Cardiovascular System: Blood Vessels and Circulation PDF

The Cardiovascular System: Blood Vessels and Circulation Chapter 20 20.1 – Structure and Function of Blood Vessels Blood vessels are the highways of the body The blood travels through the lumen of the blood vessel Arteries have smaller lumens, helps to maintain blood pressure (BP) Arteries also have...

The Cardiovascular System: Blood Vessels and Circulation Chapter 20 20.1 – Structure and Function of Blood Vessels Blood vessels are the highways of the body The blood travels through the lumen of the blood vessel Arteries have smaller lumens, helps to maintain blood pressure (BP) Arteries also have thicker walls, helps to maintain BP Veins have very low pressure and much less resistance Veins have valves to make sure blood does not flow backward 20.1 – Put on your Tunic Vasa vasorum – the tiny blood vessels that deliver nutrients and remove waste from the cells of the large vessels, further outside in arteries Tunica intima – lined by endothelium which can release chemicals to constrict smooth muscle, connected to elastic fibers and collagenous fibers, innermost Internal elastic membrane – distinct layer of elastic fibers connecting to the tunica media in larger arteries, allows structure with flexibility Tunica media – middle layer, much thicker in arteries, it is smooth muscle supported by connective tissue, innervated by nervi vasorum and controlled by hormones and local chemicals 20.1 Vasoconstriction – decreases blood flow and increases BP Vasodilation – increases blood flow and decreases BP External elastic membrane – separates the media from the outer tunic in large arteries Tunica Externa – outermost tunic, mainly collagenous fibers, some smooth muscle in and normally the largest tunic in veins, holds the vessel in position as it binds with surrounding connective tissue 20.1 - Arteries Carry blood away from the heart Thick walls to withstand high pressure, thicker closer to heart (elastic artery) Diameter from.1mm to 10mm is a muscular artery, less elastic fiber and more muscle fiber, great for vasoconstriction 20.1 - Arterioles Like a very small artery that leads to a capillary Tunica media is 1 or 2 cells thick Measured in micrometers They slow down blood flow which decreases BP Muscle fibers are always slightly contracted 20.1 - Capillaries Microscopic vessel to supply blood to tissues by perfusion They are just barely wide enough for 1 red blood cell to pass through Vessel wall may be only 1 cell thick 20.1 - Capillaries Continuous – most common, complete endothelial lining, tight junctions that are often incomplete to allow perfusion of small molecules like water Fenestrated – has pores, permeable to larger molecules Sinusoid – least common, flat with big gaps and an incomplete basement membrane, plasma proteins and cells can pass through, blood flow is very slow Metarteriole – between an arteriole and a capillary, has a precapillary sphincter to allow blood into a capillary bed or not Capillary bed – 10 – 100 capillaries 20.1 Precapillary sphincters remain closed until O2 is needed or waste needs to be removed If all sphincters were open then every drop of blood would be in a capillary bed and that person would die There is a thoroughfare channel and arteriovenous anastomosis to allow blood flow into the venous system 20.1 – Venules and Veins Venule is an extremely small vein, fed by capillaries Many venules join to form a vein Venules and capillaries are the primary sites for diapedesis Vein brings blood back toward the heart, thin walls with large lumens Have valves to prevent backflow due to very low pressure and gravity Veins are considered blood reservoirs Blood in the bone marrow, liver, and integument is known as the venous reserve 20.2 – Blood Flow, BP, and Resistance Blood flow- volume of blood per unit of time through vessel, tissue, and organ Starts at constriction of ventricles Resistance – factors that slow blood flow Blood pressure – hydrostatic pressure of a fluid against the vessel wall or chambers of the heart, normally is systemic arterial pressure BP is measured in mm Hg 20.2 – Components of BP Systolic – higher number on top of the ratio, the pressure during the ventricular contraction Diastolic – lower number on bottom of the ratio, the pressure during ventricular relaxation Pulse pressure – the