P215 SPRING 2019: CIRCULATORY SYSTEM Chaps 13, 14 & 15: pp , , , I. Major Functions of the Circulatory System

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1 P215 SPRING 2019: CIRCULATORY SYSTEM Chaps 13, 14 & 15: pp , , , I. Major Functions of the Circulatory System II. Structure of the Heart 1. atria 2. ventricles 3. atrioventricular (AV) valves a. b. i. chordae tendinae ii. papillary muscles 4. semilunar valves a. b.

2 II. Structure of the Heart (cont.) 5. septum 6. fibrous skeleton 7. heart wall The heart wall has four main layers: Overall flow of blood through the heart and body: The right atrium receives blood from and sends it to, then the right ventricle sends blood to the. The left atrium receives blood from and sends it to, then the left ventricle sends blood to the.

3 III. Electrical Activity of Heart 1. cardiac muscle structure function contractile properties action potentials

4 III. Electrical Activity of Heart (cont.) SA node depolarization mechanism 2. sinoatrial (SA) node (pacemaker potential) 3. atrioventricular (AV) node 4. atrioventricular bundle (bundle of His) 5. left & right bundle branches 6. Purkinje fibers

5 Some important questions to understand: What happens to the action potential when it meets the fibrous skeleton of the heart? How does the action potential get to the ventricles? Why does the action potential to the ventricles need to travel to the apex first? What would happen if the fibrous skeleton could conduct action potentials? IV. Regulation of Cardiac Rate Autonomic innervation of the SA node is the primary modifier of heart rate. Sympathetic nerve endings in the atria & ventricles can increase the strength of cardiac contraction. Cardiac region Sympathetic Effect Parasympathetic Effect SA node AV node Atrial muscle Ventricular muscle bradycardia = tachycardia = fibrillation =

6 V. Measurement of Cardiac Electrical Activity How can electrical signals from the heart be accurately measured from the skin? Major ECG waves: P-wave: QRS complex: T-wave: VI. Cardiac Cycle = Order of events during the cardiac cycle:

7 VII. Physiological Characteristics of a Single Cardiac Cycle 1. Cardiac Blood Volumes End systolic volume (ESV) End diastolic volume (EDV) Stroke volume (SV) 2. Cardiac Blood Pressures At this point, we are only concerned with the local pressure that blood exerts in and around the heart, we are not dealing with the systemic blood pressure (although this little picture will play an important role in the big picture). Some important questions: Why is the local blood pressure in and around the heart important? What would happen if cardiac blood pressure was constant? Does that ever happen? What is the pressure of blood entering the atria? Why? What is the pressure of blood in the aorta (on the other side of the semilunar valve)? Why?

8 3. Ventricular Pressure-Volume Loop Important events during the cardiac cycle illustrated by the pressure-volume loop A: A B: B: B C: C: C D: D: D A: Ventricular ejection fraction = / This is an important clinical measure of cardiac efficiency (normal = at rest)

9 VIII. Cardiac Output Cardiac output is. Cardiac Output (CO) = x The average cardiac output is liters per minute. The average total blood volume a person has is liters. Therefore, on average, it takes about for a red blood cell to travel through the body. Three related factors determine stroke volume (SV): 1. End-diastolic Volume (EDV) 2. Total Peripheral Resistance (TPR)

10 Three related factors determine stroke volume (cont.): 3. Contractility = a) Autonomic Activity (Extrinsic) b) Frank-Starling Law of the Heart (Intrinsic) skeletal muscle length-tension relationship cardiac muscle length-tension relationship The Big Picture of Factors That Affect Cardiac Output

11 Functional application of the three factors that determine stroke volume to the ventricular pressure-volume loop. How would the loop initially change if someone had high blood pressure? How would the loop initially change after someone had a mild heart attack? How would the loop initially change if someone had mitral valve stenosis?

12 IX. Vasculature Heart Arteries Arterioles Capillaries Venules Veins Heart circulation = path from the left ventricle, to the body & back to the heart circulation = path from the right ventricle, thru the lungs & back to the heart The rate (i.e. velocity) that blood flows through the systemic circulation is the flow rate through the pulmonary circulation. Why? Peripheral resistance in the systemic circulation is the pulmonary circulation. Why? The amount of work done by the left ventricle is times than the right ventricle. What is the anatomical result of this difference? Structure of Blood Vessels 3 layers of large Arteries and Veins:

13 IX. Vasculature (cont.) Major Characteristics of Arteries Major Characteristics of Arterioles Major Characteristics of Capillaries Three Types of Capillaries Major Characteristics of Veins & Venules

