Circulation to Special Regions Flashcards
The “special circulation” with the highest percent
pulmonary (100%)
What are the primary resistance vessels of the circulatory system?
Small arteries and arterioles
These are the three main extrinsic factors that regulate smooth muscle tone
- Autonomic Nervous System
- Hormones
- Cytokines
Cytokines have this BIG effect
significant vasodilation —opens up vessels BIG TIME
These are the three main intrinsic/local factors that regulate smooth muscle tone
- Myogenic mechanisms
- Endothelial cell-mediated factors
- Metabolic factors
In the sympathetic nervous system, what controls the outflow?
The medullary vasomotor center
In the sympathetic nervous system, vasoconstriction is controlled by which adrenoceptor?
alpha1
In the sympathetic nervous system, vasodilation is controlled by which adrenoceptor?
beta2
What controls the outflow in the parasympathetic nervous system?
medullary vasomotor center
Which nervous system sets basal tone of some vascular beds by tonic activation?
Sympathetic nervous system
The parasympathetic nervous system generally has little effect in most vascular beds. What are the two exceptions?
- GI tract (indirect)
- Genitalia
- vasodilation of erectile tissue due to NO release–>activates guanylyl cylcase –> increases cyclic GMP vasodilation
- sildenafil (viagra): inhibits PDE which is responsible for cGMP hydrolysis
State how these hormonal factors affect vascular tone (i.e dilation or constriction):
- NO
- Vasopressin
- Epinephrine
- Cytokines
- Atrial Natriuretic Peptide
- Angiotensin II
- Endothelin
- Bradykinin
- NO = dilation
- Vasopressin = constriction
- Epinephrine = high [alpha] (constriction); low [beta1] (dilation)
- Cytokines = dilation
- Atrial Natriuretic Peptide (stimulated by atrial stress) = dilation
- Angiotensin II = constriction
- Endothelin = constriction
- Bradykinin = dilation
Two important cytokines. How do they decrease BP?
Tumor Necrosis Factor (TNF) and Interleukin 5
-plummet BP by decreasing R (pressure = flow x resistance
When a patient has low cardiac output, these two major players (hormonal factors) are very important for promoting vasoconstriction:
- angiotensin II
- alpha receptors
Dilation is caused by an increase or decrease in the following metabolic (intrinsic) factors: \_\_\_ adenosine \_\_\_ pH \_\_\_ P(CO2) \_\_\_ P(O2)
dilation caused by:
- increased adenosine
- decreased pH (acidic)
- increased P(CO2)
- decreased P(O2)
Where is the only place where a decrease in P(O2) causes vasoconstriction instead of dilation?
Alveolar P(O2) / lungs.
Paradoxical phenomenon: pulmonary arteries CONSTRICT in presence of hypoxia (low oxygen, such as during pneumonia) without hypercapnia (increased CO2 levels).
- Constriction leads to redistribution of blood flow to better-ventilated areas of the lung –> increases total area involves in gaseous exchange
- improves ventilation/perfusion ratio and arterial oxygenation, but less helpful for long-term whole-body hypoxia.
Definition of perfusion and ventilation
perfusion = blood that reaches alveoli ventilation = air that reaches the alveoli
Overall, how do myogenic mechanisms play a major role in autoregulation?
Under various pressures, it attempts to maintain the same flow (called a compensatory response)
Describe the myogenic mechanism for increased pressure:
increased pressure –> (increase/decrease) stretch of vascular smooth muscle cells –> (vasoconstriction/vasodilation)
increased pressure will increase the stretch of VSM cells.
Since Pressure = Flow x Resistance, or
Flow = P/R,
the increase in pressure (indicated by increase of stretch) will stimulate vasoconstriction (which will cause an increase in resistance)
When blood vessels constrict, the flow of blood is (increased/decreased), thus (increasing/decreasing) resistance
Decreased, increasing
What type of control is most important for cerebral circulation (very sensitive to changes in blood flow)?
Intrinsic control–metabolic factors especially important
In the regulation of cerebral blood flow, what range of mean arterial pressure gives you constant flow?
Constant from 65-140 mmHg
Name of doctrine that states: The sum intracerebral blood volume + CSF volume + volume taken up by central nervous tissue MUST remain constant because of space limitations imposed by carnium
Monro-Kellie Doctrine
Equation for cerebral perfusion pressure:
Mean Arterial Pressure - Intracranial Venous Pressure
The systematic circulation is a circuit in (series/parallel). What does this allow?
Parallel circuit. Allows variable amount of flow to organs which are not regulated
What can override systemic factors and allow increased flow (i.e. muscle)?
Local factors
What is extremely important to maintain constant flow over a wide range of pressures? Where is this particularly important?
Autoregulation. Very important in the cerebral cortex
What are the consequences of increased intracranial pressure?
The intracranial pressure compresses the brain vasculature, which will decrease flow DESPITE autoregulatory vasodilation (F = P/R)
If there is an increased intracranial pressure, the ischemia (narrowing of vessel/restriction in blood supply to tissue) stimulates the vasomotor center to increase what? What effect will this have?
