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Pharmacology · chapter 16 · Introduction to the Cardiovascular System

Introduction to the Heart, Circulation, and Blood Flow

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.

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Key points

  1. The pericardium

    The heart is surrounded by a fibrous, layered sac called the pericardium. The pericardium protects the heart and provides a low-friction environment for the heart to pump in.

  2. Three layers of the heart wall

    The heart walls are composed of three layers: endocardium (inner layer), myocardium (middle layer), and epicardium (outer layer).

  3. Valves prevent backflow

    Within the heart, valves direct blood flow and prevent the backflow of blood into the heart. These valves open and close based on pressure gradients at coordinated times within the cardiac cycle.

  4. Blood supply to the heart muscle

    Although the heart pumps oxygenated blood to all tissues, the cardiac tissue also needs a supply of oxygenated blood. This is accomplished via coronary arteries that branch off of the aorta, which fill with blood during systole (when the heart pumps).

  5. Blocked coronary arteries

    This can eventually block blood flow to the heart, leading to ischemia (oxygen deprivation) and tissue death. This is known as a myocardial infarction, or heart attack (see Lipid-Lowering Drugs).

  6. Why the left ventricle is stronger

    The right ventricle pumps against a relatively low pressure in the pulmonary system, whereas the left ventricle must pump against systemic arterial pressure to deliver oxygen. Because of this, the left ventricle is more muscular and powerful than the right ventricle.

  7. Capillaries exchange oxygen and nutrients

    Capillaries are tiny, thin-walled blood vessels that facilitate the exchange of nutrients and oxygen between blood and tissues.

  8. The pulmonary artery exception

    In the pulmonary circuit, deoxygenated blood is pumped from the right ventricle into the pulmonary artery (in systemic circulation, arteries carry only oxygenated blood).

  9. What blood pressure depends on

    It is dependent on both cardiac output (the amount of blood pumped from the left ventricle per unit of time) and systemic vascular resistance (the resistance to blood flow within the artery, determined by the arterial diameter, which changes based on physiologic conditions).

  10. Systolic versus diastolic pressure

    Systolic blood pressure is the pressure in the arteries during systole, or ventricular contraction (heart pumping). Diastolic blood pressure is lower and is the pressure in the arteries during diastole, or ventricular filling/relaxation (between each pump).

  11. Baroreceptors and standing up

    This immediate effect on the sympathetic nervous system is responsible for maintaining blood pressure upon abrupt changes, such as when someone moves from a recumbent position to standing quickly.

  12. Vasopressin in shock

    Vasopressin can be administered therapeutically to maintain blood pressure in clients with vasodilatory or septic shock (Evans et al., 2021).

  13. Aldosterone and potassium

    This pump facilitates the transport of sodium (and water) back into the body, which increases blood volume and cardiac output and thus systemic arterial pressure. Aldosterone also causes increased potassium excretion.

  14. Hypertensive crisis

    Any blood pressure higher than 180/120 mm Hg is considered a hypertensive crisis and requires immediate medical attention to prevent or mitigate acute end-organ damage (Whelton et al., 2018).

Terms to know

Pericardium
The heart is surrounded by a fibrous, layered sac called the pericardium.
Myocardium
The myocardium is the heart muscle that contracts to pump blood throughout the circulatory system.
Semilunar valves
These valves are referred to as semilunar valves because their leaflets resemble crescent moons.
Systemic arterial pressure
Systemic arterial pressure is pressure measured using a sphygmomanometer (blood pressure cuff) and is commonly just referred to as blood pressure.
Venous pressure
Venous pressure is the pressure within the veins.

Practice questions

Stuck on select-all-that-apply? How to take them one option at a time.

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Every question here, with the answer

  1. A nurse measures a client's blood pressure at 186/124 mm Hg. How should the nurse interpret this reading?

    1. Hypotension
    2. Expected pressure after standing up quickly
    3. Hypertensive crisis requiring immediate medical attention
    4. Normal blood pressure

    Answer: Hypertensive crisis requiring immediate medical attention

    Any blood pressure higher than 180/120 mm Hg is a hypertensive crisis and needs immediate medical attention to prevent end-organ damage. Normal pressure is generally below 120/80, and hypotension means a systolic pressure below 90.

  2. A client with septic shock remains hypotensive. The nurse anticipates which hormone may be given therapeutically to maintain blood pressure?

    1. Renin
    2. Aldosterone
    3. Insulin
    4. Vasopressin

    Answer: Vasopressin

    Vasopressin (antidiuretic hormone) can be given to maintain blood pressure in vasodilatory or septic shock. Aldosterone and renin are part of the body's own RAAS response and are not named as treatments, and insulin is not discussed.

  3. A student asks why the left ventricle has a thicker muscle wall than the right. Which explanation by the nurse is accurate?

    1. The left ventricle has no valves, so it must work harder.
    2. The left ventricle receives blood from the venae cavae.
    3. The left ventricle pumps blood to the lungs for gas exchange.
    4. The left ventricle pumps against systemic arterial pressure, which is higher than the pressure in the lungs.

    Answer: The left ventricle pumps against systemic arterial pressure, which is higher than the pressure in the lungs.

    The right ventricle pumps against low pulmonary pressure, while the left ventricle must pump against systemic arterial pressure, so it is more muscular. The venae cavae empty into the right atrium, blood to the lungs comes from the right ventricle, and the left ventricle does have valves.

  4. Which changes increase a client's systemic arterial pressure? Select all that apply.

    1. Higher arterial resistance
    2. Loss of circulating blood volume
    3. Vasoconstriction caused by angiotensin II
    4. Higher cardiac output
    5. Increased circulating blood volume

    Answer: Higher arterial resistance, Vasoconstriction caused by angiotensin II, Higher cardiac output, Increased circulating blood volume

    Blood pressure depends on cardiac output and systemic vascular resistance, so higher output, higher resistance, angiotensin II vasoconstriction and more circulating volume all raise it. Losing volume is what triggers the baroreceptors to raise a low pressure.

  5. A nurse is reviewing blood flow with a client after a myocardial infarction. Which statements are accurate? Select all that apply.

    1. Arteries in the systemic circulation carry deoxygenated blood.
    2. Coronary arteries branch off the aorta and supply the heart muscle.
    3. Plaques in the coronary arteries can block blood flow and cause tissue death.
    4. The superior vena cava returns blood from the lower body.
    5. The pulmonary veins carry oxygenated blood from the lungs to the left atrium.

    Answer: Coronary arteries branch off the aorta and supply the heart muscle., Plaques in the coronary arteries can block blood flow and cause tissue death., The pulmonary veins carry oxygenated blood from the lungs to the left atrium.

    Coronary arteries branch off the aorta, plaque can block them and cause ischemia and tissue death, and the pulmonary veins return oxygenated blood to the left atrium. The superior vena cava drains the upper body, and systemic arteries carry only oxygenated blood.

  6. A client moves from lying down to standing, and the blood pressure stays stable. Which mechanism is mainly responsible for this immediate adjustment?

    1. The baroreceptor reflex increasing sympathetic activity
    2. Aldosterone increasing potassium excretion
    3. Antidiuretic hormone reabsorbing water in the kidneys
    4. Capillary exchange of oxygen

    Answer: The baroreceptor reflex increasing sympathetic activity

    Baroreceptors sense the drop and increase sympathetic activity, causing vasoconstriction; this immediate effect maintains pressure with abrupt position changes. Aldosterone and antidiuretic hormone act through volume more slowly, and capillary exchange does not regulate pressure.

Where every quote comes from

Section 16.1 Introduction to the Heart, Circulation, and Blood Flow 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.