Explain how airway diameter, tissue compliance, rib cage mobility and alveolar s
ID: 3524407 • Letter: E
Question
Explain how airway diameter, tissue compliance, rib cage mobility and alveolar surface tension influence ventilation.
Relate the gas laws to the process of internal and external gas exchange and to the concentrations of gases found in alveoli, arterial blood and venous blood.
Describe the homeostatic mechanisms for control of respiration under, Local controls, Neural controls (Sympathetic, Parasympathetic, Medulla Oblongata Centers, Pons Centers), Respiratory Reflexes (Chemoreceptors, Baroreceptors, Hering-Breuer reflexes, Apnea) and Voluntary Control.
Explanation / Answer
Respiration is defined as inhalation of oxygen from atmosphere and release of carbon dioxide. Oxygen is essential for many cellular activities like glucose metabolism and production of energy efficient molecules. Respiratory system is composed of upper and lower respiratory tracts. Thorax, nose cavity, pharynx and larynx are part of upper respiratory tract while trachea, bronchi, bronchiole, alveolar duct, alveoli located in thorax cavity are part of lower respiratory tract.
Mechanics of respiration:
Effect of airway diameter: Airflow occur respiratory system by the pressure difference from one end to the other. Airway resistance is the pressure difference between mouth and alveoli divided by the airflow inside. Airway resistance is inversely proportional to fourth of radius. Thus as the diameter of alveoli decrease resistance increase and therefore the pressure difference will also increase. This pressure difference is responsible of inhalation of air inside.
Tissue compliance is measure of ability of tissue to stretch and expand. Expansion of lung tissue results in inflow of air by increasing cavity volume while inflation results in outflow of air. Rib cage mobility helps in expansion and inflation of lungs.
Alveolar surface tension alveolar epithelial cell secrete surfactant which lower surface tension of water thus inhibit collapsing of lungs thereby helps in respiration
Gas law for exchange of gases:
To understand mechanism of exchange of gases, it is important to understand the law of gases. Following gas law can be applied to exchange of gases during respiration:
Boyle’s law: According to Boyle’s law in a closed space pressure is inversely proportional to volume. During inhalation lungs expand and volume inside lungs increase and therefore pressure inside lungs decrease when compared with atmospheric pressure. This difference in partial pressure result in flow of air inside the lung cavity.
Dalton’s law: Dalton’s law states that the total pressure of gases in a mixture of non reactive gases is the sum of the partial pressure of the gases in mixture. Partial pressure is important in movement of gases from one area to another and gas moves from higher partial pressure to lower. As in lungs partial pressure of carbon dioxide is higher in comparison to atmosphere and partial pressure of oxygen is lower in comparison to atmosphere. Therefore, oxygen moves inside and carbon dioxide goes outside.
Table below describe different partial pressure in different location:
Gas
Air
Alveoli
Venous blood
Arterial blood
Oxygen
158
104
40
95
Carbon dioxide
0.3
40
45
40
Table suggest how oxygen flow inside to achieve its partial pressure in tissues while carbon dioxide goes outside.
Henry’s law: According to Henry’s law concentration of gases in liquid is directly proportional to partial pressure as well as solubility of that gas into liquid. As in breathing although nitrogen is present in air but due to higher solubility of oxygen in blood, oxygen is inhaled inside.
Respiration Control
Respiration is an involuntary process.
Local control: Movement of lungs to expand and reduction result in respiration.
Neural control of repiration:
Center present in brain such as medulla, pons are mainly responsible for control of respiration.
Sympathetic and parasympathetic nervous system
Phrenic nerve stimulats the activity of diaphragm. Vagus nerve has innervations in diaphragm and it provides parasympathetic stimulation. It controls the movement in larynx and Pharynx. Posterior thoracic nerve present in pleura that stimulates the region across thorax and abdomen.
Medulla oblongata
Medulla oblongata is primary respiratory control center, and sends signal to the muscles present in alveolar cavity to control expiratory as well as inspiratory movement. Medulla is also responsible for reflexes like coughing and sneezing.
Pons:
Pons’s main function is to control the speed of respiration. It controls the stretch receptors present in pulmonary muscles and increase the volume, thereby control deep breathing. Pons is located under medulla.
Respiratory Reflexes
Chemoreceptor detects the change in blood pH and signals medulla oblongata and pns center to decrease the breathing so that level of carbon dioxide can be maintained in blood.
Baroreceptor sensors are located in almost all blood vessels, they are usually responsible for control of blood pressure. Decrease in intrasinus pressure results in activation of baroreceptor reflex and thereby respiratory frequency increased with lower tidal volume in lungs.
The Hering–Breuer inflation reflex is type of stech receptor. It is responsible for protecting overinflation of the lungs. When there is more mechanical pressure and lungs are inflated these receptors sends signal to medulla and pons and expiration stops and inhalation starts.
Gas
Air
Alveoli
Venous blood
Arterial blood
Oxygen
158
104
40
95
Carbon dioxide
0.3
40
45
40
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