Organs of the Digestive System

Our body is composed of eleven organ system.Each system has its own function to carry out for an organism. The digestive sysytem is the one responsible for providing the body energy and nutrients.

When you take in the food, it passes through a tube like structure known as the alimentary canal. It is the pathway of food beginning from the mouth and leaving through the anus. The food in the alimentary canal is squeezed by a wavelike muscle movement known as the peristalsis.

1. Mouth Food enters the mouth and goes through the alimentary canal. The mouth is consisting of teeth, tongue and the salivary gland. Digestion of food starts here. The teeth are used for chewing the food into smaller pieces and the tongue helps you know the taste and the

salivary glands lubricate the mouth and food so that it can be easily swallowed.

2. PharynxThe chamber that connects the nasal and oral cavities of the body. During digestion, it transports the food in the mouth to the esophagus. Swallowing occurs in the pharynx. When you swallow, a small tissue closes the windpipe known as the epiglottis. This prevents the food to enter in your lungs.

3. EsophagusThe esophagus is a muscular tube extending from the pharynx to the   stomach . By means of a series of contractions, called peristalsis, the esophagus delivers food to the stomach. Just before the connection to

the stomach there is a "zone of high pressure," called the lower esophageal sphincter; this is a "valve" meant to keep food from passing backwards into the esophagus.

4. StomachThe stomach is a sac-like organ with strong muscular walls. The stomach stores swallowed food and liquid, mixes the food and liquid with digestive juice it produces, and slowly empties its contents, called chyme, into the small intestine. The muscle of the upper part of the stomach relaxes to accept large volumes of swallowed material from the esophagus. The muscle of the lower part of the stomach mixes the food and liquid with digestive juice.

5. Small Intestine

Made up of three segments, the duodenum, jejunum, and ileum, the small intestine is a long tube loosely coiled in the abdomen (spread out, it

would be more than 20 feet long). The small intestine continues the process of breaking down food by using enzymes released by the pancreas and bile from the liver. Bile is a compound that aids in the digestion of fat and eliminates waste products from the blood. Peristalsis (contractions) is also at work in this organ, moving food through and mixing it up with digestive secretions.

The small intestine is made up of three parts:

1. the duodenum  the C-shaped first part2. the jejunum the coiled midsection3. the ileum the final section that leads into the large intestine

The inner wall of the small intestine is covered with millions of microscopic, finger-like projections called villi. The villi are the vehicles through which nutrients can be absorbed into the body.

6. PancreasThe pancreas is located adjacent to the duodenum. The pancreas produces a pancreatic juice containing several enzymes that break down carbohydrates, fats, and proteins in food. The pancreas delivers digestive juice to the small intestine through small tubes called ducts. It also releases insulin into the blood

that controls the sugar in your body.

7. LiverThe liver is the largest organ in the digestive system located at the

right side of the stomach. It produces bile that is used for breaking up fats into smaller ones. The bile is stored in the gallbladder. The gallbladder releases the bile when the food moves into the small intestines.

The liver also plays a major role in the handling and processing of nutrients. These nutrients are carried to the liver in the blood from the small intestine

8. Large IntestinesFrom the small intestine, food that has not been digested (and some

water) travels to the large intestine through a valve that prevents food from returning to the small intestine. By the time food reaches the large intestine, the work of absorbing nutrients is nearly finished. The large intestine's main function is to remove water from the undigested matter and form solid waste that can be excreted.

The large intestine is made up of three parts:

1. The cecum is a pouch at the beginning of the large intestine that joins the small intestine to the large intestine. This transition area allows food to travel from the small intestine to the large intestine. The appendix, a small, hollow, finger-like pouch, hangs off the cecum. Doctors believe the appendix is left over from a previous time in human evolution. It no longer appears to be useful to the digestive process.

2. The colon extends from the cecum up the right side of the abdomen, across the upper abdomen, and then down the left side of the abdomen, finally connecting to the rectum. The colon has three parts: the ascending colon and transverse colon, which absorb water and salts, and the descending colon, which holds the resulting waste. Bacteria in the colon help to digest the remaining food products.

