Foundation Histology PDF

@nebras_2029  Histology - Foundation Cell …………………………….………………………………………...…………........................................…1 Cell Membrane.…………………………………………………….….............................…………..…………..1 Vesicular transport across the c...

@nebras_2029  Histology - Foundation Cell …………………………….………………………………………...…………........................................…1 Cell Membrane.…………………………………………………….….............................…………..…………..1 Vesicular transport across the cell membrane …………...………..………................……………...4 Cell organelles ……...………………………………………………………….…............................…...………9 Centrosome …...……………………………………………………….………............................……………..38 Nucleus …….………………………………………………...………………….............................……………..43 Cell Cycle & Cell Division …………...…………………………………..……............................…………..49 Cell Proliferation & Cell Death..………………………………………........................................……..58 Epithelium …..……………………….………………………………………....................................……..69 Lining Epithelium …….…………………………………………….………...........................………………..69 Simple Epithelium …………………………………………………….................................…………………70 Stratified Epithelium ………...………………………..……………................................………………….71 Glandular Epithelium ………………….……………………………………….............................………….72 Special Types of Epithelium ….……………………………….……………………........................….…..73 Epithelial Cell Polarity …………………………………………….……….………...........................………76 Lateral Specialization & Intercellular Junctions ……………………….....................………………81 Cell Adhesion Molecules (CAMs) ………………..……………………….………….......................…….87 Connective Tissue ……………..……………..…………………………………........................………….90 Characteristics of CT ………….…….……………………………………………...........................…………90 CT Types …….………………………………………………………………………............................………..100 Skin ……………………….………………………………………........................……………...……………108 Epidermis …………………….…………………………………………...........................…………………….108 Dermis ………………………….………………………………………………………............................……..114 Hypodermis ……………..…………………………………………………………………...........................…117 Skin appendages, Hair and Nails ………………...…………………………….....................………….119 Functions of the integumentary system ………………………………………………................…..123  Histology - Foundation Cell The cell is the functional & structural unit of the body. A group of cells with similar structure & function will form tissues. These tissues are grouped to form organs. A group of organs collect to form the body systems. Cell Membrane Plasma membrane = Plasmalemma LM: It cannot be seen by light microscope because it is too thin to be seen but the conden sation of the stain on the outer surface of the cell membrane marks its. EM: 1. At Low Magnification: thin dense line 8-10 nm in thickness. 2. With Higher Magnification Magnification: a trilaminar structure, with an outer (= extracellular leaflet) and an inner (= cytoplasmic leaflet) electron dense lines and a middle electron lucent zone in between. N.B: The entire structure is known as the unit membrane. Molecular structure of the Cell membrane: 3 Components: 1. Lipid molecules: a. Phospholipids b. Cholesterol 2. Protein molecules. 3. Carbohydrate molecules N.B: The cell membrane & almost all the membranes surrounding the membranous organelles have the same structure except for minor differences. N.B: Membrane phospholipids & the associated proteins are usually present in 1:1 proportion by weight 1  Histology - Foundation 1. Lipid Molecules A. Phospholipids: Each phospholipid molecule consists of: 1. One polar hydrophilic head: faces the aqueous media on either side of the membrane. 2. Two long non polar hydrophobic tails (fatty acids): project towards the center of the membrane facing each other. They form weak non covalent bonds with each other, holding the bilayer together. Why does the cell membrane appear as a trilaminar structure? Deposition of osmium in the hydrophilic heads while the hydrophobic tails remain unstained. Functions of Phospholipid molecules: - Prevent passage of: 1. Water soluble substances. 2. Polar ions. - Allow passages of: 1. Fat soluble substances. 2. Nonpolar substances. B. Cholesterol: They are incorporated within the lipid bilayer. Functions of Cholesterol: 1. Stability of the membrane. 2. Regulation of membrane fluidity in body temperature. 2. Protein Molecules A. Integral Membrane Proteins: They are embedded within the lipid bilayer. Most of these proteins traverse the whole thickness of the membrane and are called transmembrane proteins while others are partially embedded within the membrane. 2  Histology - Foundation There are six functional forms of integral membrane proteins: 1. Pumps: transport ions (Na+, K+) actively across the membrane. 2. Channels: transport substances passively. 3. Receptors: allow binding of specific molecules e.g., hormone. 4. Enzymes: ATP synthase of the inner mitochondrial membrane and some types of digestive enzymes in the small intestine. 5. Linkers: anchor the intracellular cytoskeleton to the extracellular matrix. 6. Structural proteins: form junctions between neighboring cells. B. Peripheral Membrane Proteins: They are not embedded into lipid bilayer, but they are loosely associated with membrane. They are usually located on the cytoplasmic surface of the membrane. Function: form a link between the cell membrane and the cytoplasmic components. 3. Carbohydrate Molecules They are present as glycoproteins and glycolipids of the cell membrane. They are oriented towards the outside of the membrane forming the cell coat or glycocalyx. The cell coat is represented by the "fuzzy" material on the outer surface of the membrane. Functions of cell coat: 1. Cellular recognition e.g. the glycocalyx on the surface of red blood cells determines the four blood groups. 2. Cell cell adhesion. 3. Receptor: for ligands by the glycoproteins of the cell membrane. N.B: The glycocalyx vary from species to species/ from cell to cell. This diversity enable membrane carbohydrate to function as markers that distinguish one cell from another (e.g. The ABO blood system) 3  Histology - Foundation Vesicular transport across the cell membrane Mass transfer of materials through the cell membrane occurs by formation of vesicles. It involves 2 processes: 1. Endocytosis. 2. Exocytosis. 1. Endocytosis Definition: the uptake of material from the extracellular space. It is an active process that involves invagination of the membrane to form a vesicle. 3 mechanisms of endocytosis are present in the cell: A. Pinocytosis (cell drinking) : Definition: a non selective process, occurs in nearly all cell types for uptake of fluid containing ions and small protein molecules. Vesicle: pinocytotic vesicles are small and have smooth surface. Site: most evident in the endothelium of blood vessels. B. Receptor mediated endocytosis Definition: a highly selective process resulting in uptake of specific substances by a specific cell that has receptors for these substances e.g. protein hormones. These receptors are concentrated in specialized regions of the plasma membrane called coated pits (coated by clathrin). 1. When a substance binds to its receptor, clathrin coated pits invaginate and give rise to clathrin coated vesicles containing this specific substance. 2. Clathrin is lost and recycled leaving uncoated vesicles. C. Phagocytosis (cell eating): Definition: ingestion of large solid particles, such as bacteria and cell debris, it is a receptor mediated endocytosis; however, it does not involve formation of coated pits or vesicles. Sites: phagocytes e.g. macrophages& neutrophils. 4  Histology - Foundation 1. Binding of the receptor and foreign body results in extension of pseudopodia that engulf the particle. 2. Fusion of the membrane to internalize the particle into the cytoplasm forming a phagosome. 3. The contents of the phagosome are then digested through lysosome. Types of endocytosis Receptor mediated Pinocytosis Phagocytosis endocytosis 1. Endocytosed Fluid containing ions Specific substances Large solid particles material & small molecules. (ligand) e.g. hormone. e.g. bacteria. 2. Receptors for Nonselective. Present. Present. endocytosed material 3. Shape of the Small& smooth. Coated with clathrin. No coated vesicle but vesicle the membrane fused to form phagosomes. 4. Type of cells Nearly all cell types Specific cell that has Phagocytic cells. especially endothelium receptor for specific of blood vessels. substance. 2. Exocytosis Definition: the release of cell products into the extracellular space. During this process, a vesicle moves from the cytoplasm to the cell membrane, fuses with it and discharges its content. There are 2 types of exocytosis: A. Regulated secretion (stimulus dependent) 1. The secretory products become stored forming secretory granules. 2. As a result of a stimulus (hormonal or neural stimulus), these vesicles move to the surface and fuse with the cell membrane to pour their contents outside the cell. e.g., occurs during release of the digestive enzymes by the pancreas. 5  Histology - Foundation B. Constitutive secretion The secretory products leave the cell immediately after their synthesis. These cells lack secretory granules. The secretion is released continuously through secretory vesicles. E.g. occurs during release of antibodies by plasma cells. Types of exocytosis Regulated secretion Constitutive secretion 1. Stimulus Stimulus dependent No stimulus. They released continuously. Concentrated & stored Leave the cell membrane immediately after 2. Secretory product inside secretory granules. their synthesis. No secretory granules. 