Histology 1: Membranous Organelles Lecture Notes PDF

Course Title : Histology 1 Course Code : FM 103 Department : Basic Science Lecture Title : Membranous Organelles Lecturer Name : Shereen Shawky Elabd Assistant professor of Medical Histology and Cell Biology Faculty of Medicine.. Tanta University Lecture Objecti...

Course Title : Histology 1 Course Code : FM 103 Department : Basic Science Lecture Title : Membranous Organelles Lecturer Name : Shereen Shawky Elabd Assistant professor of Medical Histology and Cell Biology Faculty of Medicine.. Tanta University Lecture Objectives: Each student at this lecture should be able to: -List the membranous and non-membranous organelles. -Recognize the cell membrane and membranous organelles by electron microscope. -Describe the membranous organelles and correlate it to their functions. -Label the diagrams of cell membrane and membranous organelles. Dr/ Shereen Elabd Content: Membranous organelles. Cell membrane Mitochondria Endoplasmic reticulum Golgi complex Lysosomes Dr/ Shereen Elabd Remember Dr/ Shereen Elabd  Types of microscopes and stains Electron Microscope Light Microscope Acidophilia Acidic dye (Eosin) → Basic structure Protein- Cytoplasm Basophilia Electron dense Basic dye (Hematoxylin)→ Acidic structure Electron Lucent Nucleic acid (DNA) Nucleus Dr/ Shereen Elabd  Most common/ Ordinary Stain= Hematoxylin & Eosin Cytoplasm Nucleus Dr/ Shereen Elabd  Structure of the cell Cell membrane Basophilic Nucleus E Acidophilic Pt Cytoplasm Clean up Dr/ Shereen Elabd  Cytoplasmic organelles Cytoplasm contains a system of membranous organelles, non-membranous structures, inclusions and a cytoskeleton. They are living small intracellular structures that perform their functions. They are classified into membranous and non-membranous organelles. Membranous organelles Non-membranous organelles Cell membrane Ribosomes Mitochondria Microfilaments Rough endoplasmic reticulum Intermediate filaments Smooth endoplasmic reticulum Microtubules Golgi complex Centriole Lysosomes Cilia flagella Dr/ Shereen Elabd Membranous organelles 1- Enumerate membranous organelles? 2- Describe structure of ------ by light microscope? 3- What is the special stain used to demonstrate this membranous organelle 4- Describe structure of ------ by electron microscope? 5- What is the membranous organelle that is responsible for energy production? 6- What is the membranous organelle that is responsible for protein synthesis? 7- What is the membranous organelle that is responsible for protein secretion? 8- What is the membranous organelle that is responsible for degradation of materials inside t cytoplasm? Dr/ Shereen Elabd  1-THE PLASMA MEMBRANE/ CELL MEMBRANE Definition: It is the membrane that envelops every eukaryotic cell. Structure: 1- By light microscope: it cannot be seen. 2- By electron microscope: → By low power , it appears as one electron dense line. → By high power , it appears as three layers; outer and inner electron dense layers and middle electron lucent band (trilaminar unit membrane). Molecular Structure of Cell Membrane (Fluid mosaic model): Q? The principal components of the plasma membrane are; 1- Phospholipid bilayer 2- Cholesterol, 3- Proteins, Dr/ Shereen Elabd  What is the function of cell membrane? 1- It determines the shape of the cell and maintains its structure. 2- It controls the passage of materials in and out of the cell (selective permeability). 3- It keeps the ion content of the cytoplasm constant. Dr/ Shereen Elabd 1) Phospholipids bilayer: - It is the backbone of the cell membrane. - It is formed of double layer of phospholipids molecules. - Each phospholipid molecule has: Phosphate head: Polar and hydrophilic (water attracting) Two long fatty acid chains: Non-polar and hydrophobic (water repelling). - The Phosphate heads are directed to both surfaces (cytoplasmic and extracellular) contacting water, while fatty acid chains are located in the middle region away from water. II) Cholesterol molecules: - They are inserted among the closely packed phospholipids. - Function: Depending on the temperature, cholesterol controls the movement of phospholipid molecules and the membrane fluidity. Dr/ Shereen Elabd  III) Proteins: There are two types: A) Integral proteins: The proteins cross the lipid bilayer; When protrude from both membrane surfaces it is called transmembrane protein. When proteins cross the membrane many times, it called multipass proteins. B) Peripheral Proteins: They are bound to one of the two membrane surfaces of the bilayer (external or cytoplasmic).  Function of membrane proteins: 1- Exchange of materials between the cell and the environment (channel). 2- Act as enzymes or receptors. 