Biology207 views·Updated Jun 5, 2026·2 pages

IB Biology: Overview of the Circulatory System (6.2)

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The circulatory system is your body's transportation network, moving blood,...

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6.2. Circulatory System

ideas before and after William Harvey heart as a pump
separate circulation for lungs.
The heart has four chambers
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The Heart and Blood Vessels

Your heart is divided into four chambers—two atria that collect returning blood and two ventricles that pump it out. The left side handles oxygenated blood (pushing it to your body) while the right side manages deoxygenated blood (sending it to your lungs). The left side is stronger since it needs to pump blood throughout your entire body.

Blood travels through three main types of vessels. Arteries carry blood away from the heart under high pressure, featuring thick walls with elastic fibers that help maintain pulse flow. Veins return blood to the heart under low pressure and have valves to prevent backflow. Capillaries are tiny vessels where the actual exchange of materials happens between blood and body tissues.

The heart's structure is designed for efficiency. Four valves (tricuspid, bicuspid, pulmonary, and aortic) ensure blood flows in one direction. The septum divides the heart into left and right sides, preventing oxygenated and deoxygenated blood from mixing.

Did you know? Capillaries are so small that red blood cells must pass through them in single file. This tiny size is crucial for allowing efficient exchange of oxygen, nutrients, and waste products between your blood and tissues.

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The Heartbeat and Circulation

Your heartbeat is myogenic, meaning it originates within the heart itself, not from external nerve signals. The process starts at the sinoatrial (SA) node, your heart's natural pacemaker, which sends electrical impulses that trigger contractions. This signal travels to the atrioventricular (AV) node, down the bundle of His, and through Purkinje fibers, creating the coordinated pumping action.

Each heartbeat follows a cardiac cycle of systole (contraction) and diastole (relaxation). During systole, ventricles contract and push blood out through arteries. During diastole, the heart relaxes and fills with returning blood. These alternating phases create the familiar "lub-dub" heart sounds you hear through a stethoscope.

Your heart rate can be regulated by both nerve signals and hormones. Noradrenaline from sympathetic nerves and adrenaline from adrenal glands increase heart rate during stress or exercise. Conversely, acetylcholine from parasympathetic nerves slows your heart rate during rest.

Important! Blood pressure is measured as systolic/diastolic $like 120/80$ . The first number represents pressure during heart contraction, while the second shows pressure during heart relaxation. Understanding these numbers helps you monitor your cardiovascular health.

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Biology207 views·Updated Jun 5, 2026·2 pages

IB Biology: Overview of the Circulatory System (6.2)

Val@val.vasqc

Add to Google sources

The circulatory system is your body's transportation network, moving blood, oxygen, nutrients, and waste throughout your body. At its center is the heart, a powerful four-chambered pump that keeps blood flowing through a complex network of vessels. Understanding how this...

of 2

The Heart and Blood Vessels

Did you know? Capillaries are so small that red blood cells must pass through them in single file. This tiny size is crucial for allowing efficient exchange of oxygen, nutrients, and waste products between your blood and tissues.

of 2

The Heartbeat and Circulation

Important! Blood pressure is measured as systolic/diastolic $like 120/80$ . The first number represents pressure during heart contraction, while the second shows pressure during heart relaxation. Understanding these numbers helps you monitor your cardiovascular health.