a single opening that serves both the functions of ingestion of food as well as the elimination of food.
In other invertebrates, like an earthworm, the simplest form of the alimentary canal is present wherein the alimentary canal has a mouth for the ingestion of food and anus for the expulsion of the food. In primitive creatures like amphioxus, lampreys, hagfishes, etc, the alimentary canal has three components: oral cavity, pharynx, and a tubular post-pharyngeal gut without compartmentalization.
In higher vertebrates, the post-pharyngeal gut is divided into different compartments: esophagus, stomach, small intestine, large intestine, rectum, or cloaca. Cloaca is also found in marsupials and egg-laying mammals. Interestingly, the cloaca is also seen for a very short duration during the embryonic development stage of mammals. Further depending upon the feeding habits and the nature of food consumed, the alimentary canal further evolved viz.
Herbivore animals like ruminants have a multiple compartment stomach to aid in the digestion of a cellulose-based diet while humans have a monogastric alimentary canal. There are a lot of anatomical variations in the alimentary canal amongst various animals. Certain animals are mono-gastric single chamber stomach while others are multi-gastric multiple chamber stomach. Humans and rabbits have a mono-gastric alimentary canal. However, rabbits have enlarged small intestine and cecum, to provide a large surface area for the absorption of nutrients from the plant material.
Birds have dual-chamber stomach , the proventriculus, and the gizzard. In proventriculus, food is digested with the help of gastric juices while in the gizzard food is soaked, mechanically grounded, and eventually stored.
Birds also regurgitate undigested food. Birds do not have teeth in their oral cavity and do not carry out mastication of food. The beaks of the birds are adapted to grind the food and hence different species of birds have different shapes of beaks. The absorption of nutrients occurs in the small intestine and the waste is eliminated from the opening called the cloaca. Ruminants like sheep, bovine, goats, etc.
This adaptation is to digest the cellulose , which is the major component of the plant-based ruminant diet. The stomach is divided into four chambers:. The abomasum is considered to be equivalent to the mono-gastric stomach or true stomach due to the presence of gastric secretions. In the rumen and reticulum, the stomach is rich in microbial flora that aids in the breakdown of cellulose in the food. In these chambers, fermentation of the ingested food also occurs, resulting in the generation of a high volume of gases.
These gases are periodically expelled out by the animal. The ruminants regurgitate the food material or the cud from the reticulum chamber and chew it again and this cud is then transferred to the third chamber, the omasum. In omasum removal of water occurs. From the omasum, the food material is then transferred to the abomasum for digestion by the enzymes and gastric secretions and is eventually transferred to the small intestine. The absorption of nutrients occurs in the small intestine while the elimination of the waste occurs via the large intestine.
In contrast to the ruminants, pseudo-ruminants like camel have a three-chamber stomach. The rumen is absent in camels. Omasum, abomasum, and reticulum are the three compartments of the stomach of the camel. Interestingly, camels have an enlarged cecum. Cecum in camel is rich in microbial flora and is responsible for the digestion of the plant-based roughage, which forms the major part of the diet of camels.
The alimentary canal in insects like cockroaches starts at the mouth and ends at the anus and is subdivided into three parts-. Fishes do not possess a large intestine; however, they have a short rectum.
The alimentary canal of fishes has an oral cavity to ingest food followed by an esophagus to transfer the food to the stomach for digestion. The nutrients are absorbed in the intestine and eliminate the waste from the vent equivalent to anus. The intestine is classified as the proximal intestine and distal intestine in fishes. Try to answer the quiz below to check what you have learned so far about alimentary canal.
The Alimentary Canal. Eds Academic Press, pp , doi. Alimentary Tract. In: Principles of Regenerative Medicine. Atala A. Eds Academic Press, , 3rd ed. Human digestion—a processing perspective. Journal of the science of food and agriculture, 96 7 , — Intraluminal pH of the human gastrointestinal tract. Danish medical bulletin, 46 3 , —
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