3. Example of the Digestive enzymes from Antibodies from plasma cell, fibers released secretion pancreatic cell. secreted from fibroblast. Membrane Recycling During the vesicular transport, the cell membrane is maintained; the excess membrane added to the cell membrane by exocytosis is constantly recycled again into the cytoplasmic compartments by endocytosis. 6  Histology - Foundation 1) which the following substances aren't present in the cell membrane ? : a. Triglycerides b. Cholesterol c. Glycoproteins d. Phospholipids 2) The sugary coat of the outer surface of plasma membrane is called: a. Glassy membrane b. Cell wall c. Glycocalyx d. Cytoskeleton 3) In-receptor mediated endocytosis: a. Receptors are dispersed over the cell outer surface b. It is suitable for low density lipoproteins c. Receptors are aggregated in coated pits d. All the above 4) The process by which the cell membrane engulfs solid particles called: a. Pinocytosis b. Receptor-mediated endocytosis c. Exocytosis d. Phagocytosis 5) Uptake of extracellular fluid by the cell membrane is called: a. Phagocytosis b. Exocytosis c. Pinocytosis d. Autophagy 6) Transport of molecules against concentration gradient by cell membrane is called: a. Pinocytosis b. Signal transduction c. Passive diffusion d. Active transport Answers 1. A 2. C 3. D 4. D 5. C 6. D 7  Histology - Foundation 8  Histology - Foundation Cell organelles Definition: metabolically active structures carrying out specific essential functions. Types: 1. Membranous organelles: nucleus, endoplasmic reticulum, Golgi apparatus, transport vesicles, endosomes, lysosomes, mitochondria, and peroxisomes. 2. Non membranous organelles: ribosomes, centrosome, and the cytoskeleton. N.B: Haematoxylin and Eosin (H&E): Haematoxylin is a basic violet stain. Eosin is an acidic pink stain. Basophilic structure= A structure that has affinity to stain with basic dyes = acidic in nature So it stains violet with haematoxylin. Acidophilic or eosinophilic structure= A structure that has affinity to stain with acidic dyes = basic in nature So it stains pink with eosin. 1. Ribosomes Definition: granules of nucleoproteins (ribosomal RNA (rRNA) + proteins). Site: They are present in all cells especially in protein synthesizing cells. Structure: two subunits; small subunit & large subunit. Synthesis: 1. The rRNAs are synthesized inside the nucleolus. 2. Ribosomal associated proteins are synthesized in the cytoplasm. 3. Ribosomal subunits then leave the nucleus, via the nuclear pores, to enter the cytoplasm. The small and large subunits are present in the cytosol individually and do not form a ribosome until protein synthesis begins. LM: When present in large amounts they cause cytoplasmic basophilia. EM: Ribosomes are small electron dense granules. 9  Histology - Foundation Types: A. Free ribosomes: 1. Solitary particles: scattered in the cytoplasm. Function: act as a reserve. 2. Aggregated (polysomes): clusters of 10 or more connected by single strand of mRNA. Function of polysomes: responsible for synthesis of cytosolic protein e.g. in dividing cells and growing cells, synthesis of hemoglobin in developing red blood cells and contractile protein in muscle cells. B. Attached ribosomes: these are polysomes that become attached to the outer membrane of the endoplasmic reticulum. Types of Free solitary Free aggregated Attached ribosomes ribosomes ribosomes ribosomes ( polysomes) 1. LM Not seen but in large amount Not seen but in large amount give cytoplasmic basophilia. give cytoplasmic basophilia. Small electron 10 or more ribosomes Small electron dense 2. EM dense particles. connected by a single strand particles attached to rER. of mRNA. 3. Function Reserve. Synthesis of cytosolic proteins Synthesis of secretory (used within the cell) proteins, lysosomal enzymes & membrane proteins. 10  Histology - Foundation 1) cytoplasmic basophilia is due to presence of high amount of : a. Golgi apparatus b. Ribosomes c. Mitochondria d. Peroxisomes 2) Concerning ribosomes, which of the following is false: a. Free in the cytoplasm b. Attached to the outer surface of rER c. Attached to the outer surface of sER d. Attached to the outer nuclear envelope 3) All the following are membranous organelles except: a. Mitochondria b. Golgi apparatus c. Lysosomes d. Ribosomes 4) Free ribosomes are responsible for the synthesis of: a. Lipids b. Proteins used in cell growth and division c. Carbohydrates d. Proteins secreted outside the cell 5) Ribosomes are constructed in: a. Mitochondria b. rER c. Nucleolus d. Golgi apparatus Answers 1-B 2-C 3-D 4-B 5-B 11  Histology - Foundation 12  Histology - Foundation 2. Endoplasmic reticulum The endoplasmic reticulum forms the most extensive membrane system in the cytoplasm. The ER has two types: - Rough endoplasmic reticulum (rER). - Smooth endoplasmic reticulum (sER). - Both types form a single membrane system. A. Rough Endoplasmic Reticulum (rER): LM: When present in large amounts they cause cytoplasmic basophilia due to their attached ribosomes. EM: 1. It consists of interconnected parallel flattened sacs called cisternae. 2. Its outer surface is studded with ribosomes, resting by their large subunit on the membrane. 3. It is continuous with the outer membrane of the nuclear envelope. 4. The lumen contains flocculent material that represents newly formed protein. Functions: 1. Synthesis of secretory proteins, lysosomal enzymes and proteins inserted into the cytoplasmic membranes. 2. Post translational modification of the newly formed protein e.g.folding, sulfation and initial glycosylation. 3. Transport the newly synthesized protein to the Golgi body by transport vesicles. Sites: Protein synthesizing & secreting cells e.g. liver cells, pancreatic acini, fibroblasts and plasma cells. B. Smooth Endoplasmic Reticulum (sER) LM: Cells with large amounts of sER exhibit cytoplasmic eosinophilia. EM: 1. It consists of close network of interconnected branching tubules and vesicles. 2. The membranes have smooth surface. 3. The membranes of the sER are continuous with that of rER. 13  Histology - Foundation Functions: 1. Synthesis of membrane lipids; the phospholipids and cholesterol. 2. Synthesis of steroid hormones. 3. Synthesis of glycogen in liver. 4. Detoxification of toxic substances e.g. alcohol and drugs. 5. Regulation of calcium ions during muscle contraction. Sites: steroid secreting cells (in the adrenal cortex, testis and ovary), liver cells & muscles. Types of endoplasmic Rough endoplasmic reticulum Smooth endoplasmic reticulum reticulum 1. LM Not seen but in large amount give Not seen but in large amount give cytoplasmic basophilia. cytoplasmic acidophilia. 2. EM Parallel, flattened interconnected Interconnected branching tubules tubules. Studded with ribosomes. and vesicles. No ribosomes. 3. Functions 1. Synthesis of secretory proteins, 1. Synthesis of lipid & cholesterol of lysosomal enzymes& membrane the cell membrane. proteins. 2. Synthesis of steroid hormones. 2. Post translational modification of 3. Synthesis of glycogen. protein. 4. Detoxification of toxic substances. 3. Transport protein to Golgi. 5. Storage of calcium in muscles. 4. Sites Protein secreting cells e.g. liver , Steroid secreting cells, liver & muscles. fibroblasts. 14  Histology - Foundation 1) Protein is synthesized from: a. Peroxisomes b. Smooth endoplasmic reticulum c. Ribosomes d. Lysosomes 2) Rough endoplasmic reticulum is responsible for: a. Lipid synthesis b. Sorting & packaging of proteins c. Synthesis of membrane lipid d. For formation of lysosomal enzyme 3) Highly protein secreting cells are characterized by a supranuclear unstained area which represents the presence of: a. Rough endoplasmic reticulum b. ribosomes c. Golgi apparatus d. Secretory vesicles 4) Rough endoplasmic reticulum is formed of: a. Interconnecting membranous cisterna b. System of membranous vesicles c. Interconnecting microtubules d. Membranous tubules covered by lysosomes 5) Which of the following is a feature of smooth endoplasmic reticulum? a. A basophilic structure b. Covered by ribosomes c. Continuous with nuclear membrane d. Interconnecting membranous tubules Answers: 1. C 2. D 3. C 4. A 5. D 15  Histology - Foundation 16  Histology - Foundation 3. Golgi apparatus LM: 1. It is not stained with H&E in routine histological sections. 2. H&E stained sections of the cells synthesizing protein, its site could be seen as negative Golgi image e.g. plasma cells. 3. It can be seen in histological sections stained with silver stain. EM: 1. It consists of saccules or cisternae called the Golgi stacks. 2. Each stack consists of 4 6 cisternae (flattened, curved, membrane bounded, slightly expanded at the ends). 3. The Golgi stack is cup shaped with a convex surface and a concave surface: a) The cis face (forming face; immature face): - Convex in shape. - Lies near to the rER. - It is the site where the transport vesicles containing the newly formed proteins from rER enter the Golgi for further processing. b) The trans face (secretory face; mature face): - Concave in shape. - It is the site where the modified protein is packaged and released from the Golgi in large secretory vesicles. c) The medial compartment: Between the cis & trans compartments. Functions: 1. Post translational modifications of proteins e.g.removal, addition or modification of sugars 2. Packaging of different proteins in membrane bounded vesicles. 