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Trachea-Pseudostratified columnar ciliated epithelium (plus hyaline cartilage trachea histology slide)

pseudostratified columnar ciliated epithelium(plus hyaline cartilage;  trachea histology slide)

The wall of trachea is formed of following layers from within outwards .
1. MUCOSA: It is comprised of the following layers.
a. Epithelium of trachea is pseudostratlfled ciliated tall columnar with goblet cells.
The ciliary activity produces constant movements of glandular secretions towards the pharynx. The epithelium is comprised of following cells.
I.  Columnar ciliated cells (each cell bears 300 cilia)
II. Goblet cells (secrete mucous material)

III. Brush cells: These are sensory receptor cells, which are columnar and non- ciliated. Microvilli are present.
Iv. Basal or short cells (act as stem cells): These occur in the depth of epithelium
between the bases of the other types of cells and are undifferentiated cells that give
rise to goblet cells or ciliated cells.
v. Neuroendocrine (Kulchltsky) cells
vl. Migrating lymphocytes and
vll. Migrating mast cells.
vlll. Dendritic cells: A network of dendritic cells lies along the base of tracheal epithelium which function as antigen-presenting cells, i.e.. these bind the antigens and then present it to the T-lymphocytes. All these cells are evident on electron microscope; while on light microscope, one can see'only columnar ciliated cells, goblet cells and basal cells.
II. The tracheal epithelium is supported by a thick basement membrane.
II.     Beneath basement membrane lamina propria consists of loose highly vascular connective tissue, which becomes condensed at its deeper aspects to form a band of fibroelastic tissue (clear elastic membrane).

II.   SUBMUCOSA: It contains loose areolar C.T. numerous mixed seromucous and mucous tracheal glands (which decrease in number in lower part of trachea), nerves, vessels and lymphoid follicles.

II.   CARTILAGE: The submucosa merges with the perichondrium of the underlying hyaline cartilage. These cartilages (16-20) are found in the form of C-shaped rings. Between the two ends of C-shaped cartilages the submucosa directlv merges with the external adventitial layer. Bands of smooth muscles (trachealls) join the free ends of the rings posteriorly. The contraction of muscle and resultant narrowing of the tracheal lumen are useful in cough reflex.

II.   ADVENTITIA/FIBROSA: it is formed of areolar C.T. containing small blood vessel and autonomic nerves to trachea.
Histology of this is similar to that of trachea except for following differences
A.     Respiratory epithelium is less tall
B.     Goblet cells are fewer in number
C.     Lamina propria is more dense with large amount of elastic fibers
D.    Trachealis muscle spreads out as a discontinuous layer of smooth muscle, which becomes progressively weaker downwards to surround the lumina of bronchi.
E.      Submucosa has fewer seromucous glands
F.      Cartilages are arranged in flattened Interconnected plates rather than C-shaped rings.
SECONDARY BRONCHUS: It has histology almost similar to that of primary bronchus 

TERTIARY BRONCHUS: The epithelium is tall columnar but not pseudostratlfled. Goblet cells are fewer in number. The lamina propria is thin, elastic and completely encircled by smooth muscles arranged in a spiral manner. The submucosa has fewer glands. Cartilage framework is reduced to few Irregular plates. The submucosa merges with adventitia and then with alveoli.

SMALLER BRONCHI: In the wall of smaller bronchi, the hyaline cartilage is present as small isolated cartilagenous plates or islands of cartilage called Insulae cartllagenae

BRONCHIOLE: When diameter of the tube reaches about 1mm, the cartilage disappears from the wall and structure is known as bronchiole . The epithelium is pseudostratlfled dilated and contain very few goblet cells which are completely absent beyond terminal bronchiole. The epithelium is folded. The smooth muscle Is disposed in spiral manner like bronchi; being the most prominent feature of bronchiole.
Extra-Pulmonary Bronchus
intra-Pulmonary Bronchus
Mucosal folds
Less folded
Highly folded
Epithelium & goblet cells
Pseudo-stratified columnar ciliated with many goblet
Pseudo-stratified columnar ciliated with few goblet cells
Cartilagenous tissue
C-shaped cartilagenous rings
Multiple plates of cartilage connected by C.T. (C-shaped cartilagenous rings absent)
smootfi muscles
Present only at the ends of C-shaped cartilage
Arranged as encircling the whole lumen inside the cartilage
Elastic fibres
Arranged as elastic membrane in C.T. of the lamina propria
Elastic fibres are distributed between cartilage plates and in the adventitia
Mucous glands
Present in submucosa
Present between cartilage plates and in the adventitia
Lymphoid follicles
 Comparison Between Two Types of Bronchi

