The Heart

Closed Systems  - blood circulates by a continuous system of tubes being pumped by the heart a high pressure. Organs are not direct contact with the blood but bathed by tissue fluid passing through capillaries. The blood contains a pigment which carries oxygen.

Open Systems - blood is pumped from a tube shaped heart down the body into spaces (called a haemocal). Blood bathes the tissues directly and there is little control over the direction of circulation. Usually no respiratory pigment as blood is not involved in the transport of oxygen.

Transport System

Has the following common features:

• suitable medium in which to carry materials
• closed system of vessels that form a branching network to deliver blood to all parts of the body
• pump for moving blood within the vessels
• values to maintain flow in one direction
• respiratory pigment which increases the volume of oxygen that can be transported

Blood Vessels Structure

• inner layer - endothelium, one cell thick smooth lining to reduc friction, provides minium resistance to blood flow
• middle layer - elastic fibres, smooth muscle thicker in arteries to accommodate change in blood flow and pressure
• outer layer - collagen fibres, resistant to over stretching

Arteries 

• carry blood away from heart
• thick muscular walls to withstand high pressure
• contraction of muscles maintains pressure
• branch into arterioles that divide into capillaries which penetrate tissues and organs. Blood from capillaries collects in venules which empty into veins and back to the heart

Veins

• large diameter and thin walls as pressure and flow is reduced
• semi-lunar…