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Flashcards in Respiratory System Deck (138):

Define external respiration

The process in the lungs by which oxygen is absorbed from the atmosphere into blood within the pulmonary capillaries, and carbon dioxide is excreted.


Define internal (or tissue) respiration

Describes the exchange of gases between the blood in systemic capillaries and the tissue fluid and cells which surround them.


Define cellular respiration

The process within individual cells through hitch they gain energy by breaking down molecules such as glucose. It occurs in mitochondria, consumes oxygen and generates carbon dioxide.


What is meant by pulmonary ventilation?

Breathing: describes the bulk movement of the air into and out of the lungs. The ventilator pump comprises the rib cage with its associated muscles and the diaphragm.


Distinguish between the conducting part and the respiratory part of the respiratory system.

Conducting: A series of cavities and thick-walled tubes which conduct air between the nose and the deepest recesses of the lungs, and in doing so warm, humidity and clean it. The conducting airways are the nasal cavities, pharynx, larynx, trachea, bronchi and bronchioles.
Respiratory: Comprises the tiny, thin-walled airways where gases are exchanged between air and blood. The airways are respiratory bronchioles, alveolar ducts and sacs, and the alveoli themselves.


What is required for efficient gas exchange?

Air must be humidified to 100%, warmed, and filtered to clean it.


Describe the nasal cavity.

A tall, narrow chamber lined with mucous membrane. The wet membrane humidifies and warms inspired air.


Describe the medial and lateral surfaces of the nasal cavity.

Medial surface is flat. The lateral surface carries three sloping shelves (conchae) which increase the SA of the mucous membrane.


What are the paranasal sinuses? What are their functions?

They are air-filled sinuses that open into the cavity. They lighten the face and add resonance to the voice.


What does the roof of the cavity carry? What does turbulence cause? Where do olfactory axons lead from and to?

The roof of the cavity carries the olfactory epithelium. Turbulence caused by sniffing carries air up to the epithelium. Axons of olfactory receptor cells lead towards the brain through perforations in the overlying bone, the cribriform plate.


What are the three parts of the pharynx?

Nasopharynx - Air
Oropharynx - Air and Food
Laryngopharynx - Air and Food


What happens during swallowing?

Soft palate closes nasopharynx to push bolus down. Glottis is closed passively (no active mechanism or muscle contraction involved) and the oesophagus is forced open.


Describe the pharynx.

A vertical passage with three parts, each having an anterior opening. The pharynx is an airway, but also a food way. In terms of its structure, it is primarily part of the gastrointestinal system.


What is rhinositus

Chronic sinus infection


What is the glottis?

The entrance to the larynx


Cartilage does not continue beyond the _______ _____. ________ _______ stop there too.

Smallest bronchi
Mucous glands


The respiratory system always branches ____________. What does this means?

Every tube branches into 2 tubes


List the structures of the respiratory system from largest to smallest and state their generations.

Trachea (0)
Main stem bronchi (1)
Lobar bronchi (2)
Segmental bronchi (3)
Smaller bronchi (4-9)
Bronchioles (10-15)
Terminal bronchioles (16-19)
Respiratory bronchioles (20-23)
Alveolar ducts (24-27)
Alveolar sacs (28)


What is the main function of the trachea?

Open the airway


What is the size of the trachea?

The windpipe is a tube about 12 cm long and as thick as your thumb


What is the structure of the trachea?

Supported by incomplete C-shaped rings of cartilage. Free ends of the cartilage are connected by trachealis muscle (smooth) and contraction narrows the diameter of the trachea.


What is the trachea lined with?

Lined with ciliated epithelium (pseudostratified columnar). Cilia transport a mucous sheet upwards to the nasopharynx (the mucociliary escalator).


Where doe the oesophagus sit?

Oesophagus sits immediately posterior to the trachea, lying in the shallow groove formed by the trachealis muscle.


What does coughing involve?

Contraction of trachealis and thus changes in pressure.


How does smoking affect the trachea?

Chemicals destroy cilia. Can only remove mucous by coughing.


Describe the wall of a bronchus.

Thicker and more complex. More responsible for conducting of air.
- Pseudo-stratified ciliated epithelium
- Goblet cells
- Smooth muscle
- Muco/serous glands
- Cartilage


Describe the action of goblet cells.

