Resp. Physiology Flashcards
List the four functions of the respiratory system
- Gas exchange
- Protection from infection
- Acid-base balance
- Communication
What is external respiration?
Respiratory system coupled with cardiovascular system - oxygenation of blood and delivery to tissues
Describe the pulmonary circulation
Movement of blood from one side of the heart to the other via the lungs for the purpose of gas exchange
What vessels are important in pulmonary circulation?
Pulmonary arteries and vein
What is systemic circulation?
Movement of blood between heart and body
Describe the concurrent changes that occur in both the respiratory and cardiovascular system during exercise
Increased rate and depth of breathing occurs to speed up substrate acquisition and waste excretion
Heart rate and strength of contraction increases to increase substrate delivery and waste removal
Where does gas exchange occur?
In the lungs
What can be said about the net volume of oxygen exchanged in a steady state?
Its equal to the amount expended by the body’s cells
What are the average volumes of O2 and CO2 exchanged per minute?
250ml Oxygen
200ml Carbon dioxide
Describe the effect exercise has on breathing rate and quote numbers
10-20 breaths per minute at rest which increases to 40-45 breaths per minute during exercise
What is the epiglottis?
A small flap of tissue that covers the trachea when swallowing to prevent food from entering
What is the pharynx?
Shared space ‘throat’ between the respiratory and alimentary systems
What is the larynx?
The voice box, contains vocal chords which vibrate to produce sound
Where does the upper respiratory tract become the lower one?
T4
The width and angle of the right bronchi is greater and more oblique than the left one - what is the clinical relevance to this?
Most aspirated foreign bodies are lodged there
Describe the connective tissue surrounding the trachea and bronchi
Rings of cartilage ‘patency’ maintain semi-rigid tubes
Airways are categorised into two zones; what are they?
Conducting and respiratory zones
What do the tubes of the conducting zone contain?
Anatomical dead space - no gas exchange occurs
What are the components of the lining of the respiratory tract?
Epithelium, glands, lymph nodes, blood vessels, cilia and mucous
What is the function of mucous?
Trap pathogens and to moisten air
What are the two categories of pneumocytes?
Type 1 - Gas transfer
Type 2 - Surfactant releasing
What is the typical distribution of the types of pneumocytes?
97% type 1
Describe the lobular nature of the lungs
Right lung - three lobes
Left lung - two lobes (cardiac notch makes it smaller)
What does the horizontal fissure separate?
The superior and middle lobe of the right lung
What does the oblique lung fissure separate?
Middle lobe from inferior lobe in right lung
Superior from inferior lobe in left lung
What are the four Gas Laws and outline Boyle’s Law
Boyle’s Law - the relationship between the pressure of a gas an the volume of the system is directly inverse
Other laws include daltons law, Henrys law and Charles’ law
Describe the visceral pleural membrane?
Coats the inner surface of the lung
Describe the parietal pleural membrane?
Coats the outer surface of the lungs
What exists between the two pleura? What is its function?
Pleural fluid, sticks the lungs to the rib cage
What is pleurisy?
Inflammation of the pleura
What are the three relevant pressures in the lungs?
- Intra-thoracic (Alveolar) pressure - (Pa)
- Intra-pleural pressure (Pip)
- Transpulmonary pressure (Pt)
Describe intra-thoracic pressure?
Pressure inside the thoracic cavity (essentially pressure inside the lungs) - may be both negative or positive compared to atmospheric pressure
Describe intra-pleural pressure
Pressure inside the pleural cavity - always negative
Describe transpulmonary pressure
Pressure differential between the alveolar and intra-pleural pressure - always positive
What is the definition of anatomical dead space?
Approx. 150ml of air in the conducting airways and not available for gas transfer
What is the definition of TV?
Tidal volume - the average volume of air on each inhalation/expiration on rest
What is the definition of ERV?
Expiratory reserve volume - the maximum volume of air expelled from the lungs at the end of a normal expiration
What is the definition of IRV?
Inspiratory reserve volume - the maximum amount of air that can be drawn into the lungs at the end of a normal inspiration
What is the definition of RV?
Residual volume - The volume of gas in the lungs at the end of a maximal expiration
What is the definition of VC?
Vital capacity -
TV + IRV + ERV
What is the definition of TLC?
