Baroreceptors

Question 1

Baroreceptor definition

Answer 1

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.

Question 2

Where do signals from the carotid baroreceptors travel?

Answer 2

glossopharyngeal nerve (Cranial nerve IX)

Question 3

Where go signals from the aortic arch baroreceptors travel?

Answer 3

vagus nerve (cranial nerve X)

Question 4

Brief mechanism by which baroreceptors control blood pressure

Answer 4

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

Question 5

What happens once the baroreceptor is stimulated?

Answer 5

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

Question 6

What is the carotid sinus responsive to?

Answer 6

both increases and decreases in arterial pressure

Question 7

what is the aortic arch responsive to?

Answer 7

only increases in blood pressure

Question 8

orthostatic hypotension definition

Answer 8

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

Question 9

Orthostatic hypotension mechanism

Answer 9

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

Question 10

How is orthostatic hypotension prevented in healthy individuals?

Answer 10

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

Question 11

resistance is equal to

Answer 11

length divided by radius ^4

Question 12

What are arterioles referred to + why?

Answer 12

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

Question 13

What happens during vasoconstriction?

Answer 13

upstream pressure increases, downstream pressure decreases

Question 14

What happens when the radius halves?

Answer 14

the resistance increases by a factor of 16

Question 15

What happens during vasodilation?

Answer 15

upstream pressure decreases, downstream pressure increases

Question 16

How else flow be increased?

Answer 16

capillary recruitment- more capillaries perfused

Question 17

Where may tissue perfusion increase rapidly?

Answer 17

salivary glands, skin and skeletal muscle

Question 18

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

Answer 18

kidneys

Question 19

dynamic range definition

Answer 19

difference between maximum and minimum perfusion

Question 20

Myogenic mechanism definition

Answer 20

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

Question 21

Myogenic mechanism stages

Answer 21

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

Question 22

Myogenic autoregulation definition

Answer 22

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

Question 23

Bayliss effect definition

Answer 23

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

Question 24

What does the stretch of the muscle open?

Answer 24

stretch mediated ion channels, causing the cell to become depolarised

calcium voltage gated channels open, trigger muscle contraction

Question 25

Experiment to prove Bayliss effect

Answer 25

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

Question 26

What does the Bayliss Effect allow?

Answer 26

maintenance of a constant baseline flow

Question 27

over perfusion definition

Answer 27

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

Question 28

what tends to be overperfused + why?

Answer 28

kidneys- require blood to filter it and to respire

Question 29

What tends to be underperfused + why?

Answer 29

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

Question 30

What can override myogenic autoregulation?

Answer 30

raised metabolism

Question 31

Adrenergic regulation of coronary flow

Answer 31

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 4. decreases myosin light chain kinase activity 5. vasodilation locally, decreases blood pressure

Question 32

What else can cause vasodilation?

Answer 32

hypercapnia, temperature, autacoids, nitric acid

Question 33

hypercapnia definition

Answer 33

abnormally elevated carbon dioxide levels in the blood

Question 34

Stages of vasodilation due to hypercapnia

Answer 34

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

Question 35

stages of vasodilation due to temperature

Answer 35

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

Question 36

autocoid definition + examples

Answer 36

locally produced and locally expressed factors that affect physiology examples:histamine, bradykinin, prostaglandins, leukotrienes

Question 37

stages of vasodilation due to autocoids

Answer 37

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

Question 38

stages of vasodilation due to nitric oxide

Answer 38

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

Question 39

role of endothelium in regulating flow

Answer 39

secrete autocoids

Question 40

stages of vasodilation die to extracellular accumulation of potassium

Answer 40

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

Question 41

hyperaemia definition

Answer 41

increase of blood flow to different tissues in the body

Question 42

reactive hyperaemia definition

Answer 42

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

Question 43

vasomotor nerves

Answer 43

nerves that innervate blood vessels, which alter their diameter

Question 44

sympathetic vasoconstrictor stages

Answer 44

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

Question 45

Experiment to see the effect of baroreceptor innervation

Answer 45

denervate aortic baroreceptor measure BP arterial BP shown to be poorly controlled, irregular

Question 46

where are low pressure cardiopulmonary receptors found?

Answer 46

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

Question 47

Function of low pressure receptors

Answer 47

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

Question 48

increase in stretch causes

Answer 48

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