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Introduction to Healthcare Science > Respiratory system > Flashcards

Respiratory system Flashcards

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1
Q

What is the function of blood in the respiratory system?

A
  • Blood has the intrinsic capacity to pick up O2 and lose CO2 if exposed to the right gaseous environment (which is what lungs do).
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2
Q

What is the function of exchange and transport in the respiratory system?

A
  • exchange: lungs exchange gases with atmosphere.

- transport: blood carries gases to and from the tissues.

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3
Q

What is the role of water in respiratory gases?

A
  • Water vapour: in biological systems gas mixtures are always in contact with water.
  • so water molecules evaporate and gas molecules dissolve.
  • water molecules entering the gas exert a vapour pressure.
  • when molecules leave and enter at the same rate (in equilibrium) = saturation vapour pressure.
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4
Q

What is Dalton’s law?

A
  • In a mixture of gases molecules of each type behave independently so each gases exerts a partial pressure (each contributes to overall pressure):

P = Pgas1 + Pgas2 + Pgas3 etc

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5
Q

What is ventilation rate?

A
  • The amount of air moved into and out of a space per minute.
  • it’s the product of volume moved per breath and respiratory rate.
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6
Q

What are the two types of ventilation rate?

A
  • pulmonary ventilation rate and alveolar ventilation rate.
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7
Q

What is the pulmonary ventilation rate?

A
  • Tidal volume (volume of air that you move) x respiratory rate.
  • Typically 6 L.min(-1) at rest.
  • Can reach up 120 L.min(-1) during exercise.
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8
Q

What is the alveolar ventilation rate?

A
  • The actual amount of air that reaches the alveoli.
  • To calculate we need to allow for the ‘wasted’ ventilation of dead spaces (airways + non functional alveoli).
  • So AVR = PVR - DSVR.
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9
Q

What is the function of the respiratory system?

A
  • it ensures that all tissues receive the O2 they need and that they can dispose of CO2 they produce.
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10
Q

What is the major source of non elastic resistance to air flow in the respiratory passageways?

A
  • Friction.
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11
Q

What is resistance in the respiratory tree mostly determined by?

A
  • The diameters of the conducting tubules (i.e. the trachea, bronchi and bronchioles).
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12
Q

Why is airway resistance mostly insignificant?

A
  • the start of the respiratory tree has large diameters (usually).
  • gas flow stops at the terminal bronchioles, where airways have small diameters, but this is not a problem as here diffusion is the main force driving gas movements.
  • therefore the greatest resistance to gas flow occurs in the medium-sized bronchi and bronchioles.
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13
Q

Which part of the lung is the most compliant?

A
  • The lung bases are the most compliant, we therefore breathe from these parts of the lung because compliance normally determines ventilation.
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14
Q

What are the gradients of partial pressure?

A
  • P(A)O2 > P(V)O2.

- P(A)CO2

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15
Q

Give some examples of what gas has got to get across (components of diffusion barrier) to get into lungs?

A
  • tissue fluid.
  • epithelial cell of alveolus.
  • plasma.
  • red cell membrane.
  • endothelial cell of capillary.
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16
Q

What does the diffusion barrier consist of?

A
  • 5 cell membranes, 3 layers of cytoplasm, 2 layers of tissue fluid.
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17
Q

Which gas is most limited by diffusion?

A
  • CO2 diffuses much faster than O2 overall, so exchange of O2 is always limiting.
  • Overall diffusion resistance:
    Barrier is 0.45um thick.
    O2 exchange is complete within 0.5 s of a blood cell arriving in a capillary.
    Blood cells spend about 1 s in a capillary.
    So gas diffusion is not limiting respiratory function.
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18
Q

Where is surfactant found and what’s its function?

A
  • alveoli of the lungs contain surfactant.
  • it lowers surface tension in the alveoli by about x15.
  • this diminishes the required pressure for inflation of the alveoli and stops them collapsing.
  • alveoli can inflate with only about 1 mmHg excess pressure compared to the surroundings.
  • breathing in premature infants difficult due to incomplete formation of the surfactant.
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19
Q

What is lung compliance?

A
  • it describes the ability of lungs to stretch.
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20
Q

What do we know about lung compliance?

A
  • the higher the compliance of lungs the easier it is to expand them.
  • total lung compliance is determined by 2 factors: elasticity of lung tissue and the thoracic cage.
  • the lungs of healthy indivs. Have high compliance because lung tissue and thoracic elasticity are low and alveolar surface tension is low (due to surfactant) permitting efficient ventilation.
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21
Q

Name a few ways of testing lung function?

A
  • testing Forced Vital Capacity (FVC): the maximum volume that can be expired from full lungs. Typically 5 L in an average adult.
  • testing Forced Exhaled Volume: volume expired in the first second. Affected by how quickly air flow slows down so less if airways are narrowed. Typically >70% FVC.
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22
Q

How is peak expiratory flow rate measured?

