Respiratory System Flashcards
What is the conducting zone
- Consists of everything from the trachea to the terminal bronchioles, transfer air from the outside environment to the alveoli for gas exchange
- Warms and humidifies air (facilitates gas exchange), filters air (mucus cilia, macrophages in alveoli)
What is the respiratory zone
- Gaseous exchange, occurs in alveoli, 300 million alveoli
- Large surface area for diffusion total area ~60-80m2, thing wall allowing for rapid diffusion of O2 and CO2
- Secrete surfactant to prevent collapsing / sticking together
What is airway resistance
- Airflow = (PI - P2) / resistance, where P1 - P2 is the pressure difference at the two ends of the airway
- Change in pressure to facilitate flow from high pressure to low pressure
- Determined by airway diameter
- COPD, smoking asthma, flu, colds etc result in decreased flow, if the airway is reduced by half, flow decreases by 16x
What is pulmonary vs cellular ventilation
Pulmonary
- Movement of gas into and out of lungs due to pressure differences between the two ends of the passageway
- Refers to ventilation (breathing) and exchange of gases (O2 and CO2) in lungs
Cellular
- Relates to O2 utilisation and CO2 production by the cellular tissues
What are subscripts of V
- V: Volume per unit time (one minute), Va + Vd
- Vt: Tidal volume, volume inspired or expired
- Vd: Dead-space, space occupied by the volume of air not participating in gaseous exchange
- Vi: Volume inspired
- Ve: Volume expired
- Va: Air that reaches the respiratory zone, involved in gas exchange
What is partial pressure
- Tension, the pressure of a specific gas in mixture of gasses
- pO2: In the lungs is greater than in the blood so O2 moves from the lungs into the blood
- pCO2: In the blood is greater than pCO2 in the lungs so CO2 moves from blood to lungs for exhalation
What is diffusion
- Random movement of molecules from a high to low area of concentration
- Dependant upon the partial pressure gradient, inversely proportional to the membrane thickness and the solubility of gases
- Occurs rapidly in the lungs due to large SA, short diffusion distance
- O2 and CO2 tensions in blood leaving the lung is almost in complete equilibrium with O2 and CO2 tension in the lung
What occurs in the respiratory cycle
Inspiration
- Inspiratory muscles contract (diaphragm descends; external intercostals rise rib cage)
- Thoracic cavity V increases
- Lungs are stretched
- Intrapulmonary V increases, intrapulmonary P drops
- Air flows into lungs down its pressure gradient until intrapulmonary is equal to atmospheric pressure
Expiration:
- Inspiratory muscles relax (diaphragm rises; rib cage descends due to recoil of costal cartilages)
- Thoracic cavity V decreases
- Lungs recoil passively
- Intrapulmonary V decreases
- Intrapulmonary pressure rises, air flows out of lungs down pressure gradient
What are factors that affect pulmonary ventilation
- Surface Tension: Of alveolar fluid, must be overcome to expand lungs during inhalation, surfactant reduces surface tension so lungs don’t collapse
- Compliance: How much effort is required to stretch the lungs and chest wall, high compliance = easy, due to elastic fibres in lung tissue and surfactant
- Airway Resistance: Diameter of airway, smooth muscle regulates airway diameter, walls of bronchioles expand and contract like the lungs
What is partial pressure and daltons law
- The pressure of each gas in a mixture, the pressure that each gas exerts can be calculated by multiplying the percentage by the absolute pressure
- PP of O2 at sea level (159 mmHg)
- PP of N2 at sea level (600.7 mmHg)
- The total pressure of a gas mixture is equal to the sum of the partial pressures
What are the partial pressures of blood throughout respiratory cycle
- Blood Entering Lungs: pCO2 ~46 mmHg and pO2 ~40 mmHg
- Alveolar Gas: pCO2 ~40 mmHg and pO2 ~105 mmHg
- Blood Leaving Lungs: PO2 ~100mmHg and pCO2 ~40 mmHg
What is internal respiration
- Exchange of gases between blood and tissue (not lungs), aerobic and anaerobic metabolism and provision of O2 (energy production in muscle) and removal of CO2, H and H2O
What is oxygen transport and blood O2 capacity
- At alveolar PO2 of 100mmHg, 98% O2 is bound to Hb
- Each heme group can combine chemically with one O2 molecule (Hb4O2)4)
- Oxyhaemoglobin (oxygen bound) deoxyhaemoglobin (no oxygen bound)
