Physiology Flashcards
Define internal respiration
The intracellular mechanisms which consumes O2 and produces CO2
Define external respiration
Refers to the sequence of events that leads to the exchange of O2 and CO2 between external environment and the cells of the body
What are the four steps of external respiration?
- ventilation
- gas exchange between alveoli and the blood
- gas transport in the blood
- gas exchange at the tissue level
Describe the four steps of external respiration?
- Ventilation; the mechanical process of moving gas in and out of the lungs
- gas exchange between alveoli and blood; the exchange of O2 and CO2 between the air in the alveoli and the blood in the pulmonary capillaries
- gas transport in the blood; the binding and transport of O2 and CO2 in the circulating the blood
- gas exchange at the tissue level; the exchange of O2 and CO2 between the blood in the systemic capillaries and the body cells
What are the four body systems involved in external respiration?
- the respiratory system
- the cardiovascular system
- the haematology system
- the nervous system
Define Boyles law
At any constant temperature, the pressure exerted by a gas varies inversely with the volume of the gas. As the volume of a gas increases, the pressure exerted by the gas decreases
What needs to happen to the intra-alveolar pressure for air to flow into the lungs during inspiration?
The intra-alveolar pressure must become less than atmospheric pressure
During inspiration, what expands as a result of contraction of respiratory muscles?
The thorax and lungs
What are the two forces that hold the thoracic wall and the lungs in close apposition?
- intrapleural fluid cohesiveness
- negative intrapleural pressure
Describe the intrapleural fluid cohesiveness
The water molecules in the intrapleural fluid are attached to each other and resist being pulled apart. The pleural membrane tend to stick together
Describe 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 while the chest is forced to squeeze inwards
What is the atmospheric pressure, the intra-alveolar pressure and the intrapleural pressure?
Atmospheric = 760 mmHg Intra-alveolar = 760 mmHg Intrapleural = 756 mmHg
What three pressure are important in ventilation?
- atmospheric pressure
- intra alveolar pressure
- intrapleural pressure
Inspiration is an active process dependant on what?
Muscle contraction
Which nerve supplies the diaphragm?
The phrenic nerve
What occurs when the external intercostal muscle contracts?
Lifts the ribs and moves out the sternum
Why do the lungs increase in size?
To make the intra-alveolar pressure fall
Why does the intra-alveolar pressure fall when the lungs increase in size?
Air molecules become contained in a larger volume (Boyles law)
Is normal expiration a passive process or an active process?
A passive process
How do the chest wall and stretched lungs recoil to their pre-inspiratory size?
Due to their elastic properties
What does the re-coiling of the lungs do to the intra-alveolar pressure?
The intra-alveolar pressure rises
Describe the movement of the diaphragm during inhalation and exhalation
During inhalation the diaphragm contracts and moves down. During exhalation the diaphragm relaxes and moves up
Describe a pneumothorax
- loss of pressure gradient
- air in the pleural space
- can be spontaneous, traumatic or iatrogenic
- this can abolish transmural pressure gradient leading to lung collapse
- small pneumothorax can be asymptomatic
What are the physical signs and symptoms of pneumothorax?
Symptoms; shortness of breath, chest pain
Physical signs; hyper-resonant, percussion note, decreases / absent breath sounds
What is lung recoil caused by?
- elastic connective tissue in the lungs
- alveolar surface tension
Describe alveolar surface tension
- attraction between water molecules at liquid air interface
- in the alveoli this produces a force which resists the stretching of the lungs
- if the alveoli were lined with water alone, the surface tension would be too strong so the alveoli would collapse
What reduces the alveolar surface tension?
