Histology of Salivary Glands

What is a gland? Gland is an organ of secretion made up of specialized secretory cells derived from the surface epithelium on which it opens.

General Features Epithelial in origin Present as discrete organs or in layers. Secretory cells form functional units called secretory end pieces- may be flask (Acinus)or cylindrical (Tubular)shaped

Types of Secretory units

General Features Fluid secreted may be enzymes, hormones or mucus. Secretion is modulated by nervous and hormonal influences. Myoepithelial cells- star shaped, contractile, lie between the secretory cells and the basement membrane

Mixed Salivary Gland

Development Develop as invagination of the epithelium into the underlying vascular connective tissue. Distal part forms glandular or Secretory end Piece – functionally an active portion. Proximal part-Excretory Duct-opens on the surface of the epithelium Some cells get detached from the epithelial surface- Ductless or endocrine glands

Development of Gland

Glandular Epithelium

Classification of Glands Based on the site of Secretion Exocrine Gland Endocrine Gland Paracrine Gland- secretes its products into the local extracellular space affecting the surrounding cells e.g. enteroendocrine cells of gastrointestinal tract (GIT)

Classification of Glands Based on the Number of cells Unicellular Gland- goblet cells in the respiratory and intestinal tracts Multicellular Gland- all glands other than goblet cells

Classification of Glands Based on the Number of Ducts and the shape of secretory end piece Simple Gland- one duct Compound Gland- has minor and major ducts Both the types are further subdivided into Tubulo, Alveolar/Acinar or Tubulo-alveolar/acinous

Multicellular Glands

Compound Tubulo-alveolar

Compound Tubulo-alveolar

Compound Glands Simple Alveolar-Penile urethra Simple Branched alveolar-Sebaceous gland Compound Alveolar- Pancreas, Parotid, Mammary gland and glands of Respiratory tract. Simple Tubular-Crypts of Leiberkuhn Simple branched tubular-Uterine glands,Pyloric and fundic glands Compound Tubular-Brunner’s Gland, Cardiac glands Simple coiled tubular-Sweat gland Compound Tubulo-alveolar- Submandibular & Sublingual salivary glands

Mixed Salivary Gland

Classification of Glands Based on the Mode of Secretion Merocrine Gland- No loss of Cytoplasm-e.g. most of the compound glands e.g. Pancreas Also known as Eccrine or Epicrine Apocrine Gland- Partial loss of cytoplasm-e.g. lactating mammary gland, sweat glands in the axilla and external genitalia Holocrine Gland- Complete loss of cytoplasm e.g. sebaceous and tarsal gland Cytocrine Gland- Cells are released as secretion. e.g. Testis (spermatozoa)

Modes of Secretion

Classification of Glands Based on the Nature of Secretion Serous Gland- thin, watery secretion rich in enzymes e.g. Parotid gland Mucous Gland- thick, viscous secretion for protection and lubrication. e.g. Sublingual salivary gland Mixed Gland (seromucous)- both watery and viscous material.e.g. Submandibular salivary gland

Difference between Serous & Mucous Acini Thin, watery Proteinaceous secretion Zymogen granules in cyto Central rounded Nucleus Small Lumen Indistinct cell bondaries Darkly stained Enzymatic action Parotid Gland Mucous Thick, viscous Mucopolysaccharides Mucigen droplets Nucleus-flat & peripheral Large Lumen Distinct cell boundaries Lighly stained Protection & lubrication Sublingual gland

Mixed salivary gland Serous Acini Mucous Acini Seromucous Acini- having Serous demilunes

General Architecture of a Compound Gland Gland may be divided into lobes and lobules. Parenchyma- Secretory end pieces- Acini/tubules /tubulo-acinar) Ducts- Intralobular, interlobular, main excretory duct Stroma Capsule Septa (interlobular, interlobar) Loose intralobular connective tissue supporting the parenchyma

Clinical ADENOMA: Benign tumors arising in the gland ADENOCARCINOMA: Malignant growth in the gland

Serous Acinus

Ducts

Striated Duct Larger than the acinus Eosinophilic columnar cells Central nuclei Vertical Cytoplasmic stiations due to foldings in the basal plasma membranes

Parotid Gland

Parotid Gland

Intra-glandular adipose tissue in parotid gland

Submandibular Gland

Submandibular Gland

Mixed Salivary Gland

Mucous Acini

Sublingual-purely mucous gland

Sublingual

Minor salivary glands of Palate Aggregations of Mucous acini No striated duct

Minor salivary glands of Palate(High Power) Mucous acini with central Lumen Large Pyramidal cells with granular cytoplasm Nucleus towards the basement membrane

The minor salivary glands are small aggregates of unencapsulated mucous or serous glands. In the tongue they are in intimate contact with the striated muscle tissue.

Keratin cocktail stains intercalated, striated and interlobular ducts, but acinar and myoepithelial cells are mostly negative.

MCQ The serous gland can be identified by the presence of serous acinus with A) Small Lumen B)Large Lumen C)Flat peripheral Nuclei D)Mucigen droplets

MCQ When there is a complete loss of cytoplasm resulting in cell death of the secretory cell during the process of secretion, the gland is said to be A) Merocrine B) Apocrine C) Holocrine D) Cytocrine

MCQ Sebaceous gland is an example of Holocrine gland Apocrine gland Merocrine gland Unicellular gland

MCQ Mucous Acinus A) Secretes thin watery fluid B) Has flat, peripheral nucleus C) Has a small lumen D) Contains zymogen granules

MCQ Sweat glands in the axilla are an example of A) Merocrine gland B) Apocrine gland C) Holocrine gland D) Cytocrine gland