Let's experience Your Ride Home as a Chapter Overview

As you drive home from MCC today, take careful note of the route you travel; highways, major roads, side streets and even an alley. All these roads are interconnected and can form a circular pathway. The circulation of blood in the body is similar except that all roadways are one way. You will study the route of blood flow from artery, to arteriole, to capillaries, to venules, then veins. When you arrive home your work begins, you cook, eat, study, and adjust to a lot of frustrations. The circulatory system does all its work at the capillary level.

Did you experience obstacles in your travel? Stoplights? Lane restrictions? Heavy traffic? Similar problems arise in blood flow and increase blood pressure.

Part 1. Circulation routes and capillary exchange

1. Draw arrows between the structures below to indicated the direction of blood flow.

artery         arteriole          capillary          venule          vein          heart

2. This flow chart indicates you should begin the study of blood vessels with arteries.
These are the thickest and strongest containers for blood flow because they must
withstand the pressure of ventricular contraction. List the types of tissues found in
the three layers of an artery.

tunica interna ________________________________________________
__________________________________________________________
tunica media ________________________________________________
__________________________________________________________
tunica externa _______________________________________________
__________________________________________________________

3. From the contents of these layers, can you identify two major properties of arteries?

1. ___________________________________________
2. ___________________________________________

4. The interconnections between arteries are called _______________
These junctions between adjacent blood vessels

a. can bypass capillaries
b. provide an alternate route to blood

5. As blood travels away from the heart, smaller arteries branch into arterioles.
Describe the two key functions of arterioles.

1. ___________________________________________
2. ___________________________________________

6. The blood vessels branching from the arterioles are the extensive network of capillaries. Their walls are only one cell thick as they bathe individual body cells with blood and are the site of the nutrient/waste exchange. You have worked hard studying the cardiovascular system just to reach this point! The activity of an organ determines the amount of capillary supply it must have.

7. The last blood vessel to be examined in Part 1 is a vein. Small blood vessels called venules drain capillaries. These venules converge to become veins. Look at the surface of your arms and legs, the blue lines are the veins. These are thin-walled, flabby vessels that contain 2/3 of the volume of your peripheral blood. Under the microscope, it is easy to identify veins because their lumen is large and their layers (tunics) are thin.

Let's read an excerpt from "Only the Polished Skeleton" by Countee Cullen.

The heart has need of some deceit
To make its pistons rise and fall;
For less than that it would not beat,
Nor flush the sluggish vein at all.

Describe the factors that affect venous return to the right atrium. Blood flows down a
pressure gradient. By the time the flow is through veins, the pressure is so low it is
amazing that venous blood can reach the right atrium. In addition to a pressure drop
from 10 mmHg in the veins to 0 mmHg in the right atrium, blood also has to move
against the force of gravity. How do you keep blood flowing through your veins to
the heart? There are four reasons why this is possible. (Even Isaac Newton would
have wanted to know, then he could have explained the bump on his head.)

Describe the four factors that aid in venous return.

1.____________________________________________________________
2.____________________________________________________________
3.____________________________________________________________
4. ___________________________________________________________

If your remember "breathe in / belly out", it is inspirations that increase pressure in the
abdominal cavity and decrease pressure in the thoracic cavity. This serves as a venous suction pump.

8. Explain the dynamics of capillary exchange.

A. Below is a list of the body's nutrients that are in the capillaries and the body's wastes which form in tissue cells then diffuse into interstitial fluid. Draw arrows to indicate the direction of flow via diffusion for each chemical.

B. The bulk flow of these substances across the capillary membrane depends upon three pressures.
Define, in your own words, the pressures involved in filtration.

blood hydrostatic pressure (BHP)
________________________________________________________

interstitial fluid osmotic pressure
________________________________________________________

Define the pressure involved in reabsorption.

blood colloid osmotic pressure (BCOP)
_________________________________________________________
_________________________________________________________

9. Describe how BHP, BOP, and IFOP determine the fluid and solute movement
through capillaries. List the pressures at the arteriole and venule end of a capillary in the spaces below.

10. You can verify the balance between filtration at the arteriole end and reabsorption
at the venule end of the capillary with a formula. The formula calculates the net flow
of fluid movement. The answer is called the net filtration pressure or NFP. Let's use
the following formula to calculate the direction of flow of nutrients and wastes in the capillaries.

NFP     = (BHP + IFOP) - BOP

___mmHg   = (____ + ____) - ____ venule end (reabsorption)

11. Swell Samuel has noticed swelling of his arms and legs. This is called edema
and is due to an increased movement of fluid out of the capillary and into interstitial fluid.
There are reasons why his BHP, BOP or IFOP may be abnormal. List four causes that
disrupt the balance between filtration and reabsorption.

1. ____________________________________________________
2. ____________________________________________________
3. ____________________________________________________
4. ____________________________________________________

Focus Question
Can you put capillary mechanics into writing?
Explain how nutrients and wastes are exchanged at the capillary level.

Part 2: The Physiology of Circulation
    A. Dynamics of blood pressure
    B. Peripheral resistance

12. Blood flows from high pressure to low pressure. To explain how pressure
affects the flow of blood. You can use the same flow chart found at the beginning
of Part 1 and add the pressures found in each blood vessel. List the pressures below:

artery -----> arteriole -----> capillary-----> venule -----> vein
___mmHg    ____mmHg      ___mmHg         ___mmHg     ___mmHg

Blood pressure is principle force that determines blood flow through the systemic circulation.

13. In the laboratory you will measure blood pressure in the left brachial artery
using a sphygmomanometer. A normal BP is around 120/80 mmHg.

The figure 120 mmHg refers to systolic blood pressure, this is ___________________________________________________________ _____________________________________________________________

The figure 80 mmHg refers to diastolic pressure, this is
_____________________________________________________________
_____________________________________________________________

14. Another factor that determines blood flow through a vessel is peripheral resistance.

A. Remember polycythemia, the increase in red blood cell production.
Explain how this disease would affect peripheral resistance.
________________________________________________________
________________________________________________________

B. Explain what happens to peripheral resistance in anemia or hemorrhaging.
________________________________________________________

C. Suppose you are assigned to Saudi Arabia and become dehydrated in the
desert. Explain what happens to peripheral resistance?
________________________________________________________
_______________________________________________________

D. State the relationship between peripheral resistance, and blood vessel diameter.
_______________________________________________________ _______________________________________________________

15. Let's review how cardiac output, stroke volume, and heart rate affect blood pressure.
Recall the formula: CO = SV X HR.

If any of these is increased, what happens to blood pressure? ______________________________________________________
If any of these decrease, then blood pressure should ______________