Anatomy of the small intestine

Anatomy of the small intestine

The longest part of the digestive system, where most of the digestion and absorption takes place.

Biology

Keywords

small intestine, feeding, intestines, digestive system, digestion, digestive tract, absorption, duodenum, jejunum, ileum, villi, microvilli, digestive juice, digestive enzyme, intestinal juice, enzyme, pancreatic juice, bile, enterocytes, food, nutrient, carbohydrate, fat, protein, lipids, amino acids, peristaltic, pancreas, liver, smooth muscle, mucous membrane, human, biology

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Scenes

Digestive system

  • pharynx - The esophagus and the trachea start here.
  • esophagus - It propels food towards the stomach with peristaltic waves. This peristaltic motion is generated by the synchronized motion of longitudinal and circular smooth muscle layers.
  • liver - It plays an important role in removing toxins from the body and storing nutrients. It is the largest gland in the human body: it produces bile, which emulsifies fat drops to increase their surface area and thereby helps their digestion.
  • gallbladder - It stores and empties the bile secreted by the liver into the small intestine. Bile emulsifies fat drops to increase their surface area and thereby helps their digestion.
  • cecum - The first section of the large intestine. No digestion takes place in it.
  • appendix - A vestigial extension of the cecum, a lymphoid organ. Its inflammation is called appendicitis, which is a life-threatening condition and requires surgery.
  • rectum - It is the last segment of the large intestine. It absorbs water and plays an important role in forming the stool.
  • oral cavity - The digestion of starch starts here, aided by saliva. The function of the teeth is to chew and tear food. The tongue plays an important role in bolus formation and mixing it with saliva, in swallowing and in the production of speech sounds.
  • salivary glands - They secrete saliva, which makes food wet for easy swallowing. It also contains a digestive enzyme (amylase) that starts the digestion of starch. Its bactericidal enzyme is lysozyme.
  • stomach - The final part of the upper digestive tract. Its enzyme, pepsin digests proteins. Pepsin is activated in an acidic environment (about pH 2), this is provided by hydrogen chloride, also secreted by the stomach. The peristaltic waves of the stomach wall mix food and propel it to the small intestine.
  • pancreas - It secretes pancreatic juice which contains a variety of enzymes, including amylase (breaking down starch), trypsine and chymotrypsine (breaking down proteins) and lipase (breaking down fats). The pancreas also secretes hormones, the most important of these being insulin which reduces glucose level in the blood.
  • small intestine - The enzymes of its intestinal juice and pancreatic juice content break down proteins, carbohydrates and fats. The digestion of fats is aided by the bile, secreted by the liver.
  • colon - It consists of three parts: the ascending colon, the transverse colon and the descending colon. No digestion takes place in it. It is involved in the absorption of minerals and water. Certain bacteria living in the colon produce vitamins B and K.
  • anus - Faeces is expelled from the body through it. This process is controllable by two ring-like muscles, the anal sphincters. The internal anal sphincter consists of smooth muscle, while the external anal sphincter is a voluntary striated muscle.

Small intestine

  • duodenum - Enzymes of the intestinal juice and pancreatic juice break down nutrients (proteins, carbohydrates and fats) here. The intestinal juice is secreted by the small intestine, the pancreatic juice by the pancreas. Digested nutrients are absorbed through the mucous membrane of the small intestine. Bile is secreted by the liver, stored by the gallbladder and emptied into the duodenum. Bile emulsifies fat drops to increase their surface area and thereby helps their digestion.
  • ileum - In the small intestine - therefore here too - important nutrients, fats, carbohydrates and proteins are digested. Digested nutrients are absorbed through the mucous membrane of the small intestine.
  • jejunum - In the small intestine - therefore here too - important nutrients, fats, carbohydrates and proteins are digested. Digested nutrients are absorbed through the mucous membrane of the small intestine.

Villi

  • blood vessel - There are three main nutrients in the food we eat: lipids, carbohydrates and amino acids. Of these, carbohydrates and amino acids are absorbed into the blood vessels.
  • gland secreting intestinal juice - The secreted juice contains enzymes that break down important nutrients (fats, carbohydrates and proteins) in the small intestine. Digested nutrients are absorbed through the mucous membrane of the small intestine.
  • villi - The circular folds, villi and microvilli increase the absorptive surface of the small intestine.
  • lymph vessel - There are three main types of nutrients in the food we eat: lipids, carbohydrates and amino acids. Of these, lipids are absorbed into the lymph vessels.
  • connective tissue
  • smooth muscle of the mucous membrane
  • epithelial cell with microvilli

Position of the small intestine

  • small intestine

Circular folds

  • serous membrane - It consists of connective tissue and epidermis; it constitutes the outermost layer of the stomach and the intestines.
  • longitudinal smooth muscle - Together with the circular smooth muscle layer, it is responsible for peristalsis of the intestines. Peristalsis ensures that food is transferred through the intestines.
  • circular smooth muscle
  • mucous membrane - It consists of a thin layer of smooth muscle, connective tissue and epidermis. Goblet cells are embedded in the epidermic cells.
  • circular fold - The circular folds, villi and microvilli increase the absorptive surface of the small intestine.

