Lecture 13: Cardiovascular System PDF

About This Chapter 14.1 Overview of the Cardiovascular System 14.2 Pressure, Volume, Flow, and Resistance 14.3 Cardiac Muscle and the Heart Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved The Cardiovascular System Consists of the Heart, Blood vessels, and Blood • Blood ve...

About This Chapter 14.1 Overview of the Cardiovascular System 14.2 Pressure, Volume, Flow, and Resistance 14.3 Cardiac Muscle and the Heart Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved The Cardiovascular System Consists of the Heart, Blood vessels, and Blood • Blood vessels (vasculature) – Arteries vs. veins arteries: carry blood away from the heart vs veins: return blood to the heart vessels where blood – Capillaries microscopic exchanges material with the interstitial fluid ex: 2 capillary beds of the digestive tract and liver by the hepatic portail vein – Portal system joins two capillary beds in series joined 2 capillary beds connected in series in the kidneys Hypothalamic-hypophyseal portal system which connects the hypothalamus and the anterior pituitary • Heart central wall – Septum divides heart into two halves (left and right) – Atrium receives blood returning to heart – Ventricle pumps blood out of heart • Blood: cells and plasma right side of the heart receives blood from the tissues and sens it to the lungs for oxygenation while the left one receives newly oxygenated blood from the lungs and pumps it to the tissues Plasma: fluid matrix of the blood, contains plasma proteins (albumins), water, ions, organic molecules, trace elements and vitamins, gases Cells: RBC, WBC (lymphocytes, monocytes, neutrophils, eosinophils, basophils) Platelets: cell fragments that are essential to blood clotting pulmonary: blood vessels that go from the right ventricle to the lungs and back to the left atrium systemic: blood vessels that carry blood from the left side of the heart to the tissues and back to the right side of the heart arteries: blood from the right ventricle to the lungs where it is oxygenated (red) vs veins: blood from the lungs travels to the left side of the heart • Pulmonary vs. systemic circulation – Pulmonary arteries vs. pulmonary veins Blood pumped out of the left ventricle (large artery) – Aorta vs. inferior vena cava and superior vena cava veins from the lower part of the body form it veins from the upper part of the body join to form it Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 14.1 The cardiovascular system Color changes from red to blue as the blood passes through the capillaries which indicates that oxygen has left the blood and diffused into the tissues Cardiovascular system is a closed loop. The heart is a pump that circulates blood through the system. Arteries take blood away from the heart, and veins carry blood back to the heart. Blood: left ventricle —> aorta —> coronary arteries (nourish the heart muscle itself) —> capillaries —> coronary veins —> right atrium at the coronary sinus Ascending branches of the aorta —> arms, head, and brain Abdominal aorta —> trunk, legs, internal organs such as liver (hepatic artery), digestive tract, and kidneys (renal arteries) Special arrangements of the circulation: 1. Blood supply to the digestive tract and liver : both receive well-oxygenated blood through their own arteries + the blood leaving the digestive tract goes directly to the liver by the hepatic portal vein Liver: important site for nutrient processing, detoxification, filters the nutrient before it is released into the general circulation Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 14.2 Pressure, Volume, Flow, and Resistance • Blood flows because liquids move from high to low pressure regions • Pressure gradient (P) difference in pressure between two regions • Blood flows out of the heart (highest pressure) into closed loop of pressure in the vessels of the CVS = aorta and systemic arteries bc they vessels (lower pressure) highest receive blood from left ventricle lower pressure = venae cavea, just before they empty into the right atrium • The pressure of a fluid in motion decreases with distance – Pressure is lost (due to friction) as blood moves through vessels – Hydrostatic pressure: pressure exerted by a fluid not in motion fluid not moving ▪ Exerted in all directions force exerted in all directions Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Pressure Changes in Liquids Without a Change in Volume • Contraction of heart creates pressure without changing volume of of blood-filled ventricles: pressure created by contracting muscle is transferred to the blood blood contraction High pressure blood flows out of the ventricle and into the blood vessels, displacing lower-pressure blood already in the vessels it is the force that drives – Blood leaves heart to vessels, called driving pressure bc blood through blood vessels • In vessels – If blood vessels dilate, blood pressure decreases – If blood vessels constrict, blood pressure increases • Volume changes affect blood pressure in cardiovascular system • Blood