Cytology 1 PDF

 Cytology 1 BY DR: Noha Ramadan Elswaidy Assistant professor of histology and cell biology  LIGHT MICROSCOPE ELECTRONIC MICROSCOPE  Cytology It the science deals with study of cells. Cell Tissue. Organ. System The cell...

 Cytology 1 BY DR: Noha Ramadan Elswaidy Assistant professor of histology and cell biology  LIGHT MICROSCOPE ELECTRONIC MICROSCOPE  Cytology It the science deals with study of cells. Cell Tissue. Organ. System The cell is the structural and functional unit of the organism.  Cell Cell Protoplasm membrane Cytoplasm Nucleus  Cytoplasm Cytoplasmic Organelles Inclusions Cytoskeleton matrix (cytosol) Not Essential essential Cell Membrane (Plasmalemma) - All cells are surrounded by a cell membrane. It is also called plasma-membrane or plasmalemma. - Some organelles are surround by membranes that are similar to cell membrane. - Both are called unit membrane. *L.M: It can’t be seen as it is very thin (7.5-10 nm). *E.M: Low magnification: It appears as single electron dense line. High magnification: It appears as two electron dense separated by an electron lucent line so has trilaminar appearance. It appears as two electron-dense lines (2.5-3 nm each) separated by an electron-lucent (light) intermediate zone (3.5-4nm).This trilaminar appearance is known as the unit membrane.  Molecular structure of cell membrane Membrane proteins Phospholipids Cholestrol I) Phospholipids  Phospholipid bilayer: It is the backbone of the plasma membrane. It is formed of double layer of phospholipids molecules. Each molecule consists of hydrophilic (polar) phosphate head directed outwards and hydrophobic (non-polar) tails (long chain fatty acid) directed inwards 1-  II) Cholesterol molecules: - They are present in lipid bilayer. - They have one to one ratio with phospholipids. - They fill the gaps between the fatty acid tails. III) Protein  Membrane Proteins They are present within the lipid bilayer and are of two types: a- Integral (intrinsic) proteins. b-Peripheral (extrinsic) proteins.  A) Integral (intrinsic) proteins They are present among lipid molecules. Integral membrane proteins can move within the lipid bilayer. Some are partially embedded in lipid bilayer. Transmembrane proteins Some proteins extend across lipid bilayer and protrude from both membrane surfaces. They form channels for the passage of water-soluble molecules (e.g. ions).  B) Peripheral (extrinsic) protein They are associated with the cytoplasmic surfaces of cell membrane or on the extracellular surface  Cell coat (Glycocalyx).  Cell coat (Glycocalyx) Site: It is associated with the external (outer) surface of cell membrane. Chemically: It consists of oligosaccharides conjugated mainly with membrane proteins to form glycoprotein and with some membrane lipids to form glycolipids..  Structure: By E/M, it appears as a fine filamentous material of varying thickness. Function: It is important in: 1- Cell recognition. 2- Protection and intercellular adhesions. The trilaminar appearance of cell membrane is due to deposition of reduced osmium tetroxide stain on the outer and inner hydrophilic heads of the lipid bilayer.  Functions of cell membrane 1- It maintains the structural integrity of the cell. 2- It controls movements of substances into or out of the cell [selective permeability]. 3- It can recognize (via receptors) antigens; foreign cells as well as altered cells. 4-Selective transport of essential substances as hormones through specific receptors on the cell membrane 5- It can establish transport system for specific molecules: A- Passive transport B- Active transport Sodium and Potassium transport  Certain ions as sodium and potassium are transported through aqueous transmembrane channel by active transport. Some ions pass passively. Lipid soluble substances as steroid hormones diffuse rapidly through the lipid bilayer of the cell membrane.  Mass transfer It involves vesicles or vacuoles that are formed from or fuse with the cell membrane. 1- Endocytosis: 2- Exocytosis: a- Fluid phase pinocytosis. b- Phagocytosis. I) Fluid-phase pinocytosis (cell drinking): It is a non-specific ingestion of uptake of substances dissolved in fluid or solute. II) Phagocytosis (Cell eating) It is the process of engulfing large particles by the cell or into the cell e.g. bacteria, cell fragments and cells.  II- EXOCYTOSIS It means release of cell products into the extracellular compartment. In this process, a vesicle containing the product fuses with the cell membrane allowing outflow of its contents 1-Cytoplasmic Organelles. A-Membranous Organelles: They are surrounded by a membrane that is similar in structure to cell membrane. They include: 1-Mitochondria. 