Cytology (Lecture 1) PDF

Recognize some cell terminology Identify the aim of studying histology Describe microscopic structure of cell membrane by LM & EM Describe molecular structure of cell membrane Outline cell membrane function  Histology It is the science dealing with the stud...

Recognize some cell terminology Identify the aim of studying histology Describe microscopic structure of cell membrane by LM & EM Describe molecular structure of cell membrane Outline cell membrane function  Histology It is the science dealing with the study of the microscopic structure of normal cells, tissues and organs. Why do you study histology? To correlate cells’ structure and arrangement to their functions. knowledge of normal structure is essential for an understanding of pathology. The human body is composed of: Cells Tissues Organs Systems Structural Formed of Composed Group of and similar tissues to organs functional cells perform a perform units of all performing specific interrelated living a specific function function organisms function e.g. e.g. stomach digestive system There are 4 basic tissues Epithelial Nervous tissue Connective tissue Muscular tissue tissue  Cytology It is the study of the normal cells’ structure Because of the small size of cells, we use microscopes for magnification and resolution. Units of magnifications Types of microscopes: 1 cm = 10 millimeters (mm) 1- Light microscope. 1 mm = 1000 micrometers (µm) 2- Electron microscope. 1 µm = 1000 nanometer (nm) Light microscope (LM) Electron microscope (EM) Staining for light microscopy Tissues and their components are colorless Need to be stained Stains color different components with different colors  Hematoxylin and Eosin Stain (H & E) Is the most commonly used stain in routine histological examination (the ordinary stain) 1. Hematoxylin (H): Is a basic stain with a blue color Binds to acidic components of the cell e.g nucleic acids Acidophilic Structures that accept the blue color of hematoxylin are cytoplasm called basophilic 2. Eosin (E): Is an acidic stain with a red color. Nuclei Binds to basic components of the cell Structures that accept the red color of eosin are called acidophilic. N.B. Nucleus is basophilic Basophilic cytoplasm Cytoplasm may be basophilic or acidophilic ▪ Allows more magnification for more details ▪ Structures seen by EM appear either: Grey to Black (electron-dense) White (electron-lucent) The Cell  Cells are of variable in shapes and sizes. Each animal cell is composed of two main parts: 1. The cytoplasm. 2. The Nucleus. Cytoplasm Consists of Organelles Inclusions Cytosol Living structures Nonliving structures Viscous fluid containing Essential for life of each Not essential for life of enzymes, ions, O2, CO2, cell cells metabolites) Metabolically Metabolically inert Support organelles active They are classified according to the presence or absence of membrane into: Membranous Non-membranous organelles organelles ✓ Cell membrane ✓ Ribosomes ✓ Mitochondria ✓ Microtubules ✓ Endoplasmic reticulum ✓ Microfilaments ✓ Golgi apparatus ✓ Intermediate ✓ Lysosomes filaments  Membranous Cell Organelles - Definition - Structure 1- The cell membrane (LM & EM) - Function (plasma membrane or plasmalemma) Definition: It is the membrane that envelops the animal cell. Structure: By L.M.: Difficult to be seen (Why??) The cell membrane is only 7.5 - 10 nm thick and thus, it is too thin to be seen with L.M. By E.M.: ▪ At low magnification: it appears as a single electron dense line. 2 electron dense ▪ At high magnification: Electron lucent layer layers ✓ It appears as a trilaminar membrane (trilamellar Glycocalyx or unit membrane), formed of two electron dense layers separated by an electron lucent intermediate layer. ✓ The outer surface of the cell membrane is covered by the cell coat (glycocalyx) (has a fuzzy appearance).  Lipids Proteins Carbohydrates Phospholipids Cholesterol Integral Peripheral Glycoproteins Glycolipids a) Phospholipid molecules ▪ They are arranged into 2 layers (lipid bilayer). ▪ Each molecule has a polar and a non-polar end: The polar end (head): It is hydrophilic and directed towards aqueous solution. 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 (away from aqueous solutions). b) Cholesterol molecules: Are inserted among the hydrophobic tails, restricting their movement. There are two types of protein molecules in cell membrane: Integral a) The integral (intrinsic) membrane proteins; proteins i- Some of them are extending all the way from one side of the membrane to the other side (transmembrane protein). Peripheral ii- Others are only partially embedded in the proteins lipid bilayer. b) The peripheral (extrinsic) membrane proteins; Are loosely bound to the cytoplasmic side of the lipid bilayer. Integral membrane proteins act as: channels, carriers, receptors and enzymes ▪ Sugar chains are linked to proteins of cell membrane forming glycoproteins and to lipids forming glycolipids. ▪ Found at the external surface of the cell membrane. ▪ Glycoprotein and glycolipid form cell coat (glycocalyx).  Glycocalyx ▪ It is formed of glycoproteins and glycolipids. ▪ Has a fuzzy appearance by EM. ▪ Function: Cell recognition Intercellular adhesions Include digestive enzymes (as in small intestine).  Functions of cell membrane 1- It maintains the structural integrity of the cell. 2- It controls movement of substances into and out of the cell through establishing a transport system. Passive transport Active transport Vesicular transport  Simple e.g. O2 & CO2 ▪ Movement of molecules diffusion down the concentration I- Passive transport gradient ▪ Do not need energy Through transporter Facilitated diffusion proteins e.g. transport of glucose  ▪ Movement of molecules against the concentration gradient II- Active transport ▪ Need energy ▪ e.g. sodium potassium pump  III- Vesicular transport Transport of large molecules by formation of vesicles Endocytosis Exocytosis Phagocytosis Receptor-mediated endocytosis Pinocytosis  Endocytosis It is the uptake of materials across the cell membrane into the cytoplasm of the cell. It includes: 1- Phagocytosis (cell eating) Uptake of solid materials e.g. bacteria in the form of phagocytic vesicles 2- Pinocytosis (cell drinking) Uptake of fluid materials in the form of pinocytotic vesicles 3- Receptor-mediated endocytosis Specific substances need receptors to enter the cell.  Exocytosis It is the release of substances across the cell membrane outside the cell. e.g., Release of secretory proteins. Which of the following is characteristic to the structure of cell membrane? A- 2 to 3 nm B- Lined from inside by glycocalyx C- Appears bilayer by EM high magnification D- Its phospholipids are arranged in 2 rows Which of the following cellular processes describes the uptake of extracellular fluids by the cell? A- Autophagy B- Exocytosis C- Phagocytosis D- Pinocytosis 30