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.

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    heart beat and therefore provides a simple means of counting the rate of the heart. The heart beat can be counted in any artery near the surface ; but the radial artery just above the wrist is usually chosen, because it is readily accessible and the artery is just under the skin. In the veins there is no beat or pulse, the force of the blood current having been spent in passing through the wide network of capillaries lying between the ends of the arteries and the commencement of the veins. The blood flows through the veins in a steady even stream. — 50. Structure of blood-vesseis.—Both arteries and veins have muscle fibres in their walls, but these are more numerous in the arteries. The fibres, by relaxing and contracting, regulate the calibre or bore of the vessels, and admit more or less blood to the parts they supply. These muscles are under the control of the autonomic system of nerves. Flushing and pallor are the result of increasing and reducing respectively the calibre of the small blood-vessels of the skin ; they may be caused by emotion, heat, cold, or pressure. 51. Blood-supply of vital organs.—It is important that the supply of blood to all parts of the body should be uninter- rupted, and that the vital organs should receive all they need. ' These organs are placed in the chest and abdomen near the heart, which is the source 6f supply. The brain, which is a little farther off, is fed by four large arteries :— The carotid arteries, one on each side of the neck. The vertebral arteries—branches of the subclavian arteries, which themselves come from the arch of the aorta. 52. Arrangement of arteries and veins.—The aorta is the main artery of the body. Where it leaves the left ventricle of the heart it is about an inch in diameter. It forms an arch just above the heart, from which spring the great vessels to the head and upper limbs—namely, the innominate artery, on the right side, and the common carotid and subclavian arteries on the left. It then runs downwards along the left side of the spinal column and passes, through the diaphragm, out of the thorax into the abdomen, where it divides into the right and left common iliac arteries (Fig. 18). Each again divides into the internal iliac, which supplies the organs of the pelvis, and the external iliac, which is continued down into the lower limb as the femoral artery. The subclavian artery springs on the right side from the innominate artery and on the left side from the arch of the