Long, wide and its lumen is patent (not collapsed)
Short, narrow and its lumen may be collapsed as in bronchial asthma
Folded and lined by pseudostratified columnar epithelium (formed of seven types of cells similar to the tracheal tree)
Highly folded and lined with simple columnar ciliated or with cuboidal non-ciliated cells alternating with Clara cells
cell receptors
Goblet cells
Absent (few only in large bronchioles)
Lymphoid follicles In C.T. „
Plates of cartilage

The terminal bronchioles are lined with simple columnar or cuboldal epithelium. Few
Clara cells are also seen.

RESPIRATORY BRONCHIOLE: Towards periphery of chest bronchioiar epithelium becomes simple cuboldal . Number of air sacs open into its lumen at the antivascular border and now it is called as respiratory bronchiole. Goblet cells are completely absent. Non-ciliated Clara Cells become the prominent cell type in most distal parts of respiratory bronchiole. These cells secrete (I) surfactant (a phospholipid that reduces surface tension) and (II) glycosamlnoglycans that protect the bronchioiar lining. Bundles of smooth muscle become more prominent, which are discontinuous. Elastic C.T. is also prominent.
ALVEOLAR DUCTS: The respiratory bronchioles continue into thin walled small tubes called alveolar ducts . The walls of these ducts are studded with alveolar sacs and alveoli, which open into lumen of the duct. The lining epithelium is simple squamous or low cuboldal. The lamina propria consists of smooth muscles and connective tissue containing elastic and collagen fibers. Alveolar ducts terminate into pulmonary atria, which are Irregular spaces from which alveolar sacs and alveoli diverge. Elastic and reticular fibers form a complex network encircling the opening of atria, alveolar sacs and alveoli. The elastic fibers enable the aiveoli to expand with inspiration and contract passively with expiration. Reticular fibres serve as a support that prevent overdistension and damage to delicate capillaries as well as thin alveolar septa.
alveolar sacs (air sacs): These are groups of cup shaped structures (alveoli with 200 nm diameter and are the structural and functional units of respiratory gas exchange) with very thin walls and open into a common central space  . Because of interdigitating arrangement each alveolus does not have a completely separate wall. Adjacent alveoli are separated from each other by Interalveolar septa.

1.   PULMONARY ALVEOLI: These open directly into alveolar sacs or alveolar ducts or respiratory bronchioles and are lined by two types of squamous epithelial cells (pneumocytes).

I.     Type-l cells: Squamous alveolar cells are most numerous (97%) and form a very thin but complete lining of all alveoli. These cells possess a low flat nucleus and minimum cytoplasm. These possess microvilli at their alveolar surface. These have thin basement membrane, which fuses with basement membrane of endothelium of blood capillaries. These cannot divide. Main role of these cells is to provide a barrier of minimal thickness that is readily permeable to gases as well as these contain pinocytotic vesicles suggesting a probable role in surfactant turnover.

II.   Type-ll Cells/Great Alveolar Cells/Secretory Cells/ Septal Cells (3%): These are cuboldal In shape and occur in the form of groups present at corners of alveolar walls. Luminal surfaces of these cells bear microvilli. Their cytoplasm gives a vacuolated appearance due to presence of lamellar bodies of 1-2 nm in diameter (cytosomes), which contain phospholipids, proteins and glycosaminoglycans. These substances are secreted into alveoli as surfactant.

2.      INTERALVEOLAR SEPTUM: It is the two layers of squamous epithelial cells in
between which lies the Interstltlum possessing richest capillary network of the body, fibroblasts, elastic and reticular fibres and macrophages. The interalveolar septum is composed of: (1) capillary endothelial type cells (30%); (2) type I pneumocytes (08%); (3) type II pneumocytes (16%); interstitial cells (mast cells and fibroblasts etc.) (36%) and; (4) alveolar macrophages (10%).

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