Chapter 13 - cardiac function Flashcards
describe vasculature
closed system of blood vessels; heart -> arteries -> arterioles -> capillaries -> venules -> veins -> heart
arteries
large branching vessels taking blood away from heart
arterioles
small branching vessels with high resistance
capillaries
site of exchange between blood and tissue
venules
small converging vessels
veins
relatively large converging vessels that conduct blood to heart
erythrocytes
red blood cells transport oxygen and carbon dioxide
leukocytes
white blood cells defend body against pathogen
platelets
cell fragments important in clotting
plasma
fluid and solutes
what percentage do the cells in blood make up as volume
50% of blood volume
describe pulmonary circuit
supplied by right heart. blood vessels from heart to lungs, and from lungs to heart
describe systemic circuit
supplied by left heart. blood vessels from heart to systemic tissues, and from tissues to the heart
what happens in pulmonary capillaries
deoxygenated blood enters pulmonary capillaries. Oxygen from air diffuses to blood and CO2 diffuses from blood to air. blood leaving lungs in oxygenated
what happens in systemic capillaries
oxygenated blood enters tissues and becomes deoxygenated and goes on to enter right heart
describe full path of blood flow
left ventricle - aortic valve - aorta - systemic circuit - vena cavae - right atrium - AV valve - right ventricle - pulmonary valve - pulmonary trunk - pulmonary circuit - pulmonary veins - left atrium - AV valve - left ventricle
describe parallel blood flow
aorta branches - arteries branch - arterioles branch - capillaries. fully oxygenated blood is delivered to each organ independently from one another (same for each part of the organ). independent regulation of blood flow to organs is possible
describe an exception to parallel blood flow
portal circulation - blood flows from oe capillary bed to another before returning to heart.
describe sequence of blood flow returning from capillaries
capillaries - venules - veins - vena cavae
describe coronary circulation
heart muscle is not supplied by blood in heart chambers. heart has its own supply and a set of capillaries. R. and L. coronary arteries - the very first branches from the aorta
describe myocardial ischemia
decrease in blood flow through coronary arteries can lead to this (insufficient blood flow to heart muscle). chronic myocardial ischemia can lead to myocardial infraction (heart attack)
describe anatomy of heart
located in thoraci cavity (mediastinum) diaphragm separates the abdominal cavity from thoracic cavity
describe three layers of heart wall
epicardium (visceral epicardium) is outer layer that is external membrane of connective tissue. myocardium (middle) cardiac muscle layer. Endothelium inner layer of endothelial cells.
describe walls of left ventricle
very large compared to right ventricle because it pumps blood for the entire body
cardiac cycle
a series of events that occur in a heartbeat
describe pressure difference in blood flow
pressure difference drives blood flow from high pressure to low pressure
describe normal direction of blood flow
atria contract - ventricles contract - arteries. valves prevent backward flow of blood. all valves open and close passively based on pressure gradient
describe AV valves
right AV valve (tricuspid). left AV valve (bicuspid/mitral valve). papillary muscles and chordae tendinae (keep AV valves from prolapsing into atria during ventricular systole)
what determines if AV valves open or close
if atrial pressure is higher than ventricular pressure than AV valves are open. if Atrial pressure is lower than ventricular pressure AV valves close.
