Physiology of Cardiovascular System

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The cardiac skeleton consists of 4 bands of

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The cardiac skeleton consists of 4 bands of

dense collagenous tissue - fibrous rings

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central fibrous body/trigone - function

supports 4 valves + insulator that prevents contact bw myocardial cells and stops n impulses

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layers of pericardium

fibrous (outermost) and serous (visceral and parietal)

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pericarditis vs pericardial effusion

  • inflammation of the pericardium, reducing pericardial fluid (friction)

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  • fluid accumulation, increased p, tamponade (wall collapse)

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Myocytes arranged in

myofibrils - striated and branched

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Myocytes in myocardium are connected by ________ that help them adhere to desmosomes

intercalated discs

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Pores in myocardium that allow electric conductivity?

gap jxns of connexin proteins bw myocytes

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layers of cells of endocardium

outer - n, v, purkinje fibers

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middle - connective tissue

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inner - endothelial cells

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Which conducting tissue is normally suppressed instead of performing spontaneous action potentials

SA node

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Electrophysiological cardiac cycle steps (3)

  1. action potential in SA node

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  1. action potential thru atria then av bundle then ventricles (delay)

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  1. signal to bundle of His then Purkinje fibers to ventricular myocytes

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How does action potential carry out

myocardium made of sarcomeres that contract if Ca+2 released from sarcoplasmic reticulum

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What happens after action potential causes inward Ca+2 current?

triggers release more Ca2+ in sarcoplasmic reticulum, binds to troponin C, tropomyosin moves out and actin + myosin make cross-bridges

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Relaxation of action potential occurs when

ca2+ reaccumulated in sarcoplasmic reticulum by Ca2+ ATPase

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Ventricular diastole begins when

cardiac valves closed + ventricles relax

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ventricular systole begins after

atrial systole, valves close

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What happens in ventricular diastole

  • ventricles relax + p falls

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  • valves open + blood flows from atria to ventricles

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  • v + p rises, atria contract (systole)

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What happens in ventricular systole

  • ventricular p rises, closing valves

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  • isovolumic contraction until aortic + pul valves open and blood ejected into circ

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Stroke volume

The amount of blood ejected from the ventricle in one contraction

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EJection fraction

the fraction of the end-diastolic volume ejected from the heart, measures ventricular efficiency/ contractility

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cardiac output

the total volume of blood ejected from the ventricle per minute

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Cardiac output depends on

stroke volume (v ejected on 1 beat) and heart rate (# beats/min)

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Stressed volume

The volume of blood contained in the arteries

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Smooth muscles in walls of arterioles are always

contracted (tonically active)

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sympathetic adrenergic nerve fibers of arteriole's smooth muscle walls

a1 - in arterioles of vascular beds, vasoconstrictor

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b2 - in arterioles of skeletal m, vasodilator

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Lipid vs water-soluble substances thru capillary walls

lipid - cross by dissolving in and diffusing across

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water - cross by clefts or pores of fenestrated caps

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Blood flow thru vessel is determined by

pressure diff bw ends of vessel and resistance of vessel to blood flow

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Total Peripheral Resistance (TPR)

the resistance to the flow of blood through the entire systemic circulation

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Poiseuille's equation - resistance to flow is :

proportional to viscosity + length

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inversely to r 4 of vessel

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Series vs. Parallel resistance

series - total resistance equal to sum of individual resistances

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parallel - resistance in parallel way less than individuals, no loss p in big a.

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Korotkoff sounds

series of sounds that correspond to changes in blood flow through an artery as pressure is released (turbulent flow)

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positive vs neg inotropy

pos - increase contractility, SV, CO

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Pulse pressure

difference between systolic and diastolic pressure, reflects stroke volume

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pulse pressure depends on

stroke volume and arterial compliance

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Mean Arterial Pressure (MAP) (def + dependent on)

pressure forcing blood into tissues

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  • peripheral resistance and cardiac output

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in the steady state, cardiac output from the heart equals

venous return to the heart

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3 types of cardiac muscle + their levels of contractability

  1. Atrial

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  1. Ventricular

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  1. Excitatory & conductive (low)

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What do myocytes do with synaptic input from autonomic neurons?

use synapses to modulate (not initiate) electrical activity + contractile force of cardiac muscle