3. The rectum is where feces are stored until they leave the digestive system through the anus as a bowel movement.

How does digestion work?

Digestion works by moving food through the GI tract. Digestion begins in the mouth with chewing and ends in the small intestine. As food passes through the GI tract, it mixes with digestive juices, causing large molecules

of food to break down into smaller molecules. The body then absorbs these smaller molecules through the walls of the small intestine into the bloodstream, which delivers them to the rest of the body. Waste products of digestion pass through the large intestine and out of the body as a solid matter called stool.

Table 1 shows the parts of the digestive process performed by each digestive organ, including movement of food, type of digestive juice used, and food particles broken down by that organ.

Table 1. The digestive process

Organ MovementDigestive Juices Used

Food ParticlesBroken Down

Mouth Chewing Saliva Starches

Esophagus Swallowing None None

Stomach

Upper muscle in stomach relaxes to let food enter and lower muscle mixes food with digestive juice

Stomach acid

Protein

Small intestine

Peristalsis

Small intestinedigestive juice

Starches, protein, andcarbohydrates

Pancreas NonePancreatic juice

Starches, fats, andprotein

Liver None Bile acids Fats

Path of the Food in the Digestive Sytem

Two important processes that happens when food passes through the alimentary canal:digestion of food and absorption of digested food into the bloodstream.

Digestion-is a process of breaking down food into smaller components so that our body can absorb them. Chemical and physical process happens.

Physical or mechanical digestion is the physical braking down of food. Biting and chewing food, undergoes physical change. Muscular churning in the stomach and peristalsis are also forms of mechanical digestion. Mechanical digestion speeds up the chemical digestion by increasing the food area of the food exposed to enzymes.

Some foods are soluble in water but most of it are insoluble.

Chemical digestion is a chemical breaking down of food. It involves the use of enzymes. Enzymes are protein molecules that speed up the mecahnical digestion. When enzymes chemically react with food, they break into simpler substances so that our body cells can use them.

Digestion of food in the Mouth, Pharynx and Esophagus

Digestion begins as we chew food. This mechanical digestion is important in prepariing for further digestion. Teeth and tongue help in chewing food.

An adult human has a permanent 32 teeth which are divided into four types:incisors, canines, biscuspids and molars. The third molar is known as the wisdom tooth.

Chemical digestion also occur in your mouth. There are three pairs of salivary glands that are secreting saliva into the mouth. Saliva contains

enzymes called ptyalin that digest starch and change it to sugar.Salivary amylase (ptyalin) is found in saliva and breaks starch into maltose and dextrin.. Salivary amylase is inactivated in the stomach by gastric acid.Mechanical digestion is a process that begins the moment the food particles reach the mouth. The process of taking the food from mouth to the body is called ingestion. The teeth initiates the mechanical

digestion by grinding the food and this process is also called as masticating.

When initiating the chemical digestion process, the saliva secreted helps in softening the food into semi-solid lump. Salivary amylase enzyme helps in digesting the carbohydrates and mucus. This way the food particles are made finer for swallowing and chemical breakdown in the digestive track. The food thus made into semi solid lump is then pushed through the throat and esophagus, a hollow tube that connects throat and stomach.when food enters the esophagus, peristalsis occurs.

**esophagus is also known as gullet which means the entrance for eating. Food travel to esophagus in ten seconds.

The processed food is moved into rectum by small intestine. Then the food gets fermented inside large intestine by the gut bacteria. This aids in digesting the unfinished projects of small intestine.

There are four important hormones that help in regulating the digestion process.

Gastrin “gastric glands stimulates pepsinogen and hydrochloric acid on arrival of food inside stomach.

Secretin “this signals secretion of sodium bicarbonate in pancreas. Secretin helps in controlling the acidity of the chime.

