Histology 1.4. : Glands

Histology 1.4. : GlandsHistology 1.4. : Glands

Gland:Gland: a single epithelial cell, or grouping of cells specializeda single epithelial cell, or grouping of cells specializedfor secretion.for secretion.

Secretion:Secretion: energy-consuming process by which the cell takes up energy-consuming process by which the cell takes upsmall molecules and transforms them via intracellular small molecules and transforms them via intracellular biosynthesis into a more complex product then activelybiosynthesis into a more complex product then activelyreleases it from the cell. The product is utilized by thereleases it from the cell. The product is utilized by theorganism in several ways.organism in several ways.

Excretion:Excretion: the organism gets rid of harmful or toxic metabolic the organism gets rid of harmful or toxic metabolicend-products or useless waste material.end-products or useless waste material.

Classification of glands:Classification of glands: I. Based on morphology: unicellular and multicellularI. Based on morphology: unicellular and multicellularUnicellular, intraepithelial gland:Unicellular, intraepithelial gland: goblet cell goblet cell

Intestinal epithelium: Intestinal epithelium: simple columnar epithelium (2)simple columnar epithelium (2)goblet cells (1)goblet cells (1)the arrow shows the nucleus (3)the arrow shows the nucleus (3)

TEM image of the sameTEM image of the sametype of unicellular gland,type of unicellular gland,the goblet cellthe goblet cell

CLASSIFICATION OF MULTICELLULAR GLANDS:CLASSIFICATION OF MULTICELLULAR GLANDS:

With ducts: exocrine glandsWith ducts: exocrine glands Without ducts: endocrine glands Without ducts: endocrine glands

CLASSIFICATION OF EXOCRINE GLANDSCLASSIFICATION OF EXOCRINE GLANDS(based on morphology):(based on morphology):

Simple tubular

Coiled tubular

Branched tubular

Simple acinar

Branched acinar

Compound tubular

Compound acinar

Compound tubuloacinar

SOME EXAMPLES:SOME EXAMPLES:

Simple tubular glandSimple tubular gland:: intestinal gland of Lieberkühn intestinal gland of Lieberkühn

Schematic drawingSchematic drawing LM microphotoLM microphoto

Coiled tubular glandCoiled tubular gland: sweat glands of the skin: sweat glands of the skin

Schematic drawingSchematic drawing LM microphotoLM microphoto

Branched tubular gland:Branched tubular gland: fundic glands in the stomach fundic glands in the stomach

Schematic drawingSchematic drawing LM microphotoLM microphoto

Fundic gland from the stomach - endpieceFundic gland from the stomach - endpiece

Simple acinar gland:Simple acinar gland:

Frog skin: mucous Frog skin: mucous and toxin-producing glandsand toxin-producing glands

Compact form Compact form without lumen:without lumen:sebaceous gland ofsebaceous gland ofmammalian skinmammalian skin

Branched acinar gland:Branched acinar gland: larger sebaceous glands of the skinlarger sebaceous glands of the skin

Compound tubular gland: esophageal glandCompound tubular gland: esophageal gland

lumencapillarysecretory acini

capillary

duct segment

Compound tubuloacinar glands:Compound tubuloacinar glands:

Mandibular glandMandibular gland Parotid gland Parotid gland

Composition of compound glands:Composition of compound glands:Parenchyma composed of lobes and lobules, ductsParenchyma composed of lobes and lobules, ducts

The duct system of the compound glands:The duct system of the compound glands:

AcinusAcinus

Intercalated ductIntercalated duct

Striated (salivary duct)Striated (salivary duct)

Interlobular ductInterlobular duct

Lobar ductLobar duct

Main ductMain duct

Model of the gland: a bunch of grapes: berry= acinusModel of the gland: a bunch of grapes: berry= acinus

stalk of berry: intercalated ductstalk of berry: intercalated duct

Intralobular striated (salivary) ductIntralobular striated (salivary) duct

Interlobular ductInterlobular duct

II. Type of secretory product:II. Type of secretory product:

1.1. Serous gland: Serous gland: composed of acini with narrow lumen (1)composed of acini with narrow lumen (1)secretory cells have round, basally located nuclei (2)secretory cells have round, basally located nuclei (2)the cytoplasm of the cells is basophilic (3)the cytoplasm of the cells is basophilic (3)

