Mass transport

• Atria


  Thin muscular walls receiving low pressure blood returning to the heart in veins

  
• Ventricles


  Thick muscular walls contract to move blood at high pressure into arteries

  
• Right atrium


  Receives deoxygenated blood from the body, (except the lungs) via the vena cavae

  
• Right ventricle


  Contracts to move deoxygenated blood into the pulmonary artery leading to the lungs

  
• Left atrium


  Receives oxygenated blood from the lungs via the pulmonary veins
• Left ventricle


  Contracts to move oxygenated blood into the aorta leading to the rest of the body

  
• Left ventricle


  • Has a much thicker muscular wall than the right ventricle
  • Produces a greater pressure, because it has to pump blood a greater distance i.e. to all parts of the body
  • The right ventricle only supplies blood to the lungs

  
• Cardiac cycle


  1. Left atrium contracts

  2. Left ventricle contracts

  3. Pressure in left ventricle increases above aorta, opening aortic valve

  4. Left ventricle relaxes, aortic valve closes

  5. Pressure in left ventricle falls below atrium, atrio-ventricular valve opens

  
• Atrio-ventricular valves


  • Open when the atria contract and the pressure in the atria is greater than in the ventricles
  • Close as the ventricles contract, preventing back-flow of blood into the atria

  
• Tendinous cords


  Prevent the Atrio-ventricular valves 'turning inside out' as the ventricular pressure increases above that in the atria

  
• Semilunar valves


  • Open to allow blood into the pulmonary artery and aorta as the ventricles contract
  • Close as the ventricles relax, preventing backflow of blood into ventricles

  
• Cardiac output


  The volume of blood pumped out of one ventricle per minute
• Stroke volume


  The volume of blood (cm3) expelled from the left ventricle of the heart per contraction (beat)

  
• Heart rate


  The number of contractions (beats) per minute
• During exercise


  • The rate at which venous blood returns to the heart increases
  • The cardiac muscle contracts more strongly, pumping out an increased volume of blood per beat (stroke volume increases)
  • The heart rate also increases

  
• Regular exercise


  • Causes the heart muscle to produce stronger contractions and the ventricles to be larger in size and volume
  • This leads to an increased stroke volume and a reduction in the resting heart rate

  
• Risk factors for cardiovascular disease

  • Smoking
  • High blood pressure
  • High blood cholesterol levels
  • Prolonged stress
  • Genetic factors
  • Lack of exercise
• Risk factor


  Anything that increases the chance of getting a disease
• The circulatory or cardiovascular system consists of the heart (cardiac) and blood vessels (vascular = transport)
• In mammals there is a double circulatory system - blood is pumped from the heart (right ventricle) to the lungs and returns to the heart (pulmonary circulatory system) before being pumped (left ventricle) to the rest of the body (systemic circulatory system)

  
• The coronary arteries branch off from the aorta and supply oxygen and glucose to the heart muscle
• Arteries


  • Carry blood away from the heart at high blood pressure
  • The aorta has a large amount of elastic tissue that stretches when the left ventricle contracts, retaining some of the blood forced out
  • When the left ventricle relaxes the artery wall recoils due to its elasticity and forces blood to the body tissues

  
• Arterioles


  • Can control the flow of blood to different tissues or organs by contraction or relaxation of the smooth muscle in their wall

  
• Veins


  • Carry blood under low pressure towards the heart
  • The walls are thinner than arteries and contain less elastic fibres and smooth muscle
  • Veins have semi-lunar valves at intervals, preventing back-flow ensuring blood travels in one direction towards the heart

  
• Capillaries


  • The walls are one endothelial cell thick, giving a very short diffusion pathway for the exchange of substances with the tissues
  • Gaps between the endothelial cells increase the permeability of the capillary
  • There are very large numbers of capillaries and they are highly branched, giving a large surface area for exchange with the tissues
  • The total cross-sectional area of capillaries is very high producing a large frictional resistance, reducing the rate of blood flow, allowing more time for the exchange of substances
• Veins


