Blood Vessels & Blood Pressure

Transcription

1 Blood Vessels & Blood Pressure Keri Muma Bio 6 Types of Blood Vessels Heart Veins Arteries Venules Arterioles Capillary Beds Types of Blood Vessels 1

2 Blood Flow Flow rate volume of blood per unit time F = P/R Depends on: Pressure gradient difference in pressure between the beginning and ending of a vessel Vascular resistance hindrance or opposition to blood flow through a vessel Pressure gradient Blood Flow Resistance As resistance increases flow rate decreases Factors affecting resistance Viscosity friction between molecules increases resistance (# of circulating RBC) Length increased surface area increases resistance (remains constant in body) Elasticity Peripheral resistance Resistance Peripheral resistance friction between the blood and the vessel wall Radius the main determinant of resistance Increased surface area exposed to blood increases resistance Flow is faster in larger vessels than smaller 2

3 Arteries Elastic arteries offer little resistance due to their large diameter and elastic properties Function maintain constant flow of blood through capillaries despite ventricular systole and diastole Arteries distend during systole Recoils pushing blood forward during diastole Blood Pressure Force exerted by the blood on the vessel wall Systolic pressure maximum pressure during ventricular systole Diastolic pressure minimum pressure following ventricular diastole and blood moving forward into arterioles Pulse pressure difference between the two Blood Pressure Mean arterial pressure average pressure in the vessel throughout the cardiac cycle MAP = DP + 1/3 (pulse pressure) MAP = cardiac output x total peripheral resistance CO = stroke volume x HR TPR = radius and viscosity 3

4 Arterioles Arterioles small radii, have more resistance Can adjust diameter to: Vary distribution of blood to organs Regulate arteriole pressure Vasoconstriction (increased contraction of circular smooth muscle in the arteriolar wall, leads to increased resistance and decreased flow through the vessel) Vasodilation (decreased contraction of circular smooth muscle in the arteriolar wall, leads to decreased resistance and increased flow through the vessel) Arterioles Arteriole smooth muscle always displays a state of vascular tone (partial constriction) Maintained by: Myogenic activity of smooth muscle cells Sympathetic fibers Factors influencing the level of smooth muscle contraction: Intrinsic (local) controls determines distribution of cardiac output Extrinsic controls regulates systemic blood pressure Intrinsic Controls Chemical Increased metabolic activity triggers vasodilation Decreased O2 Increased CO2 Increased adenosine Increased NO Histamine and prostaglandins - vasodilation 4

5 Intrinsic Controls Physical influences Temperature Heat vasodilation Cold - vasoconstriction Myogenic response to stretch Increased perfusion increases stretch triggers vasoconstriction Decreased perfusion decreased stretch triggers vasodilation Extrinsic Controls Sympathetic Nervous System Maintains overall MAP for the system but local regulation can over ride it for tissues that need increased blood flow Hormones ADH - constriction Angiotensin II - constriction NE / Epinephrine α receptors constriction Β receptors dilation (skeletal and cardiac) Atrial Natriuretic Peptide - dilation 5

6 Blood pressure Short term regulation adjustments occur within seconds Baroreceptors monitor MAP and initiate reflex responses to maintain BP homeostasis Receptors - found in the carotid sinus and aortic arch Cardiovascular control center in the medulla Response adjusts parasympathetic / sympathetic activity Baroreceptor Reflex Blood Pressure Long term regulation minutes to days Involves adjusting blood volume Hormones Renin angiotensin II aldosterone pathway ADH 6

7 Capillaries Site for exchange of materials between the blood and the tissues Precapillary sphincters control the flow of blood through the capillary beds Smooth muscle that respond to local controls Relationship between plasma and interstitial fluid Capillaries Factors that influence diffusion Minimal diffusion distance Maximized surface area for exchange (600m 2 ) Maximized time for exchange (slow velocity of flow) 7

8 Capillaries Exchange of solutes across capillary wall Fat soluble solutes pass through endothelial cells Small water soluble solutes pass through pores Plasma proteins are too large to pass Protein hormones cross by vesicular transport Capillaries Movement of fluid across the capillary wall occurs because of differences in hydrostatic and osmotic pressures Plasma hydrostatic pressure exerted on the vessel wall due to pushing of blood Plasma osmotic pressure created by movement of water as it is pulled down its concentration gradient Net Filtration Pressure Takes into account all hydrostatic and osmotic forces on the capillary Determines if there is a net gain or net loss of fluid from the blood 8

9 Capillaries Bulk flow movement of fluid across the capillary walls Involves: Ultrafiltration movement out of the capillary into the interstitial fluid, occurs at the arteriole end Reabsorption movement into the capillary from the interstitial fluid, occurs at the venule end Lymphatic Vessels More fluid is filtered into the ECF that reabsorbed This extra fluid is picked up by lymph capillaries Fluid leaks into lymph capillaries when interstitial pressure is high and one-way flap-like valves prevent lymph from leaking back out Lymphatic Vessels Fluid is returned back to the blood by the lymph system Pump-less one way system Lymph moves towards the heart Flow is accomplished by: Valves Milking action of skeletal muscle Contraction of smooth muscle in vessel walls Pressure changes in the thorax 9

10 Veins Carry blood back to heart Large diameter, little resistance, low pressure At rest contains more than 60% of the total blood volume Veins Factors affecting venous return: Pressure gradient One-way valves Skeletal muscle contraction Respiratory pump Cardiac suction Sympathetic activity Venous Return 10

11 Summary: Cardiovascular Disease Cardiovascular disease accounts for over half of all deaths in the United States Myocardial infarction - heart attack When heart muscle does not receive blood, cells will quickly die Cause by blockage of coronary arteries Aorta Coronary artery Blockage Dead muscle tissue Figure Cardiovascular Disease Atherosclerosis Narrowing of the arteries by plaques of cholesterol and other substances that form in the inner walls of arteries Figure

12 Atherosclerosis Treatments for Cardiovascular Disease Life style changes and drugs Angioplasty use balloon or laser to remove the blockage from the artery Or insert a stent to keep artery open Coronary bypass surgery use another blood vessel from another part of the body as a bridge to get around the blockage 12