Download THE VASCULAR SYSTEM

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Lab 12 The Vascular System
Lab Day
LABORATORY 12
THE VASCULAR SYSTEM
INTRODUCTION
The vascular system is made up of blood vessels that start out by leaving the heart
as large arteries that branch into smaller arterioles and then into extremely minute
capillaries. The capillaries are the thin vessels where nutrients and wastes are exchanged
between the blood plasma and the interstitial fluid of the tissues. Blood flow through the
capillaries is controlled by the amount of visceral muscle activity in the walls of the
arterioles, since true capillaries lack contractile cells in their walls. More blood can be
sent through the capillaries by vasodilation of the arterioles through relaxation of the
wall muscles. The capillaries then connect to larger venules that finally converge into
large veins that return the blood to the heart.
Blood is pumped through the vessels by the contraction of the ventricles in the
heart. This contraction creates a pressure that opens the semilunar valves and causes the
ejection of blood into the arteries. The ejection of blood creates a pulse wave that moves
through the arteries ahead of the blood. This wave can be felt as a throbbing pulse in the
brachial, radial or carotid arteries. Blood pressure is the driving force behind the
movement of blood through the vessels. The arterial blood pressure has two values with a
high systolic pressure that is caused by the contraction of the ventricles and a low
diastolic pressure that is maintained by the elastic recoiling of the arterial walls on the
blood during ventricular relaxation.
Table 12-1 Characteristics of Systemic Blood Vessel
Vessel
Blood Pressure
Blood Velocity
Percent of Blood Volume
Arteries
100 - 85 mm Hg
300 mm/sec
15 %
Arterioles
85 - 30 mm Hg
15 mm/sec
Capillaries
30 - 15 mm Hg
0.3 mm/sec
Venules
15 - 10 mm Hg
3 mm/sec
Veins
10 - 0 mm Hg
80 mm/sec
5%
60 %
Note: The heart and pulmonary circuit contains 20 % of the blood volume.
Lab 12 The Vascular System
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ARTERIES
PULSE AND HEART RATE
The ejection of blood from the left ventricle into the arteries creates a pulse wave
that travels down the arteries. This wave can be felt or palpated as a pulse in the vessels
and corresponds to the heart rate.
Find your partner's radial artery on the anterior side of the forearm just above the
wrist. Press three of your fingers against the radial artery found in the shallow groove and
feel for the pulse. Count the first throb as zero then one, two, three, etc. for 15 or 30
seconds. Calculate the heart rate of your partner. Repeat the process with your partner
taking your pulse. Record the rates on Table 12-2.
Table 12-2 Heart Rates
Your heart rate (beats per minute)
Partner’s heart rate (beats per minute)
BLOOD PRESSURE MEASUREMENT
The sphygmomanometer or blood pressure cuff is used to take blood pressure in
the arteries. This lab exercise demonstrates taking the pressure in the brachial artery in
the arm. Identify the location of your partner's brachial artery by palpating for the pulse
one inch above the anterior bend or antecubital space on the medial surface of the arm.
Next have your partner seated with his arm resting on the table. Fasten the
sphygmomanometer cuff snugly around the brachial artery of the upper arm with the
tubing facing the forearm. The lower edge of the cuff should be one to two inches above
the antecubital space. Insert the stethoscope earplugs into the ears and hold the diaphragm
over the brachial artery about one inch above the antecubital space. Place the rubber bulb
in your hand with the tubing facing your partner. A clockwise rotation of the bulb valve
closes the valve and allows air to enter but not leave the cuff when the bulb is squeezed.
A counterclockwise rotation of the valve allows air to flow freely into or out of the cuff.
Inflate the blood pressure cuff to a pressure between 150 to 200 mm Hg by closing the
bulb valve in a clockwise fashion and squeezing the bulb. Blood flow through the
brachial artery is now occluded and no sound should be heard with the stethoscope.
Slowly release the pressure in the cuff by opening the bulb valve (counterclockwise
direction). Record the systolic pressure on the gauge when the first thumping noise is
heard.
This systolic pressure is heard because the blood is pulsating through the cuff
with each heart contraction. Record the diastolic pressure when the sound changes from a
loud to soft thumping or when it disappears all together. The sound disappears when the
blood changes from a pulsating flow to a quieter continuous flow. Blood pressure is
written as systolic pressure slash diastolic pressure (120/75).
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Lab 12 The Vascular System
Procedure
• Measure your lab partner’s blood pressure and record on Table 12-3.
• Have your partner measure your pressure and record on Table 12-3.
