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Physiology (Term 2) > Respiration 3 > Flashcards

Respiration 3 Flashcards

1
Q

What allows the lungs to inflate and deflate?

A

The lungs have elastic properties that allow them to inflate (compliance) and deflate (elastance)

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2
Q

What helps to stabilise the lungs?

A

Alveolar surface tension helps to stabilise the lungs and is generated by alveolar interdependence and surfactants

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3
Q

What can be can be used to measure some lung volumes/capacities?

A

Spirometry

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4
Q

What does restrictive lung disease result in?

A

(reduced compliance) results in reduced VC – harder to breathe in

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5
Q

What does Obstructive lung disease result in?

A

(increased compliance) gives increased RV, reduced VC - harder to breathe out

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6
Q

Does dead spaces in the airways affect gas exchange

A

Yes both in conducting airways and alveoli

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7
Q

Boyle’s law states that

A

“The absolute pressure exerted by a given mass of an ideal gas is inversely proportional to the volume it occupies if the temperature and amount of gas remain unchanged within a closed system”

P is proportional to 1/V

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8
Q

Dalton’s law of partial pressures states that

A

“The total pressure exerted by the mixture of non-reactive gases is equal to the sum of the partial pressures of individual gases”

(If you have numerouse gases present in an environment, each gas will contribute to the overal pressure)

Ptotal = P1 + P2 + P3 + … Pn

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9
Q

Henry’s law states that

A

“At a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid”

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10
Q

These gas laws basically mean that CO2 is exchanged for O2 in the lungs

A

O2 and CO2 pressure differences are most important:

H2O: Alveoli pressure is significantly higher (47mmHg) than atmospheric pressure (3.7mmHg)

O2: Higher atmospheric pressure (160mmHg) and lower alveoli pressure (104mmHg) (Boyles law)

CO2: Higher alveoli pressure (40mmHg) and lower atmospheric pressure (0.3 mmHg)

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11
Q

Gas exchange - Oxygen

desrcibe the effect of partial pressure gradient

How is oxygen transported around the body?

A
  • Oxygen is carried physically dissolved in the blood and chemically combined to haemoglobin
  • O2 enters the blood in the lungs down its partial pressure gradient
  • Inhaled air- high PO2; venous blood (deox) - low PO2
  • O2 leaves the blood in the tissues down its partial pressure gradient
  • Venous blood (ox) – high PO2; tissues (deox) - low PO2
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12
Q

Gas exchange – Carbon dioxide

How is CO2 transported around the body?

A
  • Carbon dioxide is carried physically dissolved in the blood (10%), chemically combined to haemoglobin (30%) but most CO2 (60%) is carried as bicarbonate HCO3-
  • CO2 leaves the blood in the lungs down its partial pressure gradient
  • Inhaled air- low PCO2; venous blood - high PCO2
  • CO2 enters the blood in the tissues down its partial pressure gradient
  • Venous blood – low PCO2; tissues (cellular respiration) -high PCO2
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13
Q

Describe overall gas exchange within alveoli

A

CO2 readily dissolves in the blood O2 does not therefore needs a greater partial pressure gradient

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14
Q

Factors affecting gas exchange: part i

Alveolar-capillary diffusion of gas depends on:

A
  1. Partial pressure difference
  2. ‘Diffusability’ of each gas meaning how readily it dissolves in the blood
  • ‘Diffusion Coefficient’ describes the ‘diffusability’ of the gases
  • Diffusion coefficient depends on the molecular weight of the gas and its water solubility
  • Diffusion coefficient of CO2 >> O2 (because CO2 is much more soluble in water than O2)
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15
Q

Factors affecting gas exchange: part ii

The rate of gas exchange will be reduced if:

A
  1. Partial pressure gradient is reduced (e.g. less oxgen in the atmosphere- people living at high altitudes)

gases diffuse according to partial pressure differences

  1. Surface area for exchange is reduced (e.g alveoli collapse)

Fick’s law states that the rate of diffusion = SAxDx(P1-P2)/T (SA= surface area, D=diffusion gradient, P1/2=partial pressure difference and T=thickness of the respiratory surface)

  1. Solubility of gas is reduced as temperature increases (when gases dissolve in solution th eprocess is exothermic, increased temperature= incresed kinetic energy so gas doesnt dissolve)
  2. Distance for transfer is increased

respiratory diseases (interstitial fibrosis, respiratory surfaces damaged)

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16
Q

Why can’t we rely on dissolved oxygen?

