Chapter 15 - Alterations In Blood Flow Flashcards
What is the intima and what is it composed of?
Intima is the inner most layer of arteries/veins and is composed of a single layer of endothelial cells
What is the media, and what is it composed of?
The media is the middle layer of arteries and veins, which is composed of smooth muscle and elastin. The media is thicker in arteries compared to veins.
What is the adventitia and what is it composed of?
Adventitia is the outermost layer of arteries/veins and is composed of supporting connective tissue.
What are capillaries composed of?
Capillaries are composed of a single layer of endothelial cells that are attached to a basement membrane.
What determines the permeability of capillaries?
The permeability of capillaries is determined by the tightness of the endothelial cell connection.
Are the lymphatic vessels more similar to arteries or veins?
Lymphatic vessels resemble veins, having thin walls and valves.
Explain the principles of blood flow in terms of formulas:
Flow = pressure/resistance
Blood pressure = flow(cardiac output) X resistance
Resistance = pressure/flow
What are the main factors that affect resistance to flow?
Radius and length of the vessels, and blood viscosity and turbulence.
What is the most important determinant of resistance and what makes the most important determinant of resistance so significant?
Radius of the vessel. It affects resistance inversely and to the fourth power. A small decrease in radius results in a large increase in resistance.
What affects the velocity of blood flow?
The velocity of blood flow varies inversely with the total cross-sectional area of the vascular bed.
What part of the vessels has the greatest cross-sectional area and how does this affect blood flow?
The capillaries have the greatest cross-sectional area, and therefore, the slowest flow.
Describe Laplace’s Law
Laplace’s law describes the relationships among wall tension, dis tending pressure, and vessel radius (P = T/r; T = Pr). An increase in radius or dis tending pressure results in increased wall tension.
At critical closing pressure, wall tension overwhelms dis tending pressure and blood flow ceases.
In two words, How does the transcapillary exchange of fluid and nutrients get accomplished?
Diffusion and Filtration.
Explain how diffusion and filtration work and how they are different:
Diffusion refers to movement of solutes and is determined by capillary permeability and the size of the concentration gradient.
Filtration refers to movement of fluid and is affected in the following ways:
- —-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 regulated through a particular vascular bed?
Blood flow through a particular vascular bed is regulated centrally by the autonomic nervous system and locally by the organ or tissue.
What does the SNS do in most vascular beds?
SNS causes constriction, which increases resistance and reduces blood blow.
In the smooth muscle of vascular beds, what type of receptors are present and what role do they play?
Smooth muscle cells in these vascular beds have alpha 1 receptors that bind the SNS neurotransmitter norepinephrine, causing constriction. There is no significant parasympathetic innervate on of systemic vessels.
What is autoregulation and how does it work?
Autoregulation refers to a tissue’s ability to regulate it’s own flow. Autoregulation allows a tissue to maintain optimal flow despite changes in blood pressure or metabolic demands.
In instances of high blood pressure or decreased metabolic demand, the arterioles and precapillary sphincters that control flow to the tissue constrict, reducing flow.
In instances of low blood pressure or high metabolic demand, vessels dilate, increasing flow.
How do lymphatic vessels maintain flow and prevent backflow?
Lymphatic vessels maintain flow by contracting when stretched with lymph. Intraluminal valves prevent backflow. External compression by contracting muscles enhances lymph flow.
What does altered blood flow result from?
Obstructive processes. Obstruction results in reduced flow beyond the obstruction (downstream) and increased pressure before the obstruction (upstream)
How does obstruction manifest in the arterial system Compared to the venous system?
Obstruction manifests primarily as distal ischemia in the arterial system.
Obstruction manifests as edema in the venous system.
What are the causes of vessel obstruction?
Thrombi
Emboli
Vasospasm
External compression (e.g. Compartment syndrome)
Structural alteration (e.g., atherosclerotic plaques, aneurysms)
How do alterations in pressures within the circulatory system differ from alterations in pressures in the lymphatic system?
In the circulatory system, alterations in pressure produce edema.
In the lymphatic system, impairments result in lymphedema
What are the common causes of arterial obstruction?
Atherosclerosis Inflammation Vasospasm Aneurysms Emboli - are usually the cause of acute arterial occlusion.
What is the most common cause of chronic progressive arterial obstruction?
Atherosclerosis is the most common causes of chronic progressive arterial obstruction.
What are the common risk factors for the development of atherosclerosis?
Smoking Hyperlipidemia Male gender Advancing age Sedentary lifestyle Obesity Glucose intolerance Family history of cardiovascular disease
What are the 6 Ps and what are they used for?
The six P’s are the classic manifestations of acute arterial obstruction:
Pallor Paresthesia Paralysis Pain Pulselessness Polar (cold to touch
What are common causes of venous obstruction?
Incompetent valves (as may occur with obesity, pregnancy, right heart failure, or prolonged standing)
Producing varicose veins and chronic venous insufficiency
Obstruction by deep vein thrombosis.
What usually accompanies chronic venous obstruction?
Edema, venous stasis ulcers, and pain
What makes deep vein thrombosis potentially life threatening?
DVT is life threatening due to the likelihood of emboli satin to the pulmonary circulation. It is treated aggressively with anticoagulants.
What are the most common causes for obstruction of lymph flow?
Surgical removal of, or radiation damage to, lymphatic vessels during treatment of cancer.
What are the manifestations of lymphatic obstruction?
Regional edema and thickened subcutaneous tissue.
What are the three layers of arteries and veins?
Intima - the innermost layer; composed of a single layer of endothelial cells.
Media - middle layer; composed of smooth muscle and elastin. Media is thicker in arteries than in veins.
Adventitia - the outermost layer, is compels of supporting connective tissue.
