1. Three main types of blood vessels:
1. Artery (動脈)
2. Vein (靜脈)
3. Capillaries (微血管)

2. Blood Circulation Vein Artery Heart Venule Arteriole Capillary
returns blood
to the heart
carries blood
away from
the heart
Venule
Arteriole
Capillary

3. Artery
Vein

4. Cross section of a blood vessel
Smooth muscles & elastic fibres
lumen
lining of wall
Fibrous tissue
Cross section of a blood vessel

5. Cross section of artery
Cross section of vein
Artery : thicker elastic wall
to withstand high blood pressure
relatively smaller lumen

6. Cross section of artery
Cross section of vein
Artery : thicker smooth muscles
Not contract to force blood forward
Heart drives blood forward

7. Cross section of artery Blood pressure changes along blood vessels
Cross section of vein
arteries
arterioles
capillaries
venules
veins
Blood pressure changes along blood vessels
Blood pressure / mm Hg 40 80
100
120 90
Blood flow steadily with no pulse
Blood flow with pulse

8. How can blood return to heart through vein under low pressure?
Valve open
blood can flow
Valves present to prevent backflow of blood
Valve closed
blood can’t
flow back

9. valve open contract valve close
Return of blood to heart is aided by contraction of body muscles as they squeeze the blood along the vein
valve open
contract
valve close

10. Demonstration of Venous Flow in the Fore Arm
Investigation
Demonstration of Venous Flow in the Fore Arm

11. What is the purpose of tying the arm with a piece of rubber tubing ?D B
vein Y X S R
finger X pressing down on R
finger Y squeezing blood towards S
finger X still pressing down on R
finger Y removed
both fingers are removed
elbow joint
What is the purpose of tying the arm with a piece of rubber tubing ?
Ans: This makes the vein more conspicuous.

12. A C D B
vein Y X S R
finger X pressing down on R
finger Y squeezing blood towards S
finger X still pressing down on R
finger Y removed
both fingers are removed
elbow joint
With reference to steps B & C, explain why the part of the vein between R and S has disappeared ?
Ans: Since there are valves at point S, blood is prevented from flowing back …
Ans: On the other hand, finger X is still pressing down on point R which prevents blood flowing into R.
Ans: In step B, finger Y squeezes the vein towards point S. Blood in this segment is therefore pushed along …

13. Ans: The valve in the vein.C D B
vein Y X S R
finger X pressing down on R
finger Y squeezing blood towards S
finger X still pressing down on R
finger Y removed
both fingers are removed
elbow joint
What structure in the vein is indicated by the appearance of the bulge at S shown in diagram C ?
Ans: The valve in the vein.

14. A C D B
vein Y X S R
finger X pressing down on R
finger Y squeezing blood towards S
finger X still pressing down on R
finger Y removed
both fingers are removed
elbow joint
Why is it necessary to take the rubber tubing away as soon as the demonstration has been completed ?
Ans: It is because we need to restore the normal blood flow for the arm as soon as possible.

15. cross section of capillary
Capillaries
cross section of capillary
allow exchange of materials between the blood and the body tissues by diffusion.
O2 , nutrients
arterioles
capillaries
CO2 , waste
venules
the wall is permeable to O2, CO2, glucose, amino acids,
salts, water ... etc.

16. cross section of capillary
Capillaries
Specially adapted for exchange of materials
One-cell thick walls
 diffusion distance between blood and body tissue
very small lumen
cross section of capillary
Very small lumen but large total cross sectional area
 blood flow
more time for exchange of materials
one cell thick
Greatly branched
 surface area for efficient diffusion of materials

17. Same flow rate (Volume / time) V1 = V2
Capillaries v1 A1
 Total cross sectional area
A1 > A2 d1
arteriole v2
 d2 > d1 A2
 v2 > v1 d2

18. Exchange of materials between the blood and the body cells
oxyhaemoglobin
capillary
cell
Plasma protein
Exchange of materials takes place at the capillaries only
white blood cells
water O2
nutrients
plasma
waste products
CO2
tissue fluid
Diffuse across the capillary wall
Diffuse across the capillary wall
Squeeze through the wall