Cytology Lecture 1 PDF

Cytology By Dr. Esam El-Shwihy  Light microscope – Ordinary stain – Basophilia: binding with the basic stain (hematoxylin) – Acidophilia: binding with the acidic stain (eosin) – Special stains Electron microscope – Electron dense: dark – Electron light (lucent):...

Cytology By Dr. Esam El-Shwihy  Light microscope – Ordinary stain – Basophilia: binding with the basic stain (hematoxylin) – Acidophilia: binding with the acidic stain (eosin) – Special stains Electron microscope – Electron dense: dark – Electron light (lucent): pale  CYTOLOGY - Cytology means the study of cells. - The cell is the structural and functional unit of the organism. It consists of: 1- Cell membrane (plasmalemma). 2- Protoplasm, the living substance of the cell, is subdivided into two compartments, the cytoplasm and the nucleus. The Cytoplasm contains: 1- Cytosol: It is the semifluid cytoplasmic matrix. 2- Organelles: They are the living active structures that perform distinctive functions, and are essential for the life of the cell. 4- Inclusions: They consist of storage forms of various nutrients and pigments. They are not essential for the life of the cell. Nucleus is formed of: 1- Nuclear envelope. 2- Nucleolus. 3- Chromatin 4- Nuclear matrix.  CELL MEMBRANE - All cells are bounded by a cell membrane (plasma-membrane or plasmalemma). Functions : 1- It maintains the structural integrity of the cell. 2- It controls movements of substances in and out the cell (selective permeability). 3- It can recognize antigens, foreign cells as well as altered cells. Structure: Light microscope (L/M): Cell membranes are not visible with the light microscope. Electron microscope (E/M): 1- Low magnification: it appears as a dense thin line almost 10 nm in thickness. 2- High magnification: it appears as two electron- dense lines (each is almost 3 nm thick) separated by one electron-lucent intermediate zone (almost is 4 nm thick) (trilaminar appearance). Intracellular membranes are also trilaminar and hens the name unit membrane. Intracellular membranes are thinner than the cell membrane (almost 7 nm thick). Molecular structure: -The fluid-mosaic model of Singer and Nicholson is now accepted and it suggests that the cell membrane consists mainly of: 1. Phospholipids bilayer 2. Cholesterol 3. Proteins I) Phospholipids bilayer: - It is formed of double layer of phospholipids. - Each layer is formed of: Polar hydrophilic phosphate heads Non-polar hydrophobic tails of long fatty acid chains II) Cholesterol molecules: - They are present in lipid bilayer. III) Membrane Proteins: Two types: A) Integral (intrinsic) proteins: They are present within lipid dilayer. At body temperature, the lipid bilayer is fluid. So, the mosaic disposition of membrane proteins constitutes the fluid-mosaic model for membrane structure. B) Peripheral Proteins: They are associated with the surfaces of the bilayer.  Cell coat (Glycocalyx) - It is associated with the external surface of cell membrane. - It consists of short chains of polysaccharides which are conjugated mainly with membrane proteins to form glycoprotein and to some of the membrane lipids to form glycolipids. - Functions: recognition, protection and intercellular adhesions.  Passage of materials across cell membrane a) Passive transport: The passage of molecules depends on their concentration gradients. No energy is needed during this process. b- Active transport: Certain ions and molecules are transported against their concentration gradient from low concentration to higher one (e.g. sodium-potassium pump). Energy is required in this process. II) Vesicle-mediated transport: - This type of transport involves vesicles that are formed from the cell membranes. - The process includes either getting substances into the cell (endocytosis) or getting them out of the cell (exocytosis). 1- Endocytosis: Fluid-phase pinocytosis: Cell drinks fluid forming the pinocytotic vesicle. Phagocytosis: It means cell eating solid particles e.g. bacteria forming phagosomes. This process is usually performed by specialized cells known as phagocytes as neutrophils and macrophages.  