The pulse pressure is the difference between the systolic pressure and the
diastolic pressure and can be calculated subtracting the diastolic pressure from the
systolic pressure (pulse pressure = 120 - 75 = 45).
• Calculate your pulse pressure and record on Table 12-3.
The mean arterial pressure represent the mean pressure in the arteries
throughout the cardiac cycle and usually is closer to the diastolic pressure because
ventricular diastole lasts longer than ventricular systole.
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•
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The formula for its calculation is: Diastolic pressure + 1/3 (pulse pressure).
75 + 1/3 (45) = 90 mm Hg.
Calculate your mean arterial pressure and record on Table 12.3.
Table 12-3 Arterial Pressures
Student
Blood Pressure
Pulse Pressure
Mean Arterial Pressure (MAP)
Yourself
Lab partner
1.
What event produces the systolic pressure in the arteries?
The contraction of the ventricles
2.
What feature of the large arteries maintains the diastolic pressure even though the
pressure in the left ventricle plummets to just above zero mmHg?
The elastic recoil of the arteries on the blood maintains the pressure
Lab 12 The Vascular System
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3.
What aspect of blood flow produces the thumping sound when listening and
measuring a person’s blood pressure?
The blood pulsates between the systolic and diastolic pressure.
ARTERIOLES AND CAPILLARIES
Blood flow through the capillaries can be influenced by the diameter of the
arterioles leading to the capillaries by the level of muscle activity in the arterioles.
Muscle activity in the arterioles can be influenced by nerve stimulation, mechanical
stimulation of the smooth muscle, or a variety of chemicals. Contraction of the muscle
causes vasoconstriction of the arterioles producing less blood flow through the
capillaries, while relaxation of the muscles causes vasodilation and enhances a greater
blood flow through the capillaries.
4.
How would stimulation of the sympathetic nervous system containing alpha1
receptors on the arteriolar muscle change the amount of blood flow through the
capillaries?
vasoconstrict
MECHANICAL STIMULATION
Rub or scrape a line on the anterior surface of the forearm, where there is little
arm hair, with a blunt instrument such as a fingernail, pencil eraser or weighing spoon.
The first response is where the skin turns lighter at the point where the scrape was
made. This is followed by a flushing red or darker color in the same area. Repeat the
process with a greater force if the red response is not generated.
5.
What causes the skin to blanch?
Vasoconstriction of the arterioles
6.
What causes the skin to flush red or darker?
Vasodilation of the arterioles
Lab 12 The Vascular System
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CHEMICAL STIMULATION
Chemical stimulation of the vessels can cause either vasoconstriction or
vasodilation of the arterioles. Some chemicals stimulate the triple response in the vessels
and surrounding tissues and consist of a red reaction at the point of stimulation, a
spreading flare from the red area and a wheal or raised area over the red reaction. This
wheal is caused by an increase in vessel permeability and water movement from the
vessels to the surrounding tissues.
7.
Describe the triple response of inflammation and the mechanisms that produce
each response.
The redness and the flare are caused by vasodilation while the raised wheal is due to an
increase in capillary permeability and the movement of proteins out of the bloodstream
that change the colloidal osmotic pressure that causes edema.
Procedure
Test the action of the following chemicals on the blood vessels by placing a drop
of 1:3,000 histamine, a drop of 1:1,000 epinephrine and a drop of water on the anterior
surface of the forearm. Gently scratch the skin through the drop of liquid with a sterile
pin. Use a different sterile pin for each drop. Let the solutions stay on the skin for 2
minutes before wiping off any excess fluid. Observe the color changes and any triple
response immediately and after ten minutes. Place the used pins in the beaker labeled as
such.
8.
What was the response of histamine to the skin?
Redness, a flare and a wheal should appear
9.
How would histamine change the diameter of the arterioles?
Dilated them
10.
What was the response of epinephrine to the skin?
A blanching of the skin
11.
How would epinephrine change the diameter of the arterioles?
Constricts them
Lab 12 The Vascular System
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Lidocaine is used to numb pain before a physician uses a scalpel to cut into a
patient’s skin.
12.
What is the purpose of using epinephrine with the lidocaine before cutting into a
patient’s skin?
The epinephrine vasoconstricts and reduces blood loss while being cut by the scalpel.
Extra: Epinephrine allows lidocaine to work longer
13.
Which chemical would be responsible, in part, for the red and swollen response of
your skin after an insect bite or sting?
The production of histamine and other chemicals
ACTIVE HYPEREMIA
Hyperemia is when there is an increase in blood flow to the tissues and organs.
