Lecture 12: Control of Blood Flow I Flashcards
What is acute control of local blood flow?
rapid changes in local vasodilation/vasoconstriction
occurs in seconds to minutes
basic theories: vasodilator and oxygen lack theories
What is long term control of local blood flow?
increases in size/ numbers of vessels
occurs over a period of days, weeks, or months
What is vasodilator theory?
as metabolism increases, oxygen availability decreases resulting in formation of vasodilators
What is the oxygen lack theory?
decrease in oxygen, the blood vessels relax resulting in vasodilation
What is vasomotion?
cyclical opening and closing of precapillary sphincters
Number of precapillary sphincter open at any give time is ______ to nutritional requirements of tissues
proportional
What is reactive hyperemia?
tissue blood flow is blocked and once becoming unblocked blood flow increase 4-7x normal
What is active hyperemia?
when any tissue becomes active, rate of blood flow increases
What is blood flow auto regulation?
rapid increase in arterial pressure leads to increased blood flow
within minutes, blood flow returns to normal even with elevated pressure
What theories explain auto regulation?
metabolic theory
myogenic theory
What is the metabolic theory?
increase in blood flow —too much oxygen or nutrients —washes out vasodilators to reduce blood flow
What is the myogenic theory?
stretching of vessels– reactive vasculature constriction to reduce blood flow
How does the kidney control acute blood flow?
by tuboglomerular feedback
How does the brain control acute blood flow?
increase in CO2 or H+ —–cerebral vessel dilation —washing out excess CO2 or H+
How does the skin control acute blood flow?
blood flow linked to body temperature
sympathetic nerves via CNS
What contributes to vasoconstriction in humoral circulation control?
norepinephrine
epinephrine
angiotensin II
vasopressin
What contributes to vasodilation in humoral circulation control?
bradykinin
histamine
the sympathetic system innervates all vessels except ______
capillaries
Where is the vasoconstriction area in the brain?
anterolateral portions of upper medulla
What does the vasoconstriction area in the brain do?
transits continuous singles to blood vessels
continual firing results in sympathetic vasoconstrictor tone
where is the vasodilation area of the brain located?
bilateral in the anterolateral protons of lower medulla
What does the vasodilator area of the brain do?
inhibits activity in vasoconstrictor area
Where is the sensory area of the brain?
bilateral in tractus solitarius in posterolateral portion of medulla
What does the sensory area of the brain do?
receive signals via
- vagus nerve
- glossopharyngeal nerves
What areas of the brain are controlled by higher nervous centers?
reticular substance (RAS)
hypothalamus
cerebral cortex
What causes neural rapid control of arterial pressure?
simultaneous changes
rapid response
increased blood pressure during exercise
alarm reaction
What are the simultaneous changes that cause neural rapid control of arterial pressure?
constriction of most systemic arteries
constriction of veins
increased heart rate
Where are baroreceptors located?
carotid sinuses and aortic sinus
When are carotid sinuses stimulated?
by pressure >60 mm Hg
When are aortic sinuses stimulated?
> 80 mm Hg
What are the signals from baroreceptors?
inhibit vasoconstrictor center
excite vasodilator center
signals cause either increase or decrease in arterial pressure
What is the primary function of a baroreceptor?
reduce the minute by minute variation in arterial pressure
Where are chemoreceptors located?
carotid bodies in bifurcation of the common carotids and in aortic bodies
What do chemosensitive cells do?
sense lack of oxygen, carbon dioxide excess, and hydrogen ion excess
Where do chemoreceptor signals pass through?
Herring’s nerve and vagus nerves
Chemoreceptors play a important role in ______
respiratory control
Low pressure receptors are located in the ____ and _____ arteries and play an important role in minimizing _______ in response to changes in blood volume
atria; pulmonary; pressure changes
What does increase in atrial stress result in?
reflex dilation of kidney afferent arterioles
increase in heart rate
signals to hypothalamus to decrease ADH
atrial natriurteric peptide signals kidneys to increase GFR and decrease sodium reabsorption
What happens when the kidney afferent arterioles are reflex dilated?
increase in kidney fluid loss
decreases blood volume
What is arterial pressure?
cardiac output x total peripheral resistance
Arterial pressure rises when total peripheral resistance is ______
acutely increased
