The lungs and the heart

• The lungs contain - trachea , lung , bronchus ( plural : bronchi) , alveoli ( single : alveolus + surrounded by capillary network )
• There are millions of alveoli in the lungs
• • Blood in capillaries just returned to lungs from being passed around body - from haemoglobin and has already has given up lots of oxygen to tissues - not a lot left
  • alveoli is full of fresh oxygen - perfect concentration gradient so oxygen can travel down concentration gradient into blood  
  • oxygenated blood starts cycle again
  • carbon dioxide ( transported around body dissolved in blood plasma ) higher concentration in blood then alveoli so can diffuse across into alveoli and then we can breath it out 
• Gases diffuse between the aveolus and the blood
• Breathing rate - number of breaths taken / number of minutes
• All cells must carry out process of cellular respiration and need oxygen for that 
• Lungs are apart of the respiratory system 
• The circulatory system is make up of the heart ( a pumping organ to keep things moving through vessels ) , blood vessels ( hold blood ) and blood ( carries oxygen and nutrients ) . Humans have a double circulatory system ( two circuits ) :

  Circuit 1 - heart ( right ventricle ) -> lungs -> heart

  Circuit 2 - heart ( left ventricle ) -> rest of the body -> heart
• To keep best steady , a group of cells in right atrium act as a pacemaker + these pacemaker cells produce small electrical impulses that spread thorough the muscular walls of the heart and causes them to contract 
• Some rare cases these pacemaker cells don't work properly - doctors can implant and artificial pacemaker ( just under skin about heart and has a wire that can carry electrical current down to heart telling it to contract regularly ) 
• Artery - any vessel that carries blood away from the heart 

  Vein - any vessel that carries blood to the heart 
• Heart needs own supply of oxygenated blood and gets it from small arteries that branch out of the aorta called coronary arteries - makes sure the heart muscle gets all the oxygen and nutrients that it needs 
• Left ventricle has thicker wall because it has to pump blood all the way round the body 
• Circulatory system - organ system that transports oxygen and nutrients to tissues 
• In the heart , there's 4 chambers with thick muscular walls surrounding them and veins and arteries coming in and out 

  Image of heart - their left is our right ect 

  Top chambers  - atria and individual one is an atrium 

  Bottoms chambers - ventricles 
• Between chambers and vessels - valves - prevent blood from flowing backwards - always flow in the right direction 
• Blood flows into the heart through vena carva and pulmonary vein and then flows into right and left atrium 

  Pulmonary veins blood ( left ) just came from lungs - oxygenated 

  Blood from vena carva ( right ) just came from body so deoxygenated 

  Two atrium contract together and push blood into ventricles and then they contract to push blood out to pulmonary artery ( going to lungs + on right side ) and the aorta ( to body and on the left side ) 

  Atrium will fill up with blood again and cycle repeats around 70 times a minute 
• • Blood in arteries - high pressure becuase just pumped out of ventricles 
  • Need to be strong and elastic to bare high blood pressure - thick layer of muscle tissue ( strong ) and thick layer of elastic tissue ( stretch and recoil )
  • wall of artery is thick compared to lumen ( space in middle of vessel ) 
• • Once arteries have transported blood to parts of body , it enters the capillaries 
  • The capillaries are really small
  • They exchange substances with our cells and takes away waste products  
  • Walls only one cell thick + permeable 
  • lumen is narrow which keeps blood pressure high 
  • Total cross section area is huge tissues 
• • Tiny Capillaries join up into larger vessels - veins 
  • Large and biggest lumens of all vessels 
  • Has smaller layer of elastic fibre and smooth muscle - blood carry is very low pressure so walls doesn't have to be strong 
  • They have valves - prevent blood flow from flowing backwards 
• rate of blood flow = volume of blood / time taken
• Blood is a tissue
• Nutrients that are exchanged between the blood in capillaries and body tissues - glucose and amino acids 
• Waste products that are exchanged between the blood in capillaries and body tissues - carbon dioxide and urea
• Red blood cells

  • carry out oxygen around the body
  • no nucleus so more room for oxygen
  • contains haemoglobin which binds to oxygen
  • biconcave shape = big surface area = lots of oxygen absorbed
• White blood cells

  • defend against infection
  • has a nucleus
  • Phagocytosis- engulf pathogen 
  • Produces antibodies - binds onto pathogens and help destroy them •Antitoxins - neutralise any toxins pathogens produce 
• Platelets

  • helps clot the blood when a blood vessel breaks and stops microorganism from getting in which can cause us infection 
  • fragments of cells - don't have a nucleus
• Plasma

  • carries everything in the blood : red blood cells , white blood cells , platelets , nutrients like glucose and amino acids , waste products like carbon dioxide and urea , hormones , proteins , antibodies , antitoxins 
• Artificial blood - blood substitute that consists of salt water - adds volume to circulatory systems which keeps our vessels full and allows heart to keep on pumping but it doesn't contain any red blood cells so doesn't allow us to transport any more oxygen so can only replace 1/3 of our blood 

  Blood transfusion- given real blood that's donated with red blood cells which is the key to surviving blood loss