Receptor mediated endocytosis: It is a highly selective process. Specific receptors for substances (ligands), e.g. proteins or hormones, are located at the cell surface. Binding of a ligand to its receptor forms ligand-receptor complex in coated pit. Coated pits become free in the cytoplasm and are known as coated vesicles. Then, they fuse with endosomes leading to dissociation of ligands from their receptors. Receptors move back to cell membrane to be used again (recycling). After the ligands have performed their functions it go to lysosomes. 2- Exocytosis: It refers to release of cell products into the extracellular compartment.  MITOCHONDRIA Mitochondria are membranous organelles. They are present in all cells except mature red blood cells. Their size, number and shape are variable. Structure: - L/M: Mitochoindria need special stains to be seen. They can be stained blue by iron haematoxylin - E/M: Each mitochondrion possesses a smooth outer membrane and folded inner membranes. The folds of the inner membrane are called cristae. Each of the two mitochondrial membranes is showing the trilaminar unit membrane. The large space enclosed by the inner membrane is known as the matrix space.  The outer mitochondrial membrane has no slective permeability, so the contents of the intermembrane space resembles the cytosol. The inner mitochondrial membrane has slective permeability The cristae increase the surface area. The number of cristae is directly related to the energy requirements of the cell e.g. mitochondria of cardiac muscle cell have more cristae than that of bone cells. Protein particles (elementary particles) are attached to the inner surface of the inner membrane. They are attached to cristal membrane by a short stem. The heads of elementary particles has ATP synthetase activity. They form ATP. The cristae of inner membrane contain enzymes of oxidative phosphorylation and ion transport activity.  The matrix space is filled with dense fluid composed of: 1. kreb’s cycle enzymes. 2. Ribosomes. 3. RNA. 4. DNA. 5. Dense granules consisting of Ca+ ions. Function of Mitochondria: Mitochondria are the power houses of the cell as they produce adenosine triphosphate (ATP). They concentrate calcium and maintain the general calcium environment within the cytoplasm to protect the cell from calcium toxicity. Mitochondria possess their own DNA & RNA, so they can synthesize their proteins (e.g. enzymes). Mitochondria are self replicating organelles, i.e. they are generated from preexisting mitochondria through simple fission.  RIBOSOMES Ribosomes aro non-membranous cell organelles. They are formed in nucleolus and then pass to the cytoplasm to perform their functions. It is present in all cells except mature erythrocytes. - Ribosomes may be:  1- Free ribosomes: are present scattered in the cytoplasm.  2- Attached ribosomes: are ribosomes attached to membranes forming the rough endoplasmic reticulum (rER). Structure - Ribosomes consist of two thirds rRNA and one third protein. - L/M: - Ribosomes are too small to be seen by light microscope. Free ribosomes cause diffuse basophilia as in growing cells. Attached ribosomes cause localized basophilia as in secretory cells. - E/M: Low magnification: ribosomes appear as small electron dense particles. High magnification: shows that each ribosome consists of two subunits, one is large and the other is small. The smaller subunit has a binding site for mRNA molecule while the large subunit has two binding sites for the tRNA; P (peptide) site and A (Amino acyl) site. Ribosomes also appear in small groups held together by a fine thread of mRNA forming polysomes, which may be free or attached to rER. Function: Free ribosomes are responsible for synthesis of structural proteins for internal use of the cell. Attached ribosomes are responsible for synthesis and segregation of protein which will be extruded outside cells as secretory proteins, lysosomal enzymes. Formation of ribosomal subunits: Ribosomal subunits are manufactured in the nucleolus from rRNA & protein in the nucleolus. After ribosomal subunits are formed, they are released as separated small and large subunits and stay in the cytoplasm individually. They will not form a ribosome until protein synthesis begins.  