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Renin Angiotensin Mechanism.

Anatomy & Physiology of Lungs.

 

Introduction.

  • A major organ of the respiratory system. 

  • The main function of the lungs is to perform the exchange of oxygen and carbon dioxide.

  • Two lungs are located in the thoracic cavity above diaphragm.

Gross Anatomy of the Lungs.

  • The lungs are pyramid-shaped, paired organs that are connected to the trachea by the right and left bronchi.

  • The diaphragm is the flat, dome-shaped muscle located at the base of the lungs and thoracic cavity. 

  • The lungs are enclosed by the pleurae, which are attached to the mediastinum. 

  • The right lung is shorter and wider than the left lung. 

  • The cardiac notch is an indentation on the surface of the left lung, and it allows space for the heart. 

  • The apex of the lung is the superior region, whereas the base is the opposite region near the diaphragm. 

  • The costal surface of the lung borders the ribs. 

  • The mediastinal surface faces the midline.

  • Each lung is composed of smaller units called lobes. 

  • Fissures separate the lobes from each other. 

  • The right lung consists of three lobes: the superior, middle, and inferior lobes. 

  • The left lung consists of two lobes: the superior and inferior lobes. 

  • A bronchopulmonary segment is a division of a lobe, and each lobe houses multiple bronchopulmonary segments. 

  • Each segment receives air from its own tertiary bronchus and is supplied with blood by its own artery. 

  • A pulmonary lobule is a subdivision formed as the bronchi branch into bronchioles. 

  • Each lobule receives its own large bronchiole that has multiple branches. 

  • An interlobular septum is a wall, composed of connective tissue, which separates lobules from one another.

Blood Supply to Lungs.

  • Lungs receive blood from the pulmonary circulation. 

  • This blood supply contains deoxygenated blood.

  • The pulmonary artery is an artery that arises from the pulmonary trunk and carries deoxygenated blood to the alveoli. 

  • One arteriole and an accompanying venule supply and drain one pulmonary lobule. 

  • As they near the alveoli, the pulmonary arteries become the pulmonary capillary network. 

  • The pulmonary capillary network consists of tiny vessels with very thin walls that lack smooth muscle fibers. 

  • The capillaries branch and follow the bronchioles and structure of the alveoli. 

  • It is at this point that the capillary wall meets the alveolar wall, creating the respiratory membrane. 

  • Once the blood is oxygenated, it drains from the alveoli by multiple pulmonary veins, which exit the lungs through the hilum.

Nerve Supply to Lungs.

  • Dilation and constriction of the airway are achieved through nervous control by the parasympathetic and sympathetic nervous systems. 

  • The parasympathetic system causes bronchoconstriction, whereas the sympathetic nervous system stimulates bronchodilation. 

  • Reflexes such as coughing, and the ability of the lungs to regulate oxygen and carbon dioxide levels, also result from this autonomic nervous system control. 

  • Sensory nerve fibers arise from the vagus nerve.

Pleura of the Lungs:

  • The pleura (plural = pleurae) is a serous membrane that surrounds the lung.

  • Each lung is enclosed within a cavity that is surrounded by the pleura. 

  • The pleurae consist of two layers. 

    • Visceral Pleura: Internal Layer.

    • Parietal Pleura: Outer Layer.

  • The cavity between the Visceral Pleura and Parietal Pleura is called “Pleural Cavity.

  • Pleural Cavity contains a fluid called “Pleural Fluid”.

  • The pleural fluid is secreted by mesothelial cells and its main function is as a lubricant which prevents friction between two layers while breathing.

Commonly asked Question.

  1. With a well labelled diagram explain anatomy and physiology of the lungs.
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