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Physiology Flashcards

1
Q

Define internal respiration

A

The intracellular mechanisms which consumes O2 and produces CO2

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2
Q

Define external respiration

A

Refers to the sequence of events that leads to the exchange of O2 and CO2 between external environment and the cells of the body

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3
Q

What are the four steps of external respiration?

A
  • ventilation
  • gas exchange between alveoli and the blood
  • gas transport in the blood
  • gas exchange at the tissue level
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4
Q

Describe the four steps of external respiration?

A
  • Ventilation; the mechanical process of moving gas in and out of the lungs
  • gas exchange between alveoli and blood; the exchange of O2 and CO2 between the air in the alveoli and the blood in the pulmonary capillaries
  • gas transport in the blood; the binding and transport of O2 and CO2 in the circulating the blood
  • gas exchange at the tissue level; the exchange of O2 and CO2 between the blood in the systemic capillaries and the body cells
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5
Q

What are the four body systems involved in external respiration?

A
  • the respiratory system
  • the cardiovascular system
  • the haematology system
  • the nervous system
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6
Q

Define Boyles law

A

At any constant temperature, the pressure exerted by a gas varies inversely with the volume of the gas. As the volume of a gas increases, the pressure exerted by the gas decreases

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7
Q

What needs to happen to the intra-alveolar pressure for air to flow into the lungs during inspiration?

A

The intra-alveolar pressure must become less than atmospheric pressure

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8
Q

During inspiration, what expands as a result of contraction of respiratory muscles?

A

The thorax and lungs

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9
Q

What are the two forces that hold the thoracic wall and the lungs in close apposition?

A
  • intrapleural fluid cohesiveness

- negative intrapleural pressure

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10
Q

Describe the intrapleural fluid cohesiveness

A

The water molecules in the intrapleural fluid are attached to each other and resist being pulled apart. The pleural membrane tend to stick together

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11
Q

Describe the negative intrapleural pressure

A

The sub-atmospheric intrapleural pressure creates a transmural pressure gradient across the lung wall and across the chest wall. So the lungs are forced to expand outwards while the chest is forced to squeeze inwards

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12
Q

What is the atmospheric pressure, the intra-alveolar pressure and the intrapleural pressure?

A 
Atmospheric = 760 mmHg
Intra-alveolar = 760 mmHg
Intrapleural = 756 mmHg
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13
Q

What three pressure are important in ventilation?

A
  • atmospheric pressure
  • intra alveolar pressure
  • intrapleural pressure
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14
Q

Inspiration is an active process dependant on what?

A

Muscle contraction

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15
Q

Which nerve supplies the diaphragm?

A

The phrenic nerve

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16
Q

What occurs when the external intercostal muscle contracts?

A

Lifts the ribs and moves out the sternum

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17
Q

Why do the lungs increase in size?

A

To make the intra-alveolar pressure fall

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18
Q

Why does the intra-alveolar pressure fall when the lungs increase in size?

A

Air molecules become contained in a larger volume (Boyles law)

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19
Q

Is normal expiration a passive process or an active process?

A

A passive process

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20
Q

How do the chest wall and stretched lungs recoil to their pre-inspiratory size?

A

Due to their elastic properties

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21
Q

What does the re-coiling of the lungs do to the intra-alveolar pressure?

A

The intra-alveolar pressure rises

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22
Q

Describe the movement of the diaphragm during inhalation and exhalation

A

During inhalation the diaphragm contracts and moves down. During exhalation the diaphragm relaxes and moves up

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23
Q

Describe a pneumothorax

A
  • loss of pressure gradient
  • air in the pleural space
  • can be spontaneous, traumatic or iatrogenic
  • this can abolish transmural pressure gradient leading to lung collapse
  • small pneumothorax can be asymptomatic
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24
Q

What are the physical signs and symptoms of pneumothorax?

A

Symptoms; shortness of breath, chest pain

Physical signs; hyper-resonant, percussion note, decreases / absent breath sounds

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25
Q

What is lung recoil caused by?

A
  • elastic connective tissue in the lungs

- alveolar surface tension

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26
Q

Describe alveolar surface tension

A
  • attraction between water molecules at liquid air interface
  • in the alveoli this produces a force which resists the stretching of the lungs
  • if the alveoli were lined with water alone, the surface tension would be too strong so the alveoli would collapse
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27
Q

What reduces the alveolar surface tension?

