Lecture 11 Control of Blood Flow Flashcards
True or False:
The more you increase metabolism, the more you increase oxygen availability.
False, the more you increase metabolism, then you decrease oxygen availability.
What effect does decreased oxygen availability have on blood vessels?
decreased oxygen availability -> blood vessel relaxation -> vasodilation
What is the definition of Vasomotion?
Cyclical opening and closing of pre-capillary sphincters.
What is reactive hyperemia?
Situation in which tissue blood flow is blocked (from seconds to hours or more) and then the blood flow is unblocked, thus yielding a blood flow increase of 4-7x that of normal blood flow.
*pathological condition
What is active hyperemia?
When any tissue becomes active, rate of blood flow increases.
What are the two types of blood flow control?
1) Acute Control
2) Long-term Control
What affect does long-term control (blood flow control) have on angiogenesis? What is the duration of long-term control?
Long-term control increases in sizes/numbers of vessels and occurs over a period of days, weeks, or months.
What are the two theories that regulate acute control of blood flow to tissues?
Vasodilator Theory
Oxygen (nutrient) Lack Theory
When looking at the regulation of blood flow to tissues under-control by the vasodilator theory, what would have to happen to simulate the formation of vasodilators? Vasodilators like adenosine, CO2, Histamine, K, and H+ ions.
Metabolism would have to increase, thus decreasing oxygen availability, which stimulates the formation of vasodilators.
In the oxygen (nutrient) lack theory that refers to blood flow control to tissues, what stimulates blood vessel relaxation, and thus vasodilation to increase blood flow to a specific tissue?
Decrease in Oxygen Concentration.
Fill in the Blank:
The number of _______ _______ open at any given time is roughly proportional to nutritional requirements of tissues.
The assumption is that _____ _____ require oxygen to remain contracted.
pre-capillary sphincters
smooth muscles
At 100% arterial oxygen saturation blood flow is normal. Once arterial oxygen saturation drops to 25%, how many times greater is the blood flow to that hypoxic tissue?
3 times great blood flow to that tissue.
Does autoregulation have any affect on blood pressure, or is it just regulatory of blood flow to tissues?
Autoregulation does not return blood pressure back to normal. It just regulates blood flow to tissues.
*Within minutes, blood flow returns to normal even with elevated pressure.
What are the two theories used to look at blood flow autoregulation?
Metabolic Theory
Myogenic Theory
Explain the underlying mechanism behind the metabolic theory and how autoregulation of blood flow works.
Have an increase in blood flow to a region of tissue. This is sensed as too much oxygen or nutrients to a region of tissue, thus resulting in the wash out of vasodilators. Resulting in vasoconstriction and reduced blood flow to that region of tissue.
Explain the mechanism of myogenic theory and how it’s involved in autoregulation of blood flow to a region of tissue.
The vessels in the region of tissue experiencing increased blood flow sensing stretching of the vessels. This in turn stimulates reactive vasculature constriction and the blood flow to that region of tissue is decreased.
Why does the long-term control of blood flow through a muscle remain mostly constant after autoregulation than does acute control of blood flow through a muscle after autoregulation?
Due to increase in number and size of capillaries and arterioles in the long-term control mechanism.
What is the special acute blood flow control mechanism in the kidneys? What does it involve?
Special acute blood flow mechanism is tubuloglomerular feedback
Involves the macula densa/juxtaglomerular apparatus
What is the special acute blood flow control mechanism in the brain?
There is an initial increase in CO2 and/or H+ –>
(note: this increase can be caused by increase in metabolism or a blockage of blood flow to the brain)
This causes cerebral vessel dilation –>
Causes washing out of excess CO2 / H+
What is the special acute blood flow control mechanism in the skin?
This is the system that controls body temperature by regulating blood flow.
Involves sympathetic nerves via CNS
3 ml/min/100 g tissue –> 7-8 L/min for entire body
What is endothelin and what action does it have on damaged cells?
Endothelin is a 21 amino acid long peptide that causes vasoconstriction.
What kind of cell produces nitric oxide (NO)?
Endothelial cells produce NO
Nitric oxide, along with what enzyme, activates cGTP -> cGMP?
soluble guanylate cyclase
In which cell type does cGTP get converted to cGMP?
Vascular Smooth Muscle Cells
What does cGMP activate to cause vasodilation in the endothelial cell?
cGMP activates protein kinases
Why is it so dangerous when there is damage to endothelial cells?
Hypertension can cause damage to endothelial cells, which in turn leads to the release of endothelin. Endothelin causes vasoconstriction and the damage of endothelial cells ceases the release of NO into the smooth muscle cells. Thus, cGTP is not converted to cGMP and vasodilation does not occur.
Which enzyme mediates the conversion of oxygen + L-Arginine to NO + L-Citrulline?
eNOS (nitric oxide synthetase; NO has half-life of 6 seconds)
Does norepinephrine and epinephrine control vasodilation or vasoconstriction?
Vasoconstriction
Which vasoconstriction molecule normally acts to increase the total peripheral resistance?
Angiotensin II
True or False:
Vasopressin is a very powerful vasoconstrictor and has a major function to control fluid volumes via the kidney.
