Circulation and Respiration

• • In order for an individual to be able to move, their muscles need to contract, which requires energy from respiration
  • When exercising, the number of muscle contractions increases, therefore there is a greater energy demand, which means that the muscles need a greater supply of oxygen for aerobic respiration
  • The human body reacts to the increased demand for oxygen in a number of ways:
  • The breathing rate and breath volume increase during exercise to increase the amount of oxygen absorbed into the bloodstream by diffusion, and the amount of carbon dioxide removed
  • The heart rate increases
• • If exercising vigorously, the body may not be able to supply sufficient oxygen to the muscles to meet the demand for energy
  • In this situation, some of the energy supplied to the muscles comes from anaerobic respiration, which is the incomplete breakdown of glucose without oxygen
  • This releases much less energy than aerobic respiration and results in the formation of lactic acid as glucose is incompletely oxidised
• • An “oxygen debt” is created after exercising in this way; it is a debt as “extra” oxygen is needed to react with the lactic acid produced via anaerobic respiration
  • This is why an individual still breathes heavily at an increased rate (with a higher heart rate than usual) after exercising vigorously
  • “Extra” carbon dioxide also has to be removed from the body
• Oxygen debt:

  • The body can deal with lactic acid in one of two ways
  • It can be oxidised (reacted with oxygen) to form carbon dioxide and water – the same products formed in aerobic respiration
  • Alternatively, blood flowing through the muscles transports the lactic acid to the liver where it is converted back into glucose
  • Remember the “oxygen debt” is the amount of extra oxygen the body needs after exercise to react with the accumulated lactic acid and remove it from the cells
• • Metabolism can be defined as:

  the sum of all the reactions in a cell or the body

  • Energy released during respiration allows enzyme-controlled reactions to occur inside cells, e.g. to produce new molecules
• Synthesis & breakdown of molecules

  • Organisms gain organic molecules, either by consuming food, e.g. in animals, or carrying out photosynthesis, e.g. in plants
  • The molecules gained can then be broken down and used to produce, or synthesise, new molecules
  • Metabolic reactions include the synthesis and breakdown of:
  • carbohydrates; complex carbohydrates are built from sugars, e.g. glucose
  • lipids; these are built from fatty acids and glycerol
  • proteins; synthesised from amino acids
• Examples of metabolic reactions

  • Carbohydrates
  • Glucose is used in the synthesis of:
  • starch; energy storage in plants
  • glycogen; energy storage in animals
  • cellulose; strengthens plant cell walls
  • Glucose is broken down during respiration to release energy
  • Lipids
  • Glycerol is combined with three fatty acids in the synthesis of lipids, which can be used in energy storage
  • Proteins
  • Glucose and nitrates are involved in the production of amino acids
  • Amino acids are used in the synthesis of proteins
  • Excess proteins are broken down to produce urea, which is excreted from the body
• • Digestive enzymes work outside of cells; they digest large, insoluble food molecules into smaller, soluble molecules which can be absorbed into the bloodstream
• • Metabolism is the sum of all the reactions happening in a cell or organism, in which molecules are synthesised (made) or broken down
• • Enzymes are biological catalysts made from protein
  • Enzymes speed up chemical reactions in cells, allowing reactions to occur at much faster speeds than they would without enzymes at relatively low temperatures (such as human body temperature)
• • Substrates temporarily bind to the active site of an enzyme, which leads to a chemical reaction and the formation of a product(s) which are released
  • Enzymes remain unchanged at the end of a reaction, and they work very quickly
  • Some enzymes can process 100s or 1000s of substrates per second
• • Enzymes have specific three-dimensional shapes because they are formed from protein molecules
  • Proteins are formed from chains of amino acids held together by bonds
  • The order of amino acids determines the shape of an enzyme
  • If the order is altered, the resulting three-dimensional shape changes
• • The ‘lock and key theory’ is one simplified model that is used to explain enzyme action
  • The enzyme is like a lock, with the substrate(s) the keys that can fit into the active site of the enzyme with the two being a perfect fit
• The Lungs

