What are we absorbing & how?



What is being absorbed?
Example of that type of material
How does it occur?
broken food pieces
tiny pieces of food that broke off the original piece... these can include more than one type of macromolecule
Endocytosis-- because these tiny pieces are still very large to a cell.
macromolecules
protein
carbohydrate
nucleic acid
or broken off pieces of these molecules
lipid

Endocytosis-- of proteins, carbohydrates, or nucleic acids... these molecules, even if broken a bit, are still too large to go through the membrane.
Simple Diffusion-- of lipid, only. (note: lipids tend to go into the lacteal rather than the blood)

monomers
amino acids
monosaccharides (like glucose & fructose)
nucleotides
lipids don't have monomers, but some smaller pieces of them, like fatty acids or monoglycerides can sort of fit this category.

Facilitated Diffusion-- of amino acids, monosaccharides, and nucleotides enables them to cross the membrane.
Simple Diffusion-- of the lipid. (note: lipids tend to go into the lacteal rather than the blood)


taken from:
http://faculty.stcc.edu/AandP/AP/AP2pages/Units24to26/digestion/absorp.htm

Digestion of nutrients



Digestion is the breakdown of food into smaller particles or individual [[../Met-Obe/Nutrients.html|nutrients ]]. It is accomplished through six basic processes, with the help of several body fluids—particularly digestive juices that are made up of compounds such as saliva, mucus, enzymes , hydrochloric acid, bicarbonate, and bile .
The six processes of digestion involve: (1) the movement of food and liquids; (2) the lubrication of food with bodily secretions; (3) the mechanical breakdown of [[../Ca-De/Carbohydrates.html|carbohydrates ]], fats, and proteins ; (4) the reabsorption of nutrients—especially water; (5) the production of nutrients such as vitamin K and biotin by friendly bacteria ; and (6) the excretion of waste products. Comprehension of the tasks or processes needed to break down food are essential to an understanding of how and when food really begins to function within the body. For example, not understanding that carbohydrates break down into glucose could lead one to believe that the best source of glucose is in liquid form such as a soft drink. This could cause one to miss out on the nutrients (and great taste) in fruits, vegetables, and grains. Likewise, not understanding the digestion process could lead a person to believe in the myth of "food combining," or perhaps to think it is normal to be hungry all the time. But, in fact, the digestive processes normal to human physiology can simultaneously handle carbohydrates, fats, and proteins—and allow people to go several hours between meals, especially if meals are balanced in [[../Erg-Foo/Fiber.html|fiber ]]and the individual nutrients needed.

GI Tract Physiology

Digestion begins in the mouth with the action of salivary amylase. The food material then progresses past the esophagus and into the stomach. A bolus (soft mass) of chewed food moves by muscular wave actions, called peristalsis, from the mouth to the pharynx, and then past the epiglottis that covers the larynx. The epiglottis closes off the air passage so that one doesn't choke. The cardiac sphincter prevents reflux of stomach contents into the esophagus.

From the Stomach to the Small Intestine

Food mixtures leaving the stomach are called chyme, and this empties into the small intestine after about two to four hours in the stomach. The small intestine is where most digestion takes place. A pyloric sphincter controls the rate of flow of chyme from the stomach into the small intestine.
Most digestion occurs in the upper portion of the small intestine, called the duodenum. Below the duodenum is the jejunum, and then there is the last segment, called the ileum. About 5 percent of undigested food products are broken down in the ileum. This is why some people can have a small part of their intestine removed and still seem to digest most foods with little problem.
Digestion of food that enters the small intestine is usually complete after three to ten hours. Once digestion is essentially finished, waste products leave the ileum with the help of fiber, and these solids then enter the large intestine (the colon). In the colon, water is reabsorbed; some nutrients are produced by friendly bacteria (vitamin K, biotin, vitamin B 12 ); fibers are digested to various acids and gases; and [[../Met-Obe/Minerals.html|minerals ]], such as potassium and sodium, are reabsorbed (when needed). Any fiber that is not broken down—and small amounts of other undigested products—are excreted in the feces.

