Cardiovascular Physiology

What is the pathway of conducting cells through the heart

SA node, AV node, AV bundle branches, Purkinje fibers

What type of action potential and channels are found in conducting cells?

“pacemaker potentials” that have voltage-gated channels

What is the order in which voltage-gated ion channels open. during electrical stimulation of cardiac muscle?

HCN sodium channels, calcium channels, potassium channels

What occurs during a P wave?

atrial depolarization

What occurs during the QRS complex?

ventricle depolarization

What occurs during a T wave?

ventricle repolarization

What type of neurotransmitter and receptor does the SNS use to increase heart rate?

norepinephrine and beta receptors

How does the SNS increase the rate of auto stimulation?

by increasing the number of open HCN channels

How does parasympathetic activity decrease the rate of auto stimulation?

by opening potassium channels

What type of neurotransmitter and receptor does the PNS use to decrease heart rate?

acetylcholine and muscarinic receptor

What is the direction of conduction in cardiac muscle fibers?

from one contractile cell to the next

Action potential of a contractile cell

sodium depolarizes cell to around +20 mV and then channels close

What happens after sodium channels close in contractile cells?

both calcium and potassium channels open leading to a slow depolarization

What occurs at the plateau of a contractile cell action potential?

calcium channels close but potassium channels remain open

Why do contractile cells in the heart have a long resting period?

so it is impossible to reach tetanus

How do contractile cells differ from conducting cells?

they have calcium-gated calcium channels in the SR

What is the first event of the cardiac cycle?

Late diastole, the heart is relaxed and 70% full

What occurs after late diastole in the cardiac cycle?

atrial systole adds more blood to ventricles

What even comes after the atrial systole?

isovolumetirc ventricular contraction, AV valves close

What event comes right after ventricular contraction?

ventricular ejection

What is the last event of the cardiac cycle?

isovolumetric ventricular relaxation (early diastole), semilunar valve closes

What is the function of AV valves?

they allow atria to pump blood into the ventricles

What is the function of semilunar valves?

they allow blood to be ejected from the ventricles

What causes the “lub” sound in the “lub-dub” and when does it occur?

the AV valves closing during ventricular contraction

What causes the “dub” sound in the “lub-dub” and when does it occur?

the semilunar valves closing during isovolumetric ventricular relaxation

What are two disorders that cause heart murmurs?

bicuspid valve prolapse and stenosis

Bicuspid valve prolapse

mitral valve is being pushed up too far and allows back flow of blood

Stenosis

the valve is inflamed and can’t close completely

What is the equation for cardiac output?

cardiac output = stroke volume x heart rate

What is the equation for stroke volume?

stroke volume = EDV - ESV

What is the EDV value?

how much blood was in the ventricles before ejection

What is the ESV value?

how much blood was left over after ejection

When is EDV measured?

before ventricular ejection

What is venous return?

how quickly blood is returning to the heart via the vena cava

What are two factors that affect EDV and venous return?

muscular and respiratory pumps

When is ESV measured?

after ventricular ejection

How is ESV altered?

by increasing the contractile force of the heart through sympathetic activity

What is the relation between EDV and ESV?

when EDV increases, ESV decreases

What are the effects of hypertension (high blood pressure)

a higher ESV and lower cardiac output

What are the effects of long term cardiovascular exercise on cardiac output?

the heart gets physically stronger

Which action leads to the closure of the right atrioventricular valve?

contraction of the right ventricle

Sympathetic control of the SA node occurs by:

increasing the number of sodium and calcium channels open at rest

An autorhythmic heart cell is one in which:

action potentials fire spontaneously

Which of the following contributes to the plateau in a cardiac contractile cell?

  the opening of slow voltage-gated calcium channels

For the repolarization phase of an SA nodal cell action potential,

calcium channels close and potassium channels open

An increase in the venous return could lead to an increase in which of the following:

stroke volume, cardiac output, and EDV

Just prior to atrial contraction,

all four chambers are at rest and semilunar valves are closed

Acetylcholine on the SA node would cause which of the following?

increased outflow of potassium

During ventricular systole late phase:

the semilunar valves open

During a cardiac cycle, how many of the four chambers contract at any one time?

two

If there was an increase in heart rate, what may occur?

an increase in cardiac output