--- module: 084-01 language: en chapter: 84 title: "Organ Histology and Structure–Function Recognition" module_title: "Cardiovascular and respiratory histology from vessel wall to alveolar barrier" source_sha256: ac9b5a6a7e6c8938b4ea577797d5e2811c118377f7321bb7fa3f832117a12376 --- # Cardiovascular and respiratory histology ## Organising principles ### Endothelium on walls adapted to function ### Airway conducts, then exchanges gas ### Structure changes along the pathway ## Heart wall ### Endocardium continuous with vascular intima #### Subendocardium: vessels, nerves, Purkinje fibres ### Myocardium of branching cardiomyocytes #### Atria thinner, some with natriuretic granules #### Left ventricle thickest: systemic pressure #### Mitochondria and dense capillaries ##### Ischaemia rapidly impairs contraction ### Epicardium: visceral serous pericardium ## Fibrous skeleton, valves, conduction ### Dense tissue around valve orifices #### Anchors cusps, limits dilation #### Insulates atria from ventricles ### Valve layers: collagen, proteoglycan, elastic ### Nodes: small cells, few myofibrils ### Purkinje fibres: large, pale, glycogen-rich #### Rapid subendocardial conduction ### Fibrosis or ischaemia: block, re-entry ## Arterial wall ### Intima, media, adventitia #### Large vessels need vasa vasorum ### Elastic arteries buffer pulsatile output #### Systolic stretch stores energy ##### Recoil sustains diastolic flow #### Internal elastic lamina indistinct ### Muscular arteries distribute to organs #### Prominent wavy internal elastic lamina #### Atherosclerosis arises in intima ### Arterioles set resistance, capillary pressure #### Hyaline: hypertension, diabetes #### Hyperplastic: severe hypertension ##### Chronic downstream ischaemia ## Capillaries, venules, veins, lymphatics ### Continuous: muscle, lung, nervous tissue ### Fenestrated: endocrine, gut, kidney ### Sinusoidal: liver, spleen, marrow ### Pericytes stabilise vessels, regulate flow ### Postcapillary venules: leukocyte exit ### Veins: thin media, thick adventitia #### High compliance stores blood ### Judge wall-to-lumen ratio, not shape ### Lymphatics: overlapping cells, no erythrocytes ## Upper airway and trachea ### Pseudostratified ciliated columnar mucosa #### Vascular lamina propria warms air #### Seromucous glands humidify, trap particles ### Olfactory mucosa with bipolar neurons ### True folds: stratified squamous, few glands ### False folds keep respiratory epithelium ### Trachea: C-shaped hyaline rings #### Trachealis spans the open ends #### Irritation causes squamous metaplasia ## Bronchi and bronchioles ### Cartilage becomes discontinuous plates ### Smooth muscle proportionally prominent ### Arteries follow bronchi, veins in septa ### Bronchioles lack cartilage and glands #### Terminal bronchiole: last conducting airway #### Club cells: secretion, detoxification, renewal ## Gas exchange region ### Respiratory bronchioles interrupted by alveoli ### Elastic recoil drives passive expiration #### Elastic loss: emphysema, expiratory collapse ### Type one pneumocytes cover most surface ### Type two cells secrete surfactant #### Replace both types after injury ### Surfactant lowers surface tension #### Deficiency promotes collapse ### Barrier: surfactant, epithelium, lamina, endothelium #### Oedema and fibrosis thicken barrier #### Emphysema reduces surface area ## Defence, pleura, interpretation ### Alveolar macrophages clear particles ### Interalveolar pores can spread infection ### Pleural lymphatics drain via parietal stomata ### Air or fluid separates pleural layers ### Ask which compartment is abnormal