Stroke Volume (SV): The amount of blood pumped by the heart per beat, typically around 70-75 milliliters.
Cardiac Output (CO): Calculated as SV multiplied by Heart Rate (HR). Roughly, CO is about 5 liters per minute on average.
Importance of 5 Liters: Indicates that the total blood volume circulates through the heart every minute, facilitating systemic blood flow.
Calculation: Stroke Volume = End Diastolic Volume (EDV) - End Systolic Volume (ESV).
EDV: Volume of blood in ventricle at the end of filling (diastole).
ESV: Volume of blood left in ventricle after contraction (systole).
Intrinsic Controls: Factors within the heart, such as wall stretch and filling patterns.
Extrinsic Controls: Factors outside the heart, including:
Sympathetic Nervous System: Increases heart rate and force of contraction.
Parasympathetic Nervous System: Decreases heart rate, primarily through the vagus nerve.
The SA Node: The natural pacemaker of the heart, typically sets the heart rate at around 100 beats per minute.
Effects of Vagal Influence: If the vagus nerve is severed, resting heart rate could rise closer to 100 bpm.
Epinephrine and Norepinephrine: Released during stressful situations, increasing both heart rate and contractility.
Glucagon: Increases blood glucose levels, also influencing cardiac function indirectly.
Preload: Initial stretching of cardiac muscle fibers prior to contraction, related to the volume of blood filling the heart.
Increased Preload: Leads to greater stroke volume due to enhanced contractility (Starling's Law).
Afterload: The pressure against which the heart must work to eject blood; higher afterload reduces stroke volume.
Contractility: The inherent strength of myocardial contraction; increased contractility results in lower ESV and higher stroke volume.
Blood pressure gradient must exist for blood to flow, flowing from high to low pressure zones in the cardiovascular system.
Typical Pressures: Aorta at 120 mmHg while the right side of the heart is approximately 0 mmHg.
Mean Arterial Pressure (MAP): Must be adequate to maintain organ perfusion; usually around 70-100 mmHg.
Calculation of MAP: MAP = Diastolic Pressure + (1/3) Pulse Pressure
Total Peripheral Resistance (TPR): Influenced by blood vessel diameter, blood viscosity, and vessel length.
Vasoconstriction vs. Vasodilation: Diameter changes significantly alter resistance and thus blood flow.
Arteries: Carry blood away from the heart, typically with thicker walls.
Veins: Return blood to the heart and possess valves to prevent backflow due to lower pressure.
Capillaries: Sites of gas and nutrient exchange, with varying permeability based on type.
Continuous Capillaries: Tight junctions, minimal permeability.
Fenestrated Capillaries: Allow for greater permeability, found in kidneys.
Sinusoids: High permeability, allowing cells to pass, found in liver and bone marrow.
Precapillary Sphincters: Regulate blood flow into capillary beds based on local tissue demands.
Active Hyperemia: Increased blood flow in response to heightened metabolic activity in tissues.
Reactive Hyperemia: Increased blood flow following a period of restricted blood supply.
Increased Demand: During physical activity, cardiac output rises due to increases in heart rate and stroke volume.
Redistribution of Blood Flow: Blood is directed away from non-essential organs to working muscles.