14 X. FACTORS AFFECTING BLOOD FLOW Blood Flow = Continuous movement of blood through the circulatory system Continuous blood flow requires a. Blood Flow from the arteries to the veins is a combination of the difference in pressure between those two segments and the resistance of the arterioles & capillaries between them. In the analogy of the dam, the reservoir is the arterial side with a LOT of pressure. The arterioles & capillaries are the dam (very high resistance) that keeps the water from flowing downstream. As a result, there is very low water pressure on the other side of the dam. At rest, the pressure gradient from arteries to veins remains relatively constant ( P 92 mmhg), so the body uses changes in resistance to regulate blood flow to satisfy the needs of specific organs or cells. Two ways the circulatory system actively changes resistance: 1. Vasodilation 2. Vasoconstriction Resistance will also change if the volume and/or viscosity of the blood changes. This can occur as a result of dehydration, blood doping, hemorrhage, etc.

15 XI. BLOOD PRESSURE The force blood exerts against inner walls of blood vessels (mm Hg) systolic pressure = diastolic pressure = Other more clinically relevant ways to describe blood pressure: pulse pressure = systolic BP - diastolic BP mean arterial pressure (MAP) = 1/3 (pulse pressure) + diastolic BP Arterial BP is determined by three main factors: Intrinsic Control of Blood Pressure 1. 2.

16 XI. BLOOD PRESSURE (cont.) Extrinsic Control of Blood Pressure The big picture of factors that affect Blood Pressure

17 XI. BLOOD PRESSURE (cont.) Hypertension Blood Pressure Category Subcategory Systolic BP Diastolic BP Normal < 120 mmhg < 80 mmhg Prehypertension mmhg mmhg Stage mmhg mmhg Hypertension Stage 2 > 160 mmhg > 100 mmhg Functional application of blood pressure control Orthostatic Hypotension If you stand up fast what happens to blood in your upper body? What happens to the blood pressure in your upper body? Why does that make some people faint? Why only some people and only some of the time? What changes do baroreceptors initiate to regulate blood pressure? What is this process of blood pressure maintenance called?

18 XII. BLOOD Total blood volume is between 5-6 liters. Whole blood consists of formed elements suspended & carried in plasma. plasma = Formed element types: 1) erythrocytes (RBCs) hematocrit = 2) leukocytes (WBCs) 3) platelets are the smallest formed elements Hematopoiesis = the formation of blood cells from stem cells in bone marrow & lymph nodes Erythropoiesis is the formation of RBCs. Leukopoiesis is formation of WBCs. Hemostasis = cessation of bleeding Promoted by reactions initiated by vessel injury: 1) 2) 3)

19 XIII. EXCHANGE OF FLUID BETWEEN CAPILLARIES & TISSUES Fluid Volume Review About of the water in our bodies is inside cells (intracellular fluid or ICF). About of the water in our bodies is outside the cells (extracellular fluid or ECF). The ECF is interstitial fluid (ISF) and blood plasma. Movement of water between compartments is a result of. Movement of water among ICF, plasma & interstitial fluid is in state of dynamic equilibrium. Functional Example: Sweating This is a result of the balance between filtration and absorption in the capillaries. filtration = absorption = Net Fluid Movement is determined by the difference between the sum of the filtration pressures and the sum of the absorption pressures.

20 Two types of pressures are important to determine net fluid movement: 1. hydrostatic pressure (P) = - capillary hydrostatic pressure (P CAP ) -P CAP = - interstitial fluid hydrostatic pressure (P IF ) - P IF = 2. colloid osmotic (or oncotic) pressure (ð) = - capillary oncotic pressure (ð CAP ) - ð CAP = - interstitial fluid oncotic pressure (ð IF ) - ð IF = Net Fluid Movement = (sum of pressures driving H 2 O OUT) - (sum of pressures driving H 2 O IN) Net Fluid Movement = (P CAP + ð IF ) - (P IF + ð CAP ) P CAP = Hydrostatic pressure in capillary ð IF = Oncotic pressure of interstitial fluid P IF = Hydrostatic pressure of interstitial fluid ð CAP = Oncotic pressure of blood plasma Calculate the Net Fluid Movement for the beginning of a capillary. Calculate the Net Fluid Movement for the end of a capillary. Which is the stronger of the two forces, and what does that mean to the body? What would happen if this imbalance were allowed to go unchecked?

21 XIV. LYMPHATIC SYSTEM Lymphatic system - lymphatic vessels - lymph nodes - tonsils, spleen, & thymus 3 main functions: 1. picks up excess fluid filtered out in capillary beds & returns it to veins 2. helps provide immunological defense 3. transports absorbed fat from the small intestine to the liver