Lecture Outline: The Cardiovascular System, Perfusion, and Circulation

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Introduction to the Cardiovascular System
1. Relationship to Circulatory System
  1. Cardiovascular system: heart and vessels
  2. Circulatory system: heart, vessels, and blood
2. Location of the Heart
  1. Between the two lungs, in the mediastinum
  2. Situated diagonally, apex points to lower left
  3. More to the left of the midline, making the left lung smaller
3. Membranes Surrounding the Heart
  1. Pericardium (serous membrane)
    1. Features two layers with pericardial fluid between them
    2. Allows for slippage and movement without abrasion
  2. Pericardium Layers
    1. Parietal layer (more superficial)
    2. Visceral layer (in direct contact with heart)
      1. Also called epicardium (part of heart wall)
    3. Fibrous layer (superficial to serous pericardium)
Heart Anatomy and Function
1. Heart as a Pump: Two Pumps in One
  1. Four chambers: two atria (superior), two ventricles (inferior)
    1. Right atrium and right ventricle
    2. Left atrium and left ventricle
  2. Blood does not mix between right and left sides
2. Heart Wall Layers (from superficial to deep)
  1. Epicardium (visceral layer of serous pericardium)
  2. Myocardium (thickest, cardiac muscle tissue)
  3. Endocardium (inner lining, in direct contact with blood)
3. Atria vs. Ventricles (Wall Thickness)
  1. Atria are much thinner-walled and less muscular (pump to adjacent ventricles)
  2. Ventricles are much thicker-walled and more muscular (pump blood through longer distances)
  3. Left ventricle is much thicker than right ventricle
    1. Pumps blood to the systemic circuit (rest of body)
    2. Right ventricle pumps blood to the pulmonary circuit (lungs)
4. Heart Valves: Ensure One-Way Blood Flow
  1. Atrioventricular (AV) Valves
    1. Located between an atrium and a ventricle
    2. Open downward (inferiorly)
    3. Anchored by chordae tendineae to ventricular wall (prevent backward flow)
    4. Types:
      1. Right AV valve (Tricuspid valve): between right atrium and right ventricle (3 cusps)
      2. Left AV valve (Bicuspid valve): between left atrium and left ventricle (2 cusps)
  2. Semilunar Valves (half-moon shaped)
    1. Located between a ventricle and its major artery
    2. Open upward (superiorly)
    3. No chordae tendineae
    4. Types:
      1. Right semilunar valve (Pulmonary semilunar valve): between right ventricle and pulmonary trunk
      2. Left semilunar valve (Aortic semilunar valve): between left ventricle and aorta
Blood Flow Circuits
1. Pulmonary Circuit
  1. Involves the right side of the heart
  2. Deoxygenated blood from body enters right atrium, then right ventricle
  3. Right ventricle pumps blood through pulmonary semilunar valve into pulmonary trunk
  4. Pulmonary trunk splits into pulmonary arteries, then arterioles, then capillaries in lungs
  5. Gas exchange in lung capillaries: CO2 released, O2 picked up (blood becomes oxygenated)
  6. Oxygenated blood returns to heart via venules, then larger veins, then pulmonary veins
  7. Pulmonary veins empty into the left atrium
2. Systemic Circuit
  1. Involves the left side of the heart
  2. Oxygenated blood from lungs enters left atrium, then left ventricle
  3. Left ventricle pumps blood through aortic semilunar valve into the aorta
  4. Aorta branches into arteries, then arterioles, then capillaries throughout the body
  5. Gas exchange in body capillaries: O2 delivered to cells, CO2 picked up (blood becomes deoxygenated)
  6. Deoxygenated blood returns to heart via venules, then larger veins
  7. Superior Vena Cava (from upper body) and Inferior Vena Cava (from lower body) empty into the right atrium
3. Coronary Circuit (Blood supply to the heart muscle itself)
  1. Heart muscle (myocardium) is too thick for direct diffusion of oxygen from blood in chambers
  2. Coronary arteries branch off the aorta, deliver oxygenated blood to heart muscle
  3. Coronary veins drain deoxygenated blood from heart muscle, dump into the right atrium
Electrical System of the Heart
1. Composed of specialized excitable tissues
2. Generates and transmits action potentials for rhythmic beating
3. Components and Sequence of Operation:
  1. Sinoatrial (SA) Node
    1. "Pacemaker of the heart"
    2. Located in the right atrium
    3. Creates initial action potentials, causing both atria to contract almost simultaneously
  2. Atrioventricular (AV) Node
    1. Located near the junction of atrium and ventricle
    2. Transmits signal from SA node to ventricles
    3. Delays signal to allow atria to fully empty into ventricles
