- 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:
- Provides olfactory sensation.
- Presence of olfactory receptors in mucus membrane of nostril.
- 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.
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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.
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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