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Blood Flow
Volume of blood passing a point per unit time (ml/min)
Blood Velocity
Displacement of blood in circulation (cm/s)
Pressure Gradient
Force pushing liquid through a vessel
Resistance
Opposition to blood flow in vessels
Closed System
Cardiovascular system with no openings
Mean Arterial Pressure
Average pressure in arteries driving blood flow
Pressure Drop
Decrease in pressure from arteries to veins
Ohm's Law
Flow = Pressure gradient / Resistance
Total Peripheral Resistance (TPR)
Sum of all vascular resistance in systemic circulation
Poiseuille's Law
Flow = ΔP . π r^4 / 8ηl
Vasoconstriction
Decrease in vessel radius, increasing resistance
Vasodilation
Increase in vessel radius, decreasing resistance
Arterioles
Small arteries with high resistance to flow
Blood Viscosity
Thickness of blood affecting flow resistance
Length of Blood Vessel
Longer vessels increase resistance to flow
Radius of Blood Vessel
Critical factor affecting resistance to flow
Fluid Dynamics
Study of fluid flow principles in physiology
Systemic Circulation
Flow of blood from heart to body and back
Pulmonary Circulation
Flow of blood from heart to lungs and back
Parallel Flow
Independent regulation of blood flow to organs
Pressure Variation
Changes in blood pressure throughout circulation
Cardiovascular System
System comprising heart and blood vessels
Bulk Flow
Movement of blood driven by pressure gradients
Circulatory System
Network of vessels transporting blood
Arteriolar tone
Partially contracted state of arterioles at rest
Vasodilation (function)
Decreased contraction (increased radius)
Blood flow
Defined as the volume of blood which passes a given point in the circulation per unit time, in ml/min
Blood velocity
Displacement of blood from point of the circulation to another in cm/s
Velocity of blood flow
Inversely related to the cross sectional area of blood vessels
Cross sectional area of blood vessels
Highest in capillaries and lowest in aorta
Mean Arterial Pressure (MAP)
Average pressure in the aorta throughout the cardiac cycle
Cardiac output (CO)
Volume of blood flowing through systemic circuit per minute
Pressure gradient (ΔP)
The force that drives the flow (equals pressure difference across the system)
Total peripheral resistance (TPR)
Combined resistance of the systemic organs plus all blood vessels leading to and from them
Blood pressure (BP)
Refers to the pressure in the arteries/aorta exerted by the blood in the inner wall of the blood vessels
Systolic pressure
Achieved during ventricular contraction, approximately 120-140 mmHg in a healthy resting adult
Diastolic pressure
Achieved during relaxation phase of cardiac cycle, approximately 70-90 mmHg in a healthy resting adult
Pulse pressure
Systolic BP - diastolic BP
MAP calculation
MAP = 1/3 (systolic BP - diastolic BP) + diastolic BP
Blood pressure regulation factors
BP = Cardiac output (CO) x Total peripheral resistance (TPR)
Baroreceptor reflex mechanism
High pressure sensors that respond to stretch caused by blood pressure
Afferent innervation
Sensory impulses from the aortic arch baroreceptors travel in the vagus nerve
Cardiovascular Centre (CVC)
Located in the medulla oblongata, integrates impulse from other areas in the brain
Nucleus of tractus solitaries (NTS)
Receives impulse from the vagus and glossopharyngeal nerves
Cardio-Acceleratory Centre (CAC)
Transmits excitatory impulse to the heart and blood vessel via the sympathetic nerves
Cardio-Inhibitory Centre (CIC)
Transmits inhibitory impulse to the heart via the parasympathetic nerve
Vasomotor centre
Inhibited by increased blood pressure, reducing sympathetic vasoconstrictor tone
Parasympathetic activity
Innervates SA node and AV node, releasing acetylcholine which acts on muscarinic receptors
Acetylcholine
Neurotransmitter that activates muscarinic receptors.
Muscarinic receptors
Receptors that mediate parasympathetic effects.
Heart rate (HR)
Number of heartbeats per minute.
Venodilation
Widening of veins, decreases venous return (VR).
AV nodal delay
Increased delay in electrical conduction through the AV node.
Sympathetic discharge
Nerve signals that increase heart and vessel activity.
Contractility
Strength of heart muscle contractions.
Stroke volume (SV)
Amount of blood ejected by the heart per beat.
Baroreceptor reflex
Response to changes in blood pressure via baroreceptors.
Nucleus tractus solitarius (NTS)
Brain region processing baroreceptor signals.
Cardioaccelerator center (CAC)
Stimulates sympathetic activity to increase heart rate.
Vasomotor center
Regulates blood vessel constriction and dilation.
Noradrenaline
Neurotransmitter that stimulates sympathetic responses.
β1-adrenoreceptors
Receptors that increase heart rate and contractility.
Renin-angiotensin-aldosterone system (RAAS)
Hormonal system regulating blood pressure and volume.
Atrial Natriuretic Peptide (ANP)
Hormone that decreases blood volume and pressure.
Juxtaglomerular cells
Cells in kidneys that release renin.
Angiotensin II
Hormone that increases blood pressure and volume.
Aldosterone
Hormone that promotes sodium and water retention.
Antidiuretic hormone (ADH)
Hormone that increases water reabsorption in kidneys.
Blood volume regulation
Determines venous pressure and cardiac output.
Short-term blood pressure regulation
Immediate response to blood pressure changes.
Long-term blood pressure regulation
Regulates blood pressure through fluid balance.
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