Physiology Flashcards
What are the four steps to external respiration?
Ventilation
Gas exchange between alveoli and blood
Gas transport in the blood
Gas exchange at the tissue level
What are the body systems involved in external respiration?
Respiratory system
CV system
Haemotology system
Nervous system
What is ventilation?
The mechanical process by which air is moved between the atmosphere and alveolar sacs
What is the gas exchange between alveoli and blood?
The exchange of oxygen and carbon dioxide between the air in the alveoli and the blood in the pulmonary capillaries
What is the gas transport in the blood?
The binding and transport of oxygen and carbon dioxide in the circulating blood
What is the gas exchange at the tissue level
The exchange of oxygen and carbon dioxide between the blood in the systemic capillaries and the body cells
What is boyles law?
At any constant temperrature, the pressure exerted by a gas varied inversely with the volume of the gas. As the volume of a gas increases, the pressure exerted by the gas decreases
How will air flow?
Air will flow down a pressure gradient from a region of high pressure to a region of lower pressure.
What must the intra-alevolar pressure become less than?
The atmospheric pressure to allow air to flow into the lungs during inspiration.
What is the intra-alveolar pressure before inspiration?
The intra-alveolar pressure is equivalent to atmospheric pressure but during inspiration the thorax and lungs expand as a result of contraction of inspiratory muscles
How are the lungs connected to the thorax?
Intrapleural fluid cohesivness
Negative intrapleural pressure
What is the intrapleural fluid cohesivness?
The water molecules in the intrapleural fluid are attracted to each other and resist being pulled apart and hence the pluerla membranes tend to stick together
What is the negative intrapleural pressure?
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 which forces the chest to squeeze inwards
What are the pressures associated with the alveoli?
760 mm Hg atmospheric pressure at sea level
760 mm Hg intra-alveolar pressure
756 mm Hg intrapleural pressure
What does inspiration depend on?
It is an active process and so depends on muscle contraction
What way is the volume of the thorax increased?
Vertically by contraction of the diaphragm flattening out its dome shape
What nerves supply the diaphragm?
The phrenic nerve from cervical regions 3, 4 and 5
What muscle contracts to lift the ribs and move out the sternum?
The external intercostal muscles
What is the name of the mechanism that the external intercostal muscles perform?
Bucket Handle mechanism
What happens to the intra-alveolar pressure when the size of the lungs increases?
It falls which is needed for boyle’s law as air can then enter the lungs down a pressure gradient until the intra-alveolar pressure becomes equal to the atmospheric pressure
What type of process is expiration?
A passive process by which the inspiration muscles are relaxed
How do the chest wall and stretched lungs recoil to their preinspiraotry size?
They have elastic properties
What does the recoil of the lungs make happen to the intra-alveolar pressure?
It rises
Why does the intra-alveolar pressure rise when the lungs recoil?
The air molecules become contained within a smaller volume and therefore the air will leave the lungs don its pressure gradient until the intra-alvoelar pressure becomes equal to the atmospheric pressure
What is a pneumothorax?
When air enters the pleural space from outside the lungs which abolishes the transmural pressure gradient leading to lung collapse
How can pneumothoraces occur?
Spontaneous
Traumatic
Iatrogenic
What are the symptoms of a pneumothorax?
Shortness of breath
Chest pain
Hyperresonant percussion tone
Decreased or absent breath sounds
What is lung recoiling due to?
Elastic connective tissue in the lungs which allows it to bounce back into shape
Alveolar surface tension
What is alevolar surface tension?
The attraction between water molecules at liquid air interface. In the alveoli this produces a force which resists the stretching of the lungs
What would happen if the alveoli were lined with water alone?
The surface tension would be too strong and so the alveoli would collapse and therefore the alveoli are also lines with surfactant
What is the law of laPlace
The smaller the alveoli with a smaller radius, the higher the tendency to collapse
What makes up pulmonary surfactant?
Mixture of lipids and proteins that is secreted by type 2 alveoli
What is the purpose of surfactant?
Lowers surface tension of smaller alveoli more than that of larger alveoli and prevents the smaller alveoli from collapsing and emptying their air contents into the larger alveoli
What age group does respiratory disress syndrome effect?
New-borns
What is respiratory distress syndrome?
When premature babies don’t have enough surfactnat and so the baby has to make very strenous inspiratory efforts in an attempt to overcome the high surface tension to inflate the lungs
Why do premature babies not have enough pulmonary surfactant?
