Small Intestine

• 7 meters in length
• 2.5-3 cm in diameter
• Surface area is the same as a tennis court (about 250sq.m)

Three Parts of the Small Intestine

All three sections contain the same external muscle, arranged in longitudinal and circular layers, that control peristalsis. Each section also has the same serous membranes. All sections contain villi.

• Duodenum

  • First section adjacent to stomach, connected by the pyloric sphincter valve
  • Only section to contain Brunner's Glands (glands that secrete bicarbonate)

• Jejunum

  • Similar to Duodenum

• Ileum

  • Only section to contain Peyer's Patches.

Functions of the Small Intestines

• Peristalsis

  • Muscles on the outside of the small intestines create wavelike contractions that propel food along the digestive tract.

• Digestion

  • The small intestine is where most chemical digestion takes place
  • Enzymes from the pancreas, through the pancreatic duct, aid in digestion
  • Enzymes release in response to the hormones cholecystokinin (which responds to the presence of nutrients) and secretin (which neutralizes stomach acid)

  • Protein Digestion

    • Proteins and peptides are broken down into amino acids by trypsin and chymotrypsin.
    • They are further broken down by carboxypeptidase
    • End results are freed by aminopeptidase and dipeptidase

  • Lipid Digestion

    • Lipids are broken down into fatty acids and glycerol
    • Pancreatic lipase breaks down triglycerides into free fatty acids and monoglycerides
    • To emulsify the triglycerides bile attaches so lipase can further break it down, it then goes to the villi for absorption.

  • Carbohydrate Digestion

    • Carbohydrates are broken down into simple sugars called monosaccharides.
    • Amylase further breaks monosaccharides into oligosaccharides.
    • Brush border enzymes, most importantly dextrinase and glucoamylase, further break down the oligosaccharides.
    • Other brush border enzymes are maltase, sucrase and lactase.

• Absorption

  • Digesteted food is absorbed by the villi of the small intestine.
  • The mucosa of the small intestine is simple columnar epithelium, within the epithelium are plicae circulares. These are wrinkles and folds that contain the villi.
  • Within each villi are microvilli, and the villi's main purpose it to increase the surface area of the small intestine for maximum absorbtion space.
  • Within each villi are capillaries and lacteals (lymphatic vessels) which transport nutrients to the bloodstream and in turn to the organs and tissues of the body.
  • Most digestion takes place in the jejunum, except:
    • Iron is absorbed in the duodenum
    • Vitamin b12 and bile salts are absorbed in the ileum
    • Water and lipids are absorbed by passive diffusion
    • Sodium is absorbed by active transport
    • Fructose is absorbed by facilitated diffusion (wikipedia for the preceding)

Diseases of the Small Intestine

• Celiac Disease

  • The body cannot digest gluten, a protein found in wheat, rye, barley and some other grains.
  • When gluten enters the small intestine, it enacts an inflammatory response in the villi. Once the gluten interferes with the villi, the villi are destroyed.
  • Some symptoms include:
    • Diarrhea
    • Bloating
    • Distended abdomen
    • Fatty stool
    • Dermatitis herpetaformis
    • Anemia
    • Weight Loss
  • The only way to treat Celiac is to adhere to a gluten-free diet.
  • A person can only develop Celiac if they have a genetic predispostion to it, and it may not show itself in a carrier.
  • Celiac usually presents itself after extreme trauma or stress.

• Crohn's Disease

  • An autoimmune disease in which the body's immune system attacks it's gastrointestinal tract and causes inflammation of the gastrointestinal tract
  • Those with siblings that have Crohn's Disease are more likely to get Crohn's Disease.
  • Affects between 400,000 to 600,000 in the U.S.
  • Symptoms include:
    • Abdominal Pain
    • Diarrhea
    • Blood in stool
    • Fecal incontinence
    • Ulcers of the small intestine, where the Crohn's is present
    • Inability to maintain growth
    • Weight loss
    • Decreased Appetite
  • There is no treatment or cure for Crohn's Disease itself, however symptoms can be managed and the main goal through treatment is remission
  • Those with Crohn's are more likely to have obstructions, hemorrhage, fissures and perforation
  • Colonoscopy is used to diagnose the disease

• Tropical Sprue

  • A malabsorbtion disease, usually prevalent in tropical regions, in which the villi of the small intestine flatten and the lining of the small intestine becomes inflammed. Not to be confused with Celiac Sprue.
  • Usually begins with an attack of acute diarrhea
  • Thought to be caused by a bacterial or viral infection, brought on by being in a tropical region.
  • Usually occurs 30 degrees north or south of the equator.
  • Symptoms include:
    • Diarrhea
    • Indigestion
    • Cramping Pain
    • Fatigue
    • Weight Loss
  • If left untreated:
    • There will be a deficiency of Vitamin A, B12, D, K, folic acid and calcium
  • Once diagnosed, antibiotics and vitamins will be given for at least 6 months
  • To prevent Tropical Sprue:
    • Only drink bottled water in aforementioned regions
    • Don't eat fruit with the skins on
    • Avoid tap water in aforementioned regions
    • Avoid affected regions

Worksheet:

Small Intestine Matching


Directions: Match the term in Column A with the definetion in Column B, Some terms may be used more than once.

Column A

A. Small intestine B. Crohn’s Disease C. Celiac Disease D. Tropical Sprue E. Peristalsis F. Duodenum G. Jejunum H. Ileum I. Amylase J. Simple Columnar K. Colonoscopy L. Gluten-Free Diet M. Antibiotics N. Lipids O. Carbohydrates P. Diarrhea Q. Bottled water

Column B
1.First portion of the small intestine
2.Flattening of the villi due to viral infection
3.Contraction of muscles to propel food
4.Where chemical digestion takes place
5.Avoid this to prevent tropical sprue
6.Broken down into monosaccharides
7.Treatment for Tropical Sprue
8.Common symptom of most gastrointestinal diseases
9.Broken down into fatty acids and glycerol
10.Second portion of the small intestine
11.Treatment for Celiac Disease
12.Used to diagnose Crohn’s Disease
13.Connected to stomach by pyloric sphincter valve
14.Where iron is absorbed
15.Contains Peyer’s Patches
16.Epithelium of the small intestine
17.Auto-immune disease that causes inflammation
of the gastrointestinal tract
18.Enzyme that breaks down carbohydrates
19.Third portion of the small intestine
20.Auto-immune disease in which the body cannot digest gluten

works cited
www.wikipedia.com/ small intestine
www.celiac.org