3. Sorting and targeting of vesicles to the right destination: - Formation of lysosomes. - Formation of secretory granules for exocytosis. - Membrane recycling. Sites: Protein synthesizing and secretory cells. N.B: Cytoplasmic Organelles that participate in the process of Protein synthesis: 1. Ribosomes (factories) 2. Rough endoplasmic reticulum (modification& transport) 3. Golgi apparatus (chemical modification,package,sorting& targeting) 17  Histology - Foundation 1)Golgi apparatus can be stained by: a. Silver b. PAS c. Sudan d. Haematoxylin & eosin 2)One of the following statements is not a feature of Golgi apparatus ? a. Formed of saccules arranged in stacks b. Demonstrated by silver stain c. Responsible for detoxification of drugs & hormones d. Produce secretory vesicles and lysosomes 3) which of the following isn't related to the functions of Golgi apparatus: a. Modification of protein b. Concentration of protein c. Synthesis of protein d. Sorting & package of protein 4)Transport vesicles arises from: a. Rough endoplasmic reticulum b. Smooth endoplasmic reticulum c. Golgi apparatus (GA) d. Cell membrane 5) Golgi apparatus is very prominent in: a. Embryonic cells b. Erythroblasts c. Malignant cells d. Plasma cells Answers 1. A 2. C 3. C 4. C 5. D 18  Histology - Foundation 19  Histology - Foundation 4. Endosomes Definition: are system of vesicles and tubules involved in the endocytotic pathway. Types: A. Early endosomes: - Site: at the periphery of the cell as a part in the pathway of the receptor mediated endocytosis. - Content: the receptors ligands complex. - The membrane of the endosomes pumps H+ ions into its interior lowers the pH of endosomes to less than 6 uncoupling of the receptors and the ligands. - The receptors recycle to the cell membrane and the ligands move to the late endosomes. B. Late endosomes: - Site: deep within the cytoplasm near the Golgi complex. - They receive: 1. The ligands from early endosomes. 2. Clathrin coated vesicles containing lysosomal enzymes from Golgi complex. - PH: 5.5. (The enzymes become active at the acidic pH of the late endosome). - The lysosomal enzymes in the late endosome begin to degrade the ligands accompanied by further decrease in the internal pH which then "mature" to form lysosomes. Types of Early endosome Late endosome endosomes 1. Site Periphery of cytoplasm. Deep in cytoplasm , near Golgi. 2. Content Receptor ligand complex. 1. Ligands from early endosome. 2. Lysosomal enzymes from Golgi. 3. Function Uncoupling of the receptor from Lysosomal enzymes begin to degrade ligand. ligands, then the late endosome matures to lysosome. 4. pH Less than 6. 5.5. 20  Histology - Foundation 1. Which of the following is a characteristic feature of early endosomes? A) They are located near the Golgi complex. B) They receive clathrin-coated vesicles containing lysosomal enzymes. C) They have an internal pH of less than 6. D) They degrade ligands into smaller molecules. 2. What triggers the uncoupling of receptor-ligand complexes in early endosomes? A) Movement of the endosome to the Golgi complex. B) Acidification due to H+ ions being pumped into the endosome. C) The addition of clathrin-coated vesicles. D) Binding of lysosomal enzymes to the ligands. 3. What is the fate of receptors after they are uncoupled from ligands in early endosomes? A) They are sent to the Golgi complex. B) They are degraded by lysosomal enzymes. C) They are recycled back to the cell membrane. D) They mature into lysosomes. 4. What do late endosomes primarily receive from the Golgi complex? A) Receptor-ligand complexes. B) Clathrin-coated vesicles containing lysosomal enzymes. C) Proton pumps that decrease internal pH. D) Vesicles containing receptors for recycling. 5. At what stage in the endocytic pathway does degradation of ligands begin, and what promotes this process? A) Early endosome; pH drops below 6. B) Early endosome; lysosomal enzymes become active. C) Late endosome; pH decreases to 5.5, activating lysosomal enzymes. D) Late endosome; ligands are recycled to the cell membrane. Answers 1. C 2. B 3. C 4. B 5. C 21  Histology - Foundation 22  Histology - Foundation 5. Lysosomes Definition: membrane bounded organelle containing about 40 types of acid hydrolytic digestive enzymes (proteases, nucleases, phosphatases, and lipases). Function: They are responsible for intracellular digestion of different materials. Synthesis: by a gradual maturation process as by fusion of the clathrin coated vesicles coming from Golgi complex with late endosomes. Lysosome has a surrounding membrane with unique phospholipids & specialized glycoproteins line the lysosomal membrane from inside that prevents: 1. The leak out of the enzymes to the cytoplasm. 2. Protects the membrane from hydrolysis by its own enzymes. - If a lysosome leaks its contents, the released enzymes would be inactive because of neutral pH of the cytoplasm. LM: They can be recognized by several histochemical methods used to demonstrate the lysosomal enzymes. EM: Lysosomes are heterogeneous in shape and the appearance of their interior. Some are electron dense, others show electron lucent areas. Site: are abundant in phagocytic cells. Pathways for intracellular digestion by lysosomes: 1. Extracellular small particles: internalized by pinocytosis and receptor mediated endocytosis early endosome late endosome where the endocytosed materials are degraded by the lysosomal hydrolases. 2. Extracellular large particles: are engulfed in the process of phagocytosis forms a phagosome fuses with a late endosome. 3. Intracellular particles: are removed by a process called autophagy the enclosure of this organelle by membranes from sER forms an autophagosome fuses with a late endosome. - The hydrolytic enzymes digest most of the content of the lysosomes. - Any indigestible substances remain in lysosomes forming residual bodies. - In long lived cells, accumulated residual bodies indicate cellular aging and are called lipofuscin pigments. 23  Histology - Foundation 1) which of the following statement isn't related to the lysosomes : a. Could be identified by histochemical reactions b. Abundant in plasma cells c. It is heterogeneous d. PH 5 is optimum for activity of their enzymes 2) Lysosome is present in: a. Macrophage b. Neutrophil c. Phagocytic cell d. All the above 3) Cells that are actively involved in phagocytosis of extra cellular material would contain highly levels of: a. rER b. sER c. Lysosomes d. Ribosomes 4) Vesicle enclosed by single membrane, for intracytoplasmic digestion: a. Peroxisome b. Lysosome c. Golgi d. Ribosome 5) All hydrolytic enzymes in lysosome except: a. Phospholipase b. Acid phosphatase c. Nuclease d. Oxidase 1-B 2-D 3-C 4-B 5-D 24  Histology - Foundation 25  Histology - Foundation 6. Mitochondria Function: Powerhouses of the cell as they are the sites of adenosine triphosphate (ATP) production. Sites: All cells EXCEPT terminal keratocytes & RBCs. Structure: LM: When present in large numbers contribute to the cytoplasmic eosinophilia (due to large amount of membrane they contain). EM: a. Membrane bounded organelles. b. Surrounded by two membranes: outer and inner, which define two mitochondrial compartments: - The intermembranous space: between the two membranes. - The matrix space: enclosed by the inner membrane. 1. The outer mitochondrial membrane - It is smooth and porous. - Function: allows passage of small molecules due to the presence of specific transmembrane proteins called porins. 2. The inner mitochondrial membrane a. Folded into cristae which increase its surface area; the number of cristae is greater in cells of greater demand for ATP. - Types of cristae: Lamellar cristae: most of cells. Tubular cristae: steroid secreting cells. b. Impermeable to ions and small molecules due to presence of phospholipid called cardiolipin. - Function: contains the enzymes of the electron transport system (respiratory chain enzymes) and the ATP synthase (known as elementary particles attached to the cristae and their heads are projecting toward the matrix like a lollypop). 3. Intermembranous space - Contains substances diffusing from the cytoplasm through the outer membrane and ions pumped out of the matrix space through the inner membrane. 26  Histology - Foundation 4. Matrix space - Surrounded by the inner mitochondrial membrane. - Functions: a. Enzymes involved in mitochondrial functions as citric acid cycle. b. Mitochondrial DNA and few ribosomes. c. Matrix granules: store calcium ions, play a role in mitochondrial regulation of Ca 2+ intracellular concentration. The genetic system of mitochondria: - The mitochondrial DNA: a. A circular molecule. b. Limited coding capacity. c. Represents 1% of the total DNA of the cell. - Function: Mitochondria can synthesize some of their structural proteins by their own RNAs. Most of the mitochondrial proteins are encoded by the nuclear DNA and are synthesized in the cytoplasm and imported into mitochondria. Mitochondria are self replicating organelles. How do mitochondria adapt to its function? (E/M) a. Outer membrane: smooth &porous contains mitochondrial porins allow easy passage of small molecules. b. Inner membrane is folded into numerous cristae increase surface area for energy production. c. Inner membrane contains cardiolipin make it highly impermeable to ions & small molecules. d. Matrix space: contains enzymes for citric acid cycle, mito DNA & ribosomes synthesize some of their structural proteins, also contains matrix granules store Ca thus play an important role in regulation of intracellular Ca concentration. What is your source of mitochondria? 