First source of mucous
Contains concentrated dry mucous. When it mixes with water, it expands to create more mucous.


Describe the wall of a bronchiole and what is found in it.

Smaller in diameter. Responsible for control of flow of air.
- Club cells
- Ciliated epithelium (not pseudostratified - transitional from columnar to cuboidal)
- Smooth muscle


What does smooth muscle control in the airways? What does asthma involve? How is it treated?

Flow of air into the respiratory zone. Asthma involves contraction of smooth muscles. Bronchodilator relaxes smooth muscle.


What makes a bronchiole a respiratory bronchiole?

If it has alveoli on it


What cells and fluids are found on the alveolar wall?

Type I pneumocytes - attenuated cytoplasm
Type II pneumocytes - surfactant producing cells
Alveolar macrophage - last defence against any pathogens
Surfactant layer


What does the surfactant layer do?

Breaks surface tension. Reduces work of breathing. Keeps alveoli open and stops collapsing when you exhale.


List the layers of the diffusion barrier

Alveolar air space
Squamous pneumocyte
Basement membrane squamous pneumocyte
Basement membrane capillary endothelium
Capillary endothelium
Blood plasma


What is the function of cartilage?

Supports the large airways during inspiration.


Cartilage does not continue beyond the _______ _____. ________ _______ stop there too.

Smallest bronchi
Mucous glands


How does the thickness of the epithelium vary as airway diameter decreases?

It decreases


What does the epithelium of conducting airways contain?

Secretory cells
Goblet cells secrete mucus in the large airways. Clara cells release a serous (watery) secretion in bronchioles.


Which airways have more smooth muscle in relation to their size?

The smaller airways.


When does the muscle coat cease to exist?

It does not continue beyond the smallest bronchioles.


What orientation is the smooth muscle in?

Spiral orientation


What are the subdivisions of the lung?

1) Primary bronchi are right and left main stem bronchi supplying each lung.
2) Secondary bronchi are lobar bronchi supplying lobes (2 on the left, 3 on the right)
3) Tertiary bronchi are segmental bronchi supplying segments of the lung (8 on the left, 10 on the right).


How does segmentation of lungs aid a surgeon?

Each segment has its own air and blood supply. When a localised tumour occurs in the lung, a surgeon who knows the approximate boundaries can remove one or more segments containing the tumour without excessive leakage of air or blood from neighbouring segments.


Describe how the lung is divided.

The lung is divided into ten bronchopulmonary segments, each segment being supplied by a segmental (tertiary) bronchus.


What is the root/hilum of the lung?

It is where blood vessels and bronchi enter and leave the lung. Supported by connective tissue.


What are pleurae? What do the pleurae cover? Where are they continuous?

Smooth membrane that covers each lung and also lines the thoracic cavity in which the lung sits. The two membranes are continuous at the root of the lung (hilum).


What separates the pleurae? What does this allow for?

A thin film of fluid. The fluid allows the pleurae to slide past each other without friction. Also prevents them from being separated. When the thoracic wall moves inwards or outwards, the lungs must follow. Similarly, when the diaphragm moves upwards or downwards, the lungs must follow.


What are the layers of the thoracic wall?

Visceral pleura
Pleural space
Parietal pleura
Muscles of ribs


What percentage of air movement into and out of the lungs is the movement of the ribcage responsible for?



Out of inspiration and expiration, which is active and which is passive?

Inspiration: active. Requires contraction of the external intercostal muscles which run obliquely between ribs.
Expiration: passive. The ribcage returns to its resting position without requiring muscular action.


For breathing during exercise (panting), what muscles are active?

Both sets of intercostal muscles. Externals for inspiration, internals for expiration.


Describe the action of muscles to change the thorax volume during breathing.

The ribs pivot around their joints with the vertebral column. The orientation of the external intercostal muscles means that contraction has the effect of lifting the ribs (rotating them around their pivot points). When the ribs lift, they swing upwards and outwards. This increases the volume of the thorax. The internal intercostal muscles run at right angles to the externals. When they contract, they drag the ribs downwards.


When does active contraction of the internal intercostals occur?

Forceful exhalation


What is the diaphragm?

A dome-shaped platform which forms the floor of the thorax and the roof of the abdomen.


Describe the central and lateral parts of the diaphragm.

