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University of Waterloo
BIOL 301
Vivian Dayeh

CHAPTER 20 – BLOOD VESSELS STRUCTURE OF BLOOD VESSEL WALLS − Blood vessels are the network of tubes that is used to carry blood throughout the body − There are 3 types of: o Arteries  Carries blood away from the heart  Branch/diverge into smaller arteries and then arterioles o Veins  Carries blood to the heart  Merge/converge from small venules into larger veins o Capillaries  Smallest blood vessels at tissue level − Wall structure made of: o Lumen  central blood-filled space o Wall  made of 3 layers:  Tunica intima (interna)  contains endothelium facing lumen (simple squamous epithelium)  Tunica media  circularly arranged smooth muscle and collagen and elastin fibrils • Thicker in arteries than in veins  Tunica externa  layer of CT (collagen and elastic fibers) that run longitudinally. TYPES OF BLOOD VESSELS Arteries − Carry blood away from the heart − Elastic (conducting) arteries  largest arteries near heart (exiting arteries that can withstand pressure) o Aorta and its branches − Muscular (distributing) arteries  distal to elastic arteries to supply organ groups, organs or their parts − Arterioles  smallest arteries Capillaries − Body tissues are supplied by capillary beds  a network of the smallest vessels − Smallest arterioles transition into the capillary beds via a materiole − Capillaries contain the tunica intima only  RBCs must travel single-file − 3 types of capillaries: o Continuous  most common  Endothelial cells form a complete ring except at intercellular clefts  Pericytes help support the delicate capillary o Fenestrated  kidney, small intestine  Minute filtration pores in the plasma membrane to enhance exchange o Sinusoidal  liver, bone marrow and spleen (blood cells targeted for destruction)  Wider and larger clefts and incomplete basement membrane Veins − Carry blood towards the heart − Walls are thinner than arteries  veins do not have to withstand the same pressure − Smallest veins  venules o Smallest venules are the postcapillary venules − Small veins contains valves  one-way flow of blood VASCULAR ANASTOMEOSES − A vascular anastomoses occurs where vessels interconnect − Occurs in both arteries and veins  occur more frequently in veins VASA VASORUM − Blood vessel walls need a blood supply of their own − E.g., larger arteries/veins have small arteries, veins and capillaries in the tunica externa − small blood vessels do not need such a structure PULMONARY CIRCULARTION Pulmonary circulation vessels − Pulmonary circulation moves oxygen poor blood from RV to lungs via pulmonary trunk − Path: o Pulmonary trunk branches into left and right pulmonary arteries. o Pulmonary arteries each divide into several lobar arteries  2 in left lung, 3 in right lung o Branch to form arterioles and finally capillaries around the gas exchange sacs (alveoli) o Now oxygen rich blood enters venules and larger veins o Large pulmonary veins exit lungs and enter the left atrium SYSTEMIC CIRCULATION Systemic circulation vessels − Oxygen rich blood is carried from the heart to the organs of the body via systemic arteries − Walls need to withstand pulsatile pressure  elastin Systemic arteries − The aorta o Largest artery in the body o Ascending aorta  arises from LV and branches into coronary arteries o Aortic arch  lies posterior to manubrium and supplies head and neck, upper limbs and superior part of thoracic wall  Brachiocephalic trunk  divides into right common carotid and right subclavian  Left common carotid  Left subclavian arteries o Descending aorta  continues from the aortic arch  Thoracic aorta  in the region of T5 – T12  Abdominal aorta  ends at L4  *diaphragm is between thoracic and abdominal  Divides into right and left common iliac arteries − Arteries of the head and neck o 4 pairs of arteries supply the head and neck  Common carotid arteries • Located in the anterior triangle of the neck • 2 branches of the common carotid artery: o External carotid artery  supply most tissues of head external to the brain and orbit (e.g., superficial temporal artery); feel pulse on neck o Internal carotid artery  supply the orbits and most of the cerebrum  3 branches from subclavian • Vertebral artery o Supply the posterior brain o Join to form the basilar artery  Basilar artery divides into 2 posterior cerebral arteries
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