A

Surfactant

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28
Q

Describe the law of LaPlace

A

The smaller alveoli (with a smaller radius) have a high tendency to collapse

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29
Q

Describe surfactant

A
  • complex mixture of lipids and proteins secreted by type 2 alveoli
  • lowers alveolae surface tension by interspersing between the water molecules lining the alveoli
  • lows the surface tension of smaller alveoli more than that of larger alveoli
  • this prevents the smaller alveoli from collapsing and emptying their air contents into the larger alveoli
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30
Q

Describe respiratory distress syndrome of the new born

A
  • developing foetal lungs are unable to synthesise surfactant until late in pregnancy
  • premature babies may not have enough pulmonary surfactant
  • the baby makes very strenuous inspiratory efforts in an attempt to overcome the high surface tension and inflate the lungs
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31
Q

Describe the alveolar interdependence

A
  • another factor to keep alveoli open
  • if an alveolus starts to collapse, the surrounding alveoli are stretched and then recoil exerting expanding forces in the collapsing alveolus to open it
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32
Q

Name the forces that are keeping the alveoli open

A
  • transmural pressure gradient
  • pulmonary surfactant
  • alveolar interdependence
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33
Q

Name the forces promoting alveolar collapse

A
  • elasticity of stretched lung connective tissue

- alveolar surface tension

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34
Q

What are the major inspiratory muscles?

A

The diaphragm and the external intercostal muscles

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35
Q

Name the accessory muscles of inspiration (that contract only during forceful inspiration)

A
  • sternocleidomastoid
  • scalenus
  • pectoral
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36
Q

Name the muscles of active expiration (contracts only during active expiration)

A
  • abdominal muscle

- internal intercostal muscles

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37
Q

Describe the total lung capacity

A
  • the maximum volume of air that the lungs can hold
  • vital capacity + residual volume
  • average value = 5700ml
  • residual volume cannot be measured by spirometry meaning it is not possible to measure total lung volume by spirometry
  • residual volume increases when the elastic recoil of the lung is lost eg. in emphysema
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38
Q

What does the volume time curve allows you to determine?

A
  • FVC
  • FEV1
  • FEV1/FVC ratio
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39
Q

What is forced vital capacity?

A

Maximum volume that can be forcibly expelled from the lungs following a maximum inspiration

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40
Q

What is FEV1?

A

Volume of air that can be expired during the first second of expiration in an FVC determination

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41
Q

What is the FEV1/FVC ratio?

A

The proportion of the forced vital capacity that can be expired in the first second

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42
Q

What is a normal FEV1:FVC ratio and what is the value for asthmatics?

A
  • more than 75%

- less than 75%

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43
Q

Describe the values of FVC, FEV1 and FEV1/FVC during airway obstruction

A
  • FVC = low or normal
  • FEV1 = low
  • FEV1/FVC = low
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44
Q

Describe the values of FVC, FEV1 and FEV1/FVC during lung restriction

A
  • FVC= low
  • FEV1= low
  • FEV1/FVC= normal
45
Q

Describe the values of FVC, FEV1 and FEV1/FVC during combination of obstruction and restriction

A
  • FVC = low
  • FEV1= low
  • FEV1/FVC= low
46
Q

Describe airway resistance

A
  • resistance to flow in the airway normally is very low and therefore air moves with a small pressure gradient
  • primary determination of airway resistance is the radius of the conducting airway
  • parasympathetic stimulation causes bronchodilation
  • sympathetic stimulation causes bronchodilation
  • disease states can cause significant resistance to airflow
  • expiration is more difficult than inspiration
47
Q

During inspiration what pulls the airways open?

A

The expanding thorax

48
Q

What happens to intrapleural pressure during inspiration and expiration?

A

Inspiration; intrapleural pressure falls

Expiration; intrapleural pressure rises

49
Q

What makes active expiration more difficult in patients with airway obstruction?

A

Dynamic airway compression

50
Q

Describe peak flow meters

A
  • gives an estimate of peak flow rate
  • the peak flow rate assesses airway function
  • the test is useful in patients with obstructive lung disease
51
Q

Describe how peak flow meters are used?

A
  • it is measured by the patient giving a short sharp blow into the peak flow meter
  • the best of three attempts is usually taken
  • the peak flow rate in normal adults varies with age and height
52
Q

Describe pulmonary compliance

A
  • during inspiration the lungs are stretched
  • compliance is a measure of effort that has to go into stretching or distending the lungs
  • the less compliant the lungs are, the more work is required to produce a given degree of inflation
53
Q

Describe decreased pulmonary compliance

A
  • pulmonary compliance is decreased by factors such as pulmonary fibrosis, pulmonary oedema, lung collapse, pneumonia, absence of surfactant
  • decreased pulmonary compliance means greater change in pressure is needed to produce a given change in volume (ie. lungs are stiffer) this causes shortness of breath especially on exertion
  • decreased pulmonary compliance may cause a restrictive pattern of lung volumes in spirometry
54
Q

Describe increased pulmonary compliance

A
  • compliance may become abnormally increased if the elastic recoil of the lung is lost
  • increased compliance occurs in emphysema. Patients have to work harder to get the air out of the lungs (hyperinflation of lungs)
  • remember dynamic airway obstruction will also be aggravated in patients with obstructed airway and emphysema caused by COPD
  • compliance also increased with increasing age
55
Q

When is work of breathing increased?

