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Physiology And Disease > Lecture 13: Respiratory System > Flashcards

Lecture 13: Respiratory System Flashcards

1
Q

Why do we need to breathe?

A
  • For efficient energy production.
  • For oxidative breakdown of food.
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2
Q

State the process of internal (cellular) respiration.

A

C6H12O6 + 6O2 —> 6CO2 + 6H2O + energy (ATP).

Exchange of gases between the blood and body cells.

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3
Q

What is external respiration?

A
  • External respiration is the formal term for gas exchange (between lungs and blood).

It describes both the bulk flow of air into and out of the lungs and the transfer of oxygen and carbon dioxide into the bloodstream through diffusion.

—> Deliver O2 & remove CO2.

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4
Q

Describe the structure of the respiratory system.

A
  • Respiratory tract —
    Upper (organ outside thorax - nose, pharynx and larynx)
    AND
    Lower respiratory tract (organ within thorax - trachea, bronchi, bronchioles, alveolar duct and alveoli).
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5
Q

Describe the lung structure.

A
  • Trachea
  • ~ Cartilage
  • Primary bronchi
  • Lungs
  • Thoracic cavity
  • Intercostal muscles
  • Diaphragm
  • Bronchiole
  • Alveoli
  • Capillary network
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6
Q

Define Boyle’s law.

A

A law stating that the pressure of a given mass of an ideal gas is inversely proportional to its volume at a constant temperature.

  • V ≠ P, inversely proportional.
  • Pressure = 1/volume.
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7
Q

Is the contraction of respiratory muscles required for inspiration or expiration?

A

Inspiration.

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8
Q

State what happens in inspiration.

A
  • Thoracic cavity expands.
  • External intercostal muscles contract.
  • Diaphragm contracts.
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9
Q

What happens in expiration?

A
  • Thoracic cavity reduces.
  • External intercostal muscles relax.
  • Diaphragm relaxes.
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10
Q

How are lungs held open?

A

By negative intrapleural pressure.
The negative pressure of the pleural cavity acts as a suction to keep the lungs from collapsing.

It also makes sure that the lungs follow the movement of the rib-cage.

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11
Q

What is intrapleural pressure? How is it formed?

A
  • Since the parietal pleura is attached to the thoracic wall, the natural elasticity of the chest wall opposes the inward pull created by the elastic recoil of the lungs (they have a tendency to collapse).
    Ultimately, the outward pull is slightly greater than the inward pull, creating the –4 mm Hg intrapleural pressure relative to the intra-alveolar pressure.

—> Opposite forces in the pleural cavity increase volume and decrease the pressure inside the cavity.

  • Intrapleural pressure is subatmospheric (less/lower than that of an atmosphere).
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12
Q

What happens when the atmospheric pressure outside equals the intrapleural pressure inside?

A

Equalisation of the intrapleural pressure with atmospheric pressure or intrapulmonary pressure immediately causes lung collapse to unstretched size.

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13
Q

What are factors that affect pulmonary ventilation?

A
  • Elastic recoil / lung compliance.

~ Alveolar surface tension.

  • Airway resistance.
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14
Q

What is elastic recoil?

A

Ease with which lung rebounds after stretching.

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15
Q

Define compliance.

A

Ease with which the lung stretches/expands.

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16
Q

How are elastic recoil / compliance mainly determined? What is their relationship to each other?

A
  • Elastic recoil/compliance are mainly determined by elastic fibres in lung tissue and alveolar surface tension (resisting an external force).
  • Elastic recoil and compliance are inversely related.
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17
Q

Why is reduced alveolar surface tension beneficial? How is it done?

A
  • Increases compliance.
  • Alveoli are lined by an inner thin layer of liquid. Surface tension is reduced by surfactant secreted by alveolar type II cells
    (reduces inward force caused by the water molecules that are attracted to each other).
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18
Q

What is surfactant?

A

A substance which tends to reduce the surface tension of a liquid in which it is dissolved. A phospholipid.

It reduces inward forces.

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19
Q

What is the relationship between air flow and resistance?

A

Inversely proportional.

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20
Q

What does airway resistance depend on?

A

It mainly depends on tube diameter and type of flow (turbular/laminar).

