Circulatory systems, heart & blood vessels

• Circulatory System

  A system of blood vessels with a pump and valves to ensure one-way flow of blood
• An example of a circulatory system
• Circulatory systems in Fish

  • Two-chambered heart and a single circulation
  • For every one circuit of the body, the blood passes through the heart once
• Circulatory systems in Mammals

  • Four-chambered heart and a double circulation
  • For every one circuit of the body, the blood passes through the heart twice
  • The right side of the heart receives deoxygenated blood from the body and pumps it to the lungs (the pulmonary circulation)
  • The left side of the heart receives oxygenated blood from the lungs and pumps it to the body (the systemic circulation)
• Advantages of Double Circulation

  • Blood travelling through the small capillaries in the lungs loses a lot of pressure that was given to it by the pumping of the heart, meaning it cannot travel as fast
  • By returning the blood to the heart after going through the lungs its pressure can be raised again before sending it to the body, meaning cells can be supplied with the oxygen and glucose they need for respiration faster and more frequently
• The Mammalian Heart


  • The right side of the heart receives deoxygenated blood from the body and pumps it to the lungs
  • The left side of the heart receives oxygenated blood from the lungs and pumps it to the body
  • Blood is pumped towards the heart in veins and away from the heart in arteries
  • The two sides of the heart are separated by a muscle wall called the septum
  • The heart is made of muscle tissue which are supplied with blood by the coronary arteries
• Remember A-A: Arteries carry blood Away from the heart
• Monitoring Activity of the Heart

  • Heart activity can be monitored by using an ECG, measuring pulse rate or listening to the sounds of valves closing using a stethoscope
  • Heart rate (and pulse rate) is measured in beats per minute (bpm)
  • To investigate the effects of exercise on heart rate, record the pulse rate at rest for a minute, immediately after they do some exercise, record the pulse rate every minute until it returns to the resting rate
• • Increased physical activity results in an increased heart rate and breathing rate
  • Heart rate remains high for a period of time after physical has stopped, there is a gradual return to resting heart rate
• Coronary Heart Disease


  • The coronary arteries supply blood to the heart muscle
  • If a coronary artery becomes partially or completely blocked by fatty deposits called 'plaques', the arteries are not as elastic as they should be and therefore cannot stretch to accommodate the blood which is being forced through them - leading to coronary heart disease
  • Partial blockage of the coronary arteries creates a restricted blood flow to the cardiac muscle cells and results in severe chest pains called angina
  • Complete blockage means cells in that area of the heart will not be able to respire and can no longer contract, leading to a heart attack
• Risk Factors for CHD

  • Smoking
  • High cholesterol levels
  • High blood pressure
  • Obesity
  • Lack of exercise
  • Diabetes
• Reducing the risks of developing coronary heart disease

  • Quit smoking
  • Diet - reduce animal fats and eat more fruits and vegetables - this will reduce cholesterol levels in the blood and help with weight loss if overweight
  • Exercise regularly - again, this will help with weight loss, decrease blood pressure and cholesterol levels and help reduce stress
• Identifying Structures in the Heart: Extended

  • The ventricles have thicker muscle walls than the atria as they are pumping blood out of the heart and so need to generate a higher pressure
  • The left ventricle has a thicker muscle wall than the right ventricle as it has to pump blood at high pressure around the entire body, whereas the right ventricle is pumping blood at lower pressure to the lungs
  • The septum separates the two sides of the heart and so prevents mixing of oxygenated and deoxygenated blood
• The function of valves

  • The basic function of all valves is to prevent blood from flowing backwards
  • The atrioventricular valves separate the atria from the ventricles
  • The semilunar valves are found in the two blood arteries that come out of the top of the heart and open when the ventricles contract so blood squeezes past them out of the heart, but then shut to avoid blood flowing back into the heart
• Functioning of the Heart: Extended

  1. Deoxygenated blood coming from the body flows into the right atrium via the vena cava

  2. Once the right atrium has filled with blood the heart gives a little beat and the blood is pushed through the tricuspid (atrioventricular) valve into the right ventricle

  3. The walls of the ventricle contract and the blood is pushed into the pulmonary artery through the semilunar valve which prevents blood flowing backwards into the heart

  4. The blood travels to the lungs and moves through the capillaries past the alveoli where gas exchange takes place

  5. Oxygen-rich blood returns to the left atrium via the pulmonary vein

  6. It passes through the bicuspid (atrioventricular) valve into the left ventricle

  7. The thicker muscle walls of the ventricle contract strongly to push the blood forcefully into the aorta and all the way around the body

  8. The semilunar valve in the aorta prevents the blood flowing back down into the heart
• Blood flow through the heart

  1. Blood flows from right ventricle into pulmonary artery

  2. Blood travels to lungs and through capillaries for gas exchange

  3. Oxygen-rich blood returns to left atrium via pulmonary vein

  4. Blood flows from left ventricle into aorta and around body

  5. Semilunar valve in aorta prevents backflow
• Semilunar valve

  Valve that prevents blood flowing backwards into the heart
• Physical activity increases


  Heart rate increases
• Reason for increased heart rate during exercise

  • To supply more blood, oxygen and nutrients to working muscles
  • To remove waste products faster
• Arteries


  • Carry blood at high pressure away from the heart
  • Carry oxygenated blood (except pulmonary artery)
  • Have thick muscular walls with elastic fibres
  • Have narrow lumen
  • Blood flow is fast
• Veins


  • Carry blood at low pressure towards the heart
  • Carry deoxygenated blood (except pulmonary vein)
  • Have thin walls
  • Have large lumen
  • Contain valves
  • Blood flow is slow
• Capillaries


  • Carry blood at low pressure within tissues
  • Carry both oxygenated and deoxygenated blood
  • Have walls one cell thick
  • Have 'leaky' walls
  • Blood flow is slow
• Main blood vessels in the body

  • Arteries carry blood away from heart to organs
  • Arterioles and capillaries in organs
  • Venules and veins carry blood back to heart
• Adaptations of arteries


  • Thick muscular walls with elastic fibres to withstand high pressure
  • Narrow lumen to maintain high pressure
• Adaptations of veins


  • Large lumen as blood pressure is low
  • Contain valves to prevent backflow
• Adaptations of capillaries


  • Walls one cell thick for easy diffusion
  • 'Leaky' walls to allow blood plasma to form tissue fluid
• Main blood vessels to and from the liver

  • Hepatic artery brings oxygenated blood from heart to liver
  • Hepatic vein brings deoxygenated blood from liver to heart
  • Hepatic portal vein transports deoxygenated blood from gut to liver
• Components of blood


  • Red blood cells
  • White blood cells
  • Platelets
  • Plasma
• Red blood cells


  Concave disc shape with no nucleus, transport oxygen
• White blood cells


  Usually round with a nucleus, defend against infection
• Plasma


  Transports carbon dioxide, nutrients, urea, ions, hormones, heat
• Platelets


  Involved in blood clotting and scab formation
• Blood clotting


  1. Platelets arrive at wound

  2. Fibrinogen converted to insoluble fibrin to form clot

  3. Clot dries into scab to protect wound
• Phagocytes


  • Carry out phagocytosis to engulf and digest pathogens
  • Recognisable by multi-lobed nucleus and granular cytoplasm
• Lymphocytes


  • Produce antibodies and antitoxins to destroy pathogens
  • Recognisable by large round nucleus taking up most of cell and clear cytoplasm