A
  • Dissolved oxygen obeys Henry’s law – the amount of oxygen dissolved is proportional to the partial pressure.
  • For each mmHg of PO2 there is 0.003 ml O2/ml of blood or 3 micro Litre per litre.
  • If this was the only source of oxygen, then with a normal cardiac output of 5L/min, oxygen delivery would only be 15 ml/min.
  • Tissue O2 requirements at rest are somewhere in the region of 250ml/min, so this source, at normal atmospheric pressure, is inadequate
  • We’d need cardiac output of 83.3 L/min to deliver enough oxygen when max CO is 5-7L/min for RESTING metabolism if we relied on dissolved O2 alone
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17
Q

Why is haemoglobin vital for effective oxygen transport?

A
  • Since dissolved O2 isn’t enough…
  • Most O2 in the blood is transported bound to haemoglobin
  • Haemoglobin, an iron-bearing protein molecule contained within the red blood cells, can form a loose, easily reversible combination with O2
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18
Q

Haemoglobin lets us transport the O2 we need: Describe the structure of haemoglobin

Each molecule of Hb can carry up to how many molecules of O2?

A
  • 64 kDa protein
  • 4 polypeptide chains (2 alpha + 2 beta)
  • One haem group per polypeptide
  • One iron per haem
  • One O2 per iron
  • Each molecule of Hb can carry up to 4 molecules of O2

​(Hemoglobin is a protein made up of four polypeptide chains (α1, α2, β1, and β2). Each chain is attached to a heme group composed of porphyrin (an organic ringlike compound) attached to an iron atom.)

19
Q

O2 carrying capacity is increased with Hb

A
  • Each g of Hb binds 1.34 mL O2
  • For 15g Hb per 100mL blood, total oxygen carrying capacity is 15 x 1.34 = 20.1 mL O2 /100mL blood
  • 70-fold increase compared to dissolved O2 (3mL/L)
  • At resting cardiac output of 5 L/min, O2 delivery reaches 1L/min
20
Q

Measuring haemoglobin: the haematocrit

A
  • Haematocrit measures packed cell volume (PCV)
  • Reduced in anaemia
  • Evated in polycythemia
  • Increased in doping – EPO (erythropotein) use
  • Lyse the red blood cells to measure the Hb content
21
Q

Hb promotes net transfer of O2 at the alveolar and the tissue levels

A
  • Hb-O2 binding is reversible
  • Role of Hb at the alveolar level:

–Hb acts as a “storage depot” for O2; removes O2 from solution as soon as it enters the blood from the alveoli

•Role of Hb at the tissue level:

–O2 immediately diffuses from the blood into the tissues, lowering blood PO2

22
Q

Describe the oxyhaemoglobin dissociation curve

A
  • Not linear, its sigmoid
  • Hb releases O2 according to tissue demand
  • In peripheral capillaries, O2 is removed from blood, PO2 falls to 40mmHg, Hb gives up O2, Hb saturation drops
  • Muscle activity can reduce PO2 to <20mmHg- extra 40% O2 released from Hb
23
Q

Factors affecting O2 carriage by Hb

A
  • pH
  • PCO2
  • Temperature
  • 2,3-DPG – 2,3-diphosphoglycerate
24
Q

Factors affecting O2 carriage by Hb: pH

A
  • The Bohr effect
  • Small drop to pH 7.2- more acidic
  • Shifts the oxyhaemoglobin dissociation curve to the RIGHT
  • Increases release of O2 by 15%
  • Increases oxygen supply – anaerobic exercise, lactic acid increases, pH falls
  • Lower pH reduces binding affinity of Hb for O2
25
Q

