Gas Carriage 1

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  • Created by: LBCW0502
  • Created on: 22-03-19 11:57
Outline the movement of O2 and CO2 in blood (1)
Air enters into alveoli. O2 exchange between alveoli and capillary. O2 transport (left side of the heart, oxygenated blood to the rest of the body). Across capillary endothelium to get to cells. Cells use energy, generate waste products (CO2)
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Outline the movement of O2 and CO2 in blood (2)
CO2 enters bloodstream, transported to right side of the heart, into lungs, out of capillaries, into alveoli, out of the body. Use of pulmonary and systemic capillaries
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State features of the lung capillary interface
Adult lung. Alveoli surrounded by capillary beds. Terminal bronchioles, respiratory bronchioles, alveolar ducts and alveolar sacs and blood vessels
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What are the constant factors for respiratory gases?
SA, membrane thickness and diffusion distance
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What are the variable factors for respiratory gases?
Concentration gradient (most important), pressure gradient, solubility and temperature
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Outline oxygen diffusion in the circulation system (1)
In alveoli, pO2 is 100 mmHg. O2 enters arterial side of blood (pO2 is 100 mmHg). Inside cells (pO2 is 40 mmHg). Pressure difference between arterial end and cell. O2 moves down conc pressure gradient into cell (equilibrate)
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Outline oxygen diffusion in the circulation system (2)
PO2 in venous side is 40 mmHg, returns to alveoli as 40 mmHg (diffuse into arteries)
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Outline carbon dioxide diffusion in the circulation system (1)
PCO2 in cell is >46 mm Hg and PO2 in arterial side is 40 mmHg (CO2 moves down pressure gradient/equilibrate). CO2 pushed out of cell, PCO2 in venous end is 46 mmHg, returns to alveoli (where PCO2 is 40 mmHg) to be released
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State the values for blood gases
PaO2 = 10-14 kPa (~ 90 mmHg ~ 1.75 PSI). PvO2 = 5-5.6 kPa. PaCO2 = 4.5-6 kPa (~ 33.8 mmHg ~ 0.65 PSI). PvCO2 = 5.5 - 6.5 kPa
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Oxygen diffuses over which layers?
Alveolar epithelial cells and capillary endothelial cells -> plasma. Surfactant (in alveolar space), alveolar epithelium, fused basement membranes, nucleus of endothelial cell (0.1-1.5 m), plasma and rbc (capillary lumen)
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What are the two methods for oxygen carriage?
Dissolved (3 mL/L blood) or combined with Hb (197 mL/L blood)
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Describe features of dissolved oxygen in solution (1)
Gas dissolved depends on - partial pressure of gas/solution (increase P gas, increase in gas dissolved), temperature (increase liquid temperature, decrease in gas dissolved). Anaesthesia (balance blend of gases, sedating gas vs oxygen)
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Describe features of dissolved oxygen in solution (2)
Problem - diving as rise (high to low pressure, experience 'bends' dissolved N2 blood out solution)
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Describe the Hb carriage for oxygen transport (1)
O2 transported from alveolus (through capillary endothelium) into arterial blood. O2 dissolved in plasma (~PO2, <2%). O2 in rbc combines with Hb to form Hb.O2 (>98%). Transport to cells. Hb.O2 dissociates to form Hb and O2. Oxygen dissolved in plasma
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Describe the Hb carriage for oxygen transport (2)
O2 enters into cells (used for cellular respiration)
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Describe features of the Hb molecule
4 sub units, each centred around Fe2+, iron atom formed and each binds to an O2 molecule
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Outline the oxygen-haemoglobin dissociation curve
Sigmoid shape. PO2 (mmHg) against Hb saturation (%). 75% Hb saturation at pO2 of 40 mmHg (resting cell). 100% Hb saturation at pO2 of 100 mmHg (alveoli)
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Which factors alter haemoglobin's affinity for oxygen? (1)
Temperature (lower temperature, higher affinity). pH (higher pH, more affinity). Bohr effect (lower pCO2, more affinity), DPG (decreases Hb affinity for O2), foetal Hb (higher affinity for O2 than maternal Hb). Higher affinity/curve shifts to left
