Cytology Non-Membranous Organelles PDF

 Cytology Non-Membrous organelles Dr. Dalia Eita  Intended learning outcomes (ILOS) At the end of this lecture, the student will be able to: Identify the structure and functional importance of Cytoplasmic Filaments,  RIBOSOMES non-membranous cell org...

 Cytology Non-Membrous organelles Dr. Dalia Eita  Intended learning outcomes (ILOS) At the end of this lecture, the student will be able to: Identify the structure and functional importance of Cytoplasmic Filaments,  RIBOSOMES non-membranous cell organelles concerned with protein synthesis in the cell. L/M: Stain: With basic stains (e.g. hematoxylin and methylene blue), they exhibit basophilia when present in large number in the cytoplasm due to rRNA. Molecular structure: composed of ribosomal RNA (rRNA) and proteins.  E/M: The individual ribosome appears as an electron dense granule composed of two subunits (small and large subunits). They may be held together by messenger RNA forming polyribosomes. Types of ribosomes: 1. Free ribosomes: scattered individually or attached to mRNA forming polyribosomes (polysomes) in the cytoplasm. 2. Attached ribosomes: attached to the outer surface of the endoplasmic reticulum rER. Functions of ribosomes: Ribosomes synthesize proteins, as they translate the message, which is carried by mRNA. a- Free ribosomes are concerned with synthesizing proteins for the use of the cell. b- Attached ribosomes are concerned with synthesizing proteins to be secreted outside the cell.  CYTOPLASMIC FILAMENTS Definition: They are non-membranous organelles. They are thread-like structures present in variable amounts in different cells. Subclasses of cytoplasmic filaments 2.Thick 3- 1-Thin filaments Intermediate filaments filaments  1-Thin filaments: Called micro-filaments, e.g. actin filaments. They are contractile filaments as they inter- act with myosin. E/M: They are slender rods, 6-7 nm in diameter. Distribution & function of thin filaments in the cell: 1-In the microvilli, for their movement. 2-In the cleavage furrow during cell division. 3-In muscles, for contraction 4-In blood platelets, for clot retraction.  2-Thick filaments: They are composed of myosin. They are thicker than thin filaments They have variable diameters (12-16 nm). Distribution: In muscle in association with actin filaments forming the myofibrils.  3-Intermediate filaments: Five types could be identified by using immuno-cytochemical techniques. Functions: Not capable of producing contraction. 1- Play a major role in supporting Each type has a distinct biochemical and maintaining the shape composition: of the cells. A) Desmin filaments. 2- In epithelial cells, they are B) Tonofilament. present in sites of adhesion between cells. C) Vimentin filaments. 3- Important for tumor D) Neuro-filaments. identifications. E) Glial filaments.  MICROTUBULES Definition: They are pipe-like structure of unfixed length but are of uniform diameter. Distribution: All over the cytoplasm. E/M:  They appear as hollow tubules.  The wall consists of 13 protofilaments that are composed of tubulin dimers.  In cross section they appear as tiny circles.  Function: 1. components of the cytoskeleton supporting, and maintaining the shape of the cell. 2. the main structural component of cilia, flagella and centeriole. 3. important for mitotic spindle formation. 4. act as guiding tracks for transporting material and organelles. Clinical hints: - Cytotoxic drugs as colchicine and vinblastine prevent the assembly of new microtubules. - Therefore, these drugs are used in malignant diseases as they arrest mitosis.  CENTROSOME It is a specialized zone of the cytoplasm which contains two centrioles oriented at right angle to each other. CENTRIOLES Definition: It is a non-membranous cell organelle important for cell division. Site: In nondividing cells the centriole pairs are found in juxtanuclear position and in association with Golgi apparatus. L/M: - H. & E.: could not be demonstrated. - Iron H.: They appear as two dark blue stained granules. E/M: Each centeriole appears as a short cylinder with one open end and the other end is closed. The wall of each cylinder is composed of 27 microtubules longitudinally arranged in 9 bundles. Each bundle consists of three micro- tubules (triplets) which are surrounded by fibrillar electron dense material. Function: 1- Play an important role in cell division (formation of the mitotic spindle). 2- In ciliated epithelium, each centriole replicates and gives a number of basal bodies of cilia. At E/M level the centrioles shows: a. nine triplets of microtubules and two central singles b. nine triplets of microtubules and no central singles c. nine doublets of microtubules and two central singles d. nine doublets of microtubules and no central singles  CILIA Definition: They are hair like processes projecting from the free surface of certain epithelial cells e.g. in the respiratory system (trachea and bronchioles), in female genital system (uterus and fallopian tube). L/M: Number: may be several hundreds/cell EM: Each cilium is formed of a shaft, basal body and rootlets. 1. The shaft: -also called axoneme. - surrounded by a cell membrane. - contains nine peripheral doublets of microtubules extending along its longitudinal axis and two singlets microtubules in the center. -The microtubules of the singlets are complete and are surrounded by a central sheath. -The microtubules of the nine doublets are complete in subunit-A and incomplete in subunit-B. 2. The basal body: It is a short cylindrical structure and has an identical appearance to a centeriole i.e. its wall contains nine triplets of microtubules. 3. The rootlets: They are striated fibers, which anchor the basal body to the surrounding cytoplasm.  Function of the cilia: 1- Cilia are beating rhythmically in one direction to move a thin film of fluid or mucous which is present on the surface of the cell. 2- Cilia may become modified to receive light stimuli, e.g. rods and cones in the retina. N.B.: Stereocilia are non-motile cilia and have no microtubules in their structure e.g. epidydimis.  FLAGELLA  They are cytoplasmic processes, e.g. Tail of a spermatozoan. Structure:  They are similar to cilia, having nine peripheral doublets of micro- tubules and a central singlet. However:-  They are much longer than cilia.  They have whip-like swimming movement. Number: one flagellum/cell. At E/M level, a cross section of basal body shows: a- nine triplets of microtubules and two central singles b- nine triplets of microtubules and no central singles c- nine doublets of microtubules and two central singles d- nine doublets of microtubules and no central singles e- nine doublets of microtubules and one central single Dr. Dalia Eita References  Junqueira LC, Carneiro J: Junqueira’s Basic Histology. Text and Atlas, fourteenth edition, Copyright © 2016 by McGraw-Hill Education.  Student medical histology book, Mansoura university.