In humans each lung is encased in a thin membraneous sac called the Pleura, and each is connected with the trachea (windpipe) by its main bronchus (large air passageway) and with the heart by the pulmonary arteries.
Each Pleura can be divided into two parts:
- Visceral pleura-envelops the lung.
- Parietal pleura- covers the internal surface of the thoracic cavity.
Visceral pleural covers the surfaces of both lungs and forms interlobar fissures that may be complete or incomplete in their extension to the hila. Parietal pleura on the other hand, lines both thoracic cavities and may be designated by its location as costal, diaphragmatic or mediastinal pleurae.
The visceral and parietal pleura join at the hilum, which also serve as the point of entry for the bronchus, blood vessels and nerves. The pleura consists of a double-layered serous membrane overlying the inner surface of the thoracic cage and the outer surface of the lung. Between these two delicate membranes lies the pleural cavity, a sealed space maintained ~10-20µm across. The pleural cavity, also referred to as intrapleural space, contains pleural fluid secreted by the mesothelial cells. The fluid allows the layers to glide over each other as the lungs inflate and deflate during respiration.
What Is Visceral Pleura?
The visceral pleura is the thin, slippery membrane that covers the surface of the lungs throughout the thorax and extends deep within the interlobar fissures. The visceral pleura is innervated by autonomic nerves containing fibres that are sensitive to stretch but not to pain.
What Is Parietal Pleura?
The parietal pleura is the outer membrane that lines the inner chest wall and diaphragm (the muscle separating the chest and abdominal cavities). The parietal pleura is anatomically divided into four parts:
- Costal pleura- overlying ribs, intercostal muscles, costal cartilage and sternum
- Mediastinal pleura
- Cervical pleura- extending above the 1st rib by 2-3 cm over the medial end of the clavicle
- Diaphragmatic pleura
Difference Between Visceral And Parietal In Tabular Form
| BASIS OF COMPARISON | VISCERAL | PARIETAL |
| Description | The visceral pleura covers the outer of the lungs and extends into the interlobar fissures. | Parietal pleura covers the internal surface of the thoracic cavity. |
| Thickness | It is relatively thinner than the visceral pleura. | It is thicker than the visceral pleura. |
| Sensitivity | The visceral pleura is not sensitive to pain, temperature or touch. Its sensory fibres only detect stretch. | The parietal pleura is sensitive to pressure, pain and temperature. |
| Pain | It produces a vague, dull and poorly localized pain. | It produces a sharp and well localized pain. |
| Blood Supply | Pulmonary and bronchial circulation supplies blood to the visceral pleura. | Arteries of the thoracic wall supply blood to the parietal pleura. |
| Innervation | It receives autonomic innervations from the pulmonary plexus (a network of nerves derived from the sympathetic trunk and vagus nerve). | It is innervated by the phrenic and intercostal nerves. |
| Pain Source | Visceral pain arises from distention or spasm of a hollow organ such as the discomfort experienced early in intestinal obstruction or cholecystitis. | Parietal pain arises from peritoneal irritation such as the pain of acute appendicitis with spread of inflammation to the parietal peritoneum. |