Histology of Respiratory System

Includes : the lung a system of tube

jurasicpork Divided into 2 principal regions : conducting portion : nasal cavity, nasopharynx, larynx, trachea, bronchi, bronchioles & terminal bronchioles respiratory portion : respiratory bronchioles, alveolar ducts, alveoli (alveoli : the greater part of the lung) jurasicpork

28/04/2017 Respiratory Zone 4 4

The main divisions of the respiratory tract The main divisions of the respiratory tract. The natural proportions of these structures have been altered for clarity; the respiratory bronchiole, for example, is in reality a short transitional structure.

RESPIRATORY EPITHELIUM Ciliated Pseudostratified Columnar Epithelium 5 types of cell : 1. ciliated columnar epithelium 2. mucous goblet cells 3. brush cells 4. basal cells 5. small granule cells Photomicrograph illustrating the main components of the respiratory epithelium. Pararosaniline—toluidine blue (PT) stain. High magnification.

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NASAL CAVITY Consists of : - vestibule (external) - nasal fossae (internal) VESTIBULE Is the most anterior and dilated portion of nasal cavity Numerous sebaceous & sweat glands, vibrisae Within the vestibule  keratinized (-)  respiratory epithelium before entering the nasal fossae

- superior : specialized olfactory epithelium - middle respiratory NASAL FOSSAE Conchae : - superior : specialized olfactory epithelium - middle respiratory - inferior epithelium The olfactory epithelium  olfactory chemoreceptor located Ciliated Pseudostratified Columnar Epithelium 3 types of cells : 1. supporting cells 2. basal cells 3. olfactory cells Olfactory mucosa showing the 3 cell types (supporting, olfactory, and basal) and a Bowman’s gland.

PARANASAL SINUSES Closed cavities in the : frontal, maxillary, ethmoid, sphenoid bones Lined with a thinner respiratory epithelium, few goblet cells Communicate with nasal cavity through small openings Mucous product  drain in to the nasal passages by ciliated epithelial cells

NASOPHARYNX First part of the pharynx Lined with respiratory epithelium

LARYNX Connects the pharynx to the trachea The larger cartilge : hyaline cartilage The smaller cartilage : elastic cartilage Cartilage participate in producing sounds for phonation Below the epiglottis : - false vocal sound - true vocal sound

TRACHEA Mucosa : - Ciliated Pseudostratified Columnar Epithelium with goblet cells - Lamina propria Sub mucosa : loose connective tissue Hyaline cartilage : 16-20 C-shaped rings Smooth muscle fibers Adventisia (fibrosa)

Section of trachea showing the respiratory epithelium with goblet cells and columnar ciliated cells. Also shown are serous glands in the lamina propria and hyaline cartilage. The mucous fluid produced by the goblet cells and by the glands forms a layer that permits the ciliary movement to propel foreign particles out of the respiratory system. PT stain. Medium magnification.

Light photomicrograph of the trachea in a monkey (´270)  Light photomicrograph of the trachea in a monkey (´270). There are numerous cilia (Ci) as well as goblet cells (GC) in the epithelium. Also observe the mucous glands (MG) in the subepithelial connective tissue and the hyaline C-ring (HC) in the adventitia. L, lumen; PC, perichondrium.

BRONCHIAL TREE TRACHEA BRONKUS PRIMER BRONKUS PRIMER ka : 3 CAB. BRONKUS ki : 2 CAB. BRONKUS BRONKIOLUS BRONCHIOLUS TERMINALIS BRONCHIOLUS RESPIRATORIUS DUCTUS ALVEOLARIS ALVEOLUS ALVEOLUS

BRONCHUS Ф ± 5 mm Mucosa : similar to the mucosa of the trachea (Ciliated Pseudostratified Columnar Epithelium) The bronchial cartilage are more irregular shape Larger bronchi : cartilage rings completely encircle the lumen Smaller bronchi : cartilage rings are replaced with isolated plates or islands of hyaline cartilage Lamina propria : smooth muscle layer, rich in elastic fiber, abundance of mucous & serous gland  ducts  bronchial lumen

PSEUDOSTRATIFIED COLUMNAR EPITHELIUM CARTILAGE MUSCULARIS ADIPOSE TISSUE

Hyaline cartilage

BRONCHIOLES Ф ≤ 5 mm Mucosa : - cartilage & glands (-) - scattered goblet cells TERMINAL BRONCHIOLES RESPIRATORY BRONCHIOLES

TERMINAL BRONCHIOLES Ciliated Pseudostratified Columnar Epithelium  Ciliated Simple Columnar Epithelium  Ciliated Simple Cuboidal Epithelium Clara cells : - (-) cilia - (+) secretory granules in their apex - secrete protein  protect the bronchiolar lining against oxidative pollutants and inflamation - lamina propria : smooth muscle, elastic fiber

Clara cells in the epithelium of a terminal bronchiole Clara cells in the epithelium of a terminal bronchiole. These cells show secretory granules and a bulging apical cytoplasm. PT stain. High magnification.

RESPIRATORY BRONCHIOLES Transition between conducting and respiratory Mucosa : identical to the terminal bronchioles, except their walls are interrupted by numerous sacklike alveoli  proceeding distally  alveoli » Ciliated Cuboidal Epithelium & Clara cells Smooth muscle and elastic fiber

Section of a terminal bronchiole with a small portion of a respiratory bronchiole continuous with an alveolar duct and many alveoli. PT stain. Low magnification.

ALVEOLI

ALVEOLAR DUCTS Proceeding distally  the number of alveolar openings »  alveolar ducts Alveolar duct & alveoli lined with squamous cells Lamina propria : smooth muscle  disappears at the distal ends of alveolar ducts Alveolar ducts  atria that communicate with alveolar sacs Elastic fiber : enable the alveoli to expand contract passively with expiration Reticular fibers : prevent overdistention prevent damage to the delicate capillaries and thin alveolar septa

Transition of a terminal bronchiole into an alveolar duct (arrow) Transition of a terminal bronchiole into an alveolar duct (arrow). Note the Clara cells (arrowheads). PT stain. Medium magnification.

ALVEOLUS Sacklike evaginations of the respiratory bronchioles, alveolar ducts, alveolar sacks Resemble small pockets that are open on one side similar to the honeycombs of a beehive Exchange of O2 and CO2 between air & blood Each wall lies between 2 alveoli  interalveolar septum An interalveolar septum consists of 2 thin squamous epithelial layers : type I cells = squamous alveolar cells type II cells = surfactant cells

TYPE I CELLS Line the alveolar surface Cells are so thin (25nm) Desmosomal & occluding junctions  prevent leackage of tissue fluid into alveolar air space To provide a barrier minimal thickness that is readily permeable to gases

TYPE II CELLS Interspersed among the type I cells Desmosomal and occluding junctions Divided by mitosis replace type I & II population Exhibit a characteristic vesicular or foamy cytoplasm, by presence of lamellar bodies Lamellar bodies  pulmonary surfactant  alveolar surface tension ↓ Without surfactant  alveoli collaps (expiration) Surfactant appears in the last week of gestation

Secretion of surfactant by a type II cell Secretion of surfactant by a type II cell. Surfactant is a protein-lipid complex synthesized in the rough endoplasmic reticulum and Golgi complex and stored in the lamellar bodies. It is continuously secreted by means of exocytosis (arrows) and forms an overlying monomolecular film of lipid covering an underlying aqueous hypophase. Occluding junctions around the margins of the epithelial cells prevent leakage of tissue fluid into the alveolar lumen.

LUNG MACROPHAGE = alveolar macrophage = dust cells Found in the anterior of the interalveolar septum, often seen on the surface of the alveolus The alveolar macrophage never passed through the epithelial lining that scavenge the outer surface of the epithelium  carried to the pharynx  swallowed

ALVEOLAR PORES To connect neighboring alveoli Equalize air pressure in the alveoli Promote the collateral circulation of air when a bronchiole is obstructed

BLOOD AND LYMPH CIRCULATION Blood and lymph circulation in a pulmonary lobule. Both vessels and bronchi are enlarged out of proportion in this drawing. In the interlobular septum, only one vein (on the left) and one lymphatic vessel (on the right) are shown, although both actually coexist in both regions. At the lower left, an enlargement of the pleura shows its mesothelial lining. (Modified and reproduced, with permission, from Ham AW: Histology, 6th ed. Lippincott, 1969.)