Cardiovascular System: Blood Vessels and Circulation Nestor T. Hilvano, M.D., M.P.H.

Learning Objectives Differentiate the types of blood vessels on the basis of their structure and function. Describe the factors that influence blood pressure and how it is regulated. Discuss the important processes of capillary exchange. Discuss venous return and circulatory shock. Identify the special circulation to the brain, heart, and lungs. Identify the major blood vessels of pulmonary and systemic circuits and the areas they serve. Identify the differences between fetal and adult circulation.

Anatomy of Blood Vessels _____ carry blood away from heart _____ carry blood back to heart _____ connect smallest arteries to veins Where does diffusion between blood and interstitial fluid occur? a. Capillary b. Vein c. Artery d. Lymph

Vessel Wall ____- simple squamous endothelium overlying a basement membrane, with Internal elastic membrane; inner layer ____- smooth muscle for vasomotion, with External elastic membrane; middle layer ____- loose connective tissue, with vasa vasorum (small b.v. within a large vessel); outer layer a. Tunica intima b. tunica adventitia c. tunica media

Comparison of Typical Artery and Vein Feature Artery Vein Lumen Regular Irregular Thickness of Wall Thick Thin Internal Elastic Membrane Visible Not distinct Thickest Coat T. Media T. Adventitia Valves No valvee With valves

Types of Vessels Elastic artery (large a.) Conducting artery Aorta and pulmonary trunk Muscular artery (med-sized a.) Most arteries distributes blood to specific organs Resistance artery (small a.) control amount of blood to various organ; little or no T. externa

Types of Capillaries Capillaries - smallest vessels with thin walls ____ – complete endothelial lining; found in all tissues except epithelia and cartilage ____ – pores in endothelial lining; found in choroid plexus, kidney, intestine, endocrine organs ____ – gaps in between endothelial cells, incomplete basement membrane, irregular outline; found in liver, bone marrow, spleen a. sinusoids b. continuous c. fenestrated

Veins Veins – larger diameter than arteries, have: Varicose veins ____ walls: a. thin b. thick ____ blood pressure: a. low b. high ___ aid skeletal muscles in upward blood flow: a. valves b. sphincters Veins expand easily at low pressure (capacitance vessels) Varicose veins Hemorrhoids

Principles of Blood Flow Important for delivery of ______ and ______, and removal of metabolic waste. Hemodynamics physical principles of blood flow based on pressure and resistance F  P/R, (F = flow, P = difference in pressure, R = resistance to flow)

Blood Pressure Force that blood exerts against a vessel wall S_____ pressure – BP during ventricular contraction D_____ pressure – BP during ventricular relaxation BP = SP/DP , in young adult (120/80 mm Hg) Mean Arterial Pressure (MAP) = diastolic pressure + pulse pressure 3 Effect of age in BP level? ______ BP determined by cardiac output, blood volume and peripheral resistance

Total Peripheral Resistance: Factors Blood viscosity – resistance to flow by RBC’s and albumin  viscosity with anemia (flow at low pressure)  viscosity with polycythemia (flow under high pressure) Turbulence – upset the smooth flow of blood, create eddies and swirls, increases resistance and slows blood flow Vascular resistance – friction between blood and vessel walls a) Vessel length- Blood pressure and flow decrease with distance (increases friction) b) Vessel diameter (radius)- controls resistance quickly; vasomotion; Vasoconstriction -  BP; Vasodilatation-  BP Increasing the length increases the friction (the larger the surface area in contact with the blood)

Abnormalities of Blood Pressure _____________ chronic resting BP > 140/90 consequences can weaken small arteries and cause aneurysms chronic low resting BP < 90/60 caused by blood loss, dehydration, and anemia a. hypotension b. hypertension

Regulation of BP and Flow Autoregulation (immediate, localized response) - chemical changes (histamine, bradykinin, low O2, high CO2, low pH) Neural control - Vasomotor center of medulla oblongata, integrates baroreceptor reflexes and chemoreceptor reflexes Endocrine control (direct long- term changes) - renin – angiotensinogen – aldosterone, ADH, ANP, Epi, NEpi

Capillary Exchange Mechanisms involved diffusion, filtration and reabsorption Opposing forces capillary hydrostatic pressure (CHP) drives fluid out of capillary: Filtration blood colloid osmotic pressure (BCOP) draws fluid into capillary: Reabsorption Capillary filtration at arterial end; Capillary reabsorption at venous end Edema = condition when fluids build up in peripheral tissues

Mechanisms of Venous Return Gravity drains blood from head and neck Skeletal muscle pump in the limbs Thoracic (respiratory) pump blood flows faster with inhalation Exercise  venous return Venous pooling occurs with inactivity - with prolonged standing, Cardiac Output may be low enough to cause dizziness or syncope - Shock = reduction of effective circulating blood, blood pressure and cardiac output

Pulmonary and Systemic Circulations Major vessels - pulmonary arteries and pulmonary veins Trace the blood flow beginning at the right ventricle and ending at the left atrium. The aorta Major branches of aortic arch – brachiocephalic a., left common carotid a., left subclavian a.

Fetal Circulation Umbilical vein Ductus venosus Foramen ovale Ductus arteriosus Umbilical arteries

Homework (Self-Review) Define the following: angina pectoris, myocardial infarction, capillary, blood pressure, capacitance vessels, edema, shock, aneurysm, peripheral resistance, varicose, and hemorrhoid. Compare and contrast artery and vein as to structure and function. Describe the walls of blood vessels. Describe the types of capillaries and give example where you can find them. List the 3 major branches of the aortic arch. Discuss the fetal circulation. What becomes of these fetal structures after birth? Give example of elastic artery, muscular artery, large vein, fenestrated capillary, and continuous capillary .