3- Important for cell junctions. Dr/ Shereen Elabd Cell coat (Glycocalyx): - Located at the outer surface of cells. - It is formed by conjugation of oligosaccharides either to proteins (forming glycoproteins) or to lipids (forming glycolipids). -Function: They act as a cellular marker allowing cells to recognize each other. Dr/ Shereen Elabd  Transport of Large molecules I- Endocytosis: - Entrance of macromolecules inside the cell in the form of cytoplasmic vesicles. This process includes two forms: - Phagocytosis - Pinocytosis. A- Phagocytosis [cell eating]: - The cell ingest solid materials e.g. bacteria and cell fragments. - The bacteria bind to the surface receptors of the cell (selective process). - It surrounded by folds of plasmalemma. - The folds fuse and enclose it in an intracellular vacuole called a phagosome, Dr/ Shereen Elabd  B- Pinocytosis [cell drinking]: - It is the entrap of extra cellular fluid and its dissolved contents forming pinocytotic vesicles. - Fate of pinocytotic vesicles: 1.Pinocytotic vesicles may fuse with lysosomes, or 2.Move and fuse to the plasma membrane to release the content out of cell in a process called transcytosis. II- Exocytosis: It is the exit process of material by which the cytoplasmic vesicles containing the molecules fuse to cytoplasmic surface of cell membrane to release the content into the extra-cellular compartment. Dr/ Shereen Elabd  2-MITOCHONDRIA Number: -They are the energy source so, they are present in all eucaryotic cells. -They increased in number in cells with high metabolic activity e.g. - Cardiac and skeletal muscle cells - Liver cells (hepatocytes) - Kidney tubules. Structure: - L/M: - By H&E: Can not be distinguished easily. Important - Meanwhile, presence of numerous mitochondria gives acidophilia to cytoplasm e.g. skeletal muscle cell. - By supravital staining as janus green and appear as green bodies with different sizes. Important Dr/ Shereen Elabd - E/M: 1- Each mitochondrion possesses; - an outer smooth membrane - an inner folded membrane. 2- The folds of the inner membrane are called cristae. 3- The narrow space between the outer and inner membranes is called the intermembrane space. 4- The large space enclosed by the inner membrane is known as the matrix space. 5- Elementary particles (ATP synthase) are closely packed club- shaped particles attached with to the inner surface of the inner membrane. 6- Mitochondrial matrix contains: - Enzymes of Kreb’s cycle. - Ribosomes, tRNA, mRNA and DNA, so they can synthesize their own protein. - Dense granules contain calcium ions. Dr/ Shereen Elabd  Functions: a. They are the energy house in the cell as they produce ATP. b.They concentrate calcium in their matrix leading to calcium regulation within the cytoplasm. Dr/ Shereen Elabd  3- ENDOPLASMIC RETICULUM Nearly all cells contain an extensive system of membrane- bounded tubules known as endoplasmic reticulum. There are two types continuous with each other: a. Smooth endoplasmic reticulum [without ribosomes] SER. b. Rough endoplasmic reticulum [with ribosomes] RER. Dr/ Shereen Elabd  A- SMOOTH ENDOPLASMIC RETICULUM Structure: - L/M: - SER can not be seen by LM, Important - It gives acidophilia to the cytoplasm when present in great amount. - E/M: It is composed of anastomosing smoothly surfaced tubules (not studded with ribosomes). Functions, differs according to the type of cell: 1. In all cells; SER synthesizes phospholipids of cell membrane. 2. In steroid secreting cells; the SER synthesizes steroid hormones as cortisol and testosterone. 3. In striated and cardiac muscles; called (sarcoplasmic reticulum) which regulates the Ca++ level essential for muscular contraction. 4. In liver cells; it is responsible for a) detoxification of certain drugs. b) Participates in glucose metabolism, cholesterol and lipid synthesis. Dr/ Shereen Elabd  Localized basophilia B- ROUGH ENDOPLASMIC RETICULUM Site: RER is present in cells specialized for protein secretion e.g. pancreatic acinar cells, osteoblast, fibroblasts and plasma cells. Structure: - L/M: - It gives localized basophilia to the cytoplasm due to the attachment of ribosomes and polysomes to ER cisternae. - E/M - It consists of interconnecting parallel flattened cisternae; its membrane is studded with ribosomes and polyribosomes, so they appear rough or granular. Dr/ Shereen Elabd  Functions: 1. Synthesis of the secretory proteins by the attached ribosomes to be stored into RER cisternae. 2. Synthesis of lysosomal enzymes. 3. Formation of the integral proteins of plasma membrane. 