DIGESTIVE SYSTEM

Digestion

DIGESTION :

For a nutrient to be used by the cells of an organism, it must pass through the cell membranes. In general, the nutrient molecules in food are too large to pass through cell mem­branes. Thus, to be used by the cells, most food molecules must be broken down into smaller, simpler forms. The process by which food molecules are broken down is called digestion.

        Digestion may occur with in the cell – intracellular digestion, as in protozoa; or outside the cell, in especial cavity, or tube such as stomach, as in most animals- extracellular digestion, after which the soluble molecules are absorbed into the cell.  The term digestion usually refers to the chemical break­down of food substances into simpler compounds. In many organisms, pieces of food are first cut, crushed, or broken into smaller particles without being changed chemically. This treatment results in the mechanical breakdown of the food. Mechanical breakdown increases the surface area of the food particles.

Chemical digestion is carried out by digestive en­zymes, which act only on the surface of food particles. Thus, mechanical breakdown prepares the food for more rapid chemical digestion by exposing more food surface to the ac­tion of the digestive enzymes. Chemical digestion, like mechanical breakdown, takes place in stages. Large molecules are broken down into smaller molecules, and these in turn are broken down into still simpler forms. The usable, simplest products of digestion are the end products of diges­tion.

Parts of digestive system:

The digestive system is made up of two groups of organs. One group of organs form the digestive tract, a long tube that carries food through your body. As food passes through the digestive tract, it is broken down. Organs of the include: the mouth, esophagus, stomach, small intestine, and large intestine. Your digestive tract is about nine meters long!

Another group of organs are accessory organs, called digestive glands, produces digestive liquids that break down the food you eat. A small tube, or duct, leads from each digestive gland into the diges­tive tract. Food is never found within the digestive glands, only within the alimentary canal-digestive tract, itself. The digestive liquids pass through the ducts into the digestive tract. Once inside, they mix with the food and help break it down. Draw the figure shows the location of several digestive glands. These include the salivary glands, pancreas, and liver. What small organ is located underneath the liver?

Cells in the lining of the walls of the alimentary canal also secrete slimy mucus, which acts as lubricant for the food mass. It also provides a coating that protects the deli­cate cells of the digestive tube from the action of acid, diges­tive enzymes, and abrasive substances in the food.

The Process in the Digestive System

The organs of the digestive system carry out several im­portant functions that enable your body to use the nutrients in food.

First, mechanical digestion is a process that breaks down food into small pieces. Where does mechanical diges­tion begin?

Second, chemical digestion is a process that chemically changes food into simpler compounds. The change is brought about by digestive enzymes. A digestive enzyme is a special protein that breaks down complex food nutrients into simpler food nutrients. For example, digestive enzymes break down proteins into amino acids.

Third, food is pushed through the digestive tract by muscular movements called peristalsis. Peristalsis occurs when muscles along the digestive tract contract and relax in a wavelike motion. Food is pushed forward ahead of the waves. Throughout its jour­ney, the food is mixed with mucus. The mucus helps the food move along smoothly.

Fourth, after food is broken down into simple nutrients, the nutrients are absorbed into the blood. Most absorption occurs in the small intestine. The blood carries the simple nutrients to all parts of the body.

Finally, undigested waste products are eliminated from the body through the anus. As you can see in Figure the anus is located at the end of the large intestine.

 

Structure and Functions of Digestive OrgansThe Mouth and Pharynx

Food enters the body through the mouth, where both mechanical breakdown and chemical digestion occur. Chunks of food are bitten off with the teeth and ground into pieces small enough to swallow. The tongue moves and shapes the foodmass in the mouth.

As food is chewed, it is mixed with saliva, which is secreted into the mouth by three pairs of salivary glands. There are actually two types of saliva produced. One is a thin, watery secretion that wets the food. The other is a thicker, mucus secretion that acts as a lubricant and causes the food particles to stick together to form a food mass, or bolus. Saliva also contains a digestive enzyme called ptyalin, or salivary amylase. This enzyme breaks down starch, which is a polysaccharide, into maltose, which is a disaccharide.

When the food has been chewed sufficiently, it is pushed by the tongue to the back of the throat, or pharynx. This initiates the automatic swallowing reflex, which forces food into the esophagus, the tube leading to the stomach. However, air as well as food passes through the pharynx. The air must pass through the voice box, or larynx, and down the trachea to the lungs. To prevent food and liquids from entering the larynx, it is au­tomatically closed off during swallowing by a flap of tissuecalled the epiglottis. At the same time, breath­ing stops momentarily, and the passageways to the nose, ears, and mouth are blocked. When a person "swallows the wrong way" and food enters the trachea, it is brought back up into the throat by violent coughing.