27  Histology - Foundation 1)Which of the following organelles are the powerhouse of the cell ? a. Ribosomes b. Mitochondria c. Golgi apparatus d. Endoplasmic reticulum 2)Mitochondrial DNA isn't characterized by which of the following: a. It is a single standard b. It is similar to that of bacterial chromosome c. It has a circular structure d. It is synthesized within the mitochondrion 3)Which one of the following statements is not related to mitochondria? a. They are membranous organelles b. They can be stained by Janus green B-stain c. They are the powerhouse of the cell d. Their outer membrane is provided with cristae 4)Enzymes of oxidative phosphorylation for ATP production present in the: a. Mitochondria b. Secondary lysosomes c. Primary lysosomes d. Rough ER 5) Mitochondria ATpase enzyme is mainly located in : a. Intercristae space b. External membrane c. Matrix space d. Cristae 6) In which Type of Cells Mitochondria has Tubular Cristae ? a. Protein Synthesis cells b. Steroid Secreting Cells c. Glycogen Synthesis Cells d. Cardiac muscle Cells Answer 1. B 2. A 3. D 4. A 5. D 6. B 28  Histology - Foundation 29  Histology - Foundation 7. Peroxisome Definition: membrane bounded organelles that contain oxidative enzymes. - Peroxisomes possess no genetic material of their own. Structure of Peroxisome LM: They are not seen by H&E stain. EM: a. Small, spherical bodies with fine granular electron dense content. b. Surrounded by a single membrane. Functions of peroxisomes a. β oxidation of long chain fatty acids to release energy. However, they differ from mitochondria in that they are unable to store this energy in the form of ATP. This energy is released as heat to maintain body temperature. b. Generation of hydrogen peroxide, which detoxifies toxic agents. c. Contain catalase enzyme that converts the excess hydrogen peroxide into water, thus protecting the cell. d. Detoxification of alcohol in cooperation with the smooth endoplasmic reticulum in the liver. Mitochondria Peroxisome 1. LM Not seen by H&E except in large Not seen. amount cause cytoplasmic acidophilia. By special stain (silver stain) appear as brownish granules. 2. EM Double membrane: outer is smooth, and Single membrane enclosed fine inner is folded into cristae enclosed granular contents. matrix space. 3. Function Production of energy & store it in the 1. Produce energy & released it in the form of ATP. form of heat (unable to store it). 2. Produce hydrogen peroxide. 3. Convert excess hydrogen peroxide into water. 4. Detoxification of toxic substances. 4. Sites All body cells except red blood cells & Many cells especially liver keratinocytes. 5. Genetic Present Absent material 30  Histology - Foundation 1)which of the following isn't true regarding to Peroxisomes: a. Dispersed in the cytoplasm association with SER b. Produced hydrogen peroxide c. Contain catalase enzyme d. Originate from lysosomes 2) which of the following isn't related to the functions of peroxisome: a. Beta oxidation of long chain fatty acids b. Energy that comes out as heat and not stored as ATP c. 2H2Oz(toxic)+catalase H2O+O2 H2O+O2 d. Digest nutrients, fertilization e. Oxidases are important in liver cells for detoxification 3. Which of the following correctly describes the energy release during β-oxidation of long-chain fatty acids in peroxisomes? A) Energy is stored in the form of ATP. B) Energy is released as heat to maintain body temperature. C) Energy is transferred to the mitochondria for ATP production. D) Energy is stored within the peroxisome for later use. 4. What role does catalase play in the function of peroxisomes? A) It facilitates the generation of hydrogen peroxide for detoxification. B) It breaks down long-chain fatty acids into ATP. C) It converts excess hydrogen peroxide into water to protect the cell. D) It detoxifies alcohol in cooperation with the rough endoplasmic reticulum. 5. Which of the following is TRUE regarding the structure and visibility of peroxisomes? A) Peroxisomes can be visualized using H&E staining under a light microscope. B) They have a single membrane and are filled with electron-lucent content. C) They appear as small spherical bodies with fine granular electron-dense content under an electron microscope. D) Peroxisomes contain their own genetic material for enzyme production. Answer 1-D 2-C 4-C 5-C 3-B 31  Histology - Foundation 32  Histology - Foundation 8. Cytoskeleton The cytoskeleton is a network of structural proteins (non-membranous cell organelles). Types of cytoskeletons: 3 types, depending on their thickness& their structural proteins: 1. Microfilaments (actin filaments) Diameter: 7 nm. LM: can be visualized by using immunohistochemical staining. EM: thin electron dense filaments. Structural proteins: monomers of G actin (globular actin) polymerize to form F actin (filamentous actin) arranged as a double helix. They are dynamic structures that can elongate & shorten. Functions of microfilaments: A. Cell motility for: - Cell migration. - Cytoplasmic streaming: during movement of organelles and transport of vesicles. - Cytokinesis: formation of contractile ring during cell division. - Muscle contraction associated with myosin. B. Structural role: - Maintenance of the cell shape. - Formation the core of microvilli. 33  Histology - Foundation 2. Microtubules Diameter: 25 nm. LM picture: by using immunohistochemical staining. EM picture: fine tubules. Structural proteins: A. A globular protein dimer called tubulin (each is composed of alpha and beta subunits). B. Chains of tubulin dimers form a protofilament. C. The wall of a microtubule is made up of 13 protofilaments that run longitudinally. Motor proteins associated with microtubules: Kinesin & dynein; they use ATP to provide energy for movement of vesicles and organelles along the microtubules. Microtubules are dynamic structures; can elongate & shorten Functions of microtubules: a. Transport: of organelles & vesicles in the cytoplasm. b. Structural role: - Formation of the mitotic spindle. - Formation of centrioles, cilia & flagella. The microtubule organizing centers: a. Centriole which forms the mitotic spindle. b. The basal bodies of cilia and flagella. 3. Intermediate filaments : Diameter:10 nm LM: by using immunohistochemical staining. EM: electron dense filaments thicker than actin filaments. Structural proteins: like woven ropes. Function of intermediate filaments: They are the most stable (not dynamic) types of the cytoskeletons thus they play a structural role. 34  Histology - Foundation 1)which of the following isn't considered one of the intermediate filaments: a. Desmin b. Myosin c. Vimentin d. Cytokeratin 2)which of the followings isn't considered a membranous organelle: a. Mitochondria b. Filaments c. Lysosomes d. Golgi apparatus 3) Complex network of microtubule, intermediate filaments, microfilaments: a. Ribosome b. Proteasome c. Lysosome d. Cytoskeleton 4) Fixed diameter with 13 protofilaments, their length varies according to tubulin: a. Microtubule b. Intermediate filaments c. Microfilaments 5) Which type of Cytoskeleton form mitotic Spindle: a. Intermediate filament keratin b. Microfilaments c. Microtubule d. Intermediate filament lamin Answer 1-B 2-B 3-D 4-A 5-C 35  Histology - Foundation 36  Histology - Foundation Classification Of Intermediate Filaments: According to their protein composition and their cellular distribution into: A. Cytoplasmic: 1. Keratin: epithelial cells. 2. Vimentin: in the cells of mesenchymal origin e.g., fibroblasts. 3. Desmin: muscle cells. 4. Glial fibrillary acidic protein: neuroglia. 5. Neurofilaments: nerve cells. B. Nuclear: Lamins: lining the inner nuclear envelope. N.B: The intermediate filaments (except for the lamins) are located in specific tissue types; they can be used to determine the origin of cancer by immunohistochemical staining. Cytoskeleton Microfilaments Microtubules Intermediate filaments 1. Diameter 7 nm. 25 nm. 10 nm. 2. LM Seen only by Seen only by Seen only by immunohistochemistry. immunohistochemistry. immunohistochemistry. 3. EM Thin electron dense Fine tubules. Thicker electron dense filaments. filaments. 4. Structural Monomers of G actin Tubulin dimer polymerize Woven ropes. proteins polymerize to form F to protofilaments. actin. 13 protofilaments form a microtubule, 5. Functions Dynamic Dynamic. Not dynamic. 1. Muscle contraction. 1. Transport of Structural support. 2. Contractile ring in cell organelles & vesicles. division. 2. Formation of 3. Pseudopodia in centrioles, cilia & migration. flagella. 4. Microvilli. 5. Cytoplasmic streaming. 37  Histology - Foundation Centrosome Definition: a non membranous organelle. EM: 1. It is formed of 2 centrioles, perpendicular to each other. 2. Each centriole is composed of 9 triplets of microtubules (a sum of 27 microtubules). 3. Each triplet is composed of three microtubules (one complete; formed of 13 protofilaments and 2 incomplete; each is formed of 10 protofilaments). Functions of centrosome: 1. It is the microtubule organizing center. 2. Formation of mitotic spindles. 3. Formation of cilia & flagella. Cytoplasmic Inclusions 1. Stored Food: A. Glycogen Storage form of carbohydrates. Function: source of energy. Sites: mainly in liver & muscle cells. LM: - H&E: not visualized as they dissolve during preparation of the specimen leaving a pale vacuolated cytoplasm. - Periodic acid Schiff: appears magenta red. - Best's carmine: appears bright red. EM: dense granules, larger than ribosomes. In cytoplasm of hepatocytes, glycogen appears as rosette shaped aggregates 38  Histology - Foundation B. Lipids Function: 1. Source of energy. 2. Synthesis of membranes & steroid hormones. Sites: stored in the adipocytes; many other cell types contain few small lipid droplets. LM: - H&E: not visualized because they dissolve during preparation of the specimen leaving a pale vacuolated cytoplasm. - Osmium tetroxide: appear black. EM: grey non membrane bounded small droplets or large globules. C. Proteins Site: in protein synthesizing cells e.g. salivary gland and pancreas. LM: eosinophilic zymogen granules. EM: homogenous electron dense membrane bounded secretory granules. 2. Pigments: A. Endogenous pigments 1. Hemoglobin: in red blood cells. 2. Hemosiderin: brownish granules in phagocytic cells of liver and spleen following phagocytosis of old RBCs. 3. Melanin pigment: brown to black granules. 