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Exchange

Exchange Surfaces
1. Organisms exchange substances with it's environment
  1. Cells take in oxygen/nutrients
  2. Cells excrete waste products
    1. CO2/Urea
2. Surface area to volume ratio
  1. Larger an organism gets, surface area is smaller compared to volume
  2. Single celled organisms have a large SA:V
    1. Short diffusion distances
  3. Multicellular organisms
    1. Large diffusion distance
    2. Low SA:V
    3. More active
      1. Higher need for exchange
3. Gaseous Exchange
  1. Trachea = windpipe
    1. Splits into 2 bronchi, leading to each lung
      1. Each bronchus branches into bronchioles
        End in alveoli where exchange takes place
  2. Alveoli
    1. Surrounded by capillaries
    2. Single layer of thin, flat cells - alveolar epithelium
      1. Short diffusion distance
    3. Walls contain elastic fibres
    4. O2 diffuses from alveoli, across epithelium + endothelium and into haemoglobin in capillaries
    5. CO2 diffuses from capillaries, across epithelium + endothelium and into alveoli
      1. After entering alveolar space, CO2 is breathed out
  3. Lungs
    1. Many alveoli
      1. Large surface area
      2. Alveolar epithelium and capillary endothelium only 1 cell thick
        Short diffusion distance
      3. Good blood supply from capillaries
        Maintaining steep concentration gradient
    2. Diaphragm and intercostal muscles maintain concentration gradients
  4. Features
    1. Goblet cells
      1. Secrete mucus trapping microorganisms and dust particles
        Prevent them reaching alveoli
    2. Cilia
      1. Waft mucus up airway where it is swallowed
        Prevents lung infection
    3. Elastic fibres
      1. Stretched = breathing in, recoil = push air out when exhaling
    4. Smooth muscle
      1. Controls diameter of airways, so less resistance to airflow
    5. Cartilage
      1. Walls of trachea + bronchi
      2. Strong and flexible to stop collapse of airways when you breathe in
      3. Provides support
Ventilation
1. Inspiration
  1. 1) Intercostal and diaphragm muscles contract
  2. 2) Ribcage moves upwards and outwards
  3. 3) Diaphragm increasing volume of thorax
  4. 4) Lung pressure decreases below atmospheric pressure
  5. 5) Air flows into lungs
  6. Requires energy
2. Expiration
  1. 1) Intercostal and diaphragm muscles relax
  2. 2) Ribcage moves downwards and inwards
  3. 3) Diaphragm becomes curved, decreasing volume in thorax
  4. 4) Lung pressure increases to above atmospheric pressure
  5. 5) Air forced out of lungs
  6. Does not require energy
3. Spirometers
  1. Oxygen filled chamber with lid
  2. Breathing in/out = the lid moves up and down
    1. Recorded by pen on a rotating drum = spirometer trace
  3. Soda lime in breathing tube
    1. Absorbs carbon dioxide
  4. Nose clip to prevent breathing through nose
  5. Airtight, no leaks
  6. Secure and sterilised mouthpiece
  7. Tidal volume
    1. Volume of air in each breath
  8. Vital capacity
    1. Maximum volume of air breathed in/out
  9. Breathing rate
    1. How many breaths taken per minute
  10. Oxygen uptake
    1. Rate of person uses up oxygen
Transport in Animals
1. Circulatory system
  1. Single
    1. Blood passes through heart once for each complete circuit of the body
    2. Fish
      1. Heart pumps blood to gills then to rest of body
  2. Double
    1. Blood passes through the heart twice for each complete circuit of the body
    2. Mammals
      1. Pulmonary system sends blood to lungs
      2. Systemic system sends blood to the rest of the body
  3. Closed
    1. Blood inside vessels
  4. Open
    1. Blood flows freely through body cavity
    2. Insects
2. Heart
  1. Structure
    1. Right
      1. Inferior vena cava
      2. Superior vena cava
      3. Pulmonary artery
      4. Semi lunar valve
      5. Ventricle
      6. Artium
      7. Tricuspid valve
      8. Tendons
    2. Left
      1. Aorta
      2. Pulmonary vein
      3. Atrium
      4. Semi lunar valve
      5. Bicuspid valve
      6. Tendons
      7. Ventricle
    3. Coronary arteries covering heart surface
      1. Provide heart with oxygenated blood supply
    4. Cardiac muscle
      1. Contracts creating high pressure
      2. Left ventricle has thicker muscular walls
        Pumps blood all way round body
      3. Ventricles have thicker walls than atria
        Pump blood further distance
  2. Cycle
    1. 1) Ventricles relax
    2. 2) Atria fill with blood
      1. Increasing pressure
    3. 3) Pressure opens atrioventricular valves
    4. 4) Blood flows into ventricles
    5. 5) Atria contract
      1. Increasing pressure forcing blood out
    6. 6) Ventricles contract and artria relax
    7. 7) High pressure in ventricles
      1. Atrioventricular valves close
      2. Semi lunar valves open
    8. 8) Blood forced into artery
    9. 9) Ventricles and atria relax
    10. 10) High pressure in artery
      1. Closes semi lunar valves
    11. 11) Atria fill with blood due to high pressure in vein
  3. Electrical Activity
    1. Control of Heartbeat
      1. Cardia muscle is myogenic
        Can contract/relax without signals from nerves
      2. 1) Sino atrial node in right atrium sends wave of excitement over atrial walls
        Right and left atria contract at same time
      3. 2) Non-conducting collagen tissue prevents wave passing to ventricles
        Causes delay so atria empty before ventricles contract
      4. 3) Waves transferred from SAN to atrioventricular node
      5. 4) Bundle of HIS conduct waves of electrical activity to purkyne tissue in ventricle walls
      6. 5) Purkyne tissue carries waves into ventricle walls
        Contract up from apex simultaneously
    2. Electrocardiograms
      1. Checks heart functioning