The Structure Of Teeth

The permanent teeth are arranged in the same way in upper and lower jaws. The two flat front teeth are called incisors. They have sharp edges for cutting food. Next to the incisors, at the corner of your lips on either side, is a large cone-shaped tooth. This tooth is called the canine. Behind the canine tooth are the premolars. There are two on either side. Next are the molars. You have three molars on either side if you have cut your wisdom teeth; if not, you have two. Premolars and molars have flat surfaces which are good for grinding and crushing. A tooth has three general areas. The part above the gum is called the crown. A narrow part at the gum line is called the neck. The rootis the part beneath the surface. The root is held in a socket in the jawbone. A fibrous periodontal membrane anchors it firmly in the jaw socket. Different kinds of teeth have differently shaped roots. Some are long and single. Some have two, three, or four projections.

The covering of the root is called cementum. It holds the tooth firmly together. The crown has a hard white covering called enamel.

If a tooth is cut lengthwise, you can see the dentine beneath the enamel and cementum. Dentine is very hard, but somewhat softer than the enamel and cementum. It forms the bulk of the tooth. The pulp cavity is in the center of the tooth. The pulp cavity contains blood vessels and nerve fibers.

Taste Buds on the Tongue

The tongue lies along the floor of the mouth, but it begins in the throat. This muscu­lar organ has several important functions.

• It helps you chew

• Your tongue helps you swallow

• The tongue is essential to speech

• Your tongue keeps the inner surface of your teeth clean

• It acts as an organ of taste.

Notice that the surface of your tongue is covered with tiny bumps. These bumps hold taste buds, which have nerve endings at their bases. When you eat, the food in your mouth touches these bumps. This stimulates the nerve endings to send "taste" messages to your brain.

There are four typesof taste buds. Each reacts to a different group of chemicals in food to produce a taste. The four tastes are sweet, sour, bitter,and salty. But the flavor of food does not come fromtaste alone. Flavor is a mixture of taste, texture,and odor

The Esophagus

The esophagus is a tube through which food passes from the pharynx to the stomach. A small mass of it (bolus) is pushed into the throat (pharynx), where it is swallowed. The epiglottis closes over the adjacent windpipe and prevents the food from going into the wrong tube. No digestion occurs in the esophagus

The movement of food downs the digestive tube by peristalsis.

the esophagus opens into the stomach, there is a ring of muscle called a sphincter. The sphincter controls the passage of food from the esophagus into the stomach. The sphincter between the esophagus and the stomach is called the cardiac sphincter. During vomiting, a wave of peristalsis passes upward—reverse peristalsis— causing the cardiac sphincter to open, and the contents of the stomach to be "thrown up."

 The Stomach

The stomach is a thick-walled, muscular sac that can expand to hold more than 2 liters of food or liquid. Food is stored temporarily in the stomach, and mechanical breakdown and chemical digestion occur there.

human  liver

The lining of the stomach contains two types of glands. Pyloric glands secrete mucus, which covers the stomach lining and protects it from being digested. Gastric glands secrete very acidic gastric juice, which has a pH of 1.5 to 2.5. This juice contains hydrochloric acid (HCl), water, and the digestive enzyme pepsin and rennin.

 Pepsin is secreted in an inactive form called pepsinogen, which is activated after it is mixed with the hydrochloric acid. Pepsin breaks down large protein molecules into shorter chains of amino acids, proteoses and peptones, called polypeptides. Complete digestion of protein will takes place in the small intestine. Pepsin is active only in acidic medium. Hydrochloric acid is useful in killing bacteria that may have been swallowed.

Rennin curdles the protein of milk, casein, and prepares it for digestion by pepsin.

The breakdown of starch by ptyalin, which begins inthe mouth, continues for some time after the food mass reaches the stomach. The acid in the stomach inactivates this enzyme, and starch breakdown stops.

When no food is in the stomach, only small amounts of gas­tric juice are present. When food is taken in, the flow of gastric juice increases. There are three mechanisms involved in stimulating the flow of gastric juice.

1. The thought, sight, smell, or taste of food stimulates the brain to send messages to the gastric glands, causing them to secrete moderate amounts of gastric juice.

