Respiratory Physiology Flashcards
What are the stages of respiration?
1) Ventilation - mechanical process that moves air in and out of lungs
2) Gas exchange of O2 and CO2 between air and blood in lungs and between blood and cells in circulatory system
3) Cellular respiration - use of O2 to oxidize organic molecules producing energy and CO2
Conducting vs Respiratory Zone?
Conducting zone
-airways connecting the external atmosphere to gas exchange regions of lung
-Primary bronchi transport air into each lung where they repeatedly divide into smaller and smaller bronchioles
Respiratory zone
-Region of the lung hwere gas exchange occurs
-Occurs in 300 million air sacs, alveoli, that cluster the ends of terminal bronchioles
-Alveoli contact with capillaries of pulmonary circulation
How does ventilation (inspiration and expiration) occur?
-Air moves from regions of high pressure to regions of lower pressure
-Inspiration occurs by reducing air pressure in lungs (increasing volume of lungs) to sub-atmospheric pressures
-Expiration occurs by increasing air pressure in lungs above atmospheric pressure (decreasing volume of lungs)
What law corresponds to the method of ventilation?
Boyles Law - pressure of a quantity of gas is inversely proportional to its volume
-Decreasing volume compresses the air so pressure increases and vice versa
What are the 2 pleural membranes?
-Parietal pleura lines the inner wall of thoracic cavity
-Visceral pleura covers the outer surface of lungs
-Both membranes stick tightly to eachother which causes outsides of lungs to stick to inside of thoracic cavity - so if thoracic cavity expands/contracts, lungs do likewise
What is present to adhere pleura membranes to each other?
Pleural cavity contains pleural fluid
How does normal inspiration take place?
-Normal (quiet) inspiration is driven by contraction of the diaphragm which causes it to flatten which pulls on base of thoracic cavity and increases volume vertically
-Simultaneous contraction of external intercostal muscles on rib-cage increase thoracic volume laterally
What muscles are recruited in forced inspiration?
Other muscles in neck (scalenes) and chest (pectoralis minor) also recruited to drive further thoracic expansion
What happens the pressure in normal inspiration vs forced inspiration?
-Normal - intrapulmonary or intra-alveolar pressure drops to about -3mmHg (3mmHg below atmospheric pressure)
-Forced - intrapulmonary pressure can drop to -20mmHg
What happens in normal vs forced expiration?
-Normal (passive process) - muscles that drive thoracic expansion relax, the thorax and lungs recoil to original state
-Intrapulmonary pressure increases to +3mmHg and air is forced out of lungs
-Forced - internal intercostal muscles and abdominal muscles become active and depress the thoracic cavity and lungs further
-Intrapulmonary pressure can increase up to +30mmHg
Muscles of inspiration?
Sternocleidomastoid
Scalenes
External intercostals
Parasternal intercostals
Diaphragm
Muscles of expiration?
Internal intercostals
External abdominal oblique
Internal abdominal oblique
Transversus abdominis
Rectus abdominis
What causes intrapleural pressure?
-Lungs are attached to inner wall of thoracic cavity - lung tissue highly elastic and recoils inwards and walls of thoracic cavity exerts an outward force
-Both pleural membranes are pulled in opposite directions - causes intrapleural pressure to fall below intra-alveolar pressure
-Intrapleural pressure is always lower than intra-alveolar pressure - assists in keeping lungs fully adhered to thoracic cavity
Look at diagram on slide 16
What is a pneumothorax?
Pleural membranes damaged by a broken rib or stab wound
- Entry of air into pleural fluid breaks the bond holding the membranes together
-Intrapleural and intra-alveolar pressures equalize
-Results in collapsed lung or pneumothorax - a pleural space mow exists
-Air has to be suctioned from the pleural space via chest tube to allow the lung to re-expand
What creates surface tension in the alveoli?
-Spherical alveoli secrete a thin film of fluid - interaction of fluid and air in alveoli generates surface tension
-Surface tension pulls water molecules tightly together exerting an inward force on the alveoli which opposes the expansion of lung tissue during inspiration
-Increases work done by inspiratory muscles expanded to drive inspiration
What is surfactant produced by, composed of and role?
-Surfactant produced by type2 alveolar cells in late foetal development
-Composed of lipoprotein complexes
-Disrupts cohesive forces between water molecules (breaks surface tension)
What happens in premature infants born without sufficient surfactant?
-Respiratory distress syndrome (RDS)
-Difficulty in expanding lung volume during inspiration
-Treated with artificial surfactant
What determines the resistance to air flow?
Radius of airways is the primary determinant
What triggers bronchodilation and bronchoconstriction?
Bronchioles contain smooth muscle innervated by sympathetic and parasympathetic nerves
-Noradrenaline released from sympathetic nerves triggers bronchodilation
-Acetylcholine released from parasympathetic nerves triggers bronchoconstriction
What can cause inaapropriate bronchoconstriction?
-Reflex stimulation of vagus nerve by smoke, irritants and cold air
-Products of allergic reactions such histamine, prostaglandins etc released by local mast cells and neutrophils/eosinophils inflame the airway
What is asthma? How is it treated
-Chronic inflammatory disease
-Treated w anti-inflammatory agents and w ß-adenergic receptor agonists
-Stimulation of ß2 adrenergic receptors on bronchiolar smooth muscle with epinephrine (adrenaline) or w specific pharmacological ß2 agonists (albuterol (ventolin) triggers relaxation resulting in bronchodilation
-Vital capacity is unaffected but rates of expiration and inspiration are reduced
How are pulmonary function tests carried out and what do they do?
-Measure the quantity of air inhaled/exhaled - tests done under normal and forced breathing conditions
-Spirometer is used - measures the volume of air moving with each breath - spirometry
Look at spirogram on slide 23
