The Respiratory system Flashcards

Question

Lecture summary

Answer 1

* The driving pressure difference that causes airflow is created by manipulating the volume of the thoracic cavity (Boyle’s law). * Inspiration is caused by the contraction of the inspiratory muscles that increases the volume of the thoracic cavity. Expiration is mainly a passive process but during heavy or forced breathing it is assisted by the contraction of the expiratory muscles. * Intrapleural pressure is sub-atmospheric and this prevents the lungs from collapsing by maintaining a positive transpulmonary pressure. * Surfactant ensures that small alveoli do not not collapse, and it makes the lungs easier to inflate by increasing their compliance. * Spirometry is used to measure lung volumes and assess pulmonary function. * Gas exchange happens only in alveoli (exchange zone). All other airways do not contribute to gas exchange and are acting only as conduits (conductive zone, or “dead space”).

Answer 2

Dalton’s Law The pressure of a gas mixture is equal to the sum of the pressures of the individual gases. Composition of air in atmosphere: * 78.1% Nitrogen (N 2) * 20.9% Oxygen (O 2) * 0.033% Carbon dioxide (CO2 l pressures of atmospheric gases: N 2 = 760 mmHg x 78.1% = 594 mmHg O 2 = 760 mmHg x 20.9% = 159 mmHg CO 2 = 760 mmHg x 0.033% = 0.25 mmHg Partial pressures of atmospheric gases in the lungs: N 2 = (760 mmHg – 46 mmHg) x 78.1% = 558 mmHg O 2 = (760 mmHg – 46 mmHg) x 20.9% = 149 mmHg CO 2 = (760 mmHg – 46 mmHg) x 0.033% = 0.24 mmHg

Answer 3

Rate of diffusion ∝ A T × (P1 − P2 ) × D From Fick’s law it is obvious that greater solubility for a particular gas means a greater rate of diffusion for that gas (CO2 is a lot more soluble than O2 and it diffuses across the membrane a lot easier)

Answer 4

Gas molecules move between air and liquid in order to achieve equilibrium of partial pressures. Movements of molecules depend on: * Temperature * Pressure difference * Solubility

Answer 5

Haemoglobin is an oxygen binding protein contained within the red blood cells. Each haemoglobin molecule contains four polypeptide chains (globins), and four haeme groups. In the centre of each haeme group is a ferrous atom (Fe2+) that binds oxygen

Answer 6

The respiratory muscle groups (and therefore ventilation) are controlled by the CNS

Answer 7

Breathing can be altered voluntarily: * Hyperventilation * Breath holding * Speaking, swallowing

Answer 8

Slowly adapting pulmonary stretch receptors These receptors are located within airway smooth muscle and they are active only when tidal volume approaches the physical limitations of the lung tissue for expansion. This mechanism, called the Hering-Breuer reflex, protects the lungs by initiating a signal that inhibits inspiration (the switch-off point).

Answer 9

Rapidly adapting pulmonary stretch receptors (irritant) These receptors are dense in the trachea and large airways. They respond to stimuli such as cigarette smoke, inhaled particles and cold air, by initiating reflexes such as coughing and sneezing and by causing bronchoconstriction.

Answer 10

Peripheral chemoreceptors (main stimulus is PaO2 ) Carotid chemoreceptors (carotid bodies) Aortic chemoreceptors (aortic arch)

Answer 11

Central chemoreceptors Respond to changes in PaCO2 (through changes in concentration of H + ) Although these have been defined chemically, their anatomical identity within the medulla is not well defined Only carbon dioxide can cross the very selective blood-brain barrier but the central chemoreceptors are stimulated by the resulting increase in [H + ] and not by carbon dioxide itself.

Answer 12

Reduced levels of arterial oxygen affect only the peripheral chemoreceptors, and ventilation increases substantially only after arterial oxygen reaches a value of ~60 mmHg (compare this with the oxyhaemoglobin dissociation curve). Note, that it is the PO 2 that stimulates the peripheral chemoreceptors and not the content of oxygen.

Answer 13

Carbon dioxide is a very potent stimulus for ventilation and it exerts its effects with smaller deviations from normal arterial values. Both central and peripheral chemoreceptors are involved in the response to increased PCO 2 , but central chemoreceptors are the more important of the two. Carbon dioxide exerts its effects by altering the concentration of H + in the brain extracellular fluid.

Answer 14

phase 1- Ventilation increases abruptly and as early as in the first breath after exercise has commenced. It is thought to be controlled by neural mechanisms phase 2/3- Ventilation increases gradually (phase II) until steady state is achieved (phase III). Chemical stimuli are more likely to contribute to this part of the response

Answer 15

So, what drives the exercise-induced increase in ventilation? Phase I (neural mechanisms) * Muscle afferents * Central command * Learnt response Phase II (chemical mechanisms) * P CO 2 and pH oscillations * Plasma K+ , catecholamines * Temperature * Hypoglycaemia, metabolic rate

Answer 16

Neural control of breathing Ø Breathing is involuntary and it is controlled by the respiratory rhythm centre. Ø Breathing can also be voluntary and it can be interrupted for speaking, swallowing and in order to protect the lungs. * Chemoreceptors Ø Peripheral chemoreceptors respond to changes in PO 2 . PCO 2 and [H + ] also stimulate the peripheral chemoreceptors but their role is mainly to modulate the response to PO 2 . Ø Central chemoreceptors respond only to arterial PCO 2 but the stimulus within the CSF is the [H+ ]. * Ventilatory responses. Ø Oxygen causes ventilation to rise exponentially after a slow start until PO2 drops to ~60 mmHg.. Ø Carbon dioxide is a very potent stimulus and stimulates breathing in a linear fashion. * Breathing during exercise. Ø The quick phase I response appears to be neural in origin. Phases II and III appear to be chemical. Ø The increase in ventilation happens without any obvious stimuli to the chemoreceptors.

The Respiratory system Flashcards

(42 cards)