Nervous and hormonal control of vascular tone

Question 1

What is intrinsic control?

Answer 1

→ Regulates local blood flow to organs/ tissues

→ Important - regional hyperaemia (increase in blood flow)

Question 2

What is extrinsic control?

Answer 2

→ Regulates TPR to control blood pressure

→ Brain function selectivity alters blood flow to organs according to need

Question 3

What are vasoconstrictor hormones?

Answer 3

→ Adrenaline, angiotensin II, vasopressin

Question 4

What is a vasodilator hormone?

Answer 4

→ Atrial Natriuretic Peptide

Question 5

What is the most widespread and important form of extrinsic control?

Answer 5

→Sympathetic vasoconstriction

→ Nervous system information integrated by the brain

Question 6

How does sympathetic innervation of the arterioles leads to release of NA?

Answer 6

1) Action potential moves down the axon and arrives at a varicosity
2) Depolarization at the varicosity activates voltage gates Ca2+ channels
3) Ingress of Ca2+ causes the release of neurotransmitters - mainly NA
4) NA diffuses into the vascular smooth muscle cells

Question 7

What are the three receptors NA binds to and what are the effects?

Answer 7

→ alpha 1 - contraction
→ alpha 2 - contraction
→ beta 2 - relaxation

Question 8

How can the release of NA be modulated?

Answer 8

→ by Angiotensin II acting on AT 1 receptor which increases NA release
→metabolites prevent vasoconstriction and maintain blood flow
→K+, adenosine, histamine & serotonin feedback and inhibit NA release
→ NA can also negatively feed back itself via a2 receptors to limit its own release.

Question 9

what does lots of modulation occurring at the NT level produce?

Answer 9

→ Produces vasoconstriction + vasodilation as required

Question 10

What are sympathetic vasoconstrictor nerves controlled by?

Answer 10

→ controlled by the brain stem (provides control of blood flow/ blood pressure)

Question 11

What do sympathetic vasoconstrictor nerves innervate?

Answer 11

→innervates most of the arterioles and veins of the body

Question 12

What kind of activity do sympathetic nerves have?

Answer 12

→sympathetic nerve activity is tonic

→ tonic sympathetic activity sets vascular tone

Question 13

What is an important principle in pharmacological treatment of CVS diseases with regards to sympathetic activity?

Answer 13

→a decrease in sympathetic activity producing vasodilation is an important principle in pharmacological treatment of cardiovascular disease

Question 14

How do sympathetic vasoconstrictor nerves contract resistance arterioles?

Answer 14

Produce vascular tone which allows vasodilation/increased blood flow to occur which controls TPR

Question 15

What do DISTINCT RVLM NEURONES do?

Answer 15

(sympathetic pathways innervate different tissues)

we can switch vasoconstriction on in some vessels and off in others

Question 16

What does pre-capillary vasoconstriction do?

Answer 16

→this leads to a downstream capillary pressure drop

→ increased absorption of interstitial fluid into the blood plasma to maintain blood volume

Question 17

How do sympathetic vasoconstrictor nerves control TPR?

Answer 17

→it maintains arterial blood pressure and blood flow to the brain/myocardium area (since Pa = CO x TPR)

Question 18

What does venoconstriction lead to?

Answer 18

→ venoconstriction leads to a decreased venous blood volume
→ increasing the venous return
→ increases the stroke volume via Starling’s Law

Question 19

What types of tissues contain vasodilator nerves and what is their function?

Answer 19

→ A few specialised tissues contain vasodilator nerves, as well as vasoconstrictor nerves.
→ they have a specific function controlling a specific vascular bed rather than global functions.

Question 20

How does vasodilation occur?

Answer 20

Vasodilation occurs as the vascular tone produced by sympathetic vasoconstrictor nerves is inhibited.

Question 21

What are the innervations of vasodilator nerves?

Answer 21

There are mainly parasympathetic vasodilator nerves, and a few sympathetic vasodilator nerves

Question 22

Where are parasympathetic vasodilator nerves found?

Answer 22

→salivary glands (release Ach and VIP)
→ pancreas and intestinal mucosa (release VIP)
→ male genitalia (release NO)

Question 23

Where are sympathetic vasodilator nerves found?

Answer 23

→skin (sudomotor fibres) (release Ach and VIP)

Question 24

Describe the effect of stimulation of sensory (nociceptive C fibres) vasodilator fibres

Answer 24

→The stimulationof sensory axon reflex (C-fibres) occurs by trauma, infection, etc.

