ABSORPTION OF NUTRIENTS
-The products of digestion—glucose, amino acids, fatty acids, and glycerol—are now ready to be
removed from the digestive tube and transported where needed.
-The processes of Ingestion and Digestion are now complete
-the process of Absorption is ready to begin
Absorption
-occurs in the stomach, the small intestine and the large intestine
1. Stomach:
- small amounts of water
- alcohol
- some medicines, e.g. aspirin
2. Small intestine:
jejunum - where most of the absorption takes place
ileum-where the remaining nutrients are absorbed
Absorption is greatly aided by the folded interior structure of the intestine, particularly due to the
presence of the villi and microvilli.
-villi and microvilli are finger-like projections the increase the surface area of the small intestine
↑ Surface Area= ↑ Nutrient Absorption
Structure of Villi:
- tiny finger like projections lining the interior of the intestines
- contain two types of vessels:
●capillaries
– tiny blood vessels
- collect water soluble nutrients such as glucose and amino acids
-capillaries connect to arteries, and the arteries transport glucose and amino acids to
the entire body
●lacteal
- contain lymph and connect to the lymph vessels and lymph nodes
- collect products of fat digestion: fatty acids and glycerol
-Small molecules like vitamins and minerals and are easily absorbed by the small intestine walls
-Water is absorbed throughout the alimentary (GI) tract but the majority of water absorption occurs in
the LARGE INTESTINE, also known as the COLON.
3. The Large Intestine- The Colon (the BOWEL):
Structure:
- 1.5 m in length, 5 cm in diameter (twice the diameter of SI)
- made up of sections: caecum, ascending, transverse, descending, sigmoid
-the colon ends with the rectum
Function:
- main job is to reabsorb water, all water absorption occurs here
- bacteria here produce vitamin K and vitamin B, these vitamins are absorbed through the
walls of the large intestine
Egestion Of Waste
-the processes of ingestion, digestion and absorption have occurred, the last process to take place is
egestion
Egestion:
-Cellulose: main component of feces, along with living and dead bacteria and water
- Fibre, found in plant cell walls, cannot be digested by humans
.
FECES:
- waste is stored in rectum
- removed by body removing possible toxic materials
-As wastes build up in the large intestine, receptors in the intestinal walls provide information to
the central nervous system that, in turn, prompts the large intestine to void the waste.
-Individuals who do not eat sufficient amounts of cellulose(roughage or fibre) have fewer bowel
movements and may be at risk of developing colon cancers
-Egestion controlled by anal sphincter which allows feces to leave rectum through the anus. Toilet
training is learning how to control the anal sphincter.
WEBSITES:
http://www.medtropolis.com/VBody.asp
http://www.innerbody.com/htm/body.html
http://arbl.cvmbs.colostate.edu/hbooks/pathphys/digestion/smallgut/anatomy.html
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FramesVersion.html
http://faculty.clintoncc.suny.edu/faculty/Michael.Gregory/files/Bio%20102/Bio%20102%20lectures/Dig
estive%20System/digestive%20system.htm
http://www.bartelby.com/107/241.html
http://arbl.cvmbs.colostate.edu/hbooks/pathphys/digestion/basics/index.html
Digestion REVIEW
Most higher animals, including all vertebrates, have digestive tracts, or alimentary canals,
through which food passes. Human digestion begins in the mouth. There the food is chewed and
mixed with saliva, which adds moisture and contains the enzyme amylase that begins to break down
starches. The tongue kneads the food into a smooth ball (bolus), which is then swallowed. The bolus
passes through the pharynx and esophagus into the stomach, propelled by peristaltic muscular
contractions. In the stomach the food is mixed by peristaltic contractions (about three per minute) with
highly acidic gastric juices secreted into the stomach. The hormone gastrin stimulates the secretion of
these juices, which contain water, inorganic salts, hydrochloric acid, mucin, and several enzymes, the
most abundant of which is pepsin. Pepsin breaks protein molecules into smaller molecules called
polypeptides.
The food, now in a semiliquid state called chyme, passes from the stomach into the
duodenum, the first section of the small intestine, where the greatest part of digestion takes place.
The chyme is subjected to the actions of a large number of enzymes, some secreted by the pancreas
(which is connected to the duodenum by a duct) and some produced by glands in the intestinal wall.
Each enzyme acts on specific food molecules. For example, amylase, maltase, lactase, and sucrase
complete the digestion of carbohydrates; trypsin, chymotrypsin, carboxypeptidase, aminopeptidase,
and dipeptidase break down proteins; and lipase hydrolizes fat molecules. Bile, which is produced by
the liver, also empties into the duodenum; it contains salts that break up (emulsify) fat globules,
thereby exposing fat molecules to the enzymatic action of lipase. By the time this process has been
completed, the carbohydrates have been broken down into simple sugars (monosaccharides), the
proteins into amino acids, and the fats into glycerol and fatty acids. These simple molecules are then
absorbed into the circulatory system through countless microscopic projections of the intestinal wall
called villi as the material moves through the jejunum and ileum (the remaining sections of the small
intestine).
Substances that cannot be digested, such as cellulose (plant fibre), pass into the colon, or
large intestine. There, water and ions such as sodium and chloride are reabsorbed, and the
remaining solid material (feces) is held until it is expelled through the anus. Common diseases of the
human digestive tract include infections, inflammations, ulcers, and cancers.