Blood Pressure Regulation Flashcards
Blood pressure regulation can be divided in 2 categories
Acute - regulation of circulation and rapid control of arterial pressure
Chronic- Role of Kidney in blood pressure regulation
arterial pressure control is done by
nervous control
Nervous system mainly affects
redistribution of blood flow to different areas of the body, by increasing the pumping activity of the heart and providing rapid control of arterial pressure
SNS contributes to blood circulation by
regulating vascular tone and directly affecting the pumping activity of the heart
increasing heart rate and force of contraction
PSNS contributes to blood circulation by
decreasing heart rate
what blood vessels are not innervated by SNS?
capillaries
Describe the mechanism of the SNS in the decrease of blood flow to tissue
innervation of small arteries and arterioles stimulates increase in resistance to blood flow
What causes the inervation of SNS in large veins?
It decreases the volume of the vessel = blood to the heart = increasing the blood flow to the heart and the pumping efficiency of the heart (increased cardiac output).
SNS fibers carry large # of
vasoconstrictor fibers
Where is located the vasomotor center?
Bilaterally in the reticular substance of the medulla and lower third of the pons.
3 functions of the vasomotor center
Transmits parasympathetic impulses through the vagal nerve to the heart
Transmits sympathetic impulses through the spinal cord and peripheral sympathetic nerves to almost all the blood vessels in the body.
Transmits SNS vasoconstrictor tone of the entire body maintaining a partial state of contraction in blood vessels
3 areas of the vasomotor center
vasoconstrictor area
vasodilator area
sensory area
vasoconstrcitor area of the vasomotor center location and role
Bilaterally in the anterolateral portion of the upper medulla.
neurons distribute their fibers at all levels of the spinal cord and excite the vasoconstrictor neurons of the SNS
vasodilator area of the vasomotor center location and role
Bilaterally in the anterolateral portions of the lower half of the medulla.
Fibers of neurons project upward to the vasoconstriction area and inhibit vasoconstrictor activity
sensory area of the vasomotor center location and role
Bilaterally in the tractus solitarius in the posterolateral portions of the medulla and lower pons.
Neurons receive sensory inputs through the vagus and glossopharyngeal n.
What activities control the sensory area of the vasomotor center
vasoconstrictor and vasodilator areas and reflex control of circulation
t/f the vasomotor center also controls the activity of the heart
true
The lateral portion of the VMC transmits
excitatory impulses through the SNS nerve fibers to the heart = increase heart rate and contractility.
The medial portion of the VMC transmits
Parasympathetic impulses to the heart = decrease heart rate.
Heart increases when
vasoconstriction occurs
heart decresases when
vasodilation occurs
NT released by nerve endings that causes vasoconstriction
NOREPINEPHRINE
nor-epi acts on what receptors
alpha
The adrenal glands release what and is transported where?
norepinephrine and epinephrine
into blood carried everywhere to constrict blood vessels
NT that causes vasoconstriction
nor epi and epi
t/f Epinephrine causes vasodilation through its beta receptor stimulation in certain tissue of the body
true
How does spinal anesthesia work?
blocks all sympathetic transmission from the spinal cord to the periphery.
3 factors that control rapid control of arterial pressure
constriction of all the arterioles in the body = increasing peripheral resistance = increasing arterial pressure
constriction of veins = increasing blood volume to the heart
increase heart rate and force of contraction
What does the Arterial baroreceptor control system control?
arterial pressure
how does the Arterial baroreceptor control system work?
it is negative feedback system
Reflex is initiated by the stretch of the receptors
Spray-type nerve endings in arterial wall at carotid bifurcation and aortic arch
Carotid receptors go via glosspharyngeal (IX) to vasomotor center
Aortic arch receptors go via vagus (X) to vasomotor center
baroreceptors respond to
changes in arterial pressure
steps of the baroreceptor reflex
increased arterial pressure
baroreceptor sends signal from the carotid and aortic body
nucleus solitarium of medulla
inhibition of vasoconstrictor center of medulla
excitation of vagal PSNS center
vasodilation of veins in periphery
heart rate and strength of contraction decrease
What is the net result of the baroreceptor reflex when there is increased arterial pressure?
Arterial pressure decreases because of both a decrease in peripheral resistance and a decrease in cardiac output.
