Histology Chapter 1 PDF

INTRODUCTION Histology Compound of the Greek words: histo "tissue", and logia " branch of learning" Histology is the study of cells, tissues and organs as seen with microscope. It is commonly performed by examining cells and tissues by sectioning and staining, followed...

INTRODUCTION Histology Compound of the Greek words: histo "tissue", and logia " branch of learning" Histology is the study of cells, tissues and organs as seen with microscope. It is commonly performed by examining cells and tissues by sectioning and staining, followed by examination under a light microscope or electron microscope. Cell: It is the structural and functional unit in the body. It is the basic unit of all living organisms that can exist independently. They vary in size from 4 to 200 um. So to study cells, one must view them under a microscope. Tissue: Aggregations of cells have the same general characters. There are 4 basic types of tissues: – Epithelial tissue – Connective tissue – Muscular tissue – Nervous tissue Organs: Two or more tissues are combined to give larger functional units, which are the organs, e.g. kidney, liver and spleen. Systems: Several organs having interrelated functions collect to form systems, e.g. digestive system and urinary system. MICROSCOPES Definition: Microscopes are optical instruments for examination of histological specimens. The most important types are light, transmission electron and scanning electron microscopes. Types: I- Light Microscope (L.M.) The most common microscope used in routine histological examination. Daylight or electric light is used as the source of illumination. Its magnifying system is Composed of Condenser lens, Ocular lenses and Objective lenses. The magnification power (capacity to magnify): equals the power of the objective lens × the power of the eye piece lens. So the maximum magnification power of light microscope is 15 (eye piece) x 100 (objective lens) = 1500 times. The resolution power: (capacity to reveal details i.e. separate clearly 2 points close together) = 0.2 µm.  II- Transmission Electron Microscope (T. E.M.) Electron beam is used a source of illumination (Instead of light rays). The magnification power: from 1000 to 100,000 times or more. The resolution power: 0.2 nm. It will show contents of the examined objects. III- Scanning electron microscope (SEM): To obtain 3D image of specimen, image will show only the surfaces of the examined objects. Histological stains for light microscopy: Staining :Permit the examination of the tissue by light microscope. Most tissues are colorless, so stains must be used to demonstrate different components of tissues. 1- Hematoxylin & Eosin Stain (H & E): The most commonly used in routine histological examinations. Used to identify nucleus and cytoplasm of the cell by two different colors. Hematoxylin (H): is a basic stain, blue in color. It binds to acidic components of the cell. E.g.( nuclei, ribosomes and rough endoplasmic reticulum).The affinity of acidic structures to basic stains is called basophilia. Eosin (E): is an acidic stain, red in color. It binds to basic components of the cell e.g. cytoplasm. The affinity of basic structures to acidic stains is called acidophilia, 2- Silver stain: it stains Golgi apparatus and reticular fibers with black color. 3- Orcein stain: it stains elastic fibers with brown color. 4- Trichrome stains: Three stains are used in combinations to give 3 colors to different tissue components. e.g. Masson’s trichrome: stains nucleus and basophilic structures blue, cytoplasm red and collagen green. 5- Neutral stain: it is a mixture of acidic and basic stains. The best example is the Leishman's stain which is used to demonstrate blood cells. 6- Osmic acid: stain lipid component of the cell. e.g. myelin sheath of nerve fibers with black color. 7- Vital stain: it is staining the living cells inside the living animal. e.g. trypan blue or Indian ink used to stain macrophages. 8- Supravital stain: It is the staining of living cells outside the living body, e.g. staining reticulocytes (immature RBCs) with Brilliant cresyl blue. 9- Metachromatic stain: it is the stain which gives the tissue a new color different from that of the stain, e.g. Toluidine blue. THE CELL Definition: the smallest unit of living material that can live independently and perform vital functions. It is the structural and functional unit of all living tissues. Functions: secretion, respiration, absorption, reproduction, excretion, sensation, contraction, conduction, movements, and growth.  