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Exchange and transport

A-level exchange and transport summary
by

Edward Ward`

on 15 December 2012

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Transcript of Exchange and transport

Exchange and Transport Exchange surfaces
Large surface area
Thin diffusion distance
Permeable membrane
Maintain concentration gradient
Moist (only helps gases) Lungs Adaptations
Large surface area - alveoli
Moist surfaces
Thin diffusion distance - 2 cells thick
Maintained concentration gradient - blood flow through capilleries
Membranes permeable to oxygen and Carbon dioxide Alveoli Thin diffusion distance allows for faster diffusion
Constant blood flow maintains concentration gradient
breathing brings more oxygen to alveoli and removes carbon dioxide Lung capacity Tidal volume - volume in and out with each breath
Inspiratory reserve volume - how much can breathed in above tidal volume
Exspiratory reserve volume - how much can be breathed out above tidal volume
Vital capacity - largest volume of air in and out in 1 breath
Residual volume - amount of air always left in lungs
Dead space - Air in bronchi, bronchioles and trachea
Total lung capacity - Residual volume + Vital capacity Spirometers
Chamber filled with oxygen on a tank of water
person breathes from disposable mouthpiece
Oxygen taken from chamber when breathing in - chamber lowers
Breathing out puts some oxygen back into chamber - chamber raises
Movements of chamber recorded and plotted as a spirometer trace Soda lime prevents a build up of carbon dioxide in the spirometer
Volume of gas in chamber decreases as carbon dioxide removed
Can use this information to calculate the amount of oxygen used Bronchioles Trachea and Bronchi Narrower than bronchi
Large bronchioles may contain some cartilage
Small bronchioles do not contain cartilage
Wall mostly made of smooth muscle and elastic fibres
Smallest bronchioles have alveoli at end Mostly cartilage
Form incomplete C rings
On inner surface of cartilage is a layer of:
Glandular tissue
Connective tissue
Elastic fibres
Smooth muscle
Blood vessels
(called loose tissue)
Inner lining made up of:
Ciliated epithelial cells
Goblet cells Tissues in lungs Bronchioles Trachea and Bronchi Narrower than bronchi
Large bronchioles may contain some cartilage
Small bronchioles do not contain cartilage
Wall mostly made of smooth muscle and elastic fibres
Smallest bronchioles have alveoli at end Mostly cartilage
Form incomplete C rings
On inner surface of cartilage is a layer of:
Glandular tissue
Connective tissue
Elastic fibres
Smooth muscle
Blood vessels
(called loose tissue)
Inner lining made up of:
Ciliated epithelial cells
Goblet cells Tissues in lungs Oxygen is carried in erythrocytes in haemoglobin
Haemoglobin is very complicated molecule
Made of 4 subunits
Subunit made up of polypeptide and a haem (non- protein) group
Haem group contains single Fe 2+ ions
Haem group has an affinity for oxygen
4 subunits = 4 Fe 2+ ions
Each Fe 2+ binds to 1 O₂ molecule
1 haemoglobin can carry 4 O₂ molecules Carriage of Oxygen Not all tissue fluid returns to the capillaries
Some is drained away into the lymphatic system
Lymphatic system consists of a number of vessels similar to capillaries
Eventually its returned to the blood in the chest cavity

Lymph is similar to tissue fluid
Lymph contains less oxygen and nutrients
Lymph also contains more CO₂
Lymph contains more fatty material absorbed from the intestines
Lymph contains many lymphocytes
Lymphocytes produced in lymph nodes Formation of lymph Small creatures have a large surface area to volume ratio (SA:V)
Because of the large SA:V diffusion is effective for transporting substances around creatures

Large creatures have a smaller SA:V
Therefore diffusion is not effective for transporting substances around the body
Takes too long, too slow
Larger creatures have evolved transport systems to solve this problem Surface area to volume ratio Transport in animals Change in shape allows more O₂ to diffuse into haemoglobin and associate with other haem groups relatively easily
Explains rapid increase in % saturation of haemoglobin Ability of haemoglobin to take up O₂ depends on oxygen tension At low oxygen tensions haemoglobin doesn’t readily take up O₂
Haem group at centre of molecule
Difficult for O₂ to reach haem group
Low saturation at low oxygen tension as diffusion gradient isn’t very steep Ability of haemoglobin to take up O₂ depends on oxygen tension Amount of oxygen in air expressed as pressure created by presence of O₂ measured in Kpa

