CGIER 1 - The systemic circulation, blood vessels, capillary networks

Question 1

What are the different types of circulatory systems?

Answer 1

There are two types of circulatory systems:

1. An OPEN SYSTEM is where the heart pumps blood to the tissues in closed arteries, BUT without a venous return. (Arthropods have an open circulatory system)
2. A CLOSED SYSTEM is where blood never leaves the vessels.

Question 2

What are the five fluid systems in the body?

Answer 2

1. Blood Vascular System: circulatory system
2. Lymphatic System
3. Cerebrospinal Fluid: nervous system
4. Peritoneal Fluid: lower back/lungs and heart
5. Interstitial Fluid: throughout everywhere in the body

Question 3

What is the main function of the blood system?

Answer 3

The transportation of necessary materials such as oxygen and nutrients to cells and the transportation of carbon dioxide and waste away from cells.

Question 4

List the three layers of a blood vessel.

Answer 4

1. Tunica intima
2. Tunica media
3. Tunica adventitia

Question 5

Describe the histology of the different layers of blood vessels.

Answer 5

1. Tunica intima in arteries: endothelium, collagen fibres, elastic fibres.
2. Tunica intima in veins: endothelium
3. Tunica media in arteries: smooth muscle (not in aorta), collagen fibres, elastic fibres (few in aorta sheets)
4. Tunica media in veins: thin smooth muscle
5. Tunica adventitia in arteries: collagen fibres, elastic fibres
6. Tunica adventitia in veins: thick collagen fibres

Question 6

What is vasa vasorum?

Answer 6

The name given to the blood supplied to large arteries and veins.

Question 7

List the names of the blood vessels in order from the order aorta all the way until the vena cava.

Answer 7

Aorta –> arteries –> arterioles –> metarterioles –> precapillary sphincter –> arterial capillaries –> venous capillaries –> precapillary sphincter –> venules –> veines –> Vena cava

Question 8

How much blood volume is allowed in the capillaries at any time?

Answer 8

5% of blood volume

Question 9

What are the precapillary sphincters?

Answer 9

They control the flow of blood into and out of capillary beds.

Question 10

Describe the histology of a capillary?

Answer 10

Capillaries are 8-10 micrometers in diameter, with a single layer of endothelial cells and no smooth muscle.

Question 11

What is a preferential channel?

Answer 11

A channel in which blood rushes from the arterial side to the venous side in a capillary.

Question 12

How do most cells receive oxygen and nutrients?

Answer 12

Most cells are not in direct contact with capillaries, but instead, receive oxygen and nutrients through the interstitial fluid.

Question 13

List blood statistics concerning the body.

Answer 13

• Blood volume is 8% of a person’s body weight.
• 5-6 L in male
• 4-5 L in a female

Question 14

What does blood consist of?

Answer 14

Blood consists of:

• 55% plasma (7% protein, 92% water, 1% other solids)
• 45% red blood cells
• < 1% white blood cells and platelets

Question 15

How are metarterioles and precapillary sphincters controlled?

Answer 15

Metarterioles and precapillary sphincters are not innervated, but instead, control blood flow through vasomotion. Increased oxygen levels cause the precapillary sphincters to contract and decreased oxygen levels cause the precapillary sphincters to relax.

Question 16

How do proteins enter the interstitial fluid?

Answer 16

Capillaries have endothelial pores that allow water and small molecular sized substances from the plasma to leave the capillaries and pass into the interstitial fluid. Other proteins leave the capillaries via pinocytosis.

Question 17

What are the names of the four pressures involved in fluid exchange in the capillary beds?

Answer 17

Pressures that force fluid out of capillaries

1. Hydrostatic Pressure (25 mmHg)
2. Interstitial Fluid Pressure (6.3 mmHg)
3. Interstitial Fluid Colloid Osmotic Pressure (5 mmHg)

Pressures that force fluid into capillaries
4. Plasma Colloid Osmotic Pressure (28 mmHg)

Question 18

During the fluid exchange, how much fluid returns to the capillaries and how much is lost?

Answer 18

90% of the fluid volume returns to the capillaries while 10% of the total volume passes into the Lymphatic system from the interstitial fluid.

Question 19

Explain how fluid exchange works.

Answer 19

1. The blood volume exerts a pressure of 25 mmHg against the walls of the capillaries creating a HYDROSTATIC PRESSURE that forces fluid out of the capillaries on the arterial side.
2. Additionally, there is an INTERSTITIAL FLUID COLLOID OSMOTIC PRESSURE of 5 mmHg between the tissue cells and the interstitial fluid, due to there being more solute in the cells than the interstitial fluid, therefore forcing more fluid out of the capillaries at the arterial end.
3. Moreover, there is an INTERSTITIAL FLUID PRESSURE of 6.3 mmHg against the tissue cells exerted by the interstitial fluid, forcing fluid out of the capillaries on the arterial side.
4. However, since there is more solute in the capillaries than in the interstitial fluid (containing RBC, WBC, platelets, and proteins), there is a PLASMA COLLOID OSMOTIC PRESSURE that forces fluid into the capillaries on the arterial end at 28 mmHg.
5. In all, there is a net filtration pressure of 8.3 mmHg out of the arterial capillaries, allowing for cells to receive oxygen and nutrients carried by the fluid.
6. On the venous end, HYDROSTATIC PRESSURE has now decreased to 10 mmHg due to the decrease in blood pressure against the capillary walls due to the constant diffusion occurring on the arterial end.
7. INTERSTITIAL FLUID PRESSURE, INTERSTITIAL FLUID COLLOID OSMOTIC PRESSURE, and PLASMA COLLOID OSMOTIC PRESSURE remain constant.
8. Therefore on the venous end, there is a net filtration pressure of 6.7 mmHg into the capillaries, allowing for waste and carbon dioxide particles to enter the bloodstream to eventually be excreted out of the body.

Question 20

What is the net body filtration rate?

Answer 20

The net body filtration rate is 2.5 - 5 L/day.

Question 21

What is the diffusion rate for the entire body for the capillary network?

Answer 21

The diffusion rate throughout the body is 240 L/min.