Royal Army Medical Corps training pamphlet / War Office.

Date:
1944
Catalogue details

Licence: Public Domain Mark

Credit: Royal Army Medical Corps training pamphlet / War Office. Source: Wellcome Collection.

    37/376 (page 33)
    CHAPTER 5 CIRCULATION OF THE BLOOD 4¢. The heart pumps blood to all parts of the body through a system of tubes or blood-vessels. In travelling through this system the blood eventually returns to the heart, which pumps it out again. Hence the blood is Boney in movement (circulation) round the body. The heart is a hollow muscular organ, about the size of a closed fist, situated behind the sternum between the lungs. Two-thirds of the heart lie to the left of the middle line, and one-third to its right (Fig. 26, page 50). It is conical in shape, with its base uppermost, and its point (apex) downwards and towards the left side. | It is divided into a right and left side, separated by a muscular partition so that no bload can pass directly from one to the other side. Each half is again divided into :— (a) An upper thin-walled receiving chamber, the auricle. (6) A lower thick-walled pumping chamber, the ventricle. There are thus in the heart four chambers (Fig. 17, page 35). Right auricle, left auricle. Right ventricle, left ventricle. Between each auricle and its corresponding ventricle, there is a flap or valve which allows the blood to pass in one direction only—namely, from the auricle to the ventricle. Each beat of the heart is in two parts: first the two auricles contract and force their contents into the ventricles; then, immediately afterwards, the two ventricles contract and force their contents into the arteries. A short pause follows before the next beat. 47. Blood-vesseis— Arieries are thick-walled strong elastic tubes which branch and become smaller as they get farther from the heart. Finally they divide into very small vessels with very thin walls, which are so small as to be invisible to the eye. These are the capillaries. The walls of the capillaries are so thin that the dissolved nourishment and oxygen destined for the tissues can pass through them into the lymph, while the waste-products from the tissues can pass through them imto the blood. The capillaries form a close network all over the body, and, gradually joining together and getting larger, they become veins. The veins, thin-walled tubes, beginning thus in the capil- laries, become fewer in number and larger in size until they end in the large veins which open into the heart. Veins are 2..—(2015)