Digestion in small intestine

Digestion in the Small Intestine
Although chemical digestion of some nutrients begins in
the oral cavity or stomach, most enzymatic hydrolysis of
the macromolecules from food occurs in the small intestine. The small intestine is the alimentary canal’s
longest compartment-over 6 m (20 feet) long in humans!
Its name refers to its small diameter, compared with that of
the large intestine. The first 25 cm (10 inches) or so of the
small intestine forms the duodenum. It is here that chyme
from the stomach mixes with digestive juices from the pancreas,
liver, and gallbladder, as well as from gland cells of the intestinal wall itself. As you will see in Concept 41.5, hormones
released by the stomach and duodenum control the
digestive secretions into the alimentary canal.
Pancreatic Secretions
The pancreas aids chemical digestion by producing an alkaline
solution rich in bicarbonate as well as several enzymes. The bicarbonate neutralizes the acidity of
chyme and acts as a buffer. Among the pancreatic enzymes
are trypsin and chymotrypsin, proteases secreted into the
duodenum in inactive forms. In a chain reaction similar to
the activation of pepsin, they are activated when safely located
in the lumen of the duodenum.
Bile Production by the Liver
Digestion of fats and other lipids begins in the small intestine
and relies on the production of bile, a mixture of substances that is made in the liver. Bile contains bile salts, which act as
emulsifiers (detergents) that aid in digestion and absorption
of lipids. Bile is stored and concentrated in the gallbladder.
Bile production is integral to one of the other vital functions
of the liver: the destruction of red blood cells that are
no longer fully functional. In producing bile, the liver incorporates
some pigments that are by-products of red blood
cell disassembly. These bile pigments are then eliminated
from the body with the feces. In some liver or blood disorders,
bile pigments accumulate in the skin, resulting in a
characteristic yellowing called jaundice.
Secretions of the Small Intestine
The epithelial lining of the duodenum is the source of several
digestive enzymes. Some are secreted
into the lumen of the duodenum, whereas others are bound
to the surface of epithelial cells.
While enzymatic hydrolysis proceeds, peristalsis moves
the mixture of chyme and digestive juices along the small intestine.
Most digestion is completed in the duodenum. The
remaining regions of the small intestine, called the jejunum
and ileum,
Absorption in the Small Intestine
Most of this absorption occurs at the highly folded surface of the small intestine, as illustrated in . Large folds in the lining encircle the intestine and are studded with fingerlike projections called villi. In turn, each epithelial cell of a villus has on its apical surface many microscopic projections, or microvilli, that are exposed to the intestinal lumen. The
many side-by-side microvilli give cells of the intestinal epithelium a brush-like appearance that is reflected in the name brush border. Together, the folds, villi, and microvilli of the small intestine have a surface area of 200-300 m2, roughly the size of a tennis court. This enormous surface area is an evolutionary adaptation that greatly increases the rate of nutrient absorption.
Depending on the nutrient, transport across the epithelial cells can be passive or activ. The sugar fructose, for example, moves by facilitated diffusion down its concentration gradient from the lumen of the small intestine into the epithelial cells. From there, fructose exits the basal surface and is absorbed into microscopic blood vessels, or capillaries, at the core of each villus. Other nutrients, including amino acids, small peptides, vitamins, and most glucose molecules, are pumped against concentration gradients into the epithelial cells of the villus.
The capillaries and veins that carry nutrient-rich blood away from the villi converge into the hepatic portal vein, a blood vessel that leads directly to the liver. From the liver, blood travels to the heart and then to other tissues and organs. This arrangement serves two major functions. First, it allows the liver to regulate the distribution of nutrients to the rest of the body. Because the liver can interconvert many organic molecules, blood that leaves the liver may have a very different nutrient balance than the blood that entered. Second, the arrangement allows the liver to remove toxic
substances before the blood circulates broadly. The liver is the primary site for the detoxification of many organic molecules, including drugs, that are foreign to the body.
#Digestion
#DigestionAndAbsorptionInSmallIntestine

[@MVoiceIsrar]

25-5-24
اللہ تعالیٰ ہم سب کو تمام بیماریوں سے محفوظ رکھے اور سجدے کی حالت میں موت دے آ میں ❤️🤲🤲

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[@dr.akash_deep]

Bile emulsify Fats not digest,
Wrong information 😢😢

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[@MVoiceIsrar]

25-5-2024
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it's good, if you translate lacture to arabic language.

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Teach well

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Sir kya oesophagus ko chhodkar har part main food ka absorbed hota hai?

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Sir.... Small intestine ke length 17 to 20 feet Kesay hoti ha jubke average height hi 5 to 6 ft hoti ha 😢kindly explain

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Zabardast

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Sir ap ne lacteals ke bare me kuch nahi bataya jaha se lipids ki absorption hoti he 😢

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MashaAllah

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Sir plz next lecturer for digestion

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[@ArshadKhan-fn9ec]

If gallbladder is removed from body wherebile will be stored

[@ayeshazaman3716]

directly into the small intestine instead of being stored in the gallbladder through hepatic ducts into common bile duct.

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Sir ap ulta BOL gye Hain shaid small ki length zyda nhi hoti?

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Wo sir ha unhi pata ha small ke length zyada hote ha jabke large ka diameter zyada hote ha

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Sir G ileum length 5-7 feet long ❤

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Zbrdst

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Sir small intestine may sirf absorption hoti hai am I right

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No , digestion +Absorption takes place in small intestine

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@@misbahsaba2386 ok thanks dear

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No 7m

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Supper

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Maximum digestion kha hoti b???

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Duodenum

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