Blood Pressure Prof K Sivapalan 2013 Blood Pressure

Blood Pressure Prof. K. Sivapalan 2013 Blood Pressure 1

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. 2013 Blood Pressure 2

Factors that affect cardiac output. 1. Venous return. 1. 2. 3. 4. 5. 2. Heart rate and force of contraction (end systolic volume). 1. 2. 2013 Blood volume. Veno-motor tone. Respiratory pump. Muscle pump. Peripheral resistance. Cardiac nerves. Circulating catecholamines. Blood Pressure 3

Factors that affect peripheral resistance. • R = 8ηL / πr 4. • 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. 2013 Blood Pressure 4

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] 2013 Blood Pressure 5

Baroreceptors. 2013 Blood Pressure 6

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. 2013 Blood Pressure 7

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 10 th 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. 2013 Blood Pressure 8

Nervous regulation. • Sympathetics, in addition to heart, supply blood vessels and adrenal medulla. • Impulses cause vasoconstriction and secretion of adrenaline from adrenal medulla. 2013 Blood Pressure 9

Feed back regulation. Increased blood pressure. + Baroreceptors. - + - Cardio Inhibitary Centre. + Vaso Motor Centre. - Vasodilatation. Reduce heart rate. 2013 Blood pressure. reduced Blood Pressure 10

Other factors influencing CIC. • Baro receptors: + • Thoracic volume receptors: + • Higher centers: --[excitement, anger] or ++[fear, grief]. • Respiratory centre: - Insp, and + Exp. • Chemoreceptor: +. • Pain: + • Proprioceptors: 2013 Blood Pressure 11

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: - 2013 Blood Pressure 12

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. 2013 Blood Pressure 13