Total Lung Capacity -
Vital capacity + residual volume
What is the definition of IC?
Inspiratory capacity
Tidal volume + inspiratory reserve volume
What is the definition of FRC?
Forced Residual Capacity
Expiratory reserve volume + residual volume
What is the definition of FEV1?
Forced expiratory volume in one second
What is the definition of FEV1:FVC?
Fraction of forced vital capacity expelled in one second
What is pulmonary (minute) ventilation?
The amount of air breathed in and out during one minute
What is alveolar ventilation?
Fresh air getting to the alveoli and therefore available for gas exchange
What is the typical tidal volume?
500ml
What is the typical inspiratory reserve volume?
3L
What is the typical expiratory reserve volume?
1.1L
What is the typical reserve volume?
1.2L
What is the typical vital capacity?
4.6L
How is alveolar ventilation measured?
Tidal volume -Anatomical dead space (150ml) multiplied by breath rate
What is the typical alveolar ventilation?
4.2L.min^-1
How is partial pressure determined?
Dalton’s Law tells us partial pressure is equal to the percentage of the given gas as a proportion of total atmospheric pressure
What is surfactant?
Detergent like fluid secreted by type II pneumocytes
What is the function of surfactant?
To reduce the surface tension on alveolar surface membranes and therefore reduce its tendency to collapse
What is surface tension?
A phenomenon that occurs at air-water interfaces and refers to the attraction between water molecules
What is the overall effect of surfactant on the compliance of the lung
Increases
What is the Law of LaPlace?
Shows the relationship between pressure and a equation of surface tension and radius of the alveoli
What is the equation of the law of LaPlace?
P=2T/r
How does the law of LaPlace marry the different pressures in differently sized alveoli and what role does surfactant play?
Smaller alveoli have higher pressures, surfactant reduces surface tension and the pressure is equalised
What are the gestational milestone for surfactant production?
25 week - begins
Complete at 36
What hormone stimulates surfactant production in foetuses?
Thyroid and cortisol
When babies are born prematurely what pathology can rise to do with incomplete surfactant development
Infant respiratory distress syndrome
What is compliance?
A measure of the change in volume relative to the pressure change
What is meant by high compliance?
Large increase in volume for a small decrease in pressure
What is meant by low compliance?
Small increase in volume for a large increase in pressure
Describe the pressure-volume relationship
It requires a greater change in pressure to reach a particular volume because the word done during inspiration is recovered in elastic recoil for expiration
Describe the pressure-volume relationship associated with emphysema
Loss of elastic tissue means expiration requires effort
Describe the pressure volume relationship associated with fibrosis
Inert fibrous tissue means effort of inspiration increases
How does pressure volume curve vary in different regions of the lung/
At the base, the volume change is greater than the apex for a given change in pressure
Alveolar ventilation and compliance also decrease from apex to base
Why is the volume change at the base of the lung greater than the apex for a given change in pressure?
At the base, alveoli are more compressed by the rest of the lung and the diaphragm therefore are more compliant on respiration
What is the difference between obstructive and restrictive lung diseases?
Obstructive - obstruction of airways, particularly on expiration
Restrictive - restriction of lung expansion (inspiration)
What are two examples of obstructive lung diseases?
Asthma and COPD (a combination of chronic bronchitis and emphysema)
What are three examples of restrictive lung diseases/disorders?
IRDS
Oedema
Pneumothorax
What is spirometry?
A technique used to measure lung function. Measurements can either be classes as static or dynamic
What is the difference between static and dynamic measurements in spirometry?
Static - where the only consideration made is volume exhaled
Dynamic - where the time taken to exhale a certain volume is being measured
What lung volumes and capacities can’t be directly measured by spirometry?
RV, TLC and FRC
What is a typical FEV1 value for healthy males?
4L
What is a typical FVC in healthy males?
5L
What is the typical FEV1/FVC for a healthy male as a percentage?
80%
What FEV1/FVC percentage is typically seen in obstructive pulmonary disease?
<80%
What FEV1/FVC percentage is typically seen in restrictive lung diseases?
> 80%
Why are obstructive diseases characterised by an FEV1/FVC percentage <80%?
Rate at which air is exhaled is slower; reduced FEV1 and little effect on FVC therefore ration is reduced
Why are restrictive diseases characterised by an FEV1/FVC percentage >80%?
