Blood Vessels

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

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

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.

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

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

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

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

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

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

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.