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Histology 1.4. : Glands Gland: a single epithelial cell, or grouping of cells specialized for secretion. Secretion: energy-consuming process by which the.

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Presentation on theme: "Histology 1.4. : Glands Gland: a single epithelial cell, or grouping of cells specialized for secretion. Secretion: energy-consuming process by which the."— Presentation transcript:

1 Histology 1.4. : Glands Gland: a single epithelial cell, or grouping of cells specialized for secretion. Secretion: energy-consuming process by which the cell takes up small molecules and transforms them via intracellular biosynthesis into a more complex product then actively releases it from the cell. The product is utilized by the organism in several ways. Excretion: the organism gets rid of harmful or toxic metabolic end-products or useless waste material.

2 Classification of glands: I. Based on morphology: unicellular and multicellular Unicellular, intraepithelial gland: goblet cell Intestinal epithelium: simple columnar epithelium (2) goblet cells (1) the arrow shows the nucleus (3) TEM image of the same type of unicellular gland, the goblet cell

3 CLASSIFICATION OF MULTICELLULAR GLANDS: With ducts: exocrine glands Without ducts: endocrine glands

4 CLASSIFICATION OF EXOCRINE GLANDS (based on morphology): Simple tubular Coiled tubular Branched tubular Simple acinar Branched acinar Compound tubular Compound acinar Compound tubuloacinar

5 SOME EXAMPLES: Simple tubular gland: intestinal gland of Lieberkühn Schematic drawingLM microphoto

6 Coiled tubular gland: sweat glands of the skin Schematic drawingLM microphoto

7 Branched tubular gland: fundic glands in the stomach Schematic drawingLM microphoto

8 Fundic gland from the stomach - endpiece

9 Simple acinar gland: Frog skin: mucous and toxin-producing glands Compact form without lumen: sebaceous gland of mammalian skin

10 Branched acinar gland: larger sebaceous glands of the skin

11 Compound tubular gland: esophageal gland lumen capillary secretory acini capillary duct segment

12 Compound tubuloacinar glands: Mandibular glandParotid gland

13 Composition of compound glands: Parenchyma composed of lobes and lobules, ducts The duct system of the compound glands: Acinus Intercalated duct Striated (salivary duct) Interlobular duct Lobar duct Main duct

14 Model of the gland: a bunch of grapes: berry= acinus stalk of berry: intercalated duct

15 Intralobular striated (salivary) duct Interlobular duct

16 II. Type of secretory product: 1.Serous gland: composed of acini with narrow lumen (1) secretory cells have round, basally located nuclei (2) the cytoplasm of the cells is basophilic (3) Pancreas (see the micrograph) and parotid gland are purely serous producing thin watery fluid rich in proteins (mainly enzymes) 1 2 3

17 2. Mucous glands:composed of acini with wide lumen secretory cells have flattened nuclei at the base their cytoplasm is very weakly stained Esophageal glands (see the micrograph) are purely mucous producing thick viscous fluid, rich in mucopoly-saccharides for lubrication and protection of internal body surfaces

18 3. Seromucous glands: mucous acini surrounded by serous cells forming a demilune shape The submandibular gland of some species (monkey, human, cattle) is seromucous. Red arrows point at mucous cells, blue arrows point at the demilune –shaped group of serous cells (Demilune of Gianuzzi)

19 Seromucous gland, haematein-eosin staining Seromucous gland, alciane blue staining

20 III. Modes of secretion: 1.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 pancreasSubmandibular gland

21 2. Apocrine secretion: the secretum is gathered at the apical portion of the cell the 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 droplet the cell remains alive, but a part of it goes with the secretory droplet Examples: sweat and mammary glands

22 Membrane-bound secretory droplets of a sweat gland

23 3. Holocrine secretion: the secretory cell gradually fills up with secretum the secretory cell gradually fills up with secretum the cell organelles degenerate the cell organelles degenerate the cell dies, its membrane breaks and the secretum empties the cell dies, its membrane breaks and the secretum empties The sebaceous gland is a holocrine gland. Dead cells are replaced by the mitotic divison of basal cells

24 Absorptive epithelium: its main function is to absorb. Morphology of these epithelial cells exhibit its main function is to absorb. Morphology of these epithelial cells exhibit cuticular border (intestine) or brush border (kidney tubules). Please note: at fine structural level both are microvilli ! Intestinal epithelium: the arrow shows the cuticular border EM micrograph of the apical surface with microvilli

25 Pigmented epithelium: Epithelial cells contain melamosomes: brown color Pigmented epithelium in the eye at LM level shows brown pigmentation. At EM level the melanosomes appear as electron dense bodies in the cytoplasm. LM EM

26 Sensory epithelia: Main function is sensation Types: primary, secondary sensory epithelium true nerve cells Primary sensory epithelium: olfactory epithelium

27 Secondary type of sensory epithelia: Example: sensory cells of the taste buds


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