Exchange

Exchange

1. Exchange Surfaces

   • Organisms exchange substances with it's environment
     • Cells take in oxygen/nutrients
     • Cells excrete waste products
       • CO2/Urea
   • Surface area to volume ratio
     • Larger an organism gets, surface area is smaller compared to volume
     • Single celled organisms have a large SA:V
       • Short diffusion distances
     • Multicellular organisms
       • Large diffusion distance
       • Low SA:V
       • More active
         • Higher need for exchange
   • Gaseous Exchange
     • Trachea = windpipe
       • Splits into 2 bronchi, leading to each lung
         • Each bronchus branches into bronchioles
           • End in alveoli where exchange takes place
     • Alveoli
       • Surrounded by capillaries
       • Single layer of thin, flat cells - alveolar epithelium
         • Short diffusion distance
       • Walls contain elastic fibres
       • O2 diffuses from alveoli, across epithelium + endothelium and into haemoglobin in capillaries
       • CO2 diffuses from capillaries, across epithelium + endothelium and into alveoli
         • After entering alveolar space, CO2 is breathed out
     • Lungs
       • Many alveoli
         • Large surface area
         • Alveolar epithelium and capillary endothelium only 1 cell thick
           • Short diffusion distance
         • Good blood supply from capillaries
           • Maintaining steep concentration gradient
       • Diaphragm and intercostal muscles maintain concentration gradients
     • Features
       • Goblet cells
         • Secrete mucus trapping microorganisms and dust particles
           • Prevent them reaching alveoli
       • Cilia
         • Waft mucus up airway where it is swallowed
           • Prevents lung infection
       • Elastic fibres
         • Stretched = breathing in, recoil = push air out when exhaling
       • Smooth muscle
         • Controls diameter of airways, so less resistance to airflow
       • Cartilage
         • Walls of trachea + bronchi
         • Strong and flexible to stop collapse of airways when you breathe in
         • Provides support

2. Ventilation

   • Inspiration
     • 1) Intercostal and diaphragm muscles contract
     • 2) Ribcage moves upwards and outwards
     • 3) Diaphragm increasing volume of thorax
     • 4) Lung pressure decreases below atmospheric pressure
     • 5) Air flows into lungs
     • Requires energy
   • Expiration
     • 1) Intercostal and diaphragm muscles relax
     • 2) Ribcage moves downwards and inwards
     • 3) Diaphragm becomes curved, decreasing volume in thorax
     • 4) Lung pressure increases to above atmospheric pressure
     • 5) Air forced out of lungs
     • Does not require energy
   • Spirometers
     • Oxygen filled chamber with lid
     • Breathing in/out = the lid moves up and down
       • Recorded by pen on a rotating drum = spirometer trace
     • Soda lime in breathing tube
       • Absorbs carbon dioxide
     • Nose clip to prevent breathing through nose
     • Airtight, no leaks
     • Secure and sterilised mouthpiece
     • Tidal volume
       • Volume of air in each breath
     • Vital capacity
       • Maximum volume of air breathed in/out
     • Breathing rate
       • How many breaths taken per minute
     • Oxygen uptake
       • Rate of person uses up oxygen