Active or functional hyperemia is an increase in blood flow caused by an elevated
metabolic rate. A greater blood flow is required to increase oxygen delivery and enhance
the removal of carbon dioxide and/or lactate from these metabolically active tissues.
The following procedure will mimic active hyperemia by increasing the metabolic
rate by using warm water.
Procedure
Place one finger in warm water that will increase the metabolic activity in this
finger. Notice the color change after three minutes by comparing it to another finger.
14.
What is the color change in the finger immersed in the warm water?
Finger turned red
15.
What causes this change?
An increase metabolic rate requires a greater flow of blood thus the vessels dilate.
16.
How would blood flow change in skeletal muscles during exercise?
Blood flow would increase
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REACTIVE HYPEREMIA
Reactive hyperemia on the other hand is an increase in blood flow to the tissues
when they have been deprived of oxygen.
Procedure
Wind a rubber band tightly around the second joint of another finger and notice
the color change during the three minutes the rubber band is in place. Remove the rubber
band after three minutes and observe the color change in the finger after the rubber band
is removed.
17.
What happens to the oxygen level in your finger distal to the rubber .band?
the oxygen levels decrease.
18.
Record the color change in the finger after the rubber band has been removed.
It changes form a dark color to a brighter red color
19.
How does this change in blood flow relate to reactive hyperemia?
Reactive hyperemia occurs when the tissue has been deprived of oxygen as demonstrated
with the rubber band on the finger. The oxygen hungry tissue requires more oxygen and
can acquie more when the rubber band has been removed, thus flushing the finger with
blood
20.
Compare active hyperemia to reactive hyperemia.
See the lab exercise for this answer
Lab 12 The Vascular System
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VEINS
VENOUS PRESSURE
Blood pressure in the veins is considerably lower than the pressure in the arteries
with an average pressure in the venules between 10-15 mm Hg and a venous pressure
dropping towards five mmHg as the blood enters the right atrium. The veins have but a
single pressure as compared to the systolic and diastolic pressures in the arteries. An
estimate of venous pressure can be obtained by looking at vein distension, since there is
no direct method to take venous pressure with the sphygmomanometer,
Have the subject stand against a chalkboard with his arms at his side. Observe the
distension of the superficial veins on his hands and arms.
Extend one arm upward along the chalkboard until it reaches a height equal to the
position of the right atrium (this is usually around the third rib). The veins should still be
distended. Make a chalk mark on the board at this position.
Slowly raise the arm until the veins collapse. Make a second chalk mark on the
board at this position.
Procedure
Measure the distance between the marks in centimeters and record on
Table 12-4.
This measurement reflects the height of a column of blood necessary to
produce blood flow out of the veins and into the heart. The pressure required for this
can be calculated by changing the height of blood (water) to a pressure of mercury.
Mercury has a density 13.6 times that of blood. The following formula can be used
for the pressure conversion. Calculate your venous pressure and record on Table 12-4.
Venous pressure mm Hg =
height of blood (H2O) in cm
1.36 cm H2O / mm Hg
Table 12-4 Venous Pressure
Distance in Centimeters
Venous Pressure (estimate)
VALVES
Veins contain valves that enhance blood flow to the heart by lowering the
gravitational force on blood while standing and by preventing any back flow of blood.
The location of valves can be observed in the superficial veins of the appendages.
Place a sphygmomanometer cuff around the subject's arm and inflate the cuff to
40 mm Hg. Have the subject flex his fingers vigorously until the veins of the forearm
stand out.
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Place your middle finger on the distal end of a vein and occlude the vessel. With
the middle finger in place, move the index finger proximally forcing the blood towards
the heart. The procedure should cause the vein to collapse on the distal side of the valve.
The valve is sometimes seen as a bulge caused by the force of blood against it.
21.
Are venous valves one-way or two-way structures?
Veins contain one – way values
VENOUS PRESSURE
Venous return is the amount of blood returning to the heart from the veins. Skeletal
muscle activity, venous pressure, and the pressure in the atria can influence the amount
that returns.
Have your partner remove his/her shoes and socks and stand motionless for one
minute. Observe the engorgement of blood and distension of the veins in the feet. Choose
another volunteer if the veins are not visible and distended.
Have your partner run in place for 20 to 30 seconds and then reexamine the veins and
compare their size and color to the motionless condition.
22.
What effect does exercise have on vein distension?
Exercise and muscle contractions compress on the veins thus decreasing their distension
23.
How does exercise influence venous return?
Exercise elevates venous return
24.
What would happen to venous return if the pressure in the right atrium were
increased as with congestive heart failure?
Venous return would decrease