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Ebook Cardiovascular system at a glance (4th edition): Part 2

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Nội dung chi tiết: Ebook Cardiovascular system at a glance (4th edition): Part 2

Ebook Cardiovascular system at a glance (4th edition): Part 2

Cardiovascular reflexesThe cardiovascular system is centrally regulated by autonomic reflexes. These work with local mechanisms (see Chapter 23) and t

Ebook Cardiovascular system at a glance (4th edition): Part 2the renin - angloteiblon - akhterone and antidiuretic hormone systems (see Chapter 29) to minimize fluctuations in the mean arterial blood pressure (M

ABP) and volume, and to maintain adequate cerebral and coronary perfusion. Intrinsic reflexes, including the taroreceptor, cardiopulmonary and chemore Ebook Cardiovascular system at a glance (4th edition): Part 2

ceptor reflexes, respond to stimuli originating within the cardiovascular system. Less important extrinsic reflexes mediate the cardiovascular respons

Ebook Cardiovascular system at a glance (4th edition): Part 2

e to stimuli originating elsewhere (e.g. pain, temperature changes). Figure 2? illustrates the responses of the baroreceptor and caidiopulmonary refle

Cardiovascular reflexesThe cardiovascular system is centrally regulated by autonomic reflexes. These work with local mechanisms (see Chapter 23) and t

Ebook Cardiovascular system at a glance (4th edition): Part 2rves (‘receptors') sense a change in the state of the system, and communicate this to the brain, which2Processes this information and implements an ap

propriate response, by3Altering the activity of efferent nerves controlling cardiac, vascular and renal function, thereby causing homeostatic response Ebook Cardiovascular system at a glance (4th edition): Part 2

s that reverse the change in state.Intrinsic cardiovascular reflexesThe baroreceptor reflexThis reflex acts rapidly to minimize moment-to-moment fluct

Ebook Cardiovascular system at a glance (4th edition): Part 2

uations in the MA BP. Baroreceptors are afferent (sensory) nerveendings in the walls of the carotid sinibc-s (thin-walled dilatations at the origins o

Cardiovascular reflexesThe cardiovascular system is centrally regulated by autonomic reflexes. These work with local mechanisms (see Chapter 23) and t

Ebook Cardiovascular system at a glance (4th edition): Part 2d by modifying the frequency at which they fire action potentials. Pressure elevations increase impulse frequency: pressure decreases have the opposit

e effect.When MABP decreases, the fall in baroreceptor impulse frequency causes the brain to reduce the tiring of vagal efferents supplying the sinoat Ebook Cardiovascular system at a glance (4th edition): Part 2

rial node, thus causing tachycardia. Simultaneously. the activity of sympathetic nerves innervating the heart and most blood vessels is increased, cau

Ebook Cardiovascular system at a glance (4th edition): Part 2

sing increased cardiac contractility and constriction of arteries and veins. Stimulation of renal sympathetic nerves increases renin release, and cons

Cardiovascular reflexesThe cardiovascular system is centrally regulated by autonomic reflexes. These work with local mechanisms (see Chapter 23) and t

Ebook Cardiovascular system at a glance (4th edition): Part 2ether to raise MA BP. Opposite effects occur when arterial blood pressure rises.There are two types of baroreceptors. A fibres have large, myelinated

axons and are activated over lower levels of pressure, c fibres have small, unmyelinated axons and respond over higher levels of pressure. Together, t Ebook Cardiovascular system at a glance (4th edition): Part 2

hese provide an input to the brain which is most sensitive to pressure changes between 80 and l50mmllg. The brain is able to reset the baroreflex to a

Ebook Cardiovascular system at a glance (4th edition): Part 2

llow increases in MABP to occur (e g. during exercise and the defence reaction). Ageing, hypertension and atherosclerosis decrease arterial wall compl

Cardiovascular reflexesThe cardiovascular system is centrally regulated by autonomic reflexes. These work with local mechanisms (see Chapter 23) and t

Ebook Cardiovascular system at a glance (4th edition): Part 2le J. Ccmolty.62 o 2013 John Wifey 8 Sons. Ltd Published 2013 by John Wifey 8 Sons. LtdThe baroreceptors quickly show partial adaptation to new pressu

re levels. Therefore alterations in frequency are greatest while pressure IS changing, and tend to moderate when a new steadystate pressure level is e Ebook Cardiovascular system at a glance (4th edition): Part 2

stablished. If unable to prevent a change in MABP. the reflex will within several hours become reset to maintain pressure around the new level. This f

Ebook Cardiovascular system at a glance (4th edition): Part 2

inding, together with studies by Cowley and coworkers in the 1970s showing that destroying baroreceptor function increased the variability of MA BP bu

Cardiovascular reflexesThe cardiovascular system is centrally regulated by autonomic reflexes. These work with local mechanisms (see Chapter 23) and t

Ebook Cardiovascular system at a glance (4th edition): Part 2 regulation of MA BP. However, recent evidence that baroreceptor resetting is incomplete and that electrical stimulation of baroreceptors causes reduc

tions in MABP which are sustained over many days has led some experts to re-evaluate this issue.Cardiopulmonary reflexesDiverse intrinsic cardiovascul Ebook Cardiovascular system at a glance (4th edition): Part 2

ar reflexes originate in the heart and lungs. Cutting the vagal afferent fibres mediating these cardiopulmonary reflexes causes an increased heart rat

