Ebook Cardiovascular system at a glance (4th edition): Part 2
➤ Gửi thông báo lỗi ⚠️ Báo cáo tài liệu vi phạmNội 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 (MABP) 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 2ceptor reflexes, respond to stimuli originating within the cardiovascular system. Less important extrinsic reflexes mediate the cardiovascular responsEbook 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 refleCardiovascular 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 appropriate 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 2s that reverse the change in state.Intrinsic cardiovascular reflexesThe baroreceptor reflexThis reflex acts rapidly to minimize moment-to-moment fluctEbook 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 oCardiovascular 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 opposite 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 2rial node, thus causing tachycardia. Simultaneously. the activity of sympathetic nerves innervating the heart and most blood vessels is increased, cauEbook 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 consCardiovascular 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 2hese 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 aEbook 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 complCardiovascular 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 pressure 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 2stablished. If unable to prevent a change in MABP. the reflex will within several hours become reset to maintain pressure around the new level. This fEbook 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 buCardiovascular 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 reductions 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 2ar reflexes originate in the heart and lungs. Cutting the vagal afferent fibres mediating these cardiopulmonary reflexes causes an increased heart ratEbook 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 controlling 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 2inly in animals, and their specific individual roles in humans are incompletely understood.Specific components of the caidiopulmonary reflexes includeEbook 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 bradykinin 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 mechanEbook 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 witCardiovascular 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 secretion 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 2ate in humans.Chemoreceptor reflexesChcmorcceptors activated by hypoxia, hypocapnia and acidosis are located in the aortic and carotid bodies. These aEbook 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 alsCardiovascular 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 too 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 2response develops during severe hypotension. helping to maintain the flow of blood to the brain during shock. It also causes the Cushing reflex, in whEbook 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.ExtrCardiovascular 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, possibly 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 2lar 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 bEbook 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 bodCardiovascular 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 2cardiovascular reflexes. However, the NTS. the other brainstem centres and the 1ML neurones receive descending inputs from the hypothalamus. which inEbook 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 cGọi ngay
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