Chapter 15 - Alterations In Blood Flow

Question 1

What is the intima and what is it composed of?

Answer 1

Intima is the inner most layer of arteries/veins and is composed of a single layer of endothelial cells

Question 2

What is the media, and what is it composed of?

Answer 2

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.

Question 3

What is the adventitia and what is it composed of?

Answer 3

Adventitia is the outermost layer of arteries/veins and is composed of supporting connective tissue.

Question 4

What are capillaries composed of?

Answer 4

Capillaries are composed of a single layer of endothelial cells that are attached to a basement membrane.

Question 5

What determines the permeability of capillaries?

Answer 5

The permeability of capillaries is determined by the tightness of the endothelial cell connection.

Question 6

Are the lymphatic vessels more similar to arteries or veins?

Answer 6

Lymphatic vessels resemble veins, having thin walls and valves.

Question 7

Explain the principles of blood flow in terms of formulas:

Answer 7

Flow = pressure/resistance

Blood pressure = flow(cardiac output) X resistance

Resistance = pressure/flow

Question 8

What are the main factors that affect resistance to flow?

Answer 8

Radius and length of the vessels, and blood viscosity and turbulence.

Question 9

What is the most important determinant of resistance and what makes the most important determinant of resistance so significant?

Answer 9

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.

Question 10

What affects the velocity of blood flow?

Answer 10

The velocity of blood flow varies inversely with the total cross-sectional area of the vascular bed.

Question 11

What part of the vessels has the greatest cross-sectional area and how does this affect blood flow?

Answer 11

The capillaries have the greatest cross-sectional area, and therefore, the slowest flow.

Question 12

Describe Laplace’s Law

Answer 12

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.

Question 13

In two words, How does the transcapillary exchange of fluid and nutrients get accomplished?

Answer 13

Diffusion and Filtration.

Question 14

Explain how diffusion and filtration work and how they are different:

Answer 14

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

Question 15

How is blood flow regulated through a particular vascular bed?

Answer 15

Blood flow through a particular vascular bed is regulated centrally by the autonomic nervous system and locally by the organ or tissue.

Question 16

What does the SNS do in most vascular beds?

Answer 16

SNS causes constriction, which increases resistance and reduces blood blow.

Question 17

In the smooth muscle of vascular beds, what type of receptors are present and what role do they play?

Answer 17

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.

Question 18

What is autoregulation and how does it work?

Answer 18

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.

Question 19

How do lymphatic vessels maintain flow and prevent backflow?

Answer 19

Lymphatic vessels maintain flow by contracting when stretched with lymph. Intraluminal valves prevent backflow. External compression by contracting muscles enhances lymph flow.

Question 20

What does altered blood flow result from?

Answer 20

Obstructive processes. Obstruction results in reduced flow beyond the obstruction (downstream) and increased pressure before the obstruction (upstream)

Question 21

How does obstruction manifest in the arterial system Compared to the venous system?

Answer 21

Obstruction manifests primarily as distal ischemia in the arterial system.

Obstruction manifests as edema in the venous system.

Question 22

What are the causes of vessel obstruction?

Answer 22

Thrombi
Emboli
Vasospasm
External compression (e.g. Compartment syndrome)
Structural alteration (e.g., atherosclerotic plaques, aneurysms)

Question 23

How do alterations in pressures within the circulatory system differ from alterations in pressures in the lymphatic system?

Answer 23

In the circulatory system, alterations in pressure produce edema.

In the lymphatic system, impairments result in lymphedema

Question 24

What are the common causes of arterial obstruction?

Answer 24

Atherosclerosis
Inflammation
Vasospasm
Aneurysms
Emboli - are usually the cause of acute arterial occlusion.

Question 25

What is the most common cause of chronic progressive arterial obstruction?

Answer 25

Atherosclerosis is the most common causes of chronic progressive arterial obstruction.

Question 26

What are the common risk factors for the development of atherosclerosis?

Answer 26

Smoking
Hyperlipidemia 
Male gender
Advancing age
Sedentary lifestyle
Obesity
Glucose intolerance
Family history of cardiovascular disease

Question 27

What are the 6 Ps and what are they used for?

Answer 27

The six P’s are the classic manifestations of acute arterial obstruction:

Pallor
Paresthesia
Paralysis
Pain
Pulselessness 
Polar (cold to touch

Question 28

What are common causes of venous obstruction?

Answer 28

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.

Question 29

What usually accompanies chronic venous obstruction?

Answer 29

Edema, venous stasis ulcers, and pain

Question 30

What makes deep vein thrombosis potentially life threatening?

Answer 30

DVT is life threatening due to the likelihood of emboli satin to the pulmonary circulation. It is treated aggressively with anticoagulants.

Question 31

What are the most common causes for obstruction of lymph flow?

Answer 31

Surgical removal of, or radiation damage to, lymphatic vessels during treatment of cancer.

Question 32

What are the manifestations of lymphatic obstruction?

Answer 32

Regional edema and thickened subcutaneous tissue.

Question 33

What are the three layers of arteries and veins?

Answer 33

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.