Protective Factors

During digestion in the stomach, large proteins break down into smaller protein forms, and harmful bacteria can become inactive. Hydrochloric acid is especially important for this because it lowers the pH of the stomach contents below 2. Along with the uncoiling of protein in the stomach, a little carbohydrate and lipid are broken down with the help of enzymes (called amylase and lipase, respectively).
In the stomach, carbohydrates in foods turn to starch, but it is not until the chyme reaches the small intestine and becomes more neutralized that starch turns to simple sugars that are then absorbed into the portal vein, which transports them to the liver. Also in the small intestine, lipids (mostly in the form of triglycerides ) are emulsified and form monoglycerides and free fatty acids that can then go through the lymph system to the heart and bloodstream.
As previously mentioned, the mouth, stomach, small intestine, and colon are the major organs of digestion. However, the liver, gallbladder, and pancreas are also important to the process. The liver detoxifies foreign compounds, such as natural toxicants in foods and drugs . The liver also makes bile, an emulsifier, which enters the small intestine and prepares fats and oils for digestion. This bile is stored in the gallbladder prior to delivery to the small intestine. A hormone called cholecystokinin helps control the release of bile.
The pancreas makes pancreatic juice consisting of enzymes (amylases, lipases, and proteases) and bicarbonate, which helps neutralize acidic secretions produced during digestion. The pancreas delivers the pancreatic juice to the small intestine, in response to a signal of food in the intestine and the release of the hormone secretin. The pancreas also has another function, the secretion of the hormones [[../Hea-Irr/Insulin.html|insulin ]]and glucagon, which helps maintain a steady state of blood sugar in the body (insulin decreases blood glucose concentration, while glucagon increases it).
Food moves from the mouth to the epiglottis, bypassing the trachea, into the esophagus, past the cardiac sphincter into the stomach, past the pyloric valve into the small intestine (duodenum, jejunum, ileum), and then
[[image:../images/nwaz_01_img0077.jpg width="258" height="450" caption="The tract running from the esophagus to the large intestine is called the alimentary canal, and it is where most digestion occurs. As food is pushed through the system, it encounters numerous specialized processes that act on it in different ways, extracting nutrients and rejecting waste. [Illustration by Argosy. The Gale Group.]"]]The tract running from the esophagus to the large intestine is called the alimentary canal, and it is where most digestion occurs. As food is pushed through the system, it encounters numerous specialized processes that act on it in different ways, extracting nutrients and rejecting waste. [Illustration by Argosy. The Gale Group.] past the ileocecal valve into the colon. Waste then leaves the colon through the rectum and anus. When chyme reaches the small intestine, the pancreas and liver contribute to the digestion by providing products such as bicarbonate, enzymes, and bile.

Absorption

Absorption is the movement of molecules across the gastrointestinal (GI) tract into the circulatory system. Most of the end-products of digestion, along with vitamins , minerals, and water, are absorbed in the small intestinal lumen by four mechanisms for absorption: (1) active transport, (2) passive diffusion, (3) endocytosis, and (4) facilitative diffusion. Active transport requires energy .
Nutrient absorption is efficient because the GI tract is folded with several surfaces for absorption and these surfaces are lined with villi (hairlike projections) and microvilli cells. As one nutrition textbook puts it, each person has a surface area "equivalent to the surface of a tennis court" packed into his or her gut (Insel et al., p. 81). Efficient absorption can be compromised due to [[../Kwa-Men/Lactose-Intolerance.html|lactose intolerance ]]. Lactose intolerance is not uncommon in the world, affecting about 25 percent of the U.S. population and 75 percent of the worldwide population. It is usually due to the lack or absence of the enzyme lactase, which breaks down milk sugar.
Lactose intolerance is not a food allergy . Food allergies are serious, even life threatening, but most people with lactose intolerance can digest small amounts of milk, especially in yogurt and cheese.
Protein, carbohydrate, lipid, and most vitamin absorption occur in the small intestine. Once proteins are broken down by proteases they are absorbed as dipeptides, tripeptides, and individual [[../A-Ap/Amino-Acids.html|amino acids ]]. Carbohydrates, including both sugar and starch molecules, are broken down by enzymes in the intestine to disaccharides called sucrose, lactose, and maltose, and then finally into the end-products known as glucose, fructose, and galactose, which are absorbed mostly by active transport. Lipase, an enzyme in the pancreas and the small intestine, and bile from the liver, break down lipids into fatty acids and monglycerides; these end-products then are absorbed through villi cells as triglycerides.
Alcohol is not a nutrient, but 80 percent of consumed alcohol is absorbed in the small intestine. The other 20 percent is absorbed into the stomach. Alcohol is absorbed by simple diffusion, which explains why gastric ulcers are not uncommon in people who drink excessively.

Coordination and Transport of Nutrients into the Blood or to the Heart

Hormones and the nervous system coordinate digestion and absorption. The presence of food, or the thought or smell of food, can cause a positive response from these systems. Factors that can inhibit digestion include stress , cold foods, and bacteria.
After foods are digested and nutrients are absorbed, they are transported to specific places throughout the body. Water-soluble nutrients leave the GI tract in the blood and travel via the portal vein, first to the liver and then to the heart. Unlike the vascular system for water-soluble nutrients, the lymphatic system has no pump for fat-soluble nutrients; instead, these nutrients eventually enter the vascular system, though they bypass the activity of the liver at first.


Read more: Digestion and Absorption - food, nutrition, body, carbohydrate, protein, fat, nutrients, eating, carbohydrates, vitamin, amino, acids, water, vitamins, habits, soluble http://www.faqs.org/nutrition/Diab-Em/Digestion-and-Absorption.html#ixzz0n4Ha7igm

human digestion

The Human gastrointestinal tract or digestive system is the system by which ingested food is acted upon by physical and chemical means to provide the body with nutrients it can absorb and to excrete waste products; in mammals the system includes the alimentary canal extending from the mouth to the anus, and the hormones and enzymes assisting in digestion.
In an adult male human, the gastrointestinal (GI) are 5 metres (20 ft) long in a live subject, or up to 9 metres (30 ft) without the effect of muscle tone, and consists of the upper and lower GI tracts. The tract may also be divided into foregut, midget, and hindgut, reflecting the embryological origin of each segment of the tract.

