Lecture 6: control of APB

Question 1

How is mean blood pressure calculated?

Answer 1

Diastolic pressure plus ¹/₃ of the pulse pressure

(pulse pressure is the difference between systolic and diastolic pressures)

Question 2

How does mean blood pressure change with age?

Answer 2

Increases

Question 3

Is mean blood pressure higher in men or women (between puberty and menopause)?

Answer 3

Men

Question 4

What can increase pulse pressure?

Answer 4

Reduced arterial compliance (atherosclerosis)

If blood can flow away faster in diastole

• occurs in exercise when TPR drops
• pathologically if aortic valve leaks

Question 5

What is the principle variable controlled by the cardiovascular system?

Answer 5

Arterial blood pressure

Question 6

How can Darcy’s law be used to represent the whole circulation?

Answer 6

ABP = CO x TPR

Question 7

What are the 2 main factors that affect ABP?

Answer 7

CO and TPR

these are largely independent of each other

Question 8

What are the 3 mechanisms for monitorring blood pressure within the body?

Answer 8

• High pressure baroreceptors
• Low pressure baroreceptors
• Arterial chemoreceptors

Question 9

Where are baroreceptors found in the body?

Answer 9

Carotid sinus

Aortic arch

Afferent renal arterioles

Question 10

How is the vasomotor centre inhibited?

Answer 10

Stimulation of nucleus tractus solotarius in the medulla

Question 11

What is shock?

Answer 11

When cardiac output is insufficient to adequately perfuse organs

Question 12

What are the typical signs of shock?

Answer 12

Hypotension

Tachycardia

(may be accompanied by low urine output and loss of consciousness)

Question 13

What causes hypovolaemic shock?

Answer 13

Failure of CO due to a severe loss of circulating volume

Question 14

What are the 3 types of shock associated with cardiovascular physiology?

Answer 14

Hypovolaemic

Cardiogenic

Disruptive

Question 15

What range of pressures are coverred by baroreceptors?

Why can they cover such a long range?

Answer 15

50-200mmHg

Different baroreceptor fibres have different sensitivities to blood pressure

Question 16

How does sensitivity to blood pressure vary between carotid and aortic baroreceptors?

Answer 16

Carotid sinus is more sensitive than the aortic arch

Aortic arch can respond to pressures above which the carotid sinus response saturates

Question 17

What is the effect of denervation of arterial baroreceptors on ABP?

Answer 17

Increased variability of ABP

Mean ABP stays relatively constant

Question 18

What is responsible for short term control of ABP?

Question 19

What physiological stresses cause an increased variability in ABP?

Answer 19

Exercise and changes in posture

Question 20

What is the primary role of chemoreceptors in the carotid and aortic bodies and the medulla?

Answer 20

To regulate ventilation

Question 21

How are chemoreceptors important in controlling ABP?

Answer 21

Not important in blood pressure control in normal circulation

Important in ABP control when blood pressure or PO₂ are very low as high pressure baroreceptors are relatively unresponsive under conditons of severe hypotension

Question 22

How do chemoreceptors detect and respond to low blood pressure?

Answer 22

• Low O₂ and high CO₂ detected by chemoreceptors in the medulla via resultant drop in brain pH
• afferent signals from carotid and aortic bodies travel via the glossopharyngeal and vagus nerves respectively

Question 23

What are cardiopulmonary baroreceptors?

Answer 23

Low pressure baroreceptors located at junctions of atria with corresponding veins and within the atria itself

Question 24

What do low pressure baroreceptors detect?

Answer 24

Change in RAP

Question 25

What does a high RAP suggest?

Answer 25

The circulation is overfilled such that the heart cannot maintain low venous pressures May lead to oedema as capillary pressures rise

Question 26

What does a low RAP suggest?

Answer 26

CO is maximal for the current MSFP (RAP should ideally be 0 or slightly negative)

Question 27

What is the effect of denervation on chemoreceptors alongside high pressure baroreceptors?

Answer 27

Increased mean ABP Increased variabilty of ABP

Question 28

Why are feed-forward mechanisms necessary in ABP control?

Answer 28

Common stresses such as exercise, standing up and mild blood loss do not substantially change ABP and so do not activate feedback These stresses trigger feed-forward mechanisms to preserve ABP

Question 29

How does exercise elicit a feed-forward response in ABP control?

Answer 29

Inputs into the medulla via: - cortex (where decision to exercise is made) - cerebellum (as part of a co-ordinated motor programme) - muscle and joint receptors (as a direct response to movement)

Question 30

How can pain and emotion affect ABP?

Answer 30

Rise in ABP as part of fight/flight response or in preparation for potential blood loss (feed forward control involving cortex and hypothalamus)

Question 31

What is the cortex associated with in terms of feed-forward control?

Answer 31

Decisions

Question 32

What is the hypothalamus associated with in terms of feed-forward control?

Answer 32

Emotions

Question 33

What is the cerebellum associated with in terms of feed-forward control?

