Chapter 19 Heart

cardiovascular system

heart and blood vessels

circulatory system

heart, blood vessels, and the blood

pulmonary and systemic circuit

what are the major divisions of circulatory system?

pulmonary circuit

right side of the heart that carries blood to the lungs for gas exchange and back to the heart

systemic circuit

left side of heart that supplies oxygenated blood to all tissues of the body and returns it to the heart

left side of the heart

which side of the heart does fully oxygenated blood arrive to from the lungs via the pulmonary veins? blood is sent to all organs of the body via the aorta on this side as well

right side of heart

what side of the heart does oxygen-poor blood from the inferior and superior vena cava arrive to? blood is sent to the lungs via the pulmonary trunk on this side as well

in the mediastinum, between the lungs

where is the heart located?

base

wide, superior portion of heart, large vessels attach here

apex

tapered inferior end of the heart, tilts to the left

pericardium

double walled sac that encloses the heart; it allows heart to beat without friction, provides room to expand, yet resists excessive expansion

parietal pericardium

pericardial sac; superficial fibrous layer of connective tissue; deep, thin serous layer

visceral pericardium (epicardium)

serous membrane covering heart

pericarditis

painful inflammation of the membranes

slippery fluid (gap between parietal and visceral is filled with fluid) and pericardium

what allows heart to move freely around cavity?

epicardium, myocardium, and endocardium

what are the three layers of the heart wall?

epicardium (visceral pericardium)

serous membrane covering heart; adipose in thick layer in some places; coronary blood vessels travel through this layer (outermost edge of heart itself)

endocardium

smooth inner lining of heart and blood vessels; covers the valve surfaces and is continuous with endothelium of blood vessels; extremely slippery so platelets don’t stick

myocardium

layer of cardiac muscle that is proportional to the work load (the muscle spirals around the heart which produces a wringing motion)

provides structural support and attachment for cardiac muscle and anchor for valve tissue; electrical insulation between atria and ventricles; important in timing and coordination of contractile activity (myocardium has electrically active cells)

explain the fibrous skeleton the heart (it is in the myocardium and is a framework of collagenous and elastic fibers)

right and left atria

the two superior chambers; receive blood returning to the heart; have auricles which enlarge the chamber

right and left ventricles

two inferior chambers; pump blood into the arteries

atrioventricular sulcus

separates atria and ventricles

interventricular sulcus

overlies the interventricular septum that divides the right ventricle from the left

coronary arteries (filled with blood vessels and adipose tissue which makes it less likely to pinch the blood vessels)

what does the sulci in the chambers contain?

interatrial septum

the wall that separates atria

pectinate muscles

internal ridges of myocardium in right atrium and both auricles; help direct blood flow

interventricular septum

muscular wall that separates ventricles

trabeculae carneae

internal ridges in both ventricles; may prevent ventricle walls from sticking together after contraction due to hydrogen bonding

one way flow of blood through the heart

what do valves ensure?

atrioventricular valves

control blood flow between atria and ventricles

right AV valve

has three cusps (tricuspid valve)

left AV valve

has two cusps (bicuspid valve)

chordae tendineae

cords that connect AV valves to papillary muscles on floor of ventricles; prevents AV valves from flipping or bulging into atria when ventricles contract

semilunar valves

control flow into great arteries; open and close because of blood flow and pressure

pulmonary semilunar valve

valve in the opening between the right ventricle and the pulmonary trunk

aortic semilunar valve

in opening between left ventricle and aorta

pressure drops inside the ventricles; the semilunar valves close as blood attempts to back up into the ventricles from the vessels; AV valves open; blood flows from atria to ventricles

what happens when the ventricles relax?

AV valves close as blood attempts to back up into the atria; pressure rises inside of the ventricles; semilunar valves open and blood flows into great vessels

what happens when ventricles contract?

5%

how much blood pumped by the heart is pumped to the heart itself through the coronary circulation to sustain its strenuous workload? (it needs abundant O2 and nutrients)

left and right coronary artery

what branches off the ascending aorta?

angina pectoris

chest pain from partial obstruction of coronary blood flow

obstruction partially blocks blood flow; pain is caused by ischemia of cardiac muscle; myocardium shifts to anaerobic fermentation, producing lactate and thus stimulating pain

what happens in angina pectoris?

myocardial infarction

sudden death of a patch of myocardium resulting from long-term obstruction of coronary circulation (responsible for about 27% of deaths in the US)

cardiomyocytes

striated, short, thick, branched cells, one central nucleus surrounded by light-staining mass of glycogen; have relatively high force and high endurance; have striations and electrical synapses

fibrosis (scarring)

repair of damage to cardiac muscle is almost entirely what?

intercalated discs

join cardiomyocytes end to end with 3 features: interdigitating folds, mechanical junctions, and electrical junctions

interdigitating folds

folds interlock with each other, and increase surface area of contact

mechanical junctions

these tightly join cardiomyocytes; most common type of junction; have fascia adherens

fascia adherens

broad band in which the actin of the thin myofilaments is anchored to the plasma membrane; each cell is linked to the next via transmembrane proteins

desmosomes

mechanical linkages that prevent contracting cardiomyocytes from being pulled apart from each other; they go through intercalated discs

electrical (gap) junctions

allow ions to flow between cells; can stimulate neighbors; allows entire myocardium of either two atria or two ventricles act like a single, unified cell

aerobic

cardiac muscle depends almost exclusively on what type of respiration to make ATP (it is rich in myoglobin and glycogen and has huge mitochondria)

fatty acids, glucose, ketones, lactate, amino acids

what organic fuels does cardiac muscle use? (adaptable to different fuel sources but more vulnerable to oxygen deficiency)

makes little use of anaerobic fermentation or oxygen debt mechanisms; it is also supplied directly from the left and right coronary arteries

why is cardiac muscle fatigue resistant?

heart has an internal pacemaker and nerve-like conduction pathways through the myocardium

what helps coordinate heartbeat?

it is modified cardiomyocytes; the pacemaker initiates each heartbeat and determines heart rate; it is in the right atrium near the base of the superior vena cava

describe form and function of the sinoatrial node

the signals spread throughout the atria

what happens after the sinoatrial node initiates the heart beat and determines the heart rate?

