Lec. 7 Cardiovascular Regulation PDF

**Lec. 7** Objective : - Neural control of the CVS - Local control - Systemic control **Cardiovascular Regulatory Mechanisms** Multiple cardiovascular regulatory mechanisms exist that help increase the blood supply to active tissues and increase or decrease heat loss from the body by red...

**Lec. 7** Objective : - Neural control of the CVS - Local control - Systemic control **Cardiovascular Regulatory Mechanisms** Multiple cardiovascular regulatory mechanisms exist that help increase the blood supply to active tissues and increase or decrease heat loss from the body by redistributing the blood. **[NEURAL CONTROL OF THE CARDIOVASCULAR SYSTEM]** 1. **INNERVATION OF THE BLOOD VESSELS** Most of the vasculature is an example of an autonomic effector organ that receives innervation from the sympathetic but not the parasympathetic division of the autonomic nervous system. Although the arterioles and the other resistance vessels are most densely innervated, all blood vessels except capillaries and venules contain smooth muscle and receive motor nerve fibers from the sympathetic division of the autonomic nervous system. The fibers to the resistance vessels regulate tissue blood flow and arterial pressure. 2. **INNERVATION OF THE HEART** The heart is one of organ that receives sympathetic and parasympathetic divisions of the autonomic nervous system Sympathetic stimulation through postganglionic sympathetic nerves activates β1-adrenoceptors in the heart cause increase in heart rate (chronotropy ), and the force of ventricular contraction (inotropy). On the other hand stimulation of parasympathetic (vagus) nerves will reduce the heart rate, and force of contraction. 3. **BARORECEPTORS** The baroreceptors are stretch receptors in the walls of the heart and blood vessels. The carotid sinus and aortic arch receptors monitor the arterial circulation. There are also stretch receptors in the low-pressure part of the circulation (cardiopulmonary receptors). These include receptors in the walls of the right and left atria at the entrance of the superior and inferior vena cava, in the pulmonary veins, and in the pulmonary circulation. increased baroreceptor discharge inhibits the tonic discharge of sympathetic nerves and excites the vagal innervation of the heart. These neural changes produce vasodilation, venodilation, hypotension, bradycardia, and a decrease in cardiac output. **[Local regulation ]** a. **Autoregulation** The capacity of tissues to regulate their own blood flow is referred to as autoregulation. Most vascular beds have an intrinsic capacity to compensate for moderate changes in perfusion pressure by changes in vascular resistance, so that blood flow remains relatively constant. This capacity is well developed\ in the kidneys, but it has also been observed in the mesentery, skeletal muscle, brain, liver, and myocardium. b. **Vasodilator metabolite** c. **Localized vasoconstriction** **[SYSTEMIC REGULATION BY NEUROHUMORAL AGENTS]** Many circulating substances affect the vascular system. The\ vasodilator regulators include kinins, VIP, and ANP. Circulating vasoconstrictor hormones include vasopressin, norepinephrine, epinephrine, and angiotensin II. a. **KININS** The actions of both kinins (**bradykinin,** and **kallidin),** resemble those of histamine.\ They are primarily paracrines, although small amounts are\ also found in the circulating blood. They cause contraction of\ visceral smooth muscle, but they relax vascular smooth muscle via NO, lowering blood pressure. They also significantly\ increase vascular permeability resulting in edema, attract leukocytes, and cause pain upon injection under the skin. b. **NATRIURETIC HORMONES** A family of natriuretic peptides is also involved in vascular\ regulation, including ANP secreted by the heart, B-type natriuretic peptide (BNP), and C-type natriuretic peptide (CNP). These peptides antagonize the action\ of various vasoconstrictor agents and lower blood pressure.\ ANP and BNP also serve to coordinate the control of vascular\ tone with fluid and electrolyte homeostasis via actions on the\ kidney. c. **CIRCULATING VASOCONSTRICTORS** An examples Vasopressin , Norepinephrine and angiotensin II