VASCULAR: REGULATION OF MAP I

Question 1

Give the equation for MAP

Answer 1

MAP = Q*R
= distatolic pressure + (1/3)pulse pressure

Question 2

Give the equation for flow (Q)

Answer 2

Q = MAP/R

Q also represents cardiac output

Question 3

When is mean arterial blood pressure high and low?

Answer 3

high: systole

low: diastole

Question 4

what is the pulse pressure

Answer 4

systolic pressure - diastolic pressure

Question 5

What are some factors that regulate Q (cardiac output)

Answer 5

Q = SV and HR

SV is regulated by contractility, compliance, and end diastolic volume

end diastolic volume is affected by venous return

Venous return is affected by P mean systemic filling and plasma volume

HR is affected by sympathetic and parasympathetic input and hormones

Question 6

What are some factors that regulate R

Answer 6

• Poiseuilles Law affected by length, viscosity, and radius
• Radius is affected by compliance and vascular smooth muscle activity
• Vascular smooth muscle activity is affected by
  A (and β) adrenoreceptors - angiotensin II - ADH - endothelin - ACh - NO - histamine ….

Question 7

What are the nerve endings that are sensitive to stretch?

Answer 7

spray nerve endings (terminal arbourization)

transduce blood pressure

Question 8

What are the carotid sinus baroreceptors responsible for?

Name the nerve that is depolarized

Answer 8

Senses changes in blood pressure in blood flow going to brain

When it senses stretch, produce depolarization in afferent fibres: carotid sinus nerve which joins with the glossopharyngeal nerve

Question 9

What are the aortic arch baroreceptors responsible for?

Name the nerve that is depolarized

Answer 9

Senses changes in blood pressure in blood flow going to body

When it senses stretch, produce depolarization in afferent fibres: vagus nerve

Question 10

What are the coronary artery baroreceptors responsible for?

Name the nerve that is depolarized

Answer 10

Senses change in perfusion pressure to heart

Coronary pressure is increased → coronary baroreflex mediates vasodilation → decreases mean arterial pressure

Question 11

What are the names of the parasympathetic fibres and sympathetic fibres responsible for arterial blood pressure regulation ?

Answer 11

Parasympathetic: nucleus tractus solitarius, nucleus ambiguus

Sympathetic: rostral/caudal ventrolateral medulla

Question 12

Describe how we can assess arterial baroreflex control

Answer 12

Vacuum collar around carotid sinus baroreceptors

Increased blood pressure → increased distension → increased afferent firing → medulla → increased vagal firing and decreased sympathetic firing

Question 13

What is most important for
- long term MAP regulation
- short term MAP regulation

Answer 13

long term: renal regulation

short term: baroreceptor

Question 14

What are the two ways the kidneys can regulate mean arterial pressure?

Answer 14

1. Renin-angiotensin aldosterone system
2. Pressure diuresis

Question 15

How does the renin-angiotensin aldosterone system (RAAS) control MAP?

Answer 15

Decrease in MAP results in an increase in renin released from the juxtaglomerular apparatus. Increase in renin converts angiotensinogen to angiotensin I. Angiotensin converting enzyme (ACE) converts angiotensin I to angiotensin II. Angiotensin II is a potent vasoconstrictor which will increase blood pressure. Increase in angiotensin II will also cause the release of aldosterone from the adrenal cortex. Aldosterone will act on the kidney and increase reabsorption of sodium (Na+). This will increase plasma and blood volume which will stimulate an increase in blood pressure

Question 16

What releases angiotensin converting enzyme (ACE)

Answer 16

Angiotensin converting enzyme (ACE) is released by endothelial cells of lung capillaries

Question 17

What vessel carries blood into and out of the kidney

Answer 17

Afferent arteriole: carries blood into kidney

Efferent arteriole: carries blood out of kidney

Question 18

Explain the flow of blood in the kidney starting from the afferent arteriole

Answer 18

Afferent arteriole → proximal convoluted tubule → loop of henle (thin descending limb → thin ascending limb → thick ascending limb) → distal convoluted tubule → collecting duct