Total lung volume is reduced therefore ratio can increase as a large proportion of volume can still be expelled quickly
What are the limitations for the FEV1/FVC for both types of respiratory disorder?
Both FEV and FVC fall - the ratio will stay the same despite seriously compromised function
What FEF25-75?
Forced expiratory flow - average expired flow over the middle half of the FVC
What is the advantage of using FEF25-75?
Correlates with FEV1 but changes are generally more striking
What is the disadvantages of using FEF25-75?
‘Normal’ range is greater
What vessels supply the bronchial circulation?
Bronchial arteries
What circulatory system gives rise to the bronchial circulation?
Systemic
What is the function of the bronchial circulation?
Supplies airway smooth muscle, nerves and lung tissue with oxygen
Why is the pulmonary circulation referred to as high flow, low pressure?
High flow - entire cardiac output 5L/min flows through it
Low pressure - only has systolic pressure of 25mmHg
What force influences a low pressure circulatory system?
Gravity
Expand on the following abbreviations:
a
A
v
P
a - arteriolar
A - alveolar
v - venous
P - partial pressure
Therefore what does PaCO2 refer to?
Partial pressure of carbon dioxide in the arteries
What is the partial pressure of oxygen in the alveoli and arteries?
100mmHg or 13.3 kPa
What is the partial pressure of carbon dioxide in the alveoli and arteries?
40mmHg or 5.3 kPa
What is the partial pressure of venous oxygen?
40mmHg or 5.3kPa
What is the partial pressure of venous carbon dioxide?
46mmHg or 5.6kPa
What four factors effect the rate of gas exchange?
- Partial pressure gradient
- Gas solubility
- Surface area
- Membrane thickness
What partial pressure values reflect gas concentrations in the lungs?
Arteriolar pp
What partial pressure values reflect gas concentrations in the tissues?
Venous pp
How does fibrotic alveolar membrane decrease rate of gas exchange?
Thickened membrane
How does pulmonary oedema decrease rate of gas exchange?
Increased diffusion distance through fluid
How does asthma reduce gas transfer?
Constricted bronchi increase resistance to ventilation
What is ventilation?
Air getting into the alveoli
What is perfusion?
Local blood flow
What is the optimal condition for ventilation and perfusion?
They are equal
What two forces influence distribution of blood flow?
Hydrostatic blood pressure and alveolar pressure
What is blood flow in the lungs proportional to?
Vascular resistance
What trend does blood flow demonstrate in relation to height of the lung?
Decreases with height
Why is blood flow in the base of the lung high?
Arterial pressure > alveolar pressure
Therefore vascular resistance is low
A decrease in PAO2 in the alveoli causes what to occur?
Shunt of blood to more well ventilated alveoli
What does an increase in PACO2 do?
Causes mild bronchodilation
What respond to hypoxia is unique to the pulmonary system?
Constriction
What is shunting?
Refers to the physiological changes that occur in poorly ventilated areas of the lung
What is alveolar dead space?
Alveoli the are well ventilated but poorly perfused
What volume of oxygen is transported in solution in the plasma?
3ml
The presence of haemoglobin increases the carrying capacity of oxygen to what value?
250ml/L
How is the bulk of CO2 carried in the blood?
Various forms of solution in plasma and RBC
What is the O2 demand of resting tissue?
250ml/min
What percentage of arterial O2 is extracted by peripheral tissues at rest?
25%
What form of haemoglobin makes up 92% of all types found in an RBC?
HbA
Describe the composition of the 8% of other haemoglobin types
HbA2 (delta chain replaces beta)
Glcosylaed Hb (HbA1, HbA1b and HbA1c)
What factor is the major determinant of the degree to which Hb is saturated with oxygen?
Partial pressure of oxygen
How long does it take to saturate and Hb molecule with oxygen? How does this compare to its overall exposure time?
0.25 seconds to saturate
Overall exposure is 0.75 seconds
List three factors which decrease haemoglobin oxygen affinity
Heat
PCO2 increase
Decreased pH
Where can the conditions that lead to a decreased oxygen affinity exist?
Locally in actively metabolising tissues (e.g. muscles) which helps to unload oxygen
What conditions cause a rise in haemoglobin oxygen affinity?