Its central part is a thin sheet of connective tissue (technically an aponeurosis) called the central tendon. The lateral margins are muscular. The muscle is fast-acting skeletal muscle, innervated by the phrenic nerve.


What is the effect of contraction of the diaphragmatic muscle?

Shortens and flattens the diaphragm, pulling its central dome downwards. This increases the volume of the thorax and causes inspiration.


What does the passive relaxation of the diaphragmatic muscle allow for?

Allows the diaphragm to lift back towards the thorax, reducing thoracic volume, (expiration)


Movement of the diaphragm is responsible for what percentage of bulk flow of air during quiet breathing and during exercise?

75% during quiet breathing.
Smaller proportion during exercise


What do each of these general variable symbols mean?
V, V with a dot on top, P, F, C, f

V: Volume of gas (L)
V with a dot on top: Rate of change of volume (i.e. rate of bulk flow) of a gas (L/min)
P: Pressure (kPa or mmHg (Torr) or cmH2O)
F: Fractional concentration of a gas
C: Content of a gas in blood (mL/L); Compliance (L/kPa)
f: Frequency of respiration (/min)


What do each of these symbols for the gas phase mean?
I, E, A, T, D, B

I: Inspired gas
E: Expired
A: Alveolar gas
T: Tidal gas
D: Dead-space gas
B: Barometric


What do each of these symbols for the blood phase mean?
a, v, c

a: Arterial
v: Venous
c: Capillary


In mammals breathing is ______. What can a single tidal volume range in size from?

A single tidal volume can range in size from Residual Volume to Total Lung Capacity.


What is meant by Functional Residual Capacity?

The amount of air in the lungs at the end of a normal (relaxed) expiration. When we are at rest, the lung volume always reaches this capacity.


What is meant by tidal volume?

The volume of a breath


Why is there a residual volume?

Not all air can be expelled from the lung. Residual volume is the minimal volume.


What is residual volume?

The air left in the lungs that cannot be expelled during voluntary expiration.


When is maximal inspiration achieved?

Maximum inspiration is achieved by a maximal inspiratory effort. Achieves total lung capacity (5L).


What is ventilation rate at rest and during exercise?

At rest: 0.5L x 12/min = 6L/min
Exercise: 3L x 40/min = 120L/min


What is the bulk rate of flow of air (volume per unit time) proportional to? Use an equation to describe the rate of change of volume during inspiration.

PB - PA: The difference between atmospheric pressure and alveolar pressure.
When PA is greater than PB, exhalation occurs, provided that the glottis is open.
(Pip is less than PB, thus we say Pip is less than 0)


Describe what causes air to enter the lungs.

There must exist a pressure gradient. Air enters the lungs only of alveolar pressure (PA) is less than atmospheric (barometric) pressure (PB). Alveolar pressure becomes sub-atmospheric when thoracic volume increases. This is achieved by descent of the diaphragm and elevation of the rib-cage.


How does resistance affect the equation for bulk rate of flow of air?

The rate at which the lungs expand or deflate (i.e. the rate at which air enters or leaves the lung) is reduced by any factor that increases the resistance to air-flow (R).
V with dot on top = (PB - PA)/R


What are lungs entirely devoid of? Despite this, how does inspiration and expiration occur?

Muscles under voluntary control
Under normal, resting conditions, they fill by the indirect action of skeletal muscles, and empty (expiration) via their inherent elastic recoil.


What is PB equal to?

101kPa or 760mmHg (at sea level)
It is equal to 0 if used as a reference


What is pneumothorax?

Air in the intrapleural space
Affected lung recoils inward and collapses. Chest wall recoils outward.


Describe the balance between the force on the lungs and the rib cage.

The lungs are highly elastic and tend to collapse to zero volume. This tends to separate the visceral and parietal pleura which reduces intra-parietal pressure (Pip) below atmospheric while simultaneously pulling the rib-cage inwards. A balance of forces (between the collapsing lungs and the recoiling ribcage) is achieved at functional residual capacity. Fcw = -FL


Explain how the two opposing forces acting on the lungs and rib-cage come about

- The lungs experience a force (FL) that causes the tendency for them to collapse. This force arises from the elastic recoil of stretched elastic fibres and the surface tension of wet alveolar cells.
- The rib-cage experiences a force (Fcw) that tends to cause it to spring outwards, thereby increasing its volume. The forces arises from stretched tissues in the sterno-costal and costovertebral joints.