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Which factors alter haemoglobin's affinity for oxygen? (2)
DPG changes the Hb structure - tight binding causes O2 to be removed (DPG - end product of cell metabolism present in chronic hypoxia, altitude/chronic lung disease, DPG decreases Hb affinity for oxygen phosphoglycerate)
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Which factors alter haemoglobin's affinity for oxygen? (3)
Also myglobin (Hb has higher affinity for O2 than foetal Hb)
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Describe features of oxygen binding (1)
Total O2 arterial blood = O2 dissolved plasma + bound Hb. Oxygen dissolved in plasma influenced by - composition of inspired air, alveolar ventilation (rate/depth of breathing, airway resistance, lung compliance)
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Describe features of oxygen binding (2)
Oxygen diffusion between alveoli and blood (SA, diffusion distance, membrane thickness, amount of interstitial fluid). Helps determine adequate perfusion of alveoli
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Describe features of oxygen binding (3)
Oxygen bound to Hb - % saturation of Hb affected by (pCO2, pH, temperature, 2,3-DPG), total number of binding sites (Hb content per rbc, number of rbc)
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What are the three methods for carbon dioxide carriage?
Dissolved (7%), as bicarbonate (70%), carb-amino compounds (23%, Hb + CO2 -> carbaminohaemoglobin)
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Describe how carbon dioxide forms a bicarbonate
CO2 dissolved in plasma. Diffuses into erythrocyte. Combines with water to form carbonic acid. Enzyme (carbonic anhydrase in erythrocytes). Converted immediately to H+ and bicarbonate (chloride shift)
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Describe how carbon dioxide forms a carb-amino compound
CO2 dissolved in blood. Combined reversibly with Hb to form carb-oxyhaemoglobin (23%)
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Outline carbon dioxide transport in blood (1)
CO2 in cells either dissolved in plasma (7%) or converted to Hb.CO2 (23%) or as bicarbonate (70% in plasma) with chloride shift. Transport rbc to lungs, dissolved CO2 leaves via alveoli (Hb.CO2 dissociates)
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Outline carbon dioxide transport in blood (2)
HCO3 in plasma enters rbc to be removed via alveoli (diagram)
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Summarise O2 and CO2 exchange and transport (1)
Dry air (760 mmHg), pO2 (160 mmHg), pCO2 (0.25 mmHg). In alveoli (pO2 100 mmHg, pCO2 40 mmHg). Arterial blood (pO2 100 mmHg, pCO2 40 mmHg). O2 transport (Hb carriage 98% or dissolved 2%, ~pO2). Cells (pO2 <40 mmHg, pCO2 >46 mmHg)
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Summarise O2 and CO2 exchange and transport (2)
Venous blood (pO2 40 mmHg, pCO2 26 mmHg). CO2 transport (70% bicarbonate, 23% Hb carriage, 7% dissolved). Return to alveoli
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What is hypoxic hypoxia?
Low arterial pO2. High altitude, alveolar hypoventilation, decreased lung diffusion capacity, abnormal ventilation perfusion ratio
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What is anaemic hypoxia?
Decreased total amount of O2 bound to Hb. Blood loss, anaemia (low [Hb]) or altered HbO2 binding, CO poisoning
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What is ischaemic hypoxia?
Reduced blood flow. HF (whole body hypoxia), shock (peripheral hypoxia), thrombosis (hypoxia in a single organ)
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What is histotoxic hypoxia?
Failure of cells to use O2 because cells have been poisoned. Cyanide and other metabolic poisons
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What are the causes of low alveolar pO2?
Inspired air (abnormally low oxygen, altitude). Alveolar ventilation is inadequate (decreased lung compliance e.g. emphysema, increased airways resistance e.g. asthma, overdose of drugs)
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Outline pathological conditions which reduce alveolar ventilation and gas exchange (1)
Emphysema (pO2 normal or low in alveoli, pO2 low in capillary). Fibrotic lung disease (pO2 normal or low in alveoli, pO2 low in capillary). Pulmonary oedema (pO2 normal in alveoli, increased diffusion distance, pO2 low in capillary)