Structure: 1. Cytoplasm 2. Nucleus Cytoplasm Cytoplasm formed of: I- Organelles: small living structures with a specific function. II- Inclusions: non living substances. III-Cytosol or matrix: gel-like structure composed of soluble proteins and enzymes. Cytoplasmic organelles are the permanent living structures that perform various functions essential to the life of the cell. Cytoplasmic organelles are classified according to whether they have membranes or not into: 1. Membranous: Cell Membrane, Mitochondria, Endoplasmic reticulum: (rough & smooth), Golgi apparatus, Lysosomes, Peroxisomes 2. Non-Membranous: Ribosomes, Cytoskeleton: Microtubules: Centrioles, Cilia & flagella Filaments: Thin, Thick and Intermediate 1-The Cell Membrane (Plasmalemma) Definition: A living limiting membrane forming the outermost cover of the cytoplasm LM: H & E: Cannot be seen because very thin (8-10 nm) Can be demonstrated by Special stain: Silver or PAS EM: It appears as two darkly stained layers (electron-dense) separated by a lighter zone (electron- lucent) thus creating a trilamellar appearance Cell coat (glycocalyx): an outer fuzzy layer, carbohydrate-rich and demonstrated only on the outer surface. Molecular structure  1- Lipid component: consists of phospholipids and cholesterol. a) Phospholipid molecules: Arranged into 2 layers, each molecule has: − Hydrophilic polar end: (Phospholipid head): it is directed to outside & carry charges (polar). It has affinity to H2O (Hydrophilic) − Hydrophobic non-polar end: Hydrocarbon fatty acid tail: it is directed to the center and non charged (non polar). It has no affinity to H2O (Hydrophobic). b) Cholesterol molecules: Incorporated with the hydrophobic region of phospholipids. They provide stability to the membrane. 2- Protein component: present in two forms: a) Extrinsic (peripheral) proteins: small molecules forming a non-continuous layer outside the lipid bilayer. b) Intrinsic (integral) proteins: Small molecules : extend through some distance within the thickness of cell membrane. Large globules: extend through the full thickness (Transmembrane) so act as a pathway for water soluble molecules. 3- Carbohydrate (CHO) component: formed of: a) Glycoproteins: polysaccharide chains attached to protein molecules. b) Glycolipids: polysaccharides linked to lipid molecules. They form a cell coat on the outer surface of the cell membrane. Cell coat (glycocalyx): Formed of molecules of glycoproteins & glycolipids. Present on the outer surface of cell membrane. It includes special molecules (receptors), which control the entrance of drugs, hormones, bacteria & viruses into the cell. Functions of Cell Membrane: I- Encloses the cell, maintains its shape and keep its internal composition. II- Controls transport of materials between cell and surroundings through: 1- Simple transport: a) Passive diffusion: molecules cross according to concentration gradient e.g. water, ions and gasses. b) Facilitated diffusion: fat insoluble substances need a carrier e.g. glucose & amino acids. 2-Active transport: Molecules pass against concentration gradient so needs energy e.g. Na+/K pump. 3- Bulk transport: of large substances  Endocytosis: by which substances enter the cell. The molecule invaginates a part of the cell membrane, which first surrounds the molecule and then separates to form an endocytic vesicle. Phagocytosis = if the substance is solid. Pinocytosis = if the substance is fluid. Exocytosis: in which substances leave the cell to outside. Extrusion of residuals. III - Functions of cell coats : They are important in: Cell recognition (cell identity): this layer contains antigens. In erythrocytes the glycocalyx contains blood group antigens. Cell adhesion. Cell immunity. VI-Cell membrane modifications: 1-Microvilli Definition: Long finger like projections in the cell membrane to increase surface area for absorption in absorptive epithelial cell.e.g. absorptive cell in small intestine. 2-Cilia & flagella (Will be discussed in details later) V-Conduction of excitation waves: in nerve cells and muscles. 2- Mitochondria (Mitos = thread, chondros = granules) Definition: membranous organelles, containing enzymes responsible for cell respiration and energy production. They are considered the power-house or the battery of the cell. Sites: accumulate in the cytoplasm at sites of most activity. Number: More numerous in highly active cells.. They can be found motile, contractile or they may divide by simple binary fission as they possess their own DNA and RNA. LM: Can not be seen by H&E.  