Introduction to Histology and Cell Structure PDF

Introduction to Histology and Cell Structure Histology Team, Anatomy Department, College of Medicine, King Saud University Introduction to Histology & Cell Structure Objectives: By the end of this lecture, you should be able to: Describe what histology is and how i...

Introduction to Histology and Cell Structure Histology Team, Anatomy Department, College of Medicine, King Saud University Introduction to Histology & Cell Structure Objectives: By the end of this lecture, you should be able to: Describe what histology is and how it is studied. Describe the composition of the cell: describe the Light Microscopic (L/M) and Electron Microscopic (E/M) structure and the function of each component: 1. Nucleus. 2. Cytoplasm: a) Organelles: membranous and non-membranous. b) Inclusions.  INTRODUCTION Histology is the microscopic study of normal tissues. Types of microscopes: LM & EM. Organs are made of tissues and tissues are made of cells. Thin sections are cut and mounted on glass slides. Sections are stained with Hematoxylin (H) and Eosin (E). Nucleus is always blue (basophilic). Cytoplasm may be red (acidophilic), or blue (basophilic).  THE CELL It Is the structural & functional unit of all living tissues. Cells have different shapes & sizes. THE CELL is made of: 1. Nucleus 2. Cytoplasm  NUCLEUS (L/M) Number: Cells may be mononucleated, binucleated, or multinucleated. Shape: Usually takes the shape of the cell. Special shape: Lobulated/Segmented: bilobed, multilobulated. S-shaped. Indented. Kidney-shaped. Appearance: Darkly or densely stained. Vesicular or open-face.  NUCLEUS (E/M) Formed of: 1. Nuclear envelope 2. Chromatin 3. Nucleolus 4. Nucleoplasm  1. Nuclear Envelope A double membrane with many pores. 1. Outer membrane. 2. Inner membrane. 3. Perinuclear space. 4. Nuclear pores: provide communication between nucleus and cytoplasm. Perinuclear space  2. Chromatin Formed of DNA. L/M: Basophilic granules. E/M: 2 Forms: – Euchromatin: extended, active chromatin (pale= electron-lucent areas). – Heterochromatin: condensed, inactive chromatin (dark = electron-dense areas). Functions: – Carries genetic information. – Directs protein synthesis.  3. Nucleolus L/M: It is a spherical dark basophilic mass. E/M: It is mostly a dark mass (electron-dense) not surrounded by a membrane. Usually one. Function: formation of ribosomal RNA (rRNA), which is responsible for protein synthesis in the cytoplasm.  4. Nucleoplasm It is a semi-fluid medium in which all the contents of the nucleus are embedded. Function: Provides a medium for movement of 3 types of RNA (ribosomal, messenger and transfer RNA) from the nucleus to the cytoplasm.  Functions of the Nucleus The nucleus is the maestro of the cell orchestra: 1. It is essential for the vitality and division of the cell. 2. It is the site of storage of genetic information. 3. It is the site of formation of the three types of RNA. Generated by AI.  CYTOPLASM is formed of: 1- ORGANELLES: They are specialized structures, ESSENTIAL for vital processes of the cell. 2- INCLUSIONS: They are not essential for vitality of cells. May be present or absent. Examples are lipids, glycogen, and pigments like melanin & lipofuscin. 3- CYTOSOL: The intracellular fluid.  CYTOPLASMIC ORGANELLES A. Membranous: 1. Cell membrane. 2. Mitochondria. 3. Endoplasmic reticulum (rough & smooth). 4. Golgi apparatus. 5. Lysosomes. 6. Secretory vesicles. B.Non-membranous: 1. Ribosomes. 2. Centrioles. 3. Cilia & Flagella. 4. Filaments: Actin, Myosin & Intermediate filaments. 5. Cytoskeleton: Actin, Intermediate filaments & Microtubules.  Cell Membrane A very thin membrane that surrounds the cell. L/M: Not visible. E/M: appears as 2 dark lines (electron-dense), separated by a light one (electron-lucent) (trilaminar appearance). Function: selective barrier.  Cell Membrane (Cont.) Chemical Structure: Sugar chain of glycoprotein 1- Phospholipid molecules: arranged in 2 layers. 2- Protein molecules: a) Peripheral protein. b) Integral protein. 3- Carbohydrate molecules: attached to either proteins or lipids (glycoproteins and glycolipids), forming the surface or cell coat (Glycocalyx): a) Protection of the cell. b) Cell recognition and adhesion.  Cell Membrane (Cont.) Surface Specializations: 1. Microvilli: Simple finger-like cytoplasmic projections of cell surface to increase surface area. Their core contains actin filaments. 