Glandular Tissue

Glandular Tissue

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These are epithelial cells that are specialized for secretion. Two main types of glandsExocrine glands- communicate with the surface through a duct. Endocrine glands- convey secretions to the blood stream. The two main components of exocrine glands Secretory units and ducts

Glands may exist as: • single cell in an epithelium-unicellular glands (goblet cells) • groups of cells in the wall of a viscus, the secretions are conveyed by single or branched ducts into the lumen of the viscus (gastric glands - stomach) • distinct encapsulated structures. secretory units and branching duct system are arranged within a connective framework.(salivary glands, pancreas)

Glands with a duct system• Such a gland is divided into lobules by connective tissue septa- the interlobular septa extend from the capsule. • In the lobules, are secretory units and smaller ducts called the intralobular ducts lined by simple cuboidal epithelium. • These ducts communicate with the larger interlobular ducts that lie in the connective tissue septa. • The larger ducts have a thicker lining of stratified cuboidal or columnar epithelium and open into the main duct.

Classification and characteristic features of glands vary, depending on • the form and arrangement of the component parts • the nature of the secretion • the mechanism of secretion Structural variation of glands is according to • the shape of the secretary units- tubular (elongated), alveolar (ovoid) acinar(rounded) • the pattern of branching of the ducts- simple or unbranched, compound or branched

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Tubular secretory unit Acinar – grape like Alveolar–flask shaped Tubulo-alveolar / acinar

• Simple tubular – crypts of Lieberkuhnintestine • Simple coiled tubularsweat glands • Simple branched tubular- gastric glands • Simple acinar-urethral glands • Simple branched acinar – sebaceous glands

• Compound tubularBrunner’s glands • Compound acinarPancreas • Compound branched tubuloalveolarProstate • Compound branched tubuloacinarSubmandibular gland

Nature of secretion: • Glands may be serous, mucous or mixed. • Glands that secrete a watery or serous fluid are the serous glands (parotid salivary gland, exocrine pancreas). • Glands that secrete a thick mucous like secretion are mucous glands. • Mixed glands have serous, mucous and mixed units

Serous glands: • The secretory cells are arranged in serous units • cells have a deeply stained bluish granular cytoplasm due to the presence of ribosomes and secretory granules. • The nuclei are rounded and at the base of the cell. • The secretions are protein in nature.

Mucous gland: • The cells of a mucous unit have drops of mucous in their cytoplasm • Mucous stain pale with H&E and are PAS +ve. • The nuclei are pushed to the base of the cell by the mucous droplets. (sublingual gland) Mixed glands: • made up of mucous units capped by a crescentic mass of serous cells -serous demilunes. • In the mixed units, secretions from the serous cells pass through canals between the mucous cells to open into the lumen of a mucous unit

• There may be separate serous and mucous units also in a mixed gland. • Surrounding the secretory unit are myoepithelial cells or basket cells. • They have numerous cytoplasmic processes and a contractile function. • They help to expel the secretions into the lumen. Mechanism of secretion: 3 types Merocrine type Holocrine type Apocrine type

Merocrine type of secretion• Glands store their secretions in secretory granules • discharge the secretions into the lumen by exocytosis. (salivary glands, pancreas) Holocrine type of secretion• entire cell disintegrates and form the secretion and discharged into the lumen of the gland Sebaceous gland). Apocrine secretion: • part of the cytoplasm is discharged as secretion mammary gland, large axillary sweat glands .

Endocrines glands characterized by: • simple arrangement of cells in the form of cords or small groups found in close relation to capillaries. • The secretion may pass directly into the capillaries (pituitary, adrenal) or as in the thyroid, be stored in the lumen of a follicle.