lecture 2a Circulation_42 terms

Circulation and Key Concepts

Animal Circulatory Systems

• Components: Blood, heart, and blood vessels.

Components of Blood:

• Plasma: Composed of water, ions, and proteins.

• Cellular Components: Includes erythrocytes (red blood cells), leukocytes (white blood cells), and platelets.

The Heart:

• Structure & Function: Composed of atria (thin walls for collection) and ventricles (thick walls for pumping).

• Heartbeat Regulation: Controlled by the cardiac muscle's autorhythmic characteristics and influenced by the sinoatrial (SA) node (pacemaker) and autonomic nervous system.

Blood Vessels:

• Types: Arteries, veins, and capillaries.

  • Arteries: Carry blood away from the heart; thicker walls capable of withstanding high pressure; no valves.

  • Veins: Carry blood back to the heart; thinner walls; contain one-way valves to prevent backflow; rely on muscle contractions and gravity for blood flow.

  • Capillaries: Microscopic vessels where material exchange occurs; walls are one-cell thick to facilitate diffusion.

Lymphatic System:

• Function: Returns fluid lost from capillaries to the cardiovascular system and aids immune responses.

Diseases and Therapies:

• Discusses various cardiovascular conditions like atherosclerosis and their treatments.

Circulatory Systems in Organisms

• Material Exchange: Necessary for all organisms.

  • Unicellular Organisms: Use diffusion; effective only over short distances due to the square law of diffusion time.

  • Multicellular Organisms: Require specialized circulatory systems due to larger body size and distance for material exchange.

Internal Transport in Simple Organisms:

• Gastrovascular Cavities: Found in organisms like jellyfish and flatworms to minimize diffusion distances.

Circulatory Systems in Larger Animals:

• Types: Open and closed circulatory systems.

  • Open Circulatory Systems:

    • Found in insects, arthropods, and some mollusks.

    • Hemolymph circulates without differentiation from blood and interstitial fluid; pressure quickly diminishes.

    • Results in faster heart rates or specialized accessory hearts.

  • Closed Circulatory Systems:

    • Present in all vertebrates and some invertebrates.

    • Blood contained within vessels; substances transfer between blood and interstitial fluid.

    • More efficient transportation of nutrients and gases.

Organization of Vertebrate Circulatory Systems:

• Structure: Adult humans have about 100,000 km of blood vessels, which is more than twice the circumference of the Earth.

• Blood Flow: Arteries branch into arterioles, leading to capillaries (exchange sites), which merge into venules, returning blood to veins.

Types of Circulation:

• Single Circulation:

  • Found in bony fishes, rays, and some sharks.

  • Blood passes through two capillary beds before returning to the heart, resulting in lower pressure and no "fresh" blood for heart perfusion.

• Double Circulation:

  • Occurs in amphibians (three-chambered heart), mammals and birds (four-chambered heart).

  • Maintains separation of oxygen-rich and deoxygenated blood for more efficient gas exchange.

Heart Rates Across Species:

• Varies significantly with mass and metabolic rates:

  • Mouse: 500 beats/min

  • Human: 70 beats/min

  • Elephant: 28 beats/min

• Cardiac Output: Volume of blood pumped per minute = heart rate × stroke volume.

Major Arteries and Veins in Human Circulatory System:

• Pulmonary Circuit:

  • Pulmonary Arteries: Carry deoxygenated blood to the lungs.

  • Pulmonary Veins: Return oxygenated blood to the heart.

• Systemic Circuit:

  • Aorta: Distributes oxygenated blood throughout the body.

  • Vena Cavas: Collect deoxygenated blood from the body back to the heart.

Structure of the Mammalian Heart:

• Heart Walls: Composed of myocardium, endocardium, and pericardium.

Heart Valves:

• Atrioventricular (AV) Valves: Control blood flow between atria and ventricles.