What is the net result of the baroreceptor reflex when there is decreased arterial pressure?
causes pressure to go back to normal
the primary purpose of the arterial baroreceptor system
Reduce the minute by minute, variation in arterial pressure
why aren’t baroreceptors useful in long term regulation of mean arterial pressure?
Because they reset themselves in 1 to 2 days if the arterial pressure returns to higher normal pressure.
What mechanism is used to control long-term arterial pressure?
renal body fluid pressure control system
Chemoreceptors also aid in the control of arterial pressure. How do they do this?
sensitive to changes in oxygen, CO2, or hydrogen ions in the blood
Difference between baroreceptors and chemoreceptors to control changes in arterial pressure
baroreceptors = stretch receptors
chemoreceptors = changes in O2 and H in blood
Where are chemoreceptors located?
on the carotid bodies and aortic arches
mechanism of action of chemoreceptors reflexes
excite nerve fibers that pass through the Herrings’ nerve and the vagus nerves to vasomotor centers of the brain stem
diminished O2 or excess CO2 in the blood, resulting in the activation
signal transmitted from the chemoreceptors into the VMC excites these centers and elevates AP back to normal.
chemoreceptor are only activated when
AP falls below 80 mmHg ,are effective only at low pressures.
baroreflexes and chemoreflex are located in the central or peripheral nervous system?
peripheral, outside the brain
mechanism of the CNS in response to cerebral ischemia
- Vasomotor center ACTIVATED due to an:
oxygen deficiency
increased CO2
lactic acid build-up - SNS outflow=constriction of all blood vessels
- The entire circulatory system is tightened, heart is enhanced in an effort to restore oxygenated blood to the brain
When is the CNS ischemia response activated?
Only when the blood pressure falls below 60 mm Hg
cushing rxn.
special type of CNS ischemic response.
mechanism of cushing rxn.
- Increased pressure of the cerebrospinal fluid around the brain in the cranial vault compresses the whole brain and the artery and cuts off the blood supply to the brain.
- Increases AP (arterial pressure) rise above the CSF pressure, resulting in blood flow to the brain’s vessels to relieve ischemia.
t/f too much extracellular fluid causes te AP (arterial pressure) to rise
true
2 mechanism of the kidneys to excrete excess extracellular water to decrease AP
Pressure diuresis (water)
Pressure natriuresis (salt)
When there is a lack of nervous control, the circulatory system responds to
Volume changes with no nervous reflexes active
analysis of electrolyte intake and urinary output requires two factors
The level of salt/H2O intake
The urinary output curve
In long-term control, how can the arterial pressure be increased?
shifting the urinary output curve to the right or
increasing the fluid/electrolyte intake
salt increases
AP because it is not easily excreted
mechanism of excess salt in the body
salt increases the osmolality of the body fluid
this stimulates the thirst center, making the person drink more water
diluting the extracellular salt to normal concentration increases extracellular fluid volume.
An increase in osmolality in extracellular fluid stimulates
hypothalamic neurons to increase the release of ADH
kidneys reabsorb water, diminishing urine and increasing extracellular fluid
hypertension
Mean AP greater than 110 mmHg
diastolic greater than 90 mmHg
systolic greater than 135 mmHg
consequences of hypertension
Excess workload on the heart leads to early heart failure and coronary artery disease
High pressure ruptures major blood vessels of the brain leading to stroke.
Causes multiple hemorrhages in the kidneys, destruction of renal tissue, renal failure, uremia
long term arterial pressure regulation is primarily mediated by 2 substances
Renin angiotensin system
Aldosterone
circulatory effects of angiotensin II
Angiotensin II increases AP directly by increasing TPR
acting on the kidney it causes renal retention of salt and water producing an increase in blood volume and CO over a period of time
specific mechanism of angiotensin II
- Constricts the renal arterioles = decreasing blood flow through the kidneys = less fluid filters through the glomeruli into the tubules
osmotic reabsorption of fluid from the tubules - acts on the adrenal glands to increase the production of aldosterone = increases the salt and water retention.
- aldosterone = reabsorption of sodium, thereby increasing the total body extracellular fluid sodium.
aldosteronism (tumor in adrenal gland)
Increases the extracellular fluid, salt and water absorption by tubules in kidneys, and volume, resulting in volume overload hypertension.
difference between rapid and long control of AP
RAPID=NERVOUS SYSTEM=LOSE GAIN OVER TIME
LONG=RENAL=INCREASING GAIN OVER TIME