What leads to the equilibrium between the lungs and rib-cage?

Because the lungs are effectively connected to the rib cage by the adhering forces of the intrapleural fluid, the collapsing tendency of the lungs exactly counteracts the expanding tendency of the rib-cage, thereby leaving the combined system in an equilibrium position. Provided that the pressure in the airways is zero, this unique neutral position corresponds to FRC.


Why is there a negative sign in the equation: Fcw = -FL?

The forces operate in different directions.


What causes pneumothorax?

When a penetrating injury of the chest wall creates a connection between the atmosphere and the intrapleural space, the balance of forces which normally occurs in the lungs is destroyed on the affected side. That is, the introduction of air between the pleural membranes interrupt the adhesive forces between water molecules, allowing the lung to collapse. In response, the chest wall recoils outward.


What do negative and positive values of air flow indicate? How are these related to tidal volume?

Negative: indicates that air is flowing from atmosphere into the lungs.
Positive: indicates that air flows in the opposite direction during expiration.
The total volume of air moving into (and out of) the lungs in a single breath is the tidal volume: VT


Describe the pressure-volume relations during respiration.

- Immediately before inspiration, alveolar pressure is equal to atmospheric pressure. There is no airflow, because there is no driving pressure from the atmosphere to the lungs. (Intrapleural pressure is about 4 mm Hg below atmospheric
- Inspiration starts when contraction of the inspiratory muscles (primarily the diaphragm) enlarges the thoracic cavity. As thoracic volume increases, the intrapleural pressure becomes more sub-atmospheric and the lungs expand. The increase in lung volume causes alveolar
pressure to decrease and air moves into the lungs.
- Air-flow ceases when alveolar pressure returns to atmospheric pressure. When inspiration terminates, the diaphragm relaxes, intrapleural pressure rises and the lungs recoil. The gases in the alveoli are compressed which elevates alveolar pressure above atmospheric pressure driving air from the lungs to the atmosphere.


What are the factors affecting the exchange of air?

Muscular Effort
Lung characteristics
- Compliance (change of V per change of P)
~ Inverse: Elastance (reflecting the “stiffness” of the lung tissue)
- Resistance (change of P per change of Flow)
~ Inverse: Conductance
- Dead-Space (VD)
- Diffusion


Which factor affecting the exchange of air is to do with the material of the lungs?

Compliance: how readily the lungs inflate in response to change in pressure.
Inverse: Elastance


What is meant by conductance?

How much air can go through an airway in a given amount of time.


What does pulmonary compliance measure?

Measure of the distensibility of the lungs and the chest wall and is defined as the change in volume that accompanies a small change in pressure.


What does the equation for compliance show?

Compliance = ∆V/∆P
- If a small change of pressure brings about a large change of volume, then compliance is high (or, conversely, elastance is low: elastance = ∆P/∆V).
- Conversely, if it requires a large change of pressure to achieve a small change of volume, then
compliance is low.
- Compliance is given by the slope of a graph of Volume as a function of Pressure.


What characterises emphysema?

Greatly increased compliance (loss of elastic fibres)


At low lung volume, why are the lungs incompliant? Why is it easier to fill the lungs once the alveoli are open?

This is because most alveoli have collapsed so that relatively large pressure is required to overcome surface tension in order to reopen them. Once open, the lungs distend relatively easily until they are near full inflation.


Describe the pressure-volume graph for an excised lung in air and compare it to that in saline. What did this graph reveal?

The deflation curve differs from the inflation curve and this hysteresis is primarily the result of surface tension. Much less effort is required to inflate the lungs when they are filled with saline rather than air and hysteresis is much less evident in the pressure-volume relationship. It was this observation, the left-shift of the Volume-Pressure relationship when the air-water interface is eliminated by filling the lung with liquid (saline), which first proved that the air-water surface tension, contributed by millions of ‘wet’ alveoli, is a force to be contended with in vivo.


What does the flow of air into and out of the lungs depend on?

The pressure difference between atmosphere and alveoli and on the resistance to flow through the airways. The mouth and nose contribute significant resistance to airflow,
but resistance is greatest in the medium sized tertiary (segmental) bronchi. R varies inversely with airway radius (r).
• So R is highest in smallest airways.
• But there are many small airways in parallel.
• So TOTAL R is lowest in smallest airways.
Resistance decreases as total cross-sectional area increases in the smaller respiratory airways.


