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INCLUSIONS AND SECRETORY GRANULES
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LEARNING OBJECTIVES:
By the end of the lecture, the student should be able to:
• Identify Cytoplasmic inclusions with example of each.
• List the Types of glycogen particles.
• Differentiate between Exogenous and endogenous pigments.
• Recognise Crystals and crystalloids
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Cytoplasmic Inclusions
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The inclusions are small particles of insoluble substances suspended in the Cytosol
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Inclusions are
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– stored nutrient
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– secretory products,
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– Pigment granules.
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Examples of inclusions are
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– glycogen granules in the liver and muscle cells,
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– lipid droplets in fat cells,
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– pigment granules in certain cells of skin and hair,
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Water containing vacuoles.
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Intranuclear inclusions (INI) and cytoplasmic inclusions (CI) in the motor cortex of
Huntington's disease
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Previously, inclusions were considered as non living accumulations of metabolites, cell products
resulting from synthesis, or materials from outside taken into the cell.
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Now it is known that many of them participate in the normal functioning of cell now.
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Liver section from a patient with glycogen-storage disease type IV stained with hematoxylin and
eosin. Hepatocytes are typically enlarged 2-fold to 3-fold, with faintly stained basophilic
cytoplasmic inclusions.
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Secretory Granules or Droplets:
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Bodies such as secretory granules or droplets formerly considered
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Secretory Granules or Droplets:
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Bodies such as secretory granules or droplets formerly considered as cytoplasmic inclusions , but
these are membrane bound packets of enzymes.
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Examples of Inclusions
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1. Stored foods in the form of carbohydrates and fats, which are stored in the cytoplasm as
energy reserves.
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Electron micrograph of a lipid droplet in the cytoplasm; the droplet contains triacylglycerols, the
main form of stored fat.
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Carbohydrates as a food material is absorbed from the intestine mainly as glucose and stored in
the form of polysaccharide glycogen.
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Glycogen:
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Water soluble.
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Gives a “moth – eaten” appearance to the cytoplasm.
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GLYCOGEN IN LIVER CELLS
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Stained with carmin, nuclei are stained with haematoxylin.
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1 - Glycogen (red or magenta staining)
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2 – Nuclei.
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GLYCOGEN IN LIVER CELLS Stained with carmin, nuclei are stained with haematoxylin
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1 - Glycogen (red or magenta staining) 2 – nuclei.
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Types of glycogen particles
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Two types of glycogen particles visible under transmission electron microscopy .
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– Beta particles
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– Alpha particles
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Beta particles :
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– Round, average diameter of 15 to 30 nm .
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Alpha particles
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Complexes of beta particles in the form of rosettes or alpha particles
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About 50 to hundred nanometers in diameter.
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Glycogen alpha particles in human liver
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Fat Cells
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Stored mainly in connective tissue as fat cells.
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Isolated in cytoplasm as membrane bound vacuoles and droplets containing neutral fats
(triglycerides), fatty acids, cholesterol and cholesterol esters.
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Fat droplets:
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Fat droplets appear to arise in the golgi apparatus and in relation to agranular reticulum and
are bounded by a membrane 6 to 7 nanomertes thick .
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Pigments
Materials that display colour without having been stained.
May be:
• Exogenous.
• Endogenous.
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High power stain is positive for melanin pigment at the basal cell layer and superficial lamina
propria.
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Exogenous Pigments
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Taken in by the organism from the environment.
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– Include carotenes, yellowish red pigments of vegetables that are fat soluble ( lipochromes) ;
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– Include dusts that is carbon which is particularly prominent in the cells of the lungs and
associated lymph nodes;
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– And minerals such as lead and silver.
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Endogenous Pigments
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Formed in the organism.
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– Most imp endogenous pigment is hemoglobin.
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– Melanin is an endogenous dark – brown or black pigment found in the skin and eye.
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– Melanin is produced in sun tanning and is
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produced in large amounts in the epidermis of negroid races.
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Lipofuscin
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Yellowish brown granules.
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Now considered to be membrane bound, indigestible residue of lysosomal activity.
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Amount of lipofuscin in cells increases with age.
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Cell is not able to get rid of lipofuscin by exocytosis, it accumulate in the form of residual
bodies.
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Crystals and Crystalloids
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Occur in few cell types.
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Seroli’s cells (sustentacular) and interstitial cells of the testis store these in the cytoplasm as non
– membrane bound packets.
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Also occur in some microbodies (peroxisomes).
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Occasionally within mitochondria associated with cristae