Respiratory System

RESPIRATORY SYSTEM

In human and other animals, the respiratory system can be conveniently subdivided into an upper respiratory tract and lower respiratory tract, trachea and lungs.

Air moves through the body in the following order:-

i.)                Nostrils

ii.)              Nasal Cavity

iii.)           Pharynx

iv.)            Trachea

v.)              Thoracic Cavity

vi.)            Bronchi

vii.)         Alveoli

Upper Respiratory Tract

The conducting zone begins with the Nares of the nose, which open into the nasopharynx.

Lower Respiratory Tract

The trachea leads down to the thoracic cavity where it divides into the right and the left main stem bronchi.

The Subdivisions of the bronchus are: - Primary, Secondary and Tertiary Divisions. In all, they divide 16 more times into even smaller bronchioles.

The bronchioles lead to the respiratory zone of lungs which consists of respiratory bronchioles, alveolar ducts and alveoli, the multi-labulated sacs in which most of the gas exchange occurs.

Ventilation

Ventilation of the lungs is carried out by the muscles of respiration.

Control

Ventilation occurs under the control of the autonomic nervous system from the part of the brain stem, the medulla oblongata and pons. This area of the brain forms the respiratory regulatory center, a series of interconnected neurons within the lower and middle brain stem which coordinate respiratory movements. The sections are the Pneumotaxic center, the apneustic center and the dorsal and ventral respiratory groups. This section is especially sensitive during infancy and the neurons can be destroyed if the infants is dropped or shaken violently. The result can be death due to shaken baby syndrome.

Inhalation  

Inhalation is initiated by the diaphragm and supported by t external intercostals muscles.  Normal resting respirations are 10 to 18 breaths per minute. Its time period is 2 seconds. During vigorous inhalation (rates exceeding 35 breathes per minute), or in approaching respiratory failure, accessory muscles of respiration are recruited for support. These consist of sternocleidomastoid, Plasma and the strap muscles of the neck.

Exhalation

Exhalation is generally a passive process, however active or forced exhalation is achieved by the abdominal and internal intercostals muscles.

The lungs have a natural elasticity, as they recoil from the stretch of inhalation; air flows back out until the pressure in the chest and the atmosphere reach equilibrium.

Circulation

The right side of the heart pumps blood from the right ventricle through the pulmonary semilunar valve into the pulmonary trunk: the trunk branches into the right and left pulmonary arteries to the pulmonary blood vessels. The vessels generally accompany the airways and also undezgo numerous branching. Once the gas exchange process is complete in the pulmonary capillaries, blood is returned to the left side of the heart through four pulmonary Veins, two from each side. The pulmonary circulation has a very low resistance, due to the short distance within the lungs, compared to the systemic circulation and for this reason, all the pressure within the pulmonary blood vessels are normally low as compared to the pressure of the systemic circulation loop.

Virtually all the body’s blood travels through the lungs every minute. The lungs add and remove many chemicals messengers from the blood as it flows through pulmonary Capillary bed. The fine Capillaries also trap blood clots that have formed in systemic Veins.

Gas Exchange

The major function of the respiratory system in gas exchange is as gas exchange occurs; the acid-base balance of the body is maintained a part of homeostasis of proper ventilation is not maintained two opposing conditions could occur –

i.)                Respiratory Acidosis, a life threatening condition and

ii.)              Respiration Alkalosis.

In an average resting adult, the lungs take up about 250ml of oxygen every minute while excreting about 200ml of carbon dioxide. During an average breathe, an adult will exchange from 500ml to 700ml of air. This average breathe capacity is called tidal volume.

Diseases of the Respiratory System : - Common cold, Rhinitis, Sinusitis, Pharyngitis, Tonsillitis, Laryngitis, Tracheitis, Croup, Epiglottitis, Vasomotor Rhinitis, Hay Fever, Atrophic Rhinitis, Nasal Polyp, Adenoid Hypertrophy, Peritonsillar Abscess, Vocal Fold Nodule, Laryngospasm, Influenza, Pneumonia, Bronchitis, Emphysema, COPD, Asthma, Status Asthmaticus, Brochiectasis, Pneumonitis, Pulmonary Edema, Interstitial lung disease, lung abscess, Pleura Effusion, Empyema, Pneumothorax, Homeothorax, Hemopneumothorax, medelson’s Syndrome, Respiratory Failure, Atelectasis, Mediastinal Emphysema, Mediastinitis, etc.