Cell Membrane Lecture PDF

Introduction (Lecture) Prof. Dr. Somaya Zaghloul Presented by: Dr. Asmaa Abd El Fattah  Histology is the study of the microscopic structure of the normal tissues (Histos = tissue & logia = science). The human body is composed of: Cells are bound together to form different tissues...

Introduction (Lecture) Prof. Dr. Somaya Zaghloul Presented by: Dr. Asmaa Abd El Fattah  Histology is the study of the microscopic structure of the normal tissues (Histos = tissue & logia = science). The human body is composed of: Cells are bound together to form different tissues. Tissues are combined together to form different organs. Organs having correlated functions are grouped to for Systems. Cells must be examined under the microscope for magnification and resolution of their details. Units of magnifications 1 cm = 10 millimeters (mm) 1 mm = 1000 micrometers (µm) 1 µm = 1000 nanometer (nm) Types of microscopes: 1- Light microscope. 2- Electron microscope for high very magnifications The Cell  Some special methods of staining for light microscope. 1- Vital staining: It is the staining of a living cell, inside the body, by using a vital stain (e.g. neutral red and trypan blue). It is used to stain phagocytic cells. 2- Supravital staining: It is the staining of a living tissue, outside the body, e.g. the staining of Reticulocytes (see blood) with brilliant cresyle blue. 3- Neutral stain: as Leishman stain which is usually used to stain blood cells. It acts as a fixative for the blood film. It stains both the nuclei and cytoplasm of the white blood cells. It is commonly used to stain blood films. 4- Metachromatic staining: It is the staining of a tissue by a color that differs from the color of the original stain, e.g. the granules of the mast cells accept a red color after staining with toluidine blue. 5- Histochemical methods: Used for identification of inorganic substances (Iron, Calcium, etc) and organic substances (enzymes, as acid and alkaline phosphatase, mucin, lipids and glycogen). 6- Fluorescence and immunofluorescence: In which certain substances and antibodies are labeled with a fluorescent dye to emit visible light. N.B. All the pictures of E/M are not stained. It is only Black and White, The Cell  THE CYTOPLASM 1- Matrix: It is the viscoid colloidal solution. It is made of proteins, carbohydrates, lipids, enzymes, minerals, ions and water. 2. Organelles 3. Inclusions 1. Living structures. 1. Non living structure. 2. Permanent components of 2. Temporary components of the cytoplasm. the cytoplasm. 3. Essential for life of each cell. 3. Not essential for life of cells. 4. Metabolically active 4. Metabolically inert as they because they contain do not contain enzymes. enzymes. 5. Present in all nucleated 5. Not in all cells. cells. 6. Have vital functions. 6. Result from cell vital activity  Cytoplasmic Organells They are classified according to the presence or absence of membranes Membranous organelles Non-membranous organelles 1. Cell (plasma) membrane 1. Ribosomes 2. Mitochondria. 2. Cytoskeleton: 3. Endoplasmic reticulum a) Microtubules. (rough and smooth). b) Filaments. 4. Golgi body (apparatus). 5. Lysosomes.  The Membranous Cell Organelles 1. THE CELL (PLAMA) MEMBRANE Definition: It is the outermost covering of the cytoplasm. The light microscope (LM): It cannot be demonstrated because it is very thin. The electron microscope (EM): It appears as if it is formed of three layers, therefore it is called trilamellar membrane. Its outer and inner layers appear as dark lines, while its middle layer appears as a light area. Its outer layer appears fuzzy. Staining: Could be stained red by PAS stain. Phospholipid Molecules: 1- Lipid Component: (30%) It consists of a- Phospholipid molecules: They are arranged into 2 layers (bi-lipid layer). Each molecule has a polar and a non-polar end. The polar end (head): It is hydrophilic and directed outwards, so the heads are found on the outer and the inner (cytoplasmic) surfaces of the cell membrane. The non-polar end (tail): It is hydrophobic and directed inwards, where the tails of the two layers interact with each other forming a stable center for the cell membrane. They face each other in the central part of the cell membrane. b- Cholesterol molecules: Present at the hydrophobic regions of the cell membrane. Molecular Biology 2. Protein Component: (60%) It consists of a. Extrinsic (Peripheral) protein: It is found as loosely attached protein molecules, on both surfaces of the membrane. b. Intrinsic (Integral) protein: It consists of small and large protein molecules. Most of Integral molecules are large enough to cross the membrane (Trans-membrane proteins). These large Integral proteins act as pathways for ions and molecules (Chanel proteins). c. Alfa-helix protein: It is large spiral molecule, crossing the cell membrane, it helps the cell membrane to move and enclose the phagocytosed Particles, and also it helps the cell to migrate by making pseudopodia. Also it acts as pathways for ions and molecules. The molecular structure of cell membrane 3- Carbohydrate Component: (10%) conjugated with either proteins or lipids of the external surface of the cell membrane (Glycoproteins and Glycolipids), forming the surface coat (Glycocalyx). N.B. The outer aspect of the cell membrane is covered by the cell coat and cell receptors while its inner aspect (Hydrophobic region) is rich in cholesterol. Red blood corpuscle (RBC) structure of cell membrane (The surface coat)  Functions of the Cell Membrane 1. Simple transport (diffusion): a. Passive diffusion: for gases, water, urea and non-organic ions. b. Facilitated diffusion (Carrier-mediated diffusion): The large molecules as glucose need carrier and pass through integral proteins. 2. Active transport: It needs energy as in Sodium pump (Against concentration gradient). 3. Bulk transport: a) Endocytosis: It is the uptake of materials across the cell membrane into the cytoplasm of the cell. 1. Phagocytosis: It is the power of the cell membrane to pass solid particles forming phagosomes (Phagocytic vesicles). 2. Pinocytosis: It is the power of the cell membrane to enclose and pass droplets of fluid, forming (Pinocytic vesicles). 3. Receptor-mediated endocytosis (Selective transport) : Surface coat has specific receptors which permit the passage of certain materials only. b) Exocytosis: It is the power of the cell membrane to extrude waste products outside the cell.  Functions of the surface coat 1. Cell adhesion: The glycocalyx helps in attachments of some cells to each other. 2. Cell immunity: a. It facilitates the cell to recognize cells of its own kind. This explains the rejection of transplanted tissues. b. Surface coat has the antigens of blood groups. c. It assists T- Lymphocytes and antigen-presenting cells in binding with each other in the proper fashion. d. It binds antigens to the cell surface. Cell membrane modification a. Microvilli (Increase the surface area). b. Cilia (Push particles at one direction). c. Flagella (Allow sperm movements). d. Stereocilia (Long microvilli).  Cell membrane diseases The most common and the most famous disease is Cystic fibrosis (CF) Cystic fibrosis (CF) is a hereditary disease, meaning they are passed down from generation to generation. It is a disease of the mucous secreting cells. Normally, mucus in the lungs traps germs, which are then cleared out of the lungs. But in CF, the thick, sticky mucus and the germs it has trapped remain in the lungs, which become infected. The trapped bacteria lead to frequent, serious infections and permanent lung damage. Cystic fibrosis (CF) in the pancreas Thick mucus blocks the channels that would normally carry important enzymes to the intestines to digestfoods. When this happens, the body can't process or absorb nutrients properly, especially fats. Kids with CF have problems gaining weight, even with a normal diet and a good appetite.