A
  • PEFR can be measured with a simple cheap device so often used as a simple screening test for airway narrowing but very insensitive (thing I had before where you blow in to).
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23
Q

How do you work out the total lung capacity (TLC)?

A
  • It’s the vital capacity (VC) + the residual volume (RV).
24
Q

How is oxygen transported in the respiratory system?

A
  • dissolved in plasma (only 1.5% because O2 is poorly soluble in plasma).
  • bound to haemoglobin (Hb) inside RBCs (98.5% is carried this way).
25
Q

What is haemoglobin (Hb) composed of?

A
  • 4 polypeptide chain subunits ( 2 alpha and 2 beta chains).
  • Each subunit is bound to an iron containing haem group.
  • Since iron ions serve as oxygen-binding sites each Hb can rapidly and reversibly bind 4 oxygen molecules.
26
Q

What is a Hb molecule with oxygen called?

A
  • Oxyhemoglobin (HbO2).
27
Q

What is a Hb molecule that has released its oxygen called?

A
  • Deoxyhemoglobin (HHb).
28
Q

What happens when the first oxygen molecule binds the first iron molecule in haemoglobin?

A
  • The Hb changes shape and the affinity for the other 3 oxygen molecules progressively increases.
29
Q

What happens when the first oxygen molecule is unloaded from haemoglobin?

A
  • The affinity for oxygen is decreased and it becomes progressively easier for the other 3 oxygen molecules to dissociate from the Hb.
30
Q

When is Hb fully saturated?

A
  • When all four haem groups are bound to oxygen, if fewer than all four haem groups are bound then Hb is partially saturated.
31
Q

Under normal resting conditions what are the values of pressure and saturation for arterial blood?

A
  • Pressure: P(a)O2 of 13.3 kPa.

- Saturation: 98%.

32
Q

If 100mls of arterial blood contains about 20ml of oxygen what is the oxygen content written as?

A
  • 20 vol %.
33
Q

As arterial blood flows through the systemic capillaries what happens?

A
  • O2 is released into tissue.
  • In the venous blood this decreases Hb saturation to 75% and P(V)O2 to 6kPa (therefore a large decrease in PO2 (13.3 to 6) is associated with a much smaller decrease in Hb saturation (98 to 75%)).
34
Q

What factors have a significant effect on the affinity of Hb for oxygen by modifying its 3 dimensional shape?

A
  • PO2.
  • temperature.
  • [H+] (pH).
  • PCO2.
  • 2,3-DPG (diphosphoglycerate) = a unique compound produced in RBCs that bind reversibly with Hb.
  • Generally an increase in any of these factors results in a deceased affinity for oxygen and a decrease in factors results in a increased affinity for oxygen.
35
Q

Where do the factors affecting O2-Hb dissociation tend to be at their highest level?

A
  • In the systemic capillaries where oxygen uploading is most needed (Bohr effect).
36
Q

How is regulation of gas transfer and respiration controlled? (2 ways)

A
  • Neural regulation (voluntary and involuntary).

- Chemical regulation.

37
Q

What are the two medullary respiratory centres that play a role in respiration?

A
  • dorsal respiratory group (DRG) (back).

- ventral respiratory group (VRG) (front).

38
Q

What is the dorsal respiratory group (DRG) also known as?

A
  • Inspiratory centre.
39
Q

What is the ventral respiratory centres role?

A
  • Unclear but through to be involved in forced exhalation and forced inspiration.
40
Q

What do we know about the dorsal respiratory group? (DRG)

A
  • When neurones in the DRG fire, impulses stimulate the diaphragm via the phrenic nerves and external intercostal muscles via the intercostal nerves.
  • The thoracic cavity expands and air rushes in = inspiration.
  • The DRG then becomes dormant, allowing the inspiratory muscles to relax and the passive process of expiration to occur.
  • The rhythm of the DRG creates a respiratory rate of 12-16 breathes per minutes with the inspiratory phase lasting around 2 secs and the expiratory phase lasting around 3 secs.
  • This normal respiration rate and rhythm is called eupnoea.
41
Q

What are the two pons centres that can influence and modify the activity of the medulla?

A
  • the pneumotaxic centre: coordinates transition between inhalation and exhalation by inhibiting inspiration area.
  • the apneustic centre: provides inspiratory drive by continuously stimulating the medullary inspiratory centre, unless inhibited by the pneumotaxic centre or sensory input from the lungs. Prolongs inspiration - also breath holding.
42
Q

What happens during the inflation reflex of the lung (Hering-Breuer reflex)?

