Vander's Cardiac Physiology

WITTF: the percentage of blood volume that is erythrocytes

hematocrit

When blood is centrifuged, what are the layers formed (from top down)?

plasma, platelets and leukocytes, erythrocytes

What is the normal hematocrit of a healthy male?

45%

What is the normal hematocrit of a healthy female?

42%

Estimated number of capillaries?

10 billion

WITTF: the collective term for arterioles, capillaries, and venules

microcirculation

What group of organs receives most of the blood flow in the body at rest?

abdominal organs

What organs have a portal system?

liver (hepatic portal system) and pituitary (hypophyseal portal system)

WITTF: the pressure exerted by any fluid

hydrostatic pressure

Flow rate is calculated by:

F = change in P / R

The relationship between viscosity and resistance is:

directly proportional

What can cause an increase in the viscosity of blood?

an increase in hematocrit

What can cause an increase in hematocrit?

extreme dehydration

What are the three determinants of resistance?

blood viscosity, length of blood vessel, radii of blood vessel

WITTF: the fibrous sac enclosing the heart

pericardium

WITTF: the inner layer of the pericardium closely attached to the heart

epicardium

WITTF: the walls of the heart primarily composed of cardiac muscles

myocardium

WITTF: the lining of the inner surface of the heart and blood vessels

endothelium

WITTF: a muscular wall that separates the two ventricles

interventricular septum

WITTF: the right atrioventricular valve

tricuspid valve

Why is the tricuspid valve called so?

it has three fibrous flaps

How many flaps does the mitral valve have?

two

What is another name for the mitral valve?

bicuspid valve

t/f: the opening of the AV valves is a passive process achieved by pressure differences

true

WITTF: condition in which AV valves are pushed up into the atria

prolapse

WITTF: muscular projections that the AV valves are fastened onto to prevent prolapse

papillary muscles

WITTF: fibrous strands that connect AV valves to papillary muscles

chordae tendineae

t/f: the semilunar valves are open and closed actively

false

t/f: a little blood is ejected back into the veins (vena cava and pulmonary vein) during atrial systole

true

WITTF: system of ~1% of cardiac cells that initiates the heartbeat and helps spread the impulse rapidly throughout the heart

conducting system

Cells where in the heart secrete a family of peptide hormones known as atrial natriuretic peptide?

atria

What nerve provide parasympathetic stimulation to the heart?

vagus nerve

What do sympathetic postganglionic fibers release to the heart?

norepinephrine

Where do sympathetic postganglionic fibers terminate in the heart?

everywhere

What do parasympathetic postganglionic fibers release to the heart?

acetylcholine

Where do parasympathetic postganglionic fibers terminate in the heart?

atria

What type of receptors are the norepinephrine/epinephrine receptors of the heart?

beta adrenergic

WITTF: effects that change heart rate

chronotropic

What type of receptors are the acetylcholine receptors of the heart?

muscarinic

WITTF: effects that cause a change in conduction velocity in the AV node and thus the speed of electrical conduction in the heart

dromotropic

WITTF: effects that cause a change in the force or energy of muscle contractions

inotropic

WITTF: effects that cause a change the rate in myocardial relaxation

lusitropic

An increase in the cytoplasmic calcium in cardiac myocytes leads to what?

increased inotropy but decreased lusitropy

Is dopamine a positive or negative chronotrope?

positive

WITTF: primary active transporter that pumps calcium from cytoplasm of myocyte to sarco-endoplasmic reticulum

SERCA

WITTF: arteries supplying the myocardium

coronary arteries

Where do coronary arteries exit from?

the first part of the aorta

WITTF: a single large vein that all the cardiac veins drain into

coronary sinus

Does coronary blood flow enter the vena cava?

no

Where does the initial depolarization occur during a heartbeat?

sinoatrial node

Where is the sinoatrial node located?

right atrium near superior vena cava

Where is the atrioventricular node located?

base of right atrium

How long does it take action potentials to be conducted through the AV node?

0.1 seconds

What is the point of delaying the action potential at the AV node?

Allows atrial contraction to be completed before ventricular excitation occurs

WITTF: conducting-system fibers that is the only electrical connection between the atria and ventricles

bundle of His

Within the interventricular septum, what does the bundle of His divide into?

left and right bundle branches

What do the left and right bundle branches come into contact with?