What is asthma?

Chronic condition characterised by sporadic broncho-constriction that increases airway resistance.


What is meant by dead-space? What is its purpose?

Is the volume of the conducting airways (VD). No exchange of respiratory gases occurs in this volume. Dead-space volume is an obligatory consequence of tidal ventilation. Its
presence necessarily dilutes each tidal inspiration with alveolar air remaining from the previous expiration.


At rest, what fraction of VT is comprised of VD? What does this mean for fraction of alveolar air and fresh air? What about total lung capacity?

VD (150mL) makes up about one third of VT (500mL)
VT = 1/3 ‘ alveolar’ air + 2/3 ‘fresh’ air
3% of total lung capacity


Describe Fick's Law to explain diffusion of oxygen and carbon dioxide across the surfaces within the body.

The volume of gas transported across a membrane per unit time is directly related to:
• the driving pressure or difference in partial pressure of the gas across the membrane (Pagas - Pcgas)
• the area of the membrane (by recruiting more capillaries) (exercise dependent)
and is inversely related to:
• the length of the diffusion pathway (thickness of the membrane) (d^-1)
• the square root of the molecular weight of the gas. (MolWt gas^-1/2) Graham's law


Describe respiratory distress syndrome

Absence of Pulmonary Surfactant
- failure to reduce air-water Surface Tension
- greater (negative) Pip required to inflate the lungs
- greater muscular effort
- distress / fatigue


Describe emphysema and its consequences

- Destruction of elastic peribronchial and interalveolar tissue, which normally holds small bronchioles open during expiration
- So, lungs more compliant
- Passive deflation (expiration) impaired because the bronchioles collapse, trapping air in downstream alveoli (easy to inflate but difficult to deflate)
- Functional Residual Capacity (FRC) progressively increases (‘barrel-chest’), thereby disadvantaging the muscles of inspiration


Describe asthma and its consequences

- Characterised by bronchiolar constriction (smaller r)
- therefore increased R, and thus
▪ increased P to achieve VT and, hence,
▪ increased muscular effort.


Describe pulmonary edema and what is may result from.

“Water on the lung”
• Increased diffusion distance
• Diminished gaseous exchange
- Streptococcus pneumoniae


Describe Dalton's law of gas pressures

The total pressure of a gas is the sum of the pressures exerted by each individual constituent.
PTotal = Σ Pi
where Pi is the PARTIAL PRESSURE of gas i


What is meant by partial pressure?

The partial pressure of a dissolved gas is that externally applied pressure required to prevent it diffusing out of solution.


Describe Henry's Law

C = σP
The concentration C of a dissolved gas varies directly with its partial pressure. The constant of proportionality (σ) is called solubility. The solubility of a gas depends on the solvent (O2 is more soluble in oil than in water) and (inversely) on the temperature.
- P is a physical property of the gas
- σ is a physico-chemical property of the
solution (ie, of the gas plus the solvent).


How many time more soluble in blood is carbon dioxide compared to oxygen?



What are the two ways in which oxygen is carried in the blood?

– in simple solution (but only 3 mL of O2 per L of plasma,
since σO2 is very low)
– as oxy-haemoglobin in erythyrocytes (200 mL L-1)


What is meant by oxygen content of the blood?

The total amount of O2 carried in whole blood. It is the sum of the O2 combined with haemoglobin inside erythrocytes and the O2 dissolved in plasma.


How much haemoglobin does the whole blood of healthy adults contain? How much oxygen can one gram of haemoglobin bind to?

Whole blood of healthy adults contains about 150 g of haemoglobin per litre of blood. One gram of haemoglobin can bind 1.34 mL of O2 so up to 200 mL of O2 can be bound to haemoglobin per litre of blood.


What is meant by saturation of haemoglobin?

The saturation of haemoglobin is the amount of O2 actually bound to haemoglobin relative to the maximum amount that could be bound (normally 200 mL per litre of blood). Under normal circumstances, arterial blood is around 98% saturated. Hence, per litre of blood, about 197 mL of O2 are bound to haemoglobin, while a further 3 mL are dissolved in the plasma.


What is the stoichiometry of haemobglobin?