→They release a substance called substance P or calcitonin gene-related peptide (CGRP).

→This acts on mast cells to release histamine.
→ It also acts on the endothelium and vascular smooth muscle.

→Both the histamine and CGRP produce vasodilation, seen as the ‘flare’ in the skin.

Question 25

What is the Lewis triple response?

Answer 25

→ Local redness → Wheal → Flare

Question 26

What are 3 vasoconstrictor hormones?

Answer 26

→ Adrenaline →Angiotensin II → Vasopressin (ADH)

Question 27

What are 3 hormones that affect the circulation?

Answer 27

→ estrogen, insulin, relaxin

Question 28

Where is adrenaline released from?

Answer 28

→ Adrenal medulla via the action of AcH on nicotinic receptors

Question 29

When is adrenaline released?

Answer 29

→ Exercise → fight or flight → Hypotension → Hypoglycaemia

Question 30

What are the main roles of adrenaline?

Answer 30

→ Glucose mobilization (skeletal muscle, glycogenolysis, fat lipolysis) → Stimulation of the heart rate and contractility during normal exercise → Vasodilation of coronary and skeletal muscle arteries

Question 31

Why is there vasoconstriction in most tissue?

Answer 31

→ due to alpha 1 adrenoceptors

Question 32

What receptors do skeletal muscles and coronary arteries have more of?

Answer 32

→ more beta 2 than alpha 1 adrenoceptors

Question 33

What receptor does adrenaline have a higher affinity for?

Answer 33

→ Higher affinity for beta over alpha

Question 34

What receptor does noradrenaline have a higher affinity for?

Answer 34

→ Higher affinity for alpha

Question 35

Describe the effects of iv adrenaline on the heart

Answer 35

→ the heart rate increases. →The cardiac output also increases → total peripheral resistance decreases (due to its effects on the β2 receptors) → not much of an effect on blood pressure.

Question 36

Describe the effects of iv noradrenaline on the heart

Answer 36

→ big increase in TPR (due to vasoconstriction at the α1 receptors) → causes an increase in blood pressure. → increased BP stimulates the baroreceptors' reflex to decrease heart rate.

Question 37

How does the RAAS system work?

Answer 37

1) Renin is produced by the kidney, stimulated by low renal blood flow 2) Angiotensinogen is the precursor produced in the liver 3) undergoes proteolysis and becomes Angiotensin I which goes to the lungs 4) Angiotensin converting enzyme converts it into Angiotensin II (increased sympathetic drive, thirst) 5) Aldosterone is produced causes renal NaCl + H2O retention - raises blood volume

Question 38

What is the hypothalamus response stimulated by?

Answer 38

→ An increase in osmolarity (dehydration or low blood volume)

Question 39

Where is vasopressin or ADH released from?

Answer 39

→ Posterior of the pituitary gland

Question 40

What does vasopressin or ADH release cause?

Answer 40

→ Vasoconstriction and increases renal absorption of water | → maintains blood pressure

Question 41

how does vasopressin respond to lowered BP?

Answer 41

→Stretch receptors in the left atrium send continuous signals, causing firing in the NTS (nucleus tractus solitarius). →This sends out inhibitory signals to the CVLM. →The CVLM (caudal ventrolateral medulla) stimulates the pituitary to release ADH → stretching of the heart inhibits release of ADH

Question 42

What happens to the NTs during dehydration or haemorrhage?

Answer 42

→NTS's inhibition is switched off and the CVLM stimulates vasopressin production. → The NTS is like the thermostat that sets the level at which the CVLM is inhibited.

Question 43

What is ANP released by?

Answer 43

→ Specialised atrial myocytes

Question 44

how is ANP is secreted?

Answer 44

→ Secreted by increased filling pressures which stimulate stretch receptors

Question 45

Where does ANP act?

Answer 45

→ Acts at NP receptors on vascular smooth muscle cells | →Increases the cGMP pathway (like NO)

Question 46

What does ANP do?

Answer 46

→ Systemic vasodilation | →Opposes the action of RAAS, ADH and noradrenaline

Question 47

What does the dilation of the renal afferent arteriole do?

Answer 47

→ Increases GFR → Na+ and H2O excretion by the kidney are increased → blood volume goes down decreasing the release and/or actions of aldosterone, renin + ADH