Fetal lungs do not produce surfactant until late pregnancy and so when babies are born prematurely they do not have surfactant yet
What is alveolar interdependence?
If an alveolus starts to collapse then the surrounding alveoli are stretched and then recoil exerting expanding forces in the collapsing alveolus to open it
What are the major muscles of inspiration?
Diaphragm and external intercostal muscles
What are the accessory muscles of inspiration?
They only contract during forceful inspiration and they are the sternocleidomastoid, scalenus and pectoral
What are the muscles of active expiration?
They only contract during active expiration and they are abdominal muscles and internal intercostal muscles
What is tidal volume and what is an average value?
The volume of air entering or leaving the lungs during a single breath. Average value is 0.5L
What is the inspiratory reverse volume and what is an average volume?
The extra volume of air that can be maximally inspired over and above the typical resting TV. Average volume is 3.0L
What is the expiratory reverse volume and what is an average volume?
The extra volume of air that can be actively expired by maximal contraction beyond the normal volume of air after a resting TV. Average volume is 1.0L
What is the residual volume and what is an average volume?
The minimum volume of air remaining in the lungs even after a maximal expiration. The average volume is 1.2L
What is the inspiratory capacity and what is an average value?
The maximum volume of air that can be inspired at the end of a normal quiet expiration (IC = IRV + TV). An average value is 3.5L
What is the functional residual capacity and what is an average value?
The volume of air in the lungs at the end of a normal passive expiration. An average volume is 2.2L
What is the vital capacity and what is an average value?
The maximum volume of air that can be moved out during a single breath following a maximal inspiration. Average volume is 4.5L
What is the total lung capacity and what is an average volume for it?
The total volume of air that the lungs can hold. Average volume is 5.7L
What cannot be measured by spirometry?
Residual volume and therefore total lung volume cannot be measured by spirometry.
How can residual volume increase?
When the elastic recoil of the lungs is lost for example in emphysema the residual volume increases
What is FVC?
The maximum volume of air that can be forcibly expelled from the lungs following a maximum inspiration
What is FEV1?
The forced expiratory volume in one second. The volume of air that can be expired during the first second of expiration in a FVC determination
What is the FEV1/FVC ratio?
The proportion of the FVC that can be expired in the first second = FEV1/FVC x 100
What is the normal FEV1/FVC ration?
More than 75%
What are dynamic lung volumes useful in diagnosing?
Obstructive and restrictive lung diseases
How does the FEV1/FVC ratio change in obstructive airway diseases?
FVC is low/normal but FEV1 is low and so the ratio is low
How does the FEV1/FVC ratio change in restrictive lung diseases?
FVC is low but FEV1 is also low and they change in proportion with each other and so the ratio stays the same
What does parasympathetic stimulation of the bronchioles cause?
Bronchoconstriction
What does sympathetic stimulation of the bronchioles cause?
Bronchodilation
Why is active expiration more difficult in patients with airway obstruction
The pleural pressure rises compressing the alveoli and airways which helps to push air out of the lungs but extra pressure is not always desirable and in patient with increased airway resistance can an increase in airway pressure upstream
What is a peak flow meter used for?
Gives an estimate of peak flow rate
What does peak flow rate assess?
The airway function and is useful in patients with obstructive lung diseases
How is a peak flow meter used?
Patient is asked to give a short sharp blow into the peak flow meter. Best of 3 attempts is taken and the peak flow rate in normal adults varies with age and height
What is compliance?
The measure of effort that has to go into stretching or distending the lungs. During inspiration the lungs are stretched
What is pulmonary compliance and how is it measured?
The volume change per unit of pressure change across the lungs
What can decrease pulmonary complicance?
Pulmonary fibrosis Pulmonary oedema Lung collapse Pneumonia Absence of surfactant
What happens when the lungs are less compliant?
They have to work harder to produce a given degree of inflation. A greater change in pressure is needed to produce a given change in volume because the lungs are stiffer. This causes shortness of breath especially on exertion.
What causes increased pulmonary compliance?
If the elastic recoil of the lungs is lost for example in emphysema. Patients have to work harder to get air out of the lungs and they become hyperinflated. Compliance also increases with age
When is the work of breathing increased?
Pulmonary compliance decreased
Airway resistance increased
Elastic recoil is decreased
Need for increased ventilation
What is the anatomical dead space?
When air is retained in the airways and so is not avaliable for gas exchange but takes up space into the lungs
How is pulmonary ventilation calculated?
Tidal volume x respiratory rate
E.g.
