transport in animal

• Mammalian circulatory system


  • Transport system needed due to low surface area to volume ratio and high oxygen demand
  • Double circulatory system → one loop through the heart and lungs (pulmonary circulation), one loop through the heart and body (systemic circulation)
  • Double circulation means blood is under higher pressure travelling around the body so oxygen is delivered faster for aerobic respiration and a constant body temperature can be maintained
  • Closed system → blood is contained in blood vessels
• Blood transports oxygen, carbon dioxide, glucose, amino acids, urea, hormones, and many other things
• Arteries

  • Carry oxygenated blood from the heart to the body (except pulmonary artery)
  • Outer collagen layer for strength and support
  • Thick layer of smooth muscle provides strength to withstand high blood pressure
  • Elastic tissue layer allows stretch and recoil to maintain and withstand high blood pressure
  • Folded endothelium allows stretching
• Arterioles

  • Carry oxygenated blood
  • Smaller vessels that branch off from arteries and into capillaries
  • Contain muscle tissue which can contract or relax to control blood flow to different areas of the body
• Capillaries

  • Endothelium is one cell thick to give a short diffusion pathway for exchange
  • Site of gas exchange and exchange of other substances
  • Networks of capillaries throughout tissues called capillary beds
  • Large number to increase surface area for exchange
  • Red blood cells in single file to increase surface area in contact with the endothelium
• Veins

  • Carry deoxygenated blood from the body back to the heart (except pulmonary vein)
  • Outer collagen layer for strength and support
  • Wider lumen and less muscle and elastic tissue than arteries because blood pressure is lower
  • Blood under low pressure so valves prevent backflow
  • Closer to body surface than arteries and can appear bulged
• • Venules → small blood vessels carrying deoxygenated blood

  → capillaries converge into venules, venules converge into veins
• Formation of tissue fluid

  • Tissue fluid surrounds cells and exchanges substances with them

  • Small molecules (e.g. water, oxygen, glucose) can leave the capillaries but large molecules (e.g. plasma

  proteins) and red blood cells cannot

  • Blood is under high hydrostatic pressure produced by contraction of the ventricles
• Tissue fluid formation

  1. Arteriole end: Hydrostatic pressure in capillaries is higher than in tissue fluid so fluid is forced out the capillary into intracellular space

  2. Hydrostatic pressure in capillaries decreases across the capillary bed as more fluid is forced out the capillaries

  3. Oncotic pressure from tissue fluid into capillaries increases as plasma protein concentration of blood increases and water potential of blood decreases

  4. Venule end: Fluid loss means that the concentration of large proteins in the blood increases so the water potential of the blood lowers and oncotic pressure increases

  5. Water is drawn back into the capillaries by osmosis
• Lymphatic system

  • Excess tissue fluid drains into lymph vessels (not all fluid re-enters capillaries)

  • Lymph vessels have valves to prevent backflow due to low pressure

  • Lymph fluid gets returned to the blood near the heart
• Blood

  • Red and white blood cells

  • Platelets

  • Proteins

  • Water

  • Dissolved solutes

  (e.g. glucose, salts)
• Tissue fluid

  • Small number of white blood

  cells (e.g. lymphocytes)

  • Water

  • Dissolved solutes

  (e.g. glucose, salts)
• Lymph fluid

  • White blood cells

  (e.g. lymphocytes)

  • Antibodies

  • Water

  • Dissolved solutes

  (e.g. glucose, salts)
• Human heart structure

  • Four chambers with muscular walls → two atria, two

  ventricles

  • Right side pumps deoxygenated blood to the lungs

  • Left side pumps oxygenated blood to the body

  • Walls of ventricles are thicker than walls of atria

  → more contraction force needed to get blood out of the heart

  • Wall of left ventricle is thicker than the right ventricle

  → blood must be under higher pressure to travel round the whole body so stronger contraction is needed
• Atrioventricular (AV) valves