A
  • when pulmonary compliance is decreased
  • when airway resistance is increased
  • when elastic recoil is decreased
  • when there is a need for increased ventilation
56
Q

Why is alveolar ventilation less than pulmonary ventilation?

A

Due to the presence of anatomical dead space

57
Q

What is pulmonary ventilation?

A

The volume of air breathed in and out per minute

58
Q

What is alveolar ventilation?

A

The volume of air exchanged between the atmosphere and alveoli per minute. This is more important as it represents new air available for gas exchange with blood

59
Q

How is pulmonary ventilation increased eg. during exercise?

A

Both the depth (tidal volume) and rate of breathing (rr) increase

60
Q

What is the equation for pulmonary ventilation?

A

Tidal volume x respiratory rate

61
Q

What is the equation for alveolar ventilation?

A

(tidal volume - dead space) x respiratory rate

62
Q

What is ventilation perfusion?

A

The transfer of gases between the body and atmosphere depends on ventilation and perfusion

63
Q

Define ventilation

A

The rate at which gas is passing through the lungs

64
Q

Define perfusion

A

The rate at which blood is passing through the lungs

65
Q

What is alveolar dead space?

A

Ventilated alveoli what are not adequately perfused with blood

66
Q

The physiological dead space is equal to what?

A

Anatomical dead space + alveolar dead space

67
Q

What causes pulmonary vasodilation?

A

Increase in alveolar O2 concentration as a result of increased ventilation

68
Q

What causes decreased airway resistance leading to increased airflow?

A

Accumulation of CO2 in alveoli as a result of increased perfusion

69
Q

What happens when perfusion is greater than ventilation in an area?

A
  • CO2 increases in the area
  • dilation of local airways
  • O2 decreases in the area
  • airflow increases
  • constriction of local blood vessels
  • blood flow decreases
70
Q

What happens when ventilation is greater than perfusion in an area?

A
  • CO2 decreases in the area
  • constriction of local airways
  • airflow decrease
  • O2 increases in the area
  • dilation of local blood vessels
  • blood flow increases
71
Q

What do the pulmonary arterioles do in decreased O2 and increased O2?

A 
Decreased= vasoconstriction 
Increased = vasodilation
72
Q

What do the systemic arterioles do in increased O2 and decreased O2?

A 
Decreased = vasodilation 
Increased = vasoconstriction
73
Q

What are the four factors that influence the rate of gas exchange across alveolar membrane?

A
  1. partial pressure gradient of O2 and CO2
  2. diffusion coefficient of O2 and CO2
  3. surface area of alveolar membrane
  4. thickness of alveolar membrane
74
Q

Describe daltons law of partial pressures

A
  • the total pressure exerted by a gaseous mixture = the sum of the partial pressures of each individual component in the gas mixture
75
Q

The partial pressure of a gas determines what?

A

The pressure gradient for that gas

76
Q

What is the partial pressure of a gas?

A

The pressure that one gas in a mixture of gases would exert if it were the only gas present in the whole volume occupied

77
Q

What is PaO2?

A

The partial pressure of oxygen in the alveolar air

78
Q

What is PiO2?

A

Partial pressure of O2 in inspired air

79
Q

What is PaCO2?

A

Partial pressure of CO2 in arterial blood

80
Q

What is more soluble in membranes, CO2 or O2?

A

CO2`

81
Q

The solubility of gas in membranes is known as what?

A

The diffusion coefficient

82
Q

Name non-respiratory functions of the respiratory system

A
  • route for water loss and heat elimination
  • enhances venous return
  • helps maintain normal acid base balance
  • enable speech, singing and other vocalisations
  • defends against inhaled foreign matter
  • removed. modifies, activates or inactivates various materials passing through the pulmonary circulation
  • nose serves as the organ of smell
83
Q

Describe henrys law

A
  • the amount of a given gas dissolved in a given type and volume of liquid (eg. blood) at a constant temperature is proportional to the partial pressure of the gas in equilibrium with the liquid
84
Q

What is the primary factor which determines the percentage saturation of haemoglobin with O2?

A

The PO2

85
Q

What is the oxygen delivery index?

A

oxygen delivery to the tissues is a function of oxygen content of arterial blood and the cardiac output

86
Q

What is the effect of respiratory disease on arterial PO2, Hb saturation and O2 content of the blood?

A

decreased arterial PO2
decreases Hb saturation
Decreases O2 content of the blood

87
Q

How does heart failure affect cardiac output?

