The cardiovascular control system

Question 1

What are the aims of the CV control system?

Answer 1

Maintain BP
Regulate CO
Maintain BF to different organ systems

Question 2

Purpose of the RAA system

Answer 2

Regulation of body fluids

Question 3

Factors causing increased renin secretion?

Answer 3

Decreased perfusion pressure
Increased sympathetic drive to the kidney
Decreased sodium content in tubular fluid

Question 4

Some functions of angiotensin II

Answer 4

• Primarily a vasoconstrictor
• Release of aldosterone = sodium reabsorption (also a direct action of aldosterone), followed by water reabsorption = increase circulating volume = maintained BP
• Increased secretion ADH
• SNS stimulant

Question 5

General pathway of the RAA system?

Answer 5

Angiotensinogen produced by the liver
Renin coverts it to angiotensin I
ACE produced in the lungs converts it to angiotensin II

Question 6

How are changes in BP sensed by the body?

Answer 6

Systemic aortic baroreceptors in carotid sinus and aortic body, nerve impulse firing rate increases with increased arterial pressure

Question 7

What is the pattern of negative feedback to the systemic aortic baroreceptors?

Answer 7

Info comes back from the brain via the sympathetic cardiac nerve, is effectively the opposite of the firing rate from the carotid sinus nerve impulses
So when you have low levels of carotid sinus nerve activity you have increased sympathetic drive. vice versa

Question 8

What are the neural responses to an increased BP?

Answer 8

Decreased sympathetic drive and increased vagal / parasympathetic drive
There is no vagal inhibitor so temporal rate changes less than sympathetic nerves

Question 9

Changes to said mechanism in a hypertensive patient

Answer 9

baroreceptor reflex not as good
Changes in pressure either don’t change carotid sinus nerve activity as much or they change change carotid sinus nerve activity enough but the output doesn’t change as much
Therefore the patients are prone to having more fluctuations in blood pressure because the gain of the system is low

Question 10

What is a telling prognostic indicator of outcome in hypertensive patients?

Answer 10

the severity of the decreased gain of the baroreceptor reflex

Question 11

Threshold of the carotid sinus baroreceptor?

Answer 11

below 30-50mmHg a decrease in pressure doesn’t alter the firing rate

Question 12

Saturation of the carotid sinus baroreceptor?

Answer 12

increase in pressure above 150-180mmHg also has no further effect on firing frequency

Question 13

rate sensitivity of the carotid sinus baroreceptor

Answer 13

For a given mean pressure the rate of firing is greater for pulsatile pressure than for steady pressure

Question 14

Standard responses when arterial pressure falls?

Answer 14

Increased HR and cardiac inotropic state
Graded restriction of pre capillary resistance vessels in skeletal muscle (splanchnic, cutaneous and renal circulations) but not in cerebral and coronary arteries
Venoconstriction
Increased catecholamine secretion by adrenal medulla
Increase circulating levels of ADH, AII and other hormones

Question 15

Vagal afferent in the heart sense

Answer 15

Sense changes in cardiac volume
A and B receptor fibres which fire off either atrial or ventricular contraction send info about the stretch in either the atria or ventricle
In most cases volume and pressure increase together but sometimes can be dissociated from each other

Question 16

Steep activation of myelinated RA receptors leads to?

Answer 16

Increased HR
Reduced renal sympathetic stimulation (sympathetic drive to other organs doesn’t change that much) this helps you excrete out salts and water and bring blood volume back down

Question 17

Osmoreceptors in the hypothalamus?

Answer 17

sense changes in effective plasma osmolality by measuring their volume alteration.
this modulates the synthesis and release of ADH levels leads to net water excretion (vice versa)

Question 18

Increased discharge of peripheral chemoreceptors is brought about by? and results in?

Answer 18

by low PaO2
Stimulates increased sympathetic drive to heart and heart vessels.
When oxygen delivery is deprive for instance by reduced arterial pressure chemoreceptor activation causes vasoconstriction and contributes to restoration of BP.

Question 19

What happens in the circuitry of the brain if BP increases?

Answer 19

Increased activation of CVLM which sends inhibitory signals to the RVLM do decreased excitation at the RVLM and from the RVLM sympathetic drive to all the blood vessels decreases

Question 20

The paraventricular nucleus and CV control

Answer 20

Underneath is the posterior pituitary where ADH is secreted, so cardiopulmonary receptors go up into the NTS which sends projections to the PVN which sends projections to the posterior pituitary to try and change ADH, PVN also sends projections directly and via the RVLM to the kidney to change kidney sympathetic drive

Question 21

What type of vasculature has the largest relative size of smooth muscle?

Answer 21

small arteries and arterioles

Question 22

How is the blood flow to different parts of the body regulated?

Answer 22

Alteration of lumen of pre capillary resistance vessels

Question 23

Effects of altered pre capillary resistance of distribution of mean pressure through typical vascular network

Answer 23

Constriction of pre capillary resistance vessels means that energy is dissipated as blood is funnelled through a narrower opening, pressure gradient along vessels is increased and pressure within vessels is reduced this means less fluid extrusion/ more fluid absorption
Vice versa

Question 24

Storage of blood in the systemic circulation and how does it change?