A
  • baroreceptors (stretch receptors) in the visceral pleura and airways of the lungs, are stimulated during inspiration.
  • These receptors send action potentials to the respiratory centres, via afferent fibres of the vagus nerve. These signals inhibit inspiration and allow expiration to occur.
  • As the lungs recoil, the baroreceptors stop firing and inspiration is initiated once again. This reflex protects the lungs from over inflation and excessive stretching.
43
Q

Explain the model for the generation of respiratory rhythm.

A
  • The basic pattern of inspiration and expiration is produced by the medulla. This pattern is modulated by the actions of the pneumotaxic and apneustic centres.
  • The combined outcome is a regular smooth respiratory cycle, but the rate and depth may not be optimal.
  • The rate and depth is optimised by information from the lungs relayed back to the respiratory centres.
44
Q

How can higher brain centres influence the rhythmic activity of the respiratory centres?

A
  • Hypothalamus and cerebral cortex can both influence the rhythmic activity of the respiratory centres.
  • strong emotions, pain, and changes in temperature all activate centres in the hypothalamus which in turn alters the respiration rate and rhythm:
  • apnoea can be induced by anger, pain or decrease in temperature.
  • tachypnoea can be induced by excitation or increase in temperature.
45
Q

How do the higher brain centres (hypothalamus and cerebral cortex) control breathing?

A
  • the cerebral motor cortex directly stimulates the motor neurones of the inspiratory muscles (bypassing the medullary centres) when we want to consciously control our breathing - i.e. Holding our breath, or changing the depth of our breathing.
  • however our ability to hold our breath is limited: the respiratory centres automatically reinitiate breathing when concentration of O2 in the blood reach critical levels. This is why drown victims usually have water in their lungs.
46
Q

regulation of gas transfer and respiration is controlled in two ways, what are they?

A
  • neural regulation.

- chemical regulation (chemoreceptors, ventilation-perfusion matching).

47
Q

What is the role of chemoreceptors in gas transfer and respiration?

A
  • Chemical factors: most important are arterial CO2, O2 and H+ concentrations. These chemicals are monitored by chemoreceptors of two kinds;
  • central chemoreceptors (CCRs) found on the medulla.
  • peripheral chemoreceptors (PCRs) found within the aortic arch and carotid arteries.
48
Q

What can decreasing arterial pH be a result of?

A
  • accumulation of CO2 due to disease or environment.
  • accumulation of lactic acid during excercise.
  • accumulation of fatty and ketone acids in patients with poorly controlled diabetes mellitus.
  • other metabolic causes.

Regardless of cause declining pH induces rapid and deep breathing thereby eliminating CO2.

49
Q

What does hyperventilation do to the acid-base balance?

A
  • Causes P(a)CO2 to fall. So plasma pH rises = respiratory alkalosis.
  • Can be compensated (returning pH towards normal) by the kidneys increasing [HCO3-] excretion.
50
Q

What does hypoventilation do to the acid-base balance?

A
  • Cause hypercapnia. Plasma pH falls = respiratory acidosis.
  • Can be compensated initially be raising HCO3 through cellular release then by renal excretion of carbonic acid and HCO3- retention.
51
Q

When thinking about ventilation and pH imbalance, what happens when metabolic acid is produced?

A
  • If the tissues produce acid this reacts with HCO3-.
  • The fall in [HCO3-] leads to a fall in pH = metabolic acidosis.
  • Can be compensated by increased ventilation, lowering P(a)CO2.
52
Q

When thinking about ventilation and pH imbalance, what happens when metabolic alkali is produced?

A
  • If plasma [HCO3-] rises (e.g. Relative increase after vomiting). Plasma pH rises = metabolic alkalosis.
  • Can be compensated to a degree by decreasing ventilation, raising P(a)CO2.
53
Q

What is the effect of P(a)CO2 (I.e.pH) on chemoreceptors?

A
  • pH of CO2 is most important and most closely controlled.
  • Concentration is monitored by the CCRs (PCRs are weakly responsive to P(a)CO2.
  • as CO2 diffuses from the blood into the CSF, carbonic acid is formed and quickly dissociates. The CSF contains very few proteins and therefore has no ability to buffer the free ions. The increase in [H+] leads to excitation of the CCRs, which synapse with respiratory rhythm centres.
  • Effects on ventilation: breathing becomes rapid and deep, decreases blood then CSF CO2.
54
Q

What is the effect of P(a)O2 on chemoreceptors?

A
  • Arterial oxygen levels are monitored by the PCRs in the aortic bodies of the aortic arch but mainly in the carotid bodies (at the bifurcation of the common carotid arteries).
  • P(a)O2 must drop 9.3 kPa).
  • Below 8 kPa the CCRs suffer O2 starvation and become depressed. But PCRs stimulate respiratory centres to increase ventilation, maintaining respiration despite hypoxic depression of CNS.
55
Q

What is the function of the respiratory system?

A
  • the respiratory system serves to ensure that all tissues receive the O2 they need and can dispose of the CO2 they produce.

Introduction to Healthcare Science (23 decks)

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