Blood Flow and Blood Pressure PDF

Blood Flow and Control of Blood Pressure Lecture 23 – Chapter 15 – Part A Sai Sudha Koka, PhD., RPh Associate Professor Department of Pharmaceutical Sciences, Room # 304 Irma Lerma Rangel School of Pharmacy Texas A&...

Blood Flow and Control of Blood Pressure Lecture 23 – Chapter 15 – Part A Sai Sudha Koka, PhD., RPh Associate Professor Department of Pharmaceutical Sciences, Room # 304 Irma Lerma Rangel School of Pharmacy Texas A&M University Kingsville, TX 78363 Phone: 361-221-0758 e-mail: [email protected]  About this Chapter The blood vessels Blood pressure Resistance in the arterioles Distribution of blood to the tissues Regulation of cardiovascular function Exchange at the capillaries The lymphatic system Cardiovascular disease  Learning Objectives  Compare and contrast the structure, mechanical properties, and functions of the five major types of blood vessels.  Explain what creates blood pressure and how blood pressure changes as blood flows through the systemic circulation.  Describe how blood pressure is estimated using sphygmomanometry.  Explain the contributions of cardiac output and peripheral resistance to blood pressure. Calculate mean arterial pressure.  Explain how changes in blood volume affect blood pressure.  The Blood Vessels Arteries take blood away from the heart – Elastic walls and thick layers of vascular smooth muscles – Act as pressure reservoir Veins take blood back to the heart – Thin walls of vascular smooth muscles – Act as volume reservoir A Functional Model of Cardiovascular System The elastic systemic arteries are a pressure reservoir that maintains blood flow during ventricular relaxation. Aorta Aortic valve The arterioles, shown with Left ventricle adjustable screws that alter Left heart their diameter, are the site Mitral valve of variable resistance. Left atrium Pulmonary vein Each side of the Exchange heart functions as Lungs Capillaries between the an independent blood and cells pump. takes place at the capillaries. Pulmonary artery Pulmonary valve Right ventricle Venules Right heart Tricuspid valve Right atrium Venae cavae FIGURE QUESTION Are pumps in this model Systemic veins serve as an operating in parallel or in expandable volume reservoir. series? Blood Vessel structure Veins are more numerous than arteries and have a larger diameter –hold more than half of the blood in the circulatory system Capillary Beds most numerous type of sphincter in the human body (smooth muscle).  Capillary Beds When precapillary sphincters are relaxed, blood If precapillary sphincters constrict, blood flow bypasses flows through all capillaries in the bed. capillaries completely and flows through metarterioles. Precapillary sphincters constricted Arteriole Venule Precapillary Capillaries sphincters relaxed  Capillaries: Exchange Capillaries have the thinnest walls – Single layer of flattened endothelial cells – Supported by basal lamina Plasma and cells exchange materials across thin capillary walls Capillary density is related to metabolic activity of cells Types of Capillaries Continuous and fenestrated capillaries Bone marrow, liver, and spleen do not have typical capillaries but rather sinusoids  Exchange Takes Place in the Capillaries Absence of vascular smooth muscle and elastic tissue reinforcement in capillaries facilitates exchange – One cell-thick layer of endothelial cells on basal lamina Pericytes are closely associated with many capillaries – Decrease capillary permeability – Influence capillary growth and can differentiate into endothelial cells and smooth muscle cells  Blood Return to the Heart One-way valves in the veins prevent backflow of blood (vena cava has no Skeletal pump: when one valves) the skeletal muscles compress the veins, they force the blood toward the heart Diaphragm: cause waves of contraction pressure changes of smooth muscle in that compress near the walls of the larger by veins – vena cava veins (Sympathetic (no one-way valves) innervation of veins).  Angiogenesis Development of new blood vessels – Necessary for normal development – Wound healing and uterine lining growth – Enhances heart and skeletal muscle blood flow – Needed for malignant tumor growth Controlled by cytokines – Promoted by (mitogens) by vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF) – Inhibited by angiostatin and endostatin Coronary heart disease – Collateral circulation  Arteries act as pressure reservoirs Ventricular contraction. Contraction of the ventricles pushes Ventricular relaxation. Elastic recoil in the arteries blood into the elastic arteries, causing them to stretch. maintains driving pressure during ventricular diastole. Elastic recoil of Aorta and arteries arteries sends blood expand and store forward into rest of Aorta and pressure in elastic circulatory system. arteries walls. Semilunar valve Semilunar valve shuts, preventing opens. Blood ejected flow back into from ventricles flows ventricle. into the arteries. Ventricle Isovolumic Ventricle Ventricle ventricular contracts. relaxation  Blood Pressure Pulse pressure = systolic P – diastolic P Valves ensure one-way flow in veins Mean Arterial Pressure (MAP) = diastolic P + 1/3(systolic P – diastolic P) Blood pressure is estimated by sphygmomanometry Hypotension is lower than normal MAP Hypertension is higher than normal MAP  Mean Arterial Pressure MAP proportional to cardiac output (CO) × Resistancearterioles MAP is an important measurement that accounts for flow, resistance, and pressure within your arteries. Mean Arterial Pressure Systemic Circulation Pressures Distribution o f blood flow during exercise Arteriolar Resistance  Arteriolar Resistance Arteriolar resistance is influenced by both local and systemic control mechanisms – Local control – Sympathetic reflexes – Hormones  Arteriolar Resistance Myogenic autoregulation – Role of calcium Paracrines – Active hyperemia versus reactive hyperemia – Adenosine Neural and hormonal signals Sympathetic control – SNS: norepinephrine – Adrenal medulla: epinephrine Chemicals Mediating Arteriolar Resistance  Hyperemia Hyperemia (paracrines) is a locally mediated increase in blood flow. Sympathetic Branch Controls Most Vascular Smooth Muscles Factors Influencing Peripheral Blood Flow  Sphygmomanometry Cuff pressure When the cuff is inflated so that it stops >120 mm Hg arterial blood flow, no sound can be heard through a stethoscope placed over the brachial artery distal to the cuff. Inflatable cuff Pressure gauge Cuff pressure Korotkoff sounds are created by pulsatile between 80 and blood flow through the compressed artery. Stethoscope 120 mm Hg Cuff pressure Blood flow is silent when the artery