Respiratory Physiology

Question 1

Basic functions of the respiratory system? Overview?

Answer 1

• Gas exchange leading to energy release via aerobic respiration
• Acid base balance (reg of body pH)
• Protection from infection
• Communication via speech

Question 2

Why do we breathe? Characteristics?

Answer 2

To produce energy: - respiration uses oxygen to produce energy, producing CO2 and waste

The only way this works via the integration of the CVS and the respiratory system

Question 3

Gas exchange? Characteristics?

Answer 3

Exchange of gas between lungs and blood (or via blood and cells) occurs via simple diffusion down partial pressure gradients

Part 1: between atmosphere and lungs
Part 2: between lung and blood
Part 3: transport of gases in blood
Part 4: between blood and cells

Question 4

Basic Respiratory anatomy? Upper and Lower tract?

Answer 4

Upper:

• Pharynx
• Oesophagus
• Larynx
• Tongue

Lower:

• Trachea
• Right and Left lung
• Right and Left bronchus
• Diaphragm

Question 5

Lower respiratory tract - lobes and lungs?

Answer 5

• Trachea travels down into the lungs and splits into 2 primary bronchi
• 5 secondary bronchi 1 to each lobe
• Right lung has 2 lobes (superior, middle and inferior)
• Left lung *superior and inferior) also has the cardiac notch where the heart sits

Question 6

Branching of airways? Structure?

Answer 6

• Larynx
• Trachea
• Primary bronchus
• Secondary bronchus
• Bronchiole
• Alveoli

Question 7

Structure of the lung lobule?

Answer 7

• The bronchiole is surrounded by SM and the bronchial artery, vein and nerve
• Bronchiole becomes the alveoli that has elastic fibres and capillary beds to allow gas exchange

Question 8

Alveolar structure?

Answer 8

Contains:

• Elastic fibres
• Capillaries
• Endothelial cells of capillaries
• TII cells (surfactant cells)
• TI cells

Question 9

Resistance to air flow? Characteristics?

Answer 9

Smooth muscle in bronchial wall regulates diameter of airways:
- contraction reduces diameter and increases resistance and vice versa

Question 10

Lung volumes and capacities? Names and values?

Answer 10

• Tidal volume: 500mL
• Total lung capacity: 6000mL
• Vital capacity: 4600mL
• Residual volume: 1200mL
• Expiratory reserve volume: 1100mL
• Inspiratory reserve volume: 3000mL

Question 11

Lung volumes and capacities? Definition?

Answer 11

• TV - Tidal Volume. The volume of air breathed in and out of the lungs at each breath.
• ERV - Expiratory Reserve Volume. The maximum volume of air which can be expelled from the lungs at the end of a normal expiration.
• IRV - Inspiratory Reserve Volume. The maximum volume of air which can be drawn into the lungs at the end of a normal inspiration.
• RV - Residual Volume. The volume of gas in the lungs at the end of a maximal expiration.
• VC - Vital Capacity = tidal volume + inspiratory reserve volume + expiratory reserve volume.
• TLC - Total Lung Capacity = vital capacity + the residual volume.
• IC - Inspiratory Capacity = tidal volume + inspiratory reserve volume.
• FRC - Functional Residual Capacity = expiratory reserve volume + residual volume.
• FEV1:FVC = Fraction of forced vital capacity expired in 1 second.

Question 12

Gas laws? Name and explanation?

Answer 12

• Boyle’s Law states that the pressure exerted by a gas is inversely proportional to to its volume (P a 1/V)
• Henry’s Law states that the amount of gas dissolved in a liquid is determined by the pressure of the gas and it’s solubility in the liquid.
• Dalton’s Law states that the total pressure of a gas mixture is the sum of the pressures of the individual gases.

Gases always move from areas of high Pa to areas of low Pa

Question 13

Cross-sectional structure of the lungs?

Answer 13

• Right/Left lung

- Right/Left pleural cavity

Question 14

Anatomy of the pleural sac? Structure?

