Updated March 13, 2015.
As the small intestine is filled with chyme processed by the slowly-emptying stomach, a signal from the small intestine triggers the stomach to decelerate its process of emptying. The small intestine provides a large reservoir for the absorption of nutrients, as the major points of digestion and absorption occur in the small intestine.
Hepatitis and Anatomy: A Deeper Look into the Small Intestine
The small intestine has three parts: the duodenum, jejunum and ileum.
The duodenum is the one directly fused with the stomach. It is the entering way of the processed chyme fashioned by the stomach. All in all, it’s a hollow tube which measures about 25-38 cm which connects the stomach to the jejunum, which is the second part of the small intestine. When the bolus reaches the preamble of the duodenum or the pylorus, muscle contraction starts, which squirt the bolus back to the stomach. This process is called retropulsion. An additional force is being exerted through this process, which allows the bolus to be further grounded and wrecked to smaller bits. The duodenum is also responsible in regulating the rate of stomach gastric emptying – a process of emptying liquid much more swiftly than the solid ones.
The second portion of the small intestine is the jejunum. This intermediate section of the small intestine, as well as the third section which is the ileum, is responsible for the absorption of the nutrients from food, and the main absorptive planes of the gastrointestinal tract.
The jejunum and the ileum are both attached by a long mesentery, which is a double layer of the abdominal cavity lining called peritoneum, and being connected to the posterior abdominal wall. This allows free movement and rotation for the loops of the small intestine. The cells of the jejunum create enzymatic pathways that process and absorb the dietary folic acid.
The ileum, which is the final section of the small intestine, is mainly in control of the absorption of vitamin B12 and bile salt, and all the digestion products that have not been absorbed by jejunum. Protease (an enzyme that breaks down protein) and carbohydrate enzymes, which are responsible for the final stage of the digestion of protein and carbohydrates, are let out by the cells of ileum lining. The villi, which are tiny projections of the ileum, do contain small blood vessels which take glucose and amino acids to the liver’s hepatic portal vein. The blood conducted from the hepatic portal vein to the liver and spleen is rich in nutrients, which are to be processed by the liver itself. Toxins that might have been ingested in the food are filtered and removed through the blood from hepatic portal vein. The small lymph vessels from the villi, called lacteals, absorb glycerol and fatty acids. Peristalsis will occur again to push the digested food along ileum. The waste and water, and the undigested food are channeled towards the large intestine.
Hepatitis and Anatomy: The Waste Collector Known as the Large Intestine
As the food arrives at the large intestine, also known as the colon, the nutrients from the food have already been absorbed as they’ve passed through the stomach and small intestine. This last part of the intestine measuring about 4.5 feet or 1.5 meters connected from the end of ileum absorbs the water and salt from the undigested food. It also serves as the temporary storage for the unworkable waste material from the food before it departs from the body; and so the excretion and formation of the stool is done in the large intestine.
The large intestine creates an arc-shape surrounding the small intestine. The cecum is the portion that ties the large intestine from the end of the small intestine’s ileum. The first section of the large intestine right after the small intestine is the ascending colon that sits on the right side. The portion horizontally located above the small intestine is the transverse colon; while the descending colon is located on the left side of the abdomen. The rectum is the concluding and lowest part of the large intestine, and the short, S-shaped section just above the rectum is called the sigmoid.
Present in the large intestine are symbiotic and colonic bacteria, which craft vitamins K, vitamin B12, riboflavin and thiamine, and still further break down the waste to extract small nutrients and electrolytes. It takes about 16 hours to process the absorption of water and the completion of digestion. Roughly two liters of water are absorbed back to body until the fecal matter becomes downright waste. The solid waste is moved and stocked in the rectum, and is excreted from the body through the anal canal.
References:
Kararli TT. Comparison of the gastrointestinal anatomy, physiology, and biochemistry of humans and commonly used laboratory animals. Biopharm Drug Dispos. 1995 Jul;16(5):351-80.
Ménard D. Functional development of the human gastrointestinal tract: hormone- and growth factor-mediated regulatory mechanisms. Can J Gastroenterol. 2004 Jan;18(1):39-44.
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