4. Lipofuscin pigment: yellow brown pigment present in cells with long life span. B. Exogenous pigments 1. Tattooing: colored pigments are injected into the deep layers of the skin. 2. Dust & smokes: in lung of smokers and people living in polluted areas. 39  Histology - Foundation 1. Which of the following accurately describes the structure of a single centriole in the centrosome? A) 9 pairs of microtubules, each made up of 13 protofilaments. B) 9 triplets of microtubules, with one complete microtubule and two incomplete microtubules. C) 27 microtubules, each formed from 13 protofilaments. D) 9 doublets of microtubules, each with 10 protofilaments. 2. Which function of the centrosome is related to its role as the microtubule-organizing center? A) Formation of cilia and flagella. B) Generation of cellular energy. C) Packaging of proteins into vesicles. D) Detoxification of alcohol. 3. What is the arrangement of the two centrioles in the centrosome? A) They are parallel to each other and surrounded by a membrane. B) They are perpendicular to each other and surrounded by a membrane. C) They are parallel to each other and composed of 9 pairs of microtubules. D) They are perpendicular to each other and are non-membranous. Answer 1-B 2-A 3-D 40  Histology - Foundation 1)Which of the following is an exogenous pigment? a. Lipochrome pigment b. Melanin pigment c. Haemoglobin d. Dust pigment 2)Which one of the following structures increases with age? a. Ribosomes b. Mitochondria c. Lysosomes d. Lipofuscin pigment 3)The only endogenous pigment of the following: a. Carotene b. Dust particles c. Carbon particles d. Melanin 4)which of the following isn't considered one of the inclusions: a. Glycogen b. Melanin c. Ribosomes d. Fat Answer 1-D 2-D 3-D 4-C 41  Histology - Foundation 42  Histology - Foundation Nucleus It is the largest membranous organelle of the cell. Functions: 1. It contains the chromosomes. 2. Contains the machinery for DNA replication& RNA transcription. Number: 1. Single: most of the cells. 2. Binucleated: liver cells. 3. Multinucleated: skeletal muscle fibers. 4. Absent: RBCs. Cytoplasmic Inclusions A. The Nuclear Envelope: It consists of two parallel membranes; outer & inner separated by the perinuclear cisterna. It is perforated by the nuclear pores which provide a channel between the nucleus and cytoplasm. 1. The outer membrane: It is continuous with the rough endoplasmic reticulum. It is covered with ribosomes on its outer surface. Function: The ribosomes synthesize the transmembrane proteins of the nuclear membranes. 2. The inner membrane: It is supported at its inner surface by the lamins. Functions of the lamin: 1. Supports the nuclear envelope. 2. Influences chromosome distribution and function. 43  Histology - Foundation 3. The nuclear pores: Definition: They are perforations in the nuclear envelope where the outer and inner nuclear membranes fuse. Distribution: not uniformly distributed. Number: vary according to the cell activity. Function: provide a bidirectional channel through which the nucleus and cytoplasm communicate. Nuclear Pore Complex B. The Chromatin It is formed of DNA + histone proteins. DNA is extensively packaged in chromatin as: 1. A segment of the DNA is wrapped two times around eight histone proteins to form a nucleosome. Each nucleosome is separated from the next by a region of linker DNA. 2. Repeating nucleosomes with intervening DNA (linker DNA) form a 10 nm fiber (beads on a string). 3. This chain of nucleosomes is packed to form a 30nm fiber. 4. Higher orders of packaging gives the compact structure 700nm seen in the metaphase of the dividing cell known as the chromatid of a chromosome. Types of chromatins: 1. Heterochromatin (condensed chromatin; the inactive chromatin): LM: appears as dense basophilic clumps. EM: appears as condensed filaments or granules distributed in the following Sites: - Nucleolar associated heterochromatin: around the nucleolus. - Peripheral heterochromatin: at the inner nuclear membrane(associated with the nuclear lamin). - Heterochromatin islands: swimming in the nuclear sap. Function: transform into euchromatin when needed. 44  Histology - Foundation 2. Euchromatin (extended chromatin; the active chromatin) LM: appears as lightly stained basophilic areas. EM: appears as dispersed filaments or granules. Function: It is stretched so, the genetic information in the DNA can be transcribed. The proportion between euchromatin and heterochromatin differs from one cell to another according to its activity. Types of Heterochromatin Euchromatin chromatin 1. LM Dense basophilic clumps. Lightly stained basophilic areas. 2. EM Electron dense filaments or granules Dispersed fine filaments or distributed in: granules. 1. Around nucleolus. 2. Associated with inner nuclear membrane. 3. Swimming in nuclear sap. Inactive part acts as a reserve (transformed Active part (transcribed into RNA). 3. Function into euchromatin when needed). 4. Sites Inactive cells. Active cells e.g., dividing cells. Chromosome - During cell division: chromatin is condensed into the chromosomes; formed from two chromatids held together at the centromere. Each chromatid is formed of a single DNA molecule. Karyotyping - The somatic cell contains 46 chromosomes. - Karyotyping: is the arrangement of the chromosomes during metaphase into groups of homologous pairs (22 homologous pairs of autosomes and one pair of sex chromosomes). - In females (44 autosomes +XX): one X chromosome is heterochromatic - (Barr body), it can be identified in neutrophils, attached to the nucleus in the form of a drumstick mass. 45  Histology - Foundation C. The Nucleolus Definition: It is a spherical body with no surrounding membrane. Number: single or multiple. Function: it is the site of formation of ribosomal RNA. These rRNA's are packaged with their associated protiens to form ribosomal subunits that are exported to the cytoplasm via nuclear pores to start protein synthesis D. The Nucleoplasm (nuclear matrix; sap) Definition: It is a colloidal protein solution Function: provides a medium for the rapid diffusion of metabolites. 46  Histology - Foundation 1) Largest component of the cell, not present in RBCs: a. Nucleolus b. Nucleus c. Cytoplasm d. Chromatin 2) Nucleus may be : a. Mononucleated b. Binucleated c. Multinucleated d. All the above 3) Nuclear membrane : a. Basophilic b. Double walled membrane c. Interrupted by pores d. All the above 4) which of the following isn't related to the properties of Heterochromatin: a. Coiled, inactive chromatin b. Inactive gene, electron dense c. In small lymphocyte d. Active in protein forming cell 5) Site of heterochromatin: a. Attached to inner envelope b. Scattered in nuclear sap c. Around nucleolus d. All the above 6) which of the following isn't related to the properties of Euchromatin : a. Extended, uncoiled b. Active gene c. Coarse clumps, dark basophilic d. Electron lucent, clear nucleolus 7) Which of the follow best describes the nuclear envelope a. It has few nuclear pores in active cell b. It has uniformly distributed nuclear pores c. It is supported from the inside by nuclear lamina Answer 1-B 2-D 3-D 4-D 5-D 6-C 7-C 47  Histology - Foundation 48  Histology - Foundation Cell Cycle & Cell Division The Cell Cycle: Definition: it is the alternation between interphase and mitosis. I. Interphase: a longer period between two mitotic divisions: 1. The cell increases in size. 2. Performs its normal functions. 3. Replicates its DNA for preparing itself for division. II. Mitosis: a shorter period during which parent cell gives 2 daughter cells each containing the same number of chromosomes (identical to the parent cell = 46 chromosomes). I-Interphase ( ): First gap phase (G 1 phase) It is the longest period of the cell cycle between the end of mitosis and the beginning of DNA replication: 1. The RNA and protein synthesis occurs. 2. The cell attains its full size. 3. The cell performs its function. 4. Duplication of centrosomes occurs near the transition between G1 and S phase. The GO phase: Definition: Differentiation of the cell to carry out specialized function and no longer divide (outside the cycle). GO may be permanent or temporary. 49  Histology - Foundation DNA synthesis phase (S phase): Replication of DNA, thus the amount of DNA is doubled but not the total chromosomal number. Types of chromosomes: S - Chromosomes made of one DNA molecule (interphase chromosomes = chromatin or chromatids). D - C hromosomes (mitotic chromosomes):are formed during the S phase. Each d chromosome is formed of two chromatids, linked at the centromere. Each chromatid is made of a DNA molecule. Second gap phase (G2 phase): It starts by the end of the DNA replication and lasts until the beginning of mitosis. 1. Proteins and energy essential to mitosis are stored. 2. Duplication of the centrosome is completed. 50  Histology - Foundation Cell Division: Mitosis Definition: division of the somatic cell into two daughter cells identical to the mother cell. Function: 1. Growth & development of the organism. 2. Renewal & repair of cells. A. Prophase : 1. The nucleolus disappears. 2. Condensation of chromatin gives rise to 46 rod shaped short d chromosomes. 3. Each pair of centrioles migrates to opposite pole of the cell forming the mitotic spindles. 4. The nuclear envelope breaks up into small vesicles B. Metaphase : 1. The 46 d chromosomes become maximally condensed. 2. The chromosomes aligned at the equatorial plate of the cell. Each pair of sister chromatid is attached to the mitotic spindles at the kinetochore. C. Anaphase : 1. Division of the centromere results in the separation of the sister chromatids. 