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Chapter 21 Blood Vessels Direction of Flow Heart to aorta to arteries to arterioles to capillaries. Capillaries to venules to veins to vena cava to heart. Veins Arteries • Capillaries form Microcirculation • Microscopic vessels that connect arterioles to venules • Found near every cell in the body but more extensive in highly active tissue (muscles, liver, kidneys & brain) •entire capillary bed fills with blood when tissue is active •lacking in epithelia, cornea and lens of eye & cartilage • Function is exchange of nutrients & wastes between blood and tissue fluid • Structure is single layer of simple squamous epithelium and its basement membrane Capillaries: 1. Continuous 2. Fenestrated 3. Sinusoid Venous valves Blood Distribution • • • • • 12% pulmonary vessels 8 % = heart 15% = systemic arteries and arterioles 5% = capillaries 60% = systemic veins and venules Venous flow occurs by: 1. muscle contraction 2. respiratory pump 3. valve assistance 4. Ventricular relaxation Varicose Veins • Twisted, dilated superficial veins – caused by leaky venous valves • congenital or mechanically stressed from prolonged standing or pregnancy – allow backflow and pooling of blood • extra pressure forces fluids into surrounding tissues • nearby tissue is inflamed and tender • Deeper veins not susceptible because of support of surrounding muscles Anastomoses • Union of 2 or more arteries supplying the same body region – blockage of only one pathway has no effect • circle of willis underneath brain • coronary circulation of heart • Alternate route of blood flow through an anastomosis is known as collateral circulation – can occur in veins and venules as well • Alternate routes to a region can also be supplied by nonanastomosing vessels Pulse Pressure • Pulse pressure = systole - diastole • MAP = diastolic pressure + pulse pressure/3 • MAP = mean arterial pressure • MAPB = diastole + 1/3 (systole – diastole) • MAPB = mean arterial blood pressure Blood Pressure Influenced by: • • • • • • Peripheral resistance Heart efficiency Blood viscosity Total blood vessel length Arteriole elasticity Blood volume Hormones that affect BP • • • • Renin angiotensin Epinephrine and norepinephrine Antidiuretic hormone Atrial natriuretic peptide Autoregulation of BP • Physical changes • Vasodilating and constricting chemicals Major Branches of the Aorta • • • • • • • • • Coronary arteries Brachiocephalic Left common carotid Left subclavian Celiac Superior mesenteric artery Renals Ovarian / testicular Inferior mesenteric Minor Branches of the Aorta • • • • • • Pericardial Bronchial Esophageal Mediastinal Intercostal Phrenic Thoracic Lumbar Suprarenal Celiac circulation Abdominal arteries Arterial supply and venous drainage of the liver Hypertension • Systole > 140 • Diastole > 90 • Causes: diet high in fat and sodium, obesity, older age, race, heredity, stress, and smoking. Words to Learn • • • • • • • • Aneurysm Angiogram Diuretic Phlebitis Phlebotomy Thrombophlebitis Syncope Tachycardia Shock Sphygmomanometer Korotkoff sounds Angiogenesis Hypotension Occlusion White Coat Hypertension Edema