Microvilli

  • blood vessel - There are three main types of nutrients in the food we eat: lipids, carbohydrates and amino acids. Of these, carbohydrates and amino acids are absorbed into the blood vessels.
  • lymph vessel - There are three main types of nutrients in the food we eat: lipids, carbohydrates and amino acids. Of these, lipids are absorbed into the lymph vessels.
  • intestinal epithelial cells
  • microvilli - The circular folds, villi and microvilli increase the absorptive surface of the small intestine.

Animation

  • liver - It plays an important role in removing toxins from the body and storing nutrients. It is the largest gland in the human body: it produces bile, which emulsifies fat drops to increase their surface area and thereby helps their digestion.
  • gallbladder - It stores and empties the bile secreted by the liver into the small intestine. Bile emulsifies fat drops to increase their surface area and thereby helps their digestion.
  • stomach - The final part of the upper digestive tract. Its enzyme, pepsin digests proteins. Pepsin is activated in an acidic environment (about pH 2), this is provided by hydrogen chloride, also secreted by the stomach. The peristaltic waves of the stomach wall mix food and propel it to the small intestine.
  • pancreas - It secretes pancreatic juice which contains a variety of enzymes, including amylase (breaking down starch), trypsine and chymotrypsine (breaking down proteins) and lipase (breaking down fats). The pancreas also secretes hormones, the most important of these being insulin which reduces glucose level in the blood.
  • small intestine - The enzymes of its intestinal juice and pancreatic juice content break down proteins, carbohydrates and fats. The digestion of fats is aided by the bile, secreted by the liver.
  • serous membrane - It consists of connective tissue and epidermis; it constitutes the outermost layer of the stomach and the intestines.
  • longitudinal smooth muscle - Together with the circular smooth muscle layer, it is responsible for peristalsis of the intestines. Peristalsis ensures that food is transferred through the intestines.
  • circular smooth muscle
  • mucous membrane - It consists of a thin layer of smooth muscle, connective tissue and epidermis. Goblet cells are embedded in the epidermic cells.
  • circular fold - The circular folds, villi and microvilli increase the absorptive surface of the small intestine.
  • villi - The circular folds, villi and microvilli increase the absorptive surface of the small intestine.
  • blood vessel - There are three main types of nutrients in the food we eat: lipids, carbohydrates and amino acids. Of these, carbohydrates and amino acids are absorbed into the blood vessels.
  • lymph vessel - There are three main types of nutrients in the food we eat: lipids, carbohydrates and amino acids. Of these, lipids are absorbed into the lymph vessels.
  • intestinal epithelial cells
  • microvilli - The circular folds, villi and microvilli increase the absorptive surface of the small intestine.

Narration

The human digestive system can be divided into an upper and a lower tract.

The stomach, where proteins are digested, is the final part of the upper digestive tract. The content of the stomach proceeds to the small intestine.

Here the enzymes in the intestinal juice and pancreatic juice break down the essential nutrients, that is, proteins, carbohydrates and fats. Intestinal juice is produced by the glands of the small intestine, while the pancreas secretes pancreatic juice. The bile, produced by the liver and stored in the gallbladder, is also emptied into the small intestine. The bile does not contain digestive enzymes; it emulsifies fat drops to aid in their digestion.

The outer layer of the small intestine is the serous membrane. Under this layer, there are layers of longitudinal and circular smooth muscle. The synchronized motion of these two muscle layers ensures the peristaltic motion of the stomach; it mixes and propels the content of the intestines. The digestive system is lined by a mucous membrane, which consists of a thin layer of smooth muscle, connective tissue and epidermis. The glands that secrete the intestinal juice are embedded in the mucous membrane. Circular folds increase the absorptive surface of the small intestine.

Microvilli and villi further increase the absorptive surface of the small intestine.

Carbohydrates, and amino acids released by the digestion of proteins are absorbed into the blood vessels, while lipids are absorbed into the lymph vessels.

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