  Adaptations for gas exchange

  • All gas exchange surfaces have features to increase the efficiency of gas exchange including:
  • Large surface area to allow faster diffusion of gases across the surface
  • Thin walls to ensure diffusion distances remain short
  • Good ventilation with air so that diffusion gradients can be maintained
  • Good blood supply (dense capillary network) to maintain a high concentration gradient so diffusion occurs faster
• • Remember that gas exchange occurs by the process of diffusion; breathing is essential in maintaining high concentration gradients between the air in the alveoli and the gases dissolved in the blood
  • In particular, breathing keeps the oxygen level in the alveoli high and the carbon dioxide level low
• Ribs - Bone structures that surround and protect the lungs, they also aid breathing (moving up and out or down and in)
• Intercostal muscles - Muscles between the ribs which control movement, causing inhalation and exhalation
• Diaphragm - Sheet of connective tissue and muscle at the bottom of the thorax that helps change the volume of the thorax to allow inhalation and exhalation
• Trachea - Windpipe that connects the mouth and nose to the lungs, lined with goblet cells (to produce mucus) and ciliated epithelial cells (with cilia which move mucus up to the mouth).
• Bronchus (plural =bronchi) - Large tubes branching off the trachea with one bronchus for each lung, also Lined with goblet cells and ciliated epithelial cells.
• Bronchioles - The bronchi split to form smaller tubes called bronchioles in the lungs connected to alveoli.
• Alveoli - Tiny moist dir sacs where gas exchange takes place, each alveolus is covered in capillaries.
• The Heart

  The double circulatory system

  • The human heart is part of a double-circulatory system
  • The circulatory system is a system of:
  • blood vessels
  • a pump (the heart)
  • valves that maintain a one-way flow of blood around the body
  • The heart has four chambers separated into two halves:
  • The right side of the heart pumps blood to the lungs for gas exchange (this is the pulmonarycircuit)
  • The left side of the heart pumps blood under high pressure to the body (this is systemiccirculation)
• • The benefits of a double circulatory system:
  • Blood travelling through the small capillaries in the lungs loses a lot of pressure which reduces the speed at which it can flow meaning more time for diffusion of gases at the alveoli
  • By returning oxygenated blood to the heart from the lungs, the pressure can be raised before sending it to the body, meaning cells can be supplied with oxygenated blood more quickly
• The heart structure

  • The right side of the heart receives deoxygenated blood from the body and pumps it to the lungs
  • This is where oxygen diffuses in from the alveoli and carbon dioxide diffuses out
  • 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 four chambers of the heart are divided into top and bottom:
  • Chambers at the top are the atria
  • Chambers at the bottom are the ventricles
• Pathway of blood through the heart

  • Deoxygenated blood enters the heart via the vena cava, emptying into the right atrium
  • Blood flows down through a set of valves into the right ventricle
  • When the ventricles contract, blood travels up through the pulmonary artery to the nearby lungs where gas exchange occurs (and the blood becomes oxygenated)
  • Oxygenated blood returns to the heart via the pulmonary vein, emptying into the left atrium
  • Blood flows down through a set of valves into the left ventricle
  • When the ventricles contract, blood travels up through the aorta, and to the rest of the body
• Are the walls of the atria or the ventricles thicker?

  Ventricles
• Why are the ventricle walls thicker than the atria walls?

  They pump blood out of the heart
• Why do the ventricles need to generate a higher pressure?

  To pump blood out of the heart
• Which ventricle has a thicker wall, the left or right?

  Left ventricle
• Why is the left ventricle wall thicker than the right ventricle wall?

  It pumps blood around the entire body
• At what pressure does the left ventricle pump blood?

  High pressure
• What is the destination of blood pumped by the left ventricle?

  The entire body
• What is the pressure of the blood pumped by the right ventricle?

  Lower pressure
• Where does the right ventricle pump blood to?

  The lungs
• Why does the right ventricle not require high pressure to pump blood?

  The lungs are close to the heart
• How many sets of valves are inside the heart?

  Two
• What is the function of the valves inside the heart?

  Prevent the backflow of blood
• What separates the two sides of the heart?

  The septum
• What does the septum prevent?

  Mixing of oxygenated and deoxygenated blood