BackThe Cardiovascular System: The Heart – Structure and Circuits
Study Guide - Smart Notes
Tailored notes based on your materials, expanded with key definitions, examples, and context.
The Cardiovascular System: The Heart
Overview
The heart is a muscular organ that serves as the central pump of the cardiovascular system, circulating blood throughout the body. It is divided into four chambers and operates as a double pump, supplying blood to two major circulatory circuits: the pulmonary and systemic circuits.
The Four Chambers of the Heart
Chamber Structure and Function
Right Atrium: Receives oxygen-poor blood returning from the systemic circuit (body tissues).
Left Atrium: Receives oxygen-rich blood returning from the pulmonary circuit (lungs).
Right Ventricle: Pumps oxygen-poor blood into the pulmonary circuit (toward the lungs).
Left Ventricle: Pumps oxygen-rich blood into the systemic circuit (toward the body tissues).
Each side of the heart supplies its own circuit, ensuring continuous and efficient blood flow to both the lungs and the rest of the body.
Pulmonary and Systemic Circuits
Definitions and Pathways
Pulmonary Circuit: Composed of arteries and veins that transport blood between the heart and lungs. The right side of the heart pumps deoxygenated blood to the lungs, where carbon dioxide is eliminated and oxygen is absorbed. Oxygenated blood then returns to the left side of the heart.
Systemic Circuit: Consists of blood vessels that carry blood between the heart and the rest of the body. The left side of the heart pumps oxygenated blood to body tissues, delivering oxygen and nutrients, and collecting carbon dioxide and waste products. Deoxygenated blood returns to the right side of the heart.
Key Points
Both circuits move equal volumes of blood per heartbeat, but the workload differs due to the distance and resistance each ventricle faces.
The right ventricle pumps blood into the shorter, low-resistance pulmonary circuit (low pressure system).
The left ventricle pumps blood into the longer, high-resistance systemic circuit (high pressure system), and thus has thicker muscular walls.
Illustrative Example
Blood flows from the right atrium → right ventricle → pulmonary arteries → lungs (gas exchange) → pulmonary veins → left atrium → left ventricle → aorta → systemic arteries → body tissues → systemic veins → right atrium.
Table: Comparison of Pulmonary and Systemic Circuits
Feature | Pulmonary Circuit | Systemic Circuit |
|---|---|---|
Originating Chamber | Right Ventricle | Left Ventricle |
Main Function | Gas exchange (CO2 out, O2 in) | Deliver O2 and nutrients to tissues |
Blood Oxygenation | Deoxygenated to oxygenated | Oxygenated to deoxygenated |
Relative Pressure | Low | High |
Ventricle Wall Thickness | Thin (crescent-shaped) | Thick (cylindrical) |
Additional info:
The heart's double-pump design ensures that oxygen-poor and oxygen-rich blood are kept separate, maximizing efficiency of gas exchange and nutrient delivery.
Failure in either circuit can lead to significant physiological consequences, such as hypoxia or systemic congestion.
