Circulation

• Why do large organisms need mass transport systems?

  - They have a higher metabolic rate

  - They have a smaller SA:V ratio, and lots of the cells are deep within the body so cannot be reached by simple diffusion alone from the outside.

  - For single-celled organisms, diffusion alone is enough to supply all their needs.
• What are the features of mass transport systems?


  - A system of vessels that carry substances (usually tubes, sometimes following a specific route, sometimes widespread and branching)

  - A way of making sure substances are moved in the right direction

  - A means of moving materials fast enough to supply the needs of the organism (mechanical methods, maintaining a concentration gradient)

  - A suitable transport medium
• What is the difference between an open and a closed circulatory system?


  - Open = blood circulating in large open spaces

  - Closed = blood contained within tubes
• Single circulatory system


  A circulation in which the heart pumps the blood to the organs of gas exchange and the blood then travels on around the body before returning to the heart.

  
• Double circulatory system


  A circulation which involves two circulatory systems, one of deoxygenated blood flowing from the heart to the gas exchange organs and back oxygenated to the heart, and one of oxygenated blood leaving the heart and flowing around the body, returning deoxygenated to the heart.

  
• Systemic circulation


  Carries oxygenated blood from the heart to the cells of the body where the oxygen is used, and carries the deoxygenated blood back to the heart.
• Pulmonary circulation


  Carries deoxygenated blood to the lungs and oxygenated blood back to the heart.
• How is a double circulatory system more efficient?


  - Oxygenated and deoxygenated blood cannot mix, so the tissues receive as much oxygen as possible.

  - Oxygenated blood can be delivered quickly to the body tissues at high pressure (blood in tiny blood vessels in lungs are low pressure so it doesn't damage the vessels, allowing gas exchange to take place, however if this oxygenated blood went straight into the big vessels that carry it around the body it would move very slowly)
• Cardiovascular system


  The mass transport system of the body made up of a series of vessels with a pump (the heart) to move the blood through the vessels.

  
• Circulation


  The passage of blood through the blood vessels
• What are the functions of the circulatory system?


  - Delivers the materials needed by the cells of the body and carries away the waste products of their metabolism

  - Carries hormones from one part of the body to another

  - Forms part of the defence system of the body

  - Distributes heat
• What does blood plasma transport?


  - Digested food products from the small intestine to the parts of the body where they're needed for immediate use or for storage

  - Nutrient molecules from storage areas to the cells that need them

  - Excretory products from cells to organs such as the lungs or kidneys that excrete them from the body

  - Chemical messages (hormones) from where they are made to where they cause changes in the body
• What are the other functions of blood plamsa?


  - Helps maintain a steady body temperature by transferring heat around the system from deep-seated organs (eg. the gut) or very active tissues (eg. leg muscles in someone running)

  - Acts as a buffer to pH changes
• What is the function of erythrocytes?


  Transport oxygen from the lungs to all the cells (also caries some of the CO2 produced in respiration back to the lungs). They are formed in bone marrow and have a limited life of about 120 days.

  
• What are the adaptations of erythrocytes?


  - Contain haemoglobin, a red pigment that carries oxygen and gives them their colour

  - Biconcave disc shape means they have a large SA:V ratio, so oxygen can diffuse in and out of the rapidly

  - No nucleus leaves more space for haemoglobin
• What is the function and adaptations of leucocytes?


  - Main function is to defend the body against infection.

  - Much larger than erythrocytes, but they can change their shape to squeeze through tiny blood vessels.

  - Formed in bone marrow but some mature in the thymus gland.

  - All contain a nucleus and have a colourless cytoplasm, but some types contain granules that can be stained.

  
• Granulocytes


  Leucocytes that have granules in their cytoplasm that take up stain and are obvious under the microscope. They have lobed nuclei and include neutrophils, eosinophils and basophils.

  
• Neutrophils


  Part of the non-specific immune system. They engulf and digest pathogens by phagocytosis. Have multi-lobed nuclei. Up to 70% of all leucocytes are neutrophils.
• Eosinophils


  Part of the non-specific immune system. They are stained red by eosin stain. Important in the non-specific immune response of the body against parasites, in allergic reactions and inflammation, and in developing immunity to disease.
• Basophils


  Part of the non-specific immune system. They have a two-lobed nucleus. Produce histamines involved in inflammation and allergic reactions.
• Agranulocytes


  Leucocytes that do not have granules to take up stain in their cytoplasm. They have unlobed nuclei and include monocytes and lymphocytes.

  
• Monocytes


  Part of the specific immune system. The largest of the leucocytes. Can move out of the blood into the tissue to form macrophages, which also play an important part in the specific immune system. They engulf pathogens by phagocytosis.
• Lymphocytes


  Small leucocytes with very large nuclei that are vitally important in the specific immune response of the body.
• What is the function of platelets?


  Tiny fragments of large cells called megakaryocytes, which are found in the bone marrow. Involved in the clotting of blood.
• What is the structure of haemoglobin?


  Each haemoglobin molecule is a large globular protein made up of 4 peptide chains, each with an iron-containing prosthetic group, which can pick up 4 molecules of oxygen in a reversible reaction to form oxyhaemoglobin.
• What is cooperative binding?


  - The first O2 molecule that binds to haemoglobin alters the arrangement of the molecule, making it easier for the following oxygen molecules to bind.

