A diaphragm is some sort of separating membrane. This gives rise to several meanings:

Table of contents
1 Anatomy
2 Mechanics
3 Contraception


In the anatomy of mammals, the diaphragm is a shelf of muscle extending across the bottom of the ribcage. It separates the thoracic cavity (with lung and heart) from the abdominal cavity (with liver, stomach, intestines, etc.). In relaxed state, the diaphragm is shaped like a dome. It is critically important in respiration: in order to draw air into the lungs, the diaphragm contracts, thus enlarging the thoracic cavity. (The muscles between the ribs also participate in this enlargement.) When the diaphragm relaxes, the air is pushed out by the elasticity of the lung and the tissues lining the thoracic cavity.

The diaphragm also helps to expel vomit, feces, and urine from the body and produces the pressure necessary for coughing and sneezing.

A hiccup occurs when the diaphragm contracts periodically without voluntary control. A hiatal hernia is a tear in the diaphragm.

There are three main apertures (or holes) in the diaphragm, one each for the inferior vena cava, aorta and oesophagus.


A diaphragm is a sheet of a semi-flexible material, anchored at its periphery, and most often round in shape. It serves either as a barrier between two chambers, moving slightly up into one chamber or down into the other depending on differences in pressure, or as a device that vibrates when certain frequencies are somehow applied to it. In this last sense, the human eardrum is a diaphragm. Pressure-flush valves in urinals work by means of an internal diaphragm.

See also: diaphragm pump.


A diaphragm is also a barrier method of contraception: a small rubber dome filled with a spermicidal (sperm killing) cream and placed in the vagina to wall off the cervix, thus preventing sperm from entering.

These are different from cervical caps, which are smaller and placed directly over the cervix.

Both must be initially fitted by a health care provider. They are inserted before sexual intercourse and have to remain in the vagina for 6 hours after the act.

See also: spermicide.