The cardiovascular system
In nodal cells, which ion channels change the resting membrane potential from -60mV to -40mV, the threshold potential? does this require outside stimulation?
"leaky" non-specific cation channels (ore Na+ in the K+ out). No outside stimulation is required.
Does a high ESV signify a high stroke volume or a low stroke volume?
A high ESV signifies a low stroke volume, as less blood was ejected, and more remains in the ventricles at the end of systole.
Arteries and veins carry blood in what direction to and from the heart?
Arteries carry blood away from the heart and Veins carry blood back to the heart.
What is occurring during late ventricular systole?
Atria are relaxed and ventricles are contracting/semilunar valves are forces open when pressure in ventricle surpasses pressure in arterial trunks/ AV valves are pushed closed/Blood is ejected into the arterial trunks
What happens when blood flow through one or more of the coronary arteries is blocked?
Because of anastomoses and collateral circulation, blockage of only one coronary artery may allow alternate routes of blood flow. However, blockage of more and/or larger coronary arteries may cause myocardial infarction(MI), or heart attack.
Why is it important to prevent backflow of blood in the heart?
Blood flow through the heart must occur in only one direction so that deoxygenated blood goes to the pulmonary circuit and oxygenated blood goes to the systemic circuit.
In which direction does Ca2+ move in response to the opening of voltage-gated Ca2+ channels: into or out of the cardiac muscle cells?
Ca2+ moves into the cell from both intracellular (sarcoplasmic reticulum) and extracellular (T-tubules) sources.
What causes the plateau phase of the contractile cardiac cell action potential?
Calcium ion channels open and Ca++ enters as K+ exits, prolonging the depolarization. These calcium ion channels are slow to close, which allows the plateau phase to last much linger that the initial depolarization phase.
Why can the heart continue beating even when the brain has ceased most of its functions?
Cardiac muscle has the property of autorhythmicity and it sets its own rhythm without a need for input from the nervous system. Specialized pacemaker cells generate action potentials that trigger the other cardiac muscle cells to contract.
How do pressure gradients drive blood through the heart?
Contraction of the heart muscle increases pressure in the chambers. Blood fills the heart when pressure is low during relaxation (diastole), and blood moves from ventricles to the great arteries during contraction (systole).
What electrical events occur during the cardiac action potential?
Depolarization (Na+ channels open), brief repolarization (K+ channels leak), plateau (Ca2_ channels open), repolarization (K+ channels open, Ca2+ channels close), and return to resting membrane potential (Na+/K+ pump)
What 2 features of intercalated discs provide mechanical stability and low-resistance pathway (easy flow) for ion flows between cardiac cells?
Desmosomes and gap junctions
Name the layers of the pericardium, including the pericardial cavity, from outermost to innermost
Fibrous pericardium, parietal layer of serous pericardium, pericardial cavity, visceral layer of serous pericardium (epicardium)
What ae the key differences between the right and left side of the heart?
Functionally, the right side of the heart pumps blood to the lungs (the pulmonary pump) and the left side of heart pumps blood to the rest of the body )the systemic pump) The pressure generated is also higher on the left side due to the need to pump blood to the entire body.
What are the 2 factors that determine cardiac output?
Heart rate and stroke volume. co=HRxSV
What could cause high ESV, and what would this do to cardiac output?
High BP is one factor that could cause this , and it would reduce cardiac output
How do pressure gradients influence the functioning of the heart valves?
High pressure in the ventricles during systole causes the blood flow that pushes the semilunar valves open (and causes the AV valves to close). Higher pressure from the blood in the ventricles closes the semilunar valves during diastole.
Why does left ventricular failure cause pulmonary congestion and edema?
In left ventricular failure, pulmonary edema may follow as blood backs up in the pulmonary circuit, increasing pulmonary vessel pressure, and driving fluid out of the pulmonary capillaries and into the lungs.
You notice that a patient has QRS waveforms on his ECG, indicating that his ventricles are undergoing electrical activity. Does the finding always mean that a heart is actually pumping blood?
In the normal functioning of the heart, electrical activity in the ventricles should lead to a physical contraction. However, pumping blood is most directly related to pressure-volume changes, so there can be electrical activity with no heartbeat.
What effects do positive chronotropic agents have on the heart rate? Negative chronotropic agents?
Increase and decrease the heart rate, respectively
What is the importance of the intercalated discs to heart function?
Intercalated discs join pacemaker cells to contractile cells, and join contractile cells to one another.
What is the function of the coronary sinus? Where does it drain?
It receives blood from all the cardiac veins before draining into the right atrium
What is the path of an action potential through the conduction system of the heart?
