Exam 3 Flashcards
Arteries and veins have three distinct layers
Intima, Media, Adventitia
The Intima
The innermost layer of arteries and veins, is composed of a single layer of endothelial cells
The Media
The middle layer, is composed of smooth muscle and elastin. Media is thicker in arteries than in veins
The Adventitia
The outermost layer, is composed of supporting connective tissue.
Capillaries
Smallest Vessel - only a single layer of endothelial cells attached to a basement membrane. The permeability of capillaries is determined by the tightness of the endothelial cell connection.
Lymphatic Vessels
resemble veins, having thin walls and valves
Blood FLOW =
Pressure / Resistance
BLOOD PRESSURE =
flow (cardiac output) x resistance
Resistance =
Pressure / flow
Main factors affecting RESISTANCE
Radius and length of the vessels
Blood viscosity and turbulence
Usually, the radius of the vessel is the most important determinant of resistance. It affects resistance inversely and to the fourth power. A small decrease in radius results in a large increase in resistance.
Velocity of blood flow
Varies inversely with the total cross-sectional area of the vascular bed. The capillaries have the greatest total cross-sectional area and, therefore, the slowest flow
Laplace’s law
Describes the relationships among wall tension, distending pressure, and vessel radius (P = T/r; T = Pr). An increase in radius or distending pressure results in increased wall tension. At critical closing pressure, wall tension overwhelms distending pressure and blood flow ceases.
Transcapillary exchange of fluid and nutrients
Accomplished by the processes of diffusion and filtration. Diffusion refers to movement of solute and is determined by capillary permeability and the size of the concentration gradient
Filtration
Refers to movement of fluid
What effects Filtration
Increased capillary fluid pressure and interstitial fluid colloid osmotic pressure enhance filtration.
Increased interstitial fluid pressure and plasma colloid osmotic pressure oppose filtration.
Increased permeability (K) enhances filtration.
How is blood flow through vascular beds regulated?
centrally by the autonomic nervous system and locally by the organ or tissue.
How does the Sympathetic nervous system (SNS) effect blood flow?
causes constriction, which increases resistance and reduces flow. Smooth muscle cells in these vascular beds have α1 receptors that bind the SNS neurotransmitter norepinephrine, causing contraction. There is no significant parasympathetic innervation of systemic vessels.
