Cardiovascular System

Cardiovascular System

Learning Objectives

Components of the Cardiovascular System

  • Blood:

    • Definition: Fluid that contains materials essential for the body.

    • Components:

    • Cells: Include red blood cells, white blood cells, and platelets.

    • Plasma: Liquid component containing water, salts, and proteins.

  • Heart:

    • Definition: The muscular pump responsible for moving blood throughout the body.

  • Blood Vessels (Vasculature):

    • Includes three major types:

    • Veins: Carry blood towards the heart.

    • Arteries: Carry blood away from the heart.

    • Capillaries: Connect veins and arteries; sites of exchange between blood and tissues.

Double Circulation

  • Defined as a system within which blood passes through the heart twice during one complete circuit of the body.

  • Components of Double Circulation:

    • Superior Vena Cava: Returns deoxygenated blood from the upper body to the right atrium.

    • Inferior Vena Cava: Returns deoxygenated blood from the lower body to the right atrium.

    • Right Atrium: Receives blood from the vena cavae.

    • Right Ventricle: Pumps blood through the pulmonary artery to the lungs for oxygenation.

    • Pulmonary Artery: Carries deoxygenated blood to the lungs.

    • Pulmonary Veins: Return oxygenated blood from the lungs to the left atrium.

    • Left Atrium: Receives oxygenated blood from the pulmonary veins.

    • Left Ventricle: Pumps oxygenated blood into the aorta for distribution to the body.

    • Aorta: The largest artery that distributes oxygenated blood to the systemic circulation.

    • Capillaries: Small vessels where exchange between blood and tissues occurs.

Systemic Circulation

  • Focused on delivering oxygenated blood to the body and returning deoxygenated blood back to the heart.

Pulmonary Circulation

  • Involves the movement of blood from the heart to the lungs and back, specifically for oxygenation.

Circulatory System Overview

  • Blood Vessels:

    • Main types:

    • Veins: Carry blood towards the heart (low pressure).

    • Arteries: Carry blood away from the heart (high pressure).

    • Venules: Small veins that connect capillaries to veins.

    • Arterioles: Small arteries that lead to capillaries.

    • Capillaries: Sites for exchange; connecting vessels of arteries and veins.

  • Functions:

    • Resistance Vessels: Regulate blood pressure and flow through arteries.

    • Exchange Vessels: Allow for nutrient and gas exchange in tissues.

Blood Flow and Pressure Changes

  • Key Principle: Blood flow changes in response to pressure gradients.

  • Driving Pressure: Created by ventricular contraction; blood flows from areas of high pressure to low pressure.

  • Pressure Gradient Equation: extFlowextisdirectlyproportionaltoriangleP=P<em>1−P</em>2ext{Flow} ext{ is directly proportional to } riangle P = P<em>1 - P</em>2

    • A higher gradient results in greater flow.

Cardiac Cycle

  • Definition: Refers to the rhythmic contraction and relaxation of the heart.

  • Phases of the Cardiac Cycle:

    • Systole: The contraction phase where blood is pumped out of the heart.

    • Ventricular Systole: Contraction of the ventricles, pushing blood into the aorta and pulmonary artery.

    • Diastole: The relaxation phase where the heart fills with blood.

    • Specific Timing of Phases:

    1. Atrial and Ventricular Diastole: 0.4 sec

    2. Atrial Systole and Ventricular Diastole: 0.1 sec

    3. Ventricular Systole and Atrial Diastole: 0.3 sec

Electric Conduction System of the Heart

  • Nodal Cells or Pacemaker Cells:

    • Sinoatrial Node (SA): Initiates the electrical signal for contraction; sets the rhythm of the heart.

    • Atrioventricular Node (AV): Positioned between the atria and ventricles; delays electrical signal to allow sufficient filling of the ventricles.

    • Bundle of His: Specialized conducting tissue that spreads depolarization through the heart.

    • Purkinje Fibers: Distribute the electrical impulse to myocardial cells throughout the ventricles.

  • Conducting Pathway:

    • SA Node → Internodal Pathways → AV Node → AV Bundle → Bundle Branches → Purkinje Fibers

Autorhythmic & Contractile Cells

  • Autorhythmic Cells:

    • Function: Spontaneously fire action potentials which spread to adjacent contractile cells.

    • Action Potentials: Trigger contraction in contractile cells via gap junctions.

  • Contractile Cells:

    • Receive electrical signals and generate force for heart contractions.

Electrocardiogram (ECG)

  • Definition: A recording of the electrical activity of the cardiac contractile cells.

  • Components of an ECG:

    • P Wave: Represents atrial depolarization.

    • P-R Segment: Indicates delay in the AV node.

    • QRS Complex: Signifies ventricular depolarization.

    • T Wave: Reflects ventricular repolarization.

  • Understanding Time Intervals:

    • All segments typically measured in millimeters on the ECG graph corresponding to specific time intervals (e.g., P-R interval, S-T interval, Q-T interval).

Cardiac Output

  • Definition: The volume of blood pumped into systemic circulation per minute.

  • Factors Affecting Cardiac Output:

    • Heart Rate (HR): Number of heartbeats per minute.

    • Stroke Volume (SV): Amount of blood ejected in a single contraction.

    • Formula: extCardiacOutput(CO)=extHeartRate(HR)imesextStrokeVolume(SV)ext{Cardiac Output (CO)} = ext{Heart Rate (HR)} imes ext{Stroke Volume (SV)}