Small diameter = higher resistance.

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21
Q

Describe the process of respiration.

A
  • O2 moves into, CO2 moves out.

1) O2 diffused into blood, gets pumped around the body and reaches peripheral tissues.
—> Internal respiration occurs.

2) O2 gets used up, CO2 gets produced.

3) CO2 travels the opposite direction:
* Diffuses into the blood, moves toward the lungs.
* CO2 enters the lungs and gets expired out.

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22
Q

How do you get air into the lungs?

A
  • Generate a pressure gradient (high pressure to lower pressure).

—> reduce the pressure in lungs (increase the volume).

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23
Q

What are the visceral and parietal pleurae?

A

Lungs are surrounded by two connective membranes:

  • Visceral pleura – directly lines the surface of the lungs.
  • Parietal pleura – lining of inner surface of thoracic cavity.
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24
Q

Where is the airway resistance highest and where is it the lowest? Why?

A
  • Highest at the level of medium-sized bronchi.
  • Lowest at the level of terminal bronchioles.

The reason is because of the total cross-sectional area.

Bigger diameter = smaller resistance.

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25
Q

Explain the pressure changes during breathing.

A

1) Just before inspiration starts, the pressure inside the lungs is the same as atmospheric pressure. And the pressure in the pleural cavity is negative.

2) During inspiration, when the diaphragm and intercostal muscles contract, the volume in pleural cavity increases and pressure drops.
+ This pulls the lungs further out, pressure drop. So the volume inside the lungs increases and the pressure decreases.

3) Since the pressure in the lung is negative compared to the outside world, air will move into the lungs.
So, lung pressure will get back to zero and is the same as the atmospheric pressure (equilibrium).

4) During expiration, when muscles relax, volume decreases in the pleural cavity and pressure increases.
+ Lungs will recoil a little, reduction of volume in lungs and increase in pressure.

5) Since the pressure of the lungs is higher than the outside world, this will lead to removal of air from the lungs (until it reaches equilibrium).

26
Q

Describe how the spirometer works.

A

It measures the air capacity/volume in lungs.

When a person exhales into the tube attached to the spirometer, the air flows into the air-tight chamber and causes the inverted bell (that is dipped in the water seal) to rise. The counter weight (that is attached to the bell with the same string) goes down, causing the recording device attached to it to make a negative graph.

The negative graph signifies decrease in volume (expiration), positive signifies increase (inspiration).

27
Q

Which mechanism is used to exchange gases between alveoli and capillaries?

A

Diffusion.

28
Q

How does oxygen get transported in the blood?

A

1) Oxygen diffuses from the alveoli to blood capillaries (high P to low P).

~ This movement will continue to happen until there is an equilibrium in partial pressures.

2) Oxygenated blood is moved around the body to reach the peripheral tissues.

3) The oxygenated blood with high partial pressure will diffuse into the cells, O2 will be offloaded from the haemoglobin.

29
Q

How does carbon dioxide get transported in the blood?

A

1) CO2 moves from an area of high P (peripheral cells) to an area of low P (blood capillaries).

~ Process, bicarbonate formation, and chloride shift occurs until P equilibrium has been reached (≈ 46 mm Hg).

2) CO2 rich blood moves around the body and eventually reaches the lungs.

3) The difference in P between capillaries (46 mm Hg) and lungs (40 mm Hg) will cause CO2 to diffuse from the capillaries into the lungs.

~ Chloride shift and bicarbonate formation processes are reversed. Diffusion occurs until equilibrium has reached.

30
Q

What are two types of chronic lung diseases?

A
  • Obstructive – airway obstruction increases resistance.
    ~ Example: COPD (chronic obstructive pulmonary disease) —> constriction of airways.
  • Restrictive – reduced compliance limits expansion.
    ~ Example: Pulmonary fibrosis —> thickening and scarring of connective tissue.
31
Q

What is COPD? What causes it and what does it lead to?

A

Chronic obstructive pulmonary disease.

