Lecture 5: Study Guide For Quiz Flashcards
What tissues make up the wall of an artery?
- Endothelium
- Elastic tissue (greater in artery than vein)
- Smooth muscle (greater in artery than vein)
- Fibrous tissue
What are the 3 different tissue layers in the wall of an artery?
- Intima
- Media
- Adventitia
Intima =
Innermost layer
Media =
Middle layer
Adventitia =
Outermost layer
What tissues make up the wall of an arteriole?
Endothelium and smooth muscle only
What tissues make up the wall of a vein?
- Endothelium
- Elastic tissue (less than artery)
- Smooth muscle (less than artery)
- Fibrous tissue
What is the primary function of the arterial system?
Distribute blood to the major organs
What part of the vascular system regulates the flow of blood to the various capillary beds?
Arterioles
Where is the lowest pressure in the vascular system as blood travels from the aorta back to the right atrium?
Vena cava
What is pulse pressure?
The difference between systolic and diastolic pressure
What formula can be used to estimate mean arterial pressure?
MAP = (2 x diastolic + systolic) / 3
What are some of the changes in the arterial waveform as blood travels distally to the extremities?
- High-frequency components of the pulse, such as the incisura, are damped out and soon disappear
- The systolic portions of the pressure wave become narrowed and elevated
- A hump may appear on the diastolic portion of the pressure wave
In a healthy individual, would you expect a higher or lower systolic blood pressure reading in the foot as compared to the aorta?
Higher
How does the arterial system convert pulsatile blood flow to continuous blood flow at the level of the capillaries? What is the advantage of continuous blood flow at the capillary level?
- Hydraulic filter—the arterial system is composed of elastic conduits (aorta and arteries) and high-resistance terminals (arterioles)
- Hydraulic filtering converts the intermittent output of the heart to a steady flow in the capillaries
- This minimizes the workload of the heart (more work is required to pump a given flow intermittently as compared to steadily
Does the heart have to work harder to pump blood through rigid vessels?
Yes
What are some of the factors that affect pulse pressure?
- Increased SVR increases aortic pulse pressure—increased preload, increased inotropy, decreased afterload, decreased heart rate
- Decreased aortic compliance increases aortic pulse pressure—age, arteriosclerosis, hypertension
Why do our arteries become stiffer as we get older?
Loss of elastic tissue
What are primary functions of the veins?
- Reservoir of the CV system—70% of blood volume may be stored in veins
- Venous pump helps propel blood forward—enhances venous return
What factors regulate CVP?
CVP is regulated by:
- A balance of the heart to pump blood out of the right atrium and right ventricle into the lungs
- The tendency for blood to flow from the peripheral veins to the right atrium (venous return)
If you have elevated CVP, what occurs?
- Elevated CVP = increased RA filling pressures
- Blood backs up into the venous side of circulation—peripheral edema
What factors increase CVP?
- Decreased CO (less blood leaving the heart)
- Increase in total blood volume
- Venous constriction
- Gravity (standing to supine)
- Arterial dilation
- Respiratory activity—increased rate
- Skeletal muscle pump—exercise
When a person is standing, where would you find the highest venous pressures in the body? Where would you find the lowest venous pressures in the body?
Highest = feet Lowest = head
What is a major risk of performing neurosurgery in the sitting position?
Negative pressures in the head can cause air to be sucked into the system when veins are cut
How does respiration affect venous return?—spontaneous respiration
Decreased intra-thoracic pressure results in a decreased right atrial pressure which enhances venous return
How does respiration affect venous return?—mechanical ventilation
Increased intrathoracic pressure during positive-pressure lung inflation causes increased right atrial pressure, which decreases venous return
How does respiration affect venous return?—valsalva maneuver
Causes a large increase in intrathoracic pressure, causing increased right atrial pressure which decreases venous return (to the point where someone can pass out)
How much of the total blood volume is normally found in the venous system?
70%
Where are some of the major venous blood reservoirs in the body?
- Spleen
- Liver
- Large abdominal veins
Why are the arterioles called the “stopcocks” of the circulation?
They can turn on or turn off blood flow to the capillary beds; arterioles will constrict or dilate depending on what the body needs
What are some of the characteristics of the capillaries that make them ideal for nutrient and fluid exchange with the surrounding tissues?
Thin walled, large cross-sectional area which gives them the greatest surface area for exchange
Do the walls of the capillaries contain smooth muscle?
No—capillaries are incapable of active constriction
Why can capillaries withstand high intravascular pressures?
Because they are very small and thin walled with large cross sectional areas
What are some of the mechanisms of exchange across the capillary endothelium?
- Diffusion—O2, CO2, lipid soluble substances
- Bulk flow through pores—H2O, electrolytes, small molecules
- Vesicular transport—proteins
Is the permeability of the capillary endothelium the same in all the tissues of the body?
No, it depends on density and porosity
What are the 2 major body fluid compartments?
-Intracellular fluid + extracellular fluid (interstitial fluid + capillary membrane + plasma)
Approximately what percentage of body weight is made up of total body water?
60% of total body weight
What percentage makes up each of the 2 major body fluid compartments?
Intracellular fluid = 2/3
Extracellular fluid = 1/3
If you give a person 1 liter of IV normal saline (0.9% NaCl), how would it distribute over the various fluid compartments?
0.9% saline/LR affects interstitial fluid/vasculature
If you gave a person 1 liter of IV 0.5% dextrose, how would it distribute over the various fluid compartments?
5% dextrose solution will go through all compartments