difference between systolic and diastolic pressure, should be at least 25% of systolic pressure, a high pulse pressure (100 mm Hg) is normal after strenuous exercise Mean arterial pressure (MAP) – the average force driving blood into the vessels MAP = diastolic BP + (systolic-diastolic BP) / 3 20.2 If MAP falls below 60 mm Hg for an extended period of time then ischemia and hypoxia are a concern Pulse – the expansion of the artery due to the ejection of blood from the heart A weak pulse should correspond with low systolic pressure Common pulse sites – radial artery, carotid artery, brachial artery Measuring BP – stethoscope and sphygmomanometer, listen for Korotkoff sounds, cuff around arm at level of heart and stethoscope in antecubital region 20.2 – Variables affecting BP and blood flow Cardiac output – any increase will increase BP and blood flow Compliance – ability to expand due to increased content, if arteries aren’t compliant then BP will increase and blood flow will decrease due to a higher resistance Vessel radius and length – a narrower and longer vessel will increase resistance, decrease flow, and increase pressure Viscosity – thickness of blood, thicker blood will increase pressure Blood volume – less blood (hypovolemia) means decrease blood pressure 20.2 A person at 150 lbs. has about 60,000 miles of vessels, gain 10 pounds and add 2000 – 4000 miles of vessels (reduce weight to reduce heart stress) 20.2 – Venous System Veins have very low pressure and the atria have a pressure just above zero Skeletal muscle pump – leg muscles contract to put pressure on veins to force blood back toward the heart Respiratory pump – inhalation causes an increase in thorax volume and a decrease in pressure, exhalation increases pressure on veins Venoconstriction – decreases resistance in a vein and increases flow Vasoconstriction – increases pressure and resistance in an artery, but decreases flow 20.3 – Capillary Exchange Program Circulate gases, nutrients, wastes, etc. to and from cells Gases, lipids, lipid soluble molecules diffuse through capillary wall Glucose, amino acids, Na+, K+, Ca++, and Cl- use transporters (facilitated) Glucose, ions, and large molecules move through intercellular clefts Large molecules can move through fenestrations Large plasma proteins can pass through sinusoids Water moves by osmosis 20.3 – Bulk Flow Hydrostatic pressure – pushes fluid out of capillaries and into tissues Filtration – fluid flowing from high pressure capillary to low pressure tissues Reabsorption – fluid moving back into capillary due to osmotic pressure Osmotic pressure is low because plasma proteins remain in the capillary 20.3 About 24 L of fluid are filtered each day and 20.4 L get reabsorbed The lymphatic system picks up the extra fluid and eventually dumps it into the subclavian vein in the neck 20.4 – Homeostatic Regulation of the Vascular System Organ Resting (mL/min) Mild Exercise Maximal Exercise Skeletal Muscle 1200 4500 12,500 Heart 250 350 750 Brain 750 750 750 Integument 500 1500 1900 Kidney 100 900 600 Gastrointestinal 1400 1100 600 Other (liver, spleen, etc.) 600 400 400 Total 5800 9500 17,500 20.4 – Neural Regulation BP and flow are regulated by the cardiovascular center in the medulla Cardioaccelerator – stimulate cardiac function, sympathetic Cardioinhibitor – slow cardiac function, parasympathetic Vasomotor centers – control vessel tone or contraction, norepinephrine Baroreceptors – stretch receptors in vessels and chambers send info to cardiovascular center (aorta, carotid artery, vena cava, and right atrium) Chemoreceptors – monitor O2, CO2, and H ions (pH) 20.4 – Endocrine Regulation Epinephrine and Norepinephrine – increase HR and contractility, constrict vessels to organs not essential for fight or flight Antidiuretic Hormone (ADH) – targets the kidneys to reabsorb water which increases blood volume and pressure, also constricts peripheral vessels Renin-Angiotensin-Aldosterone Mechanism – Renin is secreted due to decrease in blood flow, reactions eventually produce Angiotensin 2 which is a powerful vasoconstrictor that stimulates Aldosterone release and thirst Aldosterone – increases Na+ reabsorption and water follows Na+ Erythropoietin (EPO) – stimulates erythrocyte production in bone marrow, overproduction will lead to increase viscosity, resistance, and pressure