ENDOPLASMIC RETICULUM (ER) They are membranous organelles There are two types of ER: Smooth endoplasmic reticulum (sER) without attached ribosomes. Rough endoplasmic reticulum (rER) with attached ribosomes. Both are continuous with each other. A- Smooth Endoplasmic Reticulum (sER) LM:  - It gives acidophilia in the cytoplassm EM: - It is made of smooth-surfaced network of anastomosing tubules without ribosomes. Function of sER: In liver cells: Detoxification of certain drugs. sER participate in glycogen breakdown to glucose (glycogenolysis) and conversion of glucose into glycogen (glycogenesis).  Lipid synthesis. In striated and cardiac muscle it regulates the calcium level essential for muscular contraction. B- Rough Endoplasmic Reticulum (rER) - It is a membranous organelle. L/M: It gives localized cytoplasmic basophilia is due to the presence of ribosomes and polyribosomes attached to rER. E/M: It consists of an interconnecting network of membranous tubules, vesicles and flattened sacs (cisternae). Its outer surface is studded with ribosomes and polyribosomes giving rough or granular appearance. Functions of rER: rER synthesizes proteins which are: Secretory proteins. Lysosomal enzymes. Integral membrane proteins. Renewal of Cis-face saccules of Golgi by transfer vesicles. sER may be derived from rER.  GOLGI APPARATUS - It is a membranous cell organelle. Structure: L/M: Golgi can be seen after special techniques e.g. silver as a darkly staining network or as an irregular granular mass located near the nucleus. Its site varies according to cell type, e.g. In secretory cells it is supranuclear. In nerve cells it usually forms a network around the nucleus. Negative Golgi Image: After H&E staining in cells with intensely basophilic cytoplasm, Golgi apparatus appears as, clear unstained area near the nucleus representing the site of Golgi. This pale unstained area is called negative image of Golgi. E/M : Golgi apparatus is composed of: Golgi stacks: Each stack consists of flattened smooth cisternae (saccules). Each stack has: a) Cis-face (immature). It is directed towards rough endoplasmic reticulum. b) Trans-face (mature or secretory face) is directed towards the plasmalemma. Transport [transfer] vesicles: They pinch off from rER and migrate to cis-face of Golgi and fuse with it. They carry newly synthesized polypeptides formed in rER. Secretory vesicles: They are large in diameter. They bud off from the trans-face of Golgi stacks. They contain secretory products. The secretory vesicles will fuse with the cell membrane and release their contents (exocytosis). Primary lysosomes arise also from trans-surface of Golgi. Functions of Golgi apparatus: Modification of the newly synthesized proteins by Glycosylation, sulfation and phosphorylation Concentration and packaging primary lysosomes and secretions Membrane recycling: Golgi receives plasma membrane proteins from rER through transefer vesicles and add membranes to plasmalemma.  LYSOSOMES Lysosomes are membranous cell organelles. L/M: The site of lysosomes can be recognized with after using histochemical methods. EM: They are spherical small membranous vesicles which contain a variety of hydrolytic digestive enzymes called hydrolases They constitute an intracellular digestive system. They are numerous in phagecytic cells e.g. macrophages.  Lysosomal enzymes are synthesized in rER and transported to Golgi complex. Types of lysosomes: A- Primary Lysosomes: They are newly formed lysosomes that have pinched off from trans-face (mature face) of Golgi. They have homogenous content. B- Secondary Lysosomes: The contents are heterogeneous.  They are formed after fusion of primary lysosomes with some other substances from within or outside the cells. When primary lysosome interacts with pinocytotic vacuole it gives multivesicular body. When primary lysosome interacts with phagocytic vacuole it gives phagosome. When primary lysosome interacts with autophagic vacuole it gives autophagosome. The undigested materials remain inside the secondary lysosomes which are then called residual bodies. The cells release the materials within residual bodies by exocytosis. Functions: 1- Cellular defense mechanisms by destruction of foreign bodies such as bacteria. 2- Replace-ment of damaged organelles. 3- Autolysis of damaged cells. END LECTURE 1