Pancreas Pancreas (see the micrograph)(see the micrograph)and parotid glandand parotid glandare purely serousare purely serousproducing thinproducing thinwatery fluidwatery fluidrich in proteinsrich in proteins(mainly enzymes)(mainly enzymes)

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2. Mucous glands:2. Mucous glands: composed of acini with wide lumencomposed of acini with wide lumensecretory cells have flattened nuclei at the basesecretory cells have flattened nuclei at the basetheir cytoplasm is very weakly stainedtheir cytoplasm is very weakly stained

Esophageal glandsEsophageal glands(see the micrograph)(see the micrograph)are purely mucousare purely mucousproducing thickproducing thickviscous fluid, rich inviscous fluid, rich inmucopoly-mucopoly-saccharidessaccharidesfor lubrication and for lubrication and protection of internal protection of internal body surfacesbody surfaces

3. Seromucous glands: 3. Seromucous glands: mucous acini surrounded by serous cellsmucous acini surrounded by serous cellsforming a demilune shapeforming a demilune shape

The submandibular gland of some species (monkey, human, cattle) is The submandibular gland of some species (monkey, human, cattle) is seromucous. Red arrows point at mucous cells, blue arrows point at seromucous. Red arrows point at mucous cells, blue arrows point at the demilune –shaped group of serous cells (Demilune of Gianuzzi)the demilune –shaped group of serous cells (Demilune of Gianuzzi)

Seromucous gland, haematein-eosinSeromucous gland, haematein-eosinstainingstaining

Seromucous gland, alciane blue Seromucous gland, alciane blue stainingstaining

III. Modes of secretion:III. Modes of secretion:

1.1. Merocrine secretion:Merocrine secretion: • The secretory process is an exocytosisThe secretory process is an exocytosis• The secretory cell remains completely intactThe secretory cell remains completely intact• Most of the glands secrete in a merocrine mannerMost of the glands secrete in a merocrine manner

Exocrine pancreasExocrine pancreas Submandibular glandSubmandibular gland

2. Apocrine secretion: 2. Apocrine secretion: • the secretum is gathered at the apical portion of the cellthe secretum is gathered at the apical portion of the cell• the secretum leaves the cell membrane-bounded (pinched off)the secretum leaves the cell membrane-bounded (pinched off)• the cell remains alive, but a part of it goes with the secretory the cell remains alive, but a part of it goes with the secretory dropletdroplet

Examples: sweat and mammary glandsExamples: sweat and mammary glands

Membrane-bound secretory droplets of a sweat glandMembrane-bound secretory droplets of a sweat gland

3. Holocrine secretion:3. Holocrine secretion:

• the secretory cell gradually fills up with secretumthe secretory cell gradually fills up with secretum• the cell organelles degenerate the cell organelles degenerate • the cell dies, its membrane breaks and the secretum emptiesthe cell dies, its membrane breaks and the secretum empties

The sebaceous gland is a holocrine gland. Dead cells are replaced The sebaceous gland is a holocrine gland. Dead cells are replaced by the mitotic divison of basal cellsby the mitotic divison of basal cells

Absorptive epithelium: its main function is to absorb. Morphology of these epithelial cells exhibitits main function is to absorb. Morphology of these epithelial cells exhibitcuticular border (intestine) or brush border (kidney tubules).cuticular border (intestine) or brush border (kidney tubules).Please note: at fine structural level both are microvilli !Please note: at fine structural level both are microvilli !

Intestinal epithelium: the arrow shows Intestinal epithelium: the arrow shows the cuticular borderthe cuticular border

EM micrograph of the apicalEM micrograph of the apicalsurface with microvillisurface with microvilli

Pigmented epithelium:Pigmented epithelium:Epithelial cells contain melamosomes: brown colorEpithelial cells contain melamosomes: brown color

Pigmented epithelium in the eyePigmented epithelium in the eyeat LM level shows brown pigmentation.at LM level shows brown pigmentation.

At EM level the melanosomes appear as At EM level the melanosomes appear as electron dense bodies in the cytoplasm.electron dense bodies in the cytoplasm.LMLM

EMEM

Sensory epithelia:Sensory epithelia:Main function is sensationMain function is sensationTypes: Types: primary, secondary sensory epitheliumprimary, secondary sensory epithelium

true nerve cellstrue nerve cells

Primary sensory epithelium: olfactory epitheliumPrimary sensory epithelium: olfactory epithelium

Secondary type of sensory epithelia:Secondary type of sensory epithelia:

Example: sensory cells of the taste budsExample: sensory cells of the taste buds