  3. Atrioventricular (AV) Bundle
    1. Located in the interventricular septum
    2. Rapidly transmits signal after AV node delay
  4. Bundle Branches (two major branches, one for each ventricle)
    1. Send signals down toward the apex of the heart
  5. Purkinje Fibers
    1. Distribute signals to muscle cells in ventricular walls
    2. Ensure ventricles contract from bottom upward, efficiently ejecting blood
Cardiac Cycle (One cycle of the pump)
1. Diastole (Relaxation)
  1. Atrial Diastole: All four chambers relaxed, blood passively enters atria and spills into ventricles
2. Systole (Contraction)
  1. Atrial Systole: Only atria contract, squeezing remaining blood into ventricles
  2. Ventricular Systole: Ventricles contract
    1. Isovolumetric Contraction: Initial phase, pressure builds, volume doesn't change
    2. Ejection Phase: Pressure opens semilunar valves, blood is forced into major arteries, ventricular volume decreases
3. Isovolumetric Relaxation: Ventricles relax, ending the cycle
Blood Vessels (Beyond the Heart)
1. Categories of Blood Vessels
  1. Arteries: Carry blood away from the heart
    1. Much thicker, more muscular walls than veins
    2. Can vasoconstrict (decrease diameter) or vasodilate (increase diameter) to adjust blood flow
    3. Do not have internal valves
    4. Three layers (tunics): tunica intima, tunica media (thickest), tunica externa
  2. Arterioles: Smaller arteries
  3. Capillaries: Smallest blood vessels
    1. Site of gas exchange between blood and tissues
    2. Walls are one cell thick (endothelium)
    3. No tunics (layers)
    4. Blood pressure is continuous (zero pulse pressure)
  4. Venules: Small veins
  5. Veins: Carry blood toward the heart
    1. Much thinner, less muscular walls than arteries
    2. Have internal valves to prevent backflow due to lower pressure
    3. Skeletal muscle contractions squeeze veins, acting as a pump to push blood toward heart
    4. Three tunics: tunica intima, tunica media (thinner), tunica externa
2. Control of Blood Flow to Tissues (Perfusion)
  1. Capillary beds: Network of capillaries
  2. Pre-capillary sphincters: Rings of muscle at capillary branch points
    1. Contract to shut off blood flow to specific capillaries
    2. Relax to allow perfusion (blood flow through tissue)
  3. Vascular shunt: Direct connection from arteriole to venule, bypassing capillary bed when sphincters are contracted
  4. Not all tissues are perfused at once to prevent drastic blood pressure drop (shock)
3. Blood Flow to the Brain
  1. Brain requires continuous supply of oxygen and glucose
  2. Supplied by carotid arteries
  3. Circle of Willis: Circular arterial arrangement at base of brain
    1. Provides collateral circulation; helps maintain blood flow if one carotid artery is blocked
Blood Pressure Dynamics
1. Highest in the aorta (first artery from left ventricle)
2. Systolic pressure: Pressure during ventricular contraction
3. Diastolic pressure: Pressure during ventricular relaxation
4. Pulse pressure: Systolic pressure minus diastolic pressure (height of pressure curve)
  1. High in arteries, decreases further from heart
  2. Zero in capillaries (continuous flow needed for gas exchange)
  3. Lowest in veins (requires valves and muscle pumps to return blood to heart)
Portal Systems
1. Definition: Two capillary beds in series before blood returns to the heart
2. Hepatic Portal System (Liver)
  1. First capillary bed: surrounds digestive system (e.g., small intestine, stomach)
    1. Absorbs nutrients and toxins
  2. Blood collects into veins (e.g., hepatic portal vein) which then branch
  3. Second capillary bed: surrounds liver cells (hepatocytes)
    1. Liver processes nutrients and removes toxins
  4. Blood then returns to the heart via other veins
Major Arteries and Veins (General Overview)
1. Arteries (carrying blood away from heart)
  1. Aorta: Main artery from left ventricle
    1. Aortic arch: U-turn portion
    2. Ascending aorta, Descending aorta
    3. Branches supply lower appendages (iliac arteries), kidneys (renal arteries), and upper body (subclavian, axillary, brachial, radial, ulnar arteries)
  2. Pulmonary arteries: From right ventricle to lungs (carry deoxygenated blood)
2. Veins (carrying blood toward heart)
  1. Superior Vena Cava (SVC): Collects deoxygenated blood from upper body
  2. Inferior Vena Cava (IVC): Collects deoxygenated blood from lower body
  3. Both SVC and IVC empty into the right atrium
  4. Pulmonary veins: From lungs to left atrium (carry oxygenated blood)
  5. Other veins often named similarly to arteries (e.g., brachial vein, subclavian veins)

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