  • Have semi-lunar valves at intervals, preventing back-flow ensuring blood travels in one direction towards the heart
  • Contracting muscles in the legs and body press on the veins and squeeze the blood along

  
• Capillaries


  • Walls are one endothelial cell thick, giving a very short diffusion pathway for the exchange of substances with the tissues
  • Gaps between the endothelial cells increase the permeability of the capillary
  • Very large numbers and highly branched, giving a large surface area for exchange with the tissues
  • Total cross-sectional area is very high producing a large frictional resistance, reducing the rate of blood flow, allowing more time for the exchange of substances
  • No cells are very far from a capillary, giving short diffusion pathways
  • Have a very small diameter and red blood cells are squeezed flat against the capillary wall reducing the distance for diffusion of oxygen
• Blood


  Liquid blood plasma (90% water) with suspended blood cells and dissolved substances

  
• Exchange of substances in capillaries

  1. Blood capillaries supply cells with oxygen, glucose, amino acids, etc. and remove waste products of metabolism

  2. Smaller molecules such as water, glucose, amino acids and ions, pass through the permeable capillary wall (endothelial layer)

  3. Blood cells and large plasma proteins remain in the capillary

  4. Filtered plasma forms tissue fluid which surrounds the body cells

  5. Oxygen, glucose, minerals etc. diffuse into the body cells and carbon dioxide, urea and other metabolic waste diffuse out
• At the arteriole end of a capillary


  The hydrostatic (blood) pressure (due to contraction of the Left Ventricle) is still high

  
• High blood pressure (which forces water out)

  Is greater than the water potential of the blood (which draws water in). As a result filtration of blood plasma occurs

  
• The loss of fluid and high frictional resistance

  Cause a reduction in the blood pressure as blood flows through the blood capillaries

  
• The reduced hydrostatic pressure at the venule end of the capillaries


  Means that the osmotic potential is greater than the blood pressure, and some of the water from tissue fluid is reabsorbed by osmosis into the blood along a water potential gradient

  
• Tissue fluid which enters lymph capillaries

  Is known as lymph

  
• Haemoglobin


  An iron containing pigment, which loosely and reversibly combines with oxygen to form oxyhaemoglobin
• Haemoglobin


  • Each molecule consists of four haem units and four polypeptide chains
  • Each haem unit can combine with one oxygen molecule so that one haemoglobin molecule can transport four oxygen molecules
• Loading, transport and unloading of oxygen

  1. Blood entering lung capillaries is deoxygenated

  2. Alveoli contain a high concentration of oxygen, giving a concentration gradient for the diffusion of oxygen through the epithelium of the alveolus and the endothelium of the capillary. The oxygen enters the red blood cells and combines with haemoglobin to form oxyhaemoglobin

  3. Oxygen is carried away by the blood, maintaining a concentration gradient

  4. In the body tissues respiration uses oxygen, and oxyhaemoglobin releases oxygen which diffuses into the respiring cells
• Oxyhaemoglobin Dissociation Curve


  Shows the relationship between the amount of oxygen carried by haemoglobin and the partial pressure of oxygen in the surrounding environment (e.g. lungs or body tissues)
• Oxyhaemoglobin Dissociation Curve


  • Has a characteristic shape due to the uptake of an oxygen molecule increasing the affinity of the remaining haem units to take up oxygen - known as the cooperative nature of oxygen binding
  • The binding of the first oxygen molecule changes the tertiary/quaternary structures of haemoglobin, uncovering the binding site of the next haem unit allowing the next oxygen molecule to bind
• Bohr Effect


  The decrease in pH produced as carbon dioxide dissolves in the blood plasma to form an acid, which depresses the O2 dissociation curve i.e. it moves to the right – and haemoglobin releases more oxygen to respiring tissues