Surfactant
Describe the law of LaPlace
The smaller alveoli (with a smaller radius) have a high tendency to collapse
Describe surfactant
- complex mixture of lipids and proteins secreted by type 2 alveoli
- lowers alveolae surface tension by interspersing between the water molecules lining the alveoli
- lows the surface tension of smaller alveoli more than that of larger alveoli
- this prevents the smaller alveoli from collapsing and emptying their air contents into the larger alveoli
Describe respiratory distress syndrome of the new born
- developing foetal lungs are unable to synthesise surfactant until late in pregnancy
- premature babies may not have enough pulmonary surfactant
- the baby makes very strenuous inspiratory efforts in an attempt to overcome the high surface tension and inflate the lungs
Describe the alveolar interdependence
- another factor to keep alveoli open
- if an alveolus starts to collapse, the surrounding alveoli are stretched and then recoil exerting expanding forces in the collapsing alveolus to open it
Name the forces that are keeping the alveoli open
- transmural pressure gradient
- pulmonary surfactant
- alveolar interdependence
Name the forces promoting alveolar collapse
- elasticity of stretched lung connective tissue
- alveolar surface tension
What are the major inspiratory muscles?
The diaphragm and the external intercostal muscles
Name the accessory muscles of inspiration (that contract only during forceful inspiration)
- sternocleidomastoid
- scalenus
- pectoral
Name the muscles of active expiration (contracts only during active expiration)
- abdominal muscle
- internal intercostal muscles
Describe the total lung capacity
- the maximum volume of air that the lungs can hold
- vital capacity + residual volume
- average value = 5700ml
- residual volume cannot be measured by spirometry meaning it is not possible to measure total lung volume by spirometry
- residual volume increases when the elastic recoil of the lung is lost eg. in emphysema
What does the volume time curve allows you to determine?
- FVC
- FEV1
- FEV1/FVC ratio
What is forced vital capacity?
Maximum volume that can be forcibly expelled from the lungs following a maximum inspiration
What is FEV1?
Volume of air that can be expired during the first second of expiration in an FVC determination
What is the FEV1/FVC ratio?
The proportion of the forced vital capacity that can be expired in the first second
What is a normal FEV1:FVC ratio and what is the value for asthmatics?
- more than 75%
- less than 75%
Describe the values of FVC, FEV1 and FEV1/FVC during airway obstruction
- FVC = low or normal
- FEV1 = low
- FEV1/FVC = low
Describe the values of FVC, FEV1 and FEV1/FVC during lung restriction
- FVC= low
- FEV1= low
- FEV1/FVC= normal
Describe the values of FVC, FEV1 and FEV1/FVC during combination of obstruction and restriction
- FVC = low
- FEV1= low
- FEV1/FVC= low
Describe airway resistance
- resistance to flow in the airway normally is very low and therefore air moves with a small pressure gradient
- primary determination of airway resistance is the radius of the conducting airway
- parasympathetic stimulation causes bronchodilation
- sympathetic stimulation causes bronchodilation
- disease states can cause significant resistance to airflow
- expiration is more difficult than inspiration
During inspiration what pulls the airways open?
The expanding thorax
What happens to intrapleural pressure during inspiration and expiration?
Inspiration; intrapleural pressure falls
Expiration; intrapleural pressure rises
What makes active expiration more difficult in patients with airway obstruction?
Dynamic airway compression
Describe peak flow meters
- gives an estimate of peak flow rate
- the peak flow rate assesses airway function
- the test is useful in patients with obstructive lung disease
Describe how peak flow meters are used?
- it is measured by the patient giving a short sharp blow into the peak flow meter
- the best of three attempts is usually taken
- the peak flow rate in normal adults varies with age and height
Describe pulmonary compliance
- during inspiration the lungs are stretched
- compliance is a measure of effort that has to go into stretching or distending the lungs
- the less compliant the lungs are, the more work is required to produce a given degree of inflation
Describe decreased pulmonary compliance
- pulmonary compliance is decreased by factors such as pulmonary fibrosis, pulmonary oedema, lung collapse, pneumonia, absence of surfactant
- decreased pulmonary compliance means greater change in pressure is needed to produce a given change in volume (ie. lungs are stiffer) this causes shortness of breath especially on exertion
- decreased pulmonary compliance may cause a restrictive pattern of lung volumes in spirometry
Describe increased pulmonary compliance
- compliance may become abnormally increased if the elastic recoil of the lung is lost
- increased compliance occurs in emphysema. Patients have to work harder to get the air out of the lungs (hyperinflation of lungs)
- remember dynamic airway obstruction will also be aggravated in patients with obstructed airway and emphysema caused by COPD
- compliance also increased with increasing 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
Why is alveolar ventilation less than pulmonary ventilation?
