Histology Lecture Case 1 Week 2 PDF

Structure of the Cell Nucleus Intercellular Junctions  Dr. Shereen Shawky El-Metwally Contact: Medical Histology & Cell Biology Department. E-mail: [email protected]. Mobile(WhatsApp): 01273165442. Lecture 2 Questions  Q1 Which of the following statements co...

Structure of the Cell Nucleus Intercellular Junctions  Dr. Shereen Shawky El-Metwally Contact: Medical Histology & Cell Biology Department. E-mail: [email protected]. Mobile(WhatsApp): 01273165442. Lecture 2 Questions  Q1 Which of the following statements concerning the cilia is true? A) Single cilium per cell. B) Its shaft contains nine peripheral doublets and a central pair of microtubules. C) Not visible with the light microscope D) Their basal bodies are similar to microtubules  Q2 10. The non-membranous cell organelle responsible for mitotic spindle formation is: A) Actin B) Myosin C) Intermediate filaments D) Microtubules  Q3 Which of the following are exogenous pigments? A) Lipofuscin pigments B) Minerals C) Melanin D) Hemoglobin  Q4 The wall of centriole is composed of: A) 27 microtubules B) 28 microtubules C) 20 microtubules D) 9 microtubules  Q5 Lipid frozen sections can be stained with: A) PAS B) Sudan III C) Silver stain D) Best's carmine  Cell Structure Cells are formed of: 1- Cell membrane 2- Cytoplasm 3- Nucleus  Nucleus Definition: − The nucleus is: 1. The cell control center. 2. Playing an important role in heredity and cell division. Number: A.Mononucleated cells have one nucleus as in lymphocytes. B. Binucleated cells have two nuclei e.g. some liver cells. C. Multinucleated cells have more than two nuclei as in skeletal muscle fibers.  Nucleus Size: − The nucleus may be small, medium-sized or large. Shape: − The shape of the nuclei differs in different cells. − They may be: rounded, oval, flattened, rod-shaped, bent rod, horseshoe-shaped, kidney-shaped (indented), bilobed, segmented or lobulated.  Nucleus Position: The nucleus tends to occupy the widest part of the cell. It may be central, basal, eccentric, or peripheral. Staining: − The nucleus is basophilic, it stains blue with hematoxylin due to its content of nucleic acids  Nucleus Appearance: Vesicular (or Open- face) Nucleus It is a lightly – stained nucleus Details of its components could be seen Nuclei of nerve cells and liver cells Condensed (or deeply stained) nucleus It is a deeply basophilic nucleus No details could be seen inside Nuclei of small lymphocytes.  Nucleus Structure of the nucleus: 1 The nucleus consists of four components 3 1)Nuclear membrane. 2 2)Nucleolus. 4 3)Chromatin. 4)Nuclear sap (Karyoplasm or karyolymph).  Nuclear Membrane Definition: It is a membrane that encloses the nucleus and separates it from the surrounding cytoplasm. With the LM: − It appears as a single basophilic line surrounding the nucleus. − Its basophilia is due to the presence of peripheral chromatin on its inner surface.  Nuclear Membrane With the EM The nuclear membrane is made up of two thin membranes separated by a perinuclear space The outer nuclear membrane has many ribosomes on its surface and is continuous with the membranes of the rough endoplasmic reticulum.  Nuclear Membrane With the EM The inner nuclear membrane has chromatin granules attached to its inner surface ( peripheral chromatin). The nuclear membrane is interrupted by many nuclear pores (30-100 nm in diameter).  Nuclear Membrane Functions of nuclear membrane: 1.It separates the nucleus from the surrounding cytoplasm. 2.It allows exchange of material between nucleus and cytoplasm through nuclear pores.  Nucleolus Nucleoli are one or more rounded basophilic bodies present in the nuclei. With the LM Number: − May be one to four per nucleus. − Nucleoli are prominent in active cells e.g.: 1. Protein secreting cells. 2. Nerve cells. Position: - May be central or eccentric in the nuclear sap  Nucleolus Staining and shape: - Nucleoli are rounded, basophilic due to: The surrounding nucleolar associated chromatin Its ribonucleic acid (RNA) content With the EM: The nucleolus appears as an irregular spongy network N It is not limited by a membrane. It is surrounded by nucleolus associated chromatin  Nucleolus Function of the nucleolus 1.Synthesis of ribosomal RNA. 2.rRNA is conjugated with protein and stored in the nucleolus until it migrates through nuclear pores to reach the cytoplasm as ribosome subunits.  Chromatin Definition: Chromatin is the basophilic material of which chromosomes are formed. Structure: − It is formed of deoxyribonucleic acid (DNA) conjugated with histone protein. With the LM: − Chromatin appears as basophilic granules called chromatin granules. − The basophilia is due to the phosphoric acid component of the nucleic acid. − The granules are described as fine or coarse (thick) depending on their size.  Chromatin With the EM: Two types of chromatin are distinguished Euchromatin (Extended chromatin) Heterochromatin(Condensed chromatin) 1- Structure It represents the extended parts of the It represents the coiled parts of the chromosomal chromosomal threads. threads. 2- Activity Its genes are active. Its genes are inactive. 3- Function It directs protein synthesis in the cell. It does not direct protein synthesis in the cell. 4- With LM It is not visible with LM (It appears as clear It is visible with LM as fine or coarse basophilic areas). chromatin granules. 5- With EM It is seen, only with high magnification, as It is seen as electron-dense granules (20-30 nm in shades of grey. diameter). 6- It occupies the more central region of the It is distributed as: Distribution nucleus. 