Lab 3 Flashcards
Describe the pathway of electrical conduction from the atria to the ventricles and relate these events to the components of the ECG.
electrical signal that initiates the contraction of the heart originates in the SA node, which is located in the upper wall of the right atrium.The SA node generates an electrical impulse that spreads across the atria, causing them to contract and push blood into the ventricles.
The electrical signal then travels to the AV node, located in the lower wall of the right atrium, where it is delayed briefly before passing into the bundle of His. This delay allows time for the atria to complete their contraction and for blood to flow into the ventricles.
The bundle of His divides into two branches, which extend into the ventricles and give rise to the Purkinje fibers. The electrical signal spreads rapidly through the Purkinje fibers, causing the ventricles to contract and eject blood from the heart.
How does the SA node function as the normal pacemaker for the heart?
It serves as the normal pacemaker for the heart by generating and transmitting electrical impulses that regulate the rhythmic contraction of the cardiac muscle.
How are the heart sounds produced?
The heart sounds are produced by the closing of the heart valves as blood flows through the heart during the cardiac cycle.
There are two primary heart sounds, which are often referred to as S1 and S2.
S1: The first heart sound, S1, is produced by the closure of the atrioventricular (AV) valves (the mitral valve and the tricuspid valve) at the beginning of systole, the phase of the cardiac cycle during which the ventricles contract and eject blood into the circulatory system. The closure of these valves is caused by the pressure generated in the ventricles as they contract and push blood out of the heart. S1 is often described as a “lub” sound and is the loudest of the two heart sounds.
S2: The second heart sound, S2, is produced by the closure of the semilunar valves (the aortic valve and the pulmonary valve) at the end of systole, just before the ventricles begin to relax and fill with blood again. The closure of these valves is caused by the backflow of blood from the aorta and pulmonary artery, which causes the valve leaflets to snap shut. S2 is often described as a “dub” sound.
Irregularities and defects of the heart valves can be more directly detected by auscultation than by electrocardiography. Why do you think this is so?
Auscultation and electrocardiography (ECG) are two common diagnostic techniques used to evaluate heart function. While both techniques are valuable in diagnosing heart conditions, auscultation is generally more effective in detecting irregularities and defects of the heart valves than ECG. There are several reasons for this:
Sound: Auscultation relies on the detection of sound, specifically heart sounds and murmurs, whereas ECG records the electrical activity of the heart. Heart valve defects and irregularities often produce characteristic sounds, such as a heart murmur, which can be heard with a stethoscope during auscultation.
Timing: Heart valve defects and irregularities can produce sounds that are timed to the cardiac cycle, meaning they occur at specific points during the cycle. For example, a mitral valve defect may produce a heart murmur that is heard during systole, when the ventricles are contracting. ECG, on the other hand, records electrical activity over time and may not be able to detect these specific timing patterns.
Location: Heart valve defects and irregularities are often localized to specific regions of the heart, such as the mitral or aortic valve. Auscultation can allow the healthcare provider to pinpoint the location of the sound and identify the valve involved. ECG records the electrical activity of the heart from multiple leads, which can make it more difficult to identify the specific location of a defect or irregularity.
Overall, auscultation is a valuable diagnostic tool for identifying heart valve defects and irregularities because it is a non-invasive, relatively low-cost technique that can provide specific information about the timing, location, and characteristics of the sound. ECG, while also valuable, records electrical activity of the heart and may not always be able to detect these specific characteristics of heart valve defects and irregularities.
What could result if a person’s baroreceptor reflex did not correct for changes in blood pressure when the person stands up?
When a person stands up, blood pressure tends to decrease due to the redistribution of blood flow, and the baroreceptor reflex helps to compensate for this by increasing heart rate and constricting blood vessels to maintain adequate blood flow to the brain and other vital organs.
If a person’s baroreceptor reflex did not correct for changes in blood pressure when the person stands up, they may experience a condition called orthostatic hypotension. Orthostatic hypotension is a drop in blood pressure that occurs when a person stands up from a sitting or lying position, and the body is unable to compensate for this drop due to a malfunction in the baroreceptor reflex. As a result, there may not be enough blood flow to the brain, which can cause symptoms such as dizziness, lightheadedness, and even fainting.
List three common everyday occurrences in which the Valsalva maneuver (or a variation of it) may be performed.
The Valsalva maneuver is a breathing technique that involves forcibly exhaling against a closed airway, which can increase pressure within the chest and abdomen. There are several common everyday occurrences in which the Valsalva maneuver or a variation of it may be performed, including:
Bowel movements: The Valsalva maneuver is commonly used during bowel movements to help increase abdominal pressure and aid in the expulsion of feces.
Weightlifting: The Valsalva maneuver is often used by weightlifters to increase intra-abdominal pressure and stabilize the spine during heavy lifts. This can help to prevent injury and improve lifting performance.
Sneezing or coughing: When a person sneezes or coughs, they may perform a variation of the Valsalva maneuver by forcefully exhaling against a closed airway. This can help to clear the airways and expel mucus or irritants from the respiratory system. However, it is important to note that performing the Valsalva maneuver during sneezing or coughing can also increase intraocular pressure, which may be harmful for people with certain eye conditions.
Explain the physiological effect that each of the following manoeuvres has on heart rate.
Posture:
Valsalva maneuver:
Posture:
Changing posture, such as moving from lying down to standing up, can have an immediate effect on heart rate. When a person stands up, gravity pulls blood down to the lower extremities, reducing venous return to the heart, and decreasing the amount of blood available for the heart to pump. To compensate for this reduction in blood volume, the heart rate increases, which helps to maintain cardiac output and blood pressure. This is a normal physiological response and is regulated by the autonomic nervous system.
Valsalva maneuver:
The Valsalva maneuver involves forcefully exhaling against a closed airway, which increases intra-abdominal and intrathoracic pressure. This increased pressure can lead to a reduction in blood return to the heart, resulting in a decrease in stroke volume and cardiac output. To compensate for this, the body activates the sympathetic nervous system, leading to an initial increase in heart rate. However, over time, this increase is usually followed by a decrease in heart rate due to the reduced venous return and cardiac output caused by the Valsalva maneuver. The Valsalva maneuver can also stimulate the baroreceptor reflex, which can cause a decrease in heart rate and blood pressure, especially during the release phase of the maneuver.