  • Main risk factors include smoking, air pollution, and genetics.
  • Frequent irritation of the airways leads to irritation and inflammation.
    ~ Airways react to this by producing a lot of mucus and constricting the airways (contraction of smooth muscles). The individual ends up having chronic productive coughs.
  • Breakdown of elastin (protein that produces elastic fibres, recoil) in connective tissue of lungs.
    ~ Increased compliance. Difficulty getting the air out of the lungs because they don’t recoil properly.
  • Both of these problems lead to:
    ~ Airway obstruction/air trapping
    ~ Dyspnea (laboured breathing)
    ~ Frequent infections
  • Eventually this can lead to complete respiratory failure.
32
Q

What is pulmonary fibrosis?

A

Risk factors aren’t well known but there is a possibility that it is due to infections or autoimmune diseases.

  • Main problem of pulmonary fibrosis is that scar tissue is formed in the tissue between the alveoli.
  • Affects breathing respiration in two different ways:
    ~ Thickens the tissue between the alveoli and blood vessels (reduces the rate of oxygen diffusion).
    ~ Scar tissue is really stiff, reduces compliance. Less air can enter the lungs.
33
Q

What is air flow?

A

The speed in which the air can move in the airways.

34
Q

What are the different lung volumes?

A
  • Tidal volume (TV) – the amount of air that moves in or out of the lungs with each respiratory cycle. It measures around 500 mL in an average healthy person.
  • Inspiratory reserve volume (IRV) – the additional volume of air that can be inspired at the end of a normal or tidal inspiration.
  • Expiratory reserve volume (ERV) – the extra volume of air that can be expired with maximum effort beyond the level reached at the end of a normal, quiet expiration.
  • Total lung capacity.
  • Inspiratory capacity – the maximum volume of air that can be inspired after reaching the end of a normal, quiet expiration (TV + IRV).
  • Vital capacity – the total amount of air exhaled after maximal inhalation.
  • Residual volume – the volume of air remaining in the lungs after maximum forceful expiration.
  • Functional residual capacity (FRC) – the volume remaining in the lungs after a normal, passive exhalation. It cannot be measured by spirometry because they exclude volume that cannot be removed from the lungs.
  • Minimal volume –
35
Q

What is the relationship between concentration and P (partial pressure)?

A

Directly proportional.

36
Q

What is the total pressure of air?

A

760 mm Hg.

P(Air) = PN2 + PO2 + PCO2+ PH2O = Dalton’s law.

37
Q

What are the partial pressures of Oxygen and Carbon Dioxide in the atmosphere?

A

160 mm Hg = PO2.

0.3 mm Hg = PCO2.

38
Q

What is the P of oxygen and carbon dioxide in alveoli? Why are they different from the atmosphere?

A

PO2 = 100 mm Hg.

PCO2 = 40 mm Hg.

  • The P are different because O2 is taken into the blood & CO2 is added.
39
Q

What is the P of O2 and CO2 and in pulmonary arteries?

A

Both of these gases are in a solution.

PO2 = 40 mm Hg.

PCO2 = 45 mm Hg.

40
Q

What does it mean that something has a partial pressure in a solution?

A

This solution would be in equilibrium with a gas of the same partial pressure.

41
Q

What is Fick’s law of diffusion?

A

It describes the rate of diffusion of a gas across some tissue.

  • dV/dt = A/T x D x (P1 - P2)

dV/dt – change of volume over time.
A – area (bigger, higher rate)
T – tissue thickness (thinner, higher rate)
D – Diffusion coefficient
P – Partial pressure (bigger difference, higher rate)

42
Q

How much oxygen does a human body require?

A

250 ml/ minute.

43
Q

What is the structural feature and characteristics of alveoli?

A

They provide large surface area and thin respiratory membrane.

Majority of their cells are type I cells.

44
Q

How do oxygen molecules move from the alveoli to blood capillaries? What membranes do they have to cross?

A

They need to cross type I alveoli cells.
Alveolar cell layer, fused basement membrane, and capillary endothelium (total distance 0.5 micro-metres).

45
Q

How many alveoli are there in lungs?

A

≈ 300 million alveoli, with a total surface area ≈ 60-80 m2.

46
Q

How is oxygen transported into the blood?

A

It is bound to haemoglobin.

47
Q

What is the O2 content of plasma? How much oxygen does the human body demand? What does this suggest?

A

The O2 content of blood plasma is 3ml O2/l blood.

The human body requires 250 ml/min.

This means that solubility of O2 in blood plasma is low.

48
Q

What is the content O2 in red blood cells? How much oxygen is there in blood in total?

A

O2 content of red blood cells: 197 ml O2/l blood.

Total oxygen in blood: 200 ml O2/l blood.

( + 3ml O2/l blood in plasma)

49
Q

What is haemoglobin?

A

A protein containing iron that facilitates the transport of oxygen in red blood cells.

Composed of “heme iron” (iron porphyrin complex) and globin (a type of protein: 2 alpha chains and 2 beta chains).

50
Q

How many heme groups does one haemoglobin have?

A

4 heme groups.

51
Q

How many molecules of oxygen can one heme group carry?

A

Each Fe2+ can reversibly bind one molecule of oxygen (complex called oxyhaemoglobin).

52
Q

What is cooperative binding?

A

Once O2 has bound to heme group, it increases the affinity of the remaining heme groups to oxygen.

53
Q

How is carbon transported in blood?

A
  • Carbamino — CO2 can bind to haemoglobin, but it doesn’t bind to heme groups, instead it binds to the amino groups of the proteins.
  • HCO3^- — Blood mainly carries CO2 as bicarbonate.
  • CO2 — dissolved in plasma.
54
Q

What is chloride shift? Why does it occur?

A

Bicarbonate will move out of the cells in exchange for chloride ions.

The removal of HCO3^- from the red blood cells increases the capacity of the blood to carry CO2 (in the form of bicarbonate), as removing a product of the reaction prevents the reaction from quickly reaching an equilibrium. And the bicarbonate also acts as an important pH buffer in the blood plasma.

55
Q

What is carbonic anhydrase (CAs)?

A

An enzyme in red blood cells that catalyses the bidirectional conversion of carbon dioxide (CO2) + water (H2O) into bicarbonate (HCO3-) + protons (H+).

56
Q

How is rhythm generated in respiratory muscles to control breathing?

A

Since respiratory muscles have no intrinsic rhythmic activity, rythm is generated by groups of neurons in brainstem.

57
Q

What are some factors that act on respiratory centres to get them to adjust their rhythm according to the body’s needs?

A
  • P of CO2
  • P of O2
  • pH
  • Emotional state of an individual
  • Internal body temperature
58
Q

What are peripheral and central chemoreceptors?

A

Special nerve cells or receptors that sense changes in the chemical composition of the blood.

  • They sense changes in PO2, PCO2, and pH.
  • They send signals to the respiratory centres to adjust rate and depth of ventilation.
59
Q

What is the effect of O2 and CO2 levels in blood and on body?

A
  • If there’s more CO2 in blood, there’s more H+ (protons), so pH lowers.

More CO2, more H+ —> pH lower.

  • If there’s a high demand for oxygen, more respiration occurs.

High demand for O2: PO2 low, PCO2 high —> more respiration: More O2 is used, more CO2 is produced.

CO2 + H2O <=> H2CO3 (carbonic acid) <=> H+ + HCO3-

60
Q

Where are peripheral chemoreceptors found and what is their primary function?

A
  • Carotid (arteries that carry blood to head & neck) bodies and aortic bodies.
  • Mainly respond to blood PO2 decrease.
    ~ React to a certain extent to changes in PCO2.
61
Q

How do peripheral chemoreceptors work and signal to the respiratory centres to adjust ventilation rate and depth?

A

In the carotid bodies, glomus cells release neurotransmitters in response to low PO2.

Neurotransmitters stimulate sensory neurons that transmit signals to respiratory centres. As a result, ventilation increases.

1) Glomus cell senses low PO2 in blood.

2) K+ channels close (normally they are open and K ions can move out).

3) Cell depolarises (inside is more positive than usual).

4) Voltage-gated Ca2+ channel opens.

5) Ca2+ enters the cell.

6) Exocytosis of neurotransmitters.

7) Neurotransmitters bind to sensory neuron receptors.

8) Action potential is stimulated and signals to medullary centres to increase ventilation.

62
Q

Where are central chemoreceptors located?

A

On **ventral surface* of medulla (close to neurons of the respiratory centre).

Physiology And Disease (16 decks)

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