Non-Membranous Organelles PDF

Lecture 3 By the end of the lecture, the student should be able to: ▪ Explain the general structure of the cell. ▪ Enumerate components of the cytoplasm. ▪ Correlate structures to functions of non-membranous.  Cytology Cell. -It is the structural and functional unit...

Lecture 3 By the end of the lecture, the student should be able to: ▪ Explain the general structure of the cell. ▪ Enumerate components of the cytoplasm. ▪ Correlate structures to functions of non-membranous.  Cytology Cell. -It is the structural and functional unit of any tissue. -The cell consists of nucleus and cytoplasm The cytoplasm composed of: 1. Cytoplasmic matrix. 2. Cell organelles. 3. Inclusions. 1. The cytoplasmic matrix -This is the part of cytoplasm between the organelles and the inclusions. - It is a colloidal solution composed of soluble proteins, amino acids, carbohydrates, enzymes, minerals and ions.  2- Cell organelles These are specialized intracellular living structures permanently present in the cell to perform specific functions. They divided into: Membranous organelles Non-membranous organelles 1. The cell membrane 1. Ribosomes 2. Mitochondria. 2 cytoskeleton A- Microtubules 3. Endoplasmic reticulum(rER &sER) (Centriole& cilia) 4. Golgi apparatus. B- Filaments 5. Lysosomes. (thin, thick& intermediate) 6. Secretory vesicles.  1. Ribosomes Definition: It is a non-membranous organelles formed of (rRNA & protein), and they are synthesized in the nucleolus. LM: Too small to be seen but when abundant, they cause cytoplasmic basophilia which may be: a. Diffuse e g. embryonic cells. b. Localized in a specific part of the cell e.g. basal basophilia in cells pancreatic acini. c. Spotty as in Nissl granules of nerve cells. Each ribosome is formed of two subunits, a large subunit and a small subunit. EM: They appear as electron dense granules. Types of ribosomes: a. Free ribosomes: free particles within the cytoplasm, if attached to mRNA to form proteins called (polysomes). b. Attached: bind to the outer surface of rER. Free Attached Function of ribosomes: - The free ribosomes synthesized proteins are used by the cytoplasm to build up the cell. - The attached ribosomes synthesized proteins packed by the Golgi apparatus which secreted outside the cells as enzymes or hormones. 2-Cytoskeleton  1. Microtubules (centriole, cilia and flagella) Definition: They are straight hollow tubular non membranous structures with a diameter (25nm). They are formed of protein subunits called tubulin. LM: They do not appear easily except when present in bundles They appear by special staining methods e.g. immunofluorescent antitubulin. Functions: 1. They support the cell and determines its shape. 2. They facilitate intracellular transport of organelles and macromolecules. 3. Formation of mitotic spindle during cell division 4. Formation of centriole, cilia and flagella. Microtubules Definition: Non membranous organelles. present near the nucleus in area called (Centrosome). LM: With iron hematoxylin stains appear as 2 dots close to the nucleus EM: Close to the nucleus of non-dividing cells, the two centrioles appear, and they are surrounded by a granular electron dense area rich in tubulin protein from which new microtubules are formed called In longitudinal section: Each centriole appears as two hollow cylindrical structures perpendicular to each other. In cross section: The wall of each is cylinder consists of 27 microtubules embedded in a fibrous matrix. These microtubules are arranged in the form of 9 bundles, each bundle is formed of 3 microtubules (A,B and C) attached together called (triplets). Functions of centriole: 1. Play an important role in cell division (Before mitosis, duplication of the two centrioles occurs). 2. Formation of microtubules by МТОС. 3. Formation of mitotic spindle during cell division. 4. Formation of a basal body of cilia and flagella. The Cilia Definition: They are motile hair like processes covered by cell membrane extending from the free surface of certain epithelial cells. LM: Appear as hair like acidophilic striations. EM: Each cilium is formed of 3 parts (basal body, a shaft and rootlets). a. Basal body Its structure is identical to that of the centriole (formed of 27 microtubules arranged as 9 triplets). b. Shaft or axoneme It consists of 20 microtubules arranged in 9 bundles, each bundle 2 microtubules (doublet) and two (singlets) in the center. The shaft is covered by a cell membrane. c.Rootlets Fibers Fix the basal body and shaft to the cytoplasm.  2. Filaments Definition: These are minute threads-like structure present in the cytoplasm. They are responsible for elasticity and contractility of the cytoplasm. LM: filament cannot be seen by LM, however filament appeared by silver stain e.g. nerve cells. EM: appeared as elongated threads like structure. According to size they are divided into 3 types. 1. Microfilaments (6nm) or thin filaments as actin filaments in muscle cells, in core of microvilli and in constriction ring of dividing cell. 2. Thick filaments (15nm): as myosin filaments which present in skeletal, smooth and cardiac muscles. 3. Intermediate filaments (10nm): filaments with variable functions and distribution as: a) Desmin e.g. in muscle cells. b) Keratin e g. in epithelial cells. c) Neurofilaments e.g. in nerve cells. e) Glial filaments e.g. in neuroglia cells. Functions of filaments: 1. Form the cytoskeleton together with the microtubules which supports the cell and keep its shape. 2. Actin and myosin help in muscle contraction. 3. Play a role in cell division and movement of organelles.  Inclusions (Cytoplasmic deposits) non-living components of the cytoplasm, not essential for cell vitality and are usually temporary. Inclusions include stored food crystals. pigments 22 Glycogen: Carbohydrates are stored in the body as glycogen. Site: Glycogen is abundant in muscle cells and liver cells LM: not seen in H&E sections, but stained by PAS magenta (purple). EM: Glycogen appear as electron dense rosettes Lipid (fat): -It is stored mainly in adipocytes (fat cells) -LM: not appear in H&E, but stained orange with Sudan III EM: fat appear as rounded & electron dense droplets.  Pigments Pigments are either exogenous or endogenous. A-Exogenous pigments taken from outside. They include: -Lipo-chromes as carotene -Dust -Tattoo drawings B-Endogenous pigments - Hemoglobin - Melanin e made inside the body. They include: