2013 Blood Pressure 1 Prof. K. Sivapalan. 2013 Blood Pressure 2 Blood pressure. Pressure of the...
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Transcript of 2013 Blood Pressure 1 Prof. K. Sivapalan. 2013 Blood Pressure 2 Blood pressure. Pressure of the...
2013 Blood Pressure 1
Blood Pressure
Prof. K. Sivapalan
2013 Blood Pressure 2
Blood pressure.
• Pressure of the blood varies in different parts of the circulatory system.
• The word “Blood Pressure” refers to the lateral pressure exerted by the blood on the arterial wall at the level of the heart.
• It is maintained by,– Cardiac output and – Peripheral resistance.
Factors that affect cardiac output.
1. Venous return.1. Blood volume.
2. Veno-motor tone.
3. Respiratory pump.
4. Muscle pump.
5. Peripheral resistance.
2. Heart rate and force of contraction (end systolic volume).
1. Cardiac nerves.
2. Circulating catecholamines.
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Factors that affect peripheral resistance.
• R = 8ηL / πr4.• Viscosity is constant [anaemia and
polycythaemia].• Radius is influenced by several factors.• Smooth muscle tone.
– Sympathetic tone.– Metabloits.– Temperature.– Hormones:
• catecholamines, angeotension, histamine, 5 hydeoxy tryptamine, kinins.
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Regulation of blood pressure.
• Physiological and pathological factors affect blood pressure.
• It has to be brought back to normal levels by regulatory mechanisms.
• Regulatory mechanisms are:– Nervous- baro receptor, vasomotor centre,
sympathetics. [Immediate]– Hormonal- renin, angiotensin. [Mid term]– Volume- aldosteron and ADH.[Long term]
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Baroreceptors.
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Baroreceptors.
• Baroreceptors are stretch receptors situated in carotid sinus and arch of the aorta.
• Increase in pressure increase stretch and increase discharge of impulse.
• Chronically changed pressure – reseting.
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Nervous regulation.• The centre for cardiovascular
regulation is in the brain stem, mainly in medulla oblongata.
• Named functionally as cardio inhibitory centre (CIC) and vaso motor centre (VMC).
• Efferents from CIC go in 10th cranial nerve, vagus, to SA and AV nodes of the heart [acetyl choline].
• Sympathetics from VMC innervate the nodes and myocardium [noradrenaline]
• Stimulation causes chronotropic and ionotropic effects.
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Nervous regulation.
• Sympathetics, in addition to heart, supply blood vessels and adrenal medulla.
• Impulses cause vasoconstriction and secretion of adrenaline from adrenal medulla.
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Feed back regulation.
Cardio Inhibitary Centre.
Vaso Motor Centre.
Baroreceptors.
+ -
Reduce heart rate. Vasodilatation.
+-
Increased blood pressure.
+ Blood pressure. reduced
-
-
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Other factors influencing CIC.
• Baro receptors: +• Thoracic volume receptors: +• Higher centers:--[excitement, anger] or ++
[fear, grief].• Respiratory centre: - Insp, and + Exp.• Chemoreceptor: +.• Pain: +• Proprioceptors: -
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Other factors influencing VMC
• Baroreceptor: -• Higher centers: + or –• Chemoreceptor: +• Hypoxia and hypercapnoea (direct); +• Respiratory centre: +[insp] or –[exp]• Pain: + or –• Proprioceptors: + [motor cortex +]• Distention of right atrium- +• Stretch of lungs: -
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Renal regulation of blood pressure.
• Reduced pressure → release of renin from JGA → conversion of angiotensinogen → angeotensin I and to II. Vasoconstriction and increase in pressure.
• Angeotensin → aldosteron → sodium retention.
• ADH → water retention.