Glands

Glands

1. Classification

   • EXOCRINE
     • Apical Secretion
       • On free epithelial surface
     • Pass through duct
   • ENDOCRINE
     • Basal Secretion
       • On to underlying connective tissue
       • Secrete hormones
       • Pass through tissue fluid and blood vessels

2. Origin of endocrine glands

   • Epithelial
     • don't retain connection
   • Neuronal
     • ultimately have different phenotypes
     • Morphology retained

3. Single endocrine/exocrine cells in epithelium known as cells

4. Exocrine Shape

   • Simple
     • Unit drains directly onto surface
       • With or without duct
     • E.g. sebaceous and sweat glands
     • Rare as unwise to have perforations in protective epithelial layer
   • Compound
     • Branching duct system
     • Common
     • Epithelial layer weakened at only one place
     • Long ducts allow for duct to be far from excretion site

5. Exocrine Secretions

   • Mucous
     • Made up of mucous cells
       • Pale staining
       • Flattened nucleus
       • Collumnar
     • Secrete proteoglycans (mucus)
     • Form tubular units
   • Serous
     • Made up of serous cells
       • Pyramidal
       • Strong staining due to protein
       • Round nuclei
     • Secrete proteins
       • Mainly enzymes
     • Forms alveolar units
   • Mixed
     • Both mucus and serous
     • Tubular and alveolar units
     • Mixed units- Serous demilunes

6. Endocrine Glands

   • Unique structure means they can't be classified in same way
   • Thyroid
     • Produce T3 and T4
       • Regulate metabolic rate
       • Lipophilic
         • On formation immediately diffuse out of cell to target cells
     • T3 and T4 maintained by TGB
       • TGB produced and secreted by cells but stored in gland
     • Cells arranged in follicles
       • made of cuboidal cells
       • TGB can be secreted into follicle lumen
       • When T3 and T4 needed cuboidal cells take up TGB and break it down
     • Enlarged thyroid is known as goitre
       • Caused by defective TGB synthesis
         • Deficiency of I2
           • Animals grazing far from sea
         • Impaired I2 absorption
         • Enzyme defects impairing TGB iodination
   • Adrenal
     • Three or more glands in one
     • Adrenal medulla
       • Derived from from sympathetic neurones
       • Neurohormone secreted into blood
         • Mainly adrenaline
     • Adrenal cortex
       • Secrete steroid hormones
       • Zona
         • Glomerulosa
         • Fasciculata
         • Reticulata