Can be seen by special stains as Iron hematoxylin and Janus green. EM: appear as rounded or oval membranous vesicles consist of 2 membranes and 2 spaces: Membranes: The outer membrane: is smooth, thicker and permeable to small molecules. The inner membrane: is thinner, and less permeable (selective). It projects into the cavity forming folds called cristae. Cristae are usually transverse; however in steroid forming cells the cristae are tubular. Spaces: Inter-membranous space between the two membranes. Interior space filled with Mitochondrial Matrix composed of o Elementary particles: They contain respiratory enzymes. o Matrix granules. o DNA & RNA: carry information that enables mitochondria to duplicate themselves during cell division. Functions of Mitochondria: Cell respiration: 1- Obtaining energy from the metabolites present in cytoplasm by Kreb's cycle. 2- About 50% of this energy is stored as ATP molecules by oxidative phosphorylation and the remaining 50% is dissipated as heat used to maintain body temperature. 3- Endoplasmic Reticulum Endo = in, Rete = net) Definition: Network of communicated tubules (cisternae) that form reticulum inside the cytoplasm. There are two types: Rough & Smooth a) Rough (Granular) Endoplasmic Reticulum (rER): It is concerned with protein synthesis. Site: Well developed in protein synthesizing cells e.g. fibroblasts. LM: its sites cause localized or diffuse basophilia in H & E stained sections. EM: parallel flattened and interconnected membranous tubules called cisternae, studded with electron-dense particles, the ribosomes.  Functions of rough endoplasmic reticulum: Dealing with protein synthesis that will be secreted by the cell. 1. Protein accumulation, segregation, initial glycozylation and packing in transfer vesicles. 2. Protection of cytoplasm by packing hydrolytic enzymes. 3. Intracellular pathway for the formed substances. b) Smooth (Agranular) Endoplasmic Reticulum (sER): It is concerned with lipid synthesis. Sites: well-developed in fat & steroid hormones forming cells, e.g. liver cells & endocrine cells. LM: cannot be demonstrated, but when abundant causes cytoplasmic acidophilia. EM: anastomosing tubules in an irregular way not in parallel array like rER with smooth membranes (no ribosomes). Functions of smooth endoplasmic reticulum: 1. Lipid synthesis and storage. 2. Cholesterol & steroid hormones synthesis. 3. Glycogen storage & breakdown as in liver and muscle cells. 4. Drug detoxification in liver cells. 5. Calcium storage in muscle fibers. 6. HCl formation in stomach. 7. Acts as an intracellular pathway. 4- Golgi Apparatus Definition: membranous organelles, concerned with secretion. They are well developed in secretory cells. LM: In H & E stained sections, it doesn’t appear, but in deeply basophilic cytoplasm, it appears as unstained area near the nucleus called “negative Golgi image”, e.g. in plasma cells. With Silver stain (Ag) , it appears as a network of brown granules & fibrils. Sites: Apical or supranuclear: between the nucleus and the secretory pole of the cell, e.g. in secretory cells. Perinuclear: completely surrounds the nucleus, e.g. in nerve cells. Infranuclear: in enteroendocrine cells. EM: It is formed of flattened saccules, arranged one above the other forming stacks like saucers and inter-connected. Toward their margins the sacs are continuous with small rounded vesicles. Golgi has 2 faces:  Convex = cis face (Immature Face): Near to the nucleus which receives transfer vesicles that bud out from endoplasmic reticulum. Concave = trans face (Mature Face): Near to the cell membrane from which secretory vesicles bud off. These vesicles may move to the cell membrane to discharge their contents by exocytosis or retained within the cytoplasm as lysosomes. The cisternae of the Golgi apparatus form an independent system. Their lumen is not in communication with that of endoplasmic reticulum. Material from rER reaches Golgi through transfer vesicles. Functions: 1- Concentration & accumulation of secretory products. 2- Chemical modification of proteins. 3- Discharge of secretory products as hormones and enzymes in the form of secretory vesicles. 4- Renewal and maintenance of cell membrane. 5- Formation of lysosomes. 5-Lysosomes Definition: Spherical membranous organelles concerned with intracytoplasmic digestion as they contain hydrolytic enzymes. Origin: rER and Golgi: lysosomes are formed as the same way as secretory vesicles however, kept inside the cell. The enzymes of lysosomes are originated from the rER. They are transferred to the Golgi apparatus, which then buds off as a vesicle from the mature surface of Golgi. This vesicle contains hydrolytic enzymes and glycoprotein and forming lysosome. Number: vary according to the phagocytic activity of the cell. LM: detected by histochemical tests (acid phosphatase reaction). EM: A- Primary lysosomes: not entered into digestive events (homogenous). B- Secondary lysosomes: lysosomes started digestion process (heterogeneous). They are of many types: 1- Heterolysosomes: when a primary lysosome fuses with a phagosome. 