Factors affecting O2 carriage by Hb: PCO2

A
  • The Bohr effect (again)
  • Increased PCO2 increases and mixed with H2O to form H2CO3 (carbonic acid)
  • broken down my carbonic anhydrase to liberate H+ ions and HCO3- (bicarbonate ions) and blood is more acidic
  • Shifts the oxyhaemoglobin dissociation curve to the RIGHT (giving up O2 more readily)
  • Increases release of O2 by 15%
  • Lower pCO2 increases pH and increases binding affinity of Hb for O2
26
Q

Factors affecting O2 carriage by Hb:
3. Temperature

A
  • Small increases in temperature (exercise or fever) also shift curve to the RIGHT
  • Blood temperature is higher in metabolically active tissues
  • This effect helps to unload O2 from haemoglobin
  • At low blood temperature, Hb will not release O2- very high affinity binding
27
Q

Factors affecting O2 carriage by Hb:
4. 2,3-DPG or 2,3-BPG

Which subunit does it bind?

What is it produced by?

Does it cause Hb to release or hold onto O2?

A
  • 2,3-DPG binds with greater affinity to deoxygenated Hb (at the tissues) than to oxHb (lungs)
  • 2,3-DPG fits better in the deoxy Hb configuration
  • 2,3-DPG interacts with deoxy Hb beta subunits and decreases their affinity for oxygen
  • 2,3-DPG is produced by red blood cells during normal glycolysis
  • 15mmol/g Hb normally
  • Increased 2,3-DPG will shift the curve to the RIGHT
  • 2,3-DPG enhances the ability of RBCs to release oxygen near tissues that need it most

Physiologically important as hypoxia (a region of the body is deprived of adequate oxygen supply at the tissue level) results in 2,3-DPG production

28
Q

Factors that shift the curve to the right are

A

physiological states where tissues need more O2

29
Q

How is foetal Hb structurally different?

A
  • Foetal Hb has higher binding affinity for O2
  • Has two alpha and two gamma subunits
  • Curve is shifted to the LEFT
  • Foetal blood can acquire O2 from maternal, blood
  • Also increased 2,3-DPG in maternal circulation in pregnancy
30
Q

Does Haemoglobin have a much higher affinity for carbon monoxide than for O2

A

Yes

  • Hb: 240x higher affinity for CO than O2
  • Hb + CO forms carboxyhaemoglobin
  • This reaction is less reversible; shifts the curve to the LEFT
  • CO prevents O2 loading in the lungs AND O2 unloading in the tissues
  • Smoking/urban pollution increases COHb
31
Q

Describe the transport of CO2 by the blood, the rate of CO2 production and solubility

A
  • CO2 is produced by tissue metabolism at a rate of 250 ml per minute at rest
  • At cardiac output of 5L/min, each 100mL blood passing through the lungs must unload 4-5mL CO2
  • CO2 is 20 times as soluble as O2
  • Still too much to be carried in plasma alone
32
Q

Transport of CO2 by the blood: The chloride shift

A
  • CO2 combines with H2O to form carbonic acid (H2CO3)- this then dissociates to H+ and HCO3-
  • Conversion now is CO2 + H2O straight to H+ + HCO3-
  • HCO3- is carried out of red blood cells via facilitated diffusion via membrane carriers
  • HCO3- is more soluble in plasma than CO2- easy transport back to lungs
  • Movement of HCO3- out of red blood cell creates proton gradient (net positve charge inside RBC and net negative charge outside RBC electrostatic forces causes agglutination)
  • Cl- are taken into the red blood cell- the chloride shift
33
Q

What are the main ways to transport CO2?

A
  1. physically dissolved in the blood (10%)
  2. bound to Hb (30%)
  3. as bicarbonate HCO3- (60%)
34
Q

Describe the The Haldane effect:

What does it promote?

