Elementary Human Physiology - Tapa blanda

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1896 edition. Excerpt: ...have been formed, free acid persists, and immediately destroys ptyalin, arresting any further conversion of starch into maltose. Questions. 134. Enumerate the teeth in the jaw of an adult man. Make a drawing of a tooth, showing the position of the tissues of which it is composed. 135. Describe the position of the glands that secrete saliva. What is the chemical composition of mixed saliva? What are the uses of saliva? 136. Deglutition.--Deglutition is the act by which the food is transferred from the mouth to the stomach. The mouth leads into a cavity called the pharynx (see figs. 31 and 34). Between it and the mouth is the soft palate, which is a movable muscular partition that separates the two cavities during mastication. As soon, however, as the latter act is accomplished, and the bolus is pressed backwards by the tongue, the soft palate is drawn upwards and backwards, so as to prevent the food passing into the nose. The vocal cords (see Voice) are brought close together, and the opening of the windpipe is closed by a lid called the epiglottis. The bolus or pellet of food having arrived near the oesophagus or gullet (which is continuous inferiorly and posteriorly with the pharynx), is driven into it by the action of certain muscles, which almost surround the pharynx, and are termed its constrictor muscles. All voluntary action ceases as soon as the food is pressed backwards by the tongue into the pharynx. It is impossible to recall the pellet, and it is carried on (even without our cognisance) into the stomach. This involuntary mechanism is called a reflex action. All reflex mechanisms require a stimulus to call the parts into action. The stimulus in this case is the contact of the food with the back of the tongue and throat. The...