2. Stereocilia: long microvilli (nonmotile). 3. Cilia: see later. 4. Flagella: see later.  Cell Membrane (Cont.) Lateral Specializations (Intercellular Junctions): 1. Occluding (Tight) Junction: seals the intercellular space. 1 2. Adhering Junction: fixes adjacent cells together: 2a a) Zonula Adherens. b) Macula Adherens (Desmosome). 2b 3. Gap Junction: allows free communication between cells. 3 N.B. When a combination of 1, 2a, and 2b is present, this is called a junctional complex.  Mitochondria L/M: They can be seen by special stains. E/M: Each mitochondrion is rod-shaped. The wall is composed of 2 membranes. The outer is smooth, the inner is folded to form cristae (increase surface area). The cavity is filled with mitochondrial matrix, which contains enzymes. It also contains its own DNA & RNA. Functions: 1. Generation of ATP which is the source of energy for the cell. They are called the powerhouse of the cell. 2. They can form their own proteins and undergo self-replication.  Endoplasmic Reticulum (ER) It is a system of communicating membranous tubules, vesicles, and flattened vesicles (cisternae). There are 2 types: Rough (rER). Smooth (sER).  Rough Endoplasmic Reticulum L/M: Its sites appear as basophilic areas, due to the ribosomes on the surface. E/M: Membranous sheets of flattened tubules & vesicles with ribosomes on the surface. Functions: 1.Synthesis of proteins by ribosomes on its outer surface. 2.Transfer vesicles transfer the formed protein to Golgi.  Smooth Endoplasmic Reticulum L/M: Cannot be demonstrated. E/M: Membranous tubules and vesicles, with NO ribosomes on the surface. Functions: 1. Synthesis of lipids & cholesterol. 2. Synthesis of steroid hormones, e.g. cortisone. 3. Helps muscle contraction, by acting as a calcium pump. 4. Detoxification of drugs & toxins.  Golgi Apparatus The Secretory Apparatus of the cell. L/M: Its place appears as a negative Golgi image in deeply basophilic cells. E/M: Consists of stacked saucer-shaped flattened vesicles (saccules). Secretory Each vesicle has two faces: vesicles Convex (forming) face, receives transfer vesicles. Mature face Concave (mature) face, Transfer vesicles forms secretory vesicles. Functions: Forming face 1. Sorting, modification & packaging of proteins. 2. Secretory vesicle formation. 3. Formation of lysosomes.  Lysosomes The Digestive Apparatus of the cell. Originate from the mature surface of the Golgi apparatus, while their hydrolytic enzymes are formed in the rough endoplasmic reticulum. L/M: They can be stained histochemically for acid phosphatase. E/M: Spherical membranous vesicles with homogeneous (1ry lysosomes) or heterogeneous (2ry lysosomes) granular content. Function: Intracellular digestion of ingested material or old organelles. Defense against invading pathogens.  Ribosomes Small non-membranous particles consisting of ribosomal RNA (rRNA), combined with proteins. Formed in the nucleolus. L/M: Basophilic cytoplasm is due to numerous ribosomes. E/M: Appear as small electron- dense granules: Formed of 2 subunits (small & large). Free in the cytoplasm (may form polyribosomes), or Attached to rER. Function: Protein synthesis.  Centrioles Two cylinders, perpendicular to each other. E/M: The wall of each centriole is made of 9 triplets of parallel microtubules, i.e. 27 microtubules. Functions: 1. Essential for cell division (form the microtubules of the mitotic spindle). 2. Form the basal bodies of cilia and flagella.  Organelles Made of Microtubules 1. Centrioles: see before. 2. Cilia: L/M: Hair-like striations on the free surface of some cells. E/M: Basal body is similar to a centriole. Shaft is formed of 9 peripheral doublets and 2 central singlets of microtubules, i.e. 20 microtubules. Function: movement of particles or fluids on the free surface of the cells in one direction. 3. Flagella: Longer and larger than cilia. Form the tails of sperms. Function: movement of sperms.  Cytoskeleton It is the supporting framework (skeleton) of the cell. Functions: Maintains the shape of the cell. Allows for dynamic processes: Cell division. Cell motility. Endocytosis & exocytosis. Movement of membranous organelles within the cytoplasm. Consists of: 1. Microfilaments (actin). 2. Intermediate filaments, e.g. Keratin. 3. Microtubules.  Recommended Textbooks For Theoretical: Color Textbook of Histology, L.P. Gartner and J.L. Hiatt, Latest Edition. For Practical: Di Fiore’s Atlas of Histology, V.P. Eroschenko, Latest Edition. Thank You