Chapter 5 Circulatory system

• Average female adult


  1. 5L of blood
• Adult male


  1. 6L of blood
• Carbon dioxide is carried in blood in many ways
• Ways carbon dioxide is carried in blood


  • 7-8% is dissolved in the plasma and carried in solution
  • Another 22% or so combines with globin part of haemoglobin molecule to form a compound called carbaminohaemoglobin
  • Remainder 70% is carried in plasma as bicarbonate ions HCO3-
• Transport of carbon dioxide

  1. As blood flow through capillaries between the body cells, carbon dioxide diffuses into plasma due to difference in carbon dioxide concentration

  2. Some carbon dioxide dissolves in the plasma, some combines with haemoglobin, but most reacts with water to form carbonic acid H2CO3

  3. Carbonic acid then ionises into hydrogen ions and bicarbonate ions
• Carbon dioxide transport in alveoli

  1. Carbon dioxide is dissolved in plasma diffuses out of the blood into the air in alveolus

  2. Carbaminohaemoglobin breaks down, carbon dioxide molecules released also diffuse into alveolus

  3. Hydrogen ions and bicarbonate ions recombine to form carbonic acid, which then breaks down under enzyme action into water and carbon dioxide, this carbon dioxide also diffuses into alveolus
• Components of blood


  • Plasma- the liquid part, 55% of blood volume
  • Formed elements- non-liquid part, 45% of blood volume and consisting of erythrocytes (red blood cells), leucocytes (white blood cells) and thrombocytes (platelets)
• Plasma


  • Mixture of water with dissolved substances such as sugar and salts
  • Function to transport components of blood, including cells, nutrients, wastes, hormones, proteins and antibodies throughout the body
• Erythrocytes


  • Are most abundant cells in blood and account for 40-45% of its volume
  • Percentage is known as the haematocrit
  • Cells are biconcave shape- flattened in the middle on both sides, reason to increase surface area, so can transport more oxygen
  • Do not contain nucleus, which increases flexibility, allowing them the ability to move through blood vessels
  • Lack of nucleus also limits life span to 120 days average
  • Function is to transport oxygen from lungs to cells throughout body
• Types of leucocytes


  • Neutrophils
  • Monocytes
  • Lymphocytes
  • Basophils
  • Eosinophils
• Thrombocytes


  • Platelets are small fragments of cells
  • When blood vessel is injured, platelets adhere to the lining and form a scaffold for the coagulation of the blood to form a clot
• Nutrients transported in blood plasma


  • Inorganic nutrients transported as ions (sodium ions, calcium ions, potassium ions, chloride ions and iodide ions)
  • Organic nutrients (glucose, vitamins, amino acids, fatty acids and glycerol)
• Wastes transported in blood plasma


  • Urea, creatinine and uric acid
• Blood clotting


  1. Vasoconstriction- muscles in walls of small arteries that have been injured/broken constrict immediately to reduce blood flow

  2. Platelet plug- platelets stick to damaged blood vessel walls, attracting others to build a plug

  3. Coagulation- formation of blood clot through a complex series of reactions resulting in fibrin threads forming a mesh that traps blood cells, platelets and plasma

  4. Clot retraction- network of fibrin threads contract, becoming denser and stronger, pulling edges of damaged blood vessels together
• Oxygen transport


  • Only 3% of oxygen is carried in solution in the blood plasma, other 97% carried in combination with haemoglobin molecules in red blood cells
  • Haemoglobin is able to combine with oxygen to form oxyhaemoglobin, which can easily break down to release oxygen
• Presence of haemoglobin in red blood cells increases the oxygen-carrying capacity of the blood by about 60 to 70 times
• Oxygen uptake and release


  1. Oxygen combines with haemoglobin when oxygen concentration is relatively high, in capillaries in the lungs

  2. Oxyhaemoglobin breaks down to haemoglobin and oxygen when the concentration of oxygen is relatively low, as cells in body continually use oxygen
• Oxygenated blood


  Blood with high proportion of oxyhaemoglobin, bright red in colour
• Deoxygenated blood


  Blood with haemoglobin, dark red or purplish in colour
• Red blood cells


  • Contain haemoglobin, which is able to combine with oxygen
  • Have no nucleus, so there is more room for haemoglobin molecules
  • Shaped like biconcave discs- biconcave centre increases surface area for oxygen exchange and the thicker edges give a large volume that allows room for haemoglobin molecules
• Heart


  • The pump that pushes the blood around the body
  • Located between two lungs in the mediastinum, behind and slightly to the left of the sternum
  • Conical shape approx. 12cm long, 9cm widest point, 6cm thick making it the size of an adult human fist
  • Completely enclosed in a membrane called the pericardium
  • Wall of heart itself is made up of a special type of muscle called cardiac muscle
  • Left and right sides of heart are separated by a wall called the septum
• Chambers of the heart

  • Right atrium receives blood from body and passes to right ventricle
  • Right ventricle pumps blood to lungs
  • Left atrium receives blood from lungs and passes to left ventricle
  • Left ventricle pumps blood into body
• Atrioventricular valves


  • Flaps of tissue with edges attached by tendons (chordae tendineae) to papillary muscles
  • When ventricles contract, the blood catches behind the flaps and the billow out like a parachute, sealing off the opening between the atria and the ventricles
• Semilunar valves


  • Valves where the arteries leave the heart, have three cusps
  • When blood flows into the artery, the cusps fill out and seal of the artery, ensuring that the blood only flows in one direction
• The closing of the valves gives the heartbeats their characteristic 'lub dub' sound
• Blood flow regulation

  1. By changing the output of blood from the heart

  2. By changing the diameter of the blood vessels supplying the tissues
• Cardiac cycle

  1. Pumping phase when heart muscle contracts is called systole

  2. Filling phase as heart muscle relaxes is called diastole

  3. Atrial systole forces remaining blood into ventricles

  4. Ventricular systole forces blood into arteries
• Cardiac output


  • The amount of blood leaving one of the ventricles every minute
  • Equals the stroke volume (volume of blood forced from a ventricle with each contraction) multiplied by the heart rate (number of beats per minute)
• Types of blood vessels

  • Arteries
  • Capillaries
  • Veins
• Arteries


  • Blood vessels that carry blood away from the heart
  • Walls contain smooth muscle and elastic fibres
  • Elastic recoil keeps the blood moving and maintains the pressure
  • Muscle can contract to reduce the diameter of the artery and thus reduce blood flow (vasoconstriction)
  • Muscle can relax to increase blood flow to an organ (vasodilation)
• Arterioles


  • Very small arteries that supply blood to the capillaries, have smooth muscle in their walls
  • Contraction or relaxation of this muscle is very important in regulating blood flow through the capillaries
• As body exercises


  Muscle cells require more energy, producing wastes like carbon dioxide and lactic acid that act as vasodilators, increasing blood flow
• Vasoconstriction


  Contraction of blood vessels to reduce blood flow to an organ
• Vasodilation


  Relaxation of blood vessels to increase blood flow to an organ
• Blood flow control


  Allow for the changing needs of the body
• Arteries

  • Very large arteries that receive blood pumped by ventricles divide into smaller arteries
  • These in turn divide into very small arteries, known as arterioles
• Arterioles


  • Supply blood to the capillaries, have smooth muscle in their walls
  • Contraction or relaxation of this muscle is very important in regulating blood flow through the capillaries
• As body exercises


  Muscle cells continually require energy
• Cellular respiration in muscle cells

  1. Makes energy available

  2. Produces waste including carbon dioxide and lactic acid
• Wastes from cellular respiration


  Act as vasodilators, substances that produce local widening or dilation of arterioles