2-RER. 3-SER. 4-Golgi apparatus. 5-Lysosomes. B-Non-Membranous Organelles: They are not surrounded by unit membrane. They include: 1-Free ribosomes. 2-Microtubules. 3-Centrioles. 4- Cilia. 5-Fagella. 6-Filaments..  1- MITOCHONDRIA  Site: They are present in all cells except mature red blood cells.  Size: Their size, number and shape are characteristic for specific cell types.  Number: Their number is increased in cells of high metabolic activity e.g., liver cells (may reach 2000 in each liver cell). *L.M: They can be stained by supravital staining as janus green and appear as green rod, ovoid or thread-like bodies with different sizes *E.M: * Rounded or oval surrounded by two membranes (both are trilaminar unit membrane) 1- The outer is smooth. 2- The inner is folded & projected as shelf-like structure called cristae. The narrow space between the outer and inner membranes is referred to as the intermembrane space  Intercristal space The large space enclosed by the inner membrane is known as the matrix space  Elementary particles closely packed club- shaped particles attached with a short stem to the inner surface of the inner membrane.  Mitochondria are self- replicating (i.e., they are generated from preexisting mitochondria) by simple fission as they turn over in 10 days. Function 1-They are the energy house in the cell as they produce ATP (adenosine triphosphate) from ADP since the matrix contain enzymes of Kreb’s cycle while the inner mitochondrial membrane contains enzymes of electron transport and oxidative phosphorylation. 2-They concentrate calcium in their matrix leading to calcium regulation within the cytoplasm. 3-They can synthesize protein due to the presence of DNA, RNA and ribosomes in mitochondria  Ribosomes  Ribosomes are non-membranous cell organelles, which are present in all cells except mature erythrocytes.  Free ribosomes are manufactured in the nucleolus and released into the cytoplasm to perform their function.   Ribosomes: 1.Free ribosomes: present scattered in the cytoplasm and synthesize proteins for internal use of the cell. 2- Attached ribosomes: They are attached to membranes forming the rough endoplasmic reticulum [RER], which are responsible for synthesis and segregation of proteins (as secretory proteins) that will be secreted from the cells.  Ribosomes consist of Proteins and r-RNA that can be stained by Hematoxylin, Toluidine blue and Methylene blue (Basic dyes Each ribosome consists of two subunits; small and large.  L.M: Ribosomes are responsible for cytoplasmic basophilia due to their contents of rRNA Free ribosomes Attached ribosomes. (Rer) Diffuse basophilia Localized basophilia  Ribosomes Each ribosome High magnification Low magnification appear as consists of two small electron subunits one is dense large and the granules. other is small.  Polyribosomes [polysomes] Several ribosomes may occur in groups or rosettes attached on a fine thread of mRNA forming polysomes, which may be free or attached to RER.  Smooth Endoplasmic Reticulum *L.M: Can not be seen but give acidophilic to cytoplasm when present in great amount. *E.M: It is composed of smooth branching network of tubules present in the cytoplasm (its membranes not studded with ribosomes).  1-SER synthesizes steroid hormones in steroid secreting cells e.g. cells of adrenal cortex. 2-It synthesizes phospholipids So for all cell membranes. 3-It may be the most prominent organelle in steroid secreting cells of adrenal cortex.  Liver cells Striated and cardiac muscle. 1- It is responsible for detoxification of certain drugs in Regulates the Ca level liver cells. essential for muscular 2- It participates in glycogen, contraction cholesterol and lipid synthesis. Cytoplasmic Organelles. A-Membranous Organelles: 1-Mitochondria. 2-SER. 3-RER 4-Golgi apparatus. 5-Lysosomes. 6-Secretory vesicles. 2- Rough Endoplasmic Reticulum *L.M: Localized cytoplasmic basophilia. *E.M: 1-Network of memberanous vesicles& flat tubules called cisternea. Their surfaces are covered with ribosomes. 2-Its outer surface is studded with ribosomes and polyribosomes, so they are rough or granular. Function of RER Synthesis of proteins by attached ribosomes  Synthesis of protein Secretory Integral proteins (by Lysosomal attached protein of cell enzymes ribosomes). membrane Pancreatic Fibroblasts Plasma cells cells  Renewal of Cis-face saccules of Golgi by transfer vesicles that originate from RER.  SER may be derived from RER after losing ribosomes. 