Cholecystokinin ‘“ this helps in secretion of digestive enzymes in pancreas. This also aids in emptying the bile in gallbladder. Cholecystokinin is produced when the digestion process needs to handle fats from chime.

Gastric inhibitory peptide ‘“ this helps in decreasing the churning process. This also helps in producing insulin secretion.

Even though the mechanical and chemical digestion processes are very important for the human digestive process, chemical digestion is considered more important. This is due to the complex procedure involved in Chemical digestion.

Digestion in the stomachAs the food enters the stomach, gastric juices are secreted. The peristaltic movement known as churning will help mix the food carefully with gastric juices. Gastric juices are composed of hydrochloric acid and pepsin.

Hydrochloric acid is not an enzyme. It cause the stomach to have a high acidity which kills bacteria present in food. It also helps in functioning of pepsin. Pepsin is an enzyme used to digest proteins and converting it to simpler proteins which will need further digestion by other enzymes so that the cell can absorb it.

**stomach has three layers of muscle for mechanical digestion. It is smooth, cardiac and skeletal muscle.

Food stays in the stomach for about 4 hours wherein it is mixed, churned and becomes fluid. The stomach has a regulatory muscle known as the sphincter to prevent the food from escaping. It is a soft smooth muscle that serves as the valve at the opening of the esophagus to the stomach and then to the small intestines.

The sphincter between the esophagus and the stomach prevents the backflow of the acidic content of the stomach up to the esophagus. The sphincter between the stomach and the small intestines allows food to pass thoroughly into the small intestines.

Digestion in the small intestines

When food reaches the small intestines, insoluble materials are changed. Starch is turned into sugar by the saliva, protein is broken down to simpler substance. Sugar, proteins, carbohydrates and fats are digested in the small intestines by intestinal juices, gastric juices, bile and pancreatic juices so that the cell can utilize it.

The bile is produced in the liver and between meals it is stored in the gallblader. The gallbladder releases the bile in

the duct located near the sphincter breaking fats and oils into smaller particles.

Pancreatic juice is a mixture of three kind of enzymes that can break down fats, starch and protein.

Pancreatic juices are realesed when there is food in the small intestines.

Intestinal juices also have three enzymes which can also break fats, starch and proteins undigested by the bile and pancreatic juices.

The digestion of food ends when all proteins become amino acids, all carbohydrates became glucose and fats becomes fatty acids.

Absorption of food in the small intestines

When food is digested, it will be absorbed in the bloodstream. Some food nutrients are absorbed in the stomach but since some food is not yet digested, the absorption of nutrients takes place in the small intestines.

The walls of the small intestines have many fingerlike structure known as villi. The villi are like bumps that made the surface area of your small intestines larger. Without the villi the nutrients will go

smoothly out of the intestines. Also villi have many blood streams that can supply blood. Nutrients as absorbed will diffuse to the blood and will be carried throughout the body.

As the blood leaves the small intestines, it carries glucose and amino acids in the body cell. The glucose serves as the fuel of the body and amino acids are used to repair damaged cells in the stomach.

Absorption of food in the Large intestines

The food that is not digested will move to the large intestines like the cellulose found in the fruits and vegetables. The large intestine will absorb the water from the remaining undigested food and will be reused by the body. It also changes the undigested food into semi-solid wastes which will leave the body through the anus.

***Cellulose is an organic compound with the formula (C6H10O5)n, apolysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell wall of green plants, many forms ofalgae and the oomycetes. Some species of bacteria secrete it to form biofilms.Cellulose is the most abundant organic polymer on Earth. The cellulose content of cotton fiber is 90%, that of wood is 40–50% and that of dried hemp is approximately 45%.

Cellulose is mainly used to produce paperboard and paper. Smaller quantities are converted into a wide variety of derivative products such as cellophane and rayon. Conversion of cellulose from energy crops into biofuels such as cellulosic ethanol is under investigation as an alternative fuel source. Cellulose for industrial use is mainly obtained from wood pulp and cotton.

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