2. Each 46 chromatids migrate toward the opposite poles of the cell. 3. In late anaphase, a constriction (cleavage furrow) develops at the equatorial plate of the cell. D. Telophase : 1. The mitotic spindle disappears. 2. The nucleolus reappears. 3. The chromosomes start uncoiling (46 s chromosomes). 4. The nuclear envelope is reformed around the new sets of chromosomes. 5. Division of the cytoplasm (cytokinesis): the cleavage furrow becomes deeper due to the formation of a contractile ring of microfilaments until it divides the cytoplasm and its organelles in half resulting into two daughter cells. 51  Histology - Foundation Regulation of the cell cycle: The cell cycle is regulated by growth factors that control cell proliferation to keep its coordination with the needs of the living organism. Several checkpoints control the transition between the cycle stages. Checkpoints detect external or internal problems and stop the cycle until the problem solved. Checkpoints of the cell cycle: 1. The restriction checkpoint: It occurs in the G1 phase. It detects the cell size & its interactions with the surrounding environment. Cells that do not receive appropriate growth stimuli do not progress past this point (G1 phase) and will be die by apoptosis. It is the most important checkpoint in the cell cycle. 2. DNA damage checkpoints: It occurs in G1, S, and G2 phases. It blocks cell cycle progression until repair of the damaged DNA or cell apoptosis occurs. 3. The unreplicated DNA checkpoint: It occurs in the G2 phase. It prevents progression of the cycle into the mitosis before complete synthesis of DNA. 4. The spindle assembly checkpoint (the metaphase checkpoint): It occurs in mitosis. It prevents entry into anaphase until all chromosomes have attached properly to the mitotic spindle. 5. The chromosome segregation checkpoint: It occurs in telophase. It prevents the cytokinesis until all of the chromosomes have been correctly separated. 52  Histology - Foundation Meiosis It occurs in germ cells and results in the formation of gametes. It results in formation of 4 daughter cells (each contains 23 s chromosomes=haploid number). It consists of two successive divisions: without an intervening S phase. I. First meiotic division (reductional division): It is preceded by interphase with an S phase, in which the chromosomes are replicated (46 s chromosomes 46 d chromosomes). 1. Prophase I: A. Pairing of the homologous chromosomes occurs forming tetrads(bivalent). B. Crossing over occurs between the chromatids of the homologous chromosomes so that each homologous chromosome is no longer solely paternal or maternal but a mixture of both. C. The nucleolus and the nuclear envelope disappear, and the mitotic spindle is formed. 2. Metaphase I: The paired chromosomes arrange themselves at the equatorial plate of the cell. 3. Anaphase I: The centromeres do not divide, instead, each chromosome of homologous pairs moves separately towards the opposite poles of the cell. 4. Telophase I: Cytokinesis occurs results in two daughter cells each containing the haploid number (23d chromosomes). 53  Histology - Foundation II-Second meiotic division (equatorial division): It is similar to mitosis but, it is not preceded by S phase. It results in formation of 4 daughter cells, each contains 23 s chromosomes (haploid number). 46 d chromosomes 23 d chromosomes 23 S chromosomes Mitosis Meiosis 1. Types of cells Somatic cells Germ cells of testis & ovaries 2. No of division Single division 2 successive divisions: Meiosis I & Meiosis II. 3. Interphase Preceded by interphase with Meiosis I preceded by interphase with S S phase phase, Meiosis II not preceded by S phase. 4. Prophase No crossing over Meiosis I: Crossing over occurs 5. Metaphase 46 d chromosomes arranged In Meiosis I :23 bivalent arranged at the individually at the equatorial equatorial plane of the cells. plane of the cells. 6. Anaphase Each chromosome divides at In Meiosis I: each chromosome of a centromere into 2 chromatids bivalent moves apart. 7. Cells Two daughter cells with Four daughter cells with haploid number of produced diploid number of chromosomes (23 S) Daughter cells are chromosomes (46 S) genetically variable. Daughter cells are genetically identical 54  Histology - Foundation Meiosis Meiosis I Meiosis II 1. Preceded Present (the cell enter the prophase Absent (the cell enter the prophase S phase with 46 d chromosomes). with 23 d chromosomes). 2. Prophase Pairing of homologous chromosomes No pairing result in 23 tetrad. Crossing over No crossing over. occurs between each tetrad. 3. Metaphase 23 tetrad arranged at the equatorial 23 d chromosomes arranged plane of the cells. individually at the equatorial plane of the cells. 4. Anaphase No division of the centromere. Each Centromere splits so each chromatid chromosome moves independently moves independently to the opposite to the opposite pole of the cell. pole of the cell. 5. Telophase Cytokinesis results in 2 daughter Cytokinesis results in 4 daughter cells each with 23 d chromosomes. cells each with 23 S chromosomes. 55  Histology - Foundation 1) In which phase of mitosis occur "disappearing of nucleolus" ? a. Prophase b. Anaphase c. Metaphase d. Telophase 2)In which phase of Cell Cycle Protein Synthesis occurs: a. Interphase b. Meiosis c. S phase d. Telophase 3) Which statement describes the interphase? a. Storage of energy occurs during G1 phase b. S phase occurs in the static cell population c. The centrosome starts its duplication in G2 phase d. It is the period between two successive cell divisions 4)In which phase of Cell Cycle occur The Restriction Checkpoint: a. G1 Phase b. G2 Phase c. S phase d. G1,G2,S Answer 1-A 2-A 3-D 4-A 56  Histology - Foundation 57  Histology - Foundation Cell Proliferation & Cell Death Difference between cell proliferation and cell differentiation: Cell differentiation Cell proliferation It is the process by which unspecialized Increase in the number of cells by division. cells acquire specialized structural and/or functional features that characterize the specialized cells. Cell proliferation & differentiation: Early development: Rapid proliferation of embryonic cells, which then differentiate to produce the many specialized types of cells that makeup the organs. As cells differentiate: The rate of proliferation decreases, and many cells are arrested in the GO stage. Cell proliferation is balanced with cell death to maintain a constant number of cells. Classification of the body cells according to their ability of proliferation: 1. Static cell population (non-dividing, permanent): They leave the cell cycle to perform specialized function (GO stage), e.g. cardiac muscle fibers & neurons. 2. Stable cell population(quiescent): They are considered to be in Go stage, but they may be stimulated to divide by signals e.g. smooth muscle fibers and the epithelial cells of the liver and kidney. 58  Histology - Foundation 3. Labile cell population: They are continuously renewing cells e.g. cells have short life span as blood cells, epithelial cells of the skin &epithelial cells lining the digestive tract They are replaced by proliferation of the stem cells. Cancer and labile cells Cancer Affects more the labile cells Chemotherapy destroys the labile cells Stem Cells Definition: undifferentiated (unspecialized) cells that can proliferate & differentiate to give specialized cells. Stem cell properties: 1. Self renewal: the ability of the cell to go through numerous cycles of cell division while maintaining the undifferentiated state. 2. Potency: the capacity to differentiate into different cell types. Types of stem cells: Stage of Embryogenesis 59  Histology - Foundation 1. Totipotent stem cells They have the potential to generate all types of cells and construct a complete organism. They are derived from the cells produced by the first few divisions of the fertilized ovum (morula cells). 2. Pluripotent stem cells They can differentiate into the derivatives of the three germ layers =ectoderm, endoderm, and mesoderm. They are derived from the inner cell mass of the blastocyst. 3. Multipotent stem cells: They can produce cells of a closely related family e.g. hematopoietic stem cells that can differentiate into red blood cells, white blood cells and platelets. 4. Unipotent cells They can produce a single type of mature cell but still have the property of self renewal which distinguishes them from nonstem cells e.g. stem cells in the skin epidermis. Potential sources of stem cells for clinical application: 1. Embryonic stem cells They are pluripotent stem cells derived from inner cell mass of blastocyst. Advantage: They can specialize and become any type of body cells. Disadvantage: ethical restriction. 2. Adult stem cells: Most of them are multipotent. 3. Amniotic fluid stem cells: They are multipotent. 4. Umbilical cord blood stem cells: They are pluripotent. 60  Histology - Foundation Cell Death Types of cell death 1. Necrosis = accidental cell death: Causes: It is a pathological process due to e.g. hypoxia, radiation or pathogens such as viruses. Morphological features: A. Damage of the cell membrane with cell swelling& rupture. B. Breakdown of cell organelles. C. Denaturation or coagulation of cytoplasmic proteins. D. Inflammation with extensive damage of the surrounding tissue. 2. Apoptosis = programmed cell death: It is a physiological process controlled by several genes (loss of mitochondrial function initiates several reactions that lead to cell death). 61  Histology - Foundation 1. Which of the following statements best defines cell differentiation? A) The process by which cells undergo mitosis. B) The increase in the number of unspecialized cells. C) The process by which unspecialized cells acquire specialized structural and functional features. D) The balance between cell death and cell proliferation. 