Chapter 20 - The Heart Flashcards
- Damage to the semilunar valve of the right ventricle would affect blood flow into which vessel?
Damage to the semilunar valve of the right ventricle would affect blood flow to the pulmonary trunk.
- What prevents the AV valves from swinging into the atria?
Contraction of the papillary muscles (just before the rest of the ventricular myocardium contracts) pulls on the chordae tendineae, which prevent the AV valves from opening bak into the atria.
- Why is the left ventricle more muscular than the right ventricle?
The left ventricle is more muscular than the right ventricle because the left ventricle must generate enough force to propel blood throughout the body, except for the lungs, whereas the right ventricle must generate only enough force to propel blood a few centimeters to the lungs.
- Define automaticity
Automaticity or autorhythmicity, is the ability of cardiac muscle to contract without neural or hormonal stimulation.
- Which structure of the heart is known as the cardiac pacemaker or the natural pacemaker?
The sinoatrial (SA) node is known as the cardiac pacemaker or the natural pacemaker.
- If the cells of the SA node did not function, how would the hear rate be affected?
If the cells of the SA node did not function, the heart would still continue to beat, but at a slower rate; and the AV node would act as the pacemaker.
- Why is it important for impulses from the atria to be delayed at the AV node before they pass into to ventricles?
If the impulses from the atria were not delayed at the AV node, they would be conducted through the ventricles so quickly by the bundle branches and the Purkinje cells that the ventricles would begin contracting immediately, before the atria had finished their contraction. As a result, the ventricles would not be as full of blood as they could be, and the pumping of the heart would be as efficient, especially during physical activity.
- Give the technical terms for heart contraction and heart relaxation.
The technical term for heart contraction is systole, and the term for heart relaxation is diastole.
- List the phases of the cardiac cycle.
The phases of the cardiac cycle are Atrial systole, atrial diastole, ventricular systole and ventricular diastole.
- Is the heart always pumping blood when pressure in the ventricle is rising? Explain.
No. When pressure in the left ventricle first rises, the heart is contracting but no blood is leaving the heart. During this initial phase of contraction, both the AV valves and the semilunar valves are closed. The increase pressure is the result of increased tension as the cardiac muscle contracts. When the pressure in the ventricle exceeds the pressure in the aorta, the aortic semilunar valves are forced open, and blood is rapidly ejected from the ventricle.
- What could cause an increase in the size of the QRS complex in an electrocardiogram?
One possible cause for an increase in the size of the QRS complex, which indicates a larger-than-normal amount of electrical activity during ventricular depolarization, is an enlarged heart. Because more cardiac muscle is depolarizing, the magnitude of the electrical event would be greater.
- Define cardiac output.
Cardiac output is the amount of blood pumped by the left ventricle in one minute.
- Caffeine has effects on conducting cells and contractile cells that are similar to those of NE. What effects would drinking large amounts of caffeinated drinks have on the heart?
Caffeine acts directly on the conducting system and contractile cells of the heart, increasing the rate at which they depolarize. Drinking large amounts of caffeinated drinks would increase the heart rate.
- If the cardioinhibitory center of the medulla oblongata were damaged, which part of the autonomic nervous system would be affected, and how would the heart be influenced?
Damage to the cardioinhibitory center of the medulla oblongata, which is part of the parasympathetic division of the autonomic nervous system, would reduce the parasympathetic stimulation of the heart. The resulting sympathetic dominance would increase the heart rate.
- How does a drug that increases the length of time required for the repolarization of pacemaker cells affect the heart rate?
A drug that increase the length of time required for the repolarization of pacemaker cells would decrease the heart rate, because the pacemaker cells would generate fewer action potentials per minute.