: 0, 1, 2, 3 or 4 O2 per Hb molecule
: cooperative binding
: sigmoidal “O2 Content-PO2 relation


What dies a right-shift of the HbO2 relation mean?

The same amount of O2 can be off-loaded in the tissues with NO LOSS of PO2.


What are the factors affecting the HbO2 equilibrium

shift to the right by:
– ↓ pH (ie, ↑ acidity)
– ↑ PCO2
– ↑ Temperature
• each of which occurs during EXERCISE
• thus increased off-loading of O2 in tissues


What occurs during CO poisoning?

Binding of O2 to haemoglobin is blocked by carbon
monoxide, which has a much higher affinity for haemoglobin. This causes a substantial reduction of oxyhaemoglobin saturation.


What happens to the HbO2 content vs PaO2 graph during anaemia?

Haemoglobin is reduced to 60 mL per litre of blood, which is less than half the normal level. As a result, the total oxygen bound is substantially reduced despite the fact that haemoglobin remains around 98% saturated.


How is CO2 transported in the blood?

≈ 9% as CO2 in simple solution (high σCO2)
≈ 13% as HbCO2
as H2CO3 {CO2 + H2O ---carbonic anhydrase---> H2CO3}
≈ 78% as HCO3- {H2CO3 ---> H+ + HCO3-}


What are the different ways CO2 is excreted from the blood and the body?

CO2 is excreted from the blood:
• as CO2 in the lungs
• as HCO3- by the kidney
CO2 is excreted from the body:
• by exhalation
• by micturition (urination)


Compare the CO2 dissociation curve to the oxyhaemoglobin dissociation curve

The CO2 dissociation curve is much more linear than the oxyhaemoglobin dissociation curve. Moreover CO2 content increases O2 desaturation of haemoglobin and is decreased with O2 saturation of haemoglobin. Note that the CO2 content of whole blood is around 3 times greater than the O2 content.


Give equations for the gas exchange in the lungs and tissues and overall

Lungs: Hb + nO2 -------> HbO2 (0 Hb + nO2 (0 CO2 + H2O
3) CO2 + Hb ------> HbCO2
Lungs: HbCO2 ------> Hb + CO2
Overall: HbCO2 + O2 HbO2 + CO2


What is the name of the molecules HbCO2?



Why does H2CO3 immediately dissociate? What does it then form?

It is a weak acid. It forms H+ and HCO3- (bicarbonate), which is the most abundant form of carbon dioxide in the blood.


Use equations to explain the effect of anatomic dead space on alveolar ventilation. Explain what these equations mean.

VT = VA + VD
VA = VT - VD
Rate of flow of alveoli = fR (VT-VD)
This equation shows that:
• The alveolar volume is merely the difference between the tidal volume (VT) and the deadspace volume (VD)
• The rate at which the alveolar volume is ventilated (VA, L min-1) is proportional to the alveolar volume (L) and to the frequency of breathing (fR, min-1). Hence, the units are


What are the consequences of hyper-ventilation?

• Accumulation of O2 in the alveoli
- Increase of PAO2 and PaO2
• Decrease of CO2 in the alveoli
- Decrease of PACO2 and PaCO2
- Increase of arterial pH:
respiratory alkalosis
▪ eventually: alkalotic coma


What are the consequences of hypo-ventilation?

• Diminution of O2 in the alveoli
- Decrease of PAO2 and PaO2
• Accumulation of CO2 in the alveoli
- Increase of PACO2 and PaCO2
- Decrease of arterial pH:
respiratory acidosis
▪ eventually: acidotic coma


Show the calculations for finding how ling we can live without oxygen.

Resting rate of consumption ≈ 300 mL min-1
• O2 ‘stores’ in the body:
• In the Functional Residual Capacity
• ≈ 2.5 L @ 0.13 mL/L = 300 mL
• In the Blood (arterial and venous): HbO2
• ≈ 5 L @ 175 mL/L = 850 mL
• Maximum anoxic survival time ≈ 4 min


What is meant by anoxic?

Without oxygen


What is the respiratory system aware and unaware of with regard to O2?

- unaware of O2 content of ANY tissue
- unaware of venous PO2
- not very responsive to arterial PO2
- although, PO2 IS sensed by the peripheral chemoreceptors


Describe the experiment investigating the response to altered inspiratory partial pressure of oxygen and carbon dioxide.