• Semilunar Valves: Regulate blood flow into the aorta and pulmonary arteries; issues can cause heart murmurs due to backflow.

The Cardiac Cycle:

• Systole: Contraction phase.

• Diastole: Relaxation phase.

Electrical Coordination of the Heart:

• SA Node: Acts as the pacemaker; impulses travel to the AV node.

• AV Node: Delays impulses before they spread to ventricles, crucial for synchronized heart beats.

Electrocardiogram (ECG):

• Purpose: Graphical representation of heart's electrical activity.

  • Important for diagnosing conditions through observable waves and intervals (e.g., PR, QT).

Regulation of Heart Rhythm:

• Autonomic Nervous System Control:

  • Sympathetic Division: Increases heart rate via norepinephrine.

  • Parasympathetic Division: Decreases heart rate via acetylcholine.

  • Hormones and body temperature adjustments also influence heart rate.

Structure of Blood Vessels:

• Composed of lumen, endothelium, smooth muscle, and connective tissue.

• Arteries have thicker walls to manage high pressure; veins have thinner walls and special valves to prevent backflow.

Blood Flow in Veins:

• Mechanics: One-way valves prevent backflow; movement facilitated by smooth muscle contractions and skeletal muscle activity during expansion of chest cavity.

Structure of Capillaries:

• Features: Extremely thin walls are compatible with red blood cell size, allowing for effective material exchange.

Blood Pressure Dynamics:

• Systolic Pressure: Highest pressure during ventricular contraction.

• Diastolic Pressure: Lowest pressure during relaxation; arterial elasticity is crucial for maintaining blood pressure.

Measurement of Blood Pressure:

• Sphygmomanometer: Measures blood pressure changes as air is released.

Blood Pressure and Vessel Diameter:

• Blood Flow Dynamics: Slowest in capillary beds due to high resistance, essential for efficient material exchange.

Lymphatic System Role:

• Returns lost fluid to resume cardiovascular system operation and filters lymph for immune response assistance.

Capillary Function Regulation:

• Only a fraction of capillaries are filled at any time; blood flow regulated by arterioles and precapillary sphincters.

Blood Pressure Influences:

• Consider how height and gravity affect blood pressure; animals with long necks require higher pressures to ensure head perfusion.

Regulation of Blood Pressure:

• Diameter changes via vasoconstriction (narrowing) or vasodilation (widening) adjust blood pressure levels.

  • Nitric Oxide: Causes vasodilation.

  • Endothelin: Promotes vasoconstriction.

Blood Composition:

• Plasma: Comprises 55% of blood; contains electrolytes, proteins (for pH and osmotic balance).

• Cell Types: Majority erythrocytes, leukocytes, platelets make up 45% of blood volume.

Differentiation of Blood Cells:

• Blood cells arise from stem cells in red bone marrow, regulated by erythropoietin (EPO).

Erythrocytes Characteristics:

• Disc-shaped, rich in hemoglobin (O2 transport), lacking nuclei/mitochondria; lifespan ~120 days, dismantled in spleen and liver.

Leukocytes Functionality:

• Five major leukocyte types defend against pathogens; perform phagocytosis or immune responses.

Platelet Functions:

• Small fragments are vital for clotting; activated by tissue injury to form plugs and release clotting factors.

Coagulation Process:

• Transformation from liquid blood to clot involves conversion of fibrinogen to fibrin, supported by platelet aggregation, forming stable clots.

• Thrombus: Can obstruct blood flow if formed in the circulatory system.

Cardiovascular Disease Overview:

• A significant health concern driven by LDL and HDL cholesterol balance, inflammation, and high LDL/HDL ratios.

Atherosclerosis and Associated Risks:

• Defined by plaque buildup in arteries, can lead to angina, heart attacks, or strokes by obstructing blood flow or rupturing.

Future Therapies:

• Innovations include stem cells for heart tissue repair and angioplasty techniques for clearing arterial blockages.