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