2013 Blood Pressure 1 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 Blood Pressure 3

2013 Blood Pressure 4 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 5 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 6 Baroreceptors.

2013 Blood Pressure 7 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 8 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 9 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 10 Feed back regulation. Cardio Inhibitary Centre. Vaso Motor Centre. Baroreceptors. + - Reduce heart rate. Vasodilatation. + - Increased blood pressure. + Blood pressure. reduced - -

2013 Blood Pressure 11 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 12 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 13 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.