Respiratory System
Introduction:
Respiration is the physiological process involving movement of oxygen from outside environment into the cell within tissues and transportation of carbon dioxide in the opposite direction.
Like other systems of the body Respiratory system also works in coordination with other systems.
The branch of science that deals with the structure, function, diagnosis and treatment of diseases of lungs is called Pulmonology.
The study of Nose and Pharynx and Larynx is covered in ENT (Ear Nose Throat).
Respiratory System:
It consists of,
Nose (Nasal Cavity).
Pharynx.
Larynx.
Trachea.
Lungs.
Mechanism of Breathing:
The process of moving air in and out of the lungs is called “Breathing”.
Breathing, or pulmonary ventilation, consists of two phases: inspiration, the period when air flows into the lungs, and expiration, the period when gases exit the lungs.
The major mechanisms that cause breathing are,
Atmospheric pressure,
Intrapulmonary Pressure,
Intrapleural Pressure.
The muscles that play major role in breathing are,
Intercostal muscles.
Diaphragm.
Inspiration:
The phase of breathing when atmospheric air enters lungs is called inspiration.
Mechanism of inspiration involves following steps,
Intercostal muscles contract.
The ribs are pulled upward.
Diaphragm contracts and moves downwards.
It results in increased “Lung Volume.”
As lung volume increases intrapulmonary pressure decreases in comparison to atmospheric pressure.
The atmospheric air moves from high pressure to low pressure i.e. in lungs.
The inspiration is followed by expiration.
Expiration:
The phase of breathing in which the gases move out from lungs into the atmosphere is called expiration.
Mechanism of expiration involves following steps,
Intercostal muscles relax.
The ribs come back to normal.
Diaphragm relaxes and again forms its dome shape.
It results in decreased “Lung Volume.”
As lung volume decreases intrapulmonary pressure increases in comparison to atmospheric pressure.
The atmospheric air moves from high pressure to low pressure i.e. outside the lungs.
The expiration is followed by inspiration.
Gas Exchanges Between the Blood, Lungs, and Tissues:
The purpose of the respiratory system is to perform gas exchange.
It is divided into following phases:
External Respiration.
Internal Respiration.
Oxygen Transport.
CO2 Transport.
External Respiration:
Pulmonary artery carries deoxygenated blood to the lungs where it forms respiratory membranes (basement membranes of blood capillary and alveoli are fused with each other) with alveoli.
Because of differences in partial pressure of oxygen and CO2 in blood and alveoli the gases move from higher concentration to lower concentration.
Deoxygenated blood contains lesser partial pressure of Oxygen than alveoli and hence oxygen diffuses in the blood.
Deoxygenated blood contains higher CO2 partial pressure as compared to alveoli and hence diffuses from blood into alveoli.
The resulted oxygenated blood is sent to heart by pulmonary veins.
Internal Respiration:
The heart pumps oxygenated blood into aorta which supplies oxygenated blood to the entire body through its branches.
The capillary carrying oxygenated blood reaches in tissues where partial pressure of oxygen is less as compared to blood, this results diffusion of oxygen from blood into tissues.
The capillary pressure of CO2 is higher in tissues as compared to in blood capillary, this results in diffusion of CO2 from tissue to blood capillary.
Now this formed deoxygenated blood is collected via superior vena cava and inferior vena cava and transported to the heart.
The heart transfers this receives deoxygenated blood to the lungs via pulmonary artery for oxygenation.
Oxygen Transfer:
The oxygen has a little water solubility and hence dissolves in little amount in plasma which diffuses directly into the cells.
Around 2% of oxygen is dissolved in plasma.
About 98% of oxygen in blood combines with Hemoglobin to form a complex called “Oxyhemoglobin”.
The Oxyhemoglobin dissociation radially on reaching to the cells having lower Oxygen partial pressures and oxygen diffuses in the cells.
Carbon dioxide Transfer:
Carbon dioxide is formed in the cell as an end product of many reactions and is one of the major excretory products of cells.
The CO2 dissolves in little amounts in the interstitial fluid surrounding the cells, which diffuses easily in the blood capillaries (around 2%).
Majority of CO2 diffuses directly in Red Blood Cells from tissues due to concentration differences.
The large concentration of CO2 (70%) reacts with water in RBC to form Carbonic Acid (H2Co3).
The formed carbonic acid is broken down to water and bicarbonate ions (HCO3-) ions by action of enzyme “Carbonic Anhydrase”.
The bicarbonate ions enters the plasma from RBC and maintains the pH of blood.
Some part of Co2 entered in RBC (20%) reacts with hemoglobin and forms a complex called “Carbaminohemoglobin”.
On reaching the lungs the dissolved CO2 in plasma directly diffuses in alveoli.
The carbaminohemoglobin complex dissociates as partial air pressure of CO2 is higher in alveoli than in blood, the free CO2 diffuses into the alveoli for exchange with oxygen.
The bicarbonate ions dissolved in plasma renters RBC and combines with water to form Carbonic acid, the formed carbonic acid dissociates into water and carbon dioxide.
The formed carbon dioxide diffuses into alveoli.
Lung Volumes / Respiratory Volumes:
Following are important lung volumes,
Tidal Volume.
Inspiratory Reserve Volume,<<,, normal breathing is called “Tidal Volume”.
Normal Value: 500 ml.
Inspiratory Reserve Volume:
The maximum amount of air that can be inhaled after normal inhalation is called as Inspiratory Reserve Volume.
Normal Value: 2100 to 3200 ml.
Expiratory Reserve Volume:
The maximum amount of air that can be exhaled after normal exhalation is called the Expiratory Reserve Volume.
Normal Value: 1000to 1200 ml.
Residual Volume:
The amount of air remaining in lungs after a forceful expiration is called Residual volume.
Normal Value: 1200 ml.
This volume is necessary to keep lungs open and to prevent lungs collapse.
Lung Capacities / Respiratory Capacities:
Following are important lung capacities,
Inspiratory capacity (IC).
Functional residual capacity (FRC).
Vital capacity (VC).
Total lung capacity (TLC).
Inspiratory capacity (IC):
Total amount of air that can be inspired after a tidal expiration.
Hence it is “Tidal Volume + Inspiratory Reserve Volume”.
Functional residual capacity (FRC):
Amount of air remaining in the lungs after a tidal expiration.
It is “Residual Volume + Expiratory Reserve Volume”.
Vital capacity (VC):
It is the total amount of exchangeable air.
It is “Tidal volume + Inspiratory Reserve Volume + Expiratory Reserve Volume).
Normal value is 4800 ml. (excluding residual volume 1200ml).
Total lung capacity (TLC):
It is the sum of all lung capacities.
It is 6000ml.