2- Multivesicular bodies: when a primary lysosome fuses with a pinocytic vesicle. 3- Autolysosomes: when a primary lysosome fuses with an old organelles as old mitochondria. 4- Residual bodies: vesicles with indigestible compounds that either discharge their contents by exocytosis or accumulate within the cells as lipofuscin granules (age pigments) in long-lived cells (nerve cells and heart muscles). Functions of Lysosomes: 1. Digestion of nutrients. 2. Digestion of foreign invaders as bacteria = Defense of the cell. 3. Digestion of old organelles = Maintenance of cell health. 4. Digestion of the whole cell after death = postmortem autolysis. 5. Help the sperm to penetrate the ovum (fertilization). 6. In thyroid gland: breaks inactive hormone into the active form. Cytoplasmic Inclusions They include: A- Stored food B- Pigments C- Crystals. A- Stored Food 1-Carbohydrates (Glycogen) Stored as glycogen granules in liver and muscle cells. In H & E glycogen granules appear as vacuoles because it is water soluble. Can be demonstrated by Best’s carmine & PAS. 2- Fats Stored in fat cells as large globules or in other tissues e.g. liver cells. In H & E appear as vacuoles. Can be demonstrated by Sudan III stain (appears orange), sudan black and osmium (appears black). B- Pigments Colored particles either produced by the cells or taken from outside. May be Endogenous (produced by the body cells): as 1.Hemoglobin: in RBCs. 2.Melanin: in skin, hair and iris. Lipofuscin or lipochrome: golden brown in color and found in long lived cells e.g. liver, heart and nerve cells. Exogenous (stored in cells from outside) as Carbon particles, dust particles, Carotene pigments and Tattoo marks. NUCLEUS Largest component of the cell. Present in all cells, except RBCs and platelets (not true cells). Number: − (mononucleated) in most cells. − (binucleated) as liver cells. − (multinucleated) as skeletal muscles. Position: central, eccentric, basal or peripheral. Shape: rounded, flattened, oval, kidney-shaped, segmented or bilobed. LM: Basophilic : due its content of DNA & RNA. Structure: 4 components: 1- Nuclear membrane (Envelope). 2-Chromatin material. 3- Nucleolus. 4-Nuclear sap.  Structure of the Nucleus 1- Nuclear Membrane (Nuclear Envelope) Definition:It encloses contents of nucleus separating its contents from the cytoplasm. LM: blue line (basophilic). EM: Double walled membrane separated by a perinuclear space and interrupted by nuclear pores. Outer membrane is granular due to attached Ribosomes & rER. Inner membrane is fibrillar due to attached Chromatin. At sites at which the inner and outer membranes of the nuclear envelope fuse, there are gaps, the nuclear pores), that provide controlled pathways between the nucleus and the cytoplasm. 2-Chromatin Particles and threads in the nucleus that change into chromosomes during cell division. Chromatin is composed mainly of coiled strands of DNA bound to basic proteins (histones). LM: Basophilic masses or threads. Have two forms according to cell activity: 1- Open face (vesicular nucleus): pale in staining in active cells. 2- Closed face: dark stained nucleus in less active cells. EM: 1- Euchromatin (extended or active): appears as fine granules. – It represents extended chromosomes and contains the active genes that direct protein synthesis in protein-forming cells. II-Heterochromatin (condensed or inactive): it represents coiled chromosomes and contains the inactive genes. It appears as masses of nucleoproteins condensed at different sites in the nucleus (peripheral, Chromatin islands and Nucleolus-associated chromatin). Functions of Chromatin: 1- Carries genetic information. 2- Directs & controls protein synthesis. 3- Formation of RNA (mRNA, rRNA & tRNA). 3-Nucleolus The nucleolus is a spherical structure that is rich in rRNA and protein. LM: Rounded, deeply basophilic mass. Usually one or two in each nucleus. EM: It has dark and light areas Functions: formation of ribosomal RNA & ribosomes, 4- Nuclear Sap A colloidal solution that fills the spaces between chromatin material and nucleolus. It provides a medium for transport of RNA to cytoplasm for protein synthesis.  