Increase in pH
Fall in PCO2
Drop in temp.
What molecule can cause haemoglobin oxygen affinity to decreased?
2,3-diphosphoglycerate (2,3-DPG)
Where is 2,3-DPG synthesised?
RBCs
Where does 2,3-DPG activity increase?
Associated with areas of inadequate oxygen supply e.g. heart or lung disease and living at high altitude
What is the overall effect of 2,3-DPG?
Helps maintain oxygen release
What occurs to haemoglobin in the presence of carbon monoxide?
Forms carboxyhemoglobin
What is the partial pressure of CO required to cause progressive carboxyhemoglobin formation?
0.4mmHg
Why is the respiration rate of a person suffering with CO poisoning normal?
PaCO2 not effected
What are the five main types of hypoxia?
Hypoxic Ischaemic Histotoxic Metabolic Anaemic
What is the most common type of hypoxia?
Hypoxic
What is the cause of anaemic hypoxia?
Reduction in O2 carrying capacity due to anaemia
What is ischaemic hypoxia?
Heart disease results in poor pumping of the blood
What is histotoxic hypoxia?
Poisoning prevents cells using oxygen
Give an example of a cause of histotoxic hypoxia
CO or cyanide
What is metabolic hypoxia?
Oxygen delivery to the tissues does not reach increased oxygen demand by cells
What proportion of CO2 remains dissolved in plasma and RBCs?
7%
23% of CO2 combines with deoxyhaemoglobin to form what compounds?
Carbamino compounds
What is the compound which sequesters most of the CO2 excreted by cells?
70% converted to carbonic acid
Describe the fate of carbonic acid in the blood
Dissociates into hydrogen and bicarbonate ions - the bicarbonate is transported into the plasma by the Hamburger Phenomenon and forms a blood buffer
Why is monitoring plasma [CO2] very important?
It is capable of changing the ECF pH
What physiological process monitors plasma [CO2]?
Hypo/hyperventilation
How does hypoventilation alter plasma [CO2]?
Retains CO2
How does hyperrventilation alter plasma [CO2]?
Blows off CO2
What physical structures must be stimulated to cause inspiration?
Diaphragm and external intercostals
What innervates the thoracic-abdominal diaphragm?
The phrenic nerve
Which nerves innervate the external intercostals?
Intercostal nerves
Where are the respiratory centres located in the brain?
The pons and medulla
What can be said about the voluntary/involuntary nature of breathing?
Its mostly subconscious but can be subject to voluntary override
Severing of the spinal chord above the ventral rami of spinal nerves C3, 4 and 5 do what?
Kill you
How does the dorsal respiratory group set the rhythm for breathing?
Firing smooth repetitive bursts of action potentials
What four other aspects can modulate ventilation?
- Emotion
- Voluntary override
- Mechano-sensory input from the thorax
- Chemical changes
What two types of chemoreceptors modulate ventilation?
Central and peripheral
What chemical route, central or peripheral, is the main control for ventilatory function?
Central
Central chemoreceptors respond directly to what?
[H+] in cerebrospinal fluid
What does the [H+] indicate?
PaCO2
Where are central chemoreceptors located?
Medulla of the brain
Where are peripheral chemoreceptors located in the body?
Carotid and aortic bodies
What do peripheral chemoreceptors detect?
Changes in arterial PO2 and [H+]
Changes in plasma pH will alter ventilation via what chemoreceptor pathway?
Peripheral
If plasma pH falls ventilation will be _______
Increased
If plasma pH increases, ventilation will be _____
Inhibited
List common drugs which depress respiratory activity
Opiates, barbiturates
What effect do most anaesthetic agents have on respiratory activity
Increase breath rate but decrease tidal volume therefore decrease alveolar ventilation
What effect does nitrous oxide have on the nervous system?
Blunts the peripheral chemoreceptors to changes in PO2
In what kind of patient would the use of nitrous oxide be contraindicated?
Ones on hypoxic drive
What is hypoxic drive?
The body regulating its respiratory activity by monitoring PO2 not PCO2
What common treatment for lung diseases would aggravate a patient on hypoxic drive?
Oxygen
Describe the relationship between ventilation and swallowing
Swallowing causes the epiglottis to close and is followed by a reflex exhalation to prevent food from being aspirated
