Nervous and hormonal control of vascular tone

Question 1

Define local control? (4pts)

Answer 1

1. Myogenic response= muscular response
2. Paracrine and autocrine= A paracrine signal originates close by- if one cell secrets prostaglandins it will affect the cell next to it. An autocrine response is when a cell produces a substance which affects itself and is a self regulating substance
3. Physical factors= Temperature which causes vasodilation and vasoconstriction, sheer stress
4. Regional Hyperaemia= An increase in blood flow to a particular area

Question 2

Define extrinsic control? (6pts)

Answer 2

1. Extrinsic control regulates total peripheral resistance to control blood pressure
2. The brain selectively alters blood flow to organs according to need e.g during exercise and temperature regulation
3. Vasoconstrictors= sympathetic nerves which secrete noradrenaline
4. Vasodilators= work on acetylcholine and nitric oxide
5. Vasoconstrictor hormones= adrenaline and angiotensin II
6. Vasodilator hormones= ANP

Question 3

Define the sympathetic and vasoconstrictor system? (5 pts)

Answer 3

1. Vessels are under constant sympathetic tone
2. The medulla oblongata contains centres which coordinate reflexes
3. The main excitatory nerve down the spinal cord emerges from the sympathetic preganglionic fibres between T1 and L2 and enter the sympathetic ganglia. The sympathetic ganglia contain the sympathetic postganglionic fibres which innorvate the muscles and the heart. They also innovate the adrenal glands
4. Noradrenaline is released at the site of the vessels and the heart. The vessels contain a1 receptors which will cause constriction when noroadrnealine binds to them. The heart contains B1 receptors which increase stroke volume and heart rate when noradrenaline binds to it.
5. The adrenal medulla releases adrenaline into circulation. This will bind to B2 receptors on various vessels which will cause relaxation and dilation. Adrenaline can also bind to the a1 receptors and cause constriction in some vessels.

Question 4

Define the postsynaptic sympathetic fibre?

Answer 4

The postsynaptic sympathetic fibre innervates the vascular smooth muscles. It has varicosities which appear like beads on a string which innervate the tissue layer of the vessels. §

Question 5

Explain how the action potential moves down the axon?

Answer 5

1. An action potential moves down the axon and arrives at a varicosity
2. Depolarisation at the varicosity activates voltage gated Ca2+ channels
3. The ingress of calcium causes the release of neurotransmitters from vesicles in the varicosity
4. Sodium diffuses to the vascular smooth muscle cells where it binds mainly alpha 1 receptors for contraction and alpha 2 for contraction and B2 for relaxation. Modulation of response in both constriction and dilation
5. The noradrenaline is then taken up again and is recycled or broken down.

• Adrenal gland releases adrenaline which acts on a1 and B2 receptors causing vasodilation or vasoconstriction,

Question 6

Explain the steps in varicosity? (5pts)

Answer 6

1. The release of sodium can be modulated by angiotensin II acting on AT1 receptor increasing sodium release
2. There are some a2 receptors on the surface of the varicosity. Noroadrenlaine release will cause the varicosity to binds its own noradrenaline. This inhibits the release of more noradrenaline in a negative feedback loop. The noradrenaline release will cause vasoconstriction.
3. Angiotensin increases vasoconstriction as it increases noradrenaline release.
4. Metabolites prevent vasoconstriction to maintain blood flow. K+, adenosine, histamine and serotonin inhibit noradrenaline release.
5. Lots of modulation occurs at the neurotransmitter level at the varicosity, It produces vasoconstriction and vasodilation,.

Question 7

Explain sympathetic vasoconstriction nerves in the medulla?

Answer 7

RVLM- areas inside the medulla which integrate signals and pass one to another. It helps the brain stem control sympathetic vasoconstrictor nerves. they innovate most of the arterioles and the veins

Question 8

What does noroadrenaline do?

Answer 8

Noradrenaline activates a1-adrenoreceptors on vascular smooth muscle cells causing vasoconstriction

Question 9

What is sympathetic nerve activity?

Answer 9

Sympathetic nerve activity is tonic. It is one action potential per second. Tonic sympathetic activity sets a vascular tone.

Question 10

Explain the main roles of sympathetic vasoconstrictor nerves?

Answer 10

1. Distinct sympathetic pathways innervate different tissue
2. Pre-capillary vasoconstriction- this leads to downstream capillary pressure drop so there is increased absorption of interstitial fluid into the blood plasma which is to maintain blood volume. This is important in hypovolemia- vasoconstriction will lower hydrostatic pressure in the capillaries which will allow more blood to move from the interstitial fluid into the blood.
3. Control resistance arterioles- produces vascular tone which allows increased blood flow to occur and vasodilation which controls total peripheral resistance. It maintains arterial blood pressure and blood flow to the brain, myocardium and the kidney
4. Control venous blood volume- vasoconstriction leads to decreased venous blood volume increasing venous return. This increases stroke volume via starlings law.

Question 11

Describe parasympathetic nerves?