Answer 24

Small veins and venules
Construction reduces their capacity to store blood and increases pressure driving blood back to the right heart. vice versa.
These changes also influence post capillary vascular resistance

Question 25

About vascular smooth muscle?

Answer 25

Local pacemaker activity because all VSM cells are electrically coupled to their neighbours and this may propagate from one side to the other

Question 26

The link between blood vessel flow and metabolism is demonstrated by?

Answer 26

auto regulation )intrinsic tendency of organ to maintain constant blood flow despite changes in perfusion pressure
the cutaneous circulation has almost none whereas the cerebral circulation is tightly regulated

Question 27

Reactive hyperaemia

Answer 27

after a blood vessel is occluded for a short period, when the occlusion is released blood flow rises above the preclusion level, and is maintained for a period roughly proportional to the duration of the occlusion

Question 28

How does the myogenic control work?

Answer 28

most potent in medium sized arterioles and in small and medium veins
Increased pressure distends the vessel walls which depolarises VSM cells (stretch sensitive membrane ion channels) causing contraction

Question 29

Endothelial control of VSM?

Answer 29

endo cells release smooth muscle which acts on VSM to increase intracellular cGMP conc causing VSM relaxation
The end also releases endothelin a calcium chanel agonist and potent vasoconstrictor

Question 30

Integrated model of local control

Answer 30

When tissue metabolism is increased with respect to blood supply vasodilator metabolites are produced leading to dilation of terminal arterioles which in turn increases blood flow resulting in dilation of small arteries and more proximal arterioles that are less sensitive to metabolites and more sensitive to flow

Question 31

The role of co transmitters?

Answer 31

Produce long lasting actions that supplement the effects of primary neurotransmitter

Question 32

Cholinergic neurons

Answer 32

act as a vasodilator system
Pre capillary vessels in the heart, brain, face, tongue and urogenital tract, they release Ach
bind to M3 receptors in the vascular endothelium stimulating release of NO. But when vascular endo damaged or removed they bind to M2 receptors in the VSM causing vasoconstriction

Sympathetic cholinergic fibers innervate pre capillary vessels in the skeletal muscle beds

Question 33

Exogenous admin of noradrenaline causes?

Answer 33

Widespread vasoconstriction except for coronary and cerebral arteries

Question 34

Exogenous admin or adrenaline causes?

Answer 34

similar vascular effects to noradrenaline but resistance vessels in skeletal muscle and splanchnic circulations vasodilate, because Beta2 andregenic receptors are present in splanchnic and skeletal muscle circulations

Question 35

Other hormones that cause blood vessel changes

Answer 35

Angiotensin II a potent vasoconstrictor

Vasopressin / ADH is a vasoconstrictor

Question 36

What happens in skeletal muscle during exercise?

Answer 36

substantial fall in vascular resistance Increased perivascular concentrations of vasoactive metabolites which occur in exercise i) relax smooth muscle ii) inhibit sympathetic androgenic neurotransmission
The increased levels of adrenaline in circulation will also sustain vasodilation
Histamine released dilates pre capillary vessels

Question 37

Skin circulation

Answer 37

Low capillary densities and large numbers of superficial arteriovenous shunts to function as heat exchangers
Blood flow at rest greater than tissue requirements, auto regulation poorly developed
Powerfully innervated by the sympathetic adrenergic system
The affinity for the alpha receptor for NA decreases as the temperature rises thus local warming will lead directly to increased skin blood flow. Vice versa

Question 38

Cerebral circulation

Answer 38

tight linkage between metabolism and blood flow, tight regulation of perfusion pressure. Normal range = 60-180mmHg Autoregulation fails when PP < 50mmHg, oxidative metabolism of the brain impaired by pp of 40mg or less
Total cerebral blood flow relatively constant but large regional variation

Question 39

Cerebral BF control mechanisms

Answer 39

cons of pH, PCO2, PO2 and K+

Question 40

How are vascular cross sectional dimensions determined?

Answer 40

by pressure gradient across the vessel wall = transmural pressure Pt = Pi - Pe

Question 41

Pressures causing vessels to collapse

Answer 41

Pe > Pi = collapse
if Pe 20mmHg –> transient collapse and occlusion of post capillary vessels
However pressures will increase sufficiently throughout the vascular circuit for flow to be reinstated though possibly at a reduced level
When pressure 40mmHg there is collapse off price capillary vessels leading to impaired perfusion and sustained non-perfusion for some vascular regions
*compliancy of the compartment the vascular bed is inis significant e.g. those bounded by skin are easily distend able whereas the cranial cavity or fascial ones aren’t

Question 42

Raynaud’s Disease

Answer 42

Manly in young women
Prolonged vasoconstriction of the digital arteries of the hand when exposed to a cold stimulus. Due to inappropriate responsiveness of alpha androgenic receptors