Breathing And Exchange Of Gases

Direct respiration means exchange of gases without using any special respiratory organ and blood. In case of insects, the tracheal tubes exchange oxygen and carbon dioxide with the haemocoel which then exchange then with tissues.

•The function of the respiratory system is to move two gases: oxygen and carbon dioxide. Gas exchange takes place in the millions of alveoli in the lungs and the capillaries that envelop them.

•The respiratory system has built-in methods to prevent harmful substances in the air from entering the lungs. Hairs in your nose help filter out large particles. Microscopic hairs, called cilia, are found along your air passages and move in a sweeping motion to keep the air passages clean.

•As air passes through the nasal cavities it is warmed and humidified, so that air that reaches the lungs is warmed and moist.

Breathing takes place due to pressure gradient between the chest cavity and the atmosphere. Puncture in a person’s chest cavity causes the loss of pressure gradient hence leading to stoppage of breathing.

Carbon dioxide is a harmful poisonous gas. It has more affinity towards haemoglobin than oxygen. When a person inhales Carbon Monoxide, the Carbon Monoxide binds to the Haemoglobin and forms a very stable combination called Carboxy-haemoglobin. It leads to suffocation as carbon monoxide does not disassociate from haemoglobin which makes it unable for oxygen to bind to the haemoglobin and hence reduces oxygen transport.

An active process is one in which energy and work is required. Inhalation is an active process because it requires energy and work in contraction of the diaphragm downwards so as to make room for air in the lungs.

Passive process is one in which there is no requirement of energy and work. Expiration is a passive process because it does not require energy and work in the relaxation of the diaphragm.

O2 binding to Hb occurs when there is:

1. Lower temperature

2. Lower pCO₂

3. Higher PO₂

The diaphragm and a specialised set of muscles, called external intercostals muscles present between the ribs are involved in the normal breathing in humans. They are involved in generating pressure gradient of air between the lungs and the atmosphere, so as to facilitate the intake of air.

Emphysema is a disorder in which the alveoli or air sacs get damaged which leads to decreased availability of oxygen.This disorder is mainly caused by cigarette smoking.

CO₂ dissociates from carbaminohaemoglobin when pO₂ is high and pCO₂ is low .

(i) Incorrect, (ii) Correct, (iii) Incorrect, (iv) Correct

The oxygen - haemoglobin dissociation curve will show a right shift in case of

1. Increased Temperature

2. Increased pCO₂

3. Decreased pH

a. Tidal Volume: Volume of air inhaled and exhaled during a normal breathing cycle without any forced breathing is tidal volume.The normal range of tidal volume in a young adult is 500 ml per inspiration.

b. Residual Volume:Volume of air left in the lungs even after forced exhalation is called as residual volume. The normal range of residual volume in a young adult is 1100-1200 ml.

c. Asthma:It is an inflammatory disease of the airways of the lungs. Due to which the airway gets narrowed and excess mucus secretion takes place resulting in breathing difficulty.

Symptoms of Asthma:

1. Wheezing

2. Breathing Difficulty

3. Coughing

A fluid filled double membranous layer surrounds the lungs is called Pleura.

Functions of pleura:

1. The space between the pleura also known as pleural cavity consists of a fluid called pleural fluid.This fluid lubricates and helps the two pleural tissue to slide easily against each other during respiratory movements.

1.The primary site of exchange of gases in our body is Alveoli.Alveoli are small balloon like structures having thin walls and have numerous thin capillaries in contact with them.

2.Inhaled oxygen from the air reaches the alveoli and diffuses into the capillaries due to difference in the pressure gradient.

3.Carbon dioxide from the blood diffuses into the alveoli similarly and is exhaled.

Emphysema is a disorder in which the alveoli wall gets damaged.Excessive cigarette smoking leads to Emphysema due to the presence of various harmful chemicals like nicotine, tar, sulphur etc. Which causes damage to the alveoli wall and also decreases elasticity of the bronchioles and alveoli.

The amount of O₂ supplied to tissues through every 100 ml. of oxygenated blood under normal physiological conditions is around 5ml.

A major percentage (97%) of O₂ is transported by RBCs in the blood and the remaining percentage (3%) of O₂ transported through plasma.