Due to the presence of anatomical dead space
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. This is more important as it represents new air available for gas exchange with blood
How is pulmonary ventilation increased eg. during exercise?
Both the depth (tidal volume) and rate of breathing (rr) increase
What is the equation for pulmonary ventilation?
Tidal volume x respiratory rate
What is the equation for alveolar ventilation?
(tidal volume - dead space) x respiratory rate
What is ventilation perfusion?
The transfer of gases between the body and atmosphere depends on ventilation and perfusion
Define ventilation
The rate at which gas is passing through the lungs
Define perfusion
The rate at which blood is passing through the lungs
What is alveolar dead space?
Ventilated alveoli what are not adequately perfused with blood
The physiological dead space is equal to what?
Anatomical dead space + alveolar dead space
What causes pulmonary vasodilation?
Increase in alveolar O2 concentration as a result of increased ventilation
What causes decreased airway resistance leading to increased airflow?
Accumulation of CO2 in alveoli as a result of increased perfusion
What happens when perfusion is greater than ventilation in an area?
- CO2 increases in the area
- dilation of local airways
- O2 decreases in the area
- airflow increases
- constriction of local blood vessels
- blood flow decreases
What happens when ventilation is greater than perfusion in an area?
- CO2 decreases in the area
- constriction of local airways
- airflow decrease
- O2 increases in the area
- dilation of local blood vessels
- blood flow increases
What do the pulmonary arterioles do in decreased O2 and increased O2?
Decreased= vasoconstriction Increased = vasodilation
What do the systemic arterioles do in increased O2 and decreased O2?
Decreased = vasodilation Increased = vasoconstriction
What are the four factors that influence the rate of gas exchange across alveolar membrane?
- partial pressure gradient of O2 and CO2
- diffusion coefficient of O2 and CO2
- surface area of alveolar membrane
- thickness of alveolar membrane
Describe daltons law of partial pressures
- the total pressure exerted by a gaseous mixture = the sum of the partial pressures of each individual component in the gas mixture
The partial pressure of a gas determines what?
The pressure gradient for that gas
What is the partial pressure of a gas?
The pressure that one gas in a mixture of gases would exert if it were the only gas present in the whole volume occupied
What is PaO2?
The partial pressure of oxygen in the alveolar air
What is PiO2?
Partial pressure of O2 in inspired air
What is PaCO2?
Partial pressure of CO2 in arterial blood
What is more soluble in membranes, CO2 or O2?
CO2`
The solubility of gas in membranes is known as what?
The diffusion coefficient
Name non-respiratory functions of the respiratory system
- route for water loss and heat elimination
- enhances venous return
- helps maintain normal acid base balance
- enable speech, singing and other vocalisations
- defends against inhaled foreign matter
- removed. modifies, activates or inactivates various materials passing through the pulmonary circulation
- nose serves as the organ of smell
Describe henrys law
- the amount of a given gas dissolved in a given type and volume of liquid (eg. blood) at a constant temperature is proportional to the partial pressure of the gas in equilibrium with the liquid
What is the primary factor which determines the percentage saturation of haemoglobin with O2?
The PO2
What is the oxygen delivery index?
oxygen delivery to the tissues is a function of oxygen content of arterial blood and the cardiac output
What is the effect of respiratory disease on arterial PO2, Hb saturation and O2 content of the blood?
decreased arterial PO2
decreases Hb saturation
Decreases O2 content of the blood
How does heart failure affect cardiac output?
It decreases cardiac output
What is the effect of anaemia on Hb concentration and O2 content of the blood?
