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Flashcards in Baroreceptors Deck (48)
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1
Q

Baroreceptor definition

A

sensors located in the carotid sinus (at the bifurcation or external and internal carotids) and in the aortic arch.

Sense blood pressure and relay information to the brain, so that proper blood pressure can be maintained.

2
Q

Where do signals from the carotid baroreceptors travel?

A

glossopharyngeal nerve (Cranial nerve IX)

3
Q

Where go signals from the aortic arch baroreceptors travel?

A

vagus nerve (cranial nerve X)

4
Q

Brief mechanism by which baroreceptors control blood pressure

A

negative feedback system called a baroreflex occurs as soon as there is a change from the usual mean arterial blood pressure.

5
Q

What happens once the baroreceptor is stimulated?

A
  1. action potential becomes triggered
  2. directly conducted to the brain stem where central terminations transmit to neurones within the solitary nucleus, which lies in the medulla
  3. nerve endings present in the tunica adventitia. If there is an increase in mean arterial pressure, the rate of depolarisation of these nerve endings increases.
  4. lead to action via autonomic nerves to decrease pressure-
  5. hormones secreted to target the heart and blood vessels
6
Q

What is the carotid sinus responsive to?

A

both increases and decreases in arterial pressure

7
Q

what is the aortic arch responsive to?

A

only increases in blood pressure

8
Q

orthostatic hypotension definition

A

A medical condition wherein a person’s blood pressure falls when standing or sitting

9
Q

Orthostatic hypotension mechanism

A

gravity causes blood to pool in the lower extremities, compromises venous return leading to a decreased cardiac output and subsequent lowering of arterial pressure

10
Q

How is orthostatic hypotension prevented in healthy individuals?

A

baroreceptor reflex that causes vasoconstriction, pressing the blood from the lower extremities back into the body again

11
Q

resistance is equal to

A

length divided by radius ^4

12
Q

What are arterioles referred to + why?

A

resistance arterioles- place where there is the greatest fall in pressure

13
Q

What happens during vasoconstriction?

A

upstream pressure increases, downstream pressure decreases

14
Q

What happens when the radius halves?

A

the resistance increases by a factor of 16

15
Q

What happens during vasodilation?

A

upstream pressure decreases, downstream pressure increases

16
Q

How else flow be increased?

A

capillary recruitment- more capillaries perfused

17
Q

Where may tissue perfusion increase rapidly?

A

salivary glands, skin and skeletal muscle

18
Q

which tissues always receive close to their maximum possible blood flow?

A

kidneys

19
Q

dynamic range definition

A

difference between maximum and minimum perfusion

20
Q

Myogenic mechanism definition

A

how arteries and arterioles react to an increase or decrease of blood pressure to keep the blood flow within the blood vessel constant

myogenic refers to a contraction initiated by a myocyte itself, not a nerve innervation

21
Q

Myogenic mechanism stages

A
  1. smooth muscle reacts to stretching of the muscle by opening channels
  2. muscle depolarised
  3. muscle contracts, which decreases the lumen diameter
  4. limits the blood flow, increases the blood pressure
22
Q

Myogenic autoregulation definition

A

maintain a constant renal blood flow, despite alterations in arterial pressure

23
Q

Bayliss effect definition

A

special manifestation of the myogenic tone in vasculature

smooth muscle cells response to stretch

when blood pressure is increased the blood vessels distend, muscle reacts with a constriction

24
Q

What does the stretch of the muscle open?

A

stretch mediated ion channels, causing the cell to become depolarised

calcium voltage gated channels open, trigger muscle contraction

25
Q

Experiment to prove Bayliss effect

A

reservoir full of water lifted, leading to increase in pressure

in a dead tube, no muscle etc, flow increased and fell similarly to the pressue

arteriole flow dropped back to normal, due to Bayliss effect, despite pressure remaining high

When verapamil added, calcium channel blocked, the arteriole behaved similarly to the dead tube

26
Q

What does the Bayliss Effect allow?

A

maintenance of a constant baseline flow

27
Q

over perfusion definition

A

tissue receives larger share of cardiac output than is required for maximum oxygen consumption

28
Q

what tends to be overperfused + why?

A

kidneys- require blood to filter it and to respire

29
Q

What tends to be underperfused + why?

A

heart and brain

better able to extract oxygen from the volume of blood than other tissues

30
Q

What can override myogenic autoregulation?

A

raised metabolism

31
Q

Adrenergic regulation of coronary flow

A
  1. falling ATP supply leads to increased AMP release from cells
  2. extracellular adenosine then binds to an alpha 2 receptor

3, causes a raise in intracellular cAMP

  1. decreases myosin light chain kinase activity
  2. vasodilation locally, decreases blood pressure
32
Q

What else can cause vasodilation?

A

hypercapnia, temperature, autacoids, nitric acid

33
Q

hypercapnia definition

A

abnormally elevated carbon dioxide levels in the blood

34
Q

Stages of vasodilation due to hypercapnia

A
  1. more co2, more acidic
  2. decreases MLCK activity
  3. vasodilation
35
Q

stages of vasodilation due to temperature

A
  1. heat, detected centrally and peripherally
  2. if centrally, detected by hypothalamus, if peripherally reduces noradrenaline binding to A2
  3. reduces sympathetic signalling
  4. greater heat loss due to dilated arterio-venous anastomoses
36
Q

autocoid definition + examples

A

locally produced and locally expressed factors that affect physiology

examples:histamine, bradykinin, prostaglandins, leukotrienes

37
Q

stages of vasodilation due to autocoids

A

histamine stimulates the synthesis and release of various vascular smooth muscle cell relaxants, such as nitric oxide and endothelium-derived hyperpolarising factor

38
Q

stages of vasodilation due to nitric oxide

A
  1. l-argininine, oxygen and NADPH synthesised endogenously by various nitric acid synthase enzymes.
  2. nitric acid targets guanylyl cyclase,
  3. protect cGMP from degradation, allowing signals to be enhanced and thus vasodilation
39
Q

role of endothelium in regulating flow

A

secrete autocoids

40
Q

stages of vasodilation die to extracellular accumulation of potassium

A
  1. small rise in extracellular potassium
  2. increased potassium permeability
  3. hyperpolarisation
  4. vasodilation
41
Q

hyperaemia definition

A

increase of blood flow to different tissues in the body

42
Q

reactive hyperaemia definition

A

a period of hyperaemia that follows a brief period of ischaemia, due to the shortage of oxygen and build up of metabolic waste

43
Q

vasomotor nerves

A

nerves that innervate blood vessels, which alter their diameter

44
Q

sympathetic vasoconstrictor stages

A
  1. brainstem- nucleus tractus solitarii sends impulse to medulla
  2. sends impulse to spinal cord
  3. ACh released from preganglionic neurone
  4. NA/A released from postganglionic
  5. alpha 1 adrenergic receptor binds to epinephrine and norepinephrine in the arteriole
  6. leads to constriction of vessels- increases blood pressure
45
Q

Experiment to see the effect of baroreceptor innervation

A

denervate aortic baroreceptor

measure BP

arterial BP shown to be poorly controlled, irregular

46
Q

where are low pressure cardiopulmonary receptors found?

A

large systemic veins, pulmonary artery, walls of atria, ventricles

47
Q

Function of low pressure receptors

A

respond to changes in wall tension, which is proportional to the filling state of the low pressure side of circulation.

regulate blood volume

48
Q

increase in stretch causes

A

increase in heart rate, decrease in vasopresin- leads to an increase volume of urine excreted, serving to lower blood pressure