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Development of the digestive system The small intestine develops from the midgut of the primitive gut tube.
The loop grows so fast in length that it outgrows the abdomen and protrudes through the umbilicus. By week 10, the loop retracts back into the abdomen. Between weeks six and ten the small intestine rotates anticlockwise, as viewed from the front of the embryo. It rotates a further degrees after it has moved back into the abdomen.
This process creates the twisted shape of the large intestine. Digestion[ edit ] The small intestine is where most chemical digestion takes place. Many of the digestive enzymes that act in the small intestine are secreted by the pancreas and liver and enter the small intestine via the pancreatic duct.
Pancreatic enzymes and bile from the gallbladder enter the small intestine in response to the hormone cholecystokininwhich is produced in the small intestine in response to the presence of nutrients.
Secretinanother hormone produced in the small intestine, causes additional effects on the pancreas, where it promotes the release of bicarbonate into the duodenum in order to neutralize the potentially harmful acid coming from the stomach.
The three major classes of nutrients that undergo digestion are proteinslipids fats and carbohydrates: Proteins are degraded into small peptides and amino acids before absorption. Proteolytic enzymes, including trypsin and chymotrypsinare secreted by the pancreas and cleave proteins into smaller peptides.
Carboxypeptidase, which is a pancreatic brush border enzyme, splits one amino acid at a time. Aminopeptidase and dipeptidase free the end amino acid products. Lipids fats are degraded into fatty acids and glycerol.
Pancreatic lipase breaks down triglycerides into free fatty acids and monoglycerides. Pancreatic lipase works with the help of the salts from the bile secreted by the liver and stored in the gall bladder.
Bile salts attach to triglycerides to help emulsify them, which aids access by pancreatic lipase. This occurs because the lipase is water-soluble but the fatty triglycerides are hydrophobic and tend to orient towards each other and away from the watery intestinal surroundings.
The bile salts emulsify the triglycerides in the watery surroundings until the lipase can break them into the smaller components that are able to enter the villi for absorption.
Some carbohydrates are degraded into simple sugars, or monosaccharides e. Pancreatic amylase breaks down some carbohydrates notably starch into oligosaccharides. Other carbohydrates pass undigested into the large intestine and further handling by intestinal bacteria.
Brush border enzymes take over from there. The most important brush border enzymes are dextrinase and glucoamylase, which further break down oligosaccharides. Other brush border enzymes are maltase, sucrase and lactase. Lactase is absent in some adult humans and, for them, lactose a disaccharideas well as most polysaccharides, is not digested in the small intestine.
Some carbohydrates, such as celluloseare not digested at all, despite being made of multiple glucose units. This is because the cellulose is made out of beta-glucose, making the inter-monosaccharidal bindings different from the ones present in starch, which consists of alpha-glucose.
Humans lack the enzyme for splitting the beta-glucose-bonds, something reserved for herbivores and bacteria from the large intestine. Absorption[ edit ] Digested food is now able to pass into the blood vessels in the wall of the intestine through either diffusion or active transport.
The small intestine is the site where most of the nutrients from ingested food are absorbed. The inner wall, or mucosa, of the small intestine is lined with simple columnar epithelial tissue.
Structurally, the mucosa is covered in wrinkles or folds called plicae circulareswhich are considered permanent features in the wall of the organ. They are distinct from rugae which are considered non-permanent or temporary allowing for distention and contraction.
From the plicae circulares project microscopic finger-like pieces of tissue called villi Latin for "shaggy hair". The individual epithelial cells also have finger-like projections known as microvilli. The functions of the plicae circulares, the villi, and the microvilli are to increase the amount of surface area available for the absorption of nutrientsand to limit the loss of said nutrients to intestinal fauna.
Each villus has a network of capillaries and fine lymphatic vessels called lacteals close to its surface. The epithelial cells of the villi transport nutrients from the lumen of the intestine into these capillaries amino acids and carbohydrates and lacteals lipids.
The absorbed substances are transported via the blood vessels to different organs of the body where they are used to build complex substances such as the proteins required by our body."The length increases the surface area so that it can better absorb nutrients" is the one among the following choices given in the question that describes how the ength of the small intestine 5/5(11).
Small Intestine vs Large Intestine Size: Small intestine is long ranging from to 7 meters which large intestine is quite short (about meters). But small intestine is narrow in width i.e cm, while large intestine is broader i.e cm.
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The length of the small intestine can vary greatly, from as short as m ( ft) to as long as m ( ft). The average length in a living person is 3m-5m. The length depends both on how tall the person is and how the length is timberdesignmag.com: Superior mesenteric artery.