SA node spontaneously depolarizes with the highest frequency so it sets the temp for the rest of the heart but the atrioventricular node depolarizes at a slower frequency, so it pauses the signal before it travels down to the ventricles from the atria

difference between the sinoatrial node and the atrioventricular node?

atrioventricular node

located near the right AV valve at the lower end of the interatrial septum; it is the electrical gateway to the ventricles; has a fibrous skeleton (insulator prevents currents from getting to ventricles by any other route)

atrioventricular bundle (bundle of His)

this forks into right and left bundle branches; the branches pass through the interventricular septum toward the apex

subendothelial conducting networks (purjinke fibers)

nerve-like processes that spread throughout the ventricular myocardium; cardiomyocytes then pass signal from cell to cell through gap junctions

sympathetic nerves

what nerves increase heart rate and contraction strength?

parasympathetic nerves

what nerves slow heart rate?

systole

contraction

diastole

relaxation

sinus rhythm

normal heartbeat triggered by the SA node

no; starts at -60 mV and drifts upward due to slow Na+ inflow; this gradual depolarization is called pacemaker potential; when it reaches the threshold of -40 mV, the voltage-gated fast Ca2+ and Na+ channels open and faster depolarization occurs peaking at 0 mV; K+ channels then open and K+ leaves the cell causing repolarization; once the K+ channels close the pacemaker potential starts over

does the SA node have a stable resting membrane potential?

pacemaker potential

gradual depolarization that occurs because the SA node does not have a stable resting membrane potential

heartbeat

what does the SA node set off when it fires?

because the vagus nerve downregulates the SA node

why is our resting heart rate a little lower than what the SA node would set the pace to be?

stimulates two atria to contract almost simultaneously

what does a signal from the SA node do?

the signal slows down through the AV node; there are thin cardiomyocytes with fewer gap junctions; it delays the signal 100 ms which allows the ventricles time to fill

what happens when the signal started with the sinoatrial node reaches the AV node?

through the AV bundle and subendothelial network (the entire ventricular myocardium depolarizes and contracts in near unison)

where do signals that started at the SA node travel very quickly through?

from the apex of the heart (the spiral arrangement of myocardium twists ventricles slightly like someone wringing a towel)

where does ventricular systole progress up from?

plateau phase

calcium ions leak across membrane and into cell and slowly make it more positive counteracting potassium ions going out and leading to a gradual decline in voltage

electrocardiogram

composite of all action potentials of nodal and myocardial cells detected, amplified and recorded by electrodes on arms, legs, and chest

p wave

corresponds to beginning of cycle; SA node fires, atria depolarize and contract; atrial systole begins 100 ms after SA signal

QRS complex

ventricular depolarization; complex shape of spike due to different thickness and shape of the two ventricles (ventricles depolarize and contract)

ST segment

ventricular systole; corresponds to plateau in myocardial action potential

T wave

ventricular repolarization and relaxation

cardiac cycle

one complete contraction and relaxation of all four chambers of the heart

pressure causes flow and resistance opposes it

what two main variables govern fluid movement?

there has to be a pressure gradient (pressure difference)

what condition does there have to be for fluid to flow?

from high pressure to low pressure point

how does fluid flow?

with a sphygmomanometer

how is blood pressure measured?

when ventricle relaxes and expands, its internal pressure falls; if the left AV valve is open, blood flows into left ventricle; when ventricle contracts, internal pressure rises; AV valves close, and the aortic valve is pushed open and blood flows into aorta from the left ventricle

what events occur on the left side of the heart in relation to pressure gradients and flow?

close the semilumar valve

blood flows backwards just long enough to do what?

allows for pressure gradients which determines the direction of blood flow

what does a delay at the AV node allow for in relation to pressure?

AV valves are limp when ventricles are relaxed; semilunar valves are under pressure from blood in vessels when ventricles are relaxed

opening and closing of valves are governed by what pressure changes?

auscultation

listening to sounds made by body

lubb

which heart sound is the first one that is louder and longer and occurs with the closure of the AV valves, turbulence in the bloodstream, and movements of the heart wall

dupp

which heart sound is the second one that is softer and sharper and occurs with the closure of the semilunar valves, turbulence in the bloodstream, and movements of the heart wall

whooshing sound (S3)

which heart sound is rarely heard in people over 30 and is due to the opening of the left AV valve and the filling of the left ventricle

1) ventricular filling 2) isovolumetric contraction 3) ventricular ejection 4) isovolumetric relaxation

what are the four phases of the cardiac cycle?

AV valves open; ventricles expand and their pressure drops below that of the atria; the end diastolic volume is achieved in each ventricle

what occurs during ventricular filling (during diastole)?

ventricles begin to contract but do not eject blood; when the ventricles contract, pressure skyrockets and volume remains constant

what occurs during isovolumetric contraction (during systole)?

ventricles begin to contract and do eject blood now (ventricles should eject the same amount of blood)

what occurs during ventricular ejection (during systole)?

stroke volume

amount of blood ventricle releases

ejection fraction

stroke volume/end-diastolic volume