Submitted by:Shaswati Singh

WHAT IS DIGESTION?

The chemical breakdown of complex biological molecules into their component parts is termed as digestion. The main functions of digestion is to:• Produce various chemicals to break down the food.• Filtering out harmful substances.• Getting rid of solid wastes.

THE DIGESTIVE TRACKThe Digestive track is a long muscular tube which have many sections and areas. It begins with the Mouth and ends with Anus. The digestive track consists of:• Mouth• Pharynx• Esophagus• Stomach• Small intestine• Large intestine

• Tongue

What happens in mouth?As soon as the food particles enters our mouth, the digestion process begins. As discussed earlier our buccal cavity consists of teeth, tongue and saliva. Teeth: it helps in the mastification of food i.e. chewing and grinding of food is done with the help of teeth. The teeth helps in breaking down food into smaller particles so that digestion can take place easily. Saliva: saliva is a watery liquid secreted into the mouth by salivary glands situated below our tongue. The saliva consists of some special enzymes which helps in the process of digestion. The enzyme named salivary amylase helps in breaking down starch into simple sugars. It also contains mucus which helps in softening of food. Tongue: It is able to guide and maintain food between the upper and lower teeth until mastication is complete.

After being chewed and swallowed, the food enters the esophagus. The esophagus is a long tube that runs from the mouth to the stomach. It uses rhythmic, wave-like muscle

movements (called peristalsis) to force food from the throat into the stomach. This muscle movement gives us the ability

to eat or drink even when we're upside-down.

What really happens in stomach?The stomach is a muscular, hollow, dilated part of the digestive system which functions as an important organ of the digestive tract. From the mouth, the food is taken to the stomach through the food-pipe or esophagus. The stomach is a large organ which expands when food enters it. The muscular walls of the stomach help in mixing the food thoroughly with the help of some digestive juices. These digestion functions are taken care of by the gastric glands present in the wall of the stomach. These release :• HYDROCHLORIC ACID ( H C L )• PEPSIN• MUCUS

FUNCTIONS OF GASTRIC JUICES

Pepsin: It is a digestive enzyme which helps in the digestion of protein. It needs an acidic medium for functioning.

Hydrochloric acid ( HCL ): It provides an acidic medium for enzyme pepsin for conversion of proteins into peptides. It even kills the harmful bacteria that comes along with the food.

Mucus: It lubricates the food and protects the gastric lining from strong digestive juices.

SMALL INTESTINEAfter the stomach the food reaches the small intestine. The small intestine is a coiled tube beneath the stomach. It is about 20 feet long but is known as small intestine because it’s diameter is smaller than the large intestine. The small intestine has three regions namely:• Duodenum • Jejunum • Ileum Together with the esophagus, large intestine, and the stomach, it forms the gastrointestinal tract. In living humans, the small intestine alone measures about 6 to 7 meters long.

ABSORBTION IN SMALL INTESTINEThe internal walls of the small intestine are covered in finger-like tissue called villi. Each of these villi is covered in even smaller finger-like structures called microvilli. These villi and microvilli increase the surface area available for the absorption of nutrients. Each villus transports nutrients to a network of capillaries and fine lymphatic vessels called lacteals close to its surface. In the small intestine food that has already been broken down by chewing and stomach enzymes is further degraded by additional enzymes. Some of these chemicals are secreted in the lumen (the hollow area in the middle of the intestine), but others are transported to the intestine from other organs such as the pancreas and liver.

LARGE INTESTINE The large intestine is the last part of the digestive system—the final stage of the alimentary canal—in vertebrate animals. Its function is to absorb water from the remaining indigestible food matter, and then to pass this useless waste material from the body.

The large intestine consists of the cecum and colon. It starts in in the right iliac region of the pelvis, just at or below below the right waist, where it is joined to the bottom bottom end of the small intestine. From here it continues continues up the abdomen, then across the of the abdominal cavity, and then it turns down, continuing to its endpoint at the anus. The large intestine is about 1.5 meters (4.9 ft) long, which is about one-fifth of the whole length of the intestinal canal. Waste from large intestine is pushed into the expanded portion (rectum).

Accessory organs• These are those organs which are not in the

digestive track but helps in digestion. • Example of such organs are: Salivary gland Liver Pancreas Gall Bladder Though these organs are not present in the digestive track,

they actually play a major role in the process of digestion. They produce or store enzymes that helps in digestion.

FUNCTION OF LIVER Liver is the largest gland of the human body. It is located in the upper hand right portion of abdominal cavity. The liver, a dark reddish brown organ has multiple functions.

FUNCTIONS:• It secretes bile (a watery greeny substance ) which is stored in

the gall bladder. Bile breaks down large globules of fats into smaller globules through emulsification.

• Production of certain protein for blood plasma• Store and release glucose as needed• Conversion of harmful ammonia to urea• Regulating blood clotting• Detoxification

FUNCTION OF PANCREAS Pancreas is a gland organ that is located below the abdomen. It produces important enzymes and hormones that help break down food. The pancreas has endocrine function because it

release juices directly into the blood stream. It is also an exocrine gland because it secretes pancreatic juice in the duodenum. The pancreatic juice contains lipase, trypsin and pancreatic amylase for digestion of lipids, proteins and starch.

When food leaves the stomach, it is acidic in nature. Thus in nature. Thus in order to make the food

alkaline pancreatic juices act on it.

FUNCTION OF GALL BLADDER AND SALIVARY GLAND

• SALIVARY GLAND The salivary glands are located near the mouth. They produce and secrete saliva, a substance that helps in moistening the food. The salivary gland produces salivary amylase which helps in breaking down of sugar into starch.• GALL BLADDER The gallbladder is a pear-shaped sac that is attached to the visceral surface of the liver by the cystic duct. The principal function of the gallbladder is to serve as a storage reservoir for bile. Bile is a yellowish-green fluid produced by liver cells.

CONCLUSION

DIGESTIVE SYSTEM OVERVIEW The human digestive system is a complex series of organs and glands that processes food. In order to use the food we eat, our body has to break the food down into smaller molecules. The digestive process begins in the mouth. Food is partially broken down by the process of chewing and by the chemical action of salivary enzymes. After being chewed, crunched and swallowed, the food enters the esophagus. The esophagus is a long tube that runs from the mouth to the stomach. It uses rhythmic, wave-like muscle movements (called peristalsis) to force food from the throat into the stomach. The stomach is a large, sack-like organ that churns the food and bathes it in a very strong acid (gastric acid). Food in the stomach that is partly digested and mixed with stomach acids is called chyme. After being in the stomach, food enters the small intestine. In the small intestine, bile (produced in the liver and stored in the gall bladder), pancreatic enzymes, and other digestive enzymes produced by the inner wall of the small intestine help in the breakdown of food. After passing through the small intestine, food passes into the large intestine. In the large intestine, some of the water and electrolytes (chemicals like sodium) are removed from the food. Solid waste is then stored in the rectum until it is excreted via the anus. This finally ends the process of digestion.