Chapter 13

Blood flows from atria into

ventricles thru 1-way

atrioventricular (AV) valves

Between right atrium and

ventricle

tricuspid valve

Between left atrium and

ventricle

bicuspid or mitral

valve

Opening and closing of valves results from

pressure differences

High pressure of ventricular contraction is

prevented from everting AV valves by

contraction of papillary muscles which are

connected to AVs by chordae tendinea

During ventricular contraction

blood is pumped through

aortic and pulmonary

semilunar valves

• Close during relaxation

Systole

refers to contraction phase

Diastole

refers to relaxation phase

• Both atria contract simultaneously; ventricles

follow 0.1-0.2 sec later

End-diastolic volume

volume of blood in

ventricles at end of diastole

Stroke volume

amount of blood ejected from

ventricles during systole

End-systolic volume

amount of blood left in

ventricles at end of systole

As ventricles contract, pressure rises, closing AV valves

Called isovolumetric contraction because all

valves are closed

When pressure in ventricles exceeds that in aorta

semilunar valves open and ejection begins

As pressure in ventricle falls below that in aorta

back

pressure closes semilunar valves.

All valves are closed and ventricles undergo

isovolumetric relaxation

When pressure in ventricles falls below atria

AVs open

and ventricles fill

Atrial systole

sends its blood into ventricles

Heart sounds

Closing of AV and semilunar valves produces

sounds that can be heard thru stethoscope

Lub (1st sound/S1)

produced by closing of AV

valves

Dub (2nd sound/S2)

produced by closing of

semilunar valves

Heart Murmurs

Are abnormal sounds produced by abnormal

patterns of blood flow in heart

• Many caused by defective heart valves

• Can be of congenital origin

• In rheumatic fever, damage can be from

antibodies made in response to strep infection

• Myocardial cells are short, branched, and

interconnected by gap junctions

Entire muscle that forms a chamber is called a

myocardium

• Because action potentials originating in any cell

are transmitted to all others

• Chambers separated by nonconductive tissue

In normal heart,

sinoatrial (SA) node

functions as

pacemaker

Depolarizes

spontaneously to

threshold

(= pacemaker

potential)

Pacemaker

potentials

only

happen in the cells

involved in the

cardiac conduction

system, or

conductive cells.

Sinoatrial node pacemaker

• Membrane voltage begins

at -60mV

gradually

depolarizes to -40

threshold

Spontaneous

depolarization is caused

by Na+ flowing

through

channel that opens when

hyperpolarized (HCN

channel)

At threshold VG Ca2+

channels open,

creating upstroke

and contraction

Repolarization

via

opening of VG K+

channels

contractile fibers

Myocardial action potentials

happen in the cardiac muscle

fibers that contract

Upstroke occurs

as

VG Na+ channels open

MP rapidly goes to 15 mV and

declines to 0 - -20 mV and stays

there for 200-300 msec

plateau

phase

Plateau results from

balance

between slow Ca2+ influx and

K+ efflux

Repolarization

due to opening of

extra K+ channels

Electrocardiogram (ECG

A recording of electrical

activity of heart

conducted through ions

in body to surface

arteriosclerosis

hardening of

arteries)

• Accounts for 50% of deaths

in US

Localized plaques reduce flow

in an artery

And act as sites for

thrombus (stationary blood

clots)

Plaques begin at sites

of damage to

endothelium

e.g., from

hypertension,

smoking, high

cholesterol, or

diabetes