RESPIRATORY

• Light absorption occurs in the thylakoid membranes of chloroplasts.
• The respiratory system includes the lungs and a series of airways connecting the lungs to the external environment
• The respiratory system has two major subdivisions: a conducting portion (airways delivering air to the lungs) and a respiratory portion (structures in the lungs where gas exchange occurs)
• The conducting portion of the respiratory system includes the nose, nasopharynx, larynx, trachea, bronchi, and bronchioles of decreasing diameters, ending at the terminal bronchioles
• The nasal cavity is subdivided by the median nasal septum into right and left nasal cavities, leading to the paranasal sinuses, providing a large surface area for filtering, moistening, and warming the inspired air
• The vestibule of the nasal cavity contains vibrissae (thick, short hairs) that filter large particles from the inspired air and has a richly vascularized lamina propria with seromucous glands
• The nasal cavity contains bony shelves called conchae (turbinate bones) that divide it into separate regions, increasing the surface area for warming, filtering, and moistening the inspired air
• Paranasal sinuses are air-filled portions of bones lined by respiratory epithelium, but their function is not known
• The trachea bifurcates into the right and left primary bronchi, each entering the hilum of the lung on its side, supported by C-shaped hyaline cartilages and smooth muscle
• The tracheal mucosa contains ciliated cells, goblet cells, brush cells, diffuse neuroendocrine cells, and basal cells, with a thick basement membrane and a thin lamina propria containing seromucous glands
• Intrapulmonary bronchi arise from primary bronchi, have irregularly shaped hyaline cartilage, and are lined by respiratory epithelium with spiraling smooth muscle bundles in the submucosa
• Primary bronchioles have a diameter of 1 mm or less, lined by epithelium varying from ciliated columnar with goblet cells to ciliated cuboidal with Clara cells, dividing into terminal bronchioles
• Terminal bronchioles, the most distal part of the conducting portion, have a diameter of less than 0.5 mm, lined by simple cuboidal epithelium containing club cells, ciliated cells, and no goblet cells
• Respiratory bronchioles mark the transition from the conducting to the respiratory portion of the respiratory system
• Respiratory bronchioles are lined by a simple cuboidal epithelium that contains mostly club cells and some ciliated cells
• Alveolar ducts are linear passageways continuous with the respiratory bronchioles
• Alveolar ducts' walls consist of adjacent alveoli separated by an interalveolar septum and are lined by type II pneumocytes and highly attenuated simple squamous epithelium of type I pneumocytes
• Alveolar sacs are expanded outpouchings of numerous alveoli at the distal ends of alveolar ducts
• Alveoli are pouch-like evaginations about 200 um in diameter with thin walls for gas exchange, lined by a highly attenuated simple squamous epithelium composed of type I and type II pneumocytes
• Type I pneumocytes cover about 95% of the alveolar surface, have an extremely thin cytoplasm, form tight junctions, and may have phagocytic capabilities
• Type II pneumocytes are cuboidal, can divide and regenerate both types of alveolar pneumocytes, and synthesize pulmonary surfactant stored in cytoplasmic lamellar bodies
• Pulmonary surfactant reduces surface tension at the air-liquid interface of the alveolar surface, allowing easy expansion during inspiration and preventing collapse during expiration
• The interalveolar septum is the wall between two adjacent alveoli, containing elastic and reticular fibers, continuous capillaries, and the blood-gas barrier for gas exchange
• Lung lobules contain primary bronchioles branching into terminal bronchioles that give rise to alveoli
• The pulmonary artery carries blood to the lungs to be oxygenated, entering lung lobules and following the bronchioles
• Pulmonary veins run in the intersegmental connective tissue of lung lobules, coming close to bronchial tree divisions and accompanying bronchi to the lung root
• Bronchial arteries and veins provide nutrients to and remove wastes from nonrespiratory lung portions, following the bronchial tree's branching pattern and forming anastomoses with pulmonary vessels
• The pulmonary nerve supply consists of autonomic fibers to bronchi and bronchioles, with parasympathetic stimulation causing contraction and sympathetic stimulation causing relaxation of pulmonary smooth muscle
• The lymphatic system is involved in the immune response against infectious agents

  
• Two types of immunity exist to help the body get rid of pathogenic microorganisms: innate immunity and adaptive immunity
• Innate immunity is immediate and non-specific, examples include physical barriers like skin, mucous membranes, Toll-like receptors, natural killer cells, and leukocytes
• Chemicals forming a major part of innate immunity include hydrochloric acid, defensins, lysozyme, complement, and interferons
• An antigen is a molecule recognized by cells of the adaptive immune system, eliciting an immune response, immune cells recognize and react to small molecular domains of the antigen known as antigenic determinants or epitopes
• Antibodies are glycoproteins of the immunoglobulin family that interact specifically with an antigenic determinant, secreted by plasma cells, each antibody combines with the epitope it recognizes
• Medical terminologies related to antibodies include epitope, paratope, immunogens, haptens, and adjuvant
• Antibody classes include Immunoglobulin G (IgG), Immunoglobulin A (IgA), Immunoglobulin M (IgM), Immunoglobulin E (IgE), and Immunoglobulin D (IgD)
• Functions of antibodies include complement activation, opsonization, and NK cells activation
• Antigen-presenting cells include macrophages, lymphoid dendritic cells, thymic epithelial cells, B lymphocytes, and T lymphocytes
• T lymphocytes recognize antigenic epitopes via surface protein complexes termed T-cell receptors, several types of T lymphocytes exist including helper T cells, cytotoxic T cells, regulatory T cells, and γδ T cells
• Helper T cells help the immune system by making cytokines that activate various immune responses, some persist as memory helper T cells