flows from higher pressure to lower pressure – Flow through a tube is directly proportional to the pressure gradient ▪ Flow  P ▪ The higher the pressure gradient, the greater the fluid flow Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 14.2 Blood flows down a pressure gradient Heart creates high pressure when it contracts Blood flows out of the heart (highest pressure) into closed loop of blood vessels (lower pressure) As blood moves through the system, pressure is lost bc of friction between fluid + blood vessel walls, so pressure falls continuously as blood moves farther from the heart Highest pressure in vessels = aorta and systemic arteries as they receive blood from the left ventricle Lowest pressure: venue cave just before they empty into the right atrium Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Resistance Opposes Flow • Flow through a tube is inversely proportional to resistance (Flow  1/R) – Flow decreases as resistance increases • Poiseuille’s Law (R =8Lη/πr 4 or R  Lη/r 4 ) – Resistance is proportional to length (L) of the tube (blood vessel) ▪ Resistance increases as length increases – Resistance is proportional to viscosity (η) or thickness, of the fluid (blood) ▪ Resistance increases as viscosity increases – Resistance is inversely proportional to tube radius to the fourth power (R  1/r 4 ) ▪ Resistance decreases as radius increases vasoconstriction: decrease in blood vessel diameter —> decrease blood ▪ Vasoconstriction vs. vasodilation flow through a vessel • Flow  P /R vasodilatation: increase in blood vessel diameter —> increases blood flow through a vessel – Flow increases as the pressure gradient increases (directly proportional) or as resistance to flow decreases (inversely proportional) Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Velocity Depends on the Flow Rate and the Cross-Sectional Area how much (volume) blood flows past a point in a given period of • Flow usually means flow rate measures time – The volume of blood that passes a given point in the system per unit time • Velocity of flow measures how fast blood flows past a point – The distance a fixed volume of blood travels in a given period of time velocity of flow through a tube equals the flow rate divided by the tube’s cross-sectional area, so in a tube – Formula v = Q A of fixed diameter, velocity is directly related to flow rate, whereas in a tube of variable diameter, if the flow ▪ Q = flow rate rate is constant, velocity varies inversely with the diameter —> velocity is faster in narrow sections and slower in wider sections ▪ A = cross-sectional area of the tube • Mean arterial pressure (MAP) – Primary driving force for blood force – Pressure reserved in the arteries during heart relaxation – MAP  cardiac output (CO)  peripheral resistance (PR) volume of blood the heart pumps/min resistance of blood vessels to blood flow through them Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 14.3e The Physics of Fluid Flow As the radius of a tube decreases, the resistance to flow increases. Resistance  Tube A R  Tube B 1 24 1 R  16 1 14 R  R 1 Flow  Tube A Flow  1 radius4 1 1 Flow  1 1 resistance Tube B 1 1 16 1 Flow  16 Flow  Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 14.3 Cardiac Muscle and The Heart • The heart has four chambers left and right atriums, left and right ventricles • The heart is made up mostly of myocardium cardiac muscles – Encased in pericardium tough membranous sac thin layer of clear pericardial fluid inside it lubricates the external surface of the heart as it beats within the sac —> pericarditis (inflammation) may reduce it to the point that the heart rubs against the pericardium, creating a sound known as a friction rub • Paired atria are thin-walled upper chambers • Paired ventricles are thick-walled lower chambers • Blood vessels emerge from base of heart arteries – Aorta and pulmonary trunk carry blood from heart to the tissues and lungs, respectively – Vena cava and pulmonary veins return blood to heart – Deoxygenated: vena cava → right atrium → right ventricle → pulmonary trunk – Oxygenated: pulmonary veins → left atrium → left ventricle → aorta • Connective tissue rings serve as origin and insertion for cardiac muscles 4 fibrous connective tissue rings surround 4 heart valves arrangement that pulls the apex and base of the heart together when the ventricles contract Electrical insulator: block most transmission of electrical signals between atria and ventricle —> electrical signals directed through specialized conduction system to apex of the heart for the bottom-to-top contraction Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 14.5(a)-(b) The Heart Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 14.5d The Heart Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 14.5(e)-(f) The Heat Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 14.5(g)-(h) The Heart 2 sides contract in coordination: atria contract together, then ventricles Blood enters each ventricle at the top of the chamber but also leaves at the top bc during dev., tubular