Cytology (Membranous Organelles) - Week 1 Lecture Notes PDF

HISTOLOGY Prof. Dr. Marwa G.A. Hegazy  HISTOLOGY & HUMAN CELL STRUCTURE Histology is the science that deals with the microscopic structure of cells& tissues.  The Cell The basic unit of life The structural and functional unit of all living tissues  Types of microscopes Light...

HISTOLOGY Prof. Dr. Marwa G.A. Hegazy  HISTOLOGY & HUMAN CELL STRUCTURE Histology is the science that deals with the microscopic structure of cells& tissues.  The Cell The basic unit of life The structural and functional unit of all living tissues  Types of microscopes Light Microscope Transmission (LM) Electron Microscope Types of the cell ? Compare and Contrast Prokaryotes Eukaryotes Nucleus Endoplasmic reticulum Cell wall Golgi apparatus Contain DNA Lysosomes Ribosomes Vacuoles Cytoplasm Mitochondria Cytoskeleton  Venn Diagrams Compare and Contrast Eukaryotic cells Animal Cells Plant Cells Cell membrane Ribosomes Nucleus Endoplasmic reticulum Cell Wall Centrioles Golgi apparatus Chloroplasts Lysosomes Vacuoles Mitochondria Cytoskeleton  The cell Cytoplasm Nucleus  Cytoplasm Cytosol Organelles Inclusions It is a viscous Permanent Temporary colloidal solution living structures, formed of : structures not essential for Protein- essential for vitality of cells. carbohydrates- vital processes They may be lipids- enzymes- of the cell. present or absent minerals- ions- salts. e.g. lipid droplets, glycogen clumps,  Organelles A. Membranous B. Non-membranous Organelles Organelles 1. Cell membrane (plasma 1. Ribosomes membrane). 2. Cytoskeleton 2. Mitochondria. 3. Endoplasmic reticulum (rough & smooth). 4. Golgi apparatus. 5. Lysosomes  A. Membranous Organelles ◼ The Plasma membrane (Cell membrane) ◼ The boundary of the cell. ◼ Composed of three distinct layers. ◼ Two layers of fat and one layer of protein.  L.M.: Difficult to be seen (H&E) as it is very thin. It can be demonstrated when stained with silver (Ag). E.M.: Appears as 2 electron- dense (dark) lines, separated by an electron-lucent (light) one (trilamellar).  Molecular Structure of Cell Membrane:- 1-Lipid 3- 2- Protein Component Carbohydrate Component : Component a) b) a) Extrinsic b) Intrinsic Phospholipid Cholesterol protein protein molecules molecules (peripheral) (integral)  Molecular Structure of Cell Membrane:- 1- Lipid Component: a) Phospholipid molecules: (lipid bilayer). Each molecule has a head and two tails. Head Tails Hydrophilic (has great Hydrophobic (has no affinity to aqueous affinity to aqueous solutions). solutions). called polar as it is charged. called non-polar as it is non- charged. Heads are arranged at the Tails are directed inwards, outer and inner surfaces. they face each other in the center. Function: selective permeability to perform a barrier between internal and external environment of the cell  b) Cholesterol molecules: Present among the hydrophobic tails to stabilize the cell membrane & modulate the fluidity. 2- Protein Component: a) Extrinsic (peripheral): small molecules, loosely attached at both sides of the lipid bilayer b) Intrinsic (integral): embedded in the lipid bilayer in form of : Small molecules Large molecules (Trans-membrane protein): extend across the membrane and act as pathways for ions and molecules. ❑ Channel proteins for transport of ions and water. ❑ Carrier proteins for transport of small polar molecules as glucose and ions as Na pump.  3-Carbohydrate Component At the external surface, (glycoproteins and glycolipids), forming the cell coat (Glycocalyx). Function: ◼ it includes receptors that has important interactions: ◼ a) Cell adhesion: helps in attachment of some cells to each other & to extracellular matrix. ◼ b) Cell immunity: It binds antigens to the cell surface  Bulk transport moving substances from a) Endocytosis b) Exocytosis the cytoplasm to the outside 3- Receptor-mediated endocytosis (selective 1- Phagocytosis 2- Pinocytosis transport) Specific molecules the process of the process of bind to their receptors engulfing solid engulfing fluid that accumulate at the particles by the droplets by the cell cell membrane which cell membrane to invaginates and membrane to form pinches off, forming a form a pinocytic vesicles. coated vesicle phagosome containing the specific (phagocytic molecules and their vesicle) receptors. Endoplasmic Reticulum ◼ Complex network of transport channels. ◼ Two types: 1. Smooth- ribosome free. Functions in lipid and steroid hormone synthesis, breakdown of lipid-soluble toxins in liver cells, and control of calcium release in muscle cell contraction. 