Control of Blood Pressure and Blood Volume

Question 1

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

Answer 1

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.

Question 2

Where does the pre-ganglionic sympathetic neurones innervate?

Answer 2

T1-L2

Question 3

What are efferent cortical influences?

Answer 3

Emotion,

Volition (power of using ones will)

Question 4

Efferent complex reflex patterns

Answer 4

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

Question 5

Which two hormones effect the kidneys?

Answer 5

Vasopresin (ADH) and Renin-angiotensin

Regulate blood volume and therefore blood pressure

Question 6

What are baroreceptors?

Answer 6

Stretch receptors

Question 7

Where are baroreceptors found?

Answer 7

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.

Question 8

When do baroreceptors activity affect

Answer 8

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

Question 9

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

Answer 9

More stretch increase ABP increases baroreceptor afferent activity.

Question 10

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

Answer 10

Less stretch decreases ABP decreases baroreceptor afferent activity.

Question 11

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

Answer 11

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

Question 12

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

Answer 12

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

Question 13

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

Answer 13

Reflex renal vasocontriction

Question 14

What mechanism helps maintain cerebral blood flow (CBF)?

Answer 14

Myogenic dilation (60-140 mmHg)

Question 15

What mechanism achieves functional anaemia and what is this?

Answer 15

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.

Question 16

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

Answer 16

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

Question 17

What are the stretch receptors affected by?

Answer 17

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

Question 18

How does activity of the kidney increase blood volume?

Answer 18

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.

Question 19

Volume receptor function and how a response can be achieved?

Answer 19

Continually monitor blood volume.

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

Question 20

When does distension of the atrium decrease?

Answer 20

When ABP decreases

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

Question 21

When does distension of the atrium increase?

Answer 21

When ABP increases

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