Physiology Flashcards
What is internal respiration?
Intracellular mechanisms that consume O2 and produce CO2
What is external respiration?
Exchange of O2 and CO2 between the external environment and cells
What are the 4 steps of external respiration?
- Ventilation
- Gas exchange between alveoli and blood
- Gas transport in the blood
- Gas exchange at the tissues
What body systems are involved with external respiration?
Respiratory
Cardiovascular
Haematology
Nervous
What is ventilation?
The mechanical process of moving air between the atmosphere and alveolar sacs
Boyle’s Law means…
As the volume of the lungs increases, the pressure of gas inside the lungs decreases
How do the thorax and lungs expand during inspiration?
Contraction of inspiratory muscles
What must the pressure conditions be for air to flow into the lungs?
Intra-alveolar pressure must be lower than the atmospheric pressure
What 2 forces hold the lungs to the thoracic wall?
- Intrapleural fluid cohesiveness
2. Negative intrapleural pressure
What is the average pressure of atmosphere?
760 mmHg
What is the average pressure of intra-alveolar
760 mmHg
How would you describe the relative intrapleural pressure
sub atmospheric
What kind of process is inspiration?
Active
What kind of process is expiration?
Passive
What is the transmural gradient?
difference in pressure between two sides of thoracic wall
Define pneumothorax and list the three main common causes
Accumulation of air in pleural space
- Traumatic
- Spontaneous
- Iatrogenic
How does a pneumothorax effect transmural pressure gradient?
Abolishes transmural pressure gradient- can cause lung collapse.
what are the signs of a pneumothorax?
Hyper-resonant percussion note
Decreased/absent breath sounds
What are the symptoms of a pneumothorax?
Shortness of breath
Chest pain
what causes lungs to recoil?
Elastic CT
Alveolar surface tension
What is surfactant and it’s function?
Surfactant is a complex mix secreted by type II alveoli
It’s function is to lower surface tension by interspersing between the H2O molecules lining the alveoli
What causes respiratory distress syndrome in newborns? especially preterm babies?
Often not sufficient supply of surfactant, as produced late in pregnancy
What alveolar interdependence?
The mechanism of surrounding alveoli helping to open collapsed alveoli (using expanding forces)
What is the order of rhythm of respiration?
Inspiration, expiration
what is the major rhythm generator?
The medulla
What neuron network is believed to generate breathing rhythm?
(spontaneous action potentials)
Pre-Botzinger complex
(near upper end of medullary respiratory centre)
(previously believed to be the dorsal respiratory group)
what group of neurones are excited by the pre-botzinger complex?
Dorsal respiratory group neurones
What does firing of nerve signals do?
Leads to contraction of inspiratory muscles
which direction will the thorax increase by contraction of the diaphragm?
Vertically
which nerve signals to the diaphragm to contract?
Phrenic nerve
What do ventral respiratory group muscles do?
Activate expiratory neurones during hyperventilation (active expiration)
Where are the neurones modifying the medulla located?
The pons
stimulation of which area terminates inspiration?
Pneumotaxic centre (PC)
which respiratory neurones stimulate the PC?
dorsal respiratory neurones
what is apneusis?
prolonged inspiratory gasps followed by brief expiration- happens without PC
what does the apneustic centre do?
sends out neuron impulses to excite inspiratory area of medulla
What stimuli can influence respiratory centres?
Higher brain centres Stretch receptors in bronchi and bronchioles (Hering-Breur reflex) Juxtapulmonary receptors Joint receptors Baroreceptors (regulate BP) Central chemoreceptors Peripheral chemoreceptors
what is the hering- breur reflex?
a guard against hyperinflation in the bronchi and bronchioles by stretch receptors
What do joint receptors do?
send impulses from moving limbs to reflexly increase breathing
what are the likely receptors to contribute to increased ventilation in exercise?
Joint receptors
what are the likely factors that increase ventilation in exercise?
Reflexes from body movement Adrenaline release Impluses from cerebral cortex increase in body temp accumulation of CO2 and H+ in active muscles
Recovery stage of ventilatory response to stimuli is a result of?
removal of stimulant
what is the function of a cough reflex?
To remove dust, dirt or excessive secretions from the airway
what activates cough reflex?
irritation of airways or tight airways (asthma/tumour)
where is the cough receptor centre)
medulla
what are the physiological steps of coughing?
Short breath intake
Closure of larynx
contraction of abdominal muscles (increase alveolar pressure)
opening of larynx and rapid expulsion of air
Chemical control of respiration is an example of which feedback control system?
negative
what are the controlled variables in the chemical control of respiration?
blood gas tensions (esp. CO2)
what molecules sense the values of gas tensions?