2. Rough - contains ribosomes and releases newly made protein from the cell.  Rough Endoplasmic Reticulum Smooth Endoplasmic Reticulum (sER) (rER) Site Abundant in protein-forming cells as Abundant in steroid-forming cells as in in plasma cells. endocrine glands. L.M. basophilic due to the presence of When abundant, it causes cytoplasmic ribosomes (rRNA). acidophilia E.M. Parallel, flattened cisternae studded Branching, anastomosing tubules or vesicles, with ribosomes on their outer surface. with no ribosomes on their outer surface Functions 1. Protein synthesis by ribosomes. 1- Synthesis of Lipids (as phospholipids & 2. Initial glycosylation. Cholesterol) and steroid hormones as testosterone and cortisone. 3. Packing of formed protein in 2- Detoxification of drugs, hormones & alcohol membranous vesicles "Transfer (in liver cells). vesicles" to transfer protein to 3- Muscle contraction and relaxation in Golgi. skeletal muscle cells (storage and release of 4. Intracellular transport. Ca+2 ) 4- Breakdown of glycogen to glucose in liver cells. 5- Intracellular transport  Golgi Apparatus ◼ A series of flattened sacs that modifies, packages, stores, and transports proteins to cell surface to be secreted. ◼ Secretions include hormones, enzymes, antibodies and other molecules. ◼ Works with endoplasmic reticulum and ribosomes.  Golgi Apparatus L.M.: ◼ it does not appear. ◼ It can be seen as an unstained area (negative Golgi image) in protein secreting cells which have deeply basophilic cytoplasm. ◼ In (Ag)-stained sections: brown network of fibrils.  Golgi Apparatus E.M.. It consists of: ◼ Several membrane-bound flattened saccules, which are slightly curved, with flat centers and dilated ends. ◼ They are interconnected and arranged above each other forming stacks. ◼ Each stalk has 2 faces: ❑ The entry face (Convex, Cis face): receives transfer vesicles from rER. ❑ The exit face (Concave, Trans face): from which secretory vesicles arise. Functions: 1. Modification of proteins delivered from the rER by addition of carbohydrates and sulphates. 2. Concentration and packaging of these large molecules 3. Synthesis of lysosomes & secretory vesicles. 4. Maintenance and renewal of cell membrane. Lysosomes ◼ Recycling Center ◼ Recycle cellular debris ◼ Membrane bound organelle containing a variety of enzymes. ◼ Help digest food particles, nutrients, foreign and dead materials. Origin: Lysosomes contain hydrolytic enzymes (synthesized in the endoplasmic reticulum ) then -------- Golgi apparatus for concentration, packing and production. Site : abundant in phagocytic cells as in macrophages. L.M.: histochemical stains that detect acid phosphatase enzyme. E.M.: (I) Primary lysosomes: Appear as homogenous vesicles. (II) Secondary lysosomes: Appear as heterogeneous vesicles Types of secondary lysosomes: 1. Phagolysosome (heterolysosome): a 1ry lysosome + a phagocytic vesicle. 2. Multivesicular body: a 1ry lysosome + a pinocytic vesicle. 3. Autolysosome: a 1ry lysosome + an autophagic vesicle (vesicle containing old organelles e.g mitochondria). * The digested nutrients diffuse to cytoplasm, while undigested material is retained within vesicles called Residual bodies. Functions: 1.Digestion of materials ingested by endocytosis (nutrients, bacteria and viruses). 2.Breakdown of old cellular organelles.. 3.Fertilization by helping the sperm to penetrate the ovum. 4.Post-mortem autolysis by digestion of the whole cell after death  Mitochondrion ◼ Double Membranous ◼ It’s the size of a bacterium ◼ Contains its own DNA; mDNA ◼ Responsible for respiration and energy production in the cell (produces high energy compound ATP)  Mitochondria ◼ ◼ Number: more numerous in cells with high energy requirement e.g. muscle cells, liver, heart and sperm cells. ◼ L.M.: as rods, granules or filaments when stained with Janus green (appear green). E.M.: is oval or rounded vesicles surrounded by 2 membranes:- The outer membrane is smooth, The inner membrane forms incomplete shelves (cristae) which increase its surface area. The space in-between is called inter-membranous space. - The matrix contains :- (1) Enzymes that synthesize ATP via the Krebs cycle. (2) Matrix granules rich in Ca+2 (regulate the activity of enzymes). (3) DNA and RNA. Functions : 1- Cell respiration and production of ATP. ATP is the primary source of cell energy (power house of the cell). 2- They can form proteins for themselves and can divide (self replication) as they have their own DNA and RNA.