2023-06-18 10:00:00
It is following the exit of the pylorus, in this tube 5 to 7 m long and 3 cm in diameter, that most of the absorption of the food will take place.
The food eaten, then ground, is reduced to the sticky mush that is le chyme. But before they can pass the intestinal wall (or barrier) and join the bloodstream, lipids, proteins and carbohydrates must be broken down and broken down. It is therefore in the first “room” of the hail, the duodenum, involving the liver and the pancreas. They produce powerful digestive juices: the bile from the liver, and pancreatic juice, very rich in enzymes (amylase, lipase, peptidase and two proteinases) from the pancreas. These substances will “water” the chyme as it passes, which will facilitate the resorption of nutrients through the walls. When it arrives in the hail following parts that are jejunum and ileumthe chyme continues its crossing in small packets, propelled one following the other, thanks to peristalsis: a series of contractions slow and concentric muscles of the tube which are in charge of kneading it and helping it, with downward movements, to progress, under control of the nervous influx.
A more or less slow digestion
You should know that the amplitude and the frequency of movements change by age and gender (they are slower in women), but also depending on the time and nature of the meal, its caloric load, making digestion more or less rapid. With each contraction, millions of villi which line the intestine, take nutrients from the chyme and send them to the blood capillaries, then to the vessels to supply the organs: sugars and amino acids (resulting from the degradation of proteins) are recovered by the liver where they will be sorted, lipids through the lymph before being transported to the cells. At the end of the journey, 90% of the food will have been absorbed: there will only be waste left, sent to the colon to be dehydrated to form the stool. This fairly energetic “clearing” takes place via a powerful wave which shakes the hail from top to bottom, and is at the origin of sometimes audible gurgling.
What is the surface area of the small intestine?
The internal surface of the hail is lined with villi 1 mm long, which make it possible to multiply by regarding 10 the surface of the intestine and therefore reabsorption of nutrients! Indeed, each of them is covered with microvilli approximately 600 times smaller: a brush border which gives the intestine a total area of almost 400 m2, the equivalent of a basketball court! With one feature: this lining never gets oldbecause it renews itself constantly, at the rate of 17 billion cells per day, each with a lifespan of 2 to 6 days.
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