what determines if semilunar valves are open or closed
if ventricular pressure is greater than aorta pressure semilunar valves are open. if ventricular pressure is lower than aorta pressure semilunar valves are closed
what are the two types of cells in myocardium
cells of the conduction system and regular cardiac contractile cells
name four types of conduction system cells
SA node, AV node, AV bundle (bundle of His), and Purkinje fibers
what makes up bulk of myocardium
the regular cardiac contractile cells. conduction cells are a small fraction
describe myogenic
cardiac muscle contractions are triggered by signals within the cardiac muscle itself, therefore contractile activity of cardiac muscle is myogenic
describe autorhythmicity
the ability to generate contractions in its own rhythm
what do autorhythmic cells do
generate signal and provide a pathway for spreading carefully timed, coordinated and fast excitation through the heart
describe pacemaker cells
initiate action potentials by spontaneously depolarizing to threshold. set regular intrinsic rhythm to the heartbeat
describe conduction fibers
rapidly conduct action potentials initiated by pacemaker cells to myocardium in carefully timed and highly coordinated manner. conduction velocity = 4m/s. whereas ordinary muscle fibers have conduction velocity of 0.4 m/s
where is SA node located
wall of the right atrium near where it joins with superior vena cava
where is AV noe located
near the tricuspid valve in the interatrial septum
where are bundle of His and bundle branches located
run within interventricular septum
where are purkinje fibers located
spread throughout ventricular myocardium
name firing rate of 3 different pacemakers
SA node 60-100 AP/m. AV node 40-60 AP/m. Purkinje fibers 20-40 AP/m
what is primary pacemaker of heart
SA node. if SA fails then AV can control the heartbeat as a backup at a slower rate. if both SA and AV node fail then Purkinje fibers can act as tertiary pacemaker but it beats very slowly
describe the events of the spread of excitation between cells in order
wave of excitation - depolarization of atria - atria contract as a unit - wave of excitation - depolarization of ventricles - ventricles contract as a unit
how is coordination of excitation possible
the presence of gap junctions allows for instant communication
describe intercalated disks
connections between adjacent myocardial cells (desmosomes link cells mechanically to resist stress, gap junctions link cells electrically)
where all are intercalated disks found
only in cardiac cells
name 5 steps of initiation and conduction of an impulse during heartbeat
AP initiated in SA node. Signals spread through atrial muscle. Signal travels to AV node, AV nodal delay. Atrioventricular bundle (bundle of His). Splits into left and right bundle branches. Purkinje fibers
what is timing of excitation from SA node to right and left atrium and AV node
they propagate simultaneously. It is very rapid
how long is AV nodal delay
0.1 msec so atria contract before the ventricles
what is the only electrical pathway between Atria and ventricles
AV node
what are 3 most important ions for cardiac muscles
potassium, sodium, and calcium ions
describe intracellular levels of important ions
Na low, Ca low, K high
describe extracellular levels of important ions
Na high, Ca high, K low
describe membrane permeability leading to depolarization
increased Na and Ca permeability makes membrane potential more positive leading to depolarization
describe membrane permeability leading to repolarization
increased K permeability makes membrane potential more negative leading to repolarization and hyperpolarization
what type of potential do autorhythmic cells have
pacemaker potential (unstable membrane potential) it is a slow depolarization
name channels involved in spontaneous depolarization in pacemaker cells
closing K channels. Na in and K out (funny channels): net slow depolarization. Ca channels in: further depolarization to threshold.
what happens when pacemaker cell reaches threshold
voltage gated fast Ca channels (L-type) in are opened. this leads to rapid depolarization (action potential)
what happens after action potential in pacemaker cells
Ca channels close, Open K channels (repolarization). Repolarization activates funny channels
describe stroke volume
amount of blood pushed by ventricle per beat.
define cardiac output
volume of blood pumped by each ventricle per minute
what is average CO
5 liters (per ventricle) per minute at rest
what is average blood volume
5.5 liters
whats possible CO for conditioned athlete during strenuous exercise
30-35 L/min
how is CO regulated
cardiac output is entirely determined by stroke volume and heart rate. regulate through changes in heart rate and stroke volume
describe extrinsic CO regulation
neural (autonomic system) and hormonal
describe intrinsic CO regulation
originates within the heart - autoregulation
how are parasympathetics transmitted to heart
through the vagus nerve (originating in medulla)
what do parasympathetics innervate
the pacemaker cells but not the contractile cells. So the SA and AV nodes are innervated
what determines heart rate
SA node firing frequency
what is SA node firing rate without extrinsic control
SA node intrinsic firing rate is 100 beats/min
describe the influences on the SA node
sympathetic input ups HR. parasympathetic input slows HR. at rest the parasympathetics dominate; HR around 70 bpm. during exercise/excitement sympathetic input increases and parasympathetic input decreases so HR rises. Epinephrine from adrenal gland has effects similar to sympathetics
describe pathway of sympathetic stimulation increases in HR
sympathetic nerves release norepinephrine - B1 adrenergic receptors in SA node - open more of “funny” and Ca channels so more Na and Ca flow into cell - spontaneous depolarization is faster (threshold is reached faster) - HR is increased
describe pathway of parasympathetic stimulation decreases in heart rate
vagus nerve releases acetylcholine - muscarinic cholinergic receptor in SA node - open more K channels and close Ca channels - decrease rate of spontaneous depolarization and hyperpolarize cell (slower to reach threshold) - heart rate is decreased
describe hormonal control of heart rate
most important is epinephrine released by adrenal medulla. Has same effect as sympathetic nervous system. increases action potential frequency at SA node. increases velocity of action potential conduction in muscle fibers
name 3 primary factors affecting stroke volume
- ventricular contractility: strength of cardiac muscle contraction 2. end-diastolic volume (preload): the volume of blood in the ventricles just before the contraction 3. afterload: arterial pressure against which the ventricles pump
describe influence of end-diastolic volume on stroke volume
increased EDV stretches muscle fibers. fibers are thus closer to optimal length. optimal length leads to greater strength of contraction. this results in increased stroke volume.