3. Transport in Animals

   • Circulatory system
     • Single
       • Blood passes through heart once for each complete circuit of the body
       • Fish
         • Heart pumps blood to gills then to rest of body
     • Double
       • Blood passes through the heart twice for each complete circuit of the body
       • Mammals
         • Pulmonary system sends blood to lungs
         • Systemic system sends blood to the rest of the body
     • Closed
       • Blood inside vessels
     • Open
       • Blood flows freely through body cavity
       • Insects
   • Heart
     • Structure
       • Right
         • Inferior vena cava
         • Superior vena cava
         • Pulmonary artery
         • Semi lunar valve
         • Ventricle
         • Artium
         • Tricuspid valve
         • Tendons
       • Left
         • Aorta
         • Pulmonary vein
         • Atrium
         • Semi lunar valve
         • Bicuspid valve
         • Tendons
         • Ventricle
       • Coronary arteries covering heart surface
         • Provide heart with oxygenated blood supply
       • Cardiac muscle
         • Contracts creating high pressure
         • Left ventricle has thicker muscular walls
           • Pumps blood all way round body
         • Ventricles have thicker walls than atria
           • Pump blood further distance
     • Cycle
       • 1) Ventricles relax
       • 2) Atria fill with blood
         • Increasing pressure
       • 3) Pressure opens atrioventricular valves
       • 4) Blood flows into ventricles
       • 5) Atria contract
         • Increasing pressure forcing blood out
       • 6) Ventricles contract and artria relax
       • 7) High pressure in ventricles
         • Atrioventricular valves close
         • Semi lunar valves open
       • 8) Blood forced into artery
       • 9) Ventricles and atria relax
       • 10) High pressure in artery
         • Closes semi lunar valves
       • 11) Atria fill with blood due to high pressure in vein
     • Electrical Activity
       • Control of Heartbeat
         • Cardia muscle is myogenic
           • Can contract/relax without signals from nerves
         • 1) Sino atrial node in right atrium sends wave of excitement over atrial walls
           • Right and left atria contract at same time
         • 2) Non-conducting collagen tissue prevents wave passing to ventricles
           • Causes delay so atria empty before ventricles contract
         • 3) Waves transferred from SAN to atrioventricular node
         • 4) Bundle of HIS conduct waves of electrical activity to purkyne tissue in ventricle walls
         • 5) Purkyne tissue carries waves into ventricle walls
           • Contract up from apex simultaneously
       • Electrocardiograms
         • Checks heart functioning
         • Heart muscle loses electrical charge when contracting (depolarises)
         • Heart muscle regains electrical charge when relaxing (repolarises)
         • Electrocardiograph records changes in electrical charge
           • Electrodes placed on chest
         • 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
         • Heart rate (bpm) = 60/time taken for 1 heart beat
         • 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
   • Blood Vessels
     • Arteries
       • Carry blood from heart to body
       • Thick muscular walls
       • Elastic tissue to withstand high pressure
       • Endothelium folded allowing artery to expand
         • Withstand high pressure
       • Carry oxygenated blood
         • Pulmonary artery carries deoxygenated blood to lungs
       • High pressure
     • Capillaries
       • Branched from arteries
       • Walls one cell thick
         • Quick diffusion
     • Veins
       • Low pressure
       • Carry blood back to heart
       • Wide lumen
       • Valves to prevent backflow
       • Carry deoxygenated blood
       • Pulmonary veins carry oxygenated blood to heart from lungs
   • Tissue fluid
     • Surrounds cells in tissues
     • Cells take in oxygen and nutrients in from tissue fluid and release metabolic waste into it
     • Pressure filtration
     • Pressure filtration
       • Capillary bed
         • Network of capillaries in an area of tissue
         • Substances move out of capillaries into tissue fluid by pressure filtration
         • 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
     • Does not contain red blood cells/large proteins
       • Too large to be pushed through capillary walls
     • Lymph vessels
       • Fluid that does not re-enter capillaries at end of bed passes into lymph vessels
         • Called lymph when inside
       • Valves in lymph vessels stop it going backwards
         • Moves toward main lymph vessels in thorax, returning to blood
       • Contains white blood cells, solutes and has high water potential
   • Haemoglobin
     • Found in red blood cells, carrying oxygen around the body
     • Large protein, quaternary structure with 4 polypeptide chains
       • Each chain has a haem group with iron
       • Each haemoglobin molecule can carry 4 oxygen molecules
     • Lungs
       • Oxygen joins to iron in hb to form oxyhaemoglobin
         • Joining = association
     • Body cells
       • Oxygen leaves oxyhaemoglobin and turns back to hb
         • Leaves = disassociation
     • Affinity
       • Tendency a molecule has to bind with oxygen
       • Depends on conditions such as partial pressure of oxygen
       • pO2 = measure of oxygen concentration
         • Higher concentration of dissolved oxygen in cells = higher partial pressure
         • As pO2 increases = hb's affinity for oxygen increases
         • Oxygen associates with hb to form oxyhaemoglobin with high pO2
         • Oxyhaemoglobin disassociates oxygen with lower pO2
         • Alveoli
           • Have high pO2 = oxygen associates with hb
         • Respiring tissue
           • Low pO2 = oxygen dissociates from hb
     • Curves
       • Dissociation
         • Shows how saturated hb is with oxygen at any given pO2
         • 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
       • Fetal Haemoglobin
         • Higher affinity for oxygen than adult hb
         • Fetus gets oxygen from mother's blood across placenta
           • By reaching placenta, saturation of hb has decreased
             • Some used up by mother's body
         • Placenta has low pO2 = adult hb will dissociate it's oxygen
         • Fetal hb becomes more saturated in lower pO2 than adult hb
         • Left of adult dissociation curve
       • Carbon dioxide concentration
         • 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
         • Respiring cells release CO2, increasing rate of oxygen dissociation
         • S curve shifts right
         • 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