Control of Blood Pressure

Question 1

List 6 determinants of capillary perfusion pressure.

Answer 1

Arteriolar factors:

1 - Endothelial influences.

2 - Myogenic influences.

3 - Metabolic influences.

Venous factors:

4 - Gravity.

5 - The respiratory pump.

6 - The musculoskeletal pump.

Question 2

List 3 products of reflexes in the cardiovascular system.

Answer 2

1 - Release of catecholamines.

2 - Release of ADH.

3 - Activation of the renin-angiotensin system.

Question 3

List 5 actions that trigger complex reflexes that might lead to changes in the cardiovascular system.

Answer 3

1 - Exercise.

2 - Feeding.

3 - Alerting.

4 - Thermoregulation.

5 - Reproduction.

Question 4

What is the function of the baroreceptor reflex?

Answer 4

To regulate blood pressure.

Question 5

What type of receptors are baroreceptors?

What do they respond to?

Answer 5

• Stretch receptors.

- They respond to the magnitude of stretch and the rate of change of stretch.

Question 6

To which area of the CNS does afferent activity from baroreceptors travel?

Answer 6

The nucleus tractus solitarius (NTS).

Question 7

List 2 locations of baroreceptors.

Which nerves carry the afferent activity of each of these groups of baroreceptors?

Answer 7

1 - In the aortic arch, carried by the vagus nerve.

2 - The bifurcation of the common carotid arteries (on the internal carotid at the carotid sinus), carried by the glossopharyngeal nerve.

Question 8

List the stages of the baroreceptor reflex in response to a fall in arteriolar blood pressure

Answer 8

*Arterioles, veins, heart, ADH.

1 - A fall in arterial blood pressure is detected by a decrease in baroreceptor activity.

2 - The CNS increases arteriolar vasoconstriction , which increases TPR.

3 - Arteriolar vasoconstriction also decreases capillary hydrostatic pressure, increasing filtration of tissue fluid into capillaries and increasing EDV (and therefore SV).

4 - The CNS also causes venoconstriction, which also increases EDV (and therefore SV).

5 - The CNS increases heart contractility (and therefore SV) and rate by increasing sympathetic activity and decreasing parasympathetic activity.

6 - Increased ADH production increases circulating volume and therefore EDV, increasing SV.

7 - The increased SV and increased heart rate result in an increased cardiac output.

8 - ABP = CO * TPR, both of which have increased.

Question 9

Describe the neural pathway taken by parasympathetic nerves innervating the heart in the baroreceptor reflex.

Answer 9

1 - Parasympathetic preganglionics originate in the nucleus tractus solitarius (NTS).

2 - Parasympathetic preganglionics synapse with the vagus nerve at the nucleus ambiguus.

3 - Parasympathetic postganglionics innervate the SAN and AVN via the vagus nerve.

Question 10

Describe the neural pathway taken by sympathetic nerves innervating the heart and peripheral vessels in the baroreceptor reflex.

Answer 10

1 - First preganglionics originate in the nucleus tractus solitarius (NTS).

2 - First preganglionics synapse with second preganglionics that originate in the preoptic hypothalamus.

3 - Second AND first preganglionics (the preoptic hypothalamus can be skipped) synapse with third preganglionics at the rostral ventrolateral medulla (RVLM).

4 - Third preganglionics synapse with short sympathetic preganglionics in the sympathetic chain.

5 - Short sympathetic preganglionics synapse with long sympathetic postganglionics.

6 - Long sympathetic postganglionics synapse with the SAN, AVN, arterioles and veins.

Question 11

Describe the neural pathway taken by nerves innervating the pituitary gland in the baroreceptor reflex.

Answer 11

1 - Preganglionics originate in the nucleus tractus solitarius (NTS).

2 - Preganglionics synapse with postganglionics in the supraoptic and paraventricular nuclei.

3 - Postganglionics innervate the pituitary gland.

Question 12

In which area of the body does the baroreceptor reflex have the strongest effect?

Why is this advantageous?

Answer 12

• The gastrointestinal tract (GIT).

- Because the GIT contributes to 25% of TPR at rest.

Question 13

What proportion of TPR do arterioles supplying skeletal muscle comprise at rest?

Answer 13

20%

Question 14

Where are volume receptors located?

Answer 14

In the right atrium.

Question 15

What type of receptors are volume receptors?

What do they respond to?

Answer 15

• Stretch receptors.

- They respond to changes in right atrial stretch, and therefore CVP indirectly.

Question 16

Describe the Bainbridge reflex.

Which nerve carries afferent information from the receptors, and where is the information carried to?

Answer 16

1 - The reflex is initiated by increased stretch of volume receptors.

2 - The reflex increases sympathetic activity to the heart, increasing heart rate.

3 - The reflex also decreases sympathetic activity to the kidney, increasing renal perfusion and therefore urine production (decreases blood volume), and decreasing renin release.

4 - The reflex also decreases ADH release from the posterior pituitary (decreases blood volume).

• The vagus nerve carries afferent information from volume receptors to the nucleus tractus solitarius.

Question 17

What is the function of the Bainbridge reflex?

Answer 17

To regulate ABP over a longer time scale than the baroreceptor reflex (since the baroreceptor reflex is faster and shorter acting than the Bainbridge reflex).

Question 18

List 3 causes of decreased distension of the atrium.

Answer 18

1 - Standing (causes venous pooling).

2 - Haemorrhage.

3 - Dehydration.

Question 19

List 3 causes of increased distension of the atrium.

Answer 19

1 - When supine.

2 - Large fluid intake.

3 - Over-transfusion.

Question 20

List 3 conditions / situations in which the sensitivity and / or set point of the baroreceptor reflex can be changed.

Answer 20

1 - Exercise.

2 - Chronic hypertension.

3 - Emotional stress.