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Myocytes are surrounded by __________ which delimits the __________

sarcolemma

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sarcoplasm/cytoplasm

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A vs I bands of myofibrils

dark regions (anisotropic)

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light regions (isotropic)

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I bands are divided in the middle by darker lines called

Z lines

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Protein aggregates of sarcomere

contractile (actin and myosin), regulatory and structural proteins

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structure of myosin

2 heavy chains in helix and 4 lights chains

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2 types of myosin

a (higher atpase activity) and b (higher velocity contraction)

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cross-bridges of myosin

protruding arms and heads, that bind to actin

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3 isoenzymes of heavy chains

V1 - 2 a chains

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V2 - a and b chains

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V3 - 2 b chains

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Which isoenzyme of heavy chains is dominant in atrial myocardium vs ventricular myocardium

V1 in atrial

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all 3 in ventricular

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2 types of actin (thin filaments)

globular (G, monomer) and fibrillar (F, in vivo)

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Constitution of an actin molecule

2 G actins that make F actin - 2 F actins in helix

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The main regulatory proteins of the sarcomere are represented by

tropomyosin and troponin (only in actin)

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Where is tropomyosin bound when resting?

rest - active sites of actin (blocks interaction bw actin and myosin, no contraction)

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protein subunits of troponin + roles

troponin C - binds Ca2+

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troponin T - structural, binds troponin w/ tropomyosin

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troponin I - inhibitory

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What do the regulatory proteins do during contraction?

Ca+2 binds to troponin C, tropomyosin moves deeper into grooves bw actins, myosin sites uncovered

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Function of titin

anchors thick myosin to Z line w/ its extensible part

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power stroke

action of myosin pulling actin inward (toward the M line), when Ca2+ levels high

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sliding filament mechanism

Myosin binds to actin when it breaks down atp (closer to backbone) . The myosin then alters its configuration, resulting in a "stroke" that pulls on the actin filament and causes it to slide across the myosin filament, sarcomere shortens

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78

Sympathetic stimulation _________ activity of Ca+2 channels

increase

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Activity of Ca2+ ATPase

energy from atp cleavage expels ca2+ from cell (against gradient), stimulated by calmodulin

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Na+/Ca2+ exchanger

sarcolemmal protein w/ Transverse tubules that expulses ca2+

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the passive release of Ca+2 from sarcoplasmic reticulum occurs thru

ryanodine-receptor channels in jxnal region of sarcoplasmic reticulum

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What does Ca2+-dependent ATPase transport?

performs ca2+ reuptake into sarcoplasmic reticulum

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phospholamban

regulatory protein in contractile myocardium that inhibits Ca2+ ATPase in the sarcoplasmic reticulum

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Ca2+ storage in sarcoplasmic reticulum relies on binding to _________, a protein in jxnal region of SR

calsequestrin

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____________ of myocyte plays a buffer role of intra/extracell Ca2+ concs

mitochondria

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Action potential is caused by opening of 2 channels

  • voltage-activated fast sodium channels (same as skeletal)

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  • L-type calcium channels (slow)

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After the onset of action potential, what decreases in cardiac m membrane

permeability for K+ ions (less outflux)

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At the end of plateau of cardiac action potential, what happens?

Ca+2 influx stops and they are pumped back out into SR and T tubule extracell space, sodium transported out

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Phase 1: initial repolarization

-Na+ channels close

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-K+ leave thru open K+ channels

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Phase 2: plateau

Ca+2 channels open + influx, fast K+ channels close (efflux)

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(+ brief repolarization)

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Phase 3: Rapid Repolarization

Ca+2 channels close, slow K+ channels open

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How is the T tubule system in cardiac muscle different from skeletal muscle?

T-tubules @ Z lines - part of extracell, helps in Ca+2 diffusion from extracell

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Ca2+ induced Ca2+ release (CICR)

most important trigger for Ca+2 rise, increased Ca2+ in SR causes further release

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Action potential is conducted via

T tubules in myocyte

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_________ stimulation is the main physiological factor that modulates electro-mechanical coupling, related w/ β1-adrenergic receptors stimulation to induce ____________

sympathetic

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phosphorylation (of channels, increase Ca2+)

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100

absolute refractory period of heart

time during which normal cardiac impulse can't re-excite an already excite area, longer in ventricles

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