      2. Heart muscle loses electrical charge when contracting (depolarises)
      3. Heart muscle regains electrical charge when relaxing (repolarises)
      4. Electrocardiograph records changes in electrical charge
        Electrodes placed on chest
      5. One full heartbeat consists of P wave, QRS complex and T wave
        P wave - contraction of atria
        QRS complex - contraction of ventricles
        T wave - relaxation of ventricles
      6. Heart rate (bpm) = 60/time taken for 1 heart beat
      7. Abnormalities
        Fast heart rate
        Shows heart isn't pumping blood efficiently
        Ok in exercise
        Ventricle problems
        Some P waves not followed by QRS complex
        Impulses from AVN not travelling from atria to ventricles
        Fibrillation
        Irregular heartbeat
        Loss of rhythm of ventricles/atria
        Can result to fainting/chest pain
3. Blood Vessels
  1. Arteries
    1. Carry blood from heart to body
    2. Thick muscular walls
    3. Elastic tissue to withstand high pressure
    4. Endothelium folded allowing artery to expand
      1. Withstand high pressure
    5. Carry oxygenated blood
      1. Pulmonary artery carries deoxygenated blood to lungs
    6. High pressure
  2. Capillaries
    1. Branched from arteries
    2. Walls one cell thick
      1. Quick diffusion
  3. Veins
    1. Low pressure
    2. Carry blood back to heart
    3. Wide lumen
    4. Valves to prevent backflow
    5. Carry deoxygenated blood
    6. Pulmonary veins carry oxygenated blood to heart from lungs
4. Tissue fluid
  1. Surrounds cells in tissues
  2. Cells take in oxygen and nutrients in from tissue fluid and release metabolic waste into it
  3. Pressure filtration
  4. Pressure filtration
    1. Capillary bed
      1. Network of capillaries in an area of tissue
      2. Substances move out of capillaries into tissue fluid by pressure filtration
      3. Start of capillary bed
        Nearest arteries
        Hydrostatic pressure inside capillaries is greater than in tissue fluid
        Difference forces fluid out of capillaries, into space around cells = tissue fluid
        Reduces pressure in capillaries so at end of bed, hydrostatic pressure is low
        Fluid loss = water potential at end of bed is lower than in tissue fluid
        Water enters capillaries from tissue fluid at end by osmosis
  5. Does not contain red blood cells/large proteins
    1. Too large to be pushed through capillary walls
  6. Lymph vessels
    1. Fluid that does not re-enter capillaries at end of bed passes into lymph vessels
      1. Called lymph when inside
    2. Valves in lymph vessels stop it going backwards
      1. Moves toward main lymph vessels in thorax, returning to blood
    3. Contains white blood cells, solutes and has high water potential
5. Haemoglobin
  1. Found in red blood cells, carrying oxygen around the body
  2. Large protein, quaternary structure with 4 polypeptide chains
    1. Each chain has a haem group with iron
    2. Each haemoglobin molecule can carry 4 oxygen molecules
  3. Lungs
    1. Oxygen joins to iron in hb to form oxyhaemoglobin
      1. Joining = association
  4. Body cells
    1. Oxygen leaves oxyhaemoglobin and turns back to hb
      1. Leaves = disassociation
  5. Affinity
    1. Tendency a molecule has to bind with oxygen
    2. Depends on conditions such as partial pressure of oxygen
    3. pO2 = measure of oxygen concentration
      1. Higher concentration of dissolved oxygen in cells = higher partial pressure
      2. As pO2 increases = hb's affinity for oxygen increases
      3. Oxygen associates with hb to form oxyhaemoglobin with high pO2
      4. Oxyhaemoglobin disassociates oxygen with lower pO2
      5. Alveoli
        Have high pO2 = oxygen associates with hb
      6. Respiring tissue
        Low pO2 = oxygen dissociates from hb
  6. Curves
    1. Dissociation
      1. Shows how saturated hb is with oxygen at any given pO2
      2. S shaped curve
        When hb first combines with oxygen, it's shape alters so it's easier for other molecules to join
        As hb becomes more saturated, shape makes it harder for other oxygen molecules to join
        Curve steeps in the middle where it is easy for oxygen to join
        Less steep at ends where it is harder for oxygen to join
    2. Fetal Haemoglobin
      1. Higher affinity for oxygen than adult hb
      2. Fetus gets oxygen from mother's blood across placenta
        By reaching placenta, saturation of hb has decreased
        Some used up by mother's body
      3. Placenta has low pO2 = adult hb will dissociate it's oxygen
      4. Fetal hb becomes more saturated in lower pO2 than adult hb
      5. Left of adult dissociation curve
    3. Carbon dioxide concentration
      1. partial pressure of CO2 is a measure of concentration of CO2 in a cell
        pCO2 affects oxygen dissociation
        Hb gives up it's oxygen more at higher pCO2
      2. Respiring cells release CO2, increasing rate of oxygen dissociation
      3. S curve shifts right
      4. Bohr effect
        10% of CO2 produced binds with hb and carried to lungs
        90% of CO2 produced diffuses into red blood cells, converted to carbonic acid by carbonic anahydrase enzyme
        Carbon acid splits to give hydrogen and hydrogencarbonate ions
        More hydrogen ions = oxyheamoglobin dissociates to take up ions
        Forming haemoglobinic acid
        Prevents cell from becoming more acidic
        Hydrogencarbonate ions diffuse out of red blood cells into blood plasma
        At lungs, the low pCO2 causes hydrogencarbonate and hydrogen ions to recombine to CO2
        Then diffuses into alveoli to be breathed out

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	Created by Gemma Bradford almost 11 years ago