True
aka = ADH
Is histamine a vasodilator or a vasoconstrictor?
Vasodilator
Which 2 cell types produce the powerful vasodilator, histamine?
Mast Cells and Basophils
Which molecule that we have studied causes both vasodilation and increased capillary permeability?
Bradykinins
What is the only vessel type that is not innervated by the sympathetic nervous system?
Capillaries
Does the sympathetic nervous system, when activated, typically result in vasoconstriction or vasodilation?
Vasoconstriction
True or False:
Sympathetic innervation causes vasoconstriction in arteries, arterioles, venules, veins, and capillaries.
False, causes vasoconstriction in all of the vessels except capillaries.
What does the continual firing of sympathetic impulses from the anterolateral portion of the upper medulla (vasoconstrictor area) result in?
Sympathetic Vasoconstrictor Tone
What is vasomotor tone created by the continuous signals to blood vessels from the vasoconstrictor area?
Partial state of contraction of blood vessels.
What is the result when the anterolateral portion of the lower medulla (vasodilator area) is activated?
It inhibits activity in the vasoconstrictor area.
The sensory area in the tractus solitarius found in the posterolateral portion of the medulla receives signals from which two cranial nerves?
Vagus Nerve (CN X)
Glossopharyngeal Nerve (CN IX)
The vasomotor center in the brain is made up of three areas, sensory area, vasodilator area, and vasoconstrictor area; which portions of the higher nervous centers controls the vasomotor center?
Reticular Substance (RAS)
Hypothalamus
Cerebral Cortex
At what pressure is the carotid body in the aortic arch stimulated at?
> 30 mmHg
At what pressure are the carotid bodies in the carotid arteries stimulated at?
> 60 mmHg
Which cranial nerve is stimulated by the baroreceptor in the aortic arch, and which vasomotor area is this impulse traveling to?
Vagus Nerve (CN X)
Impulse is traveling to the sensory area.
The baroreceptor in the carotid artery stimulates which cranial nerve, and that impulse is traveling to which vasomotor area?
glossopharyngeal nerve (CN IX)
Sensory Area
True or False:
The baroreceptor stimulates the vasoconstrictor center and inhibits the vasodilator center of the vasomotor center in the brain.
False - baroreceptors inhibit the vasoconstrictor center and stimulate the vasodilator center of the vasomotor center in the brain.
Is the stimulation of the vasodilator area from the sensory area a positive or negative feedback system?
Positive Feedback System
Is the stimulation of the vasoconstrictor area by the vasodilator area a positive or negative feedback system?
Negative Feedback System
What is vasoconstrictor tone?
continual firing of the vasoconstrictor area that sends signals to blood vessels
What is the partial state of blood vessel contraction that is the result of continuous signals being delivered to blood vessels from the vasoconstrictor area?
Vasomotor Tone
Which two vasoconstrictor molecules are secreted from the adrenal medulla?
Epinephrine
Norepinephrine
What simultaneous changes does epinephrine and norepinephrine have on rapid control of arterial pressure?
1) constriction of most systemic arteries
2) constriction of veins
3) increased heart rate
When the carotid sinuses are stimulated by pressures greater than 60 mmHg, which nerve communicates this with the glossopharyngeal nerve?
Small Herring’s Nerves
True or False:
Baroreceptors are stimulated by high arterial pressures.
False - stimulated by low arterial pressures.
True or False:
Besides being stimulated by low arterial pressures, baroreceptors are also controlled by reticular substance (RAS), hypothalamus, and the cerebral cortex.
True
What is the primary function of baroreceptors?
To reduce the minute-by-minute variation in arterial pressure.
What affect does the signals from baroreceptors have on the vasoconstrictor center? Also, the vasodilator center?
Inhibits Vasoconstrictor Center
Excites Vasodilator Center
Where are chemoreceptors located?
Located in carotid bodies in bifurcation of the common carotids and in aortic bodies.
Through which nerves do signals from chemoreceptors pass?
Herring’s Nerves and Vagus Nerves
What do chemoreceptors play an important role in?
Respiratory Control
Which ion is the chemoreceptor most sensitive too?
H+ ion, but chemosensitive cells are also sensitive to the lack of oxygen, carbon dioxide excess, and hydrogen ion excess.
True or False:
Low pressure receptors are located in the atria and pulmonary arteries and play an important role in minimizing arterial pressure changes in response to changes in blood volume.
True
Does the increase in atrial stretch result in the decrease or increase of sodium reabsorption?
Decrease in Na+ reabsorption
An increase in atrial stretch results in the release of atrial natriuretic peptide (ANP), which acts on the kidneys. Does this action result in the increase or decrease of GFR? Also, what effect does ANP have on sodium reabsorption?
Increases GFR and Decreases sodium reabsorption
True or False:
The decrease in atrial stretch signals the hypothalamus to decrease ADH concentration it releases?
False - an increase in atrial stretch signals hypothalamus to decrease ADH concentration it releases.
The increase in atrial stretch results in the reflex dilation of the kidney afferent arterioles. What affect does this have on kidney fluid loss and overall blood volume?
Increases Kidney Fluid Loss
Decreases Blood Volume