Taking up oxygen
O₂ molecules diffuse into blood plasma
O₂ taken up by haemoglobin and out of solution, maintains steep concentration gradient
Allows more O₂ to diffuse into blood to be taken up by haemoglobin Oxygen tension (partial pressure) KPa Features of Blood, tissue fluid and lymph Composed of similar substances to blood
Missing: Plasma proteins Most of the cells found in blood
Tissue fluid bathes of the cells in the body
Tissue fluid carries substances to a from the blood Tissue fluid 1 cell thick
Made of squamous epithelial cells
Lumen only wide enough for 1 red blood cell
Red blood cell pressed against sides of capillary
Short diffusion distance Capilleries P = Atrial systole
Q,R&S = Ventricular systole
T = diastole The electrical activity of the heart can be monitored
Sensors placed on skin can pick up electrical excitation created by heart
Shape of ECG can indicate when part of the heart muscle is not healthy
Heart muscle respire fatty acids and must have a continuous supply of oxygen
Blood clot starves part of heart of oxygen and cells die Electrocardiograms (ECG) Made of cardiac muscle
Multi nucleic
Branched fibres
Help spread electrical impulses
Conducts electrical impulses
Similar to nerve cells
Coronary artery provides heart with blood supply The mammalian heart Haemoglobin of mammalian foetus has a higher affinity for O₂
Foetal haemoglobin must be able to take O from mother’s blood
Foetal haemoglobin must have a higher O affinity to take O from mother’s blood
O2 dissociates into placenta
Placenta has a low oxygen tension
Foetal haemoglobin takes up oxygen and returns to foetus
Maintains oxygen tension gradient Foetal haemoglobin 3rd O₂ bonding makes O₂ tension gradient very shallow
Makes it difficult for 4th O₂ to bind to haemoglobin
Need a very high O₂ tension for 4th O₂ to bind to haemoglobin
The lungs are one of the only places where it is possible to achieve 100% saturation Ability of haemoglobin to take up O₂ depends on oxygen tension As oxygen tension rises diffusion gradient into haemoglobin increases
Eventually O₂ molecule associates with haem group
Binding of O₂ molecule changes shape of haemoglobin molecule
Exposes haem groups of other chains Ability of haemoglobin to take up O₂ depends on oxygen tension Things in plasma Erythrocytes (Red Blood Cells)
Leucocytes (White Blood Cells)
platelets Cells in Blood Blood contents Sinoatrial node (SAN/1) generates electrical impulses
Electrical impulses spread over atria and make them contract
Disc of non-conducive tissue prevents spread of impulses to ventricles
Atriventricular node (AVN/3) at top of septum delays electrical impulses
Allows time for atria to finish contracting and for blood to flow down into ventricles
Electrical impulses travel down purkyne tissue (4/5)
Purkyne tissue is specially adapted muscle fibres that conduct the wave of excitation from the AVN to the base of the ventricles
Ventricles begin contracting from base so blood is pushed upward Control of the cardiac cycle Double circulatory system Blood flows from heart to organ of gas exchange then to rest of body
Blood pressure drops as it passes through capillaries
Suitable for slow creatures such as fish, but not for active creatures like humans Single circulatory system Single and double circulatory systems Where tissues are respiring there is less O₂ and more CO₂
CO₂ reacts with H₂O to form carbonic acid (H₂CO₃)
More CO₂ in blood more carbonic acid forms
More carbonic acid forms more H+ and HCO₃- ions
More H+ bonds to oxyhaemoglobin and more O₂ is released

When more CO₂ is present less O₂ is held by the haemoglobin so the O₂ affinity of the haemoglobin decreases so it shifts down to the right The effect of CO₂ concentration on the affinity of haemoglobin for O₂ The Bohr effect Vein Venule Capillaries Arteriole Artery Blood is under high hydrostatic pressure
Fluid forced out of capillaries through small gaps
Fluid and dissolved substances leave capillaries
Large molecules and cells left behind
Dissolved substances enter cells of tissues by diffusion Formation of tissue fluid Open circulatory system Blood stays entirely inside vessels
Separate fluid, tissue fluid, bathes all cells and tissues
Blood pumped at higher pressure
Blood flows faster Closed circulatory system Circulatory systems Large lumen to ease blood flow
Squamous epithelial cells provide a smooth lining to help blood flow
Veins contain valves to prevent blood flowing downward due to gravity
Elastic fibres allow veins to be flattened by surrounding skeletal muscle and return to their original shape
Flattening of veins apples pressure to blood so it moves toward the heart
Takes blood to heart at low pressure Squamous epithelial cells provide smooth lining for easier blood flow
Collagen adds strength to withstand high pressure
Smooth muscle constricts to increase pressure to aid blood flow
Constricts when heart is relaxing to maintain high pressure
Elastic fibres allow artery to return to its original shape when the smooth muscle stops constricting
Takes blood away from heart at high pressure Blood vessels Ventricular systole
Walls of ventricles contract from bottom up
Blood pushed upward
Atrioventricular valves close when pressure in ventricles is greater than the pressure in the atria
semi-lunar valves open when ventricle pressure is greater than artery pressure Atria systole
Atria contract
Blood pushed into ventricles Diastole
Atria and ventricles relax, internal volume increases, pressure drops
Blood flows into heart from major veins (vena cava, pulmonary vein)
Blood flows into atria and ventricles Cardiac cycle – describes sequence of events in a heart beat Carbonic acid Formation of HCO₃- ions
CO₂ + H₂O = H₂CO₃
Made in erythrocytes with help of carbonic anhydrase

H+ and HCO₃- ions dissociate from one another

HCO₃- ions diffuse out of red blood cell

Cl- ions move into red blood cell from plasma during chloride shift

To prevent content of red blood cells becoming very acidic H+ ions taken up by haemoglobin and O₂ is dropped Carried in 3 ways:
Dissolved in plasma (5%)
Bonded to haemoglobin as carbaminohaemoglobin (10%)
As HCO₃- ions (85%) Carriage of carbon dioxide Venule Capillaries Arteriole Artery Tissue fluid has some hydrostatic pressure
When tissue fluid hydrostatic pressure > blood hydrostatic pressure the tissue fluid is pushed back into the capillaries
Both the blood and the tissue fluid have a negative water potential
Tissue fluid has a higher Ψ than blood
Water moves back into blood by osmosis down water potential gradient
Combined effect of the osmotic pressure and the hydrostatic pressure of tissue fluid moves the fluid back into the capillaries Returning tissue fluid to blood
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