Where is CO2 loaded/unloaded

A

•The Haldane effect promotes dissociation of CO2 from Hb in the presence of O2

Electrostatic forces cause agglutination

  • This allows the blood to unload more CO2 at the lungs, where there is more oxyHb
  • This allows the blood to load more CO2 at the tissues-where there’s more deoxyHb
35
Q

Describe neural control of breathing:

Quiet breathing vs active ventilation

A

Quiet breathing vs active ventilation

  • Phrenic nerve (binds to diaphram and makes it contract) is firing at regular intervals vs rapid firing
  • External intercoastal nerves which fires as well but not so readily vs rapid firing
  • Internal intercoastal nerve doesnt fire vs firing takes place
  • Uniform inspiratory muscle tension vs larger forces of contration and relaxation
  • Expiratory muscles contraction passive vs active
  • Lung volume increases during inspiration and decreases during expiration vs lung vume increases
36
Q

Brain centres that control respiration

A

•Respiratory centers in the brain stem establish a rhythmic breathing pattern

–Inspiratory and expiratory neurons in the medulla oblongata (dorsal and ventral respiratoy groups mediate inspiration)/pons centres (Pneumotaxic center and the apneustic center mediate expiration)

–Generation of respiratory rhythm

37
Q

Control of Ventilation:

Are respiratory rate and tidal volume are fixed?

A
  • Respiratory rate and tidal volume are not fixed
  • can be increased/decreased over a wide range
  • Blood PO2, PCO2 and H+ all depend on the balance between metabolic demand and respiration
38
Q

How does supply match demand?

What are the two types of chemoreceptors?

A
  • Chemoreceptors determine PO2, PCO2 and H+ and provide feedback to the breathing centres of the brain to modify rate and tidal volume
  • Two types of chemoreceptor:

Central in the brain

Peripheral in carotid artery that send action poteintials to brain

39
Q

Where are Central chemoreceptors found?

What happens if the chemoreceptor tells the brain that there is a lot of CO2 the blood?

A

in the medulla

  1. It will fire an action potential via the phrenic nerve to the diaphram, via the thoracic nerve to the intercoastal muscles and via the glossopharyngeal nerve to the heart
  2. this facilitaes increased ventilation because heart rate increases
40
Q

What do central chemoreceptors respond to the pH of?

What do the respond to?

A

to pH of CSF

Central chemoreceptors respond to PCO2

(blood supplying the brain has thin layered wall CO2 diffuses into CSF where it mixes with water to produce hydeogen carbonate which breaks down into bicarbonate ions and hydrogen ions detected by the medulla oblongata)

41
Q

Where are Peripheral chemoreceptors are found in?

What are the properties and functions of carotid and aortic bodies?

A

the neck and thorax

  • Carotid and Aortic bodies
  • Located in the carotid artery and aortic arch
  • Exposed to arterial blood
  • Detect changes in O2 and CO2
  • Carotid body monitors O2 delivery to the brain in particular
42
Q

What does an increased PCO2 do to respiratory rate?

What is it detected by?

How is it returned to a normal level?

A
  1. Increased pCO2 blood and CSF
  2. Stimulates central chemoreceptors in medulla
  3. Stimulates inspiratory muscles
  4. Increases respiratoy rate
  5. Removes more CO2 from body
  6. Decreased pCO2
  7. Decreased chemoreceptor stimulation
  8. Slow respirations
  9. Retain more CO2
43
Q

Give a summary of this lecture

A
  • Gases move according to the pressure gradient
  • Pressure gradients mean that O2 is loaded in the lungs and unloaded in the tissues, whereas CO2 unloads in the lungs and is loaded in the tissues
  • Haemoglobin is required for efficient O2 and CO2 transport
  • pH, PCO2, temperature and 2,3-DPG affect oxygen loading
  • The respiratory control centre is in the medulla
  • The respiratory cycle maps neuronal activity to muscle contraction
  • Chemoreceptors determine the levels of PO2, PCO2 and H+
  • Central chemoreceptors monitor pH (via soluble PCO2)
  • Peripheral chemoreceptors can respond to PO2 in extreme hypoxia

Physiology (Term 2) (24 decks)

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