Non-respiratory functions of respiratory tract

  • Various non-respiratory functions are also shown by respiratory tract.
  • Not only gaseous exchange that is the primary function of it.
  • Lungs show defense barrier and metabolic functions.
  • It is the main organ of respiration.
  • Some important compounds are synthesized by it.
  • Non-respiratory functions are:

a) Olfaction

  • Provides olfactory sensation.
  • Presence of olfactory receptors in mucus membrane of nostril.

b) Vocalization

  • Larynx forms the speech apparatus.
  • It forms this apparatus along with some other structures.
  • Though it can play major role in the process of vocalization alone.
  • For this reason, also called sound box.

c) Prevention of dust particles

  • Filtration action of the hairs generally blocks the dust particles.
  • These particles from air enter the nostrils which can finally reach our lungs.
  • But due to presence of hairs in nostrils, most of the particles are filtered.
  • Though small particles escape this action which then held by mucus later on.
  • Secretion of nasal mucous membrane cannot hold all small particles even.
  • Finally, phagocytic action of macrophages plays vital role to prevent escaped dust.
  • These macrophages are present in alveoli.
  • Some particles even escape these barriers which then removed by cough reflex and sneezing reflex.

d) Defense mechanism

  • Lungs provide immunological defense mechanism to our body.
  • These functions are shown by various structures present in the lungs.
  • Lungs own defenses and various cells in mucus membrane that lines the alveoli of lungs are responsible for this function.
  • Various cells include leukocytes, macrophages, mast cells, natural killer cells and dendritic cells.

Respiratory Physiology: Gas Exchange - ppt video online download

Image source: slideplayer

i) Lung’s own defenses

  • Epithelial cells line the air passage or respiratory tract.
  • Defensins and cathelicidins are some immune factors secreted by them.
  • They are antimicrobial peptides and provide natural defenses to our lungs.

ii) Defense through leukocyte

  • Neutrophils and lymphocytes are types of leukocytes.
  • Present in the alveoli of lungs.
  • Provide defense mechanism against bacteria and virus.
  • By phagocytosis, neutrophils kill bacteria.
  • Whereas lymphocytes develop immunity against bacteria.

iii) Defense through macrophages

  • Dust particles and pathogens are looked after by macrophages.
  • They get engulfed by macrophages.
  • Thus, macrophages are also called scavengers of lungs.
  • Also develop immunity by acting as antigen presenting cells (APC’s).
  • No sooner the foreign organisms enter the body, these APC’s and macrophages kill them.
  • Antigens from organisms later on digested to polypeptides.
  • Macrophages present these polypeptides to T-lymphocyte and B-lymphocytes.
  • Interleukins, tumor necrosis factors (TNF) and chemokines are some secretions of macrophages.
  • General immune system is activated by TNF and interleukins.
  • Whereas, white blood cells are brought to site of inflammation by chemokines.

iv) Defense through mast cells

  • Resemble basophil due to its large size.
  • Allergy and anaphylaxis reactions are produced by these cells.
  • Also have some secretions like heparin, histamine, serotonin and hydrolytic enzymes.

v) Defense through natural killer cells

  • Considered third type of lymphocyte and are large granular cells.
  • Presence found more in lungs and some other lymphoid organs.
  • Hydrolytic enzymes content is high in its granules.
  • Thus, microorganisms can be easily destroyed by it.
  • These cells can act against viruses also.
  • Thus, are considered the first line defense in specific immunity.
  • Viruses, viral infected or damaged cells which can form tumor are destroyed by it.
  • Malignant cells destruction also occurs along with the prevention of cancerous tumor development.
  • Interferons and tumor necrosis factors (TNF) are its secretion.

vi) Defense through dendritic cells

  • Shows important role in immunity though present in the lungs.
  • Also act as antigen presenting cells (APC’s) like macrophages or along with it.

Lung - Alveolar and Pneumocytes - Histology | Медицинский, Наука, Химия

Image source: pinterest

e) Maintenance of water balance

  • Helps in water loss mechanism.
  • In expiration process, some water content vaporizes.
  • This cause loss of water through expired air.
  • Thus, maintains water level in our body.

f) Regulation of body temperature

  • Not only water but also some heat is lost from the body.
  • These both losses occur through exhalation.
  • Thus, assists in heat loss mechanism also.

g) Anticoagulant function

  • Secretion of mast cells acts as anticoagulant.
  • In lungs, these cells are present.
  • Thus, through heparin secretion, intravascular clotting is prevented.

h) Secretion of angiotensin-converting enzyme

  • Pulmonary capillaries contain many endothelial cells.
  • These cells secrete angiotensin-converting enzyme (ACE).
  • Angiotensin-I is acted upon by this enzyme thus angiotensin-II is formed.
  • It is the active form of angiotensin-I.
  • Thus, regulates the ECF volume and blood pressure.



i) Synthesis of hormonal substances

  • Some hormones are also secreted by lung tissues.
  • Prostaglandins, acetylcholine and serotonin are some of them.
  • They have various physiological functions in the body.
  • One of them is regulation of blood pressure.

j) Regulation of acid-base balance

  • Lungs also help to maintain acid-base balance in our body.
  • It is done by lungs by regulating CO2 content in blood.
  • In various metabolic reactions that occur in the tissues of the body, CO2 is produced.
  • Carbonic acid is formed as the CO2 dissolves in water.
  • As carbonic acid is unstable, it splits.
  • These results in the formation of hydrogen and bicarbonate ions.

Co2 + H2O → H2CO3 → H+ + HCO3

  • This reaction reverses as carbon dioxide is removed from blood into the alveoli of lungs.

H+ + HCO3 → H2CO3 → CO2 + H2O

  • Through ventilation process, carbon dioxide is removed as it is a volatile gas.
  • Increase in metabolic activities increases the carbon dioxide content in tissues.
  • This increases the hydrogen ion concentration also.
  • Thus, pH is reduced.
  • Increased pulmonary ventilation results as hydrogen ion increases.
  • It occurs through various mechanisms like chemoreceptors in aortic and carotid bodies and in medulla of the brain.
  • As ventilation increases, carbon dioxide is also removed in excess from body fluids.
  • Thus, this pH is brought back to normal.




Non-respiratory functions of respiratory tract