Ebook Cardiovascular system at a glance (4th edition): Part 2

e and vasoconstriction. especially in muscle, renal and mesenteric vascular beds. Cardiopulmonary reflexes arc therefore thought to exert a net tonic

Cardiovascular reflexesThe cardiovascular system is centrally regulated by autonomic reflexes. These work with local mechanisms (see Chapter 23) and t

Ebook Cardiovascular system at a glance (4th edition): Part 2and arc well placed to sense the Mood volume in the central thoracic compartment. These reflexes are thought to be particularly important in controlli

ng blood volume, as well as vascular tone, and act together with the baroreceptors to stabilize the MABP. However, these reflexes have been studied ma Ebook Cardiovascular system at a glance (4th edition): Part 2

inly in animals, and their specific individual roles in humans are incompletely understood.Specific components of the caidiopulmonary reflexes include

Ebook Cardiovascular system at a glance (4th edition): Part 2

the following.1Atrial mechanoreceptors with non-inyelinated vagal afferents which respond to increased atrial volumc/prcssurc by causing bradycardia

Cardiovascular reflexesThe cardiovascular system is centrally regulated by autonomic reflexes. These work with local mechanisms (see Chapter 23) and t

Ebook Cardiovascular system at a glance (4th edition): Part 2 ventricular diastolic pressure and afterload by causing a vasodilatation.3Ventricular chemoreceptors which are stimulated by substances such as brady

kinin and prostaglandins released during cardiac ischaemia. These receptors activate the coronary chemoreflex. This response, also termed the Bezold - Ebook Cardiovascular system at a glance (4th edition): Part 2

Jarisch effect, occurs after the intravenous injection of many drugs, and involves marked bradycardia and widespread vasodilatation.4Pulmonary mechan

Ebook Cardiovascular system at a glance (4th edition): Part 2

oreceptors, which when activated by marked lung inflation, especially if oedema is present, cause tachycardia and vasodilatation.5Mechanoreceptors wit

Cardiovascular reflexesThe cardiovascular system is centrally regulated by autonomic reflexes. These work with local mechanisms (see Chapter 23) and t

Ebook Cardiovascular system at a glance (4th edition): Part 2using a sympathetically mediated tachycardia (Bainbridge reflex). This reflex also helps to control blood volume: its activation decreases the secreti

on of antidiuretic hormone (vasopressin), cortisol and renin.causing a diuresis. Although powerful in dogs, this reflex has been difficult to demonstr Ebook Cardiovascular system at a glance (4th edition): Part 2

ate in humans.Chemoreceptor reflexesChcmorcceptors activated by hypoxia, hypocapnia and acidosis are located in the aortic and carotid bodies. These a

Ebook Cardiovascular system at a glance (4th edition): Part 2

re stimulated during asphyxia, hypoxia and severe hypotension. The resulting chemorcceptor reflex is mainly involved in stimulating breathing, but als

Cardiovascular reflexesThe cardiovascular system is centrally regulated by autonomic reflexes. These work with local mechanisms (see Chapter 23) and t

Ebook Cardiovascular system at a glance (4th edition): Part 2ardia resulting indirectly from the increased lung inflation. This reflex is important in maintaining blood flow to the brain at arterial pressures to

o low to affect baroreceptor activity.The CNS ischaemic responseBrainstem hypoxia stimulates a powerful generalized peripheral vasoconstriction. This Ebook Cardiovascular system at a glance (4th edition): Part 2

response develops during severe hypotension. helping to maintain the flow of blood to the brain during shock. It also causes the Cushing reflex, in wh

Ebook Cardiovascular system at a glance (4th edition): Part 2

ich vasoconstriction and hypertension develop when increased cerebrospinal fluid pressure (c.g. due to a brain tumour) produces brainstem hypoxia.Extr

Cardiovascular reflexesThe cardiovascular system is centrally regulated by autonomic reflexes. These work with local mechanisms (see Chapter 23) and t

Ebook Cardiovascular system at a glance (4th edition): Part 2pain causes tachycardia and increases MABP; however, severe pain has the opposite effects. Cold causes cutaneous and coronary vasoconstriction, possib

ly precipitating angina in susceptible individuals.Central regulation of cardiovascular reflexesThe afferent nerves carrying impulses from cardiovascu Ebook Cardiovascular system at a glance (4th edition): Part 2

lar receptors terminate in the lUK’k-Us fractux solltariuM NTS) of the medulla. Neurones from the NTS project to areas of the brainstem that control b

Ebook Cardiovascular system at a glance (4th edition): Part 2

oth parasympathetic and sympathetic outflow, influencing their level of activation. The nucleus amblguus and dorsal motor nucleus contain the cell bod

Cardiovascular reflexesThe cardiovascular system is centrally regulated by autonomic reflexes. These work with local mechanisms (see Chapter 23) and t

Ebook Cardiovascular system at a glance (4th edition): Part 2the NTS. Neurones from the NTS also project to areas of ventrolateral medulla; from these descend bulbospinal fibres which influence the filing of the

sympathetic preganglionic neurons in the intcrmediolatcral (IML) columns of the spinal cord.These neural circuits arc capable of mediating the basic Ebook Cardiovascular system at a glance (4th edition): Part 2

cardiovascular reflexes. However, the NTS. the other brainstem centres and the 1ML neurones receive descending inputs from the hypothalamus. which in

Ebook Cardiovascular system at a glance (4th edition): Part 2

turn is influenced by impulses from the limbic system of the cerebral cortex. Input from these higher centres modifies the activity of the brainstem c

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