Ischemia calls vasomotor center to tell it to increase systemic resistance! Why? It will increase blood pressure and maintain flow. Known as Cushing’s Reflex
Describe Cushing reflex mechanism
Increased ICP –> sympathetic response activates alpha1 receptors –> arterial constriction –> increases total resistance of blood flow –> elevates blood pressure (hypertension) –> attempt to restore blood flow
In addition to capillaries, what other vessels are involves in heat exchange for apical skin?
Arteriovenous anastomoses
Are arterioles under the control of local metabolites?
No-only sympathetic fibers
Sympathetic stimulation can (reduce/increase) blood flow
both!
reduce–cold weather, stress
increase–blushing
The major function of non-apical skin
thermoregulation
Changes in skin blood flow are mediated by these two branches of the sympathetic nervous system
- noradrenergic vasoconstrictors
2. cholinergic active vasodilators
Cold exposure causes (vasodilation/vasoconstriction)
vasoconstriction
How does exercise or heat exposure promote heat loss?
- By activating cholinergic sympathetic vasodilator fibers
- By activating sympathetic cholinergic fibers that innervate sweat glands–promotes sweating and evaporative heat loss
If you have someone on a beta blocker, what is one sympathetic symptom that will not be muted?
Sweating is not inhibited by the beta receptor blocker–sweat glands contain muscarinic receptors (mAChRs). Sweating can be sign that you’re hypoglycemic
A diabetic that is hypoglycemic will activate what response? Effect?
Will trigger sympathetic response, heart rate goes up, might get anxious, BP may increase, start sweating.
During exercise, what factors dominate, causing what?
Intrinsic factors can override extrinsic, leading to vasodilation
During exercise, vessels in muscles are vasodilating due to what factors?
Local intrinsic factors (metabolic–decrease PO2, increased PCO2, decreased pH, increased adenosine)
During exercise, there is a (decreased/increased) venous return. Explain why
Increased. Due to muscle contraction and activation of sympathetic nervous system –want to maximize flow to skeletal muscle by increasing CO and also recruitment of capillaries (thus decreasing SVR)
MAP = CO x SVR
What is the change in BRAIN blood flow during exercise?
There is none due to autoregulation
What happens to ejection fraction during exercise? Why?
It goes up. LV pumping harder, beta1 increases contractility
Why does pulse pressure go up during exercise?
Increased stroke volume
Why does stroke volume go up during exercise (thus increasing pulse pressure)?
Increased filling of ventricles (increased end diastolic volume) and increased contractility
Why are arterioles considered the primary vessels involved in regulation of arterial blood pressure and blood flow within the organ?
Most highly innervated with autonomic nerves–specifically sympathetic adrenergic. Responds to changes in nerve activity and circulating hormones by constricting or dilating
Which vessels have the highest pressure?
Aorta and arteries
Formal definition of blood pressure
measure of force exerted by blood against the walls
Poiseuille’s law states that flow decreases when resistance (decreases/increases)
Flow decreases when resistance increases
As a form of autoregulation, distal prearterioles undergo myogenic (dilation/constriction) if increased pressure
constriction. need to keep flow constant! flow = P / R. If P increases, need to increase R to keep flow constant. Increase R by constricting
this maintains constant pressure at the arterioles
tachycardia (increases/decreases) time in diastole
decreases
What are subendocardial coronary vessels?
vessels that enter the myocardium
When are subendocardial vessels compressed?
During systole (contraction of ventricular myocardium) due to high intraventricular pressure
(blood flow in the subendocardium thus stops)
When does most myocardial perfusion occur?
During diastole (heart relaxation) when the subendocardial coronary vessels are under low pressure
Does flow ever come to zero in the right coronary artery? Why or why not?
No, since the RV pressure is less than the LV pressure
Equation for coronary perfusion pressure to the subendocardium of the LV
aortic diastole pressure - any pressure drop across a stenosis - LV end diastolic pressure
decrease alveolar P(O2) –> (increase/decrease vasoconstriction
increase. shunts blood to better ventilated areas, ventilation/perfusion ratio
Splanchnic circulation goes to these 5 main areas
- stomach
- small and large intestines
- pancreas
- liver
- spleen
In pulmonary circulation, it is important to match ventilation with _____
perfusion
In pulmonary circulation, are extrinsic factors more important than intrinsic factors?
Intrinsic are more important
- autoregulation does not occur
- endothelial cell-mediated factors are important i.e. for inflammation
- metabolic factors are most important (PO2)
After a meal, blood flow (increases/decreases). Explain 2 mechanisms
increases (because of nutrition)
- increased mucosal activity produces vasodilator substances (adenosine and CO2)
- food ingestion causes release of GI hormones (eg cholecystokinin) increases blood flow
Increased sympathetic nervous system activity directly (constricts/dilates) splanchnic blood vessels
constricts
If a patient who exercises a lot has a noted iron deficiency anemia, what could be the cause?
The iron deficiency could come from intestinal loss of iron
-GI bleed–when pt exercises, sympathetic levels are so high, causing ischemia to the intestine and thus an iron deficiency