Answer 33

Motor programs

Question 34

Where do sympathetic outflows from the cardiovascular centre of the medulla act?

Answer 34

The heart and vasculature

Question 35

Where do parasympathetic outflows from the cardiovascular centre of the medulla act?

Answer 35

The heart only

Question 36

What are bulbospinal pathways?

Answer 36

Pathways from the medulla to the spinal cord

Question 37

Which nerves are activated by bulbospinal activity?

Answer 37

Pre-ganglionic pathways primarily at glutamatergic synapses between levels T1-L3 of the vertebral column

Question 38

How do pre-ganglionic efferents from bulbospinal pathways connect to post-ganglionic efferents? Where are the postganglionic neurons located? What response do these postganglionic fibres induce?

Answer 38

Nicotinic synapses Found within prevertebral and paravertebral sympathetic ganglia and run alongside large blood vessels vasoconstriction (including venoconstriction) via action of noradrenaline on α₁ adrenoceptors

Question 39

Which vessels show the smallest amount of vasoconstriction during cardiovascular reflex responses?

Answer 39

Arteries and arterioles supplying the heart and brain

Question 40

What is the resting action potential frequency of sympathetic vasoconstrictor nerves? What does this increase to during haemorrhage?

Answer 40

1-4Hz 10Hz (reduces blood flow to almost 0)

Question 41

How are cells in the adrenal medulla innervated?

Answer 41

Chromaffin cells supplied by pre-ganglionic fibres in the splanchnic nerves

Question 42

What is caused by stimulation of preganglionic sympathetic fibres of splanchnic nerves?

Answer 42

Release of adrenaline into the circulation which acts on heart and vasculature via α₁ receptors

Question 43

What do β₂ receptors trigger?

Answer 43

Vasodilatation

Question 44

Which tissues have more β₂ than α₁ receptors? What is the effect of this?

Answer 44

coronary blood vessels and skeletal muscle Vasodilatation increases blood flow to heart and skeletal muscle

Question 45

What limits skeletal blood flow?

Answer 45

Noradrenaline

Question 46

How can the vagus nerve be inhibitied?

Answer 46

Atropine

Question 47

What type of activity is shown by the vagus nerve?

Answer 47

Tonic

Question 48

What part of the autonomic nervous system is the vagus nerve?

Answer 48

Parasympathetic

Question 49

What is the effect of vagal nerve stimulation?

Answer 49

Decreased heart rate

Question 50

How do TPR and ABP change with increased vasodilatation?

Answer 50

TPR decreases significantly ABP remains relatively constant

Question 51

Why does a fall in TPR through vasodilatation result in an increased CO and same ABP?

Answer 51

- sympathetic venoconstriction to increase MSFP - reduced vagal and increased sympathetic stimulation to increase heart rate and contractility Ensures raised MSFP produces a rise in CO without increasing RAP

Question 52

What is hypertension?

Answer 52

A blood pressure over 140/90mmHg

Question 53

What are the clinical consquences of hypertension?

Answer 53

- Cardiac failure - Cardiac arrhythmia - Ischaemic damage to organs e.g. myocardial infarction or stroke

Question 54

How much pressure can normal blood vessels withstand?

Answer 54

Up to 400mmHg

Question 55

Do normal blood vessels rupture under high pressure?

Answer 55

No, only damaged vessels e.g. atherosclerosis

Question 56

What is atherosclerosis?

Answer 56

Build up of inflammatory lipid deposits beneath the endothelium of blood vessels. These grow to include fibrous and calcific layers`

Question 57

How may atherosclerosis cause damage?

Answer 57

1. Narrowing vessels and restricting flow 2. Endothelial damage promotting clotting (thrombosis) - local blockage - distant blockage (embolism) 3. Weakening blood vessel walls leading to aneurysm and even ruptutre

Question 58

What are the risk factors of atherosclerosis?

Answer 58

Hypertension Smoking Diabetes Obesity

Question 59

What is cardiac hypertrophy?

Answer 59

Enlargement of cardiac myocytes thus increased heart mass

Question 60

What is angina pectoris?

Answer 60

pain in chest

Question 61

What is eccentric hypertrophy and what is it caused by?

Answer 61

Ventricular volume increases along with muscle mass (the heart grows) Induced by exercise

Question 62

What is concentric hypertrophy and what is it caused by?

Answer 62

Heart muscle expands inwards, thereby decreasing ventricular volume Induced by hypertension

Question 63

What are the 3 major problems induced by concentric hypertrophy?

Answer 63

1. Increased myocardial oxygen demand 2. Diastolic dysfunction (impairment of cardiac filling and hence stroke volume) 3. Increased risk of cardiac arrhythmias

Question 64

What is systolic dysfunction? What causes it?

Answer 64

Heart is unable to empty fully Concentric hypertrophy progresses into ventricular dilatation if blood pressure remains high and cardiac blood supply is poor