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Category: absorption

Small Intestine

September 25, 2016 10:27 am

The small intestine is a long tubular organ that is approximately 460-1000cm in adults. It is divided into three sections, Duodenum, Jejunum, and Ileum. The surface area is greater than one might think due to the folds, villi, and microvilli. The surface area is approximately 30 square meters. Most of human digestion and absorption takes place within these three sections of small intestine.

Keshishian master-normal-anatomy-with-text
Keshishian master-normal-anatomy-with-text

The diagram of normal anatomy absorption in the small intestine is pictured to the right.  It is color coded based on the area of the digestive tract the absorption takes place. You may also view here: master-normal-anatomy-with-text

Overview

Length: 22 ft. (6.7 m)

Width: 1 inch

pH: neutral or slightly alkaline (5-7)

  • Steps:
    1. Neutralization in stomach, where enzymes act to breakdown food
    2. Digestion through greater breakdown with help of bile and pancreatic juices
    3. Absorption through assimilation of digested food, vitamins, and salts. Nutrients are taken into the bloodstream via specialized epithelial cells to the liver through the hepatic portal vein.

Duodenum

Length: 1 ft. (0.30 m)

pH~ 5

  • Main site of breakdown
  • C shaped turn with 4 parts: superior, descending, inferior, ascending
  • Mixes food (now in form of chyme) with bile and other digestive juices
  • Passes chyme through duodenojejunal flexure which contains suspensory muscle to widen the duodenal angle and increase movement.

Jejunum

Length: 8.2 ft. (2.5 m)

pH~ 6

  • Coiled, vascular tube that contains a thick intestinal wall
  • The wall contains epithelial projections called intestinal villi
    • Smaller projections in the villi, called microvilli work to:
  1. project specialized transport cells called enterocytes
  2. increase surface area
  3. allow more absorption

Ileum

Length: 11.5 ft. (3.5 m)

pH~ 7

  • Less vascularized and thinner intestinal wall
  • Absorbs nutrients that preceding sections of the gut did not
    • particularly works with vitamin B12 and bile salt absorption
  • Connects to the colon through the ileocecal valve for further breakdown.

The following are Member Exclusive documents.  Please be aware of your terms of use of these items.

Click for: Duodenal Switch Absorption & Anatomy (1.2 MB)

Click for:RNY Absorption Anatomy (1.1 MB)

References:

  1. Campbell NA, Reece JB, Mitchell LG. Biology. 5th ed. Benjamin-Cummings Pub Co. 1999-2002; 802-805.
  2. Ovesen L, Bendtsen F, Tage-Jensen U, Pedersen NT, Gram BR, Rube SJ. Intraluminal pH in the stomach, duodenum, and proximal jejunum in normal subjects and patients with exocrine pancreatic insufficiency. Gastroenterology. 1986; 90(4): 958-62.
  3. Stevens C. E., and Hume, I. D. 1995.Comparative Physiology of the Vertebrate Digestive System. 2nd ed. New York: Cambridge University Press.
  4. Schmidler C. Anatomy and Function of the Digestive System. Healthpages.org. 2016.

Hypertrophy of Small Bowel and Weight Gain Years After Duodenal Switch

August 21, 2015 7:53 pm

Duodenal switch (DS) operation results in the highest success rate of all weight loss surgical procedures. Patients, over time, will experience some weight gain many years after DS procedure. There are a number of suspected mechanisms that may be responsible for the weight gain:

1-Ageing may slow the metabolism and the activity down.

2-Over time patients may not be as adherent to healthy dietary and lifestyle changes as they may have been immediately after surgery.

3- Hypertrophy of the alimentary and common channels over time increases in surface area f allowing greater caloric absorption leading to increased weight gain.

It has been demonstrated in bowel resection studies, as well as rat studies, that the nutrient stimulated regions of small intestine increase villus height and total weight, crypt depth and proliferation as well as wall thickness, as an adaptation to compensate for the loss of absorptive capacity in the resected bowel. This observation may be applied to DS procedure as seen in histological slides from a patient who had to have an operation done requiring bowel resection. The segment of the bowel resected included the junction of the biliopancreatic, common and alimentary limbs.

Screen Shot 2015-08-20 at 2.09.29 PM
Side by Side comparison of Biliopancreatic and the Alimentary limb

Vitamin’s Physical State And Solubility are Two Different Things.

March 29, 2014 6:11 pm

One of the most common misconceptions regarding vitamins is that its physical shape and state (liquid versus solid) defines its solubility.  Water-soluble vitamins may be found in dry powder form (solid) or may be a form of liquid.  Fat-soluble vitamins may also be found in both solid and liquid form.  It is important to appreciate that one cannot assume that if a fat soluble vitamin is in liquid form in a gel cap it will be absorbed.  What makes a fat-soluble vitamin absorbable is not its liquid, physical state, but rather it’s molecular structure, which makes it possible to be absorbed.  When purchasing vitamins that are fat-soluble, labels such as “dry”, “water-soluble” are indications that it is water-soluble more important than its shape, size or the nature of the vitamin itself.
A liquid form of vitamin A and D may be less soluble than a dry powder form.  This is because it dry powder form may be chemically structured so that it is soluble in water versus a liquid form that is not.  An analogy will be the mixing of olive oil (liquid) with vinegar (liquid).  Olive oil will stay separated because it is not water-soluble even though it’s a liquid state.