Purkinje fibers

WITTF: large conducting cells that rapidly distribute the impulse throughout the ventricles

Purkinje fibers

What do Purkinje fibers come in contact with?

ventricular myocardial cells

Where does depolarization of the ventricles begin?

at the apex

Why is resting membrane potential closer to the equilibrium for potassium (-90mV) than for sodium (+62mV) it's -> (-60mV)?

cell membrane is more permeable to potassium than to sodium

WITTF: calcium channels that open slowly compared to sodium channels and remain open for a prolonged period of time

L-type calcium channels

What keeps the plasma membrane depolarized at a plateau value (~0mV)?

opening of L-type calcium channels that balances the outflow of potassium ions from the cell

When does repolarization occur again in myocytes?

calcium channels inactivate and potassium exits the cell

Is the plateau phase in the action potential of atrial cells longer or shorter than that of ventricular cells?

shorter

WITTF: the gradual depolarization in conducting system cells

pacemaker potential

WITTF: sodium channels in pacemaker cells that open when membrane potential is at negative values

F-type sodium channels

WITTF: calcium channel in pacemaker cells that open briefly as a final depolarizing boost to the pacemaker potential after the F-type sodium channels

T-type calcium channels

WITTF: the capacity for spontaneous, rhythmical self-excitation

automaticity

What provides the SA node with automaticity?

pacemaker potential

WITTF: other cells in the conducting system besides the SA node that produce their own action potentials with automaticity

ectopic pacemakers

What happens if the AV node fails?

autorhythmic cells in the bundle of His or Purkinje fibers begin to initiate excitement at their own inherent rate

What is the permanent treatment for all AV conduction disorders?

implantation of an artificial pacemaker that electrically stimulates the ventricles at a regular rate

t/f: atrial systole is not essential unless there is strenuous exercise

true

WITTF: the primary tool for evaluating the electrical events within the heart

electrocardiogram (ECG)

What event does the P wave correspond with?

atrial depolarization

What event does the QRS complex correspond with?

ventricular depolarization

Why is the QRS complex so complex?

the paths taken by the waves of deflection through the thick ventricular walls differ from instant to instant

What event does the T wave correspond with?

ventricular repolarization

Why is atrial repolarization not evident in the ECG?

it occurs at the same time as the QRS complex

WITTF: typical clinical ECGs with multiple combinations of recording locations on the limb and chest

ECG leads

An ECG is not what?

a direct record of changes in membrane potential across individual cardiac cells

What does an ECG measure?

the currents generated in the extracellular fluid of many cardiac cells

What type of heart defects can a ECG not detect?

mechanical defects

What is the order of electrical events for a partial/complete atrioventricular block? Why?

PQRSTP; P wave still occurs but signal cannot reach ventricles

What happens when the current through voltage-gated potassium channels is delayed and reduced?

the T wave is delayed because ventricular repolarization takes longer

What does the entrance of small amounts of calcium ions from L-type calcium channels trigger?

further release of large amounts of calcium from ryanodine receptors in the sarcoplasmic reticulum membrane

What receptors in the sarcoplasmic reticulum in cardiac muscle cells release large amounts of calcium?

ryanodine receptors

What pumps return calcium to the extracellular fluid and cytoplasm?

Ca2+-ATPase pumps, Na+/Ca2+ cotransporters

t/f: the strength of contraction in cardiac muscle can be altered by the amount of calcium released

true

Why can't the heart generate tetanic contractions?

a long absolute refractory period

What causes a long refractory period?

inactivation of sodium channels

How long does each cardiac cycle approximately last?

0.8 sec

How many secs of the cardiac cycle is systole?

0.3

How many secs of the cardiac cycle is diastole?

0.5

WITTF: the first part of systole in which the ventricles contract but all the valves are closed, so no blood is ejected

isovolumetric ventricular contraction

In isovolumetric ventricular contraction, the muscle develops tension, but does not _________

shorten

WITTF: the volume of blood ejected from each ventricle during systole

stroke volume

WITTF: what happens when the pressure in the ventricles exceeds that of aorta and pulmonary trunk after isovolumetric ventricular contraction

ventricular ejection

WITTF: the first half of diastole, where the ventricles relax and the AV and semilunar valves close

isovolumetric ventricular relaxation