Circulatory System Arteries & Veins Lecture PDF

CIRCULATORY SYSTEM ARTERIES & VEINS ‫ – تشريح عملي – تقنيات التخدير‬9 ‫محاضرة‬ BLOOD VESSELS are flexible tubes that carry blood, associated oxygen, nutrients, water, and hormones throughout the body. Blood vessels consist of 5 main types Arteries – carry blood away from the heart Arterioles....

CIRCULATORY SYSTEM ARTERIES & VEINS ‫ – تشريح عملي – تقنيات التخدير‬9 ‫محاضرة‬ BLOOD VESSELS are flexible tubes that carry blood, associated oxygen, nutrients, water, and hormones throughout the body. Blood vessels consist of 5 main types Arteries – carry blood away from the heart Arterioles. Capillaries – site of exchange. Venules. Veins – carry blood to the heart. BASIC STRUCTURE OF BLOOD VESSELS The blood vessels have three layers. 1-Tunica interna (intima) Inner lining in direct contact with blood Endothelium continuous with endocardial lining of heart Active role in vessel-related activities 2-Tunica media Muscular and connective tissue layer Greatest variation among vessel types Smooth muscle regulates diameter of lumen 3-Tunica externa Elastic and collagen fibers Vasa vasorum Helps anchor vessel to surrounding tissue ARTERIES 1.Tunica Interna a. Endothelium b. Basement membrane c. Internal elastic lamina 2.Tunica Media a. Smooth muscle b. External elastic lamina 3. Tunica Externa a. Connective tissue TYPE OF ARTERIES A. Elastic Arteries Largest arteries. Largest diameter but walls relatively thin. Function as pressure reservoir. Help propel blood forward while ventricles relaxing. Also known as conducting arteries – conduct blood to medium-sized arteries. B. Muscular arteries Tunica media contains more smooth muscle and fewer elastic fibers than elastic arteries. Walls relatively thick. Capable of great vasoconstriction/ vasodilatation to adjust rate of blood flow. Also called distributing arteries. CAPILLARIES ❑Smallest blood vessels connect arterial outflow and venous return. ❑Microcirculation – flow from metarteriole through capillaries and into postcapillary venule. ❑Exchange vessels – primary function is exchange between blood and interstitial fluid. ❑Lack tunica media and tunica externa. ❑Substances pass through just one layer of endothelial cells and basement membrane. TYPES OF CAPILLARIES Three types of capillaries 1. Continuous capillaries ❖Endothelial cell membranes from continuous tube have tight junctions with intercellular clefts (allow passage of solutes) ❖occur in most tissues, ex. Skeletal muscle 2. Fenestrated capillaries ❖Have fenestrations or pores ❖Locations-- organs that require rapid absorption or filtration - kidneys, small intestine. 3. Sinusoids capillaries ❖Endothelial cells separated by wide gaps; no basal lamina, Molecules can pass– proteins and blood cells ❖Locations-- liver, bone marrow, spleen, lymphatic organs  VEINS o The blood moves back to the heart through veins. o The blood travels from the capillaries into the venules, which are the smallest veins. As the blood moves closer to the heart, the veins get larger and larger. Like the arteries, veins have walls made up of layers called the tunica intima, tunica media, and tunica externa. 1. Tunica Interna a. Endothelium b. Basement membrane 2. Tunica Media a. Smooth Muscle 3. Tunica Externa a. Connective Tissue  VEINS Medium and large veins have venous valves, similar to the semilunar valves associated with the heart, that help keep the blood flowing toward the heart. Venous valves are especially important in the arms and legs, where they prevent the backflow of blood in response to the pull of gravity. There are some important differences between the arteries and veins: o In veins, the walls have less smooth muscle and connective tissue. o The walls of veins are thinner than artery walls. o Veins have less pressure and can hold more blood than arteries. BLOOD PATHWAY THROUGH THE VESSELS ▪ As the heart contracts, it forces blood into the large arteries leaving the ventricles. ▪ The blood then move to smaller arteries, finally reaching their smallest branches, the arterioles (little arteries), which feed into the capillary beds (collection of capillaries) of body organs and tissues. ▪ Blood drains from the capillaries into venules (little veins), and then on into larger and larger veins that merge to form the large veins that ultimately empty into the heart.