Class 12 Respiratory System Vocal Cords NEET AIIMS

Vocal Cords

In larynx 2 pairs of vocal cords are present:

1.   Anterior pair: False vocal cords composed of membranes are pink in colour.  They keep larynx & true vocal cords moist and do not help with phonation.

2.   Posterior pair: True vocal cords are yellow in colour and composed of yellow fibrous CT. They are stretched by laryngeal muscles and the air passing between them vibrates them, producing a sound which is converted into speech by articulation (with the help of lips and tongue)

Note: The process of speech is under the control of the speech centre in the cerebrum. It started to develop in Neanderthal-man.

6.   Trachea (Windpipe): A 10 – 12 cm long tube in the neck and upper part of the thoracic cavity. 16 -20  C-shaped rings of hyaline cartilage are present. The rings are incomplete dorsally & make trachea non-collapsible. 7.  Bronchial tree & Respiratory tree: Branches of primary bronchus up to terminal bronchioles make a bronchial tree. Terminal bronchioles are divided to form respiratory bronchioles & its branches make a respiratory tree.

8.   Alveoli:

ü    Are the structural and functional units of the lung?

ü    300 million alveoli are present in each lung.

ü    Wall of alveoli consists of 2 layers:

(a) Outer layer: of Yellow Fibrous Connective Tissue (YFCT) in which a network of blood capillaries is present.  (b) Inner layer: composed of simple squamous Epithelium. Cells of this layer are called pneumocytes.

ü    Lecithin: surfactant secreted by pneumocytes. It reduces the surface tension of alveoli and prevents them from collapsing.

(2) Lungs:

A pair of soft organs are located in the thoracic cavity.

Are covered by two peritoneal layers (pleura)

–   Outer: parietal pleura &

–   Inner: visceral pleura

Pleural cavity: Space between the 2 pleura. It is filled with a fluid called Pleural Fluid.

Pleurisy: Increase in the amount of pleural fluid due to infection. This leads to difficulty breathing and pain called Dyspnoea.

2.   Exchange of gases in the lungs: It is also called external respiration.

It involves a.  Exchange of gases in the lungs.

       b.  Exchange of gases in tissue

(a) Exchange of gases in the lungs:

       Involves diffusion of O2 from the alveolar air to blood in pulmonary capillaries and CO2 from pulmonary capillaries to alveolar air.

       Occurs by simple diffusion i.e., due to partial pressure differences in gases on the two sides of the respiratory membrane.

       The partial pressure of a gas: It is defined as the pressure exerted by a particular gas in a mixture of gases.

       The partial pressure of a gas  = %age of gas in mixture × total pressure

       So, pO2 =21%×760 mm Hg (1 atm) =159mm Hg

       In alveolar air, pO2 is more than pulmonary capillaries. So it diffuses in pulmonary capillaries.

       While, in capillary blood, pCO2 is more, so, it diffuses in alveolar air.         

(b)       Exchange of gases in tissue:  In tissues, the exchange of gases occurs between blood and tissue cells. Due to this: pO2 of blood decreases & pCO2 of blood increases. This process is called Internal Respiration.

The blood gets deoxygenated by internal respiration. It then comes to the right side of the heart with veins which then pump it into the lungs where it is oxygenated.

3. Transport of gases: Blood carries O2 from respiratory organs (lungs) to tissue and CO2 back from tissue to lungs for elimination.

(A) Transport of oxygen: O2 is transported as oxy-haemoglobin and as a dissolved form in plasma.

ü          As dissolved form: 3% of O2

As Oxy-Hb: 97% of O2 is transported in the form of oxy-Hb. It is formed by oxygenation of Hb. Oxygenation of Hb is a reversible reaction.