Response to brief anoxia. Healthy men breathed gas mixtures low or high in O2 for 8 min. Measurements are average values over the last 3 min. Vertical lines represent
one standard deviation from the mean. Note the wide variation in individual responses to inhalation of the same gas mixtures; this is an index of the wide range of sensitivity of the chemoreceptor response to anoxia in man. The men who increased their ventilation most in response to low O2 had the highest arterial O2 saturation. Some men showed no respiratory stimulation even when breathing 10% O2.


What does breathing rely on?

Neural input to the muscles of ventilation


What is the basic respiratory rhythm generated by?

Two groups of neurones in the medulla oblongata. These medullary centres are: the Dorsal Respiratory Group (DRG, neurons of which are active primarily during inspiration)
and the Ventral Respiratory Group (VRG, some neurons of which are active during inspiration, others during expiration and some during the transition).


How does the rhythmic drive originating in the brainstem effect the muscles involved in breathing?

The rhythmic drive which originates in the brainstem is transmitted to motoneurons in the brainstem (cranial motoneurons) and spinal cord which, in turn, drive the muscles involved in breathing (diaphragm, intercostals and upper airway muscles).


Describe the action of slowly adapting stretch receptors.

Slowly adapting stretch receptors located in walls of the bronchi and bronchioles send signals, via
myelinated fibres in the vagus nerve, to brainstem respiratory centres. Activation of these receptors
by lung inflation terminates inspiration.


What is the function of irritant sensors? What do they respond to? What does the activation of these receptors lead to?

Irritant Sensors in the airways send signals via myelinated and unmyelinated (C-fibres) in the vagus nerves and respond to:
• noxious mechanical and chemical stimuli (smoke, smog, pollen, “food going down the
wrong pipe”, etc),
• histamine and prostaglandins produced in response to allergies and inflammation, and
• lung hyperinflation.
Activation of these receptors can lead to reflex constriction of bronchioles (smooth muscle), coughing, rapid shallow breathing, and increased mucous secretion.


What is the purpose of peripheral sensors in the carotid bodies and aortic bodies?

Peripheral sensors in the carotid bodies and aortic bodies
detect primarily arterial PO2 and PCO2, informing the central respiratory control centre if more ventilation is required in order to maintain blood gases at appropriate levels.


Where are the carotid bodies located? Describe them. What are they well suited for? What do they respond to?

The carotid bodies are located at the bifurcation of the
common carotid arteries. They are highly vascularized,
having a very high blood flow relative to their metabolic
needs, and are well suited to sense the O2 and CO2 levels in the blood. They respond to decreases of PaO2 or increases of PaCO2.


Afferents from the carotid bodies travel in the _______ ______ ______ (along with afferents from the carotid sinus
baroreceptors), which joins the _____________ (IXth
cranial) nerve as it enters the medulla.

Carotid sinus nerve


Where are the aortic bodies found? Where are their afferents found?

In the aortic arch and subclavian arteries. Their afferents travel in the vagus nerve (Xth cranial nerve).


Where are central chemoreceptors located and what are they sensitive to?

Central chemoreceptors located on the ventral surface of
medulla are sensitive to the pH of the cerebrospinal fluid.


How is pH sensed?

Centrally on the ventral medulla - bathed by cerebrospinal fluid (CSF).


How is pH sensed if protons cannot readily cross the blood-brain barrier? What is ventilation sensitive with regard to pH?

CO2 is readily soluble in CSF
CO2 readily crosses cell membranes
CO2 diffuses across cerebral capillary membranes
(ie, the Blood-Brain Barrier): CO2 + H2O ---> H2CO3 ---> HCO3- + H+
Ventilation is sensitive to ventral medullary pH


What is ventilation most sensitive to?

Peripheral PaCO2
Central pH


How can intrinsic sensitivity of ventilation to O2 and CO2 be revealed?

By measuring the ventillatory response to changing each, in turn, while artificially holding the other constant.


What are the conflicting requirements of the respiratory system (involuntary and voluntary)?

- Ventilation
- Coughing, Sneezing
- Sighing
- Expectoration
- Thoracic stabilisation
- Ventilation
- Singing, Whistling, Yodelling, Speech
- Parturition
- Defecation, Urination