Muscle Junctions

  • Types of Muscle Junctions:
    • Desmosomes:
    • Adhere to mechanically hold cells together
    • Example: Abundant in cardiac tissue (heart) where mechanical stress is high
    • Function: Withstand forces during contraction and movement.
    • Gap Junctions:
    • Found in areas of low resistance, do not require intense mechanical support
    • Function: Allow low electrical impulses to pass between cells

Pericardial Sac

  • Definition:
    • Surrounds and protects the heart
    • Comprised of two layers:
    • Fibrous Layer: Provides structural support
    • Serous Layer: Secretes fluid to reduce friction during heart movement
  • Pericarditis:
    • Inflammation of the pericardial sac, can cause friction, pain
    • Often due to viral or bacterial infections.

Heart's Electrical Activity

  • Autorhythmicity:
    • The heart's ability to contract rhythmically; begins with action potentials generated within cardiac cells
    • Contractile Cells:
    • 99% of cardiac muscle cells, responsible for pumping blood
    • Autorhythmic Cells (Pacemaker):
    • Initiate and conduct action potentials; do not contract
    • Responsible for starting the cardiac cycle.

Cardiac Cycle

  • Phases of Heart Function:
    • Systole: Heart muscle contraction
    • Diastole: Heart muscle relaxation
  • Cardiac Output:
    • Volume of blood each ventricle pumps per minute, influenced by:
    • Heart Rate (beats per minute)
    • Stroke Volume (amount of blood pumped per beat)
  • Normal Range of Heart Rate: Approximately 60-100 beats per minute

Abnormal Heart Conditions

  • Bradycardia: Slower than normal heart rate
  • Tachycardia: Faster than normal heart rate
  • Arrhythmia: Abnormal heart rhythms
  • Myocardial Ischemia: Inadequate delivery of oxygenated blood to heart muscle
    • Can lead to a Myocardial Infarction (Heart Attack).

Heart Failure

  • Types of Heart Failure:
    • Systolic Heart Failure: Difficulty in pumping blood out
    • Diastolic Heart Failure: Trouble filling with blood
  • Cause: Reduced contractility over time leads to weaker heart function and fluid retention, resulting in edema.
  • Forward Failure: Heart fails to pump enough blood to tissues
  • Congestive Heart Failure: Long-term failure where heart cannot meet body’s demands.

Coronary Artery Disease (CAD)

  • Narrowing of coronary arteries diminishes blood flow
  • Risk Factors and Consequences:
    • Major cause of death globally
    • Can lead to myocardial ischemia and heart attacks
  • Mechanisms causing CAD:
    • Vascular spasms
    • Atherosclerotic plaques
    • Thromboembolism (blood clots).

Vascular Resistance and Blood Pressure

  • Arterioles: Control blood flow through organs, can narrow (vasoconstriction) or widen (vasodilation)
  • Blood Pressure: Force of blood against vessel walls, influenced by cardiac output and vascular resistance
  • Assessment: Measured with systolic (pressure during contraction) and diastolic (pressure during relaxation) values.

Lymphatic System and Edema

  • Returns interstitial fluid to blood, aids in immune function
  • Edema: Swelling due to excess fluid accumulation, often linked to reduced plasma protein concentrations.

Hemostasis

  • Process that prevents or stops bleeding, crucial for body injury repair
  • Key Factors: Platelet activation, blood clot formation
  • Example: Response to a broken bone.