4. SER may be derived from RER after losing ribosomes Dr/ Shereen Elabd 4- GOLGI APPARATUS Site: - It is found in nearly all cells. - It is well developed in protein secreting cells. e.g. Nerve cell – Plasma cell. Location: always it is related to the nucleus. - It is supranuclear in protein secretory cells. - It surround the nuclei in nerve cells (multiple Golgi). Structure: L/M: -By H&E stain, Golgi appears in actively protein synthesizing cells (plasma cell); as clear unstained area near the nucleus surrounded by deeply basophilic cytoplasm (Negative Golgi image). -By silver impregnation; it appears as dark brown network and granules around the nucleus as in nerve cells. Dr/ Shereen Elabd - E/M: Golgi apparatus is composed of: - 1- Stacks: - Each stack consists of 3- 10 flattened, slightly curved, smooth cisternae. - Each stack has two distinct sides or faces: - Cis-face / entry/ immature face:/ forming : is convex and towards RER. - Trans-face / exit/ mature face/ secretory : is concave and towards cell membrane. The secretory products are moved through the stack from cis-face to the trans-face by vesicles budding off from one cisterna and fusing with the next one in the stack. -2 -Transport vesicles: -They are small in diameter. -They carry the newly synthesized proteins from RER cisterna to cis-face of Golgi apparatus. -3- Secretory vesicles:- - They arise from the trans-face cisterna. - Secretory vesicles carry and direct the modified concentrated proteins toward the cell membrane to be released by exocytosis. Dr/ Shereen Elabd  Functions: 1- Modification of new proteins then concentration and packaging to be released by exocytosis. 3- Forming the lysosome. Dr/ Shereen Elabd Dr/ Shereen Elabd  5- LYSOSOMES Definition:-They are spherical membranous organelles contain hydrolytic enzymes as, proteases, nucleases, acid phosphatases and lipases etc…. Site: - They are numerous in some cells e.g. macrophages, neutrophils and osteoclasts. Origin: 1- Lysosomal enzymes are synthesized in RER and transported to Golgi complex. 2- In the Golgi, they are modified, packaged and pinched off from trans-face as vesicles. 3- The vesicles go deep in the cytoplasm forming the primary lysosome pH (~5.0). Structure: -L/M: They can be demonstrated by histochemical and immunohistochemical methods that target the hydrolytic enzyme inside. Dr/ Shereen Elabd  Functions: Lysosomes play an important role in: 1. Defence mechanisms by digestion of foreign invaders such as bacteria. 2. Digestion of old organelles. 3. Autolysis that occurs after death. Primary lysosome Type of lysosomes / EM of lysosome: Lysosomes can be classified into two groups: Secondary lysosome Primary lysosomes: -They are the newly formed lysosomes before fusion with any substance. -They have a homogenous granular content. Secondary lysosomes: They are formed after fusion of the primary lysosomes with other substances. They are larger than primary lysosome and have heterogeneous content. 2ry lysosomes are divided into three types according to the digested substance. Dr/ Shereen Elabd Types of secondary lysosome: I- Exogenous macromolecules are taken by endocytosis (phagocytosis or pinocytosis): 1- After phagocytosis, the phagosome merges with the primary lysosome forming heterolysosome. 2-After Pinocytosis, the pinocytotic vesicles merge with the primary lysosomes forming multivesicular body. II- Endogenous macromolecules or damaged organelle: 1- The damaged organelle is enclosed with a bilayer membrane forming autophagic vacuole. 2- The autophagic vacuole then merges with primary lysosome forming autophagosome. The indigestible material as pigments or lipids remains inside the secondary lysosomes, forming residual bodies released by exocytosis. In certain cell types as nerve cells and cardiac muscle, residual bodies accumulate with age and are called lipofuscin pigment. Dr/ Shereen Elabd Dr/ Shereen Elabd Dr/ Shereen Elabd Organelles responsible for protein Secretion (outside the cell): - RER (synthesis) - Golgi complex (secretion and release) - Mitochondria (E) Organelles responsible for acidophilia: - SER - Mitochondria Organelles responsible for basophilia - Diffuse----------- Ribosome - Localized ----- RER  Endoplasmic Reticulum Smooth (SER) Rough (RER)  Phospholipids synthesis (all cells) Secretory protein synthesis  Ca + regulation (muscle cell)  Steroid hormone  Glucose metabolism (liver cell) Special stain *Mitochondria------------ Janus green *Golgi complex --------- 1- Silver 2- Immunohistochemical *Lysosome -------- Immunohistochemical Dr/ Shereen Elabd Dr/ Shereen Elabd Dr/ Shereen Elabd Questions Regarding cell membrane, which statement of the following is WRONG? A- It can be seen by electron microscope. B- It is formed by of phospholipid bilayer. C- It allow the free passage of small molecules D- It contains protein. Regarding Golgi apparatus, what is the side facing RER? A- Cis face. B- Trans Face. C- Secretory face. What is the name of the secondary lysosome containing a damaged organelle? A- Heterolysosome. B- Pinocytotic vesicle. C- Autophagic vacuole. D- Autophagosome Which of the following stain is used to observe mitochondria by light microscope? A- Hematoxylin and eosin. B- Janus green B. C- Silver impregnation. D- osmium tetroxide. Enumerate two membranous organelles in this electron micrograph Dr/ Shereen Elabd Enumerate two membranous organelles in this electron micrograph Dr/ Shereen Elabd References: 1-Mescher Anthony L (2016): Basic Histology, 14th edition. McGraw-Hill, Medical Publishing Division. 2-Victor P. Eroschenko (2008): DiFiore`s atlas of Histology with Functional Correlations. 11th edition. Lippincott Williams & Wilkins Dr/ Shereen Elabd Thank You SUE