Respiratory Physiology Flashcards
Paranasal Sinuses
Pneumatised areas of bone to reduce weight of skull, help voice resonance and moisten air
Frontal - asymmetric and above eyebrows
Maxillary - in the bones of the maxilla
Ethmoid - ethmoid bones between the eyes
Sphenoid - in the sphenoid bones between eyes
Bronchoconstriction
By parasympathetic system
Vagus nerve neurons terminate in parasympathetic ganglia in airway wall
Short post-synaptic nerve fibres reach the muscles and release acetylcholine
Acts on muscarinic receptors of the M3 subtype on the muscle cells
Bronchodilation
Nerve fibres originating in the spinal cord terminate in ganglia near the cord
Release noradrenaline which activates adrenergic receptors
Activation of beta-2 receptors on the airway smooth muscle causes muscle relaxation
Immune defence - Acute inflammation
Vasodilation leads to exudation of plasma – including antibodies
Activation of biochemical cascades
Migration of blood leukocytes into the tissues
Initiated in the tissues by specialist macrophages
Neutrophils in inflammatory response
Migrate through gaps in capillaries to source of inflammation
Can release proteases to kill extracellular bacteria
Neutrophils then undergo apoptosis
Macrophage engulfs them and becomes anti-inflammatory
Alveolar Macrophages in immunity
Resident phagocyte
Acts like normal macrophages
Co-ordination of the inflammatory response (cytokine production
Induction and clearance of apoptotic cells
Non-respiratory functions of the lung
Synthesis, activation and inactivation of vasoactive substances, hormones and neuropeptides
Lung defence – complement activation, leucocyte recruitment, host defence proteins, cytokines and growth factors
Speech, vomiting, defecation, childbirth
Non-immune defense mechanisms - Epithelium secretions
Antiproteases – SLPI, lysozyme, phospholipase A
Anti-fungal peptides – Alpha-defensins
Surfactant-A and D – opsonize pathogens for enhanced phagocytosis
Pericellular fluid secreted by seromucosal glands behind respiratory epithelium acts like mucous
Non-immune defense mechanisms - physical
Coughing - An expulsive reflex that protects the lungs and respiratory passages from foreign bodies
Sneezing - Defined as the involuntary expulsion of air containing irritants from the nose
Basal cells give rise to other cells in the respiratory epithelium - can repair
Dead space
Space in the lungs where there is no gas exchange so is not useful
Like the trachea and bronchi
Can be alveolar dead space as well though
approximately 175mls of dead space in body
Perfusion in lungs
1000 capillaries per alveolus
Most dependent (lowest) part of lung and are preferentially perfused with blood at rest
Most dependent (lowest) part of lung and are preferentially perfused with blood at rest
At rest 25% the way through lung all blood is oxygenated
Hypoxic pulmonary vasoconstriction for matching perfusion/ventialtion
CO2 carried in three ways
Bound to Haemoglobin
Plasma Dissolved
As carbonic acid
Alveolar Gas Equation
PAO2 = PiO2 – PaCO2 / R
Causes of low PaO2 (hypoxaemia)
Alveolar hypoventilation
Reduced PiO2
Ventilation/perfusion mismatching
Diffusion abnormality
Blood and tissue buffers
Carbonic acid/bicarbonate buffer in particular
CO2 under predominant respiratory control (rapid)
HCO3 under predominant renal control (less rapid)
Respiratory system able to compensate for increased carbonic acid production
Henderson-Hasselbalch Equation
pH = 6.1 + log10([HCO3-]/[0.03*PCO2])
in order to keep pH at 7.4, log of ratio must equal to 1.3
as PaCO2 rises HCO3 must also rise (renal compensatory mechanism) to allow this
Basic breathing rhythm setting
Centers located in the Pons - pneumotaxic and apneustic centers
Medulla oblongata - phasic discharge of action potentials
Dorsal respiratory group - mostly for inspiration
Ventral respiratory group - active in both
Inspiration
progressive linear increase in inspiratory muscle activation
Lungs fill at constant rate till tidal volume achieved
End of inspiration - rapid decrease in excitation of respiratory muscles
Expiration
Largely passive due to elastic recoil of thoracic wall
First part of expiration; active slowing with some inspiratory muscle activity
With increased demands, further muscle activity recruited
Central chemoreceptors
60% influence from PaCO
Blood brain barrier relatively impermeable to H+
CO2 diffuses through which creates H+ in cerebrospinal fluid - H+ generated here is what triggers receptors
Located in brainstem - Pontomedullary junction, Not within the DRG/VRG complex
Peripheral chemoreceptors
40% influence from PaCO2
Stimulated by H+ concentration and gas partial pressures in arterial blood
Carotids - Bifurcation of common carotid - IX cranial nerve afferents
Aortic bodies - Ascending aorta - Vagal nerve afferents
Lung receptors
Stretch, Juxtapulmonary (J) and irritant
Afferents; vagus (X)
Combination of slow and fast adapting receptors
Assist with lung volumes and responses to noxious inhaled agents
Airway receptors
Nose, nasopharynx and larynx
Chemo and mechano receptors
Some appear to sense and monitor flow
Stimulation of these receptors appears to inhibit the central controller