Chemoreceptors
where are central chemoreceptors situated?
medulla
what do central chemoreceptors respond to?
H+ concentration of cerebrospinal fluid
What separates CSF from the blood?
blood-brain barrier
which gasses readily diffuse over the blood-brain barrier?
CO2
How is CSF less buffered than blood?
it contains less protein than blood
what is hypercapnia?
increased CO2
Ventilation is very sensitive to which gas?
CO2
what helps CO2 generate H+
central chemoreceptors
what is the normal arterial PO2 in a person?
13.3 kPa
What effect does hypoxia have on CNS neurones?
It depresses them
at which PO2 values are the peripheral chemoreceptors stimulates?
> 8 kPa
when does hypoxic drive become important?
Patients with chronic CO2 retention (eg. COPD)
At high altitudes
What is hypoxia at high altitudes caused by>
decreased PiO2
what are the accute responses of hypoxia at high altitudes?
Hyperventilation & increased cardiac output
symptoms of acute mountain sickness
headache fatihue nausia tachycardia dizziness sleep disturbance exhaustion shortness of breath unconsciousness
chronic adaptions to high altitudes hypoxia
increased RBC production (polycythaemia) increased 2,3 BPG produced in RBCs increased no. of capillaries increased no. mitochondria kidneys conserve acid (decreased arterial pH)
H+ drive is mediated through which chemoreceptors?
Peripheral
How readily does H+ cross the blood brain barrier?
not much
how do peripheral chemoreceptors adjust acidosis in the blood?
causes hyperventilation to increase elimination of CO2
what stimulated peripheral chemoreceptors?
increased H+ in blood
what are the major inspiratory muscles?
Diaphragm
External intercostal muscles
what are the accessory muscles of inspiration?
Sternocleidomastoid
Scalenus
Pectoral
What are the muscles of active expiration?
Abdominal muscles
internal intercostal muscles
What is tidal volume (TV) and the average value?
Volume of air entering/leaving the lungs during a single breath
0.5 L
what is inspiratory reserve volume (IRV) and the average value?
extra volume of air that can be maximally inspired over and above the typical resting tidal volume
3.0 L
what is expiratory reserve volume (ERV)?
extra volume of air that can be actively expired by maximal contraction beyond the normal volume of air after a resting tidal volume
1.0 L
what is residual volume (RV)?
minimum volume of air remaining in the lungs even after a maximal expiration
1.2 L
what is inspiratory capacity (IC)?
maximum volume of air that can be inspired at the end of a normal quiet expiration
IC= ERV + TV
3.5 L
what is functional residual capacity (FRC)
Volume of air in the lungs at end of normal passive expiration
FRC = ERV + RV
2.2 L
what is vital capacity (VC)
maximum volume of air that can be moved out during a single breath following a maximal inspiration
VC = IRV + TV + ERV
4.5 L
what is total lung capacity? (TLC)
total volume of air the lungs can hold
TLC = VC + RV
5.7 L
which volume cannot be measured by spirometry?
Residual volume
What causes residual volume to increase?
When the elastic recoil of the lungs is lost (eg. emphysema)
what can be determined from volume time curve?
FVC
FEV1
FEV1/FVC ratio
what are dynamic lung volumes useful for?
Obstructive and restrictive lung disease
what is FVC?
forced vital capacity- maximum volume that can be forcibly expelled from the lungs after a maximum inspiration
what is FEV1?
Force expiratory volume in one second- volume of air that can be expired during the first second
what is FEV1/FVC?
proportion of FVC that can be expired in first second
Normally >70%
what would the spirometry results of a patient with an airway obstruction be?
Low/normal FVC
Low FEV1
Low FEV1/FVC%
what would the spirometry results of a patient with a lung restriction be?
Low FVC
Low FEV1
Normal FEV1/FVC%
What would the spirometry result of a patient with both obstruction and restriction?
Low FVC
Low FEV1
Low FEV1/FVC%
What is the primary determinant of airway resistance?
Radius of conducting airway
bronchoconstriction is caused by which type of stimulation?
Parasympathetic
bronchodilation is caused by which type of stimulation?
Sympathetic
expiration is more difficult than inspiration with patients with COPD or asthma due to?