Answer 14

The lungs and interior of the thorax are covered by pleural membranes between the surfaces of which is an extremely thin layer of intrapleural fluid

• left/right pleural sac
• parietal pleura
• visceral pleura
• pleural cavity filled with intrapleural fluid`

Question 15

Functions of the pleural membranes? Functions?

Answer 15

• Stick the lungs to the rib cage
• Visceral pleura is “stuck” to the surface of the lungs
• Visceral pleura is “stuck” to the parietal pleura via the cohesive forces of the pleural fluid
• Parietal pleura is “stuck” to the rib cage and diaphragm

The lungs will therefore follow the movements of these bones and muscles

Question 16

Muscles of Breathing? Overview?

Answer 16

These muscles are responsible for creating the pressure gradient that determines air flow (remember, air flows from high pressure to low pressure)

Inspiration:

• Sternocleidomastoids
• Scalenes
• External intercostals
• Diaphragm

Expiration:

• Internal intercostals
• Abdominal muscles

Question 17

Mechanism of breathing action? Diaphragm?

Answer 17

• At rest, the diaphragm is relaxed
• Diaphragm relaxes and the thoracic volume decreases
• Diaphragm contracts and the thoracic volume increases

Question 18

Mechanics of breathing? Ribs?

Answer 18

Pump handle: motion increases anterior-posterior dimensions of rib cage

Bucket handle: motion increases lateral dimensions of rib cage

Question 19

Relevant pressures within the lungs?

Answer 19

Intra-thoracic Pa: pressure inside the thoracic cavity (inside lung)

Intra-pleural Pa: pressure inside the pleural cavity

Transpulmonary Pa: difference between alveolar Pa and intra-pleural Pa

Question 20

Pressure changes within the lungs during inspiration and expiration?

Answer 20

During inspiration:

• the alveolar pressure decreases and increases by 1 mmHg ending at 0 Pa difference
• the interapleural pressure drops by -3 mmHg

During expiration:

• the alveolar Pa increases by 1 and drops by 1 ending at a 0 Pa chnage
• the intrapleural Pa increases back to -3 mmHg (from -6)

Question 21

Importance of the relationship between pleural membranes?

Answer 21

Normal:

• the intrapleural Pa is subatmospheric (-3mmHg), which drives air into the lungs
• elastic recoil tries to pull chest wall outward and creates and inward pull

Pneumothorax:

• stab wound
• lung collapses

Question 22

Bulk flow of air equation and explanation? lung elasticity explanation?

Answer 22

• Bulk flow of air between the atmosphere and alveoli is proportional to the difference between the atmospheric and alveolar pressures and inversely proportional to the airway resistance: F = (Patm- Palv)/R
• The lungs are stretched and are attempting to recoil, whereas the chest wall is compressed and attempting to move outward. This creates a subatmospheric intrapleural pressure and hence a transpulmonary pressure that opposes the forces of elastic recoil

Question 23

Surfactant? definition and function?

Answer 23

Detergent like fluid produced by Type II Alveolar cells

• Reduces surface tension on alveolar surface membrane thus reducing tendency for alveoli to collapse
• surface tension occurs wherever there is an air-water interface and refers to the attraction between water molecules

Question 24

How does surfactant work? Example? Principle of surface tension?

Answer 24

Water molecules is attracted to other water molecules, forming larger droplets

All of these droplets causes the overall force to be brought inwards that causes surface tension within the alveoli

Surfactant’s role us to surround the other water molecules to stop the attraction

Increases lung compliance, reduces lung’s tendency to recoil, makes breathing easier and more effective in small alveoli

Question 25

How does surfactant prevent alveolar collapse?

Answer 25

Pa is greater in the smaller alveoli than the larger ones and so air flows into the larger alveoli Surfactant reduces surface tension which equalises the large and small alveoli, which allows greater gas exchange due to increased SA

Question 26

Pulmonary ventilation? Definition?

