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Physiology > Neural Reflexes and Control of Arterial Blood Pressure (B2: W3) > Flashcards

Neural Reflexes and Control of Arterial Blood Pressure (B2: W3) Flashcards

1
Q

What two major physical factors determine the arterial (pulse) pressure?

A
  1. Arterial blood volume
  2. Areterial compliance
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2
Q

What physiological factors influence arterial blood volume and compliance?

A
  • Cardiac output (stroke volume x heart rate)
    • SV
    • HR
  • Peripheral resistance (diameter, for the most part)

If we are able to change/regulate these factors, we can change/regulate the arterial blood pressure

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3
Q

What is responsible for feedback control of blood pressure?

A

Baroreceptors

When they sense an increase in blood pressure, they send a message to the brain stem that regulates HR, SV and vessel diameter (resistance)

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4
Q

What are the components of the baroreceptor reflex?

A
  1. Signal - change in arterial pressure
  2. Dectectors/sensors - arterial baroreceptos
  3. Afferent pathways that translate the signal to a coordinating center
  4. A neural network (CNS, coordinating center), which compares a signal from the sesors with a comand signal which orginates in CNS
  5. A neural output which connects the nervous system to the target cells in the effector organs (efferent pathways)
  6. The target organs themselves (heart and peripheral blood vessels)
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5
Q

Where are the baroreceptors located?

A
  • In the wall of the carotid sinus, at the biforcation of the common carotid artery
  • In the aortic arch

They are branched and coiled bare ends of myelinated sensory nerve fibers

The cell bodies are in the ganglia near the brainstem

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6
Q

What exactly do the arterial baroreceptors sense?

A

Stretch

They are stretch receptors

Vascular wall tension indicates change in blood pressure

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7
Q

What is the effect of increased or decreased blood pressure on the baroreceptors?

A

Sudden increase in BP causes increased activity of baroreceptors

Sudden decrease in BP does the opposite

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8
Q

What is the purpose of the arterial baroreceptors?

A

To buffer acute changes in blood pressure

Second to second, minute to minute changes

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9
Q

At what pressure will the baroreceptors be fired up?

A

Pressures range over which the baroreceptors can monitor systemic arterial blood pressure

  • Aortic: 100-200 mmHg (very high pressure)
  • Carotid: 50-200 mmHg (range is wider)
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10
Q

How do changes in arterial blood pressure affect carotid sinus nerve activity?

A

Lower pressure, lower activity

Higher pressure, higher activity

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11
Q

Where are the cardiopulmonary baroreceptors (low pressure baroreceptors)?

A

At strategic low-pressure sites

  • Pulmonary artery
  • The junction of the atria with their corresponding veins
  • Atria themselves
  • Ventricles
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12
Q

What is the function and mechanism of the cardiopulmonary baroreceptors?

A

The purpose is the monitor venous volume

Help control blood volume through reflex release of antidiuretic hormone

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13
Q

What exactly do the cardiopulmonary baroreceptors sense?

A

Stretch!!

Stretches in venous return to the heart indicate changes in blood volume

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14
Q

Where is the coordinating center for the cardiovascular system?

A

Medullary cardiovascular center - in the medulla

Points on the medulla: vasoconstrictor, cardioinhibitor, vasodilator

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15
Q

What is the medullary cardiovascular center and what does it do?

A

Collection of neurons in the medulla that receives sendory information from a variety of sources

  • Compares this information with the set point for systemic arterial blood pressure
  • Initiates the rsponses to maintain an appropriate blood pressure
  • Also receives input from higher areas
    • Can override the homeostatic activity of the cardiovascular system
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16
Q

What are the efferent organs of cardiovascular control?

A

Target organs

  • All of the efferent pathways come down to the heart and blood vessels
  • Efferent pathways are parasympathetic AND sympathetic fibers
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17
Q

What happens when the mean arterial pressure decreases (e.g. from standing up or from acute hemorrhage)?

A
  • Decrease in stretch on the baroreceptors
    • Decrease nerve activity (Hering’s nerve)
      • Decreased parasympathetic outflow to heart and blood vessels
    • Increased sympathetic outflow to heart and blood vessels
      • ß: increase HR and contractility
      • a: increase resistance
  • All of this increases mean arterial pressure
18
Q

What happens when there is a sudden increase in arterial pressure?

A
  • Increase in aortic pressure
  • Baroreceptors sense stretch → increased afferent nerve activity
  • Reciprocal changes in efferent sympathetic and parasympathetic nerve activity to the heart and blood vessels
  • Decrease in aortic pressure back to normal
19
Q

Massage of the neck over the carotid sinus area in a person experiencing a bout of paroxysmal atrial tachicardia is often effective in terminating the episode. Why?

A

Decreases the HR

  • Fools the baroreceptors to think that ther is high pressure
  • They will respond by controlling the heart rate and decreasing it
20
Q

What would happen to blood pressure if the arterial baroreceptors were surgically cut?

A

The mean arterial pressue would not change, but the fluctuations around the mean would

  • BP is determined by input from several systems, largely coordinated by the kidneys - RAAS, ADH, ANP
  • The others just don’t respond instantaneously
  • Range increases
  • Fluctuations will be around 100 mmHg
  • Blood pressure is less stable
21
Q

What would happen to blood pressure if BOTH the arterial and cardiopulmonary baroreceptors were surgically cut?

