Cytology - Membranous Organoids PDF

Cytology Department of histology and cell biology  Objectives By the end of these lectures the student should know: 1. Members of membranous organoids. 2. Site, identification (L/M & EM) and function of each member of the membranous organoids. Membranous organoids are C...

Cytology Department of histology and cell biology  Objectives By the end of these lectures the student should know: 1. Members of membranous organoids. 2. Site, identification (L/M & EM) and function of each member of the membranous organoids. Membranous organoids are Cell membrane Endoplasmic reticulum (ER) Golgi complexes Lysosomes and Peroxisomes Mitochondria  Cell Membrane It is the envelope of the cell that encloses its cytoplasmic compartments and preserves its shape. L/M:- appears as a very thin limiting border line. E/M:- appears as a 3-layered membrane (trilamellar or unit- membrane). - usually about 7.5-10 nm. in thickness. The unit membrane two electron dense lines (2.5 nm each) separated by an electron- lucent intermediate zone (2.5 - 3 nm).  Endoplasmic Reticulum - It is a network of channels present allover - the cytoplasm, connected intermittently - with the cell and nuclear membranes - It exists in 2 forms: I. Rough endoplasmic reticulum ( rER ) L/M: Appears as a basophilia of the cytoplasm. E/M: Present in the form of tubules, vesicles or cisternae. Ribosomes attached to its cytoplasmic surface. - Well developed in the cells which synthesize proteins for internal use as fibroblasts and for export as glandular secretory cells. II. Smooth endoplasmic reticulum ( sER ) L/M: Appears as a acidophilia of the cytoplasm. E/M: Present in the form of tortuous tubules, concentric or spiral arrays of highly fenestrated cisternae.Absence of ribosomes from its outer walls. - Well developed in the cells of the adrenal cortex and the interstitial cells of the testis. Functions: A) Related to rER: Protein synthesis on the ribosomes. B) Related to SER: Lipid synthesis e.g. steroid hormones in adrenal cortex.  Golgi complex (apparatus) - It is one of the membranous organoids - It is present in nearly all cells and of variable position depending upon the cell activity. - In glandular cells, it is present at one side of the nucleus (basal or apical) but in nerve cells, it is present surrounding the nucleus. - It is also variable in size and shape. L/M: In living cells: under the phase contrast microscope or after vital staining. In fixed cells: after osmic acid fixation or silver impregnation. - Appears as a fibrillar or granular network (positive Golgi image). E/M: As consisting of 3 components: A) Flattened vesicles or cisternae - These are a series (3-12 in number) of parallel, elongated, smooth-surfaced, double-walled memberanous sacs forming stacks. - They have a convex face towards the base (immature or Cis face) and a concave face (mature orTrans face). - These sacs or cisternae are continuous in their central regions while peripherally they often show dilatations and fenestrae or pores and may be connected with the ER. B) Microvesicles or transfer vesicles - These are smooth-surfaced small spherical vesicles arising by budding from the rER and seen around the periphery of the stack. - They are migrating through the cytoplasm to fuse with the immature face where they discharge their contents thus causing expansion of the saccules. - Some of the vesicles may be in the form of coated vesicles. C) Macrovesicles or secretory vacuoles -These are smooth-surfaced large spherical vesicles, usually present at one pole of the Golgi complex (at the mature face) and contain formed substances. -They either migrate to fuse with the cell membrane and discharge their contents through it to the outside forming secretory granules or remain in the cytoplasm as lysosomes.  Functions Processing, concentration and packaging of secretory products e.g. - Converting the inactive proinsulin, by enzymatic cleavage, into active insulin. - Addition of carbohydrate fractions to proteins coming from RER to form glycoproteins.  Lysosomes -They are membranous vesicles containing hydrolytic enzymes which are active at an acid PH e.g. lipases, nucleases, sulphatases,... -They are present in all cells, especially reticuloepithelial system. - They are variable in number, size, shape and origin in different cells. L/M: Can be demonstrated after especial cytochemical methods for their enzymes. E/M: - Appears as homogenous (without internal structure) membrane bound vesicles, with a single unit membrane. -They contain visible reaction products of their enzymes. According to their contents (by histochemical studies) and their appearance, the following types can be distinguished: Heterophagosomes: containing exogenous substrates as bacteria, b) Autophagosomes: containing endogenous substrates as cytoplasmic organoids. 1. Primary lysosomes: They are small, spherical and their contents are homogenous or finely granular. They contain only hydrolytic enzymes. 3. Secondary lysosomes: -They are larger in size and their contents are pleomorphic. -They are formed by the fusion of the primary lysosomes with substrate Post lysosomes (residual bodies): - They are of large size and contain electron-dense pigments, granules and lipid-like inclusions. - They have no enzymatic activity. - -The hydrolytic enzymes digest most of the contents of the phagosome. Lipids are resistant to complete digestion and they remain within the lysosome forming residualbody  Functions 1. Defensive mechanism against bacteria, viruses etc. 2. Remodeling tissues and removing of the dead cells as in bone and cartilage.  Mitochondria These are membrane-bounded organoids distributed allover the cytoplasm in nearly all cells. They tend to accumulate in parts of intense metabolic activity as the apical ends of ciliated cells, middle piece of spermatozoa and base of ion transferring cells. L/M: In living cells: as cultured cells, under the phase contrast microscope or after supervital staining (Janus green B stain). In fixed cells: after Fe hematoxylin stain. They appear as granules, rods or filaments of variable number , length and size. They are capable of movement, change shape, division and fusion. E/M: Elongated, spherical, rounded or filamentous organoid which is formed of: A) Outer membrane: It is formed of the unit membrane and is smooth and permeable to water and ions. B) Inner membrane:. It is formed of a special type of the unit membrane known as the tripartite repeating unit membrane. C) Cristae: The inner membrane is thrown into shelf- like projections known as cristae D) Spaces 1. Inter membrane space: which lies in between the 2 membranes and contains a low-density fluid. 2. Inter cristae (matrix) space: is enclosed by the inner membrane and filled with a fine granular material E) Mitochondrial matrix - Contains a dense fluid which may be viscous or semisolid with occasional spherical or ovoid dense granules rich in such cations as Ca and Mg. - The matrix rich in protein and containing some DNA and the 3 types of RNA. - Enzymes for the citric acid (Kreps) cycle and fatty acid β-oxidation are found to reside within the matrix space.  Functions Mitochondria are known as the powerhouses of the cell; being the site of Krebs cycle and oxidative phosphorylation thus providing the ATP which is an energy rich compound. THANK YOU