Blood pressure

Question 1

What is the normal BP for a dog/cat at rest?

Answer 1

120/80

Question 2

How should blood pressure be calculated?

Answer 2

Take 3 readings and taken an average

- remember to take stress into account

Question 3

What is the potential impact of a persistently high BP?

Answer 3

• Afterload on the ventricles is high
• More force is needed to overcomethe pressure in the arteries
• Increased heart workload
• Can lead to muscle thickening
• Backwards heart failure
• Damage to kidneys
• Eyes can be impacted

Question 4

What is the potenital impact of a persistantly low BP?

Answer 4

• Leads to low perfusion of tissues
• Exercise intolerance and muscle wastage
• Reduced urine production
• Reduced filtration of blood

Question 5

What is the equation for cardiac output?

Answer 5

SV x HR

Question 6

What is the equation for aortic pressure (Pa)?

Answer 6

Pa = CO x TPR

Question 7

What factors influence stroke volume?

Answer 7

EDVV and ESVV

Question 8

What is the equation for SV?

Answer 8

SV = EDVV - ESVV

The volume of blood ejected into the circulation by one ‘stroke’ or contraction of the ventricle

Question 9

What is the pathological effect of a high heart rate?

Answer 9

CO is reduced because EDVV is reduced so there isnt enough time for diastolic filling

Question 10

What is the physiological effect of a high heart rate?

Answer 10

Sympathetic nervous system will shorten systole to allow more time for diastolic filling
- faster conduction of APs

Question 11

What are the 2 main intrinsic mechanisms to control local blood flow?

Answer 11

• Metabolic autoregulation

- Paracrine control

Question 12

What is metabolic autoregulation?

Answer 12

Increase in metabolic rate increases blood flow to tissues

• Increased production of CO2, K+, and lactic acid
• Causes vasodilation

Question 13

What is paracrine control?

Answer 13

Locally acting hormones that lead to vasodilation e.g. nitric oxide

Question 14

What are the 2 extrinsic mechanisms that preserve flow to essential tissues?

Answer 14

• Baroreflex

- RAAS

Question 15

What is the baroreflex?

Answer 15

• First to kick in when theres decreased blood pressure
• Decreases CO and vasoconstriction to try and balance BP
• Doesn’t change overall volume of blood

Question 16

What is the RAAS?

Answer 16

Can replace lost fluid volume

• Vasoconstriction
• ADH
• Thirst centres in hypothalamus

Question 17

Where are baroreceptors located?

Answer 17

In the aortic arch and carotid sinuses

Question 18

Where do baroreceptors send input and where does the output of that go?

Answer 18

To the CV centre in the medulla oblongata which sends outputs via the ANS

Question 19

What are the main actions of the ANS in the baroreflex?

Answer 19

• Drop in BP = increased sympathetic NS
• Increased HR and contractility = increased SV
• Vasoconstriction of non-essential tissues

Question 20

Which receptors are involved in the sympathetic NS, which response are they involved in?

Answer 20

Adrenergic - α1 α2 β1 β2

- fight or flight

Question 21

Where are the different adrenergic receptors located in the body and what does stimulation of each of them cause?

Answer 21

α1 α2 = found in blood vessels, stimulation causes vasoconstriction
β1 = in cardiomyocytes and nodal tissue, stimulation causes increased contractility and HR
β2 = In the coronary arteries, stimulation causes vasodilation

Question 22

Which receptors are a part of the rest and digest response?

Answer 22

Cholinergic = M2 and M3

Question 23

Where are cholinergic receptors found and what does stimulation of each of them cause?

Answer 23

M2 = in cardiac tissue, causes decreased contractility and HR
M3 = on blood vessels, leads to vasodilation

Question 24

What is the role of nitric oxide in the control of blood flow?

Answer 24

• Released from endothelial cells when there is an increase in the speed of blood flow
• part of the parasympathetic NS
• causes vasodilation

Question 25

What is first released in the RAAS and where is it released from?

Answer 25

Renin - from the liver in response to a decrease in BP

Question 26

What is the effect on renin, within the RAAS?

Answer 26

- Causes angiotensinogen to be converted to angiotensin I

Question 27

What then happens to angiotensin 1?

Answer 27

An enzyme in the lungs called ACE converts angiotensin I to angiotensin II

Question 28

What is the role of angiotensin II?

Answer 28

- causes vasocontriction (increases BP) and release of aldosterone

Question 29

What is the role of aldosterone?

Answer 29

- Causes the kidney to conserve sodium and water which increases the blood volume - Increases thirst

Question 30

How does angiotensin II also act on the pituitary gland?

Answer 30

Causes it to release antidiuretic hormone which causes the kidneys to conserve water, increasing blood volume and further vasoconstriction

Question 31

Where is aldosterone produced?

Answer 31

Adrenal gland

Question 32

Which organ is central to long term regulation of BP?

Answer 32

The Kidney

Question 33

Which part of the kidney leads to activation of the RAAS?

Answer 33

The afferent arteriole detects changes in BP within the vessel, which leads to activation of the RAAS

Question 34

What is pressure naatriuresis?

Answer 34

Kidney pressure changes affect sodium (and water) excretion

Question 35

Which cells in DCT activate the RAAS?

Answer 35

Macula densa cells in the DCT sense reductions in sodium causing activation of the RAAS

Question 36

Give the key points of how the ANS controls blood volume

Answer 36

Alpha 1/2 --> vasoconstriction & venoconstriction --> effectively increasing central blood volume & preload

Question 37

How does a change in blood vessel diameter affect BP?

Answer 37

Causes a change in TPR, which affects the pressure of the atria, which changes the blood pressure

Question 38

How do you increase heart rate and contractility at a cellular level?

Answer 38

β1 adrenoreceptor on nodal tissue and cardiac myocytes binds adrenaline/noradrenaline - leads to formation of cAMP

Question 39

What is the function of cAMP?

Answer 39

Activates PK-A which phosphorylates Ca channels causing an influx of Ca, which leads to contraction

Question 40

How can vascular smooth muscle be made to contract - i.e. what are the stimuli?

Answer 40

- Stretch - Electrical stimulus - Chemical stimulus

Question 41

How do these stimuli on vascular smooth muscle lead to contraction?

Answer 41

- Stimuli causes increased cellular calcium ions - these activate myosin light chain kinase - MLC phosphorylation causes cross bridge formation - leads to muscle contraction