What is inside stomach?

The stomach is divided into four regions. They are the fundus, body, antrum and pylorus.

Within the stomach, but particularly in the small intestine, the surface area of the mucosa is greatly increased. The mucosal and submucosal layer is folded into microscopic villi on the surface of larger folds or ridges.

Intestinal villi are leaf-like or finger-like mucosal projections that lend a velvety appearance to the mucosa of the small intestine. On their surface, the villi are covered by absorptive epithelial cells known as enterocytes.

At the bases of the villi are the “crypts” where new epithelial cells are formed that migrate upward to the villi. These cells are sloughed off at a fairly rapid rate: the lifespan of villus cells in the small intestine is as little as 2 - 3 days (in man), that of colonic cells 3 – 8 days).

In general, the crypts are primarily involved in cell renewal, ion and water secretion, whereas the villus epithelium functions in nutrient acquisition.

The crypts of Lieberkuhn are interspersed among the villi. It is multi-potent stem cells that give rise to a series of committed progenitors, which subsequently undergo differentiation to defined cell types in each location.

The crypts are sub-epithelial tubular glands that secret intestinal juice for regionally varying composition.

Glandular cells are important in signaling the initiation and coordination of digestive processes, involving a large number of hormones neurotransmitters and paracrine factors.

As the enterocytes mature and migrate to the villus tip, they alter the type and distribution of membrane transporters and change from being secretory cells to absorbing cells.
What is inside stomach? 

Digestion and absorption at infant age

The mechanisms for digesting and absorbing major nutrients are not fully mature in the premature and term infant.

The complex process of digestion/absorption can be optimally effective only when the GI tract and accessory organs are totally develop and fully functioning. The primary function of the GI tract is the digestion and absorption of nutrients.

Not only must the muscular tube (alimentary canal) with it a mucosal lining and endocrine cells be operating efficiently in conjunction with the nervous system, but the accessory organs (pancreas, liver, and gallbladder) with their important digestive secretions also must be physiologically mature.

Normally, the initial breakdown or hydrolysis of carbohydrates depends on both salivary and pancreatic amylase. However, in the infant, carbohydrate hydrolysis is limited by the fact that although salivary amylase is present by 34 weeks’ gestation, secretion of pancreatic amylase does not begin until age 4 to 6 months.

The feeding of infants is based on primarily in degree of maturation of the GI tract and accessory organs. Good examples of the emphasis on GI tract maturity are the care given to the fat in infant formula and the time and sequence of the introduction of various foods into the infant’s diet.

Only those fats possessing an ease used in commercial formulas and the introduction of solid food, beginning with baby cereal usually occurs no earlier than 4 months of age. The absorption coefficient of fats is 90 to 95% during the first week of life and at least 96% at 1.5 months of age.

The infant pancreas, although structurally mature at term, is usable for several months to produce enzymes sufficient for effective digestion.
Digestion and absorption at infant age

Digestion and absorption of carbohydrates

The carbohydrates in the diet are broken down by the enzymes on the mouth, pancreas and intestinal epithelium.

Digestion resumes in the small intestine where more polysaccharide splitting enzymes from the pancreas break the carbohydrate down completely into disaccharides. The enzyme released through the common bile duct into the small intestine.

Then enzymes on the surface of the cells of the small intestine break these into simple sugars or monosaccharaides.  Maltose is split into two glucose molecules; lactose is split into one glucose and one galactose; and sucrose into one glucose and one fructose.

However the great majority of carbohydrates in human meal are digested and absorbed as glucose, if a blood glucose levels are measured before such a meal and at half hourly intervals thereafter, it would show a rise in blood glucose, peaking at about the half hour mark and returning to fasting levels almost as quickly.

If a person were to abstain from carbohydrates for considerable periods say a week, the blood glucose levels would still be normal in spite of a minimal or zero intake.

The active absorption of glucose across the intestinal mucosa is thought to be by phosphorylation in the mucosal cell.

The body’s capacity to maintain blood glucose within specific limits is achieved by a variety of hormones, the two most important of which are insulin and glucagon. Both are secreted by the pancreas into bloodstream, as required.

When the blood glucose level arises, the body adjusts by storing the excess. The frost organ to detect the excess glucose is the pancreas, which releases the hormone insulin in response.
Digestion and absorption of carbohydrates

What is gastrointestinal tract (GI)?

The digestive system includes the gastrointestinal tract, which starts at the mouth, where food and fluids are taken into the body and ends at the anus, where the final waste products are eliminated in the feces.

The gastrointestinal tract consists of all structures derived from the primitive gut tube and distal to the esophagus.

As such the gastrointestinal tract includes the stomach, small intestine, large intestine and those accessory structures that have formed from that part of the gut (liver, gallbladder, pancreas, hepatopancreatic duct, anal tonsils).

The accessory organs contribute needed materials for the breakdown and processing of the food entering the system.

The gastrointestinal tract (GI) is bordered by a layer of epithelial cells (with glands) sitting on a lamina propria (or basement membrane), comprising the mucosa and adjacent to the sub-mucosa, which is penetrated by blood capillaries, lymphatics and nerves.

Beneath the mucosa and sub-mucosa are two layers of smooth muscle, lying in longitudinal and transverse directions, to allow contractions and peristalsis,

The stomach contains the same tissue layers as are found in the esophagus, small intestine and colon, with some important variations in the secretions and structure of the mucosa layer.

The surface of the mucosa is a layer of simple columnar epithelial cells called surface mucous cells.

The mucosa contains a lamina propria (areolar connective tissue) and a muscularis mucosae (smooth muscle).
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Within the stomach, but particularly in the small intestine, the surface area of the mucosa is greatly increased. The mucosal and sub-mucosal layer is folded into microscopic villi on the surface of larger folds or ridges.

The main functions of the gastrointestinal system consist of digestion and absorption.
What is gastrointestinal tract (GI)?

The digestion of fat in human body

While a small amount of fat splitting may take place in the stomach, most of the digestion of food fat is carried on in the intestine through the action of intestinal and pancreatic enzyme and of bile.

In human body fat occurs mainly as neutral fat in the form of triglycerides of oleic, palmitic and stearic acid. In addition to neutral fats, fats include phospholipids, cholesterol and its ester. Neutral fats are triglycerides i.e, glycerol combined with three molecules of fatty acids.

The first step of fat digestion begins in the stomach. Lingual lipase secreted from the serous glands of the tongue, and gastric lipase, secreted from the chief cells of the gastric mucosa, digest approximately one third of the dietary triglycerides.

Main digestion of fats is carried out by pancreatic lipase at optimum pH 8 and temperature of 40° C.

Bile salts are helpful and break up the fat droplets, which are emulsified. This emulsification results in increase of the fat surface on which pancreatic lipase can act.

The main path of fat digestion progresses from triglycerides to 1,2-diglycerides, to 2-monoglycerides and finally to free fatty acids and glycerol, perhaps after isomerization to the 1-monoglyceride.

During digestion, exchange of free fatty acids with glyceride fatty acids occurs.

Fats are involved in brain development, inflammatory processes, atherosclerosis, carcinogenesis, aging and cell renewal.
The digestion of fat in human body