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.