Chapter 12 - Cardiovascular System PART 1

The inability of the heart to generate tetanic contractions is the result of the long ___________ ____________ ____________

absolute refractory period

sinonatrial node depolarization generates:

depolarization generates the action potential that leads to depolarization of all other cardiac muscle cells.

Nutrients and metabolic end products move between capillary blood and the interstitial fluid by

diffusion

Flow rate is ____________ to the pressure difference between two points

directly proportional

Chordae tendineae

fibrous strands of the AV valves

P wave of an ECG

first deflection, shows current flow during atrial depolarization.

Blood is composed of

formed elements (cells and cell fragments) suspended in plasma

The semilunar valves allow blood to flow into the arteries during

ventricular contraction

The semilunar valves prevent blood from moving in the opposite direction during

ventricular relaxation

Approximately ________% of cardiac cells do not function in contraction but have specialized features that are essential for normal heart excitation

1%. This is why its a conducting system

reasons for continued depolarization (plateau) in cardiac muscle

1) K+ permeability declines below the resting value due to the closure of the K+ channels that were open in the resting state, and 2) a large increase in the cell membrane permeability to Ca2+ occurs.

three ion channel mechanisms that contribute to pacemaker potential

1) progressive reduction in K+ permeability 2) "funny" F-type channels: cation channels that open when the membrane potential is negative 3) T-type Ca channels- opens briefly but contributes inward Ca2+ current and an important final depolarizing boost to the pacemaker potential

Epicardium

2nd layer

T wave of an ECG

3rd deflection, shows ventricular repolarization

Myocardium

3rd layer, muscle wall of the heart

repolarization in nodal cells

As in cardiac muscle cells, the long-lasting L-type Ca2+ channels prolong the nodal action potential, but eventually they close and K+ channels open and the membrane is repolarized

2nd step of excitation contraction coupling in cardiac muscle cells

Ca+ activation of thin filaments and cross-bridge cycling then lead to generation of force, just as in skeletal muscle

3rd step of excitation contraction coupling in cardiac muscle cells

Contraction ends when Ca2+ is returned to the sarcoplasmic reticulum and extracellular fluid by Ca2+-ATPase pumps and Na+/Ca2+ countertransporters.

why is it a good thing that cardiac muscle cannot undergo contraction summation?

If a prolonged, tetanic contraction were to occur in the heart, it would cease to function as a pump because the ventricles can only adequately fill with blood while they are relaxed

Units for blood flow

L/min

L-type calcium channels

Slow, long acting channels that open during cardiac depolarization AKA DHP channels

how do L-type Calcium channels cause the plateau phase

The flow of positive calcium ions into the cell just balances the flow of positive potassium ions out of the cell and keeps the membrane depolarized at the plateau value.

internodal pathways

The action potential is conducted relatively rapidly from the SA node to the AV node through internodal pathways

3 main parts of the cardiovascular system

The heart (a pump), Blood vessels (interconnected tubes), Blood (fluid connective tissue)

atrioventricular (AV) node

The link between atrial depolarization and ventricular depolarization is a portion of the conducting system

Pulmonary valve

The openings of the right ventricle into the pulmonary trunk

Bulk flow

The rapid flow of blood throughout the body is produced by pressures created by the pumping action of the hear. All constituents of the blood move together

1st step of excitation contraction coupling in cardiac muscle cells

The small amount of extracellular Ca2+ entering through L-type Ca2+ channels during the plateau of the action potential triggers the release of a larger quantity of Ca2+ from the ryanodine receptors in the sarcoplasmic reticulum membrane.

Difference between skeletal and cardiac muscle contraction

Unlike skeletal muscle cells, which can be rested for prolonged periods and only a fraction of which are activated in a given muscle during most contractions, every heart cell contracts with every beat of the heart

Venomous pulse

a little blood is ejected back into the veins, often seen in the neck veins when the atria are contracting

bundle of his

a bundle of modified heart muscle that transmits the cardiac impulse from the atrioventricular node to the ventricles causing them to contract

Once the pacemaker mechanisms have brought a nodal cell to threshold, what can occur?

an action potential

Coronary arteries

arteries supplying the myocardium

Efficient pumping of blood requires that the _____________ to contract first, followed almost immediately by the _______________

atria, ventricles

the pacemaker potential provides the SA node with _______________

automaticity

why are L-type calcium channels also called DHP channels

because they are modified versions of the DHP receptors that function as voltage sensors in excitation-contraction coupling of skeletal muscle

Systemic circulation

blood is pumped from the left ventricle through all the organs and tissues of the body, except the lungs, and then to the right atrium

Hemodynamics

blood pressure, blood flow, and resistance to blood flow

Plasma volume

blood volume minus erythrocyte volume

Movements btwn the interstitial fluid and the cell interior are accomplished by

both diffusion and mediated transport across the plasma membrane

Contraction of cardiac muscle, like that of skeletal muscle and many smooth muscles, is triggered by __________________ of the plasma membrane.

depolarization

bundle branches

branches of the bundle of His, divided into right and left sides that separate at the bottom (apex) of the heart and enter the walls of both ventricles

Veins

carries deoxygenated blood to the heart

Arteries

carries oxygenated blood away from the heart

Platelets

cell fragments, creates blood clots

When a contracting ventricle achieves an internal pressure greater than that in its connected atrium, the AV valve between them is forced

closed

Microcirculation

contains the arterioles, capillaries, and venules

The blood leaves the lungs by

four pulmonary veins

Resistance ® to flow

friction divided by pressure

pacemaker potential

gradual depolarization in SA node cells that brings the membrane potential to threshold, at which point an action potential occurs.

