Circulatory Systems Overview
📌 The circulatory system in most animals uses blood vessels, a pump, and valves to transport nutrients and gases.
🐠 Fish possess a single circulatory system where blood passes through the two-chambered heart (atrium and ventricle) only once per full body circuit.
🔄 In fish, deoxygenated blood moves through the heart to the gills for oxygenation (Gill circulation), then to body capillaries (systemic circulation).

Double Circulation in Mammals
🐘 Mammals utilize a double circulatory system, meaning blood passes through the four-chambered heart twice per body circuit.
🩸 Pulmonary circulation involves the right side of the heart pumping deoxygenated blood via the pulmonary artery to the lungs for oxygen absorption.
🌊 Systemic circulation involves the left side of the heart pumping oxygenated blood via the aorta to the rest of the body.
💪 Double circulation maintains a higher blood pressure, efficiently supplying large animals like mammals with necessary oxygen and glucose.

Mammalian Heart Structure and Function
❤️ The heart has four chambers: two atria (receiving chambers) and two ventricles (pumping chambers).
➡️ Deoxygenated blood enters the right atrium via the vena cava, passes through the tricuspid valve to the right ventricle.
⬅️ Oxygenated blood enters the left atrium via the pulmonary vein, passes through the bicuspid valve to the left ventricle.
🧱 Ventricles have thicker muscle walls than atria; the left ventricle wall is the thickest as it pumps blood to the entire body.
🛑 The septum separates the two sides, preventing the mixing of oxygenated and deoxygenated blood.

Heart Response and Disease
🏃 During exercise, heart rate increases to meet the higher demand for oxygen and glucose for respiration and to remove waste products faster.
🩺 Coronary arteries supply oxygen-rich blood to the heart muscle tissue itself.
💔 Coronary heart disease (CHD) occurs when coronary arteries become blocked, often by cholesterol/fatty deposits, starving the heart muscle of oxygen, potentially causing a heart attack.
📉 Risk factors for CHD include high intake of saturated fats, lack of exercise, stress, smoking, genetic predisposition, older age, and being male.

Key Points & Insights
➡️ Remember blood flow direction: Arteries carry blood AWAY from the heart (Aorta, Pulmonary Artery); Veins carry blood TOWARDS the heart.
➡️ The left ventricle muscle is thicker than the right because it pumps blood throughout the entire body under higher pressure.
➡️ To reduce CHD risk, one should quit smoking, maintain a healthy diet low in animal fats, and exercise regularly.
➡️ Heart activity can be monitored by measuring pulse rate (which increases with exercise) or listening to valve sounds with a stethoscope.

📸 Video summarized with SummaryTube.com on Nov 30, 2025, 13:49 UTC