General features of blood vessel structure

Blood is pumped from the ventricles of the heart into large elastic arteries that branch repeatedly to form many smaller arteries. As they became smaller, the arteries undergo a gradual transition from having walls that contain a large amount of elastic tissue and a smaller amount of smooth muscle to having walls with a smaller amount of elastic tissue and a relatively large amount of smooth muscle.

Blood flows from the arteries into the capillaries. Most of the exchanges that occur between the interstitial spaces and the blood occurs across the walls of the capillaries. Their walls are the thinnest of all blood vessels, blood flows though them slowly, and there is a greater number of them than any other blood vessel type.

From the capillaries blood flows into the venous system. When compared to arteries, the walls of the veins are thinner and contain less elastic tissue and fewer smooth-muscle cells. The veins increase in diameter and decrease in number, and their walls increase in thickness as they project towards the heart.

Ex. 20. Speak on the vessels, their morphological and functional characteristics.

Ex. 21. Translate the following sentences into English:

1. Артерії – судини, по яких кров тече від серця до органів. 2. Стінки артерії побудовані з трьох оболонок: внутрішньої, середньої (tunica media) та зовнішньої (external tunica). 3. Вени – судини, які несуть кров до серця. 4. Вони містять венозну кров. 5. Стінка вен тонша, ніж у відповідних артеріях та відсутня зовнішня еластична мембрана. 6. Капіляри – найтонші судини, діаметром від 4,5 до 30 мкм. 7. Стінка капіляра утворена лише одним шаром ендотелію.

Ex. 22. Pronounce and memorize the words to the theme studied:

Ascending aorta [eI'O:tq] висхідна частина аорти; descending aorta низхідна частина аорти; carotid artery сонна артерія; brachiocephalic плечо-головний; subclavian artery підключична артерія.

Ex. 23. Read the following text. Compose the dialogue on the composition of aorta:

AORTA

All arteries of the systemic circulation are derived either directly or indirectly from the aorta, which usually is divided into three general portions: the ascending aorta, the aortic arch, and the descending aorta. The descending aorta is divided further into a thoracic aorta and an abdominal aorta.

At its origin from the left ventricle the aorta is approximately 2.8 cm in diameter. Because it passes superiorly from the heart, this portion is called the ascending aorta. It is approximately 5 cm long and has only two arteries branching from it, the right and left coronary arteries, which supply blood to the cardiac muscle.

The aorta then arches posteriorly and to the left as the aortic arch. Three major branches, which carry blood to the head and upper limbs, originate from the aortic arch: the brachiocephalic artery, the left common carotid artery, and the left subclavian artery.

The next portion of the aorta is the descending aorta. It is the longest portion of the aorta and extends through the thorax on the left side of the mediastinum and trough the abdomen to the superior margin of the pelvis. The thoracic aorta is that portion of the descending aorta located in the thorax. It has several branches that supply various structures between the aortic arch and the diaphragm. The abdominal aorta is that portion of the descending aorta between the diaphragm and the point at which the aorta ends by dividing into the two common iliac arteries. The abdominal aorta has several branches that supply the abdominal wall and organs. Its terminal branches, the common iliac arteries, supply blood to the pelvis and the lower limbs.

OVERVIEW

Blood vessels form a closed system of tubes, which transports the blood and allows exchange of gases, nutrients, and wastes between the blood and the body cells. The tubes include arteries, arterioles, capillaries, venules, and veins. Except for capillaries and venules, blood vessels have three layers: the inner tunica intima (consisting of endothelium, basement membrane, and internal elastic lamina), the tunica media (containing circular smooth muscle and elastic fibers), and the outer tunica adventitia (which is connective tissue). The arteries are adapted to carry relatively high pressure of blood away from the heart. Veins carry deoxygenated blood to the heart. Many veins contain valves that allow blood to move toward the heart, but prevent from moving away from the heart. Capillaries form connections between arterioles and venules.

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