Answer 26

Total air movement in and out of the lungs

Question 27

Alveolar ventilation? Definition?

Answer 27

Fresh air getting to the alveoli and therefore available for gas exchange

Question 28

Anatomical dead space volume? Characteristics?

Answer 28

- 150 mL | - volume of gas occupied by the conducting airways and the gas is not available for exchange

Question 29

Inhalation and exhalation process - air volumes?

Answer 29

Exhalation: 500mL loss; - which is 150mL dead space and 350mL stale air and the remaining 150mL (stale air) is present in the conducting airways Inhalation: 500mL gain; - 150mL stale air from the dead space enters the lungs, and only 350mL of fresh air enters the alveoli, and another 150mL of fresh air is trapped in the dead space

Question 30

Hypoventilation vs Hyperventilation? Differences?

Answer 30

Hypoventilation: Higher TV and lower frequency (but alveolar ventilation is still normal) Hyperventilation: Lower TV and higher frequency (but the alveolar ventilation is much lower) Hyperventilation is bad in a clinical sense

Question 31

Dalton's Law? Definition?

Answer 31

The pressure of an entire gaseous mixture is equal to the sum of the pressures of the individual gases in that mixture Atmospheric Pa - 760 mmHg Composition of air: 78% N, 21% O2 and 0.04% CO2

Question 32

Alveolar ventilation and partial pressues? PO2 and PCO2?

Answer 32

Normal ventilation: 4.2L/min - PO2: 100 mmHg - PCO2: 40 mmHg Hyperventilation: >4.2L/min - PO2: 120 mmHg - PCO2: 20 mmHg Hypoventilation: < 4.2L/min - PO2 30 mmHg - PCO2 100 mmHg

Question 33

Compliance? Definition?

Answer 33

Change in volume relative to change in pressure - It represents the stretchability of the lungs e. g. how much does volume change for any given change in pressure

Question 34

Difference between low and high compliance?

Answer 34

HIGH COMPLIANCE = large increase in lung volume for small decrease in interpleural pressure LOW COMPLIANCE = small increase in lung volume for large decrease in interpleural pressure Changes in disease and age

Question 35

Pressure, volume and distribution of ventilation? Differences in orientation?

Answer 35

- The pressure volume curve varies between apex and base of the lung. At the base the volume change is greater for a given change in pressure. - Alveolar ventilation declines with height from base to apex. - Compliance is lower at the apex due to being more inflated at FRC. At the base the lungs are slightly compressed by the diaphragm hence more compliant on inspiration. - A small change in intrapleural pressure therefore brings about a larger change in volume at the base compared with the apex.

Question 36

Gas transport in the blood? Process?

Answer 36

- Blood transport O2 from the lungs to the tissues, used to produce energy and then the waste and CO2 is removed - Haemoglobin carries O2 (200ml/L) - Bulk of CO2 is transported in various forms

Question 37

Blood supply to the lungs? Pulmonary circulation?

Answer 37

- Consists of L and R pulmonary arteries originating from the RV - These both supply the capillary network around the alveoli and returns oxygenated blood to the LA, via the pulmonary vein (high flow - low pressure)

Question 38

The rate of diffusion across the alveoli? Factors?

Answer 38

- Directly proportional to the partial pressure gradient - Directly proportional to the solubility of the gas - Directly proportional to the available SA - Inversely proportional to the thickness of the membrane - Most rapid over short distances

Question 39

Gas exchange in the alveoli and blood? Partial Pa?

