Cardiovascular System pt 1
The Heart: Overview
Size: Roughly the size of a fist.
Function: Beats continuously throughout life, potentially up to 3 billion times.
Self-nourishment: Uses its own blood supply to sustain itself.
Autorhythmicity: Capable of initiating its own contractions without external stimuli.
Cardiovascular System
Type: Closed loop system composed of the heart and blood vessels.
Functions:
Transport oxygen (O2) and nutrients to tissues.
Remove waste products from tissues.
Help regulate body temperature.
Structure of the Heart
Chambers: 4 chambers, which are two pairs of pumps.
Right Atrium (RA) & Right Ventricle (RV).
Left Atrium (LA) & Left Ventricle (LV).
Valves:
Tricuspid Valve: Right Atrioventricular (AV) Valve.
Bicuspid Valve: Left AV Valve, also known as the Mitral Valve.
Pulmonary Valve: Right Pulmonary Semilunar Valve.
Aortic Valve: Left Pulmonary Semilunar Valve.
Major Vessels:
Vena Cava (Superior and Inferior).
Pulmonary Arteries.
Pulmonary Veins.
Aorta.
Interventricular Septum: Separates the right and left sides of the heart.
Peripheral Chemoreceptors: Located in the aorta, monitor blood composition.
Circuits of the Heart
Systemic Circuit
Function: Pumps oxygenated blood from the Left Ventricle (LV) to the entire body via the aorta.
Return: Collects deoxygenated blood into the Right Atrium (RA) via the vena cavae.
Pulmonary Circuit
Function: Pumps deoxygenated blood from the Right Ventricle (RV) to the lungs via pulmonary arteries for gas exchange.
Return: Brings oxygenated blood back to the Left Atrium (LA) via pulmonary veins.
Pulmonary Circulation
Deoxygenated blood enters:
Inferior/Superior Vena Cava → Right Atrium →
Tricuspid Valve → Right Ventricle →
Pulmonary Valve → Pulmonary Artery → Lungs → Oxygenated Blood.
Systemic Circulation
Oxygenated blood flows:
Pulmonary Vein → Left Atrium →
Bicuspid (Mitral) Valve → Left Ventricle →
Aortic Valve → Aorta → Tissues, Muscles, Organs → Deoxygenated Blood.
Blood Vessels Functions
Veins/Venules: Return blood to the heart; operate under very low pressure; valves prevent backflow.
Capillaries: Sites of oxygen and nutrient exchange within tissues.
Arteries/Arterioles: Carry blood away from the heart under high pressure; characterized by a smooth muscle layer (Tunica media).
Pericardium
Also Known As: Pericardial Sac.
Function: Protective covering over the heart; anchors the large blood vessels entering and exiting the heart.
Heart Wall Layers
Endocardium: Protective inner lining of the heart chambers.
Myocardium: Muscular layer responsible for contractions that eject blood from the heart chambers.
Epicardium: Also known as the Visceral Pericardium; serves as a lubricative outer covering.
Myocardium
Muscle Fiber Type:
Striated fibers with actin and myosin; contracts similarly to skeletal muscle.
Contains only Type 1 fibers (slow-twitch, aerobic).
Functional Unit: Depolarizes and contracts as a single functional unit due to interconnected fibers; lacks motor units.
Metabolism: Relies primarily on aerobic metabolism; significant ischemia can cause irreversible damage.
Coronary Circulation
Begins with right and left main coronary arteries that branch into smaller arteries.
Most blood flow occurs during diastole, supplying the heart with necessary blood.
Cardiac Cycle
Definition: A repeating cycle of contraction and relaxation; one complete cycle includes one contraction (systole) and one relaxation (diastole).
Phases:
Systole (Contraction Phase): Ejection of blood from ventricles; approx. 40% of the cardiac cycle.
Diastole (Relaxation Phase): Filling of ventricles with blood; approx. 60% of the cardiac cycle.
Phases of Cardiac Cycle
Cardiac Diastole: All chambers are relaxed, allowing blood to flow into the heart.
Atrial Systole & Ventricular Diastole: Atria contract, pushing blood into the ventricles.
Atrial Diastole & Ventricular Systole: After atrial relaxation, ventricles contract to push blood out of the heart.
Cardiac Cycle Dynamics
Diastole
Process: Blood flows from the atria to the ventricles.
Valves: AV valves open, semilunar valves close; right side fills with deoxygenated blood, left side fills with oxygenated blood.
Systole
Process: Blood flows from ventricles into the aorta and pulmonary arteries.
Valves: Semilunar valves open; AV valves close; right side ejects deoxygenated blood to the lungs, left side ejects oxygenated blood to the body.
Time Spent in Cardiac Cycle: Rest vs. Exercise
Systole: 0.3 seconds during heavy exercise (180 beats/min).
Diastole: 0.5 seconds at rest (75 beats/min) and 0.13 seconds during exercise.
Volume and Pressure Changes During Cardiac Cycle
Diastole: Low pressure during filling; increase in volume.
Systole: Rise in pressure during contraction; decrease in volume; produces heart sounds:
"Lubb": First sound at the end of diastole (AV valves close).
"Dupp": Second sound at the end of systole (semilunar valves close).
Measuring Blood Volume
Stroke Volume (SV): Volume of blood pumped from the left ventricle per beat.
Cardiac Output (CO): Amount of blood pumped by the heart per minute (CO = SV x HR).
Typical resting values: 70 mL stroke volume, 4900 mL/min cardiac output.
Stroke Volume Calculation
End Diastolic Volume (EDV): Volume of blood in ventricle after filling.
End Systolic Volume (ESV): Volume of blood remaining in ventricle after contraction.
Formula: SV = EDV - ESV.
Ejection Fraction (EF): Proportion of blood ejected; typically ~50-60% at rest.
Arterial Blood Pressure
Systolic Pressure: Pressure during ventricular contraction.
Diastolic Pressure: Pressure during relaxation.
Clinical Measurement: Systolic/Diastolic: Normal <120/80 mmHg, Hypertension ≥140/90 mmHg.
Mean Arterial Pressure (MAP): Average pressure in arteries; calculated as MAP = DBP + 0.33(SBP - DBP).
Factors Influencing Arterial Blood Pressure
Mechanisms: Blood volume, heart rate, stroke volume, blood viscosity, peripheral resistance.
Equation: MAP = Cardiac Output (Q) x Total Vascular Resistance.