Hb concentration decreases
O2 content of the blood decreases
The partial pressure of inspired oxygen depends on what?
- total pressure
- proportion of oxygen in gas mixture
How do you convert kPa to mmHg?
Multiply by 7.5
Describe myoglobin
- present in skeletal and cardiac muscles
- one haem group per myoglobin molecule
- no co-operative binding of O2
- dissociation curve is hyperbolic
- myoglobin releases O2 at very low PO2
- provides a short term storage of O2 for anaerobic conditions
- presence of myoglobin in the blood indicates muscle damage
Describe foetal haemoglobin
- differs from adult haemoglobin in structure
- has 2 alpha subunits and 2 gamma subunits
- HbF interacts less with 2,3 biphosphoglycerate in RBC
- has a higher affinity for O2
- allows O2 to transfer mother to foetus even if the PO2 is low
Describe the Haldane effect
Removing O2 from Hb increases the ability of Hb to pick up CO2 and CO2 generated H+
The breathing rhythm is generated by what?
A network of neurons called the pre-botzinger complex
The pons respiratory centre s include what?
- pneumotaxic centre
- apneustic centre
The medullary respiratory centre include what?
- dorsal respiratory group
- ventral respiratory group
What gives rise to inspiration?
- rhythm generated by pre-botzinger complex
- excites dorsal respiratory group neurones
- fire in bursts
- firing leads to contraction of inspiratory muscles
- when firing stops, passive expiration
Describe the muscle movement during inspiration
- the volume of the thorax is increased vertically by contraction of the diaphragm flattening out its dome shape
- the external intercostal muscle contraction lifts the rib and moves out the sternum
Describe active expiration during hyperventilation
- increased firing of dorsal neurones excites a second group of neurones
- ventral respiratory group neurones
- excites intercostals, abdominals etc. forceful expiration
- in normal breathing, ventral neurones do not activate expiratory muscles
Describe the apneustic centre
- impulses from these neurones excite inspiratory area of medulla
- prolong inspiration
- rhythm generated in medulla
- rhythm can be modified by inputs from the pons
The respiratory centres are influenced by stimuli received from where?
- higher brain centres
- stretch receptors
- juxtapulmonary receptors
- joint receptors
- baroreceptors
- central chemoreceptors
- peripheral chemoreceptors
Name some examples of involuntary modifications of breathing
- pulmonary stretch receptor hering-breur reflex
- joint receptors reflex in exercise
- stimulation of respiratory centre by temperature, adrenaline or impulses from cerebral cortex
- cough reflex
Name some factors that may increase ventilation during exercise
- reflexes originating from body movement
- adrenaline release
- impulses from the cerebral cortex
- increase in body temperature
- later; accumulation of CO2 and H+ generated by active muscles
Describe central chemoreceptors
- situated near the surface of the medulla of the brainstem
- respond to the [H+] of the cerebrospinal fluid
- CSF is separated from the body by the blood-brain barrier
- relatively impermeable to H+ and HCO3-
- CO2 diffuses readily
- CSF contains less protein than blood and hence is less buffered than blood
Describe hypoxic drive of respiration
- the effect is all via the peripheral chemoreceptors
- stimulated only when arterial PO2 falls to low levels (<8.0 kPa)
- it is not important in normal respiration
- may become important in patients with COPD
- important at high altitudes
What is hypoxia at high altitudes caused by?
Decreased partial pressure of inspired oxygen (PiO2)
Name the symptoms of acute mountain sickness
- headache
- fatigue
- nausea
- tachycardia
- dizziness
- sleep disturbance
- exhaustion
- shortness of breath
- unconsciousness
Describe the chronic adaptations to high altitudes hypoxia
- increased RBC production (polycythaemia), O2 carrying capacity of blood increased
- increased 2,3 BPG produced within RBC - O2 offloaded more easily into tissues
- increased number of capillaries blood diffuses more easily
- increased number of mitochondria, O2 can be used more efficiently
- kidneys conserve acid, arterial pH decreases