Hence, the arrangement of these terms according to their volume in ascending order would be :

Tidal Volume (TV) <Residual Volume (RV) <Expiratory Capacity (EC) <Inspiratory Reserve Volume (IRV) .

a. Inspiratory Capacity (IC) = _Tidal Volume (TV)____ +IRV

b. _______Expiratory Capacity____________ = TV + ERV

c. Functional Residual Capacity (FRC) = ERV + ____ Residual Volume

The important parts involved in creating a pressure gradient between lungs and the atmosphere during normal respiration are :

1. Diaphragm

2. Internal Intercostal Muscles of the ribs

3. External Intercostal Muscles of the ribs

Around 75% of the CO₂ is transported via blood and the remaining 25 % of it is transported via plasma.The three main ways by which CO₂ is transported in blood are:

1. In Red blood cells carbon dioxide combines with water and forms carbonic acid. It is an unstable form and gets disassociated into hydrogen and bicarbonate ion.

2. Carbon dioxide is also transported through plasma in the form of bicarbonate ions.

Diffusion rate of any gas depends upon the solubility rate of the gas. Diffusion rate is directly proportional to the solubility rate.As the solubility of Carbon dioxide is much higher than oxygen it’s diffusion rate through the diffusion membrane per unit difference in partial pressure is much higher.

The correct sequence would be:

1. Pulmonary ventilation by which atmospheric air is drawn in and CO2 rich alveolar air is released out.

2.Diffusion of gases (O₂ and CO₂) across alveolar membrane.

3.Transport of gases by blood.

4.Diffusion of O₂ and CO₂ between blood and tissues.

5.Utilisation of O₂ by the cells for catabolic reactions and resultant release of CO₂.

So, the correct sequence would be d,a ,b, e and c.

a.

b.

C.

Transportation of oxygen:

1. When oxygen is inhaled it reaches the alveoli (tiny balloon like structures which are in close proximity of various thin capillaries).

2. Now, the partial pressure of oxygen is more in the alveoli than the capillaries .

3. This causes the diffusion of oxygen into the capillaries

4. After which oxygen combines with Haemoglobin to form oxyhaemoglobin

5. This oxygenated blood reaches the organs which have low partial pressure than the capillaries.

6. In these organs the bond between oxygen and haemoglobin becomes unstable and breaks releasing oxygen into the organs.

Transportation of Carbon Dioxide:

Carbon dioxide is transported by three different methods which are :

3. Blood carries released carbon dioxide from various organs to the alveoli via capillaries which have lower intra pulmonary pressure than the organs.

4. Now, carbon dioxide is then diffused into the alveoli from the capillaries due to lower intra pulmonary pressure in the alveoli than the capillaries

5. In Red blood cells carbon dioxide combines with water and forms carbonic acid. It is an unstable form and gets disassociated into hydrogen and bicarbonate ion.

6. Carbon dioxide is also transported through plasma in the form of bicarbonate ions.

Breathing is the process by which oxygen is inhaled into the body also known as inspiration and carbon dioxide is released outside the body also called as expiration.

Mechanism of breathing involves two processes which are:

A. Inspiration

B. Expiration

Inspiration: It is the process of taking in external air or oxygen into the lungs.

1. It starts when the diaphragm contracts.

2. This leads to increased volume of thoracic chamber.

3. After which the intercostal muscles contracts and leads to the pulling of ribs and sternum which also increases the volume of the thoracic chamber.

4. Now, the increased volume of thoracic chamber also increases the pulmonary volume.

5. This increased pulmonary volume decreases the intra pulmonary pressure less than the atmospheric pressure.

6. Which further causes the entry of external air or oxygen into the lungs also known as inspiration.

Expiration:

1. It starts when the diaphragm relaxes.

2.This leads to decreased volume of thoracic chamber.

3.After which the intercostal muscles relaxes and leads to the relaxation of ribs and sternum which also decreases the volume of the thoracic chamber.

4.Now, the decreased volume of thoracic chamber also decreases the pulmonary volume.

5. This decreased pulmonary volume increases the intra pulmonary pressure less than the atmospheric pressure.

6.Which further causes the exit of external air or carbon dioxide into the atmosphere also known as expiration.

There are various centres in the neural system that plays significant a role in the regulation and control of respiration.Such centres include:

1.Pneumotaxic centre:

It is present in the dorsal part (back) of the pons varoli of the brain.

Function:This centre decreases the duration of inspiration hence alter the respiration rate.

2. Respiratory Rhythm centre orMedullary inspiratory centre:

It is present in the medulla of the brain.

Function:It regulates the respiratory rhythm.

3. Apneustic centre:It is present in the lower part of the pons varoli of the brain.

Function:It increases the duration of inspiration.

4. Chemosensitive centre:Present in the medulla oblongata and the pons area of the brain.

Function:This area is highly sensitive to carbon dioxide and hydrogen ions.This area starts eliminating these ions when their level is increased.Receptors present in the carotid artery and aortic arch also recognises the difference in carbon dioxide and hydrogen ion concentration.Which thereby send signals to rhythm centre.