Nucleus Histology PDF

HISTOLOGY dr.Mahmoud Mansour NUCLEUS Defnition:  The largest and most distinct component of all cells  contain genetic informations.  No nucleus in RBCs and platelets (not true cells)   Usually (mononucleated).  (...

HISTOLOGY dr.Mahmoud Mansour NUCLEUS Defnition:  The largest and most distinct component of all cells  contain genetic informations.  No nucleus in RBCs and platelets (not true cells)   Usually (mononucleated).  (binucleated) as liver cells.  (multinucleated) as skeletal muscles.  Usually central, may be eccentric, basal or peripheral.  Rounded, fattened, oval, kidney-shaped, segmented, lobulated, or bilobed. Page | 40 HISTOLOGY dr.Mahmoud Mansour  Dark blue with basic stains as hematoxylin or methylene blue.  Its basophilia is due its content of DNA & RNA.  1. Nuclear membrane (Envelope). 2. Chromatin material. 3. Nucleolus. 4. Nuclear sap. Page | 41 HISTOLOGY dr.Mahmoud Mansour Nuclear Membrane (Nuclear Envelope) Basophilic line due to:  chromatin on its inner side  ribosomes on its outer side  Double membrane formed of 2 unit membranes separated by perinuclear space.  interrupted at intervals by nuclear pores.  Outer nuclear membrane: It is rough & granular due to attached polyribosomes It is continuous with rER.  Inner nuclear membrane: It is fbrillar due to attached chromatin threads. It is associated with Lamins for stabilization of nuclear envelope.  Nuclear pore complexes: circular openings at intervals. Functions of nuclear pores: 1) Transport of proteins to the nucleus. 2) export of RNA & ribosomal subunits to the cytoplasm Page | 42 HISTOLOGY dr.Mahmoud Mansour Chromatin  (DNA + Histones & non-histone proteins).  two forms according to cell activity: Euchromatin Heterochromatin  Extended filaments  Coiled filaments nature  contain active genes  contain inactive genes  « seen as : Fine & coarse  Not seen (very thin basophilic granules (highly filaments) LM coiled filaments)  pale nucleus (vesicular -  Dark nucleus (closed face open face nucleus) nucleus)  Electron dense granules  Electron lucent among EM (mention sites of Heterochromatin heterochromatin)  Active : direct protein Function  Inactive. synthesis Page | 43 HISTOLOGY dr.Mahmoud Mansour Sites of heterochromatin: a) Peripheral Chromatin: attached to the inner surface of nuclear membrane. b) Chromatin islands: aggregated clumps scattered in the nuclear sap. c) Nucleolus-associated chromatin: condensed around the nucleolus. Page | 44