1. Peripheral chromatin. 2. Nucleolar-associated chromatin. 3. Chromatin islands.  Chromatin Functions of chromatin: 1. It directs and guides protein synthesis in the cell in order to produce the specific protein required by the cell to perform its specialized function. 2. It stores the specific genetic information on its genes and transfers them through successive generations.  Nuclear sap (karyoplasm) Definition: It is a semifluid colloidal clear solution in which chromatin and nucleoli are suspended. Structure: − It contains: Proteins and nucleoproteins. Enzymes for the synthesis of DNA and RNA. With the LM − It appears as clear or empty areas in the nucleus. With the EM − The nuclear sap is electron-lucent.  Nuclear sap (karyoplasm) - Vesicular (Open-face) nuclei contain a large amount of nuclear sap. - Condensed (deeply stained) nuclei contain a small amount of nuclear sap. Function of nuclear Sap: It serves as the medium in which ribonucleic acids (rRNA, mRNA and tRNA) move towards nuclear pores.  Intercellular Junctions Definition: Membrane associated structures that join the adjacent cells and provide communication between them. Types: 1- Occludens (Tight) junctions 2- Adherens junctions 3- Gap junctions  Intercellular Junctions 1- Occludens (tight) junctions: In which the outer surfaces of adjacent cell membranes fuse to form a seal between the intercellular and luminal fluids. Types: Zonula occludens: fusion of the membranes completely encircle the cell Occluding junction: fusion not completely encircle the cell Fascia occludens: fusion between the membranes is patchy Function: forms a seal that prevent flow of materials between the lumen and intercellular fluid  Intercellular Junctions 2- Adherens junctions: In this type, there is no direct contact between the adjacent membranes, but joined by an intercellular binding material. Types: Zonula adherens: the intercellular space is filled with an electron dense binding substance which surrounds the cell completely. Macula adherens (desmosome): present in the form of a spot between membranes of adjacent cells Function: hold and prevent separation between cells  Intercellular Junctions 2- Gap junctions: In this type of connections the cytoplasm of the two adjacent cells is joined by a gap across the intercellular space. Function: 1- Allow direct passage of ions between cells 2- Conduction of contraction wave in the muscles of intestine 3- Allow the spread of depolarization as in cardiac muscle fibers General Revision on Organelles Membranous Organelles Organelle L/M E/M Functions Mitochondria Hx&E: not seen 2 membranes: outer smooth, inner Provide the cell with ATP Iron Hx: blue with cristae (fold like projections) Histochemical: succinic The membranes enclose the matrix dehydrogenase containing matrix granules Endoplasmic RER basophilic RER parallel flattened membranous RER protein synthesis SER not identified cisternae SER lipid synthesis, reticulum SER communicating narrow muscle contraction & membranous tubules detoxification of certain compounds Golgi apparatus Hx&E: pale unstained area in Saccules (4-10, mature face& Modification and sorting deep basophilic cytoplasm immature face) proteins Silver: brown Microvesicles (immature face) Macrovesicles (mature face) Lysosomes Hx&E: not identified 1ry: membranous vesicles with a contain a large variety of Histochemical: acid homogenous moderate electron acid hydrolases for intra- phosphatase dense granular core cytoplasmic digestion 2ry: heterogenous electron dense core. Organelle L/M E/M Functions Peroxisomes Hx&E: not identified Tiny membrane bounded Prevent damaging effect Histochemical: catalase vesicles containing a of H2O2 homogenous moderate Play a role in lipid and electron dense finely alcohol metabolism granular material Detoxicate D-amino acid (human) present in the bacteria With electron dense semicrystalline core (rodent) Non-Membranous Organelles Organelle L/M E/M Function Ribosomes Hx&E: basophilia Electron dense granules, may be Ribosomes synthesize proteins held together forming polyribosomes May be free or attached to RER Microtubules Hx&E: not identified Hollow tubules Cytoskeleton supporting the cell In cross section they appear as shape, main structural component tiny circles of centriole, cilia & flagella. The wall consists of 13 Important for mitotic spindle protofilaments formed of tubulin formation and act as guiding track dimers for material movements Centrioles Hx&E: not identified The wall of each cylinder is Cell division Iron H: two dark blue composed of 27 microtubules Act as basal body of cilia granules longitudinally arranged in 9 bundles (triplets) Cilia Hx&E: can be seen vaguely Shaft: nine peripheral doublets of Beating rhythmically in one on the cell surface microtubule and two central direction to move a thin film of singlets (20 microtubule) fluid or mucous on the cell surface Basal body: as centriole Flagella Similar to cilia by one/cell and much more longer Whip-like swimming movement  Microfilaments Thin filaments Thick filaments Intermediate filaments Type Actin Myosin Many types: Desmin, Tonofilament, Vimentin, Neuro-filaments and Glial filaments. Diameter 6-7nm 12-16nm 10nm-12nm Contractility Contractile Contractile Non-contractile Distribution 1. In the micro-villi, for their 1. In muscle in 1. Supporting & maintaining the and Function movement association with shape of the cell 2. In the cleavage furrow actin filaments forming the 2. Tumor identification during cell division. myofibrils 3. In muscles, for contraction 4. In blood platelets, for clot retraction.