Alveoli (A) are terminal air space for actual gas exchange between air and blood. Alveolar surface is mainly composed of Type I alveolar cells (P1, purple arrow) and Type II alveolar cells (P2, red arrows). Type I alveolar cells (P1) are squamous cells and cover 95% of the alveolar surface. Type II alveolar cells are cuboidal in shape, have large nuclei with prominent nucleoli and secrete a phospholipid-rich pulmonary surfactant. Lung macrophages (M, green arrows) could be found both in the connective tissue of alveolar walls and in the alveoli (also called dust cells). Extensive capillary(C, orange arrow) and vessel (V) are presented.

This electron micrograph shows alveoli (A) separated by an alveolar septum. The alveolar septum includes thin and thick portions, as indicated. Capillaries (C) lined with endothelial cells (E) are located in the alveolar wall and around alveoli (A). The alveoli are covered with Type I alveolar cells and Type II alveolar cells (P2, red arrows). Alveolar surface cell and capillary endothelial cells could be identified by tracing their basement membranes. Alveolar surface cell is on the convex side, while capillary endothelial cells are on the concave side and erythrocytes may be observed within the capillary.

This electron micrograph shows alveoli (A) separated by an alveolar septum including thin and thick portions (dashed line), as indicated. Capillaries (C) lined with endothelial cells (E, orange arrow) are located in the alveolar wall and around alveoli (A). The alveoli are mainly covered with Type I alveolar cells (P1) and Type II alveolar cells (P2). Type I alveolar cells (P1) are squamous and their cytoplasm cover most of the alveolar surface (their nuclei are not presented in this photo). Type II alveolar cell (P2) has a dome-shaped apical surface with short microvilli (red arrow) at its periphery. Type II alveolar cell (P2) could be recognized by lamellar bodies (red triangles ) which are largely dissolved in this specimen, but their lamellar character still could be observed in the picture. The cell margins of the Type I alveolar cells are overlain to a variable degree to Type II alveolar cell.

This electron micrograph shows alveoli (A) separated by an alveolar septum. Thick portion (dashed line) is shown here with a fibroblast (F) and elastic fibers (black star). Capillaries (C) lined with endothelial cells (E, orange arrow) are located in the alveolar wall. The alveoli are mainly covered with Type I alveolar cells (P1) and Type II alveolar cells (P2). Type I alveolar cells (P1) are squamous and their cytoplasm cover most of the alveolar surface. Type II alveolar cell (P2) has a dome-shaped apical surface with short microvilli (red arrow) at its periphery. Type II alveolar cell (P2) could be recognized by lamellar bodies (red triangles ) which are largely dissolved in this specimen, but their lamellar character still could be observed in the picture. The cell margins of the Type I alveolar cells are overlain to a variable degree to the Type II alveolar cell by occluding junctions (black arrows).

This electron micrograph shows alveoli (A) separated by an alveolar septum. Thick portion (dashed line) is shown here with a fibroblast (F) and elastic fibers (black star). Capillaries (C) are lined with endothelial cells (E, orange arrow) in which pinocytotic vesicles (blue arrows) are present. The alveoli are mainly covered with Type I alveolar cells (P1) and Type II alveolar cells (P2). Type I alveolar cells (P1) are squamous and their cytoplasm cover most of the alveolar surface. Type II alveolar cell (P2) has a dome-shaped apical surface with short microvilli (red arrow) at its periphery. Type II alveolar cell (P2) could be recognized by lamellar bodies (red triangles ) which are largely dissolved in this specimen, but their lamellar character still could be observed in the picture. The cell margins of the type I alveolar cells are overlain to a variable degree to the type II cell by occluding junctions (black arrows).

This micrograph shows the thick portion of the alveolar septum where Type I alveolar cells (P1, purple arrows) rests on a basement membrane (partial indicated as the black dashline), and on the opposite side is connective tissue in which the cytoplasm of a fibroblast (F) and elastic fibers (black star) are shown. Elastic fibers (black star) have a relatively amorphous appearance. The left corner shows the cell margins of the type I alveolar cells are overlain to the type II cell by occluding junctions (black arrows).

The thin portion of the air–blood barrier consists of Type I alveolar cells (P1, purple arrows), capillary endothelium (E, orange arrow) , and the fused basement membrane (BM).

The photograph shows the wall of the trachea consisting of four layers: mucosa, submucosa, cartilaginous layer, and adventitia. Mucosa is composed of a pseudostratified columnar epithelium with cilia and lamina propria. Submucosa contains connective tissue with numerous tracheal glands (red star). Cartilaginous layer is composed of C-shaped hyaline cartilages. Adventitia is composed of connective tissue.

The photograph shows the tracheal mucosa and cartilaginous layer, while submucosa is not shown here. Mucosa is composed of a pseudostratified columnar epithelium with cilia and lamina propria. Cartilaginous layer is composed of C-shaped hyaline cartilages and obvious perichondrium is shown

The low magnification photograph shows the tracheal mucosa composed of a pseudostratified columnar epithelium with cilia and lamina propria. Lamina propria consists of loose connective tissue with highly vascular supply and two capillaries (V) are indicated.

This electron micrograph illustrates the surface of a trachea and the cross section of cilia (red arrows) and microvilli (blue arrows) are shown.

This higher electron micrograph illustrates the cross section of cilia (9 doublet+2, red arrows) and microvilli (blue arrows) in the surface of trachea.

Micrograph shows part of lamina propria and hyaline cartilage with its perichondrium. The perichondrium is a dense irregular connective tissue composed of spindle-shaped cells that resembles fibroblasts. In the cartilage, the chondrocytes (blue triangles) are arranged in clusters with lacunae.

Micrograph shows part of hyaline cartilage with its perichondrium. The perichondrium is composed of collagen fibres (Col) and spindle-shaped cells (F) that resembles fibroblasts, but these cells are transforming into small chondroblasts (Cb). Inside the cartilage, the chondrocytes (blue triangles) are arranged in clusters with lacunae.

Micrograph shows part of hyaline cartilage with its perichondrium. The perichondrium is composed of collagen fibres (Col) and spindle-shaped cells (F) that resembles fibroblasts, but these cells are transforming into small chondroblasts (Cb). Collagen fibres (Col) shown here include cross-sectioned (Col-c) and longitudinal-sectioned (Col-l)

Micrograph shows perichondrium of hyaline cartilage. The perichondrium is composed of collagen fibres (Col) and spindle-shaped cells (F) that resembles fibroblasts. Collagen fibres (Col) shown here include cross-sectioned (Col-c) and longitudinal-sectioned (Col-l). The banding pattern could be in longitudinal-sectioned collagen fibrils (Col-l).

The perichondrium is composed of collagen fibres (Col) and spindle-shaped cells (F) that resembles fibroblasts. Collagen fibres (Col) shown here include cross-sectioned (Col-c) and longitudinal-sectioned (Col-l). The banding pattern could be in longitudinal-sectioned collagen fibrils (Col-l, black dashed line).

A chondrocyte is lying within lacuna and surrounded by cartilaginous matrix material (M). The chondrocytes have very prominent rough endoplasmic reticulum (rER) which is distended with secretory material. Some recently secreted extracellular matrix material (MM) are shown here.