- SpO2is the % saturation of Hb, = (O2 actually combined with Hb) / (O2 capacity of Hb)
- Fully saturated Hb carries 1.34ml O2
What is the arteriovenous oxygen difference
- The difference between concentration of O2 in arterial and venous blood
- Represents amount of O2 that is extracted or consumed by tissues per 100ml of blood
- Fick
- VO2 = Q x a-vO2
What are the mechanisms of CO2 transport
- Plasma: 9-10% of CO2 is transported dissolved
- Haemoglobin: 20% combines with Hb (carbamino-haemoglobin), unloading O2 to tissues facilitates loading of CO2, CO2 has a higher affinity for Hb than O2
- Ions: 70% of CO2 as H ion and HCO3 ion
- Carbonic Anhydrase: Facilitates combination of water and H to form carbonic acid (H2CO3)
What is blood buffering
- H+ ions formed when H2CO3 dissociates will increase acidity of venous blood, free H+ ions buffered by Hb
- As O2 is released from Hb and diffuses into the tissues buffering of H+ ions is facilitated (Root effect)
- In turn, more HCO3- can be formed and more CO2 transported without change in blood acidity
What is the ventilation perfusion ratio
- Normal gas exchange requires a matching of ventilation to blood flow (perfusion)
- An alveolus can be well ventilated, if blood flow to alveolus doesn’t match ventilation, normal gas exchange does not occur
- At rest V/Q (ratio of ventilation / cardiac output) is around 0.82, during exercise V/Q may exceed 5
- Athletic population doesn’t have a larger lung however changes in heart cause the differences
What is the oxygen-haemoglobin dissociation curve
- Flat Portion: Provides protection against low atmospheric pO2, large decrease in pO2 only results in a small desaturation of the Hb, resting state (100%), arteries / lungs
- Steep Portion: Provides protection at tissue level for unloading of O2, small decrease in tissue O2 results in large unloading of O2 from Hb, venous blood, easily provided to tissues
- Relationship: Loading (combination of O2 with H) and unloading (release of O2 with Hb)
- Deoxyhaemoglobin + O2 ↔ Oxyhaemoglobin
What causes changes in the dissociation curve
- pH / Temperature: Increase in temp / acidity (H+ / exercise) results in a downward and rightward shift, increased availability / unloading of oxygen to tissues (warm up essential)
- Bohr Effect: Effect of acidity, CO2 and increased temperature on the oxyhemoglobin dissociation curve
- 2-3 DPG: By-product of RBC metabolism, rightward shift of curve, assists with unloading of O2, at altitude (hypoxia), not a major cause of rightward shift during exercise
What is the myoglobin / haemoglobin dissociation curve
- The higher affinity of myoglobin for O2 compared with haemoglobin assists in the exchange (off-loading) of O2 bound to haemoglobin and transported to muscle tissue
- Myoglobin: Flat portion is large, high affinity to load oxygen, mitochondria, loosely bound
- Haemoglobin: Affinity to unload oxygen, blood
What is the acid base balance and how does it affect ventilation
- Acid-Base Balance: Pulmonary ventilation removes H+ from blood by the HCO3– reaction
- Equation: Muscles CO2 + H2O ← carbonic anhydrase → H2CO3 ←→ H+ + HCO3- Lungs
- Increase Ventilation: CO2 exhalation, reduces pCO2 and H+ concentration (pH increase)
- Decrease Ventilation: Buildup of CO2, increases pCO2 and H+ concentration (pH decrease)
What is / the function of the respiratory control centre
- Brain stem (medulla oblongata and pons)
- Controls rhythm of ventilation, inspiratory area nerves innervate diaphragm and external intercostals via the phrenic nerves, impulses last ~2sec = contraction, relaxation lasts ~3sec \ 5sec cycle
What are the 3 different inputs to respiratory control centre
- Neural: Higher brain centres, voluntary regulation of breathing and emotional response via hypothalamus and limbic system
- Sensory: Skeletal muscle / right ventricle mechanoreceptors, chemoreceptors in muscle
- Humoral: Central chemoreceptors (medulla, changes in pCO2 and H+) and peripheral chemoreceptors (aortic and carotid bodies, increase in pCO2 / H+ and decrease in pO2 / K+
Describe ventilatory effects of sub maximal vs maximal
- Sub-Maximal: Primary drive, higher brain centres (central command), “fine tuned” by humoral chemoreceptors and neural feedback from muscle
- Maximal: Non-linear rise in VE, increasing blood H+ stimulates carotid bodies, concentration of K+, body temperature, and blood catecholamines may contribute