2. Food touching the lining of the stomach stimulates the secretion of moderate amounts of gastric juice.

3. When a food mass enters the stomach, it stretches the stomach walls. This stretching, as well as the presence of pro­teins, caffeine, alcohol, and certain other substances, stimu­lates the lining of the stomach to secrete a hormone called gastrindirectly into the blood. Gastrin stimulates the gastric glands to produce large amounts of gas­tric juice.

Liquids pass through the stomach in 20 minutes or less. Solids must first be reduced to a thin, soupy liquid called chyme. The chyme passes in small amounts at a time through the pyloric sphincter, the muscle that controls the passage of food from the stomach into the small intestine. The stomach empties from 2 to 6 hours after a meal. Hunger is felt when an empty stomach is churning.

If the thick mucus layer that protects the stomachwallbreaks down, a part of the stomach wall may be digested, and a painful ulcer develops. It is thought that some ulcers are caused by the over secretionof gastric juice brought on bynervousness or stress. Ulcers are treated bydiet, medication, or, in severe cases, by surgery.

The Small Intestine

     The small intestine is a coiled tube about 6.5 meters long and about 2.5 centimeters in diameter. The first 30 centimeters of the small in­testine are called the duodenum. Pancreatic juice and bile from liver and pancreas mix with the food in the duodenum. Most chemical digestion and almost all absorption occur In the small intestine. Unlike the stomach with its acid secretions, fluids inthe small intestine are generally alkaline.

 In the small intestine, chyme is mixed with bile from the liver, pancreatic juice from the pancreas, and intestinal juice from glands in the wall of the intestine. These three secretions contain the enzymes and other substances necessary to complete digestion

Intestinal juice.

The walls of the small intestine contain mil­lions of intestinal glands, which secrete intestinal juice. Intes­tinal juice contains enzymes that complete the digestion of carbohydrates, fats, and proteins.

In the small intestine, molecules of proteins, carbohydrates, and fats are broken down into the end products of digestion.

Proteins are broken down into amino acids,

Carbohydrates are broken down into simple sugars,

Fats are broken down into fatty acids and glycerol.

A sum­mary of the secretions of the human digestive system and their functions is given in Table.

Intestinal juice contains the following enzymes:

Erepsin—digests proteins into amino acids.

Maltase—digests maltose into glucose,

Lactase—digests lactose (milk sugar) into glucose and galactose.

Sucrase—digests sucrose (cane sugar) into glucose and fructose.

Lipase (Small quantities) —digest fats into fatty acids and glycerol.

Pancreas

The pancreas is a soft, triangular organ located between the stomach and the small intestine. The pancreas produces a substance called pancreatic juice, which is a mixture of several enzymes.

The pancreas also produces substances called insulin and glucagon, which are important in controlling the level of blood sugar.

 Pancreatic juice:

When the acid chyme from the stomach enters the small intestine, it stimulates cells in the intestinal lining to secrete two hormones into the blood, Secretin and Cholecystokinin. These hormones stimulate the pancreas to secrete pancreatic juice and pancreatic enzymes, which pass through the pancreatic duct into the upper part of the small intestine. Pancreatic juice contains sodium bicarbonate, which neutralizes the acid in the chyme and makes the pH of the contents of the small intestine slightly alkaline (pH 8). The enzymes secreted by the pancreas act on every major compo­nent of food—proteins, carbohydrates, fats, and nucleic acids,

 Pancreatic juice:  Contains three enzymes

Proteases (Trypsin and chemotropism): digests peptones into amino acids.

Amylase (Amylopsin): changes starch into maltose.

Lipase:  changes fats into fatty acids and glycerol.

Bile.

The cells of the liver produce bile, which passes through ducts into the gallbladder, where it is stored. Bile passes from the gallbladder to the upper part of the small intestine through the bile duct. The release of bile from the gallbladder is stimulated by the hormone Cholecystokinin. Bile contains no enzymes, but it aids in the digestion of fats and oils by breaking them up into tiny droplets. This process, called emulsification, increases the surface area for enzyme action. Since bile is alkaline, it aids in neutralizing the acid chyme from the stomach,

 Liver

The liver is the largest organ in the body. Besides form­ing bile, it also has a number of other functions.

It changes excess glucose to glycogen and stores it;

It destroys old, worn-out red blood cells;

It converts amino acids into glucose and a nitrogenous waste called urea, which is removed from the blood in the kidneys;

    Itproduces prothrombin, one of the substances needed in the clotting of blood,

It prepares fat for use by the body;

It serves as a reservoir for storing blood.

