Blood Vessels: Arteries, Veins, and Capillaries
📌 Arteries carry blood away from the heart, typically oxygenated blood (except the pulmonary artery), featuring thick muscular walls and elastic fibers to handle high blood pressure and flow.
🩸 Veins transport blood toward the heart, usually deoxygenated (except the pulmonary vein), possessing thin muscular walls, large lumens, and valves to prevent backflow due to low pressure.
🔬 Capillaries are the smallest vessels, only one cell thick with thin, permeable walls, facilitating the exchange of oxygen, nutrients, and waste products between blood and cells.

Circulatory Routes and Major Vessels
➡️ The vena cava delivers deoxygenated blood from the body to the heart, while the aorta carries oxygenated blood from the heart to the body.
💨 The pulmonary artery carries deoxygenated blood to the lungs, and the pulmonary vein returns oxygenated blood to the heart from the lungs.
💧 Specific vessels serve organs, such as the renal artery/vein for the kidneys and the hepatic artery/vein for the liver.

Components and Functions of Blood
🔴 Red blood cells are biconcave discs lacking a nucleus; they contain hemoglobin to efficiently transport oxygen around the body.
🛡️ White blood cells defend the body: Phagocytes engulf pathogens via phagocytosis, and lymphocytes produce specific antibodies.
🩸 Plasma acts as a transport medium for cells, ions, nutrients, waste (like urea), hormones, and gases (like CO₂).

Blood Clotting Mechanism
🩹 Platelets initiate clotting by forming a plug at the injury site, preventing further blood loss and pathogen entry.
🕸️ During clotting, the protein fibrinogen is converted into insoluble fibrin, which forms a mesh structure where more platelets adhere, creating a scab to block the cut.

Key Points & Insights
➡️ Arteries maintain high pressure via narrow lumens and thick walls, whereas veins have large lumens and valves to manage slow flow under low pressure.
➡️ The structural feature of capillaries being one cell thick is crucial, allowing substances like O₂ and nutrients to easily diffuse into the tissue fluid and cells.
➡️ Identify key white blood cells: Phagocytes have a lobed nucleus, while lymphocytes have a large, round nucleus.

📸 Video summarized with SummaryTube.com on Nov 30, 2025, 13:55 UTC