1. Blood Vessels

2. Learning Intentions
Explain the meaning of the terms closed and open circulatory system with reference to insects and fish.
Describe the structures and functions of arteries, veins and capillaries

3. Closed circulation Blood stays in blood vessels.
All vertebrates fish, birds and mammals

4. Open system Insects 1mm to 13cm Blood not always held in vessels
Blood circulates through body cavity
Lymph and blood not distinguished-haemolymph
Dorsal muscular pumping organ
Insects have a separate trachael system to transport oxygen and carbon dioxide.
Blood enters through pores called ostia, the heart then pumps the blood towards the head by persitalis, near the head the blood just pours into body cavity.
Active insects like locust have open ended tubes attached to heart to direct blood to active muscles.
Insects and many other invertebrates have an open circulatory system, where the blood flows freely within the body cavity, but passes through a series of open blood vessels and heart(s), whose pumping maintains a directional flow.

5. Blood Vessels Arteries: Carry blood away from the heart
Capillaries: Link arterioles to veins
Veins: Carry blood towards the heart

6. Structure of Blood Vessels
Tough outer layer – resists pressure
Muscle layer – can contract and control the flow of blood
Elastic layer – can stretch and recoil to maintain blood pressure
Endothelium – smooth layer to prevent friction
Lumen – not a layer – a cavity

7. Look at microscope slides of the different blood vessels and draw an annotated diagram of each.

8. Structure of Arteries Thin lumen to maintain high pressure
Thick muscle layer – control the flow of blood
Thick elastic layer – allows the wall to stretch and recoil when the heart pumps
No valves

9. Structure of Veins Large lumen to allow blood to flow easily
Thin muscle layer
Thin elastic layer
Valves

10. Structure of Capillaries
Single layer of flattened endothelial cells only
The lumen is very narrow.

11. Capillary Structure to Function
Thin layer of cells – short diffusion distance.
Numerous and highly branched – large SA for diffusion.
Narrow diameter – keep all cells close by.
Narrow lumen – bring RBC close to the cells = short diffusion distance.
Spaces between cells – allow WBC to escape.