Absorption:

The small intestine is the site of absorption. Simple sugars, amino acids, vitamins, minerals, and other sub­stances are absorbed through the wall of the small intestine into the blood vessels of the circulatory system. Fatty acids and glycerol are absorbed into tiny vessels of the lymphatic system called lacteals, lymph vessels.

The small intestine has a number of structural features that increase its surface area and make it ideally suited for absorp­tion.

(1)    The small intestine is very long.

(2)    Its lining has many folds.

(3)    The lining is covered with mil­lions of fingerlike projections called villi.

(4)    The epithelial cells have tiny projections called microvillus that further increase the surface area.

  Within each villus there is a network of blood capillaries, and in the center is a lacteal. During absorption, digested nutrients pass through the epithelial cells and enter either the capillaries or the lacteal. Absorption involves both diffusion and active transport,

The Large Intestine

    Undigested and unabsorbed materials pass from the small intestine into the large intestine. The large intestine is about 1.5 meters long and 6 centimeters in diameter. No digestion occurs in this portion of the digestive system.

On the lower right side of the abdomen, where the small intestine joins the large intestine, is a small sac, the appen­dix. The appendix plays no part in the function­ing of the human digestive system. Occasionally, however, the appendix becomes infected, a condition known as appen­dicitis.

One of the principal functions of the large intestine is the reabsorption of water from the food mass. If too little water is absorbed, diarrhea results; if too much water is ab­sorbed, constipation results.

A second function of the large intestine is the absorption of vitamins produced by bacteria. Intestinal bacteria live on undigested food material. They produce vita­min K, which is essential for blood clotting, and some of the B vitamins. When large doses of antibiotics destroy the intes­tinal bacteria, a vitamin K deficiency may result.

The third function of the large intestine is the elimination of undigested and indigestible material from the digestive tract. This material consists of cellulose from plant cell walls, large quantities of bacteria, bile, and mucus, and worn-out cells from the digestive tract. As this material travels through the large intestine, it becomes feces. Fecal matter is stored in the last part of the large intestine, the rectum, and periodically eliminated, or defecated, through the anus.

Digestive system in Ruminansia

Ruminant animal ( ruminansia) have different tooth formation with human being. Molar tooth used to digest food ,and incisor used to nip and cut food in the form of grass. Kramer ( 1995:130) explaining that stomach of ruminansia , like sheep, ox and buffalo consist of rumen ( abdomen), retikulum ( stomach of fish-net), omasum(book stomach), abomasum ( acid stomach). Grass that eaten  still harsh and come into rumen and  reticulum to be digested mechanicly by thick wall movement, chemically by ferment bacterium.

Abomasum similar to human being stomach. In abomasum, food digested mechanicly by wall of abomasum and chemically digestion of by yielded enzyme. Food of abomasum come into small intestine to be digested furthermore.  At ruminansia , there are functioning cellulose enzyme digest cellulose, where do not there are at human being.

Mechanism of animal digestion of ruminansia the following:  mouth - throat - rumen - reticulum - trap - throat - omasum - abomasum - small intestine - large intestine - anus.

DIGESTIVE PROCESS

 Diparity /Desease on Digestive system

Disparity in digestive System its immeasurable.  The cause factor : among others unfavourable food, malnutrition, health and hygiene, balance of nutrition, pattern eat less precise, existence of disparity and infection  at  digestive organ.

1. Diarrhea, condition where  flow of feces from stomach to intestine is too fast so defecation becomes more often with feces much contains water. Diarrhea can be caused by stress, bad diet, and food that can cause irritation in intestine wall
2. Constipation, it happens if chime to the intestine very slowly so water is much absorbed by intestine. This caused feces becomes hard and dry. Constipation can be caused by lack in consuming fibrous food or too much consuming meat.
3. Peritonitis ( the inflammation of abdominal cavity membrane ), that is infection in abdominal cavity membrane ( peritoneum )
4. Appendixitis ; that is inflammation in appendix
5. Cholic, the appearance of pain in stomach because of wrong digesting for example  because of eating too much or the influence of alcohol  and chili
6. Ulcus, inflammation in stomach wall that is caused by the production of gastric juice (particulary HCl) is high, while the amount of food entering is a little amount
7. Parotitis, infection in parotis gland, its often called goiter disease
8. Xerostamia, that is a condition where the amount of saliva produced is very small in amount