Pharmacology · chapter 16 · Introduction to the Cardiovascular System
Pumping Action of the Heart
The 14 things this section of the textbook says that you are most likely to be asked about — quoted word for word, not retold. Then 6 practice questions with the reasoning.
Key points
What systole means
Ventricular systole (or just systole if not specified) refers to the active pumping or contraction of the ventricles. The contraction of the heart muscle increases pressure within the ventricles.
When the semilunar valves open
When the pressure in the ventricles exceeds the pressure in the attached blood vessel (right ventricle: pulmonary artery; left ventricle: aorta), it causes the connected semilunar valve to open, and blood is ejected into the vessel.
What diastole means
After systole, the ventricular heart muscle relaxes, and the chamber refills with blood. This phase of relaxation and filling is referred to as ventricular diastole, or just diastole.
Left ventricle works harder
For example, the left ventricle must pump blood into the high-pressure arterial circulation (~90 mm Hg), whereas the right ventricle pumps blood only through the low-pressure pulmonary circulation (8–20 mm Hg). Accordingly, the left ventricle must work harder as compared to the right.
Heart failure and lowering pressure
When clients experience heart failure, it is commonly an issue with the left ventricle’s ability to pump (e.g., heart failure with reduced ejection fraction; see Heart Failure Drugs). One way to alleviate heart failure symptoms is by reducing systemic arterial pressure with drugs, making it easier for the left ventricle to pump blood out.
Blood follows pressure gradients
Blood flows from areas of higher pressure to areas of lower pressure based on pressure gradients, or differences in pressure among different spaces.
Atrial kick opens the tricuspid valve
During atrial contraction (known as atrial systole or atrial kick), the pressure increases within the cavity of the atrium and eventually exceeds the pressure in the right ventricle. This causes the tricuspid valve to open, and blood flows into the right ventricle (ventricular diastole).
Right ventricle to the lungs
During ventricular systole, the pressure in the ventricle increases and becomes greater than the pressure within the pulmonary artery, causing the pulmonary valve to open. Blood flows into the pulmonary artery and then the lungs for gas exchange.
Left atrium fills the left ventricle
During atrial contraction (known as atrial systole or atrial kick), the pressure in the left atrium eventually exceeds that of the left ventricle. This causes the mitral valve to open, and blood flows into the left ventricle (ventricular diastole).
Systemic circulation
Systemic circulation: Oxygenated blood is delivered to the tissues via arteries and capillaries, and deoxygenated blood returns to the heart via veins and the venae cavae to restart the cycle with right atrial diastole.
Heart rate and stroke volume
Cardiac output is dependent on the heart rate (the number of times the ventricle contracts per unit of time) and stroke volume (the volume of blood ejected with each contraction).
Diuretics lower preload; afterload defined
Diuretics are drugs that decrease circulating blood volume, thus decreasing preload. Afterload: This is the amount of systemic pressure the heart must overcome to eject blood during systole.
Afterload and antihypertensives
Higher afterload decreases stroke volume. Drugs that decrease systemic vascular resistance, such as antihypertensive medications, decrease afterload.
Sympathetic system and contractility
Contractility: Cardiac contractility refers to the strength of the force of left ventricular contraction. Increased activation of the sympathetic nervous system increases cardiac contractility via the actions of epinephrine and norepinephrine.
Terms to know
- Cardiac output
- Cardiac output is the amount of blood being pumped from the heart into the systemic circulation per unit of time.
- Preload
- The stroke volume (and thus cardiac output) is dependent on multiple variables: Preload: This is the volume of blood that fills the left ventricle at the end of diastole.
- Afterload
- Afterload: This is the amount of systemic pressure the heart must overcome to eject blood during systole.
- Inotropes
- A class of drugs called inotropes increase cardiac contractility.
Practice questions
Stuck on select-all-that-apply? How to take them one option at a time.
The graded version needs JavaScript. Every question is below anyway, with the answer and why.
Every question here, with the answer
A client with heart failure is receiving a diuretic. The nurse explains that this drug helps the heart mainly by doing what?
- Increasing the heart rate
- Increasing cardiac contractility
- Increasing systemic vascular resistance
- Decreasing circulating blood volume, which decreases preload
Answer: Decreasing circulating blood volume, which decreases preload
Diuretics decrease circulating blood volume and so decrease preload, the volume filling the left ventricle at the end of diastole. They are not described as raising contractility, resistance or heart rate.
A client with heart failure with reduced ejection fraction is started on an antihypertensive. How does the nurse explain the benefit?
- Lower pressure increases the volume of blood in the ventricle.
- Lower pressure closes the aortic valve during systole.
- The drug makes the right ventricle work harder instead.
- Lower systemic pressure makes it easier for the left ventricle to pump blood out.
Answer: Lower systemic pressure makes it easier for the left ventricle to pump blood out.
Heart failure is commonly a problem with the left ventricle's pumping, and reducing systemic arterial pressure (afterload) makes it easier for the left ventricle to eject blood. The other options are not supported by the section; the aortic valve opens during systole.
A client in shock is started on a drug classified as an inotrope. Which effect should the nurse expect?
- Decreased circulating blood volume
- Decreased cardiac contractility
- Decreased heart rate
- Increased cardiac contractility
Answer: Increased cardiac contractility
Inotropes are a class of drugs that increase cardiac contractility, the strength of left ventricular contraction. Decreased contractility is a side effect of some other drugs, and inotropes are not described as changing volume or heart rate.
Which factors increase cardiac contractility? Select all that apply.
- Inotrope drugs
- Increased calcium levels
- Higher afterload
- Ischemia
- Increased sympathetic nervous system activation
Answer: Inotrope drugs, Increased calcium levels, Increased sympathetic nervous system activation
Sympathetic activation (epinephrine and norepinephrine), increased calcium and inotropes all increase contractility. Ischemia decreases contractility, and higher afterload decreases stroke volume rather than increasing contractility.
A nurse reviews the factors that determine cardiac output. Which statements are accurate? Select all that apply.
- Antihypertensive medications increase afterload.
- Diuretics increase preload.
- A higher preload leads to a higher stroke volume.
- Cardiac output depends on heart rate and stroke volume.
- Higher afterload decreases stroke volume.
Answer: A higher preload leads to a higher stroke volume., Cardiac output depends on heart rate and stroke volume., Higher afterload decreases stroke volume.
Cardiac output depends on heart rate and stroke volume; higher preload raises stroke volume and higher afterload lowers it. Antihypertensives decrease afterload, and diuretics decrease preload.
During the cardiac cycle, what causes the mitral valve to open?
- Blood returns through the venae cavae.
- The right ventricle contracts during systole.
- Pressure in the left atrium exceeds that of the left ventricle during atrial contraction.
- Pressure in the aorta exceeds that of the left ventricle.
Answer: Pressure in the left atrium exceeds that of the left ventricle during atrial contraction.
Valves open based on pressure gradients: during atrial kick, left atrial pressure exceeds left ventricular pressure and the mitral valve opens. Aortic pressure concerns the aortic valve, right ventricular contraction opens the pulmonary valve, and the venae cavae fill the right atrium.
Where every quote comes from
Section 16.2 Pumping Action of the Heart of Pharmacology for Nurses by Tina Barbour-Taylor, Leah Mueller (Sabato), Donna Paris, Dorie Weaver, OpenStax, 2024. Read the whole section free at openstax.org.
The textbook is licensed under CC BY-NC-SA 4.0. This page quotes it word for word and adds the headings, the order and the practice questions; references to the book's figures and stray spaces left by its formatting are removed. The page is shared under the same licence. Nothing here is sold.