The slope of the pacemaker potential—that is, how quickly the membrane potential changes per unit time—determines:

how quickly threshold is reached and the next action potential is elicited

unlike other excitable tissues, the reduction in Na+ permeability in cardiac muscle is NOT accompanied by-

immediate repolarization of the membrane to resting levels Instead, there is a partial repolarization caused by a special class of transiently open K+ channels, and then the membrane remains depolarized at a plateau of about 0 mV

Pulmonary circulation

includes blood pumped from the right ventricle through the lungs and then to the left atrium

what causes the depolarizing phase of a nodal cell action potential?

influx through L-type Ca2+ channels. These Ca2+ currents depolarize the membrane more slowly than voltage-gated Na+ channels, and one result is that action potentials propagate more slowly along nodal-cell membranes than in other cardiac cells

Conducting system

initiates the heartbeat and helps spread an action potential rapidly throughout the heart

Endothelium

inner layer

Flow rate is ____________ to the resistance

inversely proportional

resting membrane permeability to K and Na in cardiac muscle

just like skeletal muscle, the rrsting membrane is much more permeable to K than Na. the resting membrane potential is much closer to the K+ equilibrium potential (−90 mV) than to the Na+ equilibrium potential (+60mV)

Purkinje fibers

large-diameter, rapidly conducting cells connected by low-resistance gap junctions. The branching network of Purkinje fibers conducts the action potential rapidly to myocytes throughout the ventricles.

length of absolute refractory period in cardiac muscle

lasts almost as long as the contraction (approximately 250 msec), and the muscle cannot be re-excited multiple times during an ongoing contraction

Bicuspid valve

left AV valve (mitral valve)

Ventricle

lower chamber of the heart

The parasympathetic fibers innervate

mainly on special cells found in the aorta and release primarily acetylcholine. Contain muscarinic receptors

Units for pressure difference

mmHg

length of absolute refractory period in skeletal muscle

much shorter 2 to 4 msec than the duration of contraction 20 to100 msec, so a second action potential can be elicited while the contraction resulting from the first action potential is still under way

Pillory muscles

muscle projections of the ventricular walls in the AV valves

When the blood pressure in an atrium is greater than in the corresponding ventricle, the valve is pushed

open and blood flows from atrium to ventricle

Pericardium

outer layer, protective fibrous sac

the blood returning from the body's peripheral organs and tissues via the systemic veins is (oxygenated or deoxygenated)

oxygenated before it is pumped back to them

The opening and closing of the AV valves are what type of processes

passive processes resulting from pressure differences across the valves

Layers of the heart

pericardium, epicardium, myocardium, endothelium

Atrioventricular valves (AV)

permit blood to flow from atrium to ventricle but not backward from ventricle to atrium. Bicuspid and tricuspid valves

Serum

plasma with fibrinogen and other proteins involved in clotting removed

Sodium ion entry depolarizes the cell and sustains the opening of more Na+ channels in a ______________ feedback fashion

positive feedback

electrocardiogram (ECG)

recording of the electrical changes that occur in the myocardium during a cardiac cycle

Erythrocytes

red blood cells, carry oxygen to the tissues and carbon dioxide from the tissues

The propagation of action potentials through the AV node is

relatively slow (requiring approximately 0.1 sec). This delay allows atrial contraction to be completed before ventricular excitation occurs.

Tricuspid valve

right AV valve

QRS complex of an ECG

second deflection, shows ventricular depolarization

pathway of blood

superior vena cava, right atrium, tricuspid valve, right ventricle, pulmonary semilunar valve, pulmonary artery, lungs/oxygen, pulmonary veins, left atrium, bicuspid valve, left ventricle, aortic semilunar valve, aorta body

Blood leaves the left ventricle via

the aorta, which branches into arterioles, which branch into capillaries.

The AV node and the bundle of His constitute the only electrical connection between

the atria and ventricles

Coronary blood flow

the blood flowing through the coronary arteries

automaticity

the capacity for spontaneous, rhythmic self-excitation

The sympathetic postganglionic fibers innervate

the entire heart and release norepinephrine. Contain beta adrenergic receptors

Semilunar valves

valves between the ventricles and their corresponding artery. pulmonary and aortic valves

Therefore, the discharge rate of the SA node determines

the heart rate, the number of times the heart contracts per minute.

main mechanism for absolute refractory period

the inactivation of sodium channels

What does it mean that the heart is a dual pump

the left and right sides of the heart pump blood separately, but simultaneously, into the systemic and pulmonary vessels

Aortic valve

the opening of the left ventricle into the aorta

the depolarizing phase of the action potential is due mainly to

the opening of voltage-gated Na+ channels.

why do SA node cells normally initiate action potentials and determine the pace of the heart?

the pacemaker currents of SA node cells bring them to threshold more rapidly than AV node cells

sinoatrial (SA) node

the pacemaker; responsible for initiating electrical conduction of the heartbeat, causing the atria to contract and firing conduction of impulses to the AV node. located in the right atrium

Hematocrit

the percentage of blood volume that is erythrocytes

absolute refractory period

the period during and following an action potential when an excitable membrane cannot be re-excited

Hydrostatic pressure

the pressure exerted by any fluid

Blood leaves the right ventricle via

the pulmonary trunk (a single large artery), which divides into the two pulmonary arteries.

In systemic circulation, blood comes back into the heart through

the superior vena cava and inferior vena cava

True or False: There are no valves at the entrances of the superior and inferior venae cavae

true

true or false- Cardiac muscle is incapable of undergoing summation of contractions like that occurring in skeletal muscle

true

true or false- action potentials propagate more slowly along nodal-cell membranes than in other cardiac cell

true

Atrium

upper chamber of the heart

Prolapse

when the AV valves from being pushed up and opening backward into the atria when the ventricles are contracting

Leukocytes

white blood cells, protect against infection and cancer