What are the contents of most part of the alimentary canal?

Answer 1

Mouth. Stomach.

Pharynx. Small intestine.

Œsophagus. Large intestine.

Secretions from various glands are poured into it, by which digestion of food takes place.

The food taken in at the mouth and masticated by the teeth is at the same time mixed with saliva, which is secreted by three large glands, the parotid, submaxillary, sublingual.

The parotid lies under and in front of the ear at the angle of the lower jaw ; its duct passes through the cheek, and opens into the mouth opposite the second molar tooth. The submaxillary lies under the angle of the jaw. The sublingual lies under the tongue. The ducts of these glands open under the tongue in front of the mouth.

There are also numbers of small glands in the mucous membrane which lines the mouth, which secrete a glairy fluid called mucus, which mixes with the saliva.

Saliva is watery ; it moistens the food and facilitates swallowing. It contains a substance called ptyalin, which converts the starch in the food, which is insoluble, into sugar, which is soluble and readily absorbed.

In the act of swallowing, the bolus of food passes into the pharynx, a muscular and membranous bag which lies behind the nose, mouth, and larynx.

Beside the opening into the œsophagus, the pharynx has two connecting with the nose, two with the ears, one with the mouth, and one with the larynx ; it is about 4.5 inches long, and extends from the base of the cranium to the œsophagus. By muscular contractions the food is pushed onward and downwards through the œsophagus, its passage being facilitated by mucus, which is secreted by glands in the inner coat, which is a mucous membrane drawn up into longitudinal folds. The outer coat is thick and muscular ; between the two and uniting them is a middle coat of areolar tissue.

The food passes into the stomach through the cardiac orifice. The chief secretion of the stomach is gastric juice secreted by the gastric or peptic glands, and which is poured out during digestion.

Gastric juice is a colourless fluid containing two ferments : pepsin and rennet ferment, hydrochloric acid and salt. It converts the proteids into peptones. Peptones dissolve in water, and thus are readily absorbed by the bloodvessels in the mucous membrane. Water, salts, and sugar are also absorbed by the bloodvessels and by the mucous membrane. Gastric juice dissolves the connective tissue which binds the fat-cells together. It is an antiseptic, and neutralizes the action of the swallowed saliva. It mixes with the food, which undergoes a sort of churning process ; by contraction and relaxation of the muscle fibres in the coats of the stomach, it is squeezed and turned round till it becomes a thick soup-like fluid, which is called chyme. The average time occupied in producing this change is two to four hours. The ejection from the pylorus begins in about two hours. The pylorus is kept closed at first by a circular muscle, which slowly relaxes and allows the contents of the stomach to pass into the duodenum; It is now a mixture of digested, partly digested, and undigested food ; some of the starch has been turned into sugar, and some of the proteids into peptones, and the fat-cells have been set free. Further digestion of all these takes place in the intestines by the secretions of two glands, which are poured into the duodenum. They are the liver and pancreas.

From the blood brought by the portal vein, the liver manufactures bile and glycogen. Bile is being continually secreted, but it flows into the intestines only during digestion ; at other times it is stored in the gall-bladder. Two ducts-the right and left hepatic ducts-from the right and left lobes, convey the bile from the liver. They unite to form the hepatic duct, which is joined by the cystic duct from the gall-bladder, the union of which gives rise to the common bile duct, which opens into the duodenum.

In the intestines bile excites peristaltic action, and is a. natural purgative ; it assists in the emulsification and absorption of fats ; it neutralizes the gastric juice preparatory to the pancreatic action, and though not absolutely antiseptic, it retards putrefaction. From 30 to 40 ounces are secreted daily.

The other important function of the liver is the formation of glycogen. This substance is similar in its nature to starch, and is produced mainly, though not entirely, from the various starchy and sugary elements of the food which have been absorbed and carried to the liver by the portal vein. It is in itself insoluble, but under the influence of some ferment it is readily converted into soluble grape-sugar. It is stored in the cells of the liver, and carried away in small quantities when wanted by the blood. It supplies heat and energy to the body.

The pancreatic duct, which carries the secretion of the pancreas to the intestines, joins the common bile duct and enters by the same orifice. The pancreatic juice is the main digestive fluid ; it contains three ferments-amylopsin, trypsin, and steapsin-which act respectively on starch, proteids, and fat ; so it combines the action of all the other digestive fluids. Saliva acts only on starch, gastric juice on proteids, bile slightly on fats ; the pancreatic juice acts on all, turning starch into sugar, proteids into peptones, and emulsifies fat, so that all the food that passes unchanged into the intestines is there digested and the products absorbed, the fats by the lacteals and the remainder by the bloodvessels. The intestines secrete a fluid called succus entericus, which completes the action of the other juices. In the small intestine the chyme is turned into chyle. All that has not been absorbed in the small intestine is urged on through the caecum into the large intestine, return being prevented by the ilio-caecal valve. Absorption is continued, and the contents of the colon become more and more solid till they are ejected from the body.

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Answer 2

The contents of most parts of the alimentary canal include food, digestive enzymes, acids, and fluids. The specific contents may vary depending on the location within the alimentary canal. For example, in the stomach, the contents include partially digested food, stomach acid, and digestive enzymes, while in the small intestine, the contents consist of further digested food, digestive enzymes, bile, and other digestive fluids.