Control of Blood Pressure and Blood Volume Flashcards

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1
Q

What is the reflex arch for controlling the heart and blood vessels?

A

Reflex responds to sensory neurones that enter the CNS via afferent nerves. Exiting the CNS via efferent nerves or hormones. Effector neurones will affect the heart and blood vessels.

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2
Q

Where does the pre-ganglionic sympathetic neurones innervate?

A

T1-L2

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3
Q

What are efferent cortical influences?

A

Emotion,

Volition (power of using ones will)

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4
Q

Efferent complex reflex patterns

A
Exercise
Feeding/satiety (feeling or state of being satisfied)
Alerting/defence
Thermoregulation
Reproduction
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5
Q

Which two hormones effect the kidneys?

A

Vasopresin (ADH) and Renin-angiotensin

Regulate blood volume and therefore blood pressure

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6
Q

What are baroreceptors?

A

Stretch receptors

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7
Q

Where are baroreceptors found?

A

In the neck, runs up into the brain. Found in the aortic arch and carotid sinus.
Baroreceptors found in the carotid sinus are connected to the sinus nerve into the IX glossopharyngeal nerve.
Baroreceptors found in the aortic arch are connected to the aortic nerve into the X vagus nerve which enter the CNS via the medulla.

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8
Q

When do baroreceptors activity affect

A

Baroreceptors are firing afferent activity to the medulla even at normal arterial pressure.

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9
Q

What does more stretch mean for ABP and baroreceptor afferent activity?

A

More stretch increase ABP increases baroreceptor afferent activity.

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10
Q

What does less stretch mean for ABP and baroreceptor afferent activity?

A

Less stretch decreases ABP decreases baroreceptor afferent activity.

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11
Q

What is the effect on sympathetic activity when there is an decrease in ABP

A

A decrease in ABP decreases baroreceptor afferent activity. Sympathetic activity increases meaning more noradrenaline is released to act on alpha receptors. Arterioles constrict increasing TPR, a decrease in hydrostatic pressure (increasing filtration into capillaries) in addition to constriction of venous vessel there is an increase in EDV. Noradrenaline is also acting on B-receptors causing constriction decreasing ESV. An increase in EDV and a decrease in ESV causes an increase in SV therefore an increase in CO.
ABP = CO x TPR

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12
Q

What is the effect of parasympathetic activity when there is an increase in ABP

A

A decrease in ABP decreases baroreceptor activity. A decrease in ACh on muscarinic receptors decreases parasympathetic activity to allow an increase in heart rate to increase CO.
ABP = CO x TPR

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13
Q

If there is a large decrease in ABP what reflex is used?

A

Reflex renal vasocontriction

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14
Q

What mechanism helps maintain cerebral blood flow (CBF)?

A

Myogenic dilation (60-140 mmHg)

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15
Q

What mechanism achieves functional anaemia and what is this?

A

Functional anaemia is an increase in blood flow when the tissue is active. Coronary circulation shows functional anaemia as a response to increase cardiac work (reflex, increase HR, increase contractility). More work, more metabolites are released which causes functional hyperaemia.

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16
Q

How does blood flow maintain constant over a range of mABP?

A

Due to arteriolar resistance (myogenic responses = pressure auto-regulation)
80-140 mmHg
Prevents going bellow 80 = fainting
Prevents going above 140 = stroke

17
Q

What are the stretch receptors affected by?

A
  1. Affected by renal changes in blood volume
  2. By changes in distribution of blood volume (standing, sitting, lying)
    Increase in stretch = Increase in activity
    Decrease in stretch = Decrease in activity
18
Q

How does activity of the kidney increase blood volume?

A
  1. Increase in sympathetic activity to the kidney causing renal vasoconstriction a decrease in renal perfusion therefore a decrease in renal tubular flow.
  2. Increase in renin release, therefore an increase in angiotensin II = increased reabsorption of Na+ and therefore H2O. This maintains body fluid volume.
  3. Increase in ADH (antidiuretic hormone) from the pituitary gland in the hypothalamus causing an increase in water absorption from the filtrate and a decrease in urine flow rate.
    All three help to increase blood volume back to normal, but causes opposite effect on the kidneys.
19
Q

Volume receptor function and how a response can be achieved?

A

Continually monitor blood volume.

  1. Affect distension of the atrium
  2. Reflex adjust sympathetic activity to the kidneys
  3. Affects ADH release.
20
Q

When does distension of the atrium decrease?

A

When ABP decreases

In the standing position (venous pooling), haemorrhage, dehydration.

21
Q

When does distension of the atrium increase?

A

When ABP increases

In supine position, large fluid intake, over-transfusion.