Physiology Flashcards
What is internal respiration?
The intracellular mechanisms which consumes O2 and produces CO2
What is external respiration?
The sequence pf events that leads to the exchange of O2 and CO2 between the external environment and the cells of the body
What are the four stages of external respiration?
- ventilation
- Gas exchange between alveoli and blood
- gas transport in blood
- gas exchange at tissue level
What is Boyles law?
At any constant temperature the pressure exerted by a gas varies inversely with the volume of the gas
What are the two forces that hold the thoracic wall and the lungs in close opposition?
- the intrapleural fluid cohesiveness
2. The negative intrapleural pressure
what is meant by intrapleural fluid cohesiveness?
The water molecules in the intrapleural fluid are attracted to each other and resist being pulled apart. hence the pleural membranes tend to stick together
what is meant by the negative intrapleural pressure
The sub atmospheric intrapleural pressure creates a transmural pressure gradient across the lung wall and he chest wall. so the lungs are forced to expand outwards while the chest is forced to squeeze upwards
What are the 3 pressures that are important in ventilation
Atmospheric (760mmHg)
Intra - alveolar (760mmHg)
Intrapleural (756 mmHg)
what are the 2 important muscles that contract during inspiration?
- Diaphragm - increases the volume of the thorax vertically upon contraction
- The external intercostal muscle - lifts the ribs and moves the sternum on contraction
what is pneumothorax?
Air in the pleural space. Can be spontaneous, traumatic or iatrogenic
How does pneumothorax affect the transmural concentration gradient?
- Air enters the pleural space from outside or from the lungs
- can abolish the concentration gradient leading to lung collapse
what causes the lungs to recoil during expiration?
- Elastic connective tissue in the lungs
2. alveolar surface tension
What is alveolar surface tension?
Attraction between water molecules at liquid air. interface, this produces a force in the alveoli which resists stretching of the lungs
How can surfactant reduce alveolar surface tension?
- pulmonary surfactant is a complex mixture of lipids and proteins secreted by type II alveoli
- it intersperses between the water molecules of the alveoli
How does surfactant act on small alveoli in comparison to larger alveoli?
- It lowers the surface tension of smaller alveoli more
- prevents the smaller alveoli from collapsing and emptying their air contents into the larger alveoli
Describe the alveolar interdependence?
If an alveolus starts to collapse the surrounding alveoli are stretched and then recoil exerting expanding forces in the collapsing alveolus to open it
What are the major inspiratory muscles
Diaphragm and external intercostal muscles
what are the accessory muscles of inspiration?
Sternocleidomastoid, scalenus, pectoral
What are the muscles of active expiration?
Abdominal muscles and internal intercostal muscles
What is tidal volume?
Volume of air entering or leaving the lungs during a single breath. the average is 0.5L
What is inspiratory reserve volume?
Extra volume of air that can be maximally transpired over and above the typical resting tidal volume. Average is 3.0 litres
What is the expiratory reserve volume?
Extra volume of air that can be actively expired by maximal contraction beyond the normal volume of air after a resting tidal volume. Average is 1.0L
What is residual volume?
Minimum volume of air remaining in the lungs even after a maximal expiration. Average is 1.2L
What is the inspiratory capacity?
Maximum volume of air that can be inspired at the end of a normal quiet respiration . calculated by IC = IRV + TV. average is 3.5L.
What is the functional residual capacity?
volume of air in lungs at the end of normal passive expiration. calculated by FRC = ERV +RV. Average is 2.2L
What is the vital capacity?
Maximum volume of air that can be moved out during a single breath following maximal inspiration. Calculate by VC = IRV+TV+ERV. Average is 4.5L
What is the total lung capacity?
Total volume of air that the lungs can hold. calculated by TC = VC +RV. Average volume is 5.7L
What does the FEV1/FVC ration tell you?
The proportion of the forced vital capacity that can be expired in the first second. Normal score is > 70%
What is the primary determinant of airway resistance?
The radius of the conducting airway
how does intrapleural pressure change during inspiration and expiration?