4- Golgi apparatus It is membranous organelle found in nearly all cells. LM:By silver method: Golgi appears as dark brown network LM: By Hx&E: Negative Golgi image G N Golgi is variable in its site according to the type of cell: I-In secretory cells Golgi is present between the nucleus and apical secretory surface. II. In nerve cells It is present perinuclear (around the nucleus), and it is multiple. Each stack consists of 3- 12 flattened cisternae (saccules). The lumen of each saccule is narrow, but the periphery is dilated. Each stack has two faces: 1- Cis-face (immature face) which is convex and directed to RER. 2- Trans-face or mature face which is concave and directed towards the cell membrane. The secretory products are moved through the stack from cis- face to the trans-face by vesicles budding off from one saccule and fusing with the next one in the stack.  Transfer (transport) vesicles  They are small in diameter.  They pinch off from small portions of RER devoid of ribosomes.  They migrate to cis-face of Golgi and fuse with its dilated rim.  They carry newly synthesized polypeptides formed in rER to be modified and secreted by Golgi.  Condensing vacuoles and secretory vesicles  Condensing vacuoles are large in diameter that arise from the trans-face.  They concentrate the proteins by elimination of water to give rise to secretory vesicles.  The secretory vesicles are smaller than condensing vacuoles and migrate to cell membrane where they fuse with it and release their content to the exterior of the cell by exocytosis. Primary lysosomes arise also from trans- surface of Golgi but remain inside the cell.  Function of Golgi apparatus 1- Modification of secretory proteins. 2- Concentration and packaging of secretory products into secretory vesicles. 3- Modification, segregation, and packaging of lysosomal enzymes. 4- Synthesis of membrane protein and membrane recycling. 5- Lysosomes Definition: Lysosomes are membranous cell organelles. Origin of lysosomal enzymes: They are synthesized in rER and transported in vesicles to Golgi complex. Sorting of lysosomal enzymes occurs also in Golgi. Contents: Lysosomes contain hydrolytic digestive enzymes called hydrolases e.g., acid phosphatase, proteases, nucleases and lipases. Lysosomal enzymes have optimal activity at pH 5... Site: They are found in all cells except mature erythrocytes but are numerous in phagocytic cells. Structure: L.M: They can be seen by specific histochemical reactions to demonstrate their acid phosphatases E.M: They are rounded small membranous vesicles which are classified into:  a- Primary lysosomes: 1-They are newly formed lysosomes and are not involved in any digestive events. 2-They are homogenous when seen by electron microscope.  b- Secondary lysosomes: 1- They are formed after fusion of primary lysosomes with other substances from within or outside the cells. 2- The contents of secondary lysosomes are heterogeneous.  Vs Primary lysosome Secondary lysosome  Enzymatic digestion breaks down the contents into small molecules that pass back across the lysosomal membranes into the cytoplasm. Residual body  The indigestible material as pigments or lipids remains inside the secondary lysosomes. and are known as residual bodies which are released by exocytosis.  In certain cell types e.g., nerve cells and cardiac muscle, residual bodies accumulate with age and are called lipofuscin pigment Function of Lysosome Digestion of certain substances  1-Digestion: They constitute an intracellular digestive system capable of breaking down materials originated from outside and inside the cell.  2- Heterophagy: Break-down of materials from outside the cell such as bacteria for cellular defense mechanisms.  3- Autophagy: Digestion of materials from inside the cell for normal replacement of cellular components and organelles.  4- Autolysis: Lysis and breakdown of the dead cells.  Peroxisomes Definition: They are membranous cell organelles. Site: They are present in nearly all cell types. Number: Their number increase in metabolically active cells such as liver. Contents: They contain more than 40 oxidative enzymes (e.g. enzymes for oxidation of long chain fatty acids). Origin of peroxisomal enzymes: Peroxisomal enzymes are synthesized on free poly ribosomes. Structure EM: 1- They have finely granular homogeneous contents surrounded by unit membrane. 2- In some animal species, peroxisomes have a denser central region called nucleoid, which contains a crystal of urate oxidase Function 1- Catabolism of very-long-chain fatty acids and formation of hydrogen peroxide. 2- Detoxification of ethanol and killing micro-organisms by hydrogen peroxide (H2O2). 3- Peroxisomes break excess H2O2 into water and O2.