embryonic heart twists back on itself, which puts the arteries (through which blood leaves) close to the top of the ventricles, so they must contract from the bottom up so that blood is squeezed out of top Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Table 14.2 The Heart and Major Blood Vessels Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Heart Valves Ensure One-Way Flow in the Heart The opening between each atrium and its ventricle guarded by AV valve that is formed from thin flaps of tissue joined at the base to a connective tissue ring, the flaps are slightly thickened at the edge and connect on the ventricular side to collagenous tendons = chord tendinae • Atrioventricular valves – Between atria and ventricles the act of turning inside out prevent valve from being pushed back into the atrium since when a ventricle contracts, blood pushes against the bottom side of its AV valve and forces it upward into a closed position – Chordae tendineae prevent eversion during ventricular contraction stability for chord, but can’t actively open ▪ Attached to valve flaps from papillary muscles provide and close AV valves – Tricuspid valve on the right side – Bicuspid valve (mitral valve), on the left side • Semilunar valves – Between ventricles and arteries – Aortic valve left: between left ventricle and aorta – Pulmonary valve right: between right ventricle and pulmonary trunk • The coronary circulation supplies blood to the heart – Coronary arteries vs. coronary veins across the surface of the heart in shallow grooves, branching into smaller and smaller arteries until finally the arterioles disappear into the heart muscle itself blood from coronary circulation returns to heart via 3 routes: 1. Most venous blood leaves myocardium through cardiac veins that empty into the coronary sinus on the posterior aspect of the heart and the blood in the coronary sinus empties directly into the right atrium 2. Deep in the heart muscle, smaller blood channels empty their blood directly into it 3. Few small veins on the anterior portion of the right ventricle drain directly into right atrium Lower in oxygen than venous blood returning through venal cave) run in parallel with coronary arteries Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 14.7(a)-(b) Heart valves create oneway flow through the heart Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 14.7(c)-(d) Heart valves create oneway flow through the heart Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 2 primary coronary arteries originate at the start of the aorta, just superior to semilunar valve leaflets of aortic valve RCA runs from aorta around right side of the heart in a groove (coronary sulcus) between right atrium and ventricle —> feed right atrium, most of the right ventricle and some of the left ventricle and posterior portion of the inter ventricular septum LCA: leaves left side of aorta —> divided in 2 branches = circumflex branch (continuous around left side of heart to posterior surface) and anterior inter ventricular branch called LAD (runs in a groove toward the apex of the heart) —> supply blood to left atrium, most of left ventricle and inter ventricular septum and some of the right ventricle Figure 14.8 The coronary circulation Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Cardiac Muscle Cells Contract without Innervation • Autorhythmic cells (pacemakers) – Signal for contraction – Smaller and fewer contractile fibers compared to contractile cells – Do not have organized sarcomeres so they don’t contribute to the contractile force of the heart • Contractile cells typical started muscle with contractile fibres organized into sarcomeres – Striated fibers organized into sarcomeres • Cardiac muscle vs. skeletal muscle 1. Smaller and have single nucleus per fiber 2. 3. that have 2 components: desmosomes (strong connections tie adjacent cells together, Branch and join neighboring cells through intercalated disks that allowing force created in 1 cell to be transferred to adjacent cell) + electrically connect cardiac muscle cells to one another gap junction Gap junctionsallow eaves of depolarization to spread rapidly from cell to cell, so that all the heart muscle cells contract almost simultaneously 4. T-tubules are larger and branch muscle depends in part on extracellular Ca2+ to initiate contraction 5. Sarcoplasmic reticulum is smaller cardiac —> resembles smooth muscle for that part 6. Mitochondria occupy one-third of cell volume high energy demand Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 14.9 Cardiac muscle Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Calcium (not cardiac) Cardiac Entry is a Feature of Cardiac EC Coupling excitation-contraction • Action potential starts with the heart pacemaker cells and spreads into the contractile cells through gap junctions • Ca2+ -induced Ca2+ release process of EC coupling – Voltage-gated L-type Ca2+ channels in the cell membrane open – Ryanodine receptors (RyR) open in the sarcoplasmic reticulum (SR) open in response to inflow of Ca2+ ▪ Called Ca2+ spark bc stored Ca2+ flows out of the SR into the cytosol can be seen using special biochemical methods – Summed sparks create a Ca2+ signal • Calcium binds to troponin and initiate movement (contraction takes place by the same type of sliding • Crossbridge cycle as in skeletal muscle and filament movement than skeletal muscle • Relaxation calcium removed from cytoplasm – Into the SR with Ca2+ -ATPase – Out of cell through the Na+ -Ca2+ exchanger (NCX) Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 14.10 EC coupling in cardiac muscle Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Cardiac Muscle Contraction Can Be Graded If additional calcium enters the cell from ECF, more calcium is released from the SR and binds to troponin which enhance ability of myosin to form cross bridges with actin and creating additional force • Force generated is proportional to number of active crossbridges – Determined by how much calcium is bound to troponin • Sarcomere length affects force of contraction In intact heart, stretch on individual fibres is a function of how much blood is in the chambers of the heart Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 14.11 Action potential of a cardiac contractile cell see slide 28 Phase* Membrane channels 0 Na+ channels open 1 Na+ channels close 2 + Ca2+ channels open; fast K channels close 3 Ca2+ channels close; slow 4 Resting Potential K + channels open *The phase numbers are a convention. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 14.12(a)-(b) Refractory periods and summation Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Figure 14.13 Action potentials in cardiac autorhythmic cells see slide 29 Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Myocardial Action Potentials Vary (1 of 2) • Myocardial contractile cells see figure 14.11 – Phase 4: resting membrane potential – Phase 0: depolarization ▪ Due to Na+ inflow -90 mV – Phase 1: initial repolarization ▪ Na+ channels close – Phase 2: plateau ▪ Long action potential due to Ca2+ inflow ▪ Sustains refractory period and prevents tetanus – Phase 3: rapid repolarization ▪ Due to K+ outflow Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Myocardial Action Potentials Vary (2 of 2) See figure 14.13 • Myocardial autorhythmic cells – Unstable membrane potential called pacemaker potential current to flow = HCN – Depolarization is initially due to open lf channel → Na+ inflow – Depolarization → opening of voltage-gated Ca2+ channels → Ca2+ channel inflow ▪ → lf channels close → decreased Na+ inflow – At threshold, 2nd type of voltage-gated Ca2+ channels open → steep depolarization – At peak, Ca2+ channels have closed, slow K+ channels open → decreased Ca2+ inflow and increased K+ inflow ▪ Pacemaker potential returns to lowest point Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Table 14.3 Comparison of Action Potentials in Cardiac and Skeletal Muscle Blank Skeletal Muscle Contractile Myocardium Membrane Potential Stable at – 70-80 mV Stable at –90 mV Events Leading to Threshold Potential Net Na entry through AChoperated channels Depolarization enters via gap junctions Rising Phase of Action Potential Na+ entry Na+ entry + Repolarization Phase Rapid; caused by K + efflux Hyperpolarization Due to excessive K + efflux at high K + permeability. When K + + channels close, leak of K + and Na restores potential to resting state Duration of Action Potential Short: 1–2 msec Refractory Period Generally brief Na+ Autorhythmic Myocardium Unstable pacemaker potential; usually starts at – 60 mV + Net Na entry through lf channels; reinforced by Ca2+ entry Ca2+ entry Extended plateau caused by Ca+ + entry; rapid phase caused by Na+ Rapid; caused by K efflux efflux Normally none; when repolarization hits –60 mV, None; resting potential is –90 the lf channels open again. mV, the equilibrium potential for Ach can hyperpolarize the K+ cell Variable; generally 150+ Extended: 200+ msec msec + Long because resetting of Na Not significant in normal channel gates delayed until end function of action potential Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Key words • arteries, veins, atrium, ventricle, pulmonary arteries, pulmonary veins, pulmonary circulation, aorta, capillaries, superior vena cava, inferior vena cava, systemic circulation, portal system, hepatic portal system, hydrostatic pressure, resistance (R), viscosity (η), Poiseuille’s law, vasoconstriction, vasodilation, flow rate, velocity of flow, mean arterial pressure (MAP), cardiac output, peripheral resistance, apex, base, pericardium, myocardium, pulmonary trunk, atrioventricular (AV) valves, semilunar valves, chordae tendineae, papillary muscles, tricuspid valve, bicuspid valve, mitral valve, aortic valve, pulmonary valve, myogenic, autorhythmic cells, pacemakers, intercalated disks, desmosomes, gap junctions, voltage-gated L-type Ca2+ channels, ryanodine receptor Ca2+ release channels (RyR), Ca2+-induced Ca2+ release (CICR), Na+-Ca2+ exchanger, If channels, graded contractions Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved