BIO 102 Lecture 9 -24 Section 2 : Circulatory System: Closed vs. Open, and Blood Vessel Types

  • Closed Circulatory System vs. Open Circulatory System

    • Closed Circulatory System: The blood is confined to blood vessels and does not leave them unless there is an issue. This is the type of circulatory system humans possess.

      • Exchange: In a closed system, all nutrient and gas exchange (e.g., picking up oxygen, dropping off carbon dioxide) occurs across the walls of capillaries.

    • Open Circulatory System: Found in animals like octopuses and squids, the blood can leave blood vessels and come into direct contact with tissues and organs within body chambers.

  • Types of Blood Vessels in a Closed Circulatory System

    • Arteries:

      • Carry blood away from the heart.

      • With one exception, arteries always contain oxygen-rich blood.

      • Have thick, layered walls; some arteries can be contractile.

      • Blood is under high pressure in arteries, which is why blood can spurt from a cut artery.

      • The lumen (inner space) is proportionately smaller due to the thick walls.

      • The aorta is the major artery that carries oxygen-rich blood out of the heart into the body.

      • Cannot afford to be without oxygen, hence the robust structure and propulsion.

    • Arterioles: Smaller arteries, which split further.

    • Capillaries:

      • Minute blood vessels where the exchange of gases, nutrients, and waste products occurs between blood and tissues.

      • Form extensive networks called capillary beds (e.g., in the lungs around alveoli, and in the kidneys).

    • Venules: Small veins, formed after capillaries merge.

    • Veins:

      • Carry blood toward the heart.

      • With one exception, veins always contain oxygen-poor blood.

      • Have semilunar valves to ensure blood flows only in one direction (toward the heart).

      • Blood pressure is not as high as in arteries, so there is a tendency for backflow; valves prevent this pooling and backward movement.

      • Varicose veins (or spider veins): Occur when the layers of the vein break down, allowing blood to pool and causing bulging. This can be exacerbated by jobs requiring prolonged standing.

  • The Pulmonary Exception

    • The general rule (arteries carry oxygen-rich blood away; veins carry oxygen-poor blood toward) is reversed for the pulmonary circuit.

    • Pulmonary Artery: Carries oxygen-poor blood from the heart to the lungs.

    • Pulmonary Vein: Carries oxygen-rich blood from the lungs to the heart.