Answer 11

1. Salivary glands= Release acetylcholine and VIP
2. Pancreas and intestinal mucosa= release VIP. Both these tissued need high blood flow to maintain fluid secretion. Acetylcholine and VIP act on the endothelium to cause the release of nitric oxide which causes vasodilatation.
3. Male genetalia= release nitric oxide. The release of nitric oxide by parasympathetic nerves causes the production of cGMP which leads to vasodilation. Viagra enhances this effect of nitric oxide by inhibiting the breakdown on cGMP by phosphodiesterase.

Question 12

Explain sympathetic nerves?

Answer 12

Skin ( sudomenter fibres)= release acetylcholine and VIP causing vasodilation via no associated routes. Increased blood flow causes more sweat and allows more heat loss via the skin.

• sympathetic activity vasoconstriction would reduce blood flow, limit sweat production and limit cooling
• emotional centres in the brain have control over these fibres, head, face, upper chest and involved in blushing.

Question 13

Explain nocipetive c fibres? ( 3pts)

Answer 13

1. The sensory nocipetive c fibres are stimulated in response to trauma or infection
2. This activation causes the release of substance P or CGRP
3. These act on mass cells to release histamine and endothelium and vascular smooth muscle
4. These both will produce vasodilation called flare in the skin.

Question 14

Explain the Lewis Triple response?

Answer 14

1. Local redness
2. Wheel
3. Flare

LWF

Question 15

Name vasoconstrictors?

Answer 15

1. Adrenaline
2. Angiotensin
3. Vasopressin

Question 16

Name vasodilators?

Answer 16

ANP

Question 17

Describe the action of adrenaline?

Answer 17

1. Adrenaline is released from the adrenal medulla via the action of acetylcholine on nicotinic receptors
2. Receptors are triggered during:
3. Exercise
4. Fight-Flight-fear response- increases sympathetic drive
5. Hypotentison- baroreceptor reflex occurs at very low blood pressures
6. Adrenaline mobilises glucose
7. Adrenaline stimulates heart rate and contractility during excercise
8. Adrenaline causes vasodialation of coronary and skeletal muscle arteries

Question 18

Explain adrenaline vs noroadrenaline on resistance vessels?

Answer 18

1. In most vessels vasoconstriction occurs due to a1 adrenoreceptors
2. Skeletal muscle and coronary arteries have more B2 receptors than a1 receptors
3. Adrenaline has a higher affinity for B over a, mainly acts at B2 to dilate vessels
4. Noradrenaline has a higher affinity for a, mainly acts as a1 receptors to constrict vessels

Question 19

Explain the effect of noroadrenline on circulation? (6pts)

Answer 19

1. Inject noradrenaline
2. The a1 receptors will constrict
3. The total peripheral resistance will increase due to vasoconstriction
4. The increase in total peripheral resistance will increase blood pressure by stimulating baroreceptors
5. The increase in blood pressure stimulates baroreceptors reflex to decrease heart rate
6. The drop in heart rate will cause cardiac output to decrease

Question 20

Explain the effect of adrenaline on circulation? (6pts)

Answer 20

1. Inject adrenaline
2. This causes skeletal muscles to vasodialate due to the presence of b1 receptors
3. This causes a reduction in total peripheral resistance
4. Adrenaline will bind to the b1 receptor on the heart causing an increase in heart rate and cardiac otuput
5. Cardiac output goes up and total peripheral resistance goes down so there is not much effect on blood pressure

Question 21

Exoplain RAAS? (6pts)

Answer 21

1. Stimulus is low renal blood flow. Low NACL is detected
2. The kidneys perfuse
3. The kidneys responds by releasing renin
4. Renin is an eznyme which cleaves angiotensin produced in the liver to produce a decapeptide called angiotensin 1
5. Angiotensin 1 moves around the circulation and as it passes through the lungs it is converted to angiotensin 2 by angiotensin converting enzyme.
6. Angiotensin 2 is an octappetide and has several effects:
7. Increases sympathetic drive and increases thirst
8. Causes vasoconstriction which raises total peripheral resistance
9. Causes aldosterone release. Aldosterone causes retention of more sodium in the kidneys which causes more water to be reabsorbed by the kidneys which raises blood volume
10. Increases blood pressure

Question 22

Explain the release of vasopressin?

Answer 22

1. Stretch receptors on the left atrium send continuous signals to the NTS which is in the medulla
2. The NTS sends out inhibitory nerves to the CVLM
3. The CVLM signals stimulate the pituitary gland to release vasopressin so stretching of the heart inhibits this.
4. Vasopressin is released from the posterior of the pituitary gland. It causes increased reabsorption of the fluid by the kidney and also causes vasoconstriction which both maintain blood pressure.

Question 23

Explain the steps in ANP? (4pts)

Answer 23

1. ANP is released by specialised atrial myocytes
2. They are secreted by increased filling pressures which stimulates stretch receptors
3. ANP acts at ANP receptors on vascular smooth muscle cells increasing cGMP pathway
4. This causes systemic vasodilation. This opposes the action of noradrenaline, RAAS and ADH.

Question 24

Explain ANP and the kidneys?

Answer 24

1. High blood pressyre
2. Atrial myoctyes release ANP
3. This causes systemic vasodilation
4. This increases water loss from the kidneys