Physiology Flashcards
Internal respiration refers to the intracellular organisms which
consume O2 and produce CO2
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
4 steps of external respiration
- Ventilation
- Gas exchange between alveoli and blood
- Gas transport in blood
- Gas exchange at tissue level
Ventilation
Process of moving gas in and out of lungs
Boyle’s Law
At any constant temperature the pressure exerted by a gas varies inversely with the volume of the gas
Linkage of Lungs to Thorax
- Intrapleural fluid cohesiveness
2. Negative intrapleural pressure
Intrapleural fluid cohesiveness
Water molecules in intrapleural fluid are attracted to each other and resist being pulled apart
Pleural membranes stick together
Negative intrapleural pressure
Below atmospheric pressure in intrapleural space creates a transmural pressure gradient across lung wall and chest wall
Lungs expand and chest tightens
Inspiration
Active Volume of thorax increases External intercostal muscles contract Ribs move up and out Diaphragm contracts (phrenic nerve from C3,C4,C5) Intra-alveolar pressure falls Air enters lungs down pressure gradient
Expiration
Passive
Lungs recoil to normal size
Alveolar pressure rises
Air leaves down pressure gradient
Pneumothorax
Air in pleural space
Complications of pneumothorax
Can cause lung to collapse
Treatment of tension pneumothorax
Decompression by insertion of IV cannula in 2nd intercostal space, midclavicular line, on affected site
Causes of tension pneumothorax
Asthma Injury penetrating chest Rupture of sub-pleural pleb TB Infection Growth (Carcinoma) Hereditary Tissue (connective)
Presentation of tension pneumothorax
Pleuritic chest pain Tracheal deviation Hyper-resonance Onset sudden Reduced breath sounds Asymptomatic sometimes Xray shows collapse
What causes recoil during expiration?
Alveolar surface tension
Elastic connective tissue in lungs
Alveolar surface tension
Attraction between water molecules at liquid air interface
Produces a force in alveoli that resists stretching of lungs
Law of LaPlace
Smaller alveoli are more likely to collapse
Pulmonary surfactant
Complex mixture of lipids and proteins secreted by type II alveoli
Lowers alveolar surface tension
Lowers that of smaller alveoli more, preventing them from collapsing
Respiratory Distress Syndrome in New Born
Foetal lungs unable to produce surfactant
Causes RDS
Baby makes strenuous respiratory efforts to overcome high surface tension
Alveolar interdependance
If an alveolus starts to collapse, the surrounding alveoli are stretched and then recoil, bringing collapsing alveoli with them to reopen it
Major inspiratory muscles of respiration
Diaphragm and external intercostal muscles
Accessory muscles of inspiration
Sternocleidmastoid, scalenus, pectoral
Muscles of active expiration
Abdominal muscles and internal intercostal muscles
tidal volume
Volume of air entering or leaving lungs in a single breath
Residual volume
minimum volume of air remaining in lungs after maximal expiration
Inspiratory capacity
maximum volume of air that can be inspired at the end of a normal expiration
Total lung capacity
Vital capacity + residual volume
FVC
Forced vital capacity
Maximum volume that can be forcibly expelled from lungs following maximum inspiration
FEV/FEC
should be >70%
parasympathetic stimulation causes
bronchoconstriction
sympathetic stimulation causes
bronchodilatation
Pulmonary compliance
Measure of effort that has to go into stretching of distending the lungs
Less compliant = more work required
Increased pulmonary compliance
Emphysema
Patients have to work harder to inflate lungs
Decreased pulmonary compliance
Pulmonary fibrosis, pulmonary oedema, pneumonia
Shortness of breath
Pulmonary ventilation
Volume of air breathed in and out per minute
Tidal volume x resp rate
Alveolar ventilation
Volume of air exchanged between atmosphere and alveoli per minute
Ventilation
Rate at which gas passes through lungs
Perfusion
Rate at which blood passes through lungs
Alveolar Dead Space
Ventilated alveoli that aren’t adequately perfused with blood
Perfusion > ventilation
Increased Co2
Dilatation of airways
Decreased O2
Constriction of blood vessels
Ventilation > perfusion
Decreased Co2
Constriction of airways
Increased O2
Dilatation of blood vessels
4 factors affecting Rate of Gas Exchange Across Alveolar Membrane
- Partial pressure gradient of O2 and Co2
- Diffusion coefficient for Co2 and O2
- Surface area of alveolar membrane
- Thickness of alveolar membrane
Daltons Law
Total pressure exerted by a gaseous mixture = sum of all partial pressures of each individual gas
Alveolar Gas Equation
PAO2 =
PiO2 - (PaCO2/0.8)
Diffusion coefficient for Co2
Solubility of Co2 in membranes
20 X that of O2
Large gradient between PAO2 and PaO2
Problems with gas exchange in lungs or a right to left shunt in heart
Henry’s Law
Amount of gas dissolved in a given type and volume of liquid at a constant temp is proportional to the partial pressure of the gas in equilibrium with the liquid
2 forms O2 present in blood
Bound to haemoglobin
Physically dissolved
Oxygen binding to haemoglobin
Binds reversibly
Each Hb has 4 haem groups
Oxygen delivery index
DO2I = CaO2 X CI
Oxygen delivery to tissues can be impaired by
Respiratory disease
Heart Failure
Anaemia
Sigmoid curve of haemoglobin
Binding of one O2 to haemoglobin increases affinity of Hb for O2
