Nonrespiratory Functions of the Lung
Apart from its well-studied classical function, the nonrespiratory function of the lungs is also multidimensional, as outlined in Table 7.5.
Learning Outcomes
• Respiration is vital to the survival of any animal species.
The respiratory system is comprised of a conducting zone and respiratory zone, the latter taking part in gaseous exchange in the lungs. In birds, the air sacs play a prominent role in respiration. The respiratory system serves basic functions of providing pulmonary ventilation that involves the exchange of air between the atmosphere and alveoli of the lungs. Next, it facilitates the diffusion of gases such as carbon dioxide and oxygen between the alveolar membrane and blood, followed by the transport of oxygen and carbon dioxide dissolved in plasma and combination with Hb to and from the tissues. The respiration is regulated by the respiratory centres located in the medulla oblongata and pons. The medullary respiratory centre is divided into the dorsal group of respiratory neurons in the nucleus of tractus solitarius, which controls inspiration. The other part is the ventral group of respiratory neurons that causes expiration when stimulated. The respiratory centre sends impulses after receiving sensory inputs from peripheral chemoreceptors and mechanoreceptors. The respiratory system also performs nonrespiratory functions such as providing immune protection, neuroendocrine and filtering functions.Table 7.5 Nonrespiratory functions of the lung
| Functions | Significance | Description |
| Circulatory reservoir | Recruitment and distension Helps cope with the alterations in the cardiac output (during extraneous exercise) | A transition from the stage of incomplete perfusion of the pulmonary vascular bed during the resting phase to complete perfusion occurs during the high cardiac output phase. It is accomplished by recruitment of under perfused pulmonary vasculature followed by distension (smooth muscle relaxation) to accommodate increased blood flow. The pressure in the pulmonary circulation is six times less than systemic. This phenomenon helps in altering the blood volume by 500-1000 mL. |
| Change instance and circulatory redistribution of blood flow | The blood volume in pulmonary vessels decreases by 50% and increases by 100% during forced expiration and inspiration, respectively. The blood flow in the pulmonary vessels is equivalent to right ventricular output. Around 70-100 mL of this flow is in pulmonary capillaries in gas exchange. | |
| Immunity | Pulmonary alveolar macrophages (PAMs) are majorly responsible for lung immune function | • Engulfs the particles in the alveolar region and directs them to blood or lymph for removal: • Antigen presentation. • T-cell activation. • Neutrophil activation triggers the release of trypsin and elastase with high antibacterial activity and damages the self-mucociliary lining. The binding of these proteases with alpha-anti-trypsin may result in its inactivation (advocated in the treatment of pulmonary emphysema). |
| Other immune mediators | • Epithelial cells in the air passage secrete lactoferrin, nitric oxide, defensins, mucin, lysozyme, etc., which are reported to have function against a diverse range of microbes. • Reactive oxygen species (ROS), cytokines like tumour necrosis factor-alpha (TNR-α), interleukins (IL-1β) and platelet-activating factors are potential mediators of inflammation. IgA in bronchial secretions resists infection. | |
| Natural purifier against inspired substances | Pulmonary epithelium forms the first line of defence against inspired chemicals. The pseudostratified epithelium of air passages is carefully encased under a protective covering called a “mucous blanket”. It is made up of mucopolysaccharide gel (secreted by goblet and mucous cells) and forms the first line of defence in air passages. | • Mucociliary escalator is the unique phenomenon in lungs characterised by cilia beating with 10-15 Hz frequency that moves the overlying mucosa @ 1 mm/min in the pharynx and 20 mm/ min in the trachea. • Particulate matter of 5 μm deposits on larger airways, while that in 2-5 μm deposits on smaller airways. The cilia with these entrapped particles shift the mucus from peripheral to central airways from where the mucus is either swallowed or expectorated. Particles the three primary systems that manage the acid-base balance in the body. Clinical disorders impacting hydration, acid-base balance, and electrolyte status can have serious, even life-threatening repercussions; therefore, it is critical to recognise and treat them. N. Madhavan Unny Department of Veterinary Clinical Medicine, College of Veterinary and Animal Sciences, Thrissur, Kerala, India A. Zarina ∙ V. Beena (X) Department of Veterinary Physiology, College of Veterinary and Animal Sciences, Thrissur, Kerala, India e-mail: beenav@kvasu.ac.in © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 193 P. K. Das et al. (eds.), Textbook of Veterinary Physiology, https://doi.org/10.1007/978-981-19-9410-4_8 Graphical Abstract
Description of the graphic: Total body water (TBW) constitutes 60-65% of body weight (1). About 65% of TBW is ICF and 35% is ECF. Electrolytes are differentially distributed with respect to the concentration in both ECF and ICF, sodium being the major extracellular cation and potassium being the major intracellular cation (2). Along with the chemical buffer system, respiratory and renal systems are also involved in the acidbase regulation of the body (3). Respiratory or metabolic alterations can cause acidosis or alkalosis (4). Clinical management by parenteral fluid administration is decided by the level of dehydration, pH, and electrolyte imbalance (5) Keywords Acid-base balance ∙ Electrolytes ∙ Dehydration and fluid therapy ∙ Total body water ∙ Transcellular fluid Various systems involved in maintaining acid-base balance Causes for acid-base balance disturbances Clinical management of dehydration, acid-base imbalance, and electrolyte disturbances Learning Objectives • To know about the different body water compartments and regulation of water balance • The physiological importance of electrolytes and various causes of electrolyte disturbances • Different types of transcellular fluids and their physiological importance 8.1 More on the topic Nonrespiratory Functions of the Lung:
-
Veterinarian -
|
