38 Questions
What is the main reason why the wall of the left ventricle is thicker than the wall of the right ventricle?
It generates a greater pressure than the right ventricle
What is the approximate pressure increase in the left ventricle when it contracts?
120 mm Hg
What is the name of the valve located between the left atrium and left ventricle?
Mitral valve
What happens to the atrioventricular valves when the ventricles relax?
They open
What is the function of the atrioventricular valves?
To prevent blood from flowing back into the atria
What type of valve is located in the aorta and pulmonary trunk?
Semilunar valve
What happens to the semilunar cusps when the ventricles relax?
They bulge toward the center and meet
What is the function of the semilunar valves?
To prevent blood from flowing back into the ventricles
What percentage of oxygen does blood flowing through the coronary arteries of the heart typically give up?
70%
Where do the two coronary arteries originate from?
The base of the aorta
What is the most common cause of angina?
Coronary atheroma
What is the primary reason why cardiac muscle is very dependent on an increased rate of blood flow during exercise?
Because it needs more oxygen
What is the typical percentage of oxygen released to skeletal muscle during rest?
25%
What is a common symptom of angina?
All of the above
Where does the left coronary artery originate from?
The left side of the aorta
What is the effect of exercise on the percentage of oxygen released to skeletal muscle?
It increases to 70% or more
What is the reason for the self-excitation of the sinus nodal fibers?
The inherent leakiness of the sinus nodal fibers to sodium and calcium ions
What happens to the sodium-calcium channels after 100-150 milliseconds of opening?
They become inactivated and close
What is the effect of the increased potassium channels opening?
A rapid efflux of positive potassium ions
What is the purpose of hyperpolarization in the sinus nodal fibers?
To terminate the current action potential
What happens to the potassium channels after the action potential is over?
They close progressively over the next few tenths of a second
What is the potential at which the 'resting' potential reaches the threshold level for discharge?
-40 millivolts
What is the result of the inward-leaking sodium and calcium ions overbalancing the outward flux of potassium ions?
Drifting of the 'resting' potential upwards
What level does the membrane potential drop to during hyperpolarization?
-55 to -60 millivolts
What is the purpose of electrodes placed on the surface of the body?
To detect the small electrical changes resulting from the action potentials
Why does the hyperpolarization state not last indefinitely?
Because the potassium channels close
What does the P wave in an ECG represent?
Depolarization of the atrial myocardium
What is the minimum potential required for the sodium-calcium channels to become activated?
-40 millivolts
What is the process that continues indefinitely throughout a person's life?
The entire process of self-excitation, recovery, hyperpolarization, and re-excitation
What is the record of the electrical events in the heart?
Electrocardiogram (ECG)
What is the characteristic of the heart that enables highly coordinated contractions?
All or none law
In which phase of the action potential in cardiac muscle do Ca++ channels begin to open?
Depolarization phase
What is the function of the atrioventricular (AV) node in the conduction system of the heart?
Allowing the atria to complete their contraction before action potentials are delivered to the ventricles
What is the result of the slow rate of action potential conduction in the AV node?
The atria contract before the ventricles
What is the name of the bundle of specialized cardiac muscle that transmits action potentials from the AV node to the ventricles?
Atrioventricular bundle
What is the location of the atrioventricular (AV) node in the heart?
In the lower portion of the right atrium
What is the function of the sinoatrial (SA) node in the conduction system of the heart?
Originating action potentials
What is the result of the K+ channels closing at the end of the repolarization phase in skeletal muscle?
The membrane potential returns to its resting value
Study Notes
Heart Structure and Function
- The left ventricle wall is thicker than the right ventricle wall due to generating higher pressure (approx. 120 mm Hg) to pump blood to the entire body, compared to the right ventricle (approx. 1/5 of the left ventricle pressure) which pumps blood to the lungs.
- Atrioventricular valves (tricuspid and bicuspid/mitral) separate the atria from the ventricles, allowing blood to flow from atria to ventricles but preventing backflow.
- Semilunar valves (aortic and pulmonary) are located at the base of the aorta and pulmonary trunk, respectively, and prevent backflow from the aorta and pulmonary trunk into the ventricles.
Blood Supply to the Heart
- Coronary arteries, originating from the aorta, supply blood to the heart wall, with the left coronary artery supplying the anterior wall and most of the left ventricle, and the right coronary artery supplying most of the right ventricle.
- In a resting person, 70% of oxygen is released from blood flowing through the coronary arteries, compared to 25% from blood flowing through skeletal muscle arteries.
Coronary Artery Disease (CAD)
- Angina pectoris is the most common clinical manifestation of CAD, resulting from an imbalance between myocardial oxygen supply and demand, often due to atherosclerotic coronary artery obstruction.
- Clinical features of angina include chest pain or crushing sensation, radiation to the neck, jaw, arms, and back, as well as shortness of breath and dizziness.
Electrical Activity of the Heart
- Action potential in cardiac muscle has three phases: depolarization, repolarization, and final repolarization, involving the opening and closing of Na+, K+, and Ca++ channels.
- The conduction system of the heart consists of the sinoatrial (SA) node, atrioventricular (AV) node, atrioventricular bundle, and Purkinje fibers, which coordinate the contraction of atria and ventricles.
Electrocardiogram (ECG)
- An ECG records the electrical activity of the heart, measured through electrodes on the body surface, and consists of a P wave, QRS complex, and T wave.
- The P wave represents depolarization of the atrial myocardium, preceding atrial contraction.
Learn about the function of heart valves, coronary arteries, and blood supply to the heart. This quiz covers cardiac muscle, coronary arteries, and their role in maintaining heart health.
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