Digestive System Part:1
STOMACH:-The stomach is a pear-shaped muscular bag that partially digests food before it passes into the intestines. Its muscular wall churns the semi liquid contents and produces the digestive enzyme pepsin, which breaks down protein. The stomach also produces hydrochloric acid, which destroys harmful bacteria in food. A meal spends about four hours in the stomach before being discharged.
Structure:-The stomach is joined to the esophagus, which connects it to the mouth by a ring of muscle called the cardiac sphincter. This relaxes to admit food into the stomach, and then closes to keep the food in place. At the other end of the stomach is the pyloric sphincter, which allows food to leave the stomach when it is ready to pass into the intestines. Lining the stomach inside wall is a mucous membrane made of a layer of epithelial cells resting on connective tissue. When the stomach is empty, the mucous membrane is thrown into folds called rugae; when it fills, its wall stretches and the rugae flatten out.
Under the mucous membrane and connective tissue are three layers of smooth muscle. Each layer of muscle cells is aligned at a different angle. which enables the stomach wall to move in a flexible and relatively powerful manner. The whole of the organ is covered by the peritoneum – a double-layered membrane that lines the interior of the abdomen and covers all the abdominal organs.
Function:
Embedded in the lining of the stomach are little pits called gastric glands. These secrete mucus and a liquid called gastric juice when stimulated by the approach of food. Gastric juice contains several ingredients, including an enzyme called pepsin, which breaks down protein; hydrochloric acid, which destroys harmful bacteria and creates the acidic conditions needed for pepsin to work; and intrinsic factor, which is needed for absorption of vitamin B12 in the small intestine. In babies, an enzyme called rennin, which coagulates milk, is also present. The stomach becomes distended just enough to accommodate its contents, and the movements of its muscular wall churns the food, mixing it with the gastric juice. After several hours, food in the stomach turns into a semi liquid substance called chyme. The stomach then begins to discharge its contents: the muscular wall pushes the chyme towards the pylorus, which opens to let it flow out. A meal spends about four hours in the stomach before passing into the small intestine. None of the products of digestion is absorbed by the stomach, however, certain drugs, including alcohol, can pass rapidly through the stomach lining into the bloodstream.
INTESTINES:-The human intestines consist of a long, convoluted tube running between the stomach and the anus. Food is pushed along by contractions in its muscular wall, and is digested by secretions produced by its inner lining.
Stomach disorders:-The human digestive system consists of a long tube called the alimentary canal. A series of organs along its length breaks down food, extracts the nutrients, and then absorbs them into the body. Digestion starts in the mouth, where the teeth cut and grind food. After swallowing. the food passes down the esophagus into the stomach, and much of it is broken down into food molecules. These enter the small intestine where they are absorbed into the blood stream. Water is absorbed in the large intestine. The remaining undigested matter is stored in the colon until it is egested as feces.
MOUTH:-
The mouth is the first part of the human digestive system. Food is crushed by the action of the jaws, teeth, and tongue, and is mixed with saliva, which contains a digestive enzyme called salivary amylase. The swallowing reflex carries chewed food out of the mouth and into the esophagus, which leads to the stomach.
Structure the roof of the mouth consists of a hard, bony plate at the front, called the hard palate, and a soft fleshy structure at the back, called the soft palate. Most of the floor of the mouth is occupied by the tongue, which contains specialized sensory cells grouped in pits called taste buds. These are sensitive to four tastes: salty, sweet, acidic, and bitter (other flavors are detected by the nose). Surrounding the palate and tongue are the teeth, the roots of which are embedded in jawbone. Covering the bone under the teeth is the shock-absorbent tissue of the gums. Humans. have two sets of teeth: 20 primary teeth, or milk teeth, which appear in the first three years and start to fall out at around age six; and 32 permanent teeth. Enclosing them all are the cheeks and lips, which contain a ring of muscle that helps keep food in the mouth. The inside of the mouth is lined with mucous membrane and lubricated with saliva. Function:-chewing (mastication) and
The first stages in the digestive process salivation – take place in the mouth. The purpose of chewing is to crush and grind the food into small particles to aid subsequent digestion. Saliva is secreted into the mouth from three pairs of glands, called the parotid, submandibular, and sublingual glands. The parotid gland secretes clear saliva, while the other two glands produce saliva made thick and sticky by a glycoprotein called mucin. The saliva moistens and binds the chewed food so that it can be rolled by the tongue and soft palate into a soft mass, or bolus.
Saliva also has an important chemical action, in that the enzyme salivary amylase starts to convert starch in the food into maltose, a kind of sugar. When the food is sufficiently chewed, it is pushed backward by the tongue and the swallowing reflex propels it into the esophagus, from where it is carried into the stomach by waves of muscular contraction (peristalsis) in the wall of the esophagus.
The products of digestion are absorbed into the blood and lymphatic system through the intestinal wall, the surface area of which is greatly increased by the presence of thousands of tiny, fingerlike projections called villi. Most digestion and absorption takes place in the small intestine. The large intestine absorbs water from the undigested residue, which then passes to the rectum to be expelled as feces
:SMALL INTESTINE Structure
The small intestine is a gradually narrowing tube, about 7 m long. It starts at the stomach and, after many convolutions, ends at the caecum (the first part of the large intestine). It occupies the lower and middle part of the abdomen, and is divided into three portions: the duodenum, jejunum, and ileum.
The duodenum, which is about 25 cm long and 4 cm in diameter, is the shortest and widest part of the small intestine. It is C-shaped, curving around the head of the pancreas. The middle part of the duodenum receives secretions from the gall bladder (bile) and pancreas (pancreatic juice). The jejunum is about 3 m long and 3.5 cm in diameter, and occupies the upper and left part of the abdomen. It gradually merges into the ileum, which is about 4 meter long and 3 cm in diameter. The ileum occupies the lower and right part of the abdomen and is highly convoluted.
The wall of the small intestine consists of layers of circular and longitudinal smooth muscle with an inner lining (the mucous membrane) and an external covering (the serosa). Food is pushed along by coordinated waves of contraction (peristalsis) in the muscles. In the duodenum and jejunum, the mucous membrane is folded into closely placed pleats, which increases the surface area available for absorption. Covering the internal surface of the small intestine are masses of small, fingerlike projections called villi, which are covered with thousands of even tinier projections called microvilli. The villi and microvilli increase the surface area through which the products of digestion are absorbed. There are two kinds of secretory gland in the small intestine. Between the villi are tiny pits called crypts of Lieberkühn, which secrete digestive enzymes. The duodenum also contains Brunner’s glands under the mucous membrane, which secrete alkaline mucus to neutralize stomach acid.
The membrane lining the small intestine contains many thousands of goblet cells among the epithelial cells. These secrete mucus to lubricate the wall of the intestine and protect it from self-digestion.
Function:-The main function of the small intestine is to break down food into small molecules that can dissolve in water and cross the epithelium (surface layer of cells) of the mucous membrane to be absorbed. Several secretions make this possible: intestinal juice, which is produced by the crypts of Lieberkühn in the intestinal wall; pancreatic juice from the in stomach.