the heart and circulatory system

Job: to ensure that the blood only flows in one direction through the heart

When are they used: as the atria contract, valvesclose as the ventricles open and blood is forced into the ventricles. theses valves close as the ventricles contact so there is no backflow

How: tendons prevent them from inverting

• small lumen so the blood is under high pressure
• walls made from elastic tissue so it can stretch
• muscle layer can contract to control flow and push blood along
• blood flows through fast so there is no risk of backflow and therefore no valves
• 

• thinner wall because they don't have to withstand high blood pressure
• lots of energy has been lost and the wide lumen both result in slow flowing blood
• this means there's a risk of backflow so veins have valves
• located next to muscles so as the muscle contracts it presses on the vein walls, pushing blood through
• 

• found all over the body
• walls are only one cell thick
• substances move in and out of the blood, through the walls, to the surrounding tissues
• they are microscopic and the lumen is so small that only one red blood cell can pass through at a time
• 

Plasma: pale yellow liquid that carries all cells and dissolved substances (CO2, nutrients, ions, hormones, water)

RBCs: contain haemoglobin (the red pigment that binds with O2 to carry it from the lungs to the tissue)  

WBCs: part of your immune system, they engulf pathogens and produce anti-bodies/toxins

Platelets: fractions of cells that cause clotting to cover the site of damaged cells and dry to form scabs                                                                                                                                          

Part of the Blood      Substance Transported    Transported from   Transported to

Blood Plasma             Carbon Dioxide                    Various Organs       Lungs

Blood Plasma             Soluble products                  Small intestine        Various Organs

                                   of digestion    

Blood Plasma             Urea                                      Liver                       Kidneys

Red Blood Cells         Oxygen                                  Lungs                     Various Organs

Rate of Blood Flow = Volume of Blood / time

(cm3/s)                       (cm3)            (s)

Cardiac Output       =        Stroke Volume       x       Heart Rate

(volume of blood                                  (volume of blood                             (number of Beats 

leaving the heart                                   leaving the heart                             per minute)

in 1 minute)                                           per beat)