EPITHELIAL TISSUE The human body is composed of four basic types of tissue: 1-Epithelial 2-Connective 3-Muscular 4- Nervous. These tissues are formed by cells and molecules of the extracellular matrix in variable proportions, forming different organs and systems of the body. The characteristics of epithelial tissue: Epithelial tissues are composed of closely aggregated cells with very little extracellular substance. These cells have strong adhesion to form cellular sheets that cover the surface of the body and line its cavities. Epithelium may be derived from ectoderm, mesoderm or endoderm. Epithelium lacks blood vessels of its own and depends on the diffusion of nutrients from the underlying connective tissue. Epithelium has high power of regeneration. Epithelium forms glands (glandular epithelium) or acts as receptors (neuroepithelium) or has a contractile function (myoepithelium). The functions of epithelial tissues: are the covering surfaces (e.g. skin), absorption (e.g. intestines), secretion (e.g. glands), sensation (e.g. neuroepithelium) and contractility (e.g. myoepithelial cells). The characteristic features of epithelial Cells The shape of epithelial cells range from high columnar to cuboidal to low squamous cells. Epithelial cell nuclei have different shapes. The form of the nuclei of epithelial cells corresponds to the cell shape; so, cuboidal cells have rounded nuclei and squamous cells have flattened nuclei. All epithelial cells rest on a connective tissue (C.T). It supports the epithelium, binds it to neighboring structures and provides nutrition. Types of Epithelial tissues Surface epithelium Glandular epithelium Neuroepithelium Myoepithelium Surface Epithelium Its cells cover the external surface or line the cavities of the body. They can be classified according to the number of cell layers and the shape of the cells in the surface layer. 1- Simple epithelium contains only one layer of cells. 2- Stratified epithelium contains more than one layer. Common Types of Surface Epithelia in the Human Body. Type Cell shape Examples Function 1-Simple Squamous Lining of vessels & heart Provide smooth surface for (endothelium). easy passage, Facilitates the movement Serous lining of cavities; of the viscera. pericardium, pleura, Allow gas exchange and peritoneum facilitate filtration (mesothelium). Lung alveoli and Bowman,s capsule of kidney. Cuboidal Covering the ovary, thyroid, Covering, secretion and tubules in glands and reabsorption kidney. Columnar Lining of intestine, stomach, Lubrication, absorption, gallbladder and uterus. secretion. Pseudo- Lining of trachea, bronchi, Protection, cilia-for transport stratified nasal cavity. of particles trapped in mucus. columnar 2- squamous Epidermis. Protection; prevents water Stratified keratinized (dry) loss. squamous Mouth, esophagus, larynx, Protection, secretion; nonkerat-inized vagina, anal canal. prevents water loss. (moist) Cuboidal Sweat glands, developing Protection, secretion. ovarian follicles. Transitional: Bladder, ureters, renal Protection, distensibility. domelike to calyces. flattened, depending on the functional state of the organ Columnar Conjunctiva. Protection.  Based on cell shape, simple epithelium can be squamous, cuboidal, columnar or pseudostratified. Columnar epithelium may be ciliated as in lung bronchioles, uterus and fallopian tube or non ciliated as in stomach, intestine and gall bladder. Pseudostratified epithelium, so called because the nuclei appear to lie in various layers, all cells are attached to the basal lamina, although some do not reach the surface. The example of this tissue is the ciliated pseudostratified columnar epithelium in the respiratory passages. Stratified epithelium is classified according to the cell shape of its superficial layer: squamous, cuboidal, columnar, and transitional. Stratified squamous epithelium is found in places subject to friction (skin, mouth, esophagus, and vagina). Its cells form many layers, and the basal cells are usually columnar. The superficial cells become irregular in shape, flatten and squamous. Stratified squamous keratinized epithelium covers dry surfaces such as the skin. Non keratinized epithelium covers wet surfaces. The most superficial cells of keratinized epithelia are transformed into dead scales of protein without nuclei (keratin). Transitional epithelium: a special form of epithelium, in which the cells can alter their shape. It lines the urinary bladder, the ureter and the upper part of the urethra where number of layers is changeable during filling or emptying. In empty bladder: It is formed of 6-8 layers, lies on non-clear basement membrane. Basal cells are high cubical with rounded nuclei.Cells of intermediate layers are polygonal with rounded nuclei. Intercellular spaces contain mucous-like substance, allow gliding of cells. Superficial cells are large cuboidal cells with upper convex Surface, known as dome cells and may be bi-nucleated. In Full (expanded) bladder: Cells glide over each other, helped by intercellular mucous like substances. Epithelium compressed and stretch without damage, becomes thinner & formed of 3-4 layers, allowing distention of bladder.