what is the significance of starling’s law
at any given heart rate an increase in venous return will automatically force an increase in cardiac output
what is the cardiac cycle
events associated with the flow of blood through the heart during a single complete heartbeat
name the two main periods of cardiac cycle
systole: ventricles contraction and diastole: ventricles relaxation
why do valves open
they open passively due to pressure gradients. AV valves open when atrial pressure is greater than ventricular pressure. semilunar valves open when ventricular pressure is greater than arterial pressure
describe phase 1 of cardiac cycle
ventricular filling: we start in middle of diastole. venous return, AV valves are open, blood moves from atria to ventricles, pulmonary and aortic valves are closed, passive filling until atria contract
describe phase 2 of cardiac cycle
isovolumetric contraction: this is start of systole. ventricles contracting causes increase in pressure. all 4 valves are closed. no blood entering or exiting ventricle
describe phase 3 of cardiac cycle
ventricular ejection. remainder of systole. pressure in ventricles exceeds pressure in arteries, semilunar valves open, blood exits ventricles (ejection), ventricular pressure falls below aortic pressure, semilunar valves close, end of systole
describe phase 4 of cardiac cycle
diastole starts. ventricles relax so pressure decreases, all 4 valves are closed, no blood entering or exiting ventricles, ends with AV valves opening
describe change in atrial and ventricular pressure for phase 1
ventricular filling. atrial pressure rises slowly with filling of blood, ventricular pressure (VP) stays low. small rise in VP at end due to atrial contraction
describe change in pressures in phase 2
isovolumetric contraction. rapid rise in VP, atrial pressure falls
describe change in pressures in phase 3
VP continues to rise and then starts to fall, atrial pressure falls further until late systole
describe pressure changes in phase 4
VP pressure falls rapidly to almost zero
describe aortic pressure (AP) in diastole (phases 4,1)
aortic valve closes, blood is moving from aorta to periphery, so pressure falls. lowest point in AP = diastolic pressure
describe aortic pressure (AP) in systole (phases 2,3)
aortic valve opens as soon as VP pressure exceeds AP. pressure rises rapidly with ejection. highest point in AP = systolic pressure. blood flow into aorta decreases, AP decreases. aortic valve closes, systole ends. closure of aortic valve causes slight increase in AP (dicrotic notch)
describe walls of aorta and large arteries
they have very elastic walls. act as pressure reservoir that stores energy during systole as elastic walls expand and releases energy during diastole as walls recoil inward.
what does aortic pressure do
maintains continuous blood flow through the entire cardiac cycle
what is end-diastolic volume (EDV)
volume of blood in ventricle at the end of diastole
what is end-systolic volume (ESV)
volume of blood in ventricle at the end of systole
what is stroke volume (SV)
volume of blood ejected from ventricle each cycle
what is normal stroke volume
SV = EDV - ESV. so SV = 130ml - 60ml = 70ml
what is ejection fraction (EF)
fraction of EDV ejected during heartbeat so EF = SV/EDV so EF = 70ml/130ml = 54% at rest
describe pressure-volume curve through 4 phases
phase 1: ventricular volume increases from 60mL to 130mL, small pressure increment with filling phase 2: volume is constant; pressure increases dramatically phase 3: volume decreases to 60mL during ejection; pressure rises, then starts falling phase 4: pressure falls rapidly; volume is constant
what is the soft lubb heart sound
it is the first sound of AV valves closing simultaneously
what is louder dupp heart sound
it is the second sound of semilunar valves closing simultaneously