0.5L x 12 breaths/min
6L/min under resting conditions
Why is alveolar ventilation less than pulmonary ventilation?
Because of the presence of anatomical dead space
How is alveolar ventilation calculated?
(TV - dead space volume) x resp rate
E.g.
(0.5-0.15) x 12
4.2L/min under resting conditions
What is pulmonary ventilation?
The volume of air breathed in and out per minute
What is alveolar ventilation?
The volume of air exchanged between the atmosphere and alveoli per minute. More important that pulmonary ventilation as it represents the new air available for gas exchange with the blood
What does the transfer of gases between the body and atmosphere depend on?
Ventilation - rate at which gas is passing through the lungs
Perfusion - rate at which blood passes through the lungs
What is the physiological dead space?
The anatomical dead space + alveolar dead space
When can the alveolar dead space increase significantly?
In disease
How it airflow matched to blood flow in the lungs?
Local controls act on the smooth muscles of airways and arterioles
What does the accumulation of carbon dioxide in the alveoli result in?
It results due to increased perfusion which decreases airway resistance leading to increased airflow
What does an increase in alveolar oxygen conc result in?
It is as a result of increased ventilation and results in pulmonary vasodilation which increases blood flow to match larger airflow
What are the areas in which perfusion is greater than ventilation?
Areas of increased carbon dioxide concentration Dilation of local airways Increase in airflow Areas where oxygen conc in decreased Constriction of local blood vessels Areas of decreased blood flow
Where are the areas in which venitlation is greater than perfusion?
Areas of decreased carbon dioxide conc Local constriction of airways Areas of decreased airflow Areas of increased oxygen conc Areas of increased blood flow Dilation of local blood vessels
What are factors that influence the rate of gas exchange across the alveolar membrane?
Partial pressure gradient of oxygen and carbon dioxide
Diffusion coefficient for oxygen and carbon dioxide
SA of alveolar membrane
Thickness of alveolar membrane
What determines the pressure gradient for gases?
The partial pressure
What is dalton’s law of partial pressure?
The total pressure exerted by a gaseous mixture = the sum of the partial pressure of each individual component in the gas mixture
What is partial pressure?
The pressure that one gas in a mixture of gases would exert if it were the only gas present in the whole volume occupied by the mixture at a given temperature
What is the partial pressure of oxygen in the atmosphere?
160 mm Hg (21 kPa)
What is the total atmospheric pressure?
760 mm Hg (101 kPa)
How do you calculate the partial pressure of oxygen in the alveolar air PAO2?
PAO2 = PiO2 - (PaCO2/0.8)
Where:
PAO2 = Partial pressure of oxygen in alveolar air
PiO2 = Partial pressure of oxygen in inspired air
PaCO2 = Partial pressure of carbon dioxide in arterial blood
0.8 is the respiratory exchange ration (RER) for someone eating a mixed diet
What does the partial pressure gradient state?
Gases will move from a higher to lower partial pressure
What is the air in the resp tract saturated with?
Water, and the water vapour contributes to aobut 47 mmHg of the total pressure in the lungs and so the pressure of inspired air = atmospheric pressure - water vapour pressure = 750 - 47 mmHg = 713 mmHg at sea level
What is the normal PaCO2 in arterial blood?
40 mmHg
Why is the partial pressure for carbon dioxide less than the partial pressure of oxygen?
Carbon dioxide is more soluble in membranes than oxygen and the solubility of gas in membranes is known as the diffusion coefficient for the gas. The diffusion coefficient for carbon dioxide is 20 times that of oxygen
What does fick’s law of diffusion state?
The amount of gas that moves across a sheet of tissue in unit time is proportional to the area of the sheet but inversely proportional to its thickness. The lungs provide a large SA with thin membranes to facilitate effective gas exchange. The airways also divide repeatedly to increase SA. They have a very extensive pulmonary capillary network which allows them to receive the entire cardiac output
What are the components of a respiratory membrane?
Aveoli are thin walled inflatable sacs that function in gas exchange. The walls consist of a single layer of flattened type 1 alveolar cells
Pulmonary capillaries encircle each alveolus with a narrow interstitial space between them
What are the nonrespiratory functions of the resp system?
Route for water loss and heat elimination
Enhances venous return
Helps to maintain normal acid-base balance
Enables speech, singing and other vocalisations
Defends against inhaled foreign matter
Removes, modifies, activates or inactivates various materials passing throuhg the pulmonary circulation
Nose serves as the organ of smell
What is henry’s law?