- intra pleural pressure falls during inspiration
- intra pleural pressure rises during expiration
Describe dynamic airway compression during active respiration?
The increased airway resistance causes an increase in airway pressure upstream. This helps open the airways by increasing the driving pressure between the alveolus and the airway.
How can dynamic airway compression during active respiration affect a patient with airway obstruction?
The driving pressure between the alveolus and airway is lost over the obstructed segment. This causes a fall in airway pressure along the airway downstream resulting in airway compression by the rising pleural pressure during active expiration
What is the role of a peak flow meter?
- Gives an estimate of peak flow rate
- assesses airway function
what is pulmonary compliance?
Measure of the effort that has to go into stretching or distending the lungs
What is decreased pulmonary compliance?
- greater pressure is needed to produce a given change in volume
- occurs in patients with fibrosis, oedema act
- causes shortness of breath and my cause a restrictive pattern of lung volumes in spirometry
What is increased pulmonary compliance?
- may occur if elastic recoil of the lungs is lost (emphysema)
- patients have to work harder to get air out of the lungs
- compliance increases with age
When is work of breathing increased?
- when pulmonary compliance is decreased
- when airway resistance is increased
- when elastic recoil is decreased
- when there is a need for increased ventilation
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 the alveoli per minute
What are the 2 factors that the transfer of gases between the body and the atmosphere depends on?
- ventilation: the rate at which gas is passing through the lungs
- perfusion: the rate at which blood is passing through the lungs
What is alveolar dead space?
ventilated alveoli which are not adequately perfused with blood
What is ventilation perfusion match in the lungs?
- accumulation of CO2 in alveoli results in increased airflow
- accumulation of O2 in the alveoli results in increased blood flow
What are the four factors that influence the rate of gas exchange across the alveolar membrane?
- Partial pressure gradient of O2 and CO2
- Diffusion coefficient for O2 and CO2
- Surface area of alveolar membrane
- Thickness of alveolar membrane
What is daltons law of partial pressures?
The total pressure exerted by a gaseous mixture = the sum of each individual component in the gas mixture
What is the partial pressure of a gas?
The pressure that one gas in a mixture of gasses would exert if it were the only gas present in the whole volume occupied by the mixture at a given temperature
What is the effect of surface area and membrane thickness on gas diffusion?
- small airways form out pockets to help increase the surface area for gas exchange
- The lungs have a very extensive capillary network
What are the respiratory membranes?
- Alveoli: thin walled inflatable sacs
- walls consist of a single layer of flattened type 1 alveolar cells
- pulmonary capillaries encircle each alveolus
- narrow interstitial space
Name some of the non respiratory functions of the respiratory system?
- route for water an heat elimination
- enhances venous return
- helps maintain normal acid/base balance
- enables vocalisation
- defends against inhaled foreign material
- removes, modifies, activates or inactivates materials passing through the pulmonary circulation
- nose serves as organ of smell
What is Henrys law?
The amount of a given gas dissolves in a given type and volume of liquid at a constant temperature is proportional to the partial pressure of the gas in equilibrium with the liquid
What is the effect of partial pressure on gas solubility?
If the partial pressure in the gas phases increased the concentration of the has in the liquid phase would increase proportionally
Name the two forms that oxygen is found as in the blood?
- bound to haemoglobin
2. Physically dissolved (very little O2)
Describe oxygen binding to haemoglobin?
- Each Hb molecule contains 4 haem groups which can each reversibly bind one oxygen molecule
- Haemoglobin is considered fully saturated when all the Hb present is carrying its maximum O2 load
What is the Po2?
it is the primary factor that determines the percent saturation of haemoglobin with O2
What can impair oxygen delivery to the tissues?
- Respiratory disease
- Heart failure
- Anaemia
What is the partial pressure of inspired oxygen dependent on?
The total pressure (atmospheric) and proportion of oxygen in the gas mixture (21% in atmosphere)
Describe co-operativity?
binding of one O2 to Hb increases the affinity of Hb for O2
What is the Bohr effect?
