Cytology 3 PDF

By Dr. Eman Samy Endoplasmic reticulum (ER): is a membranous system, which branches inside the cytoplasm, it forms a continuous channels connecting the nuclear membrane and passible with the plasma membrane. Through these channels pass certain chemicals from the nucleus to the cytoplasm...

By Dr. Eman Samy Endoplasmic reticulum (ER): is a membranous system, which branches inside the cytoplasm, it forms a continuous channels connecting the nuclear membrane and passible with the plasma membrane. Through these channels pass certain chemicals from the nucleus to the cytoplasm and vice versa. Types of endoplasmic reticulum: Two types of endoplasmic reticulum can be recognized in the cytoplasm. Rough (granular) endoplasmic reticulum : is due to the presence of small dense granules, which are known as ribosome it is especially abundant in cells specialized for protein secretion e.g pancreatic cells. Role of RER in protein synthesis: 1. Amino acids are arranged in a certain place on the ribosomes, to form a specific polypeptide chain (protein) 2. The polypeptide chain will enter through the cisternae of RER. 3. The formed protein (semi- fluid) will be condensed at one end of RER where budding occurs forming transport vesicle. 4. Transport vesicle, transfers the formed condensed protein from RER to the immature face of Golgi apparatus.  Smooth endo plasmic reticulum (SER): It is made of branched tubules, Its limiting membrane is smooth with no ribosomes. Function of SER: Lipid synthesis. Drug detoxification >Calcium distribution.  Golgi Apparatus The Golgi apparatus varies in size from one type of cells to another. it is large and active in secretary cell, relatively smaller in cells in which no obvious secretory activity. Structure: a) Golgi apparatus of vertebrates seen by the electron microscope consists of a number of elongated flattened sacs or cisternae running parallel to each other. Each sac has a concave mature surface called transface and a convex immature surface, called cis face. b) Transport or micro vesicles: They are small rounded sacs filled with protein. These transfer vesicles originate from the rough endoplasmic reticulum. They fuse with the flat vesicles of Golgi apparatus where their contents are transformed into secretory vesicles. C) Secretory or Macro vesicles: The entered proteins are collected, concentrated and enveloped by membranes to be transformed into the following vesicles: 1-Excretory vesicles: containing the excreted enzymes and the excreted hormones. 2- Excreted protein vesicles: which migrate from Golgi area to the cell membrane. They help in the process of renewal of cell membranes. 3- Lysosomal vesicles: They carry inside them the Lysosomal enzymes. These Lysosomal vesicles remain in the cytoplasm as primary Lysosomes. Function of Golgi apparatus: Production of secretions in various types of externally secreting glands (e.g secretion of pepsin by peptic cells of stomach, bile by the liver cells). Golgi and the endoplasmic reticulum share in the formation of lysosomes. Pathological changes: 1. Vitamin B-complex deficiency causes fragmentation of the network of the Golgi apparatus of mammalian neurons. 2. Electrical stimulation, irradiation and phosphorous poisoning effects on the morphology and behavior of the Golgi apparatus. 3. Treatment with insecticides produce fragmentation to small particles.