Histology L1 PDF

# INTRODUCTION Histology is the study of the microscopic structure of the normal tissues ("histos" = tissue & "logia" = science). - Human body is composed of cells, tissues, organs and systems. - Cells are minute in size (4-150 µm), so microscope is needed for magnification & resolution of their d...

# INTRODUCTION Histology is the study of the microscopic structure of the normal tissues ("histos" = tissue & "logia" = science). - Human body is composed of cells, tissues, organs and systems. - Cells are minute in size (4-150 µm), so microscope is needed for magnification & resolution of their details. - Magnification power: degree of enlargement - Resolution power: least distance between two points can be seen as two # Microscopy | | LM | EM | | :------- | :-------------------------------------- | :--------------------------------------- | | Source of illumination | Day light/ electric light | Beam of electrons | | Stains used | Many stains so many colors | 1 stain only (Osmic acid): shades of grey | | Magnification Power | Maximum X 1500 | ↑ X 100,000 | | Field Examined | Many cells (tissue) | 1 or 2 cells | - Cells and their components are colorless; therefore, need to be stained before examination. - The most commonly used stain for L.M. examination is: ## Haematoxylin and Eosin Stain (H&E) Haematoxylin (H) is a basic stain that stains the acidic components of the cell with a blue color. Such components are described as "Basophilic". Eosin (E) is an acidic stain that stains the basic components of the cell with a red color. Such components are described as "Acidophilic". - Nuclei are always basophilic because of their content of nucleic acids. Cytoplasm may be acidophilic or basophilic according to cell activity. # The Cell The Cell is the structural and functional unit of all living tissues. A cell is composed of: - Nucleus - Cytoplasm ## Cytoplasm - It is formed of: - Matrix: It is a viscous colloidal solution formed of protein-carbohydrates-lipids-enzymes-minerals-ions-salts. - Organelles: They are differentiated-permanent living structures, essential for vital processes of the cell. - Inclusions: They are temporary structures, not essential for vitality of cells. They may be present or absent. ### Organelles Organelles are classified according to the presence or absence of membranes into: #### Membranous Organelles (contain enzymes) 1. Cell membrane (plasma membrane). 2. Mitochondria. 3. Endoplasmic reticulum (rough & smooth). 4. Golgi apparatus. 5. Lysosomes #### Non-membranous Organelles (Do not contain enzymes) 1. Ribosomes 2. Centrioles ## The Cell The Cell is the structural and functional unit of all living tissues. A cell is composed of: - Nucleus - Cytoplasm ## Cytoplasm - It is formed of: - Matrix: It is a viscous colloidal solution formed of protein-carbohydrates-lipids-enzymes-minerals-ions-salts. - Organelles: They are differentiated-permanent living structures, essential for vital processes of the cell. - Inclusions: They are temporary structures, not essential for vitality of cells. They may be present or absent. ### Organelles Organelles are classified according to the presence or absence of membranes into: #### Membranous Organelles (contain enzymes) 1. Cell membrane (plasma membrane). 2. Mitochondria. 3. Endoplasmic reticulum (rough & smooth). 4. Golgi apparatus. 5. Lysosomes #### Non-membranous Organelles (Do not contain enzymes) 1. Ribosomes 2. Centrioles # NUCLEUS ## Definition The nucleus is the largest and the most distinct component of the cell. - It is not found in RBCs & platelets (Not True Cells). - Nuclei may have different numbers, shapes, sizes, and locations. ## L.M. It appears as a large, basophilic structure that usually occupies the widest part of the cell. ## Appearance: May be - Pale-stained (Vesicular) (open face nucleus) (as in nerve cells). - Darkly-stained (Condensed) (closed face nucleus) (as in lymphocytes). ## Structure of the Nucleus - Nuclear membrane (envelope) - Nucleolus - Chromatin - Nucleolar sap ## Cell Nucleus Anatomy The cell nucleus is comprised of a nuclear envelope, nucleolus, and nucleoplasm. Nuclear pores are located in the nuclear envelope. ## 1. Nuclear Membrane (Envelope): ### L.M. It appears as a single basophilic line. ### E.M. It surrounds the nucleus and consists of two parallel membranes separated by a perinuclear space. The two membranes fuse at intervals forming openings called nuclear pores. ## 2. Nucleolus: ### L.M. It is a spherical, highly basophilic structure in the nuclei of cells. It is active in protein synthesis. It is basophilic due to the presence of RNA and DNA. ### E.M. It consists of: - Pars amorpha (Nucleolar organizer): Composed of filaments of DNA carrying the genes encoding for ribosomal RNA (rRNA). - Pars fibrosa: Small fibrils representing the newly formed rRNA. - Pars granulosa: Large granules representing mature rRNA ## 3. Chromatin: ### It is the substance of genetic materials composed of double-stranded DNA bound with histone and non-histone proteins. It condenses to form chromosomes during cell division. - Euchromatin - Heterochromatin ### In non-dividing cells, chromatin is found in two forms: #### Heterochromatin - Condensed (coiled) inactive chromatin - Present in closed face nuclei - Contains inactive genes - Predominates in metabolically inactive cells. - L.M.: appears as coarse granules and the nucleus appears dark basophilic - E.M.: electron dense #### Euchromatin - Extended (uncoiled) active chromatin - Present in open face nuclei - Contains active genes - Predominates in metabolically active cells involved in protein synthesis. - L.M.: Invisible by LM and the nucleus appears pale basophilic - E.M.: electron-lucent ### Sites: 1. Adherent to the inner nuclear envelope (peripheral chromatin). 2. Around the nucleolus (nucleolus associated chromatin). 3. Scattered throughout the nuclear sap (chromatin islands). ## 4. Nuclear sap: It is a semifluid colloidal solution found between the chromatin and the nucleolus and contains enzymes and lipoproteins. ## Functions of the Nucleus: - It carries genetic information encoded in the DNA. - It is important for cell division. - It forms RNA for protein synthesis. # 1. Cell Membrane ## Definition Limiting membrane that surrounds the cell. ## L.M Difficult to be seen when stained with H&E as it is very thin (7.5-10 nm). It can be demonstrated when stained with Ag or PAS. ## E.M: Appears as 2 electron-dense (dark) lines, separated by an electron-lucent (light) one (trilamellar). ## Molecular Structure of Cell Membrane: 1. **Lipid Component (30%):** a) **Phospholipid molecules:** Arranged into 2 layers (lipid bilayer). Each molecule has a head and two tails. - **Heads:** - Hydrophilic (has great affinity to aqueous solutions). - Called polar as it is charged. - **Tails** - Hydrophobic (has no affinity to aqueous solutions). - Called non-polar as it is non-charged. Heads are arranged at the outer and inner surfaces. Tails are directed inwards, they face each other in the center. b) **Cholesterol molecules:** Present among the hydrophobic tails. They restrict the movement of phospholipid molecules to stabilize the cell membrane. 2. **Protein Component (60%):** a) **Extrinsic protein (peripheral):** Small molecules loosely attached at both sides of the lipid bilayer. b) **Intrinsic protein (integral):** Are present in the lipid bilayer in the form of: - **Small molecules** - **Large molecules (Trans-membrane protein):** Extend across the membrane and act as pathways for ions and molecules (Trans-membrane transport). 3. **Carbohydrate Component (10%):** At the external surface, conjugated either with proteins or lipids (glycoproteins and glycolipids), forming the cell coat (Glycocalyx). ## Functions of the cell membrane: 1. **Passive transport: (with Conc. Gradient - No Energy)** a) **Passive diffusion**: Movement of solute from a high concentration to a lower concentration. b) **Facilitated diffusion (carrier-mediated diffusion):** They need carrier and pass through integral protein (with concentration gradient) e.g. glucose. 2. **Active transport: (against concentration gradient) needs energy.** e.g. Sodium pump. 3. **Bulk transport:** **A. Endocytosis:** Is the uptake of materials across the cell membrane into the cytoplasm of the cell. - **1- Phagocytosis:** The process of engulfing solid particles by the cell membrane to form an internal phagosome (phagocytic vesicle) - **2- Pinocytosis:** Is the process of engulfing fluid droplets by the cell membrane to form pinocytotic vesicles. **3- Receptor-mediated endocytosis (selective transport).** - Specific molecules bind to their receptors that accumulate at the plasma membrane. - Gradual invagination of the plasma membrane forms coated pits that become surrounded on the cytoplasmic side by protein molecules called clathrin. - Clathrin molecules form a basket like cage that changes the shape of the plasma membrane into vesicle like invagination called coated vesicle containing the specific molecules and their receptors. **B. Exocytosis:** Is a process for moving substances from the cytoplasm of the cell to the outside. ## 4- Functions of the cell coat (glycocalyx): It includes receptors that participate in important interactions such as: - **a) Cell adhesion:** The glycocalyx helps in attachment of some cells to each other & to extracellular matrix components. - **b) Cell recognition.** - **c) Cell immunity:** It binds antigens to the cell surface. ## 5- Cell membrane modification: - Microvilli (increase the surface area for absorption) - Cilia (push particles at one direction) - Flagella (allow sperm movement) - Stereocilia (long microvilli) ## 6- Conduction of excitation waves: Transduction of extracellular signals into intracellular events. - **a) Cell adhesion:** The glycocalyx helps in attachment of some cells to each other & to extracellular matrix components. - **b) Cell recognition.** - **c) Cell immunity:** It binds antigens to the cell surface. ## 5- Cell membrane modification: - Microvilli (increase the surface area for absorption) - Cilia (push particles at one direction) - Flagella (allow sperm movement) - Stereocilia (long microvilli) ## 6- Conduction of excitation waves: Transduction of extracellular signals into intracellular events.