Histology Lecture Non-Membranous Organelles I PDF

Histology Lecure Non-membranous Organelles I 2024-2025  Learning Objectives Identify histological structure of ribosomes at LM and EM levels. Describe histological structure and function of microtubules at EM level. Identify histological structure of centriole at EM level. Describe...

Histology Lecure Non-membranous Organelles I 2024-2025  Learning Objectives Identify histological structure of ribosomes at LM and EM levels. Describe histological structure and function of microtubules at EM level. Identify histological structure of centriole at EM level. Describe histological structure of cilia at LM and EM levels.  Non-membranous organoids Ribosomes Microtubules Centrioles Cilia and flagella Cell Filaments.  RIBOSOMES These are small particles, non membranous dynamic structure These are dynamic and flexible structures, present either free or attached to the ER. They are found in all cells except the mature RBCs and mature sperms. Origin The ribosomal RNA is formed in the nucleus,then migrates to the cytoplasm through the nuclear pores.  RIBOSOMES small particles, nonmembranous dynamic organelles, present either free or attached to rER. L/M:- basophilia of the cytoplasm which may be: a)Diffuse basophilia. b)Localized basophilia E/M:- Electron-dense granules either free in cytoplasm or attached to rER. Pancreatic acinar basophilia Nissel garanules E/M: Appears as electron-dense spherical or ellipsoidal granules. May be either free in the cytoplasm or attached to the rER. A) Free ribosomes: may be Single:- representing the inactive form of ribosomes. Polysomes:- which are aggregation in clusters, in the form of spiral chains or rosettes of ribosomes linked by long molecules of mRNA. - They represent the active form of ribosomes as in reticulocytes of the blood for the synthesis of hemoglobin. E/M: Each ribosome is formed of two subunits (large and small) that clamp together, leaving a central channel through which mRNA is drawn. Alongside the channel are three distinct sites formed by the 2 subunits The P site (peptidyl) holds the tRNA carrying the growing polypeptide. The A site (aminoacyl) holds the tRNA carrying the next amino acid to be added to the chain. The E site (exit) discharged tRNA's leave the ribosome through this recently discovered site. Free Ribosomes B) Attached ribosomes: attached to the rER by the large subunit Functions They are concerned with protein synthesis. 1. The free ribosomes are concerned with the protein synthesis needed for growth and building up of the cell organoids and for the synthesis of special proteins as hemoglobin. 2. The attached ribosomes are concerned with the synthesis of proteins for secretion.  MICROTUBULES Def: Microtubules are non- membranous organelles. Site: In all cells especially where stiffness, shape or oriented motion are needed as in blood platelets, cilia, flagella, mitotic spindle,……. L/M: Appears as filaments after using special techniques as making a fluorescent antibody against tubulin. E/M: - Appears as long, straight, slender, cylindrical, non- branching structures, of variable length and of uniform diameter (LS). - Each one resembles a tubule with a less dense central core and a wall which is composed of (13) globular subunits (protofilaments) arranged in a spiral fashion (TS).  Functions 1- Cytoskeleton of cell: has a role in the development and maintenance of cell shape due to their rigidity. 2- Formation of mitotic spindle, necessary for chromosomal movement. 3- They form centrioles and the axoneme of cilia and flagella.  CENTRIOLE Def: Non- membranous organoid. Site: Present close to the nucleus & Golgi apparatus in all cells except those that do not divide as RBCs & nerve cells. L/M: In living cells: can be demonstrated by using the phase contrast microscope. In fixed cells: after staining with iron hematoxylin stain, they appear as 2 cylindrical structures (diplosomes) perpendicular to each other forming a T-shaped configuration and embedded in a pale mass of cytoplasm known as centrosome E/M: Appear as one fully formed (parent centriole) and one small partially formed (daughter or pro-centriole). A) Parent centriole Appears as a short cylinder with its wall composed of 9 longitudinal arranged microtubular complexes parallel to the long axis.  