Physiology of blood vessels Flashcards
Hemodynamics
A collection of mechanisms that influence the dynamic (active and changing) circulation of blood
- circulation of different volumes of blood per min is essential for healthy survival
- circulation control mechanisms must accomplish two functions:
1. Maintain circulation
2. Vary the volume and distribution of the blood circulation
Primary principle of circulation
- blood flows because a pressure gradient exists between different parts of its volume; this is based on Newton’s first and second laws of motion
- P1-P2 is the symbol used to represent a pressure gradient; P1 represents the higher pressure and P2 the lower pressure
- a perfusion pressure (PP) gradient is needed to maintain blood flow through a local tissue
Arterial blood pressure
- the primary determinant of arterial blood pressure is the volume of blood in the arteries
- a direct relationship exists between arterial blood pressure and arterial blood volume
- cardiac output (CO) is the volume of blood pumped out of the heart per unit of time (mL/min or L/min)
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Cardiac output
CO (vol/min) = SV (vol/beat) x HR (beats/min)
- the cardiac reserve is the amount the CO can increase above the resting CO
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Factors that affect SV
- starling’s law of the heart
- within limits, the longer or more stretched, the heart fibers are at the beginning of contraction, the stronger the contraction
- the amount of blood in the heart at the end of diastole determines the amount of stretch or preload placed on the heart fibers
- unlike mechanical pumps, the myocardium contracts with enough strength to match its pumping load (within certain limits) with each …
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Contractility
Strength of contraction
- also influenced by chemical factors: (1) neural: norepinephrine (2) endocrine: epinephrine (3) triggered by stress, exercise
Ejection fraction
EF is the ratio of SV to end-diastolic volume (EDV)
- usually expressed as a percentage:
EF = (SV / EDV) x 100
- in a healthy adult, the EF is at least 55% …
Afterload
The pumping work the heart must do to push blood into the arteries
- the harder it is to push blood out of the ventricles, the lower the stoke volume
- abnormally high afterload form flow resistance in the arteries can cause heart failure
Cardiac pressoreflexes
- aortic baroreceptors and carotid baroreceptors are located in the aorta and carotid sinus
- they affect the autonomic cardiac control center in the medullla, and therefore parasympathetic and sympathetic outflow, to aid in control of blood pressure
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Carotid sinus reflex
- located at the beginning of the internal carotid artery
- sensory fibers from carotid sinus baroreceptors run through the carotid sinus nerve and the glossopharyngeal nerve to the cardiac control center
- parasympathetic impulses leave the cardiac control center and travel through the vagus nerve to reach the SA node
Aortic reflex
- sensory fibers extend from baroreceptors in the wall of the aortic arch through the aortic nerve and through the vagus nerve to terminate in the cardiac control center
- stimulation causes the cardiac control center to increase vagar inhibition, this slowing the heart
