The small intestine is involved in the digestion, absorption and transport of food. Food breaks down further in the small intestine after passing through the stomach, and the absorption of vitamins, minerals, carbohydrates, protein, and fat takes place.
The
small intestine is the largest part of the
gastrointestinal tract and is composed of the
duodenum which is about one foot long,
jejunum (5-8 feet long), and
ileum (16-20 feet long).
The Digestive ProcessThe duodenum is the major portion of the small intestine where enzyme secretion takes place. The small intestine secretes sucrase (breaks sucrose into
glucose and fructose); maltase (breaks maltose into glucose); and
lactase (breaks lactose into glucose and galactose - lactase is missing in many people). It also secretes petidase to split peptides (from protein) into
amino acids, and
lipase to break down fat into glycerol and
fatty acids.
The
duodenum receives
bile from the
liver and
gallbladder, to decrease the surface tension between the large fat globules and water, and break them into smaller globules that can be acted upon by lipase. Lipase,
amylase,
trypsin,
chymotrypsin and
sodium bicarbonate are received from the
pancreas upon hormonal signals from pancreozymin and other hormones (produced in the
small intestine) and neural signals from the
vagus nerve.
Epithelial cells in the small intestine secrete over half a gallon of a neutral fluid daily to supply a watery substance to mix with the
chyme and provide a substance to aid in
electrolyte and vitamin absorption through the
villi.
Brunner's glands in the
duodenum secrete mucus in response to secretin, vagal stimulation, and direct stimulation of food in the small intestine. This mucus protects the
duodenal wall from the digestive juices. Goblet cells in the
mucosa also produce mucus.
Approximately 50% of the
carbohydrate digestion is performed by
amylase from the
pancreas, 40% by amylase from
saliva, and 10% by intestinal amylase. About 95% of the fat digestion is performed by
pancreatic lipase and 5% by intestinal and stomach lipase.
Almost 90% of our daily fluid intake is absorbed in the
small intestine. The small intestine is covered with
villi and
microvilli, which increase by a factor of 600 the surface area of the intestinal wall exposed to
chyme. The increased surface area makes the small intestine very efficient in absorption. Capillaries in the villi absorb
amino acids,
glucose, fructose, and galactose while lacteals absorb
fatty acid and glycerol to travel through the
lymphatic vessels.
As chyme enters the small intestine, its acidity causes secretion of the hormone secretin, which signals the
pancreas to secrete
alkaline juices to neutralize the chyme. The chyme also initiates a type of small intestine contraction known as segmentation which helps to mix and chop the chyme and propel it along. These contractions occur about once every 5 seconds in the
duodenum but only half as fast in the
ileum. Peristaltic waves also occur and aid in chyme propulsion. It takes about 2-3 minutes for the chyme to advance 1 inch; food will normally remain in the small intestine for between 3 and 10 hours.
Harmful irritants reaching the small intestine can initiate what is called a peristaltic rush which can empty the entire small intestine into the
colon within a few minutes. Food that you are allergic to can also do this and lead to
diarrhea due to the lack of time for fluid absorption.
Causes and Development
Causes of
Small Intestine Dysfunction:
- Some causes are related to the liver, pancreas, gallbladder, and stomach, all affecting digestion in the small intestine. The cause must be determined.
- Nerve pressure in the lower thoracics can affect small intestine function.
- Stress can alter enzyme secretion and cause dysfunction.
- Antibiotic therapy (for infections, etc.) can kill off helpful bacteria in the small and large intestine and can cause an alkaline gut where harmful gas producing bacteria will proliferate. Lack of HCl will contribute to this also.
- Spices, alcohol and caffeine can cause irritation and result in oversecretion of mucus in the small intestine. This can "plug" the villi and decrease vitamin and mineral absorption leading to various deficiencies. In this case even a healthful diet won't be assimilated properly.
- Causes of duodenal ulcers:
- Increased HCl secretion in the stomach up to 15 times normal.
- Stress causing increased sympathetic nerve flow and decreasing secretion of mucus from Brunner's glands.
- An overworked pancreas from overeating, eating between meals, etc., not secreting enough bicarbonate.
- Eating any food you're allergic to can cause disturbances in the small intestine.
Signs and Symptoms
Symptoms of
Small Intestine Dysfunction:
- General symptoms of small intestine dysfunction include abdominal bloating and pain, gas, diarrhea, nausea.
- Lactase deficiency can cause gas, nausea, bloating, cramps, diarrhea, asthma, congestion, on ingestion of dairy products.
- It is thought by many that congestion in the lacteals and lymphatics of the small intestine contributes to narcolepsy.
- Symptoms of duodenal ulcers include midmorning and middle of the night pain relieved by eating. The pain lasts for 1-3 weeks at a time and then subsides.
Treatment and Prevention
Prevention and Treatment of
Small Intestine Dysfunction:
- 15 minutes before each meal take one-quarter teaspoon of high silica clay to "scrub" out the mucus. If there is mucus in your stool from this treatment, don't be concerned.
- Make sure your liver, pancreas, gallbladder and stomach are functioning properly.