Cardiovascular Physiology Flashcards
Discuss the renin-angiotensin-aldosterone system.
☛ A decrease in arterial pressure stimulates the secretion of renin by the kidneys.
☛ Renin acts on a protein known as angiotensinogen and converts it to angiotensin I.
☛ Angiotensin I is then converted to angiotensin II by an enzyme known as angiotensin converting enzyme (ACE). This process occurs in the lungs.
☛ Angiotensin II causes vasoconstriction of arterioles and veins and this will cause an increase in total peripheral resistance. An increase in total peripheral resistance will result in an increase in arterial pressure.
☛ In addition to this, angiotensin II stimulates the adrenal cortex [zona glomerulosa📌] to secrete aldosterone [a mineralocorticoid], which acts on the kidneys, promoting the reabsorption of sodium ions and water. This will increase cardiac output and consequently increase arterial pressure.
[Diagram 1] [Diagram 2]
Explain each of the following “landmarks” on a normal electrocardiogram:
(a) P wave
(b) QRS complex
(c) T wave
(d) PR interval
(e) PR segment
(a) P wave: It represents the atrial depolarization.
(b) QRS complex: It represents the ventricular depolarization.
(c) T wave: It represents ventricular repolarization.
(d) PR interval: It reflects the time interval from the start of atrial depolarization to the start of ventricular depolarization.
(e) PR segment: It is an isoelectric portion of the ECG that corresponds to conduction through the AV node.
[Diagram]
Explain each of the following “landmarks” on a normal electrocardiogram:
(a) ST segment
(b) QT interval
(c) RR interval
(a) ST segment: It represents the isoelectric period when the ventricles are between depolarization and repolarization.
(b) QT interval: It represents the total time for ventricular depolarization and repolarization.
(c) RR interval: It represents the time between two cardiac cycles.
[Diagram]
When does atrial repolarization occur?
Atrial repolarization occurs during the QRS complex; it is not seen in the ECG because it is masked by the much greater electrical activity in the ventricle.
Explain the Frank-Sterling principle.
The Frank-Starling principle describes the relationship between systolic volume and end-diastolic volume. Increased diastolic filling produces greater stretch of heart muscle, resulting in a larger systolic volume.
State the function of atrial natriuretic peptide.
Atrial natriuretic peptide acts as a vasodilator, promoting relaxation of blood vessels, which helps reduce blood pressure. It also promotes natriuresis (excretion of sodium) by acting on the kidneys.
What causes release of atrial natriuretic peptide?
Increased atrial pressure due to higher venous returns.