2. What happens to cell proliferation as cells undergo differentiation during early development? A) The rate of proliferation increases. B) Cells are arrested in the G1 phase. C) Cells are arrested in the G0 stage. D) Cell proliferation continues at the same rate as in early development. 3. Which type of cells are classified as non-dividing, permanent cells that leave the cell cycle to perform specialized functions? A) Labile cells. B) Stem cells. C) Stable cells. D) Static cells. 4. Which of the following is an example of a stable cell population? A) Cardiac muscle fibers. B) Neurons. C) Smooth muscle fibers. D) Epithelial cells of the skin. 5. Cancer treatments such as chemotherapy primarily affect which type of cells? A) Static cells. B) Labile cells. C) Stable cells. D) Totipotent stem cells. 62  Histology - Foundation 6. Which property of stem cells allows them to go through numerous cycles of cell division while maintaining their undifferentiated state? A) Potency. B) Totipotency. C) Self-renewal. D) Differentiation. 7. Which type of stem cell has the ability to generate all types of cells and form a complete organism? A) Pluripotent stem cells. B) Multipotent stem cells. C) Totipotent stem cells. D) Unipotent stem cells. 8. From which source are pluripotent stem cells derived during embryogenesis? A) The morula. B) The inner cell mass of the blastocyst. C) Hematopoietic stem cells. D) The zygote. 9. Which of the following stem cells has the capacity to differentiate into cells of a closely related family, such as hematopoietic stem cells? A) Pluripotent stem cells. B) Totipotent stem cells. C) Multipotent stem cells. D) Unipotent stem cells. 10. What is a key advantage of using embryonic stem cells for clinical application? A) They can differentiate only into hematopoietic cells. B) They can specialize into any type of body cell. C) They are not affected by ethical restrictions. D) They are multipotent. Answer 1-C 2-C 3-D 4-C 5-B 6-C 7-C 8-B 9-C 10-B 63  Histology - Foundation 64  Histology - Foundation What makes a cell decide to commit suicide? I-During embryonic development: Removal of excess cells that have no function e.g. during morphogenesis and for determination of organ size. II-In adult: 1. Hormone dependent: Involution of the endometrium during the menstrual cycle. Regression of lactating mammary gland after weaning. Regression of prostate in old males 2. Elimination of cells during cell cycle when their DNA damage is not repaired. 3. Maintaining a constant number of cells in proliferating cell populations, e.g. intestinal epithelium. Morphological features of apoptosis: 1. Loss of microvilli and intercellular junctions. 2. Shrinkage of the cell with membrane blebing. 3. Breakdown of DNA with hypercondensation of chromatin and its collapse against the nuclear periphery. 4. Change of cell membrane characters without loss of its integrity. 5. Cell organelles remain apparently normal but become clumped inside the cytoplasm. 6. Fragmentation of the cell into apoptotic bodies that contain fragments of the nucleus, mitochondria, and other organelles. 7. The apoptotic bodies are removed by the phagocytic cells. 65  Histology - Foundation Necrosis Apoptosis 1. Type Pathological. Physiological. 2. Cell membrane Damage with loss of its Change of some characters without loss of integrity. its integrity. 3. Organelles Broken down. Intact. 4. Proteins Denatured or coagulated. Broken down of DNA with hypercondensation of chromatin. 5. Apoptotic Absent Present bodies 6. inflammation Present Absent 66  Histology - Foundation 1. Which of the following is NOT a morphological feature of necrosis? A) Damage of the cell membrane with swelling and rupture. B) Denaturation or coagulation of cytoplasmic proteins. C) Formation of apoptotic bodies containing nuclear fragments. D) Breakdown of cell organelles. 2. What is a key feature that differentiates apoptosis from necrosis at the cellular level? A) Loss of mitochondrial function. B) Involvement of inflammation with extensive tissue damage. C) Cell swelling and rupture leading to tissue damage. D) Release of viral particles causing cell damage. 3. Which of the following examples illustrates hormone-dependent apoptosis in an adult? A) Elimination of damaged intestinal epithelial cells. B) Involution of the endometrium during the menstrual cycle. C) Cell swelling and denaturation of proteins in the prostate. D) Removal of excess cells during embryonic morphogenesis. 4. During apoptosis, what happens to the chromatin inside the nucleus? A) It undergoes random fragmentation with loss of membrane integrity. B) It remains unchanged while the cytoplasmic organelles break down. C) It hypercondenses and collapses against the nuclear periphery. D) It is released into the cytoplasm, triggering immune responses. 5. What is the fate of apoptotic bodies formed during apoptosis? A) They cause inflammation and extensive tissue damage. B) They swell and rupture, releasing cellular contents into surrounding tissue. C) They are engulfed and removed by phagocytic cells. D) They fuse together, forming large necrotic areas in tissues. Answer 1-C 2-A 3-B 4-C 5-C 67  Histology - Foundation 68  Histology - Foundation Epithelium Basic tissues: A group of similar cells specialized to perform a commonfunction. These tissues exist in associations forming body organs.They are 4: Connective tissue Muscular tissue Epithelial tissue Nervous tissue Arises from mesoderm Arises from mesoderm Arises from mesoderm, Arises from ectoderm ectoderm,mesoderm Epithelium Characteristics of Epithelium: Classification of Epithelium: I-Lining Epithelium EpitheliumClassification of covering epithelia 69  Histology - Foundation Simple Epithelium 1. Simple Squamous: Side view: Flat cells & Flattened nucleus. Surface view: polygonal. Sites: a. Filtration: Bowman, s capsule of kidney. b. Diffusion: alveoli of lung. c. Smooth passage: endothelium of blood vessels and lymph vessels. d. Allows free mobility: mesothelium of leura, pericardium and peritoneum.. 2. Simple cuboidal: Shape: cubical cells with central rounded nuclei. Sites: Kidney tubules & Thyroid follicles (ion exchange). 3. Simple columnar: Shape: columnar cells, the nuclei are oval & basal Types & Sites: a. Non ciliated: Secretion & absorption (stomach, small intestine, gall bladder). (may have microvilli) b. Ciliated: Secretion (uterus, fallopian tube). 4. Pseudostratified columnar epithelium: a. Crowded cells, all cells lie in contact with the basement membrane, but they do not all reach the surface. b. The cells that reach the surface are tall columnar cell, while the other cells which do not reach the surface are short and triangular. c. Several layers of nuclei, each lies at the widest portion of the cell, giving false appearance of stratification. Types & Sites: a. Non ciliated with microvilli: male genital tract. b. Ciliated: most of respiratory system (pseudostratified ciliated columnar epithelium with goblet cells). 70  Histology - Foundation Stratified Epithelium It is classified according to the shape of the most superficial layer of cells. 1. Stratified squamous: Function: protection. Structure: a. Basal layer: low columnar; cuboidal cells. b. Intermediate layers: Polygonal cells. c. Superficial layer: Squamous cells. Types: a. Keratinized: The superficial cells are filled with keratin (skin). b. Non keratinized: In wet surfaces subjected to wear & tear (cornea, esophagus, mouth cavity & vagina). 2. Stratified cuboidal: Uncommon type. Two layers of cuboidal cells. Ducts of sweat glands 3. Stratified columnar: Uncommon type. The superficial cells are columnar in shape. Transitional Epithelium: Conjuctival fornix Change its shape and number of layers, according to the functional state of the organ, e.g. urinary bladder& ureter. Empty bladder 1. A basal layer: low columnar cells. 2. Intermediate layers: polygonal cells,tend to be pear shaped near surface. 3. The surface layer: large cuboidal (dome shaped cells; umbrella cells). Full bladder 1. Superficial: large, flattened cells. 2. Basal: cuboidal cells. How does the transitional epithelium adapt to its function? 1. Decrease of number of layers due to gliding of the cells. Increase surface area 2. Flattened cells 71  Histology - Foundation II-Glandular Epithelium Function: fluid secretion. Origin: from the covering epithelium Types Of Glandular Epithelium: 1. According to number of cells a. Unicellular glands: consist of one cell e.g., goblet cells present in the small and large intestine and the respiratory tract. b. Multicellular glands: consist of groups of cells e.g., most glands of the body. 2. According to the presence or absence of a duct system: a. Exocrine glands: in which the secretion is carried by ducts e.g., salivary glands. b. Endocrine glands or ductless glands: in which the secretion is released into the blood vessels e.g., thyroid gland and suprarenal gland. c. Mixocrine (mixed exocrine and endocrine) glands: contain the two types e.g., pancreas. 3. secretory (the secretion of mode the to Accordingmechanism): a. Merocrine glands: the secretory granules are discharged by exocytosis through the cell membrane without losing any part of the cell e.g., pancreas& salivary glands. b. Apocrine glands: the secretion is discharged together with the apical parts of the cytoplasm e.g., mammary gland. c. Holocrine glands: the secretion is discharged with the whole cell leading to its complete destruction e.g., sebaceous gland. 4. According to the nature of secretion: a. Serous glands: secrete a watery secretion e.g., parotid salivary gland. b. Mucous glands: secrete mucous e.g., goblet cells and sublingual salivary gland. c. Mixed glands: secrete both mucous and serous secretions e.g., submandibular salivary gland. d. Glands with special secretions: ceruminous glands which secrete ear wax and sebaceous glands which secrete a fatty secretion (sebum). 