Note: For background on this series, please read the Introduction to the 32-Parts Project.
The diaphragm is the membrane separating the thoracic and abdominal cavities.
A membrane is a sheet-like structure that forms a boundary between one space and another. In addition, some membranes allow for passage of some things through it while excluding others. The human body has several different kinds of membranes. On a microscopic level, the contents of each cell is surrounded by a membrane called a phospholipid bilayer. Built into the cell wall are molecular gateways that control the passage of materials in and out.
I doubt, though, that the Buddha, even in his infinite wisdom, understood the mechanics of cellular biology when he recommended his monks contemplate on the 32 parts of the body as a means of overcoming sensual desire and attachment to one’s own body.
On a macroscopic level, the grosser membranes are more easily discernible. The heart, for example, is surrounded by a thin, shiny double-walled membrane called the pericardium. The visceral organs are covered in peritoneum. It also has two layers, with the outer layer serving as the lining of the abdominal cavity. The mesentery is the portion of the peritoneum that anchors the small intestine to the rear abdominal wall. The mesentery has a rich blood supply, which picks up digested food for circulation throughout the body. It is the selective nature of the peritoneum that allows for peritoneal dialysis, a process that keeps alive many people whose kidneys have failed.
We also have synovial membranes that line joint capsules and produce a lubricant called synovial fluid, and mucous membranes that line passages that connect internal organs to the external environment. Mucus secreted by the membrane traps foreign particles and aids in expelling them.
The most obvious membrane in the human body is the diaphragm. Unlike the other membranes, which are thin layers of specialized cells, the diaphragm is a muscle that separates the thoracic cavity (chest) from the abdominal cavity. It has several openings that allow for the passage of the esophagus, the inferior vena cava, the abdominal aorta, and other structures. The principle function of the diaphragm is breathing. When this muscle contracts, it pulls down on itself, increasing the volume in the thoracic cavity, thereby reducing the air pressure, which allows for the intake of air into the lungs.
This change in air pressure, which is essential to breathing, would not be possible without another membrane, the pleura. Like the pericardium and peritoneum, the pleura has two layers, one that covers the lungs and the other that lines the thoracic cavity. The two layers slide against one another, reducing friction. There is also a negative air pressure between the air-tight layers, which keeps the lungs in contact with the chest wall. If the outer membrane is torn, air will get between the layers and the lung will collapse.
Through breathing, oxygen and carbon dioxide are exchanged within body tissues. The simple act of breathing is one of the mechanisms that keeps the body alive. Mindfulness of in and out breathing is the simplest form of Buddhist meditation practice. When you train the mind to observe the breath you see that each breath is a microcosm of all that happens in the universe. What comes into existence must, eventually, go out of existence. Everything that comes into existence sets the conditions for what comes next. Change the conditions, change the outcome.
Note: For background on this series, please read the Introduction to the 32-Parts Project.
