Cardiovascular system

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Here is a concise overview of the cardiovascular system — its anatomy and physiology.

The Cardiovascular System: Overview

What It Does

The cardiovascular system is a closed-loop transport network that delivers oxygen, nutrients, hormones, and immune cells to tissues while removing carbon dioxide and metabolic waste. It consists of the heart, blood vessels (arteries, veins, capillaries), and blood.

The Heart — Anatomy

The heart is a four-chambered muscular pump divided into two parallel circuits:

Chamber	Role
Right atrium	Receives deoxygenated blood from superior & inferior vena cavae
Right ventricle	Pumps blood to the lungs via the pulmonary artery
Left atrium	Receives oxygenated blood from pulmonary veins
Left ventricle	Pumps oxygenated blood to the body via the aorta (thick-walled, high-pressure)

Four valves prevent backflow:

AV valves (between atria and ventricles): Tricuspid (right), Mitral (left)
Semilunar valves (at outflow): Pulmonary, Aortic

Wall layers (inner → outer): Endocardium → Myocardium → Epicardium → Pericardial space → Fibrous pericardium

The ventricular wall is mostly cardiomyocytes but 60–70% of cardiac cells are actually fibroblasts, which produce collagen to maintain structural integrity. — Goldman-Cecil Medicine

Cardiac Muscle — Special Features

Cardiac muscle is striated like skeletal muscle but unique in that:

Cells are connected by intercalated discs containing gap junctions → ions flow freely → the heart acts as an electrical syncytium (one cell depolarizes, all depolarize)
It has automaticity — specialized pacemaker cells (SA node) generate rhythmic action potentials without external input
The left ventricle has a double-helix fiber arrangement that creates a wringing/twisting motion during systole, aiding ejection. At end-systole, the ventricle recoils like a spring during diastole to rapidly fill. — Guyton & Hall Medical Physiology

Two Circuits of Circulation

Body tissues → [Veins] → Right heart → Pulmonary artery → Lungs (gas exchange)
     ↑                                                              ↓
  [Arteries] ← Left heart ← Pulmonary veins ←←←←←←←←←←←←←←←←←←←←

Pulmonary circuit (right heart → lungs → left heart): low pressure; CO₂ out, O₂ in
Systemic circuit (left heart → body → right heart): high pressure; delivers O₂ and nutrients

Coronary Circulation

The heart itself is supplied by coronary arteries arising from the aorta just above the aortic valve. Key features:

Coronary flow to the epicardium occurs during both systole and diastole
Flow to the endocardium occurs predominantly during diastole (compressed during systole by high LV pressures) — Goldman-Cecil Medicine

Regulation of Cardiovascular Function

System	Effect
Sympathetic (SNS)	↑ Heart rate, ↑ contractility, vasoconstriction (via norepinephrine/epinephrine)
Parasympathetic (vagus)	↓ Heart rate, slows AV conduction (via acetylcholine at SA/AV nodes)
Renin-angiotensin system	↑ Blood pressure via angiotensin II (vasoconstriction) + aldosterone (Na⁺/water retention)
Local metabolites	Nitric oxide, adenosine, CO₂ → coronary vasodilation (up to 6-fold)

Cardiac Energetics

The heart relies almost entirely on aerobic metabolism — primarily oxidizing fatty acids and glucose. It has virtually no capacity for anaerobic metabolism, making it exquisitely sensitive to hypoxia and ischemia. — Goldman-Cecil Medicine

Sources: Goldman-Cecil Medicine (International Ed.) | Guyton & Hall Textbook of Medical Physiology

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