A shift of the sigmoid curve to the right because of release of O2 by conditions at the tissues
How does foetal haemoglobin differ from adult haemoglobin?
- It has 2 alpha and 2 gamma subunits
- it interacts less with 2,3 Biphosphoglycerate in red blood cells
- it has a higher affinity for O2 than adult Haemoglobin
What is myoglobin?
- It is present in skeletal and cardiac muscles
- one haem group per myoglobin molecule
- provides short term storage of O2 for anaerobic conditions
What does presence of myoglobin in the blood indicate?
Muscle damage
How is CO2 transported in the blood?
- solution (10%)
- As bicarbonate (60%)
- As carbamino compounds (30%)
How is bicarbonate formed in the blood?
- by carbonic anhydrase
- occurs in red blood cells
What are carbamino compounds?
- formed by a combination of CO2 with terminal amine groups in blood proteins
What is the Haldane effect?
Removing O2 from Hb increases the ability of Hb to pick up CO2 and CO2 generated H+
what do the Boher and Haldane effect work together to facilitate?
- O2 liberation and uptake of CO2 and CO2 generated H+ at tissues
What is the role of the Pre - Botzinger complex?
- located near the upper end of the medullary respiratory centre
- generates the breathing rhythm
What gives rise to inspiration?
- rhythm generated by Pre - Botzinger complex
- excites dorsal respiratory group neutrons
- fire in bursts
- Firing leads to inspiration
- when firing stops = passive expiration
How does active expiration during hyperventilation occur?
- increased firing of dorsal neurons excites ventral respiratory group neutrons which then excites internal intercostal and abdominal muscles leading to forceful expiration
What is the role of the pneumotaxic centre?
- stimulation terminates inspiration
- It is stimulated when dorsal respiratory neurones fire
What would happen if the pneumotaxic centre didn’t work?
- breathing is prolonged inspiratory gasps with brief expiration
- Apneusis
Give examples of involuntary modifications of breathing
- pulmonary stretch receptors hering Breuer reflex
- Joint receptors reflex in exercise
- stimulation of respiratory centre by temperature, adrenaline or impulses from cerebral cortex
- cough reflex
Describe the role of pulmonary stretch receptors?
- activated during inspiration, afferent discharge inhibits inspiration - Hering Breuer reflex
Describe the role of joint receptors?
- impulses from moving limbs reflexly increase breathing
- probably contribute to the increased ventilation during exercise
Describe some of the factors that may increase ventilation during exercise?
- reflexes originating from body movement
- adrenaline
- impulses from cerebral cortex
- inc in body temp
Describe the cough reflex
- afferent discharge stimulates short intake of breath followed by closure of the larynx, then contraction of abdominal muscles (inc intra alveolar pressure) and opening of the larynx and expulsion of air at high speed
Describe chemical control of respiration?
- an example of a negative feedback control system
- controlled variables are the blood gas tensions (CO2)
- chemoreceptors sense the values of the gas tensions
What is the role of the peripheral chemoreceptors?
sense tension of oxygen and CO2 and [H+] in the blood
What is the role of the central chemoreceptors?
- respond to the [H+] of the CSF
What is the hypoxic drive of respiration?
- effect is produced via the peripheral chemoreceptors
- stimulated when kPa < 8
- may be important in patients with chronic CO2 retention and at high altitude
What causes hypoxia at high altitudes?
Decreased partial pressure of inspired oxygen (PiO2)
What is the acute response and what are the symptoms of hypoxia at high altitude?
acute response = hyperventilation and increased cardiac output
symptoms = headache, fatigue, nausea, tachycardia, dizziness, sleep disturbance , shortness of breath, unconsciousness
What are the chronic adaptations to high altitude hypoxia?
- inc RBC production
- 2,3 BPG produced within RBC
- inc no of capillaries
- inc no of mitochondria
- kidneys conserve acid
Describe the H+ drive of respiration?
- effect produced via peripheral chemoreceptors
- their stimulation by H+ causes hyperventilation and increases elimination of CO2 from the body
