Exhalation

This happens due to elastic properties of the lungs, as well as the internal intercostal muscles which lower the rib cage and decrease thoracic volume.

As the thoracic diaphragm relaxes during exhalation it causes the tissue it has depressed to rise superiorly and put pressure on the lungs to expel the air.

Exhalation has a complementary relationship to inhalation which together make up the respiratory cycle of a breath.

The main reason for exhalation is to rid the body of carbon dioxide, which is the waste product of gas exchange in humans.

[2] Exhalation takes longer than inhalation and it is believed to facilitate better exchange of gases.

People with asthma and COPD show decreases in exhaled air due to inflammation of the airways.

Numerous things cause inflammation; some examples are cigarette smoke and environmental interactions such as allergies, weather, and exercise.

[citation needed] Dead space can be determined by two types of factors which are anatomical and physiological.

Some physiological factors are having non-perfuse but ventilated alveoli, such as a pulmonary embolism or smoking, excessive ventilation of the alveoli, brought on in relation to perfusion, in people with chronic obstructive lung disease, and "shunt dead space," which is a mistake between the left to right lung that moves the higher CO2 concentrations in the venous blood into the arterial side.

Dead space is a key factor for the lungs to work because of the differences in pressures, but it can also hinder the person.

The internal surface of the lungs on average in a non-emphysemic person is normally 63m2 and can hold about 5lts of air volume.

Disease such as, emphysema, tuberculosis, can reduce the amount of surface area and elasticity of the lungs.

[citation needed] The neurological pathway of voluntary exhalation is complex and not fully understood.

[9][10] The pathway of the electrical signal starts in the motor cortex, goes to the spinal cord, and then to the respiratory muscles.

The inferior portion of the primary motor cortex may be involved, specifically, in controlled exhalation.

[citation needed] Involuntary respiration is controlled by respiratory centers within the medulla oblongata and pons.

The bulbospinal pathway descending from the VRG allows the respiratory centers to control muscle relaxation, which leads to exhalation.

A non-respiratory gas movement is another process that moves air in and out of the lungs that do not include breathing.

Yawning is a reflex that tends to disrupt the normal breathing rhythm and is believed to be contagious as well.

Although there is not a concrete explanation as to why we yawn, others think people exhale as a cooling mechanism for our brains.

They respond to changing blood levels of oxygen, carbon dioxide, and H+ by signaling the pons and medulla.