AP Exam 2

Cardiac Conduction System

  • SA Node (Sinoatrial Node)

    • The natural pacemaker of the heart.

    • Located in the right atrium.

    • Sets the heart rhythm: 60–100 beats per minute (bpm).

    • Causes atrial depolarization represented by the P wave.

  • AV Node (Atrioventricular Node)

    • Delays impulse transmission to allow adequate ventricular filling.

    • Acts as a backup pacemaker with a rate of 40–60 bpm.

  • Bundle of His

    • The only electrical connection between the atria and ventricles.

  • Right & Left Bundle Branches

    • Conduct electrical impulses down the interventricular septum.

  • Purkinje Fibers

    • Spread impulses throughout the ventricles.

    • Operate at a rate of 20–40 bpm.

    • Responsible for coordinated ventricular contraction depicted by the QRS complex.

Systemic vs Pulmonary Circuits

  • Pulmonary Circuit

    • Pertains to the right side of the heart.

    • Responsible for carrying deoxygenated blood to the lungs.

    • Returns oxygenated blood to the left atrium.

  • Systemic Circuit

    • Pertains to the left side of the heart.

    • Pumps oxygenated blood to the body.

    • Returns deoxygenated blood to the right atrium.

  • Memory Cue:

    • Right = Respiratory (lungs)

    • Left = Larger systemic loop

Hematocrit Levels

  • Group Normal Range

    • Men: 42–52%

    • Women: 37–47%

  • Reason for Differences:

    • Testosterone increases red blood cell (RBC) production, affecting hematocrit levels in men.

    • Menstruation can lower hematocrit levels in females.

Blood Pressure Basics

  • Systolic Pressure

    • The pressure exerted during ventricular contraction.

    • Represented by the top number in a blood pressure reading.

    • Normal range: <120 mmHg.

  • Diastolic Pressure

    • The pressure exerted during ventricular relaxation.

    • Represented by the bottom number in a blood pressure reading.

    • Normal range: <80 mmHg.

  • Pulse Pressure

    • Calculated by subtracting diastolic pressure from systolic pressure:

    • extPulsePressure=extSystolic−extDiastolicext{Pulse Pressure} = ext{Systolic} - ext{Diastolic}

  • Mean Arterial Pressure (MAP)

    • Calculated using the formula:

    • extMAP=extDiastolic+rac13(extPulsePressure)ext{MAP} = ext{Diastolic} + rac{1}{3} ( ext{Pulse Pressure})

  • Where pulse pressure disappears:

    • Functionally dampened in arterioles, indicating the dynamic nature of blood pressure in the circulatory system.

Key High-Yield Facts

  • Atrial repolarization is concealed within the QRS complex.

  • The left side of the heart transports oxygenated blood.

  • The first branches off the aorta are the coronary arteries, supplying blood to the heart itself.

  • Standing up quickly can induce reflex tachycardia, a physiological response to changes in body position.

  • An Rh-negative mother with her first Rh-positive baby has a low immediate risk, but future pregnancies may require monitoring.

  • The chordae tendineae and papillary muscles work to prevent AV valve prolapse, maintaining heart function.

  • Aortic valve auscultation can be performed at the 2nd intercostal space, located at the right sternal border, allowing clinicians to assess heart function.