Respiratory Physiology Flashcards
Describe the location(s) and the role of the neural control centres in initiating and automatically controlling ventilation.
Breathing is controlled by elements from the medulla oblongata and the pons, both located in the brain stem
Medulla oblongata: Houses the DRG and the VRG, which control inspiration and expiration respectively.
Pons: Houses the apneustic and pneumotaxic centres, which modulate and smooth breathing respectively
Function of the DRG of the medulla
DRG - CONTROLS INSPIRATION
Receives input from the 9th and 10th nerves and the apneustic centre.
Function of the VRG of the medulla
VRG - CONTROLS EXPIRATION
The VRG is not usually active, as expiration is passive in normal quiet breathing.
During times of laboured breathing, e.g. exercise, lung disease, the VRG is active.
Functions of the apneustic and pneumotaxic centres of the pons
Apneustic centre - Modulates the breathing cycle (e.g. gasps)
Pneumotaxic centre - Smooths the breathing cycle
Describe influences on respiratory rhythm.
- Higher centres:
Cerebral cortex (VOLUNTARILY CHANGES BREATHING PATTERN),
Hypothalamus/limbic system (emotional) - Baro/thermos/mechano receptors (e.g. in muscles)
- Chemoreceptors: Central and peripheral chemoreceptors. Sensitive to changes in PaO2, PaCO2 and pH.
Describe why breathing can be voluntarily controlled.
By the higher centres of the brain (cerebral cortex)HOWEVER, these changes are overridden detection of changes in CO2 and H+ in arterial blood
e.g. holding breath until fainting and then breathing will resume
State the location of the peripheral chemoreceptors within the body
The carotid bodies (predominate, immediate effect on ventilation) and the aortic bodies (greater effect on CV system)
Describe the sensitivity of peripheral chemoreceptors
- PaO2: Primarily respond to decreased PaO2 (not O2 content) but must be dramatic.
CAROTIDS ARE THE ONLY CHEMORECEPTOR TO RESPOND TO HYPOXIA - pH: Sensitive to changes in arterial pH
- PaCO2: Provide the initial response to changes in CO2 (20%)
Which chemoreceptors are sensitive to hypoxia?
Carotid bodies
*Hypercapnia makes increases their sensitivity to hypoxia
State the location of the central chemoreceptors within the body
Located in the medulla oblongata, close to the respiratory centres
*Main source of tonic drive to breathe
Describe the sensitivity of central chemoreceptors
DIAGRAM
- PaCO2: Very sensitive to PaCO2 changes, which manifest as pH changes in the CSF (80%)
INSENSITIVE TO HYPOXIA
Describe why O2 should not be administered to those with chronic hypercapnia
In chronic hypercapnia compensation returns the brain back to physiological pH, depressing the drive of the central chemoreceptors (as pH is reduced).
Respiration is now dependent upon carotid body peripheral chemoreceptors to drive respiration in response to hypoxia.
If oxygen is administered then this hypoxic drive is lost and ventilation decreased, PaCO2 increased and may induce a coma.
Deduce the effect of altered pulmonary ventilation (e.g. hyperventilation, hypoventilation, breath-holding) on PaO2 and PaCO2.
Hyperventilation: Decreased CO2, increased O2
Hypoventiliation: Increased CO2
Breath holding: Increased CO2
Describe the functions of the conducting and respiratory zones and relate these to their anatomical and histological features
Conducting: Filters, warms and moistens the air. Allows air to be transported to the respiratory zone.
Respiratory: Site of gas exchange between the air and blood.
Define anatomical and physiological deadspace. Explain influential factors in the volume of each.
Deadspace = Volume of air not participating in gas exchange
Anatomical: Morphological. Volume of the conducting zones. Influenced by position, weight
Physiological: Function. The total volume of breath that does that participate in gas exchange (conducting and respiratory zones). Similar to anatomical in health. Influenced by how intact alveoli are, amount of mucus
Explain the principles underlying gas flow and exchange across the alveolar-capillary walls. How can this be measured?
Fick’s Law:
Proportional to surface area and difference in partial pressure (concentration gradient)
Inversely proportional to the thickness of the diffusion surface
Can be measured using the diffusing capacity (DL gas). Compare inspired and expired CO content
Describe the partial pressure gradients for O2 and CO2 exchange. State normal values across circulation
x
Explain the clinical relevance of VQ matching and how it can be disrupted. State the normal range.
Normal ratio: 0.8 -1 (a range seen from the apex - base)
VQ matching maximises exchange.
Loss of VQ matching is the most common cause of decreased PaO2.
Can be disrupted by pathology (alveolar dysfunction, lack of inspired O2, decreased perfusion). Leads to an increased surface not involved in gas exchange.
Describe the means by which oxygen is transported in the blood
Bound to haemoglobin - 98 %
Free in the plasma - 2 %
Describe the means by which carbon dioxide is transported in the blood
As bicarbonate ion - 78 %
In plasma - 13 %
As carbaminoglobin - 9 %
Describe the structure and function of oxygen binding proteins
Myoglobin: Has a single oxygen binding site. Mostly found in muscles, used during periods of intense physical activity. Acts to shuttle oxygen from capillaries to mitochondria.
Haemoglobin: Formed from 2 alpha and 2 beta chains. Has a central iron molecule. Has 4 oxygen binding sites. Acts to transport oxygen
Explain the shapes and significance of oxygen and carbon dioxide binding curves
Oxygen: Sigmoidal shaped curve, resultant of allosteric shape change which allows for cooperative binding of haemoglobin. Plateau observed as haemoglobin becomes saturated.
Carbon dioxide: The curve is more linear. Plateau not observed (not limited by transport protein)
Describe factors which affect gas transport and cause left and right hand shifts of the oxygen-haemoglobin dissociation curve.
Factors: Exercise, body temperature, metabolic rate, respiratory rate
Right hand shift: Reduced oxygen affinity. Increased H+ (Bohr effect), increased CO2, increased 2, 3-DPG and increased temperature
Left hand shift: Increased oxygen affinity. Decreased H+, decreased 2, 3-DPG and decreased temperature
Axis: x-axis = PO2 y-axis=Saturation
Normal plasma pH range
7.35 - 7.45
Describe factors involved in pH homeostasis
PaCO2, [HCO3-], respiratory rate, metabolic disturbance
Define PaO2
The amount of O2 DISSOLVED in plasma
Define O2 content
Amount of dissolved and bound O2
Define O2 capacity
Amount of O2 bound to haemoglobin
Define O2 saturation
Number of binding sites (haemoglobin) bound by oxygen
Define haemoglobinopathy
Caused by a defect in the genetically determined molecular structure of haemoglobin e.g. sickle cell anaemia (becomes sticky)
Effect of anaemia on O2 transport
Reduced amount of haemoglobin leads to a reduced ability to transport O2.