SA node>AV node>AV bundle>bundle branches>Purkinjie fibers> through ventricles.
Why do both right and left ventricular failure cause peripheral edema?
Similarly, right and left ventricular fialure may ccause peripheral edema, in which blood backs up in the systemic capillaries, forcing fluid out of the capillaries and into the tissues.
Why is there a delay at the AV node?
The AV node delay allows extra time for the action potential to spread from the SA node to the AV bundle, which allows the atria to depolarize (and contract) before the ventricles.
What pressure change cause the closing of the AV valves and the opening of the semilunar valves?
The AV valves close as pressure in the ventricles exceed atrial pressure. The semilunar valves open as the pressure in the ventricles surpasses the atrial trunk pressure.
What part of the heart has an anomaly if the P wave is abnormal on an ECG?
The P wave represents the depolarization of the cells within the atria (except the SA node). So, P wave anomalies would pint to atrial abnormalities such as atrial fibrillation.
Why is the SA node referred to as the pacemaker?
The SA node initiates the signal of the heartbeat
If a person has a stroke volume of 55 Ml. and a heart rate of 80 bpm , what is the cardiac output? Is this a normal value? If not, how is it abnormal?
The person would have a cardiac output of 4400 ml/min (4.4L/min). Although this is a little lower than 5+ L/min often considered average, there are numerous normal factors that affect cardiac output (eg- body temp, gender, size), as well as abnormal factors (eg- high BP, reduce stroke volume) which could account for this value.
Why is the plateau phase so important to the electrophysiology of the heart?
The plateau phase lengthen the cardiac action potential to about 200-300 msec. which slows the heart rate, providing the time required for the heart to fill with blood.
How is the right side of the heart different structurally from the left side? Why?
The right ventricle is wider and has thinner walls than the left ventricle. This is because of the pressure differences in the pulmonary and systemic circuits.; the right ventricle has less resistance to overcome, and the left ventricle pumps against much greater resistance. also, the right ventricle is shorter and crescent-shaped in cross section.
How does the serous pericardium envelop the heart? What is its function?
The serous pericardium has 2 continuous layers; the parietal pericardium that is fuse to the inner surface of the fibrous pericardium, and the visceral pericardium (aka epicardium) which lies directly on the heart as the most superficial layer of the heart wall.
Why do skeletal muscle lack intercalated discs?
They contain gap junctions which provide for electrical synapses between cells for easy spread of action potentials.
What can cause blockage of coronary arteries?
This often follows when plaques in the coronary arteries rupture and a clot forms that obstructs blood flow to the myocardium.
What would happen if the delay at the AV valve was too long?
Too long a delay might allow time for the atria to start to relax and pull blood back in their direction before the ventricles could contract and force closure of the AV valves.
Which structure prevent backflow in the heart? How do they function?
Valves with overlapping flaps close when the pressure increases on one side such that blood cannot flow back where it came from
Which of the following increase stroke volume? a) increased venous return B)increased Ca2+ in sarcoplasm c)afterload
a) increased venous return ^preload (Starling's law) b)Increased Ca2+ in sarcoplasm (^ force of contraction) Increased afterload decreases stroke volume
A final factor that influence stroke volume is _______________________, which is the force against which the heart must pump.
afterload
Which set of valves is associated with papillary muscle and chordae tendineae?
bicuspid and tricuspid (AV valves)
The heart's ____________________________ is its inherent ability to pump. As this increases, the stroke volume also ____________________ and the _____________________ volume __________________________.
contractility, increases, end-systolic, decreases
When afterload increases, stroke volume generally ________________________ and _______________________ volume ___________________________.
decreases, end-systolic, increases
The Frank-Starling Law states that cells contract ____________________________ when their sarcomeres are stretched prior to contraction.
forcefully
As preload increases, stroke volume also _____________________ due to a phenomenon known as the ____________________________________.
increases, Frank-Starling Law
What is the structure that separates the 2 ventricles?
interventricular septum
The _________________________refers to the amount a ventricular cell is stretched before contracting.
preload
Trace the path of blood through the heart, starting at the right atrium, including valves and vessels
right atrium >right AV valve (tricuspid)>right ventricle>pulmonary semilunar valves>pulmonary trunk>pulmonary arteries>pulmonary capillaries>pulmonary veins left atrium>left AV valve (bicuspid)>left ventricle>aortic semilunar valve>aorta, systemic circulation>systemic capillaries>systemic veins>superior and inferior vena cava>right atrium
One of the major determinants of preload is _____________________, or the amount of blood veins deliver to the heart.
venous return