The amount of a given gas dissolved in a given type and volume of liquid (blood) at a constant temp is proportional to the partial pressure of the gas in the equilibrium with the liquid
What is the partial pressure of oxygen dissolved in the blood?
13.3 pKa and 3ml of oxygen
What are the respective percentages of oxygen carried bound to haemoglobin and in the dissolved form
98.5% and 1.5%
How many haem groups are there for every molecule of haemoglobin?
4 and each haem group can carry one oxygen molecule. The partial pressure of oxygen is the primary factor which determines the % sat of haemoglobin with oxygen
What is saturation depedent on?
The PO2, not the concentration of haemoglobin
What is the oxygen delivery index?
The oxygen delivery to the tissues is a function of the oxygen content of arterial blood and the cardiac output
How can you calculate the oxygen delivery index?
DO2l = CaO2 x CI
Where:
DO2l is the oxygen delivery index
CaO2 is the oxygen content of arterial blood
CI - cardiac index
CI relates the cardiac output to the normal body surface
How do you calculate the oxygen content of arterial blood?
CaO2 = 1.34 x Hb x SaO2
One gram of Hb can carry 1.34ml of oxygen when fully saturated
SaO2 is the % of haemoglobin saturation with oxygen - determined by the partial pressure of oxygen
How can oxygen delivery to the tissues be impaired?
Respiratory disease
Heart failure
Anaemia
What does the partial pressure of inspired oxygen depend on?
Total pressure (atmospheric) Proportion of oxygen in gas mixture (21% in atmosphere)
What is PAO2?
The partial pressure of alveolar air
What is PiO2?
The partial pressure of oxygen in inspired air
What is PaCO2?
The partial pressure of carbon dioxide in arterial blood
What does haemoglobin show and what type of curve does it show?
It shows cooperactivity and shows a sigmoid curve
What does the sigmoidal curve mean?
The flat upper portion of the curve means that a moderate fall in alveolar partial pressure will not affect the oxygen loading but at the steep lower part of the curve, the peripheral tissues get alot of oxygen for a small drop in capillary partial pressure
What is the Bohr effect?
The shift of the curve to the right, e.g. the release of oxygen from tissues
What increases the Bohr effect?
Increased carbon dioxide conc
Increased proton conc
Increased temp
Increased 2,3-biphosphoglycerate conc
What is myoglobin?
Only present in skeletal and cardiac muscle cells, one haem group per myoglobin molecule, no cooperactivity
What is the shape of the dissociation curve of myoglobin?
Hyperbolic not sigmodal
Will release oxygen at very low partial pressures of oxygen which provides a short-term storage for exygen in anaerobic conditions
Presence of myoglobin in blood indicates muscle damage
What are the mean of carbon dioxide in the blood?
Solution (10%)
Bicarbonate (60%)
Carboamino compounds (30%)
How is bicarbonate formed in the blood?
Carbon dioxide and water bind to form bicarbonate and protons
What is the enzyme that converts carbon dioxide and water to bicarbonate?
Carbonic anhydrase and it occurs in red-blood cells
Includes a chloride shift and the excess proton ion is used to bind with haemoglobin
How are carboamino comounds formed?
Combination of carbon dioxide with terminal amine groups in blood protein, is a rapid process even without an enzyme as as catalyst. Reduced haemoglobin can bind to more carbon dioxide than haemoglobin bound to oxygen
What is the haldane effect?
Removing oxygen from haemoglobin increases the ability of haemoglobin to pick up carbon dioxide and carbon dioxide generates protons
What do the bohr effect and haladane effect work in synchrony to facilitate?
Oxygen liberation
Uptake of carbon dioxide and carbon dioxide generation of protons at tissues
At the lungs, the haemoglobin picks up oxygen which reduces its ability to bind to carbon dioxide and protons
Where is the rhythm of inspiration and expiration controlled?
The medulla
What is the name of neurons that generates breathing rhythm?
Pre-botzinger complex. These neurons display pacemaker activity and are located near the upper end of the medullary respiratory centre
What is the mechanism of inspiration?
Rhythm is generated by the pre-botzinger complex
Excited the dorsal respiratory group of neurones
This fires in bursts
The firing leads to the contraction of inspiratory muscles
When firing stops, there is a passive expiration
What is the muscle contraction that allows for active inspiration?
Volume of the thorax is increased vertically by the contraction of the diaphragm flattening out its dome shape. Mediated by phrenic nerve from C3,4,5
External intercostal muscle contraction lifts the ribs and moves out the sternum. This is called the bucket handle mechanism
When is active expiration used?
