Flow and Pressure Flashcards
systemic blood pressure
-sum total of all the local blood pressures and flows
acute control of blood flow
- mediated by changes in the vessel wall that causes dilation or constriction
- vasodilator theory - the greater the rate of metabolism or the less availability of O2, the greater the rate of formation of vasodilator substances
- oxygen demand theory - O2 is a metabolic nutrient required for vascular muscle contraction so the absence of O2 causes relaxation
- they probably both exert some effect
long term control of blood flow
-EXERCISE: angiogenesis enhances blood flow. Muscle cells also increase number of mitochondria in sarcoplasm
Autoregulation of blood pressure
- increased pressure causes rise in flow which resolves after about 1 minute
- metabolic theory: increases or decreases in metabolic activity determine the dilation/constriction of the supplying vessels (ex. when the arterial pressure becomes too great, the excess flow provides too much O2 and nutrients to the tissues and “washes out” the vasodilators released by the tissues - this then causes the blood vessels to constrict)
- myogenic theory: smooth muscle, when stretched, will vasoconstrict to decrease flow, which maintains constant flow through the vessel
reflexive washout in the brain
when acid or CO2 builds up, there will be vasodilation that helps to wash out the tissue of the brain to get rid of those substances
NO (acute)
- nitric oxide
- released with stress on arterial wall
- causes vasodilation
- only lasts for seconds so it is a very short term regulator
humoral regulators
- vasoconstrictiors (angio II) - increase Ca
- vasodilators (NO) - decrease Ca
- ions (Ca) are needed to cause vasoconstriction and vasodilation
vasomotor center
- in the medulla of the brainstem with the reticular activating system and cardiopulmonary center
- mediates vascular tone - responds to cells in the medulla and causes effects through sympathetic nerve fibers
vasoconstrictor tone
-constant low level of sympathetic activity that keeps a little bit of contraction in vasculature at all times
three changes that occur when to create a rapid increase in arterial pressure
- occurs when you have a “near miss”
- tachycardia, vasoconstriction, and contractility
effect of exercise on blood pressure
- local vasodilation of the muscle vasculature
- elevation of arterial pressure caused by sympathetic stimulation of overall circulation
- reticular activating system of brain stimulation of the vasoconstrictor and cardioacceleratory areas of the vasomotor center
Baroreceptors
- reflex is initiated by stretch receptors located at points in the walls of several large arteries (wall of each internal carotid, wall of the aortic arch)
- rise in pressure stretches them causing them to transmit signals to CNS
- habituation - all sensory nerves habituate to their stimulus
chemoreceptors
- not as important as baroreceptors
- location: pons and medulla - you have a top down influence which means that its about experience, memories, and associations
orthostatic hypotension
- as we age, reflexes diminish
- in this case, people have problems with sitting to standing (reflex doesnt kick on fast enough)
bainbridge effect
- increase HR due to increase in central venous pressure (atrial pressure)
- stretch receptors of atria respond by increasing HR and contractility to prevent damming of blood in the veins, atria, and pulm circulation
- very local reflex that involves the venoatrial junction
- can cause a 40-60% increase in HR