Flattens when all sites occupied
Bohr Effect
Shift of haemoglobin curve to right
Foetal haemoglobin
Higher affinity for O2, curve shifted to left
Allows mother to transfer O2 at low partial pressures
Myoglobin
Present in skeletal and cardiac muscles One haem group per myoglobin molecules Dissociation curve hyperbolic Releases O2 at VERY LOW pO2 Provides short term storage of O2 for anaerobic conditions
Presence of myoglobin in blood indicates
Muscle damage
Ways Co2 is transported around blood
Solution (10%)
As bicarbonate (60%)
As carbamino compounds (30%)
Co2 as bicarbonate
Co2 + H20 -> H2Co3
Catalyst for Co2 forming a bicarbonate
Carbonic Anhydrase
Where does Co2 become H2Co3
Red blood cells
How are carbanimo compounds formed
Combination of Co2 with terminal amine groups in blood proteins
Especially globin from haemoglobin
Haldane Effect
Removing O2 from Hb increases ability of Hb to pick up Co2 and Co2 generated H+
The Bohr Effect and Haldane Effect work in synchrony to facilitate
O2 liberation and uptake of Co2
How does the Bohr Effect facilitate the removal of O2
Shifts curve to right meaning Hb has a lower affinity to O2
Neural control of rhythm of heart
Medulla
Pre-Botzinger complex
How is 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
Pneumotaxic centre
Stimualtion terminates inspiration
Occurs when dorsal neurones fire
Prevents inspiration being too long - deep breaths (apneusis)
Examples of involuntary modifications of breathing
- Pulmonary stretch receptors
- Joint receptors reflex in exercise
- Cough reflex
Pulmonary Stretch Receptors
Activated during inspiration
Afferent discharge inhibits inspiration
Hering Breur Reflex
DOESN’T HAPPEN NORMALLY, BABIES
Joint receptors
Impulses from moving limbs increase breathing
Increased ventilation during exercise
Increased ventilation during exercise
Adrenaline released
Impulses from cerebral cortex
Increase body temp
Accumulation of Co2 and H+ created by active muscles, that must be removed
Cough reflex
Afferent discharge stimulates:
- Short intake of breath
- Closure of larynx
- Contraction of abdominal muscles
- Increases alveolar pressure
- Opening of larynx and expulsion of air at high speed
Peripheral Chemoreceptors
Sense tension of oxygen, Co2 and H+ in blood
Found in carotid bodies and aortic bodies
Central Chemoreceptors
Respond to H+ in cerebrospinal fluid
Found near surface of medulla
Cerebospinal fluid
Separated by blood brain barrier
Co2 diffuses readily
Responsive to PCo2
Rise in arterial PCo2 results in
increased ventilation
Fall in arterial PO2 results =
Hypoxia
Stimulates peripheral chemoreceptors
When are peripheral chemoreceptors stimulated
<0.8 Kpa
Hypoxic Drive
Important in high altitudes
Rise in H+ only
Stimulates peripheral receptors
Causes hyperventilation
Increase elimination of Co2 from body
Chronic adaptations of hypoxia
Increased RBC production
Increased number of capillaries
Increased number of mitochondria
Kidneys converse acid (Arterial pH drops)
Type 1 Respiratory Failure
Short of oxygen
Hypoxia
Type 2 Respiratory Failure
Short of Oxygen
Too much Co2
Hypoxia + Hypercapnia
Hypercapnia
Too much Co2
V/Q mismatch
ventilation and perfusion not matched
Restrictive thoracic disease causes outwith the lungs
Skeletal
Muscle Weakness
Obesity
DPLD
Diffuse Parenchymal Lung Disease
or
Interstitial Lung Disease
Group of disease that effect the interstitum (tissue space around alveoli)
Effort Dependant Pulmonary Function Tests
FEV Flow rates (spirometry)
Effort Independant Tests
Relaxed vital capacity (spirometry) Helium/N2 washout static lung volumes Whole body plethysmography Impulse oscillometry Exhaled nitric oxide Gas diffusion tests
Spirometry Graph for Asthma and COPD
Asthma depressed but ends same volume
COPD ends lower volume
Obstructive Disease Lung Function Patterns
PEFR decreased
FEV decreased
FVC normal in asthma, decreased in COPD
FEV/FVC = <75%
Restrictive Disease Lung Function Patterns
PEFR normal
FEV decreased
FVC decreased
FEV/FVC = >74%
Forceful expiration
Active process controlled by firing ventral neurons in the medulla
Results in increased pulmonary compliance, produces overinflated lungs and will show an obstructive defect on spirometry
Emphysema
Causes shortness of breath on exertion, a restrictive defect on spirometry and reduced pulmonary compliance but no sign of infection
pulmonary fibrosis
Will show low FVC, low FEV and low FEV/FVC%
Combined restrictive lung disease
Chronic adaptation by hypoxia
Increased mitochondria, 2,3-BGP capillaries and polycythaemia with a metabolic acidosis
Acute mountain sickness
Fatigue, headache, tachycardia, dizziness and shortness of breath, slipping into unconciousness
Diabetic Ketosis
Hyperventilation with severe metabolic acidosis
Chemoreceptors that detect arterial oxygen partial pressure and cause hyperventilation and increased cardiac output
Peripheral Chemoreceptors
Chemoreceptors found in brainstem. Respond to CSF
Central chemoreceptors in medulla
Chemoreceptors that when stimulated can compensate for metabolic acidosis by increasing elimination of Co2
Peripheral Chemoreceptors
Volume of air left in lungs after maximal expiration
Residual volume
Sum of inspiratory reserve volume, tidal volume and expiratory reserve volume
Vital capacity
Volume of air left in lungs after normal expiration
Functional residual capacity