Hyperventilation
What is the mechanism of active expiration?
Increased firing of dorsal neurones excites a second group called the ventral respiratory group neurones
These ventral respiratory group neurones excite internal intercostals and abdominal muscles that induce forceful expiration
In normal quiet breathing, ventral nerones do not activate expiratory muscles
Where can rhythm generated in the medulla by modified?
By neurones in the pons
What is the mechanism by which the rhythm is modified in the pons?
Occurs in thte pneumotaxic centre in the pons (PC)
Stimulation of PC terminates inspiration
PC is stimulated when the dorsal respiratory neurones fire to inhibit inspiration
Without PC breathing would be prolonged inspiratory gasps with brief expiration - this called apneusis
What occurs in the apneustic centre?
Impulses from these neurones excite the inspiratory centre of the medulla prolonging inspiration
Where are respiraotry centres influenced by stimuli from?
Higher brain centres such as cerebral cortex, limbic system and hypothalamus
Stretch receptors in the walls of the bronchi and bronchioles - the inflation of hering-breur reflex that is a guard against hyperinflation
Juxtapulmonary (J) receptors - stimulated by pulmonary capillary congestion , pulmonary oedema and pulmonary emboli that results in rapid shallow breathing
Joint receptors - stimulated by joint movement
Baroreceptors - increased ventilatory rate in response to decreased BP
Central chemoreceptors
Peripheral chemoreceptors
What are examples of involuntary modifications of breathing?
Pulmonary stertch receptors - hering breur reflex
Joint receptors - reflex in exercise
stimulation of resp centre by temperature, adrenaline, or impulses from cerebral cortex
Cough reflex
How are pulmonary stretch receptors activated?
Only activated during inspiration, afferent discharge inhibits inspiration. This is the Hering-Breur reflex. They only switch off inspiration when tidal volumes are large. Prevent overinflation of lungs during hard exercise
How are joint reflexes activated?
Impulses from moving limbs relexely increases breathing. This contributes to the increased ventilation during exercise
What factors will increase ventilation during exercise?
Reflexes originating from body movement Adrenaline release Impulses from cerebral cortex Increase in body temp Accumulation of carbon dioxide and protons generated by active muscles
Why do we need a cough reflex and what does it do?
It is a vital part of the bodies defence mechanisms. It helps to clear airways of dust, dirt or excessive secretions
How is the cough reflex activated?
Irritation of airways or tight airways such as asthma
The centre is in the medulla
What is the basic mechanism of a cough?
Short intake of breath
Closure of larynx
Contraction of abdominal muscles which increases intra-alveolar pressure
Opening of larynx and expulsion of air at high speed
What type of system is chemical control of respiration?
Negative feedback control system
What are the controlled variables in the chemical control of respiration?
Blood gas tensions such as carbon dioxide
What senses the values of gas tensions in the chemical control of respiration?
Chemoreceptors
Peripheral chemoreceptors sense tension of oxygen, carbon dioxide and H+ in the blood
Central chemoreceptors respond to the H+ of the CSF
Where are central chemoreceptors located?
Near the surface of the medulla
How is the CFS separated from the blood?
By the blood brain barrier which is relatively impermeable to H+ and HCO3 but carbon dioxide diffuses readily across is. CSF contains less protein than blood and hence is less buffered than blood
What is hypoxic drive?
It is all vis the peripheral chemoreceptors and is stimulated where the arterial PO2 falls to low levels of less than 8.0 kPa. This is not important in normal respiration but is important in patients with chronic CO2 retention and at high altitudes
What happens when hypoxia is severe?
The neurones are depressed and the peripheral chemoreceptors are stimulated
What does the partial pressure of inspired oxygen depend on?
Total pressure (atmospheric pressure) Proportion of oxygen in gas mixture
What is hypoxia at high altitudes caused by?
Decreased partial pressure of inspired oxygen (PiO2)
This results in hyperventilation and increased cardiac output
What are chronic adaptations to high altitude hypoxia?
Increased RBC production
Increased 2,3 BPG production within RBC that means oxygen is offloaded into tissues more easily
Increased number of capillaries
Increased number of mitochondria
Kidneys conserve acid and so arterial pH is more acidic
What is the H+ drive of respiration?
H+ doesnt cross the blood brain barrier so peripheral chemoreceptors adjust for acidosis by the addition of non-carbonic acid H+ to the blood and the stimulation by H+ causes hyperventilation which increases the elimination of CO2
