Human Digestive System :
The human digestive system constitutes the alimentary canal and the digestive glands.
Alimentary canal :
The alimentary canal extends from the mouth to the anus. It has the following parts.
Mouth :
Mouth is a specialized organ for receiving food and breaking up large organic masses. In the mouth, food is changed mechanically by biting and chewing. Humans have four kinds of teeth: incisors are chisel-shaped teeth in the front of the mouth for biting; canines are pointed teeth for tearing; and premolars and molars are flattened, ridged teeth for grinding, pounding, and crushing food.
In mouth, food is moistened by saliva, a sticky fluid that binds food particles together into a soft mass. Three pairs of salivary glands—parotid, submaxillary, and sublingual—secrete saliva into the mouth. During chewing, the tongue moves food about and manipulates it into a mass called a bolus. The bolus is pushed back into the pharynx (throat) and is forced through the opening to the esophagus
Mouth is a specialized organ for receiving food and breaking up large organic masses. In the mouth, food is changed mechanically by biting and chewing. Humans have four kinds of teeth: incisors are chisel-shaped teeth in the front of the mouth for biting; canines are pointed teeth for tearing; and premolars and molars are flattened, ridged teeth for grinding, pounding, and crushing food.
In mouth, food is moistened by saliva, a sticky fluid that binds food particles together into a soft mass. Three pairs of salivary glands—parotid, submaxillary, and sublingual—secrete saliva into the mouth. During chewing, the tongue moves food about and manipulates it into a mass called a bolus. The bolus is pushed back into the pharynx (throat) and is forced through the opening to the esophagus
Pharynx :
The oral cavity opens into the pharynx. The swallowing mechanism guides the masticated food through the pharynx.
Esophagus :
Esophagus is a muscular, tubular part of the alimentary canal. The muscular walls of the oesophagus move in a rhythmic wavelike manner, which carries the food down to the stomach. This muscular movement is Known as peristalsis. Here also salivary amylase acts on starch and glycogen in the chewed food.
The oral cavity opens into the pharynx. The swallowing mechanism guides the masticated food through the pharynx.
Esophagus :
Esophagus is a muscular, tubular part of the alimentary canal. The muscular walls of the oesophagus move in a rhythmic wavelike manner, which carries the food down to the stomach. This muscular movement is Known as peristalsis. Here also salivary amylase acts on starch and glycogen in the chewed food.
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.The stomach stores food and prepares it for further digestion. In addition, the stomach plays a role in protein digestion. Gastric glands called chief cells secrete pepsinogen. Pepsinogen is converted to the enzyme pepsin in the presence of hydrochloric acid. Hydrochloric acid is secreted by parietal cells in the stomach lining. Pepsin then digests large proteins into smaller proteins called peptides. To protect the stomach lining from the acid, a third type of cell secretes mucus that lines the stomach cavity.
Small intestine :
From the stomach, food enters the duodenum, the first part of the small intestine. It then enters the jejunum and then the ileum (the final part of 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.
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 is also at work in this organ, moving food through and mixing it up with digestive secretions. The duodenum is largely responsible for continuing the process of breaking down food, with the jejunum and ileum being mainly responsible for the absorption of nutrients into the bloodstream.
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.The stomach stores food and prepares it for further digestion. In addition, the stomach plays a role in protein digestion. Gastric glands called chief cells secrete pepsinogen. Pepsinogen is converted to the enzyme pepsin in the presence of hydrochloric acid. Hydrochloric acid is secreted by parietal cells in the stomach lining. Pepsin then digests large proteins into smaller proteins called peptides. To protect the stomach lining from the acid, a third type of cell secretes mucus that lines the stomach cavity.
Small intestine :
From the stomach, food enters the duodenum, the first part of the small intestine. It then enters the jejunum and then the ileum (the final part of 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.
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 is also at work in this organ, moving food through and mixing it up with digestive secretions. The duodenum is largely responsible for continuing the process of breaking down food, with the jejunum and ileum being mainly responsible for the absorption of nutrients into the bloodstream.
Liver :
Liver has an important function in processing of human digestion. It secretes bile, which helps indigestion. Bile juice produced by the liver is stored in the gall bladder. The liver also functions in amino acid metabolism. In a process called deamination, it converts some amino acids to compounds that can be used in energy metabolism. In doing so, the liver removes the amino groups from amino acids and uses the amino groups to produce urea. Urea is removed from the body in the urine.
Liver has an important function in processing of human digestion. It secretes bile, which helps indigestion. Bile juice produced by the liver is stored in the gall bladder. The liver also functions in amino acid metabolism. In a process called deamination, it converts some amino acids to compounds that can be used in energy metabolism. In doing so, the liver removes the amino groups from amino acids and uses the amino groups to produce urea. Urea is removed from the body in the urine.
Pancreas:
Pancreas secretes pancreatic juice, which is carried by the pancreatic duct into the duodenum. Pancreatic juice contains a number of digestive enzymes such as amylase for the splitting of polysaccharides, lipase for the breakdown of fats, and trypsin and chymotrypsin for the breakdown of proteins.
Large intestine :
From the small intestine, food passes into the large intestine. The large intestine is divided into ascending, transverse, and descending portions, each about one foot in length. The colon’s chief functions are to absorb water and to store, process, and eliminate the residue following digestion and absorption.
The intestinal matter remaining after water has been reclaimed is known as feces. Feces consist of non-digested food (such as cellulose), billions of mostly harmless bacteria, bile pigments, and other materials. Feces are stored in the rectum and passed out through the anus to complete the process of digestion.
Pancreas secretes pancreatic juice, which is carried by the pancreatic duct into the duodenum. Pancreatic juice contains a number of digestive enzymes such as amylase for the splitting of polysaccharides, lipase for the breakdown of fats, and trypsin and chymotrypsin for the breakdown of proteins.
Large intestine :
From the small intestine, food passes into the large intestine. The large intestine is divided into ascending, transverse, and descending portions, each about one foot in length. The colon’s chief functions are to absorb water and to store, process, and eliminate the residue following digestion and absorption.
The intestinal matter remaining after water has been reclaimed is known as feces. Feces consist of non-digested food (such as cellulose), billions of mostly harmless bacteria, bile pigments, and other materials. Feces are stored in the rectum and passed out through the anus to complete the process of digestion.