Why the Cardiovascular System Matters in Pharmacy
Cardiovascular diseases are among the most prevalent conditions globally, and pharmacists regularly dispense medications for hypertension, heart failure, arrhythmias, and angina. A solid understanding of cardiovascular anatomy and physiology is not just for passing exams — it is directly applicable to your professional practice.
Structure of the Heart
The heart is a muscular pump located in the mediastinum (middle of the thoracic cavity), slightly to the left of the midline. It is enclosed in a double-layered sac called the pericardium.
Layers of the Heart Wall
- Epicardium — Outermost layer; also forms the inner layer of the pericardium
- Myocardium — The thick muscular middle layer; responsible for pumping action
- Endocardium — Inner smooth lining that reduces friction as blood flows through
The Four Chambers
| Chamber | Function | Blood Received From | Blood Sent To |
|---|---|---|---|
| Right Atrium | Receives deoxygenated blood | Superior & Inferior Vena Cava | Right Ventricle |
| Right Ventricle | Pumps blood to lungs | Right Atrium | Pulmonary Arteries |
| Left Atrium | Receives oxygenated blood from lungs | Pulmonary Veins | Left Ventricle |
| Left Ventricle | Pumps oxygenated blood to entire body | Left Atrium | Aorta |
Heart Valves: Ensuring One-Way Blood Flow
Heart valves prevent backflow of blood between chambers and into vessels:
- Tricuspid valve — Between right atrium and right ventricle (3 cusps)
- Pulmonary (semilunar) valve — Between right ventricle and pulmonary artery
- Bicuspid (mitral) valve — Between left atrium and left ventricle (2 cusps)
- Aortic (semilunar) valve — Between left ventricle and aorta
Blood Circulation: Two Circuits
Pulmonary Circulation
Carries deoxygenated blood from the right side of the heart → lungs → left side of the heart. In the lungs, carbon dioxide is exchanged for oxygen (gas exchange).
Systemic Circulation
Carries oxygenated blood from the left side of the heart → body tissues → right side of the heart. Delivers oxygen and nutrients to all organs while collecting metabolic waste.
The Cardiac Cycle
The cardiac cycle refers to one complete sequence of heart contraction and relaxation:
- Diastole (Relaxation): All chambers relax; blood flows passively into atria from veins
- Atrial Systole (Atrial Contraction): Atria contract, pushing remaining blood into ventricles
- Ventricular Systole (Ventricular Contraction): Ventricles contract; blood is ejected into pulmonary artery and aorta
Normal resting heart rate is 60–100 beats per minute. The heart sounds ("lub-dub") are caused by the closing of the AV valves (lub) and semilunar valves (dub).
Cardiac Output: The Key Measure
Cardiac Output (CO) = Heart Rate (HR) × Stroke Volume (SV)
Where stroke volume is the amount of blood ejected per beat (typically ~70 mL at rest). At rest, a normal adult has a cardiac output of approximately 5 litres per minute. Understanding this equation explains how drugs like beta blockers (which reduce HR) lower cardiac output and blood pressure.
Clinical Relevance: Drugs Acting on the Cardiovascular System
- Beta Blockers (e.g., atenolol) — Reduce heart rate and force of contraction; used in hypertension and angina
- ACE Inhibitors (e.g., enalapril) — Reduce blood pressure by preventing vasoconstriction
- Digoxin — Increases myocardial contractility; used in heart failure
- Diuretics (e.g., furosemide) — Reduce blood volume, lowering cardiac preload
Exam Tips for the Cardiovascular System
- Always draw a labeled diagram of the heart — name all four chambers, four valves, and the major vessels.
- Trace the path of a red blood cell from the right atrium back to the right atrium through systemic circulation.
- Know the cardiac cycle stages and what happens at each valve during each phase.
- Understand the cardiac output formula and be able to calculate it from given values.