Answer 39

``` Alveoli: - PO2 (100) - PCO2 (40) Blood at lungs: - PO2 (40) - PCO2 (46) Blood at cells - PO2 (100) - PCO2 (40) Cells: - PO2 (<40) - PCO2 (>46) ```

Question 40

Alveoli to RBC transfer? Characteristics?

Answer 40

The alveoli has a very thin membrane which allows simple diffusion of o2 to the passing RBCs in the bloodstream

Question 41

Haemoglobin? Characteristic?

Answer 41

Structure: 2 alpha chains and 2 beta chains - 98% O2 bound to haemoglobin Each haemoglobin contains 4 haem groups, each of which contains one Fe which binds one o2 and so each haemoglobin can bind 4 molecules - The degree of haemoglobin binding depends on oxygen partial pressure

Question 42

Blood with haemoglobin vs blood without haemoglobin?

Answer 42

Hb effectively sequesters O2 from the plasma, thus maintaining a partial pressure gradient that continues to suck O2 out of the alveoli, until the Hb becomes saturated with O2. Partial pressure of O2 in plasma is fundamental in determining how much O2 binds to Hb.

Question 43

Oxygen-haemoglobin dissociation curve?

Answer 43

Haemoglobin is almost 100% saturated at the normal systemic arterial PO2 of 100 mm Hg. The fact that saturation is already more than 90% at a PO2 of 60 mm Hg permits a relative normal uptake of oxygen by the blood even when alveolar PO2 is moderately reduced. Haemoglobin is 75% saturated at the normal systemic venous PO2 of 40 mm Hg. Thus, at rest only 25% of the oxygen dissociates from haemoglobin and enters the tissues.

Question 44

Factors affecting the oxygen-dissociation curve? Factors?

Answer 44

- pH (reduced pH, reduced affinity and vice versa) - PCO2 (increased CO2, reduced affinity and vice versa) - Temperature (increase temp, reduced affinity and vice versa) - DPG (addition of DPG, reduces affinity)

Question 45

Carbon dioxide transport? Process?

Answer 45

CO2 transport is much simpler than the transport of O2. CO2 is much more soluble than O2 and after CO2 diffuses from the tissues into the blood down it’s partial pressure gradient, 7% remains dissolved in the plasma and is transported in simple solution. The remaining 93% moves into the red blood cells where 23% forms carbamino compounds with the now desaturated haemoglobin while the remainder is converted to bicarbonate ions, exchanged for Cl- across the RBC membrane and transported in the plasma in the form of HCO3-

Question 46

Distribution of blood flow in lungs - influenced by? perfusion? alveolar? resistance chnages?

Answer 46

The distribution of blood flow in the lung is influenced by both hydrostatic (blood) pressure and alveolar pressure. At the base of the lungs blood flow is high since perfusion pressure exceeds alveolar pressure and hence vascular resistance is low. At the apex of the lungs blood flow is low because perfusion pressure is less than alveolar pressure. This compresses the arterioles and vascular resistance is increased.

Question 47

Matching ventilation and perfusion? Characteristics?

Answer 47

In the upright position the ratio of ventilation to perfusion within the lung changes from the base of the lung (bottom) to the apex (top) owing to the effect of gravity. Over 75% of the height the healthy lung performs quite well in matching blood and air (right y-axis). The majority of the mismatch takes place in the apex. This is then auto regulated to keep the ventilation perfusion ratio close to 1.0

Question 48

Autoregulation of ventilation:perfusion?

Answer 48

Ventilation > perfusion: - alveolar PO2 rises, PCO2 falls - causes pulmonary vasodil and bronchial constrict Perfusion > ventilation: - alveolar PO2 falls, PCO2 rises - pulmonary vasoconstrict and bronchial dilation

Question 49

Ventilatory control? Innervation and brain centres?

Answer 49

- requires stimulation of the (skeletal) muscles of inspiration. This occurs via the phrenic (to diaphragm) and intercostal nerves (to external intercostal muscles) - subconcious, but can have voluntary modulation - entirely dependent on signalling from the brain (sever spinal cord above origin of phrenic nerve (C3-5) breathing ceases)

Question 50