The GI tract releases hormones as to help regulate the digestion process. These hormones, including gastrin, secretin, cholecystokinin, and grehlin, are mediated through either intracrine or autocrine mechanisms, indicating that the cells releasing these hormones are conserved structures throughout evolution.


What is digestion
In mammals, food enters the mouth, being chewed by teeth, with chemical processing beginning with chemicals in the saliva from the salivary glands. Then it travels down the esophagus into the stomach, where acid both kills most contaminating microorganisms and begins mechanical break down of some food (e.g., denaturation of protein), and chemical alteration of some. After some time (typically an hour or two in humans, 4–6 hours in dogs, somewhat shorter duration in house cats, ...), the results go through the small intestine, through the large intestine, and are excreted during defecation.

external image aparatodigestivo.jpg


Ingestion, digestion and absorption

You saliva begins to form in the mouth. When you eat, the saliva begins the process of decomposition of the chemicals contained in food and helps to soften them for easier swallowing. The language helps push food through the mouth while you chew with the teeth. When you are prepared to swallow, the tongue pushes a piece of crushed and softened food called bolus toward the back of the throat, so that the opening between the esophagus by the second part of the gut.



The esophagus is a hose that measures about 25 inches long. Carries food from the back of the throat to the stomach. But in the back of the throat is also the windpipe, which allows air in and out of your body. When you swallow a wad of crushed and softened food or liquids, a tab of a special tissue called the epiglottis closes the opening of the trachea to ensure that food enters the esophagus, rather than the trachea.

Once the food enters the esophagus, is not going directly into the stomach. Instead, muscles in the walls of the esophagus move describing a wave motion to go crushing the food while they do lower down the esophagus. This lasts about 2 or 3 seconds. El estómago está unido al extremo inferior del esófago. Se trata de un "saco" elástico que tiene la forma de la letra "j". Desempeña tres funciones importantes:
The stomach is attached to the lower end of the esophagus. This is a "bag" elastic in the shape of the letter "j". Performs three major functions:

Store the food you eat
Breaking down food into a liquid mixture
Empty the liquid slowly into the small intestine


The stomach acts as a blender, mix and grind all food pellets from the esophagus into smaller and smaller fragments. This is done with the help of the strong muscles you have in your walls and they secrete digestive juices. In addition to fragment and break down food, gastric juices also help kill germs and bacteria that may contain the food you eat.

The small intestine is a long tube with a diameter or contour between 3.5 and 5 centimeters, which was folded on itself within you, below the stomach.
If your small intestine fully extended, would measure about 6.7 meters long


The small intestine plays an important role of separating the mixture of food from the stomach even more, so your body can absorb all the nutrients that contains vitamins, minerals, proteins, carbohydrates, and fats The foods you eat can stay up to four hours in your small intestine, until mixture becomes a liquid and watery.

has drawn most of the nutrients in the liquid mixture of food, is what is known as waste products, the material that the body could not use and must be expelled outside. Before being expelled, waste products pass through the portion of the large intestine called the colon, which is where the body is the last chance to absorb water and some minerals, pouring into the bloodstream. As waste products are losing water, will harden as they move through the large intestine into a solid

after the stool reaches the rectum where they have to be expelled

taken from: http://kidshealth.org/kid/en_espanol/cuerpo/digest_esp.html

Ingestion in living things
Ingestion is the consumption of a substance by an organism. In animals, it normally is accomplished by taking in the substance through the mouth into the gastrointestinal tract, such as through eating or drinking. In single-celled organisms, ingestion can take place through taking the substance through the cell wall.
Besides nutrional items, other substances which may be ingested include medications, recreational drugs, and substances considered inedible such as foreign bodies or excrement. Ingestion is a common route taken by pathogenic organisms and poisons entering the body.


external image 1090.jpg

http://en.wikipedia.org/wiki/IngestionWhere is absorption occurring?

Mainly in the small intestines. A teeny bit in the stomach and a teeny bit in the large intestines, but mainly in the small intestines.
Because of this, the small intestines are nicely designed for absorption. They have tons and tons of apical membrane on their epithelium. The epithelial cells have microvilli, kind of like I tried to show you in the diagram at the top.
The small intestines are also highly vascularized, to facilitate transport of the nutrients from the epithelium to the blood. They also have lymphatic vessels throughout... these pick up the lipid nutrients in the specific lymphatic capillary called a lacteal. They also tend to pick up infectious agents that may be in our chyme, so that these agents can be destroyed by our immune systems.

taken from:
http://faculty.stcc.edu/AandP/AP/AP2pages/Units24to26/digestion/absorp.htm