Airway resistance
what is dynamic airway compression?
pressure applied to alveolus pushes air out of the lungs
pressure applied to the airway is not desirable
What happens with dynamic airway compression in patients with airway obstruction?
driving pressure is lost over obstructed segment
Causes fall in airway pressure along airway downstream
results in airway compression by rising pleural pressure during active expiration
when is a peak flow test useful?
with patients with obstructive lung disease
What is pulmonary compliance?
measure of effort that has to go into stretching or distending the lungs
what decreases pulmonary compliance?
pulmonary fibrosis pulmonary oedema lung collapse pneumonia absence of surfactant
what are the effects of decreased pulmonary compliance?
Lungs are stiffer
causes shortness of breath on exertion
Can cause a restrictive pattern of lung volumes in spirometry
what increases pulmonary compliance?
If elastic recoil of lungs is lost
emphysema (hyperinfation of the lungs)
Age
work of breathing is increased in which situations?
Decreased pulmonary compliance
Increased airway resistance
Decreased elastic recoil
When there’s a need for increased ventilation
How would you calculate pulmonary ventilation?
the tidal volume x respiratory rate
How would you calculate alveolar ventilation?
(tidal volume - dead space volume) x respiratory rate
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
Why is it more advantageous to increase the depth of breathing?
Dead space
what is ventilation?
the rate at which gas is passing through the lungs
what is perfusion?
the rate at which blood is passing through the lungs
what is considered as alveolar dead space?
Ventilated alveoli which are not adequately perfused with blood
what is physiological dead space?
anatomical dead space + alveolar dead space
what does accumulation of CO2 in the alveoli as a result of increased perfusion do?
decrease airway resistance leading to increased airflow
What is the partial pressure of O2 in the atmosphere?
~21 kPa
what is the partial pressure of O2 in alveolar air?
not much difference between this, pulmonary capillaries and arterial blood
~13.3 kPa
what is Henry’s law?
Gas dissolved in a liquid (blood) at constant temp. is proportional to the partial pressure of gas in equilibrium with the liquid.
How much O2 is taken to the tissues as dissolved O2 under resting conditions?
15 ml/min
How much O2 is taken to the tissues as dissolved O2 under strenuous exercise?
90ml/min
What is the resting O2 consumption of our body cells?
250 ml/min
How much of of O2 is carried by haemoglobin?
98.5%
How many haem groups does haemoglobin have?
4
How many oxygen molecules does each haem group reversibly bind to?
1
How is haemoglobin described when all the Hb is carrying its maximum O2 load?
Fully saturated
What is the primary factor determining the percent saturation of haemoglobin with O2?
PO2
What shape is the oxygen haemoglobin dissociation curve?
sigmoidal
Whats the average resting PO2 at systemic capillaries?
5.3 kPa
What is DO2I?
oxygen delivery index
How do you calculate DO2I?
CaO2 x CI (oxygen content of arterial blood x Cardiac Index)
How do you calculate the oxygen content of arterial blood (CaO2)?
1.34 x [Hb] x SaO2
What can impair O2 delivery to the tissues?
Resp. disease- decreases arterial PO2, deccreases Hb saturation
Heart failure- decreases cardiac output
Anaemia- Decreases Hb concentration
What happens to atmospheric pressure as altitude increases?
Atmospheric pressure decreases
How to calculate the Partial pressure of O2 in alveolar air (PAO2)?
PiO2 - [PaCO2/0.8]
What is the significance of the sigmoid correlation for haemolglobin?
Flat upper portions- moderate fall in alveolar PO2 will not affect O2 loading
Steep lower part- peripheral tissues get lots of O2 for small drop in capilliary PO2
The bohr effect shows what on the sigmoid graph?
shift to the right
What are the results of the bohr effecr?
increased release of O2 by tissues increased PCO2 increased [H+] increased temp increased 2,3- Biphosphoglycerate
What shape is the myoglobin dissociation curve?
Hyperbolic
What does presence of myoglobin in the blood indicate?
muscle damage
What is the function of myoglobin?
Provides short term storage for O2 in the muscles for anaerobic conditions
What are the three methods of CO2 transport in the blood?
Solution 10%
Bicarbonate 60%
Carbamino compounds 30%
how more soluable is carbon dioxide to oxygen?
20 times
what enzyme catalyses the formation of bicarbonate from water and CO2?
Carbonic anhydrase
what is the chloride shift?
when chloride enters the RBC and HCO3- leaves
what are carbamino compounds formed from?
CO2 and terminal amine groups in blood proteins (globin)
which can bind more CO2, HbO2 or Reduced Hb?
Reduced Hb
What is the haldane effect?
Remoing O2 from Hb increases Hb’s affinity to pick up Co2 and Co2 generated H+
what is the haldane effect on the CO2 dissociation curve?
Oxygen shifts the curve to the right