5. According to the shape of the secretory portion: a. Tubular: the secretory units are tubular in shape. b. Alveolar (acinar): the secretory units are rounded. c. Tubuloalveolar (tubuloacinar): the secretory units have both tubular and alveolar parts. 72  Histology - Foundation 6. According to the branching of the ducts and branching of the secretory portion: a. Simple glands: have only one unbranched duct and one secretory unit. b. Simple branched glands: have one unbranched duct and branched secretory units. c. Compound glands: have branched duct system& branched secretory units. III-Special Types of Epithelium 1. Neuroepithelium: The epithelial cells act as nerve receptors. Sites: a. The taste buds of the tongue. b. The organ of Corti in the ear. c. The retina of the eye. 2. Germinal epithelium: The epithelium carrying the function of reproduction. Sites: in the testis and ovary. 3. Myoepithelial cells: Definition: modified stellate epithelial cells which surround the secretory units (the acini) and the ducts of the glands. Structure: contain myosin and actin myofilaments. Function: they are able to contract and squeeze the secretion from the glands. Sites: a. Salivary gland. b. Mammary gland. c. Sweat glands Functions of Epithelium: 1- Protection (stratified) 5- Secretion (glandular) 2- Absorption (simple) 6- Contraction (special) 3- Filtration (simple) 7- Reproduction (special) 4- Gas diffusion (simple) 8- Perception (special) 73  Histology - Foundation 1)Called uro-epithelium: a. Transitional b. Stratified squamous c. Stratified cubical d. Stratifies columnar 2)Its function is distensibility: a. Transitional b. Stratified squamous c. Stratified cubical d. Stratified columnar 3)The epithelium lining of the blood vessels is called : a. Transitional epithelium b. Simple columnar epithelium c. Mesothelium d. Endothelium 4)The epithelial lining of the serous (need mobility) membrane is called : a. Transitional epithelium b. Simple columnar c. Mesothelium d. Endothelium 5) Neuro epithelium is present in: a. Bone marrow b. Thymus c. Trachea d. Tongue Answer 1-A 2-A 3-D 4-C 5-B 74  Histology - Foundation 75  Histology - Foundation Epithelial Cell Polarity Definition : The epithelial cell has an apical,basal, and lateral surfaces, each surface exhibits special structural modifications to carry out specific functions. I- Apical Modifications 1. Microvilli: Definition: non motile, finger like cytoplasmic projections arise from the apical surface of epithelial cells. Structure: a core of actin filaments. Function: increase the surface area for absorption. Sites: The cells of the intestine and kidney tubules. 2. Stereocilia: Definition: long, branching microvilli. Function: increase the surface area for absorption. Site: the non ciliated pseudostratified columnar epithelium of the male genital ducts e.g. the epididymis. 3. Cilia and flagella: Definition: motile cytoplasmic projections that extend from the cell surface. Cilia: are hair like processes that are longer than microvilli. Flagella: resemble cilia in structure but they are much longer and are single for each cell e.g., flagellum of the sperm. Structure: each cilium is formed of: a. The basal body: replicate of the centrioles (9 triplets of microtubules) from which the shaft arises. The basal body is present in the apical cytoplasm. b. The shaft (axoneme): extends from the cell surface. It contains 9 peripheral doublets of microtubules + a central pair of singlet microtubules (9x2+2=20 microtubules). c. Rootlets: extend from underneath the basal body, in the form of radiating microtubules anchoring the cilium into the cytoplasm. 76  Histology - Foundation N.B: Abnormal proteins of cilia or flagella resulting from mutation.. Male infertility: due to immotile sperm.. Chronic respiratory infection : caused by lack of cleaning action of cilia in the epithelium of respiratory tract. Apical Microvilli Stereocilia Cilia modifications 1. Motility Non motile Non motile Motile 2. Length Shorter. Longer. Longer. 3. Shape Finger like cytoplasmic Branching microvilli. Hair like cytoplasmic projections. projections. 4. Structure Core of actin filaments. Core of actin filaments. Consists of basal body, shaft & rootlets, all formed of microtubules. 5. Function Increase surface area Increase surface area Move a layer of fluid. for absorption. for absorption. 6. Most In & testinal cellskidney Male genital tracts e.g. Respiratory tract. common sites tubules. epididymis. II- Basal Modification: 1. Basal infoldings: Definition: the basal cell membrane is thrown into folds. Function: increase the surface area for ions transport. Site: kidney tubules 2. Basement membrane: Site: in the interface between epithelium and connective tissue. Structure: A. The basal lamina: formed of adhesive glycoprotein. B. The reticular lamina: formed of fine network of collagen fibrils. Some non epithelial cells are invested by a basal lamina like material called external lamina e.g., muscle fibers, Schwann cell and adipocytes (the external lamina protects the fat cells from mechanical stress ). It is not called basal lamina because these cells have no basal surface. 77  Histology - Foundation Functions of Basement Membrane: A. Structural attachment: attachment of the epithelial cells to the underlying connective tissue. B. Filtration: regulates exchanges of macromolecules between the epithelium and the surrounding tissues. C. Tissue scaffold: it directs the migration of epithelial cells (re epithelization) during wound repair. It acts as barrier against passage of malignant cells. 3. Basal cell to matrix adhesions: Hemidesmosomes 78  Histology - Foundation 1)Fix epithelium to basement membrane and C.T: a. Hemidesmosome b. Basement membrane c. Basal infoldings d. Desmosome 2) These are motile has like structures on surface some epithelial cells: a. Flagella b. Cilia c. Stereocilia d. Micro villi 3) Long motile structure on the surface of some epithelial cells are known as : a. Microvilli b. Cilia c. Flagella d. Stereocilia 4) It is brush border shaped: a. Stereocilia b. Cilia c. Microvilli d. Flagella 5)Has core of actin filament inserted in terminal web: a. Stereocilia b. Cilia c. Microvilli d. Flagella 6) With EM, finger like projections on the apical surface of epithelial cells are called : a. Inter digitations b. Infoldings c. Filaments d. Microvilli Answer 1-A 2-A 3-C 4-B 5-B 6-D 79  Histology - Foundation 80  Histology - Foundation Lateral Specialization & Intercellular Junctions Lateral Specialization: 1. Cellular interdigitations: increase the surface area for transport. Sites: cells of the intestine and kidney tubules. 2. Intercellular junctions: link the neighboring cells together. Types Of Cell Junctions 1. Cell to cell adhesion. 2. Cell to matrix adhesion. Cell adhesion is a dynamic process: 1. Non adhesive cells become adhesive. 2. Adhesive cells become non adhesive. 81  Histology - Foundation Cell To Cell Junctions I. Tight junction (occluding Junction, zonula Site: at the apical parts of the cells. Function: restrict the passage of molecules between the epithelium (barrier) e.g. epithelial cells of intestine. Structure: A. The outer leaflets of adjacent cell membranes are fused together, forming a belt like junction. B. 2 transmembrane proteins (occludin & claudin) join together to seal (occlude) the intercellular space no intercellular space between the adjacent cells. II. Anchoring junctions Site: in cells that are subjected to severe mechanical stress e.g. cardiac muscles and epidermis of skin. Function: provide strong attachment and act as a link between the cytoskeleton of adjacent cells. Histological structure: 2 types: - Zonula adherens: 1. Belt like specialization that encircles the apical part of the 2adjoining cells. 2. The intercellular space between the adjacent cell membranes is 20 nm (the usual intercellular. space). 3. Cadherins adhere the two cells together (ca dependant). 4. The cytoplasmic part of cadherins is attached to actin filaments inside the cells. Removal of Ca2+ leads to disruption of the junction. 82  Histology - Foundation - Macula adherens (desmosomes): 1. A spot like specialization of the cell membrane 2. Two plaques located opposite each other on the cytoplasmic aspects of the adjacent cell membranes , to which cytokeratin filaments are inserted. 3. Cadherins connect the two cells together ( Ca dependent). 4. The intercellular space between the opposing cell membranes is 30 nm. 5. Dense vertical filamentous material is present in the intercellular space that represents the extracellular domains of cadherins. In the presence of a calcium chelating agent, the desmosome breaks into 2 halves and the cells separate. N.B: Intercellular junctional complexes: In several epithelia the zonula occludens, the zonula adherens and macula adherens are present in a definite order from the apex toward the base of the cell. III-Communicating junction (gap junction, nexus): Sites: in epithelial cells, cardiac and smooth muscle cells. Function: - They permit communication rather than adhesion. - They permit the exchange of molecules e.g., ions, amino acids allowing passage of signals involved in contraction and communication from one cell to another. Histological structure: 1. A spot like junction, formed of protein channels. 2. The channel is called connexons which are formed of 6 transmembrane proteins called connexins. 3. When two connexons of opposing cell membranes are in register, they form a channel connecting the cytoplasm of adjacent cells. 4. The intercellular space is 3nm. 83  Histology - Foundation Cell To Matrix Junctions Hemidesmosomes (basal cell polarity): Definition: half of des