Understanding Allergies

Allergies and Their Treatment

• Allergy occurs when IgE triggers Mast cell degranulation
• IgE is produced by plasma B cells in lymph nodes or locally at the site of inflammation
• Certain antigens and routes of delivery favor IgE production
• Inhaled allergens can cause allergic rhinitis and allergic asthma
• Allergens entering through the skin cause rashes and other symptoms
• Ingested allergens can lead to symptoms such as diarrhea, vomiting, and hives
• Chemical mediators of allergic responses include lipids, toxic mediators, cytokines, and enzymes
• Treatment of allergies includes desensitization, blockade of effector pathways, and potential future therapies involving recombinant allergens and DNA vaccines
• Severe anaphylaxis should be treated with epinephrine injection
• The Hygiene Hypothesis suggests that early childhood exposure to Th1-inducing pathogens may prevent bias towards Th2 responses later
• Environmental pollution may not necessarily increase allergic asthma
• Allergies and asthma are lower in areas with high helminth burdens, and the presence of helminth may suppress allergy.

Development of Body Cavities, Lungs, and Larynx in Embryos

• Mesoderm develops into paraxial, intermediate, and lateral plate mesoderm, divided into parietal and visceral layers by intraembryonic coelom
• Lateral folding of the embryonic disc causes the entrapment of intraembryonic coelom into a closed body cavity, lined by somatic and visceral lateral plate mesoderm
• The embryonic disc folds in two planes, leading to the movement of the developing heart and septum transversum
• Primitive body cavities undergo partitioning, forming pleural cavities and pleuropericardial folds that form fibrous pericardium
• The diaphragm separates thoracic and abdominopelvic cavities, formed by the fusion of pleuroperitoneal membranes, mesentery of oesophagus, and myoblasts
• The central tendon of the diaphragm and its peripheral scaffold are formed by the fusion of specific embryonic structures
• The respiratory diverticulum (lung bud) develops from the foregut, with tracheoesophageal ridges fusing to form the tracheoesophageal septum, separating the trachea and esophagus
• Pharyngeal arches 4 and 6 contribute to larynx development, with associated cranial nerves
• Laryngeal muscles and cartilages come from the fusing of mesenchyme from arches 4 and 6
• Lung development involves generational divisions to create the bronchial tree, with four distinct phases from prenatal to childhood
• The four phases of lung development include pseudoglandular, canalicular, saccular, and alveolar periods, each characterized by specific changes in lung structure and function
• Congenital diaphragmatic hernia, occurring in 1 in 2000 births, can lead to abdominal organs entering the thoracic cavity, potentially requiring intervention such as fetoscopic endoluminal tracheal occlusion.

Anatomy and Mechanics of the Diaphragm

• The diaphragm is a musculotendinous sheet that separates the thoracic and abdominal cavity, with a central tendon surrounded by muscle.
• It has attachments to the margins of the inferior thoracic aperture, including the sternal part (xiphoid process, T8/9 vertebral level) and costal part (costal cartilages 7-10, ribs 11, 12).
• The diaphragm also has lumbar attachments, including the right and left crura, median arcuate ligament, medial arcuate ligaments, and lateral arcuate ligaments.
• The diaphragm has three major openings: caval opening (level of T8), oesophageal hiatus (level of T10), and aortic hiatus (level of T12).
• It is crossed by various structures, including the phrenic nerve, sympathetic trunks, splanchnic nerves, intercostal nerves, and vessels such as the superior epigastric vessels and musculophrenic vessels.
• The diaphragm's arterial supply includes superior phrenic, musculophrenic, and pericardiophrenic arteries, while its venous drainage mirrors the arteries.
• It is innervated by the phrenic nerve (C3, C4, C5) and receives additional peripheral sensory innervation from intercostal and subcostal nerves.
• The diaphragm plays a key role in the mechanics of breathing, primarily driving inspiration at rest by increasing thoracic volume and drawing air into the lungs.
• During inspiration, the diaphragm contracts, causing the domes to descend, while external intercostals act to move ribs superiorly and laterally, increasing thoracic volume and drawing in air.
• Forced inspiration involves the diaphragm aiding in increasing thoracic volume by raising ribs when anchored via the pericardium, with accessory muscles such as the SCM, scalenes, trapezius, pectoralis major, and minor, among others, aiding in the process.
• The surface anatomy of the lungs and pleurae includes the apex of the lungs being 3cm superior to the mid clavicle, and the midclavicular line being at the 6th rib for the lungs and the 8th rib for the pleurae, among other details.
• The lungs and pleurae have specific anatomical landmarks, such as the apex of the lungs, midclavicular line, midaxillary line, and scapular line, with corresponding levels for the pleurae.

Larynx Anatomy and Function Overview

• Larynx located inferior to the hyoid bone, connected to the thyroid and cricoid cartilages
• Composed of three large unpaired cartilages, four pairs of smaller cartilages, and membranes
• Various ligaments and membranes cover the cartilages, divided into vestibule, ventricle, and infraglottic space
• Intrinsic and extrinsic muscles control the airway, vocal cord tension, and diameter of rima glottidis
• The larynx is innervated by the recurrent laryngeal nerve, except for the cricothyroid muscle
• Muscle functions include protection/closure of airway, controlling the size of rima glottidis, and altering vocal ligament tension
• The larynx has a complex subconscious process for airway protection involving muscle coordination
• Innervation of the larynx is via the vagus nerve, with specific branches serving sensory and motor functions
• Arterial supply to the larynx comes from the superior and inferior laryngeal arteries
• Venous drainage occurs through superior and inferior laryngeal veins, draining into the internal jugular and brachiocephalic veins
• Lymphatic drainage from the larynx occurs to the deep cervical and pre/paratracheal nodes
• Clinical considerations include choking, anaphylaxis, laryngospasm, aspiration pneumonia, cricothyroidotomy, and recurrent laryngeal nerve damage