Summary outlines for Cardiovascular Physiology
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Cardiac Cycle
● Overview: The cardiac cycle is a series of electrical and mechanical events that occur
from the beginning of one heartbeat to the start of the next. It encompasses the
relaxation (diastole) and contraction (systole) phases of both the atria and ventricles,
facilitating blood flow through the heart and body.
● Diastole:
○ Relaxation phase of the heart.
○ Atria fill with blood as they relax.
○ Ventricular filling occurs passively until pressure builds enough to open AV
valves.
● Systole:
○ Contraction phase of the heart.
○ Atrial systole forces blood into the ventricles.
○ Ventricular systole consists of two phases:
■ First phase: Ventricular contraction pushes AV valves closed.
■ Second phase: Semilunar valves open, ejecting blood into the aorta and
pulmonary artery.
● Pressure Changes:
○ Series of pressure changes within the heart chambers drive blood movement.
○ Pressure changes result from electrochemical activity in the myocardium leading
to muscle contraction.
○ Valves ensure unidirectional blood flow based on pressure gradients.
● Volume Changes:
○ Volume of blood in each chamber changes throughout the cycle.
○ Initial filling of the atria is passive; volume remains constant during isovolumetric
phases.
○ Blood fills ventricles passively during late diastole before contraction.
● Phases of Cardiac Cycle:
○ Atrial contraction (mitral valve closes).
○ Ventricular isovolumetric contraction (both valves closed, aortic valve opens).
○ Rapid ventricular ejection (blood pushed out).
○ Slow ventricular ejection (aortic valve closes).
○ Ventricular isovolumetric relaxation (both valves closed, mitral valve opens).
○ Ventricular filling (passive and active phases).
○ Diastasis (initial passive filling until pressure builds).
, Blood Pressure Regulation
● Overview: Blood pressure regulation involves complex interactions between the
autonomic nervous system and hormonal mechanisms. Key components include
baroreceptors, chemoreceptors, and both sympathetic and parasympathetic nervous
systems, which work together to maintain stable blood pressure in response to various
stimuli.
● Baroreceptors:
○ Located in carotid sinuses and aortic arch.
○ Detect changes in arterial pressure through stretch-sensitive nerve endings.
○ Increased firing rate leads to decreased heart rate and arterial pressure.
○ Acts as a buffer for acute changes in posture and blood volume.
○ Can reset to higher setpoints if blood pressure remains elevated.
● Chemoreceptors:
○ Monitor blood chemistry (e.g., oxygen, carbon dioxide levels).
○ Influence cardiovascular responses based on chemical changes.
● Sympathetic Nervous System:
○ Activates during stress or low blood pressure.
○ Increases heart rate and contractility via cardiac accelerator nerves.
○ Enhances vasoconstriction to raise blood pressure.
● Parasympathetic Nervous System:
○ Primarily mediated by the vagus nerve.
○ Decreases heart rate and promotes relaxation of blood vessels.
○ Counteracts sympathetic stimulation to lower blood pressure.
● Hormonal Mechanisms:
○ Long-term regulation mainly through the Renin-angiotensin-aldosterone system
(RAAS).
○ Hormones like adrenaline and noradrenaline also play roles in short-term
adjustments.
○ Aldosterone increases sodium and water retention, raising blood volume and
pressure.
Electrical Activity of the Heart
● Overview: The electrical activity of the heart is crucial for coordinating cardiac function
and ensuring efficient blood flow. It involves action potentials generated by specialized
cells, primarily in the SA node, which propagate through the conduction system to
stimulate heart muscle contraction.
● Action Potentials:
○ Generated by movement of ions across cell membranes.
○ Triggered when membrane potential reaches a threshold.
○ Essential for initiating heart contractions.
● SA Node (Sinoatrial Node):
sync
Cardiac Cycle
● Overview: The cardiac cycle is a series of electrical and mechanical events that occur
from the beginning of one heartbeat to the start of the next. It encompasses the
relaxation (diastole) and contraction (systole) phases of both the atria and ventricles,
facilitating blood flow through the heart and body.
● Diastole:
○ Relaxation phase of the heart.
○ Atria fill with blood as they relax.
○ Ventricular filling occurs passively until pressure builds enough to open AV
valves.
● Systole:
○ Contraction phase of the heart.
○ Atrial systole forces blood into the ventricles.
○ Ventricular systole consists of two phases:
■ First phase: Ventricular contraction pushes AV valves closed.
■ Second phase: Semilunar valves open, ejecting blood into the aorta and
pulmonary artery.
● Pressure Changes:
○ Series of pressure changes within the heart chambers drive blood movement.
○ Pressure changes result from electrochemical activity in the myocardium leading
to muscle contraction.
○ Valves ensure unidirectional blood flow based on pressure gradients.
● Volume Changes:
○ Volume of blood in each chamber changes throughout the cycle.
○ Initial filling of the atria is passive; volume remains constant during isovolumetric
phases.
○ Blood fills ventricles passively during late diastole before contraction.
● Phases of Cardiac Cycle:
○ Atrial contraction (mitral valve closes).
○ Ventricular isovolumetric contraction (both valves closed, aortic valve opens).
○ Rapid ventricular ejection (blood pushed out).
○ Slow ventricular ejection (aortic valve closes).
○ Ventricular isovolumetric relaxation (both valves closed, mitral valve opens).
○ Ventricular filling (passive and active phases).
○ Diastasis (initial passive filling until pressure builds).
, Blood Pressure Regulation
● Overview: Blood pressure regulation involves complex interactions between the
autonomic nervous system and hormonal mechanisms. Key components include
baroreceptors, chemoreceptors, and both sympathetic and parasympathetic nervous
systems, which work together to maintain stable blood pressure in response to various
stimuli.
● Baroreceptors:
○ Located in carotid sinuses and aortic arch.
○ Detect changes in arterial pressure through stretch-sensitive nerve endings.
○ Increased firing rate leads to decreased heart rate and arterial pressure.
○ Acts as a buffer for acute changes in posture and blood volume.
○ Can reset to higher setpoints if blood pressure remains elevated.
● Chemoreceptors:
○ Monitor blood chemistry (e.g., oxygen, carbon dioxide levels).
○ Influence cardiovascular responses based on chemical changes.
● Sympathetic Nervous System:
○ Activates during stress or low blood pressure.
○ Increases heart rate and contractility via cardiac accelerator nerves.
○ Enhances vasoconstriction to raise blood pressure.
● Parasympathetic Nervous System:
○ Primarily mediated by the vagus nerve.
○ Decreases heart rate and promotes relaxation of blood vessels.
○ Counteracts sympathetic stimulation to lower blood pressure.
● Hormonal Mechanisms:
○ Long-term regulation mainly through the Renin-angiotensin-aldosterone system
(RAAS).
○ Hormones like adrenaline and noradrenaline also play roles in short-term
adjustments.
○ Aldosterone increases sodium and water retention, raising blood volume and
pressure.
Electrical Activity of the Heart
● Overview: The electrical activity of the heart is crucial for coordinating cardiac function
and ensuring efficient blood flow. It involves action potentials generated by specialized
cells, primarily in the SA node, which propagate through the conduction system to
stimulate heart muscle contraction.
● Action Potentials:
○ Generated by movement of ions across cell membranes.
○ Triggered when membrane potential reaches a threshold.
○ Essential for initiating heart contractions.
● SA Node (Sinoatrial Node):
