Chapter 14: The Cardiovascular System: The Heart

Bios 213

heart -

hollow organ about the size of a fist located in the thoracic cavity

With each beat, the heart pumps blood into two closed circuits:

pulmonary circulation and systemic circulation

pulmonary circulation - 

blood vessels that carry blood from the right side of the heart to the alveoli (air sacs) of the lungs and then back to the left side of the heart

systemic circulation - 

blood vessels that carry blood from the left side of the heart to all organs and tissues of the body (except the alveoli) and then back to the right side of the heart

arteries -

large blood vessels that carry blood away from the heart

arterioles -

smaller vessels branched from arteries

capillaries -

smaller vessels branched from arterioles

venules -

large vessels that take blood from the capillaries

veins -

larger vessels derived from venules that carry blood to the heart

pericardium -

membranous sac that encloses the heart and confines it to its position in the thoracic cavity while allowing sufficient freedom of movement for vigorous and rapid contraction

epicardium -

outer layer; visceral layer of the pericardium, consisting of epithelium and connective tissue

myocardium -

middle layer that forms the bulk of the heart wall, consisting of cardiac muscle and is responsible for the pumping action of the heart

endocardium -

inner layer; thin layer of epithelium that lines the chambers of the heart and covers heart valves; continuous with epithelium cells

endothelial cells -

epithelial cells that line the heart, bloods vessels, and lymphatic vessels

parietal pericardium -

anchors the heart to diaphragm

visceral pericardium -

surface of the heart

pericardial cavity -

contains serous fluid to cushion the heart and reduce friction

4 chambers of the heart:

right atrium, right ventricle, left atrium, left ventricle

right side of the heart:

pump that carries deoxygenated blood and serves pulmonary circuit

left side of the heart:

pump that carries oxygenated blood and serves systemic circuit

Great vessels that supply blood to the right atria:

superior and inferior vena cava

Great vessels that supply the left atria:

right and left pulmonary veins

Great vessels leading blood away from the right ventricle:

pulmonary trunk (right and left pulmonary arteries)

Great vessels leading blood away from the left ventricle:

aorta

Atrioventricular and semilunar valves ensure:

one way blood flow

atrioventricular valves:

tricuspid and bicuspid

tricuspid -

prevents back flow of the right atrium from the right ventricle

bicuspid -

prevents back flow of the left atrium from the left ventricle

semilunar valves:

pulmonary and aortic

pulmonary valve -

prevents back flow from the right ventricle to the pulmonary artery

aortic valve -

prevents back flow from the left ventricle to the aorta

valves have a:

fibrous skeleton

fibrous skeleton -

connective tissue that surrounds the valves of the heart, fuse with one another, and merge with the interventricular septum; prevents valves from stretching

cardiac muscle tissue is connected via:

intercalated disks

intercalated disks -

irregular transverse thickenings of the sarcolemma

Interconnected cells of cardiac muscle act as a:

functional syncytium

functional syncytium -

mass of interconnected muscle fibers act as a single, coordinated unit

All cardiac muscle cells _____ and _____ at the same time

depolarize; contract

intercalated disks consist of:

desmosomes and gap junctions

desmosomes -

mechanically bind cardiac muscle fibers together; resistant to mechanical stress

gap junctions -

electrically couple cardiac muscle fibers to each other; allows potentials to conduct from one muscle fiber to its neighbors

the structure of cardia muscle shares properties with both _____ and _____ muscle

skeletal; smooth

Two types of cells in cardiac muscle:

autorhythmic (conductile) cells and contractile cells

the conduction system ensures:

coordinated contraction

the conduction system has a collection of modified muscle cells:

pacemaker and autorhythmic cells

the conduction system initiates:

action potentials

the conduction system conducts:

action potentials to other heart cells via gap channels

the conduction system does not:

contribute significantly to contractile forces

The conduction system starts at the:

superior wall of the right atrium and continues through the apex of the heart and myocardium of the ventricles

Conduction system structures include:

Sinoatrial (SA) node, Artioventricular (AV) node, Atrioventricular (AV) bundle (Bundle of HIS), right and left bundle branches, and purkinje fibers

pressure atria > pressure ventricle =

AV valves open

pressure atria < pressure ventricle =

AV valves closed

pressure ventricle < pressure of aorta or pulmonary trunk

SL valves closed

pressure ventricle > pressure of aorta or pulmonary trunk

SL valves open

Sinoatrial (SA) node -

primary pacemaker of the heart; sends impulses to AV nodes

atrioventricular (AV) node -

receives signals from the SA node and passes them to the bundle of His; secondary pacemaker

atrioventricular (AV) bundle (Bundle of His) -

receives AP from AV node and transmits signal to the ventricles

Right and left bundle branches -

two crucial pathways that carry signals from the bundle of His to the ventricles, causing them to contract

Purkinje fibers -

branch from the right and left bundle branches located in the ventricular wall that rapidly transmit electrical impulses from the bundle branches that cause the ventricular walls to contract

parasympathetic neurons secrete ACh →

slows the HR

Contractile cells produce:

contraction force of the heart

contractile cells don’t:

spontaneously depolarize

contractile cell produce action potentials in response to signals from:

nodal cells

cardiac muscle cells have a resting potential of:

-85mV

contractile cells are depolarized to threshold by:

AP from the SA node

In excitation contraction coupling, voltage-gated Ca²⁺ channels ___ coupled to calcium release channels in sarcoplasmic reticulum

are not

entering calcium triggers:

calcium-induced calcium release channels in SR

____ of calcium comes from SR

90%

____ of calcium comes from the ECF

10%

a refractory period in cardiac muscles lasts:

200msec

Because the atria and ventricles contract as single units, they cannot:

sustain a contraction

Because the AP of cardiac cells is long, they also have:

long refractory periods before they contract again

refractory periods prevent:

tetnus and fatigue

refractory periods help:

heart fill with blood

electrocardiogram -

measures AP in contractile cells and records electrical signals of the heart

electrocardiogram waves and intervals:

P wave, P-Q interval, QRS wave, S-T segment, T wave

P wave -

atrial depolarization

P-Q interval -

atrial systole

QRS wave -

ventricular depolarization

S-T segment -

plateau phase, ventricular systole

T wave -

ventricular repolarization

the cardiac cycle -

all the events associated with one heartbeat

systole -

contraction phase

diastole -

relaxation phase

The cardiac cycle has 5 phases:

passive ventricle filling, artial contraction, isovolumetric ventricular contraction, ventricular ejection, isovolumetric ventricular relaxtion

passive ventricular filling -

blood passively filling ventricles

In passive ventricular filling, AV valves are ____; SL valves are ____

open; shut

In passive ventricular filling:

all four chambers relax

blood from the superior and inferior vena cava (+sinusoids) passively fill:

right atrium → right ventricle

blood from pulmonary veins passivly fill:

left atrium → left ventricle

Atrial systole -

contraction of atrium

depolarization of SA node causes ____, which causes ____

atrial depolarization; atrial systole

Atrial systole pushes ___ into ventricles

~25mL

~ 130mL =

end-diastolic volume

end-diastolic volume -

the total volume of blood in the left or right ventricle at the end of diastole (relaxation), right before the heart contracts

end of atrial systole =

end of ventricle diastole

In atrial systole, AV valves are ____; SL valves are ____

open; closed

In isovolumetric contraction, AV valves are ____; SL valves are ____

closed; closed

isovolumetric contraction is known as:

early ventricular systole

ventricular depolarization leads to:

isovolumetric contraction