CVS Responses & Integrated Control PDF

CVS RESPONSES CADIOVASCULAR REFLEX RESPONSES AND THEIR INTEGRATED CONTROL Curriculum: Phase 1/ Semester3/ CVS/ Session 6/L 2 Lecturer: teacher Dr. Shahlaa khazaal chabuk Degrees: MSc/Ph.D. Phsiology Objectives Describe the cardiovascular reflex response control  Describe the reflex origination...

CVS RESPONSES CADIOVASCULAR REFLEX RESPONSES AND THEIR INTEGRATED CONTROL Curriculum: Phase 1/ Semester3/ CVS/ Session 6/L 2 Lecturer: teacher Dr. Shahlaa khazaal chabuk Degrees: MSc/Ph.D. Phsiology Objectives Describe the cardiovascular reflex response control  Describe the reflex origination of the heart. Effect of meal ,exercise , standing up  (1)The carotid sinuses : These are dilatations at the carotid artery bifurcation innervated by a branch of glossopharyngeal nerve “ Іx cranial nerve” also termed “nerve of Hering” which serves as an afferent limb. Sensitive to stretch. Found in the adventitia of the arterial wall (2) The carotid bodies are small rounded organs found just near the carotid sinuses. contain special sensory cells which respond to chemical stimuli The afferent pathway lies in the glossopharyngeal nerve. (3) Aortic bodies Are chemoreceptor found near the aortic arch and pulmonary artery and perhaps near the coronary arteries Other receptors Stretch receptors also known to exist in the : Atrial wall Pulmonary vein-left atrial junctions Lungs Coronary arteries Ventricles Both vagal and sympathetic nerves constitute this pathway RELELEX REGULATION OF THE HEART BARORECEPTOR CONTROL These receptors are sensitive to stretch. They are affected by the rate of change of blood pressure or by an increase of pulse pressure. Their stimulation by rise of BP causes a response of decrease of heart rate, a decrease in LV contractility and lowering of blood pressure are not sensed to pressures below 50mmHg or > BARORECEPTOR RESPONSE MODULATION Baroreceptor sensitivity may be decreased in: oEssential prolonged hypertension oHeart failure o“Due to increased Na+ in the arterial wall which decreases Baroreceptor sensitivity” CHEMORECEPTORS CONTROL Stimulation of the receptors (in the carotid & aortic bodies) during sever hypoxia causes decrease of heart rate and cardiac muscle contractility and rise of blood pressure. Stimulation of the receptors (mainly those exist in the left ventricle) causes bradycardia and hypotension. These receptors also simulated by metabolites and hypoxia during myocardial injury. ATRIAL RECEPTORS Are vagal nerve endings sensitive to stretch or distention. mainly Located in the right atrium and at the pulmonary vein-left Atrial junctions. Stimulation of these receptors by stretch or distention by small balloons results mainly in a reflex increase of heart rate, without change in the inotropic state of the heart or in B.P RULES OF THE CVS total peripheral (TPR) resistance is inversely proportional to the need for blood At a constant Cardiac output – falls in TPR increase venous pressure decrease arterial pressure At a constant TPR – increases in CO decrease venous pressure increase arterial pressure SO - increases in venous pressure increase cardiac output - decreases in arterial pressure increase cardiac output EATING A MEAL increased activity of the gut leads to - local vasodilatation: TPR falls venous pressure rises arterial pressure falls - rise in venous pressure causes a rise in cardiac output fall in arterial pressure triggers rise in heart rate and so CO - venous pressure reduced by extra pumping of heart arterial pressure also raised demand met EXERCISE in exercise there is – an enormous increase in demand – ‘muscle pumping’ which forces extra blood back to the heart with no other changes – venous pressure would rise greatly – arterial pressure would fall greatly?? these changes may be too big to cope with EXERCISE the great increase in venous pressure is the main problem tends to overfill the heart pushes the ventricles into the flat part of the Starling Scurve. so there is a risk of pulmonary oedema because the outputs of the right and left ventricles cannot be matched overfilling of the ventricles is prevented by a rise in heart rate which occurs as exercise begins EXERCISE so when the venous pressure starts to rise, heart rate is already high keeping stroke volume down. STANDING UP on standing blood ‘pools’ in the superficial veins of the legs because of gravity, so central venous pressure falls by Starlings law, cardiac output falls so arterial pressure falls….? now both arterial and venous pressure changing in the same direction