So this chapter is a mix of biology and physics:)

Please review xx

Katie xx

It was just after lunch and max walked to Zoe's office. He knocked on the door.

"Come in. Oh max it's you."

"Oh charming. I came to see if you were up for another lesson."

"Yeah I need a break from this. What do you want to know more about."

"Umm how about the heart."

"Fine well I'll add more information as well."

"Alright by me."

Zoe and max moved to the sofa.

"The blood is made up of plasma which is a pale yellow liquid that carries everything in the blood. It carries: red and white blood cells, platelets, glucose and amino acids, Carbon dioxide, oxygen, urea, hormones, antibodies and antitoxins.

Red blood cells are biconcave disks, this increases the surface area. Also they have no nucleus which makes more room for haemoglobin. Oxygen is carried by the red blood cells what combining with the haemoglobin.

An iron deficiency can cause anaemia which means the red blood cells can't carry enough oxygen.

White blood cells engulf microbes and produce antibodies and antitoxins. If you have a low count you run the risk of infection.

Platelets clot the blood, to stop bleeding and to prevent microbes from entering the body."

Max smiled at Zoe, how had he managed to form a relationship with her. She was so intelligent.

"Max have you finished gawping."

"Oh yeah sorry do carry on."

"So you have arteries these carry blood away from the heart. They carry blood at high pressure around the body. The walls are strong and elastic. The walls are thick compared to the lumen.

Arteries branch off into capillaries.

Capillaries exchange materials with the tissues. They are really small and the walls are only once cell thick, this increases the rate of diffusion by decreasing the distance over which it occurs.

Capillaries branch off into veins.

Veins carry blood at a low pressure and the walls of the vessels are not as thick as arteries. They have a bigger lumen to help blood flow and they also have valves to prevent the back flow of blood and keep it flowing in the right direction."

Zoe kissed max.

"What was that for."

"Thought you might need to regain some focus"

"Oh yeah. Let's hear more."

"The heart is split into four chambers. Deoxygenated blood enters the heart through the vena cava into the right atrium. Then a valve stops the back flow of blood as it passes into the right ventricle. Then the blood passes the through the pulmonary artery to the lungs. The oxygenated blood then enters the heart though the pulmonary vein. It travels through the left atrium into the left ventricle and out through the aorta and around the body."

"Electrocardiographs or ECGs measure the action potential of the heart. When the heart beats, and action potential passes through the atria making them contract. Then another action potential passes through the ventricles making them contact too. Once the action potential has passed the muscle relaxes. These action potentials produce weak electrical signals on the skin. An ECG records the action potentials of the heart using electrodes stuck onto the chest, arms and legs.

Using an ECG you can work out the heart rate.

Frequency (hertz) = 1/time period (seconds)"

"Wow. Your such a great teacher, I love you you know."

"I know. Come on back to work you. Your distracting me."

"Oh you love it really."

Max kissed Zoe before walking out of her office. It was his turn to teach her something next.

Please review. There'll be more soon xx