Question 19

Define: juxtaglomerular apparatus

Answer 19

Juxtaglomerular apparatus: where the distal tubule comes in close proximity to glomerulus; site for renin release

Question 20

Define: glomerulus

Answer 20

Glomerulus: site for filtering of the blood

Question 21

Define: macula densa cells

Question 22

Define: granular cells/juxtaglomerular cells in afferent arterioles

Answer 22

site for release of renin

Question 23

What are the 3 ways that renin secretion can be regulated

Answer 23

1. Granular cells sense decreased pressure in the afferent arteriole and release renin
2. Decreased systemic blood pressure → arterial baroreceptor response is to increase sympathetic activity → increase in renin sympathetic nerve activity → renin release
3. Macula densa cells sense decreased [NaCl] or filtrate flow at the macula densa which signals for the increase release of renin

Question 24

Describe how pressure diuresis regulates MAP

Answer 24

Pressure diuresis: large loss of fluid due to high blood pressure. Increased urine output

Increase in mean arterial pressure → increase in glomerular filtration rate → increase in filtrate volume → increase in excretion → decrease in plasma volume → decrease venous return → decrease in cardiac output → decrease in mean arterial pressure

Question 25

What is another name for ADH

Answer 25

vasopressin

Question 26

How does ADH regulate MAP? (2)

Answer 26

1. Reduce urine output
2. Cause vasoconstriction (can do this indirectly and directly)

Question 27

What neuron’s stimulation results in the secretion of ADH?

Answer 27

Stimulation in paraventricular neurons of hypothalamus results in increased release of ADH from posterior pituitary

Question 28

What regulates ADH release? (2)

Answer 28

1. Increased plasma osmolarity which is detected by hypothalamus → increased ADH release → increase water conserved → increased blood pressure and osmotic correction
2. Decreased blood pressure → increased ADH → increase plasma volume → increase MAP

Question 29

Describe the actions of ADH in high concentrations within the blood vessel

Answer 29

In high concentration → ADH acts on V1a receptors in the renal system which activates Gq protein → increase PLC concentration → PLC converts PIP2 to IP3 and DAG → IP3 acts on IP3 channels increasing SR calcium release; DAG activates PKC which inhibits myosin light chain phosphorylation→ both result in increase in cross bridge formation and force of contraction → vasoconstriction

Question 30

Describe the actions of ADH in low concentrations within the blood vessel

Answer 30

In low concentrations → ADH acts on V1a receptors → phospholipase D activates PKC which inhibits myosin light chain phosphorylation → result in increase in cross bridge formation and force of contraction → vasoconstriction

In low concentrations ADH also acts on KCNQ5 and inhibits it. Results in less potassium extrusion from the cell which causes relative depolarization which brings the cell closer to threshold to open voltage gated calcium channel and activates them bringing calcium into the cell contributing to vasoconstriction

Question 31

How does ADH mediate plasma volume?

Answer 31

ADH increases the expression of aquaporin water channels in the collecting duct resulting in increased water reabsorption and decreased urine output resulting in preserved blood volume and MAP

Question 32

What inhibits ADH?

Answer 32

alcohol

Question 33

What stimulates the release of atrial natriuretic peptide?

Answer 33

Atrial natriuretic peptide: hormone released from atria; released in response to increased venous return which stretches the atrial wall and stimulates atrial stretch receptors → ANP secretion

Question 34

What is the function of atrial natriuretic peptide

Answer 34

Causes a reduction in aldosterone secretion and increase in glomerular filtration rate → net effect: increase in natriuresis (sodium excretion) and diuresis (urinating) and decrease in sodium reabsorption

Overall: increase sodium excretion, decreased plasma volume, decreased venous return, decreased cardiac output, decrease MAP

ANP also dilates resistance and capacitance vessels which contributes to a reduction in MAP