The lungs possess two distinct circulatory systems, each serving a unique purpose. The pulmonary circulatory system is capable of accommodating large volumes of blood at low pressure, facilitating the transportation of deoxygenated blood from the right ventricle to the gas-exchanging units within the lung. In conditions like pulmonary fibrosis, characterized by the formation of scars, the total volume of the lungs decreases due to the loss of alveoli and impaired diffusion of oxygen into the capillaries caused by a thickened, impermeable matrix. The lack of specific therapeutics has historically made idiopathic pulmonary fibrosis challenging to treat, as they are unable to inhibit collagen deposition. However, clinical trials have shown that two therapeutic compounds, pirfenidone and nintedanib, can slow down the progression of the disease and improve outcomes in patients with idiopathic pulmonary fibrosis. Pirfenidone, a small low-molecular-weight compound, possesses anti-inflammatory properties and reduces the synthesis of procollagen types I and II. On the other hand, nintedanib is a tyrosine kinase inhibitor that inhibits vascular endothelial growth factor and fibroblast-derived growth factor. The bronchial circulation, arising from the aorta, provides nourishment in the form of oxygen to the lung parenchyma. Breathing is an automatic process, with the lungs being innervated by the autonomic nervous system of the peripheral nervous system while under the control of the central nervous system. Parasympathetic stimulation leads to the constriction of airway smooth muscles, resulting in airway narrowing, while sympathetic stimulation causes relaxation of airway smooth muscles, leading to airway opening. Inspiration, the active phase of breathing, is primarily driven by the contraction of the diaphragm. This contraction creates a pressure difference between the thorax and diaphragm, inducing inspiration through a mechanoreceptor response. The respiratory center, located in the medulla, regulates respiration with input from sensory feedback loops, including mechanoreceptors and chemoreceptors. The development of the lung involves various molecular and physiological determinants, and the structural aspects of postnatal lung development, such as alveolar formation and growth, play a crucial role. The cell surface mucins, as well as epithelial cell-mesenchymal interactions, are essential for lung development. The structure and function of mammalian cilia are also relevant, and lung inflammation and fibrosis can be understood from an alveolar macrophage-centered perspective. Overall, lung organogenesis is a complex process that requires an understanding of the interplay between various factors.
The lungs have unique, dual circulatory systems. The pulmonary circulatory system has the ability to accommodate large volumes of blood at low pressure and brings deoxygenated blood from the right ventricle to the gas-exchanging units in the lung. The exchange.Inlungdiseasethatinvolvesscarformation(i.e.,pulmonaryfibrosis),thetotallungvolumedecreasesasaresultofthelossofalveoliandimpairmentofO2diffusionintothecapillariesbyathickened,nonpermeablematrix.Historically,idiopathicpulmonaryfibrosishasbeenverydifficulttotreatbecauseofthelackofspecifictherapeutics,whichcaninhibitcollagendeposition.Twotherapeuticcompounds(pirfenidoneandnintedanib)havebeenshowninclinicaltrialstoslowtheprogressionofthediseaseandimproveoutcomesinpatientswithidiopathicpulmonaryfibrosis.Pirfenidoneisasmalllow-molecular-weightcompoundwithanti-inflammatoryproperties(itdecreasesprocollagentypesIandIIsynthesis),andnintedanibisatyrosinekinaseinhibitor(inhibitsvascularendothelialgrowthfactorandfibroblast-derivedgrowthfactor).
bronchial circulation arises from the aorta and provides nourishment (O2) to the lung parenchyma.
5.
Breathing is automatic; the lungs are innervated by the autonomic nervous system of the PNS while under the control of the CNS. Parasympathetic stimulation results in constriction of airway smooth muscles (airway narrowing) whereas sympathetic stimulation results in relaxation of airway smooth muscles (airway opening).
6.
Inspiration is the active phase of breathing. The diaphragm is the major muscle of respiration, and its contraction creates a pressure difference (mechanoreceptor response) between the thorax and diaphragm (negative pressure in the chest), which induces inspiration.
7.
The respiratory center is located in the medulla and regulates respiration with input from sensory (mechanoreceptor and chemoreceptor) feedback loops.
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Upon completion of this chapter, the student should be able to answer the following questions: 1.
Define the different pressures in the respiratory system.
2.
Explain how a pressure gradient is created.
3.