Each microtubular complex forms a triplet being formed of 3closely associated microtubules ( a, b & c ). The a tubule is circular in cross section and has 2 arms, one with a free end and the other joined to the c tubule, its wall is composed of 13 protofilaments, while that of each of the b and c tubules has only 10 protofilaments. B) Daughter centriole - Lies opposite the proximal end of the parent one and separated from it by a distance. - It resembles the parent in all aspects except for the absence of the central vesicle, the DNA strand, the cart-wheel and the octagonal end structures. NB. Pericentriolar bodies Are associated with the centrioles and from which microtubules arise. They represent the organizing center for microtubules.  MICROTUBULES Functions 1- Cytoskeleton of the cell: has a role in the development & maintenance of cell shape due to their rigidity. 2- Formation of mitotic spindle, necessary for chromosomal movement. 3- Formation of centrioles & the axoneme of cilia & flagella. 4- Movement of organelles and vesicles in the cytoplasm.  CILIA AND FLAGILLA A) CILIA - Def.These are elongated motile structures forming outgrowths of the free cell surface. - Site:They are present in the ciliated epithelium as respiratory tracts and genital tracts. L/M: - Appear as short, fine hair-like processes, which may reach several hundreds, arising from the free cell surface. - Each is connected with a deeply- stained cytoplasmic body known as basal body. E/M: - Appear as outgrowths of the cell which are covered with plasma membrane. - Each cilium is formed of: 1. Basal body 2. This is a centriole which has migrated to near the cell surface and to which the cilium is anchored. 2. Shaft ( axoneme ): Which is formed of : a) 2 single (singlets) microtubules: in the center, each being circular in cross section, and both are joined together with a bridge and are surrounded with a solid cylindrical sheath. From this sheath, extend slender spokes to the subunit a of each doublet. The spokes are important to convert the sliding of the tubules into bending. b) 9 paired (doublets) microtubules: circularly arranged around the periphery, each being formed of 2 subunits, a and b which are unequal in size. Subunit a :- lies nearer the cilium axis, smaller in size and forms a complete circle in cross section. Its wall is made of about 13 protofilaments. Subunit b :- lies away from the axis, larger in size and has a C-chaped in cross section. Its wall is made of about 11 protofilaments. c) Inter-doublet links: are present at periodic intervals, attaching the subunit a of one doublet to the subunit b of the adjacent doublet. They are made of an elastic substance known as nexin. 3. Rootlets: Which extend from the deep aspect of the basal body into the cytoplasm acting as anchoring structures. 4. Basal foot: Which is a striated structure attached laterally to the basal body and has cytoplasmic microtubules attached to its free end.  CILIA Functions: 1. Spreading of a thin film of fluid or mucus across a surface through the rhythmic beating in one direction. 2. Become modified to receive stimuli as: light stimuli in rods & cones of the retina, odor stimuli in the olfactory epithelium …….etc. N.B. (Clinical Presentation Session) Absence of dynein arms in some inborn diseases leads to immotile cilia as in Kartagener’s syndrome (presenting with sinusitis, bronchiectasis, dextrocardia or situs inversus totalis and male infertility. B) FLAGELLA -They resemble the cilia but are rather longer and usually single as in the tail of spermatozoa. -They are used for movement through exhibition of an undulating motion resulting from propagation of successive waves of bending from the base to the tip. The function of attached ribosomes to RER is to synthesize: A. lipid. B. carbohydrate. C. protein that will be secreted by the cell. D. protein that will be used by the cell. E. glycogen. In electron micrograph a cross section of the cilium shows: A. Nine triplets of microtubules and two central singlets. B. Nine triplets of microtubules and no central singlets. C. Nine doublets of microtubules and two central singlets. D. Nine doublets of microtubules and no central singlets. E. Nine doublets of microtubules and one central singlets. Microtubules are formed from : A. Albumin. B. Tubulin. C. Actin. D. Globulin. E. Myosin.  REFERENCES Pawlina, W. (2016): A text of Atlas with cell and molecular biology. 7th ed. Lippincott, Williams and Wilkins.  Junqueira, L.C.; Carneiro, J. and Kelly, R.O.(2014): Basic Histology. 11th ed. Appleton and Lange. New York. Gartener, L.P. and Haiat, J.L. (2011): C.V.S. In: Colour Text Book of Histology, 4th ed. Saunders Elsevier. THANK YOU