A

It decreases cardiac output

88
Q

What is the effect of anaemia on Hb concentration and O2 content of the blood?

A

Hb concentration decreases

O2 content of the blood decreases

89
Q

The partial pressure of inspired oxygen depends on what?

A
  • total pressure

- proportion of oxygen in gas mixture

90
Q

How do you convert kPa to mmHg?

A

Multiply by 7.5

91
Q

Describe myoglobin

A
  • present in skeletal and cardiac muscles
  • one haem group per myoglobin molecule
  • no co-operative binding of O2
  • dissociation curve is hyperbolic
  • myoglobin releases O2 at very low PO2
  • provides a short term storage of O2 for anaerobic conditions
  • presence of myoglobin in the blood indicates muscle damage
92
Q

Describe foetal haemoglobin

A
  • differs from adult haemoglobin in structure
  • has 2 alpha subunits and 2 gamma subunits
  • HbF interacts less with 2,3 biphosphoglycerate in RBC
  • has a higher affinity for O2
  • allows O2 to transfer mother to foetus even if the PO2 is low
93
Q

Describe the Haldane effect

A

Removing O2 from Hb increases the ability of Hb to pick up CO2 and CO2 generated H+

94
Q

The breathing rhythm is generated by what?

A

A network of neurons called the pre-botzinger complex

95
Q

The pons respiratory centre s include what?

A
  • pneumotaxic centre

- apneustic centre

96
Q

The medullary respiratory centre include what?

A
  • dorsal respiratory group

- ventral respiratory group

97
Q

What gives rise to inspiration?

A
  • rhythm generated by pre-botzinger complex
  • excites dorsal respiratory group neurones
  • fire in bursts
  • firing leads to contraction of inspiratory muscles
  • when firing stops, passive expiration
98
Q

Describe the muscle movement during inspiration

A
  • the volume of the thorax is increased vertically by contraction of the diaphragm flattening out its dome shape
  • the external intercostal muscle contraction lifts the rib and moves out the sternum
99
Q

Describe active expiration during hyperventilation

A
  • increased firing of dorsal neurones excites a second group of neurones
  • ventral respiratory group neurones
  • excites intercostals, abdominals etc. forceful expiration
  • in normal breathing, ventral neurones do not activate expiratory muscles
100
Q

Describe the apneustic centre

A
  • impulses from these neurones excite inspiratory area of medulla
  • prolong inspiration
  • rhythm generated in medulla
  • rhythm can be modified by inputs from the pons
101
Q

The respiratory centres are influenced by stimuli received from where?

A
  • higher brain centres
  • stretch receptors
  • juxtapulmonary receptors
  • joint receptors
  • baroreceptors
  • central chemoreceptors
  • peripheral chemoreceptors
102
Q

Name some examples of involuntary modifications of breathing

A
  • pulmonary stretch receptor hering-breur reflex
  • joint receptors reflex in exercise
  • stimulation of respiratory centre by temperature, adrenaline or impulses from cerebral cortex
  • cough reflex
103
Q

Name some factors that may increase ventilation during exercise

A
  • reflexes originating from body movement
  • adrenaline release
  • impulses from the cerebral cortex
  • increase in body temperature
  • later; accumulation of CO2 and H+ generated by active muscles
104
Q

Describe central chemoreceptors

A
  • situated near the surface of the medulla of the brainstem
  • respond to the [H+] of the cerebrospinal fluid
  • CSF is separated from the body by the blood-brain barrier
  • relatively impermeable to H+ and HCO3-
  • CO2 diffuses readily
  • CSF contains less protein than blood and hence is less buffered than blood
105
Q

Describe hypoxic drive of respiration

A
  • the effect is all via the peripheral chemoreceptors
  • stimulated only when arterial PO2 falls to low levels (<8.0 kPa)
  • it is not important in normal respiration
  • may become important in patients with COPD
  • important at high altitudes
106
Q

What is hypoxia at high altitudes caused by?

A

Decreased partial pressure of inspired oxygen (PiO2)

107
Q

Name the symptoms of acute mountain sickness

A
  • headache
  • fatigue
  • nausea
  • tachycardia
  • dizziness
  • sleep disturbance
  • exhaustion
  • shortness of breath
  • unconsciousness
108
Q

Describe the chronic adaptations to high altitudes hypoxia

A
  • increased RBC production (polycythaemia), O2 carrying capacity of blood increased
  • increased 2,3 BPG produced within RBC - O2 offloaded more easily into tissues
  • increased number of capillaries blood diffuses more easily
  • increased number of mitochondria, O2 can be used more efficiently
  • kidneys conserve acid, arterial pH decreases

Respiratory (7 decks)

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