1-Lec. 1 (Cytology part 1).pdf

Histology & Cell Biology Dentistry Students Dr. Asmaa Elshafei Assistant Prof. of Histology and Cell Biology  Lecture 1 CYTOLOGY PART (I) Aim: Understand the general structure of the cells , cell membrane and nucleus....

Histology & Cell Biology Dentistry Students Dr. Asmaa Elshafei Assistant Prof. of Histology and Cell Biology  Lecture 1 CYTOLOGY PART (I) Aim: Understand the general structure of the cells , cell membrane and nucleus. Reference Junqueira's Basic Histology, Text and Atlas. Mescher AL, 17th Edition, 2024  Learning Objectives By the end of this lecture, you should be able to: Define cytology. Explain the general structure of the cells of the human body. Identify the components of the cell membrane. Correlate the molecular structure of the cell membrane with its function. Enumerate the components of the nucleus. Define the different structures of the nucleus and their function. Identify components of the cytoplasm. Compare membranous and non-membranous organelles. 3  What is the meaning of Cytology ? Cyto = cell, Logia = branch of learning 4  Cytology LM ✓ Cell is the structural & functional unit of the organism. ✓ Cells are too small to be seen by naked eye. To facilitate the study & recognition of cells : EM ▪ Light microscope LM For more sophisticated & detailed structure: ▪ Electron microscope EM 5  Staining of sections Routine stains: H & E stains Other special stains: eg. (silver, orcein, PAS) Hematoxylin (H) Eosin (E) Basophilic Acidophilic ✓ Basic stain ✓ Acidic stain ✓ Binds to acidic ✓ Binds to basic components components ✓ Blue in color ✓ Red to pink in color ✓ e.g. Nuclei ✓ e.g. cytoplasm, (DNA& RNA), Collagen fibers, ✓ Ribosomes , Mitochondria , ✓ RERneucleus Secretory granules General structure of the cell 7 Definition: Plasma membrane (Plasmalemma): The limiting membrane of the cell. 8  Structure of cell membrane Light microscope (L/M): ✓ Cell membranes are not visible. o 7.5 - 10 nm in thickness. Electron microscope (E/M): another 1 cell ✓ It appears as: o Two electron-dense lines separated by 3 layers an electron-lucent intermediate zone. 1 cell Trilaminar appearance (unit membrane) 9 Why does the cell membrane appear trilaminar by EM? 10  Molecular structure of cell membrane 11 Phospholipid bilayer Outside cell Outside cell 12  Cell Coat (Glycocalyx) oligosaccharide chains linked to: Membrane proteins: Membrane phospholipids: ✓ located on the outer surface only of plasma membrane. 13  Functions of Cell membrane 1. It maintains the structural integrity of the cell. 2. It controls movements of substances in & out of the cell (selective barrier). 3. It facilitates the transport of specific molecules by passive, active or bulk transport. 4. It plays the key role in interactions of the cell within its environment. 14 1 2 15  3 Bulk transport Active movement of substance into the cell by forming vesicles. Active movement of substance from inside to outside of the cell by forming vesicles 16 17  (Cell eating) extended from the cell membrane to surround solid particle e.g. bacterium. ✓ Ends of pseudopodia fuse enclosing bacterium to form an internal. can use to destroy invading bacteria. 18  (Cell drinking) (pocket) of cell membrane formed to surround extracellular fluid. ✓ Ends of pocket fuse then detach off from the cell membrane forming 19  (Integral proteins) accumulate at the cell membrane to bind specific ligands. ✓ They associate with protein on the cytoplasmic side ✓ The coated pit invaginates gradually and pinches off, forming containing ligands and their receptors. ✓ Ex: Uptake of hormones as GH. 20 Exocytosis 21  Question No 1 How you can see the cell membrane by the light microscope? A. Bilayer structure. B. Not visible. C. One layer structure. D. Trilaminar structure. 22  Question No 2 As regarding transport of substances across the cell membrane, protein hormones enter the cell by which one of the following mechanisms? A. Diffusion. B. Phagocytosis. C. Receptor mediated endocytosis. D. Pinocytosis.  Vesicular Nuclei H&E ▪ due to its content of DNA & RNA. May be: ✓ Pale–stained (vesicular) present in active cells Condensed Nuclei e.g nerve cell & liver cell ✓ Darkly–stained (condensed) present in inactive cells e.g small lymphocyte 24  Components of the nucleus 1. Nuclear envelop 4. Nuclear sap 2. Chromatin 3. Nucleolus  1. Nuclear envelop ❑ Two parallel unite membranes: o The outer membrane: studded with ribosomes. o The inner membrane: have condensation of chromatin. o The outer & inner membranes are separated from each other by the perinuclear space. The nuclear envelope have nuclear pores that allow passage of materials between cytoplasm and nucleus. 26  2. Chromatin ❑ Composed mainly of strands of DNA & proteins into 2 forms: 2 Heterochromatin 3 sites 1 ▪ Peripheral chromatin Euchromatin ▪ Islands of chromatin ▪ Nucleolus associated chromatin 27  Euchromatin: extended chromatin & active form. ✓The nucleus contains mainly euchromatin appears pale basophilic by LM. ✓ It controls protein synthesis in the cells. Heterochromatin: condensed chromatin & inactive form. ▪ Peripheral chromatin. ▪ Islands of chromatin. ▪ Nucleolus associated chromatin. ✓ The nucleus contains mainly heterochromatin appears dark basophilic by LM. 28  3. Nucleolus ▪ It is composed of: DNA, rRNA & Basic proteins. By LM: appear small rounded basophilic bodies. By EM: appears as electron dense (dark) network without surrounded membrane. It is responsible for formation of ribosomal rRNA. 4. Nuclear matrix (Sap, nucleoplasm ): A colloidal solution fills spaces between chromatin & nucleolus providing a transport medium inside the nucleus. 29  Question No 3 What is the structure of the nucleus that is responsible for the passage of molecules from outside to inside the nucleus and vice versa? A. Nuclear sap. B. Nuclear pores. C. Extended chromatin. D. Condensed chromatin. 30  Question No 4 The nucleolus is surrounded by which of the following structures ? A. Extended chromatin. B. A double membrane envelop. C. A single layer of unite membrane. D. There is no membrane around the nucleolus. 31  1. Organelles 2. Inclusions ✓ Living ✓ Non-Living ✓ Permanent ✓ Temporary ✓ Essential ✓ Not essential 3. Cytosol ▪ Semifluid cytoplasmic matrix 32 ▪ Covered by membrane ▪ Uncovered by membrane Cell (Plasma) membrane Ribosomes Mitochondria Cytoskeleton Rough endoplasmic reticulum (rER) Smooth endoplasmic reticulum (sER) Golgi apparatus Lysosomes 33