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BIOL 109 Ch 42_Circulation and Gas Exchange

Chapter 42: Circulation and Gas Exchange

Overview of Circulation and Gas Exchange

  • External Environment: Specialized structures (lungs, gills) facilitate gas exchange.

  • Circulation: Body tissues require thick-walled vessels for efficient circulation.

  • Fluid Movement: A pump (heart) drives fluid flow necessary for gas exchange between CO2 and O2.

42.1 Circulatory Systems Link Exchange Surfaces with Cells

  • All organisms require material exchange with their environment.

    • In directly exposed organisms, materials are exchanged directly with the environment.

    • In other organisms, diffusion of gases over larger distances is inefficient.

  • Natural Selection Solutions:

    1. Body Design: Shapes/size keep cells in direct environmental contact.

    2. Transport Systems: Connect organs of exchange with body cells (internal transport systems).

Gastrovascular Cavities

  • Found in organisms like cnidarians (e.g., jellyfish, flatworms).

  • They have a two-cell thick body wall containing a gastrovascular cavity aiding digestion, circulation, and gas exchange.

Open vs. Closed Circulatory Systems

  • Complex animals utilize either:

    • Open Circulatory Systems: Found in arthropods and some mollusks.

      • Hemolymph: Bathes organs directly; allows substance exchange with body cells.

      • Advantage: Lower energy requirements.

    • Closed Circulatory Systems: Found in earthworms and vertebrates.

      • Blood is confined to vessels, separate from body fluids.

      • Advantage: Higher blood pressure allows more efficient nutrient/O2 delivery.

Vertebrate Circulatory Systems

  • Known as the cardiovascular system.

  • Types of Blood Vessels:

    • Arteries: Carry blood from the heart to organs.

    • Arterioles: Smaller; direct blood to capillaries.

    • Capillaries: Microscopic vessels for gas/chemical exchange.

    • Venules: Collect blood from capillaries.

    • Veins: Return blood to the heart.

  • Heart Structure: Comprises muscular chambers; differences across vertebrates in chamber number and separation.

Single and Double Circulation

  • Single Circulation:

    • Observed in fish with a 2-chambered heart. Blood passes through two capillary beds before returning.

  • Double Circulation:

    • Found in amphibians, reptiles, and mammals.

    • Right heart sends O2-poor blood to lungs (pulmonary circuit) and left heart pumps O2-rich blood to body (systemic circuit).

Heart Function and Regulation

  • Mammalian Circulation:

    1. RV pumps blood to lungs.

    2. Blood loads O2, unloads CO2 in lungs.

    3. O2-rich blood returns via pulmonary veins.

    4. Blood flows to LV.

    5. LV pumps it through the aorta to body tissues.

    6. Blood returns to RA via vena cavae.

  • Cardiac Cycle: Heart beats in cycles. Four valves prevent backflow.

  • Cardiac Output (CO): Total volume of blood pumped/minute, = Heart Rate (HR) x Stroke Volume (SV).

  • Heart’s Rhythm: Controlled by the SA node (pacemaker) with signals spread through heart tissue for synchronized contraction.

Blood Vessel Structure and Function

  • Arteries:

    • Thick, elastic walls to withstand high blood pressure.

  • Veins:

    • Thinner walls, lower velocity, one-way valves prevent backflow.

  • Capillaries:

    • Thin-walled for efficient diffusion of gases/chemicals.

Blood Pressure Regulation

  • Blood pressure: Hydrostatic pressure against vessel walls.

  • Systolic/diastolic pressures reflect heart cycle stages.

  • Vasoconstriction: Smooth muscle contraction in arterioles increases BP.

  • Vasodilation: Smooth muscle relaxation decreases BP.

Capillary Function

  • Capillaries have 5-10% filled at times; control of blood flow regulated by smooth muscle and precapillary sphincters.

Lymphatic System

  • Transports lymph back to circulatory system; includes lymph nodes filtering pathogens.

Blood Composition and Function

  • Plasma (55%):

    • Contains water, ions (sodium, potassium), plasma proteins (albumin for osmotic balance, fibrinogen for clotting), nutrients, waste products, gases.

  • Cellular Elements (45%):

    • Erythrocytes (RBCs): Most abundant, transport O2 via hemoglobin.

    • Leukocytes (WBCs): Defense/immune response.

    • Platelets: Assist in blood clotting.

Blood Clotting and Cardiovascular Diseases

  • Coagulation: Forms a clot from liquid blood; complex cascade activates fibrinogen turning into fibrin.

  • Cardiovascular Diseases (CVD): Most prevalent turning out of Chester Avenue; includes atherosclerosis and heart attacks.

  • Atherosclerosis: Caused by plaque buildup from LDL in arteries reducing blood flow.

  • Heart Attack: Damage due to blockage of coronary arteries; symptoms include chest pain.

  • Stroke: Death of brain tissue from lack of O2.

Gas Exchange Mechanisms

  • Includes ventilation (movement of respiratory medium over surfaces) and surface adaptations (gills, lungs).

  • Gills: Aquatic animals; utilize counter-current exchange for efficient O2 absorption.

  • Lungs: Terrestrial adaptation; facilitate gas exchange within alveoli, facilitated by capillary networks.

Breathing Mechanisms

  • Amphibians: Positive pressure breathing, pushing air into lungs.

  • Mammals: Negative pressure, pulling air into lungs through diaphragm and rib muscle contractions.

Control of Breathing

  • Governed by the medulla oblongata responding to CO2 levels detected in the blood.