Introduction To Respiratory System

RESPIRATORY SYSTEM Respiration - The process by which food is oxidized in the body to release energy is called as respiration. This involves the exchange of gases i.e. Oxygen and carbon dioxide between the body and the external environment .the various organs required for this exchange of gases together constitute the respiratory system. The various organs of the respiratory system are: 1. Nose 2. Pharynx 3. Larynx 4. Trachea 5. Bronchi 6. Bronchiole 7. Lungs The nose is first part of the respiratory system through which the air enters and passes through the various parts of the respiratory system to the lungs. The main function of nose is to moisten the air and make it warm along with this; it also filters the various impurities present in the air. The pharynx communicates with posterior nose, Eustachian tube , mouth , esophagus and larynx. The larynx is a passage for the air from the pharynx to the trachea and like nose it also helps in further moistening and filtering of the air. It is called as voice box. The trachea is a cylindrical cartilaginous tube, 11-12 cm long , from the larynx to the bronchial tubes. It extends from the 6th cervical to the 5th dorsal vertebrae. Here it divides at a point called carina into two bronchi, one leading to each lung. It is lined with mucous membrane and its inner surface is lined with ciliated epithelium .It is also called as wind pipe. STRUCTURE OF LUNGS The two lungs lie on each side of midline, in thoracic cavity. They are cone shaped and consist of an apex and base. The right lung is larger then the left. The lower surface of the lung is concave and is present very close to the

diaphragm, which divides the body into the thoracic cavity and the abdominal cavity. The lungs are divided by the double layered membrane called pleura which contains a small amount of serous fluid in it. Each major branch from the trachea enters the root of the lung and divides and subdivides to give progressively smaller bronchi and then still smaller bronchioles. The small terminal bronchioles branch into respiratory which branch into alveolar ducts ending ultimately into alveoli. The walls of alveoli are surrounded by a dense network of capillaries. The walls of the alveoli and capillaries are made up of a single layer flattened epithelial cells. The exchange of gases between the alveoli and capillaries takes place across this thin layer

TRACHEOBRONCHIAL TREE 1. Made up of cartilage, smooth muscle, and epithelium containing cilia and glands. 2. Function: passage of gas movement from to alveoli. 3. Divide into conducting and respiratory zone. 4. Weibel’s classification of airway generations from trachea to alveolar sac. Airways division occurs 23 times. Zero generation – trachea, 1- 16 - conducting zone (bronchi, bronchioles and terminal bronchioles.) 17 – 23 - respiratory zone. (respiratory bronchioles, alveolar ducts and alveoli.

TIPS TO REMEMBER 1. Cartilage and glands are present only in trachea and bronchi. 2. Cilia present up to respiratory bronchiole. Two type of alveolar epithelial cells: 1. TYPE I 2. TYPE II ( granular pneumocytes) cells secrete surfactant.

PROPERTIES OF GASES: PARTIAL PRESSURE OF GASES.: Pressure exerted by any one gas in a mixture of gases. P = nRT / V. P IS PRESSURE,

n is number of moles, R IS gas constant, T is absolute temperature., V is volume.

DALTON’ S LAW: Total pressure exerted by mixture of gases = sum of partial pressure of all gases present.

COMPOSITION OF AIR ( mmHg)

PO2 PCO2

INSPIRED AIR 158 0.3

ALVEOLAR ARTERIAL AIR BLOOD 100 97 -100 40

40

VENOUS BLOOD. 40. 46.

FUNCTIONS OF LUNG: 1. 2. 3. 4. 5.

Gaseous exchange. Humidification. Prevents foreign bodies from entering the alveoli. Phagocytic action by pulmonary alveolar macrophages. Surfactant release that prevents the development of surface tension in alveoli. 6. Conversion of Angiotensin I to Angiotensin II by activating the enzyme, ACE. 7. Removal of various substances from blood - prostaglandins, bradykinin, serotonin, nor epinephrine.