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Outline pathological conditions which reduce alveolar ventilation and gas exchange (2)
Asthma (pO2 in alveoli low due to bronchioles constricted, pO2 low in capillary)
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Describe features of gas behaviour and laws (1)
Gas molecules move about and collide exerting pressure. Pressure is dependent on temperature (P increase, T increase) and concentration (P increase, C increase)
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Describe features of gas behaviour and laws (2)
In mixture gases that don't react with each other, gas molecules behave independently, each individual pressure (partial pressure P). Total pressure = sum of all individual pressures (Dalton's Law)
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Describe air composition (1)
Air is a mixture mainly of two gases (N2 and O2). Pressure exerted = atmospheric pressure = 760 mmHg or 101.3 kPa at sea level (varies with altitude/weather conditions). Air is 78.1% N2 + 21% O2, 0.9% inert gases (Ar, He), CO2 <0.04%
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Describe air composition (2)
Fractional concentrations (F) = relative quantities gases in mix. FN2 = 0.79 (inert) and FO2 (0.21)
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Describe air composition (3)
Individual partial pressures using atmospheric pressure: PN2 = 101.3 x 0.79 = 80.0 kPa. PO2 = 101.3 x 0.21 = 21.2 kPa (atm pressure on Everest/29,000 ft is 33.6 kPa so pO2 = 33.6 x 0.21 = 7.1 kPa, very low)
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Describe features of water vapour (1)
Air in lungs - saturated with water vapour. Water vapour exerts a partial pressure like other gases. This reduces pressures exerted by O2 and N2. Degree air saturation with water increases with temperature
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Describe features of water vapour (2)
At 20 degrees Celsius water can exert max. of 2.33 kPa (17.5 mmHg). At 37 degrees Celsius max is 6.3 kPa (47 mmHg in lungs)
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Describe features of water vapour (3)
Effect of inspired air - will warm quickly/reach saturation. Decreased partial pressure exerted other gases (O2). pO2 in inspired air = (Patm. - sat. vapour pressure at 37 degrees celsius) x 21% = (101.3 - 6.3) x 21 = 19.9 kPa (149 mmHg)
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Describe features of partial pressures of gases dissolved in liquids (1)
A gas (O2) with high P exposed to liquid will diffuse into liquid down its partial pressure gradient until equilibrium is reached
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Describe features of partial pressures of gases dissolved in liquids (2)
If dissolved gas with high P (CO2) is exposed to gas phase, diffusion will occur out of liquid phase down P gradient to gas phase
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Describe features of partial pressures of gases dissolved in liquids (3)
At equilibrium partial pressure of a gas dissolved in a liquid equal the partial pressure of that gas in the gas phase
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What is Henry's Law? (1)
The amount of gas dissolved in a liquid of given type is directly proportional to partial pressure of that gas in equilibrium with that liquid
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What is Henry's Law? (2)
For a given liquid/gas combination, the number of dissolved gas molecules will be determined by partial pressure and solubility constant for the gas in that particular liquid
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Describe features of partial pressure for gases in solution (1)
Partial pressure - better measure for activity of gas in solution (tendency to diffuse between compartments). Concentration depends on solubility which varies by fluid and gas. O2 bound to Hb not in solution (doesn't contribute to partial pressure)
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Describe features of partial pressure for gases in solution (2)
O2 solubility poor: dissolved O2 = only ~ 0.3 mL/100 mL in arterial blood with pO2 of ~ 13 kPa
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Describe features of partial pressure for gases in solution (3)
CO2 solubility good (20x soluble in water than O2). Arterial blood contains dissolved CO2 at 2.74 mL/100 mL despite lower pCO2 of ~ 5 kPa
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Outline the composition of gases in: atmospheric air, mixed expired air, trachea (during inspiration) and alveolar gas