  - The same process happens in reverse when oxygen dissociates from haemoglobin - it gets progressively harder to remove oxygen.

  
• Explain how oxygen is picked up by red blood cells


  - Oxygen concentration in red blood cells when the blood enters the lungs is relatively low, so oxygen moves into the red blood cells from the air by diffusion.

  - Because oxygen is picked up and bound to haemoglobin, the free oxygen concentration in the cytoplasm of red blood cells stays low, maintaining a steep concentration gradient.
• Explain how oxygen is unloaded from the blood into the tissues

  - In body tissues the oxygen levels are relatively low, so the concentration of oxygen in the cytoplasm of red blood cells is higher than the surrounding tissue.

  - As a result, oxygen moves out into the body cells by diffusion down a concentration gradient - the haemoglobin gives up some of its oxygen.

  - When you are at rest or exercising gently, only 25% of O2 carried by haemoglobin is released into cells, there is a 75% reserve in the transport system for when you're very active.
• What is the effect of haemoglobin's strong affinity with oxygen?


  - A small change in the proportion of oxygen in the surrounding sir can have a big impact on the saturation of the blood with oxygen.

  - In the lungs the haemoglobin loads up rapidly with oxygen, in the tissues as the oxygen saturation of the environment falls, oxygen is released rapidly.
• Describe the oxygen dissociation curve in human haemoglobin


  - A sigmoid curve

  - Low partial pressure = conditions in the respiring tissues

  - High partial pressure = conditions in the lungs

  - As deoxygenated blood approaches the lungs, the steep part of the curve means that a small increase in partial pressure causes a large increase in % saturation

  - As oxygenated blood approaches the tissues, a small decrease in partial pressure causes a large decrease in % saturation (large release of O2)

  
• Explain the Bohr effect


  - When the partial pressure of CO2 is high, the affinity of heamoglobin for O2 is reduced, so haemoglobin needs higher levels of oxygen to become saturated and gives up O2 more easily.

  - In active tissues with high CO2 levels, haemoglobin releases oxygen very readily.

  - CO2 levels in lung capillaries are relatively low, making it easier for O2 to bind with haemoglobin.

  
• Fetal haemoglobin


  - Only found in the developing fetus, where the fetus is dependent on its mother to supply it with oxygen

  - Oxygenated blood from the mother runs through the placenta close to deoxygenated fetal blood. If the blood of the fetus had the same affinity for O2 as the mother's, very little oxygen would be transferred.

  - Fetal haemoglobin has a higher affinity for O2, so can remove O2 from maternal blood.

  - Maternal and fetal blood flow in opposite directions, so there's a countercurrent exchange system.

  
• Myoglobin


  - A respiratory pigment found in the muscle tissue of vertebrates; a small bright red protein.

  - Similar structure to a single haemoglobin chain (contains a haem group which binds to O2)

  - A much higher affinity for O2 than haemoglobin, so easily becomes saturated; this affinity isn't affected by the partial pressure of O2 in the tissues.

  - Once myoglobin binds to an O2 molecule, it doesn't give it up easily, so acts as a store - O2 can be released in very active muscle tissue in low O2 levels and high CO2 levels.

  
• How is carbon dioxide transported in the blood?


  - Waste CO2 diffuses from the respiring tissues to the blood, where it reacts slowly with water to form carbonic acid H2CO3; this separates into H+ and HCO3-.

  - The enzyme carbonic anhydrase controls the rate of reaction between CO2 and H2O to form H2CO3. This reaction is reversible, so in tissues (high CO2 conc) the formation of H2CO3 is catalysed, in the lungs the reverse is catalysed.

  - Some CO2 combines with haemoglobin to form carbaminohaemoglobin.

  
• Why is blood clotting important?


  - If blood vessels get cut, your blood volume will fall and pathogens can get into the body through the open wound.

  - The clotting mechanism of the blood seals up damaged blood vessels to minimise blood loss and prevent pathogens getting in.
• What are the 2 main substances that platelets release when they break open?


  Serotonin and thromboplastin
• What is the function of serotonin?


  Causes the smooth muscle of the blood vessel to contract, which narrows the blood vessel and cuts off blood flow to the damaged area.
• What is the function of thromboplastin?


  An enzyme that sets in progress a cascade of events that leads to the formation of a clot.
• What is the sequence of events in the blood clotting cascade?

  - Thromboplastin catalyses the conversion of a large soluble protein called prothrombin found in the plasma into another soluble protein, the enzyme thrombin. Calcium ions need to be present in the blood at the correct concentration for this reaction to happen.

  - Thrombin acts on another soluble plasma protein called fibrinogen, converting it into insoluble fibrin.

  - Fibrin forms a mesh of fibres to cover the wound.

  - More platelets and blood cells pouring from the wound get trapped in the fibrin mesh to form a clot.

  - Proteins in the structure of the platelets contract, making the clot tighter and tougher to form a scab that protects the skin and vessels underneath as they heal.

  
• What are arteries, veins and capillaries?


  - Arteries = vessels that carry blood away from the heart towards the body cells (exceptions: pulmonary artery, umbilical artery)

  - Veins = vessels that carry blood towards the heart from the body cells (exceptions: pulmonary vein, umbilical vein)

  - Capillaries = minute vessels that spread through the tissues of the body