A

Mean arterial pressure and fluctuation around the mean would increase

  • Unstable BP
  • There will be no acute response to sudden change in BP
22
Q

What happens to baroreceptors during chronic hypertenstion?

A

Baroreceptors reset at a higher level of blood pressure

  • They are not important in regulating control of hypertension because they measure accute changes only
  • After about two days they adjust their set point
23
Q

Aside from baroreceptors, which type of receptors play a role in acute blood pressure control?

A

Peripheral (arterial) chemoreceptors

Located in the exact same places as the baroreceptors

24
Q

What is the purpose of the arterial chemoreceptors?

A

They buffer acute changes in pO2, pCO2, and pH

25
Q

What do the arterial chemoreceptors sense?

A

Hypoxemia (low oxygen)

Hypercapnia (increased carbon dioxide)

Acidosis (low pH)

26
Q

What is the response of peripheral chemoreceptors to decreases in the partial pressure of O2?

A
  • Decreases in pO2 activate vasomotor center that produce vasoconstriction → increase total peripheral resistance and increase arterial pressure
  • Decreases in pO2 <60 mmHg cause hyperventilation
27
Q

Which is more powerful: chemoreceptors or baroreceptors

A

Baroreceptors

  • Chemoreceptor reflex is not a powerful arterial pressure controller in the normal BP range
    • Stimulated when the pressure falls below 80 mmHg
  • Chemoreceptors play a role only during severe hypoxia (e.g. hemorrhagic hypotension)
28
Q

What are the two chemoreceptor mechanisms for increasing the heart rate?

A

Decreased O2, increased CO2, and decreased pH

  • Decrease parasympathetic stimulation of the heart
  • Increase sympathetic stimulation of the heart (also increases stroke volume)

In addition, there is increased sympathetic stimulation of blood vessels to increase vasoconstriction

29
Q

What happens in the chemoreceptor reflex when breathing has been stopped (asphyxia)?

A
  • Triggers chemoreceptor pathways
  • Excitatory signals to the CNS and NTS (nucleus tractus solitarii)
  • Efferent vagal activity increases to the heart → bradycardia
  • Sympathetic activity to the kidney increases → renal constriction and activation of RAAS
  • Respiratory rate and depth increased → increased tidal volume
30
Q

What are the chemoreceptors in the medulla responsible for?

A
  • Control breathing
    • Increases in pCO2 and [H+] stimulate breathing
    • Decreases in pCO2 and [H+] inhibit breathing
  • Resulting hyperventilation then returns the arterial pCO2 toward normal
31
Q

What happens if a decrease in PO2 or a decrease in pH is the primary insult?

A
  • Bradycardia occurs when ventilation is fixed or prevented
  • When we do breathe, mechanism is different
    • The effects of breathing overcome the intrinsic cardiovasculare response, producing tachycardia
32
Q

What is the Renin-Angiotensin System?

A

Renin-angiotensin-aldosterone system plays important role in the regulation of arterial blood pressure and blood volume

33
Q

What triggers the RAAS and in what context is it used?

A
  • Triggered by a decrease in renal perfusion pressure
  • Relatively slow, hormonal mechanisms and is used in long-term blood pressure regulation by adjustment of blood volume and vascular resistance
34
Q

What happens in the event of a CNS ischemic response?

A
  • Increased PCO2 stimulates vasomotor center
  • Increased sympathetic ouflow to heart and blood vessels
    • Increased HR, SV, and peripheral vasoconstriction
    • Increased systemic arerial pressur
  • Increased parasympathetic outflow to heart - decreased heart rate

Same thing as the Cushing response to increased cranial pressure

35
Q

When is vasopressin (ADH) released an what is its function?

A
  • Released in response to hemorrhage (decreased blood volume)
  • Released in response to activated low-pressure baroreceptors
  • Causes vasoconstriction (mediated by V1 receptors)
  • Increases water reabsorption and ultimately increases blood volume and interstitial fluid volume
36
Q

What effect does increased extracellular fluid volume have on the arterial pressure?

A

Increases aterial pressure

  • Increased cardiac output has both a direct effect by increasing arterial pressure and indirect effect by increasing total peripheral resistance
37
Q

When are natriuretic peptides (ANP, BNP) released and what is their function?

A
  • Released from the atria in response to increased atrial pressure
  • Cause vasorelaxation and decreased TPR
  • Cause increased excretion of Na+ and water by the kidneys - reduces blood volume
  • Inhibit renin secretion
38
Q

What is the relationship between the various mechanisms that work to control arterial blood pressure?

A

Mutiple mechanisms work over different time scales to correct arterial blood pressure back to normal

  • Some of the regulating factors act very quickly
  • Others act more slowly
  • The strength of the reflex response varies widley
39
Q

Which mechanism for controlling arterial blood pressure responds the quickest?

A

Baroreceptors

40
Q

Which is the slowest of the mechanisms for controlling arterial pressure?

A

Renal mediated fluid retention

Also has the greatest gain

41
Q

Which system for controlling arterial blood pressure is the least powerful?

A

Renin-angiotensin system

  • Small, but still very important
  • Keeps MAP in normal range
42
Q

Which system for control of the arterial blood pressure is the most powerful?

A

Renal-mediated fluid retention

Physiology (29 decks)

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