Atmospheric air (pO2 21, pCO2 0, pH2O variable). Mixed expired air/mixture of alveolar and dead space gas (pO2 16, pCO2 3.5, pH2O variable). Trachea (pO2 20, pCO2 0, pH2O 6.3). Alveolar gas (pO2 13.5, pCO2 5.3, pH2O 6.3)
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Describe the O2 uptake into blood across the alveolar wall (1)
Partial pressure gradient drives O2 and CO2 through large area of thin alveolar capillary membrane. At rest, pulmonary capillary pO2 = alveolar pO2 by ~1/3 of the way along the capillary - takes ~ 0.1 sec
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Describe the O2 uptake into blood across the alveolar wall (2)
pO2 5.3 kPa, alveolar air pO2 13.3 kPa, pO2 becomes 13.3. kPa (O2 entering RBCs)
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Describe the partial pressure gradients for O2 and CO2 (1)
Rate of transfer of gas through sheet tissue is directly proportional to A/T. (P1-P2). solubility. 1/square root of mole.weight. O2 gradient large (13.3 to 5.3), CO2 gradient small (6.1 to 5.3)
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Describe the partial pressure gradients for O2 and CO2 (2)
Good CO2 exchange (very soluble, compensates for small P gradient)
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What is gas transfer reduced by?
Reduction in alveolar - capillary area (e.g. emphysema/collapsed alveoli, conditions resulting in reduced lung volumes). Increased thickness of alveolar - capillary membrane e.g. pulmonary oedema, pulmonary fibrosis. Anaemia (reduced blood Hb)
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What is gas transfer increased by?
Increased pulmonary blood volume (exercise). Polycythaemia (increased red cell numbers and hence increased blood Hb content)
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Why is the pO2 in arteries less than pO2 in alveoli, despite rapid transfer of O2 across alveoli wall (alveolar pO2 13.3 kPa, arterial circulation pO2 12.5 kPa)?
Mixing of some blood from bronchial veins (not involved in gas exchange) with that from pulmonary vein. Results in lower pO2 overall and some coronary venous blood draining directly into the left ventricle lowering pO2
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Outline O2 delivery and gas diffusion in tissues
O2 taken to tissues via bulk flow (blood). At tissues O2 movement is by diffusion down P gradient. pO2 in mitochondria >1 mmHg (0.13 kPa). pO2 tissue at rest (5.3 kPa). Adequate pO2 (gradient for pO2 transfer)
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What happens if the capillary pO2 falls below 12.5?
Rate of diffusion becomes too slow for tissue needs and tissues become hypoxic (pO2 in capillary normally changes from 12.5 kPa to 5.3 kPa due to O2 delivery)
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Outline CO2 transport and gas diffusion in tissues (1)
Highest pCO2 is at site of production (mitochondria). Cellular pCO2 6.1 kPa (at rest - or more in exercise). Arterial blood pCO2 (5.3 kPa). CO2 diffuses from cells to capillaries. Venous circulation pCO2 is the same as tissues (6.1 kPa)
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Outline CO2 transport and gas diffusion in tissues (2)
CO2 taken by blood to lungs for removal. pCO2 restored to 5.3 kPa in alveoli
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Summarise the gas partial pressures in airways and blood (1)
In kPa (values x 7.5 for mmHg). Inhaled air (pO2 21, pCO2 0). Inspired air in airways (pO2 20, pCO2 0, pH2O 6.3). Alveolus (pO2 13.3, pCO2 5.3). Arterial blood (pO2 12.5, pCO2 5.3). Capillary/tissues (pO2 <5.3, pCO2 >6.1)
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Summarise the gas partial pressures in airways and blood (2)
Mixed venous blood/resting (pO2 5.3, pCO2 6.1). Exhaled air (pO2 16, pCO2 3.5)
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Other cards in this set

Card 2

Front

Outline the movement of O2 and CO2 in blood (2)

Back

CO2 enters bloodstream, transported to right side of the heart, into lungs, out of capillaries, into alveoli, out of the body. Use of pulmonary and systemic capillaries

Card 3

Front

State features of the lung capillary interface

Back

Preview of the front of card 3

Card 4

Front

What are the constant factors for respiratory gases?

Back

Preview of the front of card 4

Card 5

Front

What are the variable factors for respiratory gases?

Back

Preview of the front of card 5
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