Exam 2 Study Guide: The Heart and Blood Vessels

The Heart: Structure and Function

Heart Location, Pericardium, and Heart Wall

The heart is a muscular organ located in the mediastinum, slightly left of the midline and posterior to the sternum. It is surrounded by protective coverings called the pericardium, which consists of several layers.

• Mediastinum: Central compartment of the thoracic cavity where the heart resides.

• Pericardium: Double-walled sac enclosing the heart, consisting of the fibrous pericardium (outer layer) and serous pericardium (inner layer).

• Visceral Pericardium (Epicardium): The innermost layer of the serous pericardium, directly covering the heart.

• Heart Wall Layers:

  • Epicardium: Outer layer, also the visceral pericardium.

  • Myocardium: Middle, muscular layer responsible for contraction.

  • Endocardium: Inner layer lining the heart chambers.

Chambers and Associated Great Vessels

The heart has four chambers: two atria and two ventricles. Blood enters and exits these chambers through major vessels.

• Atria: Receive blood returning to the heart.

  • Right atrium receives blood from the Superior Vena Cava (SVC), Inferior Vena Cava (IVC), and Coronary Sinus.

  • Left atrium receives blood from four Pulmonary Veins.

• Ventricles: Pump blood out of the heart to the lungs and body.

Blood Flow Through the Heart

Pulmonary vs. Systemic Circulation

Blood flows through two main circuits: pulmonary (to the lungs) and systemic (to the body).

• Pulmonary Circuit: Right ventricle → pulmonary arteries → lungs → pulmonary veins → left atrium.

• Systemic Circuit: Left ventricle → aorta → body tissues → veins → right atrium.

• Key Difference: Pulmonary circuit exchanges gases in the lungs; systemic circuit delivers oxygen and nutrients to tissues.

Coronary Circulation and Cardiac Valves

Coronary Circulation

The heart receives its own blood supply via the right and left coronary arteries.

• Right Coronary Artery (RCA): Supplies right side of heart.

• Left Coronary Artery (LCA): Supplies left side of heart.

Cardiac Valves

Valves ensure unidirectional blood flow and prevent backflow.

• AV Valves: Tricuspid (right) and Mitral (left); open during ventricular diastole, close during systole.

• Semilunar Valves: Pulmonary and Aortic; open during ventricular systole, close during diastole.

• Valve Support Structures: Chordae tendineae and papillary muscles prevent AV valve prolapse.

• Heart Sounds: "Lub" (AV valves close), "Dup" (semilunar valves close).

Cardiac Muscle and Action Potentials

Cardiac vs. Skeletal Muscle

Cardiac muscle is striated like skeletal muscle but has unique features:

• Intercalated discs: Specialized junctions for electrical and mechanical connection.

• Autorhythmicity: Cardiac muscle can generate its own action potentials.

Action Potentials

• Pacemaker Cells: Spontaneously depolarize; phases involve opening/closing of Na+, Ca2+, and K+ channels.

• Contractile Cells: Action potential phases include rapid depolarization (Na+ influx), plateau (Ca2+ influx), and repolarization (K+ efflux).

Conduction System and ECG Basics

Conduction Sequence

The heart's electrical system coordinates contraction.

• Sequence: SA node → AV node → AV bundle → Bundle branches → Purkinje fibers

ECG Overview

• P wave: Atrial depolarization

• QRS complex: Ventricular depolarization

• T wave: Ventricular repolarization

Cardiac Cycle and Wiggers Diagram

Cardiac Cycle Pressure and Volume Concepts

The cardiac cycle describes the sequence of events in one heartbeat.

• Systole: Contraction phase

• Diastole: Relaxation phase

• Pulse Pressure: Difference between systolic and diastolic pressure

• Mean Arterial Pressure (MAP): Average pressure in arteries during one cardiac cycle

• Ventricular Volumes:

  • EDV (End Diastolic Volume): Volume at end of filling

  • ESV (End Systolic Volume): Volume at end of contraction

• Pressure Gradients: Drive valve opening/closing and blood flow direction

Cardiac Output, Stroke Volume, and Contractility

Definitions and Relationships

• Stroke Volume (SV): Blood ejected per beat

• Cardiac Output (CO): Total blood pumped per minute

• Formula:

  • $CO = SV \times HR$

• Contractility: Strength of contraction; influenced by inotropic (force) and chronotropic (rate) factors

• Frank-Starling Mechanism: Increased preload (venous return) increases SV

• Ejection Fraction: Proportion of EDV ejected per beat

  • $\text{Ejection Fraction} = \frac{SV}{EDV}$

Regulation of Heart Rate and Timing

Autonomic Regulation

• Sympathetic: Increases heart rate and contractility

• Parasympathetic: Decreases heart rate

Blood Vessels: Structure and Types

Vessel Wall Layers

• Tunica intima: Inner layer

• Tunica media: Middle, muscular layer

• Tunica externa: Outer layer

Types of Vessels

• Elastic arteries: Stretch and recoil to maintain blood pressure

• Arterioles: Major resistance vessels; regulate blood flow and pressure

• Capillaries: Thin walls for exchange by diffusion

• Veins: Return blood to heart; contain valves to prevent backflow

Blood Pressure and Peripheral Resistance

Blood Pressure Basics

• Systolic: Pressure during ventricular contraction

• Diastolic: Pressure during ventricular relaxation

Determinants of Peripheral Resistance

• Diameter: Smaller diameter increases resistance

• Length: Longer vessels increase resistance

• Viscosity: Thicker blood increases resistance

Relationship Between Flow, Pressure, and Resistance

• Formula:

  • $\text{Flow} = \frac{\text{Pressure}}{\text{Resistance}}$

Venous Return Aids

• Muscle pump: Skeletal muscle contraction helps move blood

• Respiratory pump: Breathing changes thoracic pressure, aiding return

• Venous valves: Prevent backflow

Baroreceptors and Chemoreceptors

• Baroreceptors: Detect changes in blood pressure

• Chemoreceptors: Monitor blood chemistry, influence respiratory rate

Summary Table: Cardiac Cycle Vocabulary

Term	Definition
Systole	Contraction phase of the heart
Diastole	Relaxation phase of the heart
Pulse Pressure	Difference between systolic and diastolic pressure
MAP	Mean arterial pressure; average pressure in arteries
EDV	End diastolic volume; volume at end of filling
ESV	End systolic volume; volume at end of contraction

Summary Table: Types of Blood Vessels

Type	Main Function	Key Features
Elastic Arteries	Conduct blood from heart	Stretch/recoil
Arterioles	Regulate flow/resistance	Small diameter
Capillaries	Exchange	Thin walls
Veins	Return blood	Valves, low pressure

Example: Cardiac Output Calculation

• If stroke volume (SV) is 70 mL/beat and heart rate (HR) is 75 beats/min:

• $CO = 70 \times 75 = 5250$ mL/min

Additional info: Academic context was added to clarify definitions, relationships, and formulas, and to ensure completeness for exam preparation.