  Prevent backflow of blood
• Semi-lunar (SL) valves

  Prevent backflow of blood
• Left atrioventricular valve

  Bicuspid valve (has two flaps)
• Right atrioventricular valve

  Tricuspid valve (has three flaps)
• Cords

  • Prevent atrioventricular valves being forced into atria
• Coronary arteries


  Supply heart muscle tissue with blood
• Blood flow

  1. Unidirectional

  2. Pressure changes cause valves to open or close

  3. When pressure is higher in the atria than the ventricles the atrioventricular valves open

  4. When pressure is higher in the ventricles than the atria the atrioventricular valves close
• • Stroke volume → volume of blood pumped out of the left

  ventricle during one cardiac cycle (beats per minute)

  • Cardiac output is the volume of blood pumped out of the heart per min (cm3)

  • Cardiac output (cm3 min-1) = stroke volume x heart rate
• Cardiac muscle

  Myogenic - contracts and relaxes without nervous stimulation
• Heart activity

  1. Sino-atrial node (SAN) in wall of right atrium sends out waves of electrical excitation

  2. Atrial walls depolarise and contract

  3. Impulses transferred to atrioventricular node (AVN)

  4. Impulses passed down bundle of His and around Purkyne tissue

  5. Ventricular walls depolarise and contract from bottom up
• A band of non-conducting collagen tissue prevents the depolarisation spreading from the atrial walls to the ventricles
• Cardiac muscle takes a short while to repolarise after depolarisation which means that diastole follows systole
• External structure of the heart

  • Blood vessels may appear branched and crossed over
• Cardiac cycle

  Changes in volume and pressure due to contraction and relaxation of the atria and ventricles
• Ventricular diastole

  1. Atrial systole → volume decreases, pressure increases

  2. Atrioventricular valves are open

  3. Blood forced into ventricles (volume and pressure rise slightly)
• Atrial diastole

  1. Ventricular systole → volume decreases, pressure increases

  2. Atrioventricular valves close

  3. Pressure in arteries is lower than ventricles

  4. Semilunar valves open

  5. Blood forced into aorta and pulmonary artery
• Atrial diastole

  1. Ventricular diastole

  2. Pressure in arteries is higher than ventricles

  3. Semilunar valves close

  4. Blood returns to the atria → volume and pressure increase gradually

  5. Atrioventricular valves open → passive flow from atria to ventricles
• Electrocardiographs

  • Records changes in electrical activity → can see when the heart muscle depolarises and repolarises

  P wave = depolarisation (contraction) of atria → atrial systole

  QRS complex = depolarisation of ventricles → ventricular systole

  T wave = repolarisation (relaxation) of ventricles → diastole
• Tachycardia = fast heart rate

  Bradycardia = slow heart rate

  Ectopic heartbeat = early contraction of the atria or ventricles

  Ventricular fibrillation = irregular contraction of the ventricles

  Atrial fibrillation= irregular contraction of the atria
• Structure and function of Haemoglobin

  • Conjugated protein consisting of four polypeptide chains and four haem groups which contain iron ions

  • Each haemoglobin protein can bind four oxygen molecules to form oxyhaemoglobin (the haem groups bind oxygen) in a reversible reaction

  • Found in erythrocytes (red blood cells)
• Partial pressure of oxygen (pO2)


  Concentration of oxygen
• Haemoglobin

  • Higher affinity for oxygen at high pO2
  • Lower affinity for oxygen at low pO2
• High pO2

  Oxygen loads where there lots of oxygen e.g. at the alveoli
• Low pO2

  Oxygen unloads where oxygen is low e.g. at respiring tissues
• Oxyhaemoglobin dissociation curve


  Shows the percentage saturation of haemoglobin with oxygen at different pO2
• Oxyhaemoglobin dissociation curve

  • S-shaped curve
  • Binding of first oxygen molecule changes the quaternary structure of haemoglobin
  • Another haem group is uncovered for the second oxygen molecule to bind to so it binds more easily