Rhythmic breathing and voluntary override? Overview?

Answer 50

Breathing depends upon cyclical activation of the phrenic and intercostals nerves stimulating contraction of the inspiratory muscles (diaphragm/external intercostals). This neural activity is triggered by the medullary inspiratory neurones but with voluntary override

Question 51

Respiratory centres have rhythm modulated by? factors affecting rhythm?

Answer 51

- Emotion (via limbic system in the brain) - Voluntary over-ride (via higher centres in the brain) - Mechano-sensory input from the thorax (e.g. stretch reflex) - Chemical composition of the blood (PCO2, PO2 and pH) – detected by chemoreceptors.

Question 52

Respiratory centre flow chart of action? flow chart?

Answer 52

- Located in the medulla and pons of the brain - Factors affecting rhythm influence the VRG and DRG (dorsal/ventral respiratory group) - the most significant factor is chemoreceptor input - the VRG innervates the tongue, pharynx, larynx and epiratory muscles - the DRG (via the phrenic or intercostal nerves) innervate the inspiratory muscles

Question 53

Chemoreceptors? Types and overview on how they work?

Answer 53

Types: - Central and Peripheral Central: - medulla - responds directly to the H+ (reflects PCO2) - primary ventilatory force Peripheral: - carotid and aortic bodies - responds to plasma H+ and PO2 - secondary ventilatory drive

Question 54

Central chemoreceptors in the medulla? Characteristics and what it detects?

Answer 54

- Detect changes in H+ in CSF - Causes reflex stim of ventilation following rise in H+ (driven by raised PCO2 = hypercapnea) CO2 + H20 = H2CO3 = H+ + HCO3- Ventilation is reflexly inhibited by a decrease in arterial PCO2

Question 55

Process of central chemoreceptor action? Process?

Answer 55

When arterial PCO2 increases carbon dioxide crosses the blood-brain barrier not H+ Central chemoreceptors monitor the PCO2 indirectly in the cerebrospinal fluid. Bicarbonate and H+ are formed and the receptors respond to the H+ Feedback via the Respiratory Centres increases ventilation in response to increased arterial PCO2 . Decreased arterial PCO2 slows ventilation rate.

Question 56

Peripheral chemoreceptors? Characteristics and what it detects?

Answer 56

- Located in the carotid and aortic bodies - Detect changes in arterial PO2 and H+ - Causes reflex stim of ventilation following significant fall in arterial PO2 or a rise in H+ - respond to arterial PO2 not oxygen content - increased H+ usually accompanies a rise in arterial PCO2

Question 57

Oxygen-haemoglobin dissociation curve? Description?

Answer 57

- Haemoglobin is highly saturated across many mmHg of PO2 - And so a large fall in mmHg will occur before the peripheral chemoreceptors to detect a change and influence a response

Question 58

Good Chemoreceptor reflex slide

Answer 58

GHD - Resp 4

Question 59

Emotion and the respiratory centres? the link?

Answer 59

Limbic system input allows emotional responses to alter breathing e.g. rapid, shallow breathing often accompanies anxiety

Question 60

Other aspects of controlling breathing? Characteristics?

Answer 60

Descending neural pathways from cerebral cortex to respiratory motor neurons allow a large degree of voluntary control over breathing Respiration is inhibited during swallowing to avoid aspiration of food or fluids into the airways. Swallowing is followed by an expiration in order that any particles are dislodged outwards from the region of the glottis

Question 61

Pharmacological influences on ventilatory control? Drug examples and their influence?

Answer 61

- Barbiturates – e.g. thiopental (iv. anaesthesia). Inhibit phrenic nerve activity, decrease depth of breathing (alv. ventilation) - Opioids – e.g. morphine. sensitivity to pH and therefore response to PCO2 . Also peripheral chemoreceptor response to PO2 - Benzodiazepines – e.g. diazepam (anxiolytic, sedative). Similar effects to opioids but much less severe. Relatively safe and widely used. - Nitrous oxide – Little effect on response to PCO2 but significantly depresses response to falling PO2. Caution with COPD patients! Widely used.