Introduction To Histology PDF

1 INTRODUCTION TO HISTOLOGY ILOs Upon successful completion of this course student will be able to: -Define histology. -Know the common types of microscopes &their applications in medical research. -Define magnification &resolution power of different microscop...

1 INTRODUCTION TO HISTOLOGY ILOs Upon successful completion of this course student will be able to: -Define histology. -Know the common types of microscopes &their applications in medical research. -Define magnification &resolution power of different microscopes. -Know the different types of stains -Know the mostly commonly used stain &their applications in medical field. Histology: is the subject dealing with the microscopical structure of normal tissue. The aim of histology course is:  To help the student to understand the microanatomy of cells, tissues & organs.  To make correlation structure with function. The study of histology is carried out by using microscopes of different types. The commonly used types of microscopes are: 1- Light microscope (L.M.) 2- Electron microscope (E.M.) 3- Light microscope &electron microscope differ in their optical resolution & magnification (enlargement). Resolution power: means the least distance at which two points appear separate from one another, if the distance is less the two points will appear as one point. Resolution power of the eye = 0.2 mm Resolution power of the LM. = 0.2 um Resolution power of the EM. = 0.2nm Maximum magnification power in case of L.M. is about X1000 while in case of EM. magnification power is about X100.000. Common stains used for Light microscopy Cells are colorless and usually indistinguishable by LM unless stained. 1) Acidic stain: e.g. eosin, it can stain basic structures, so these structures are acidophilic. 2) Basic stain: e.g. hematoxylin which stains acidic structures, so these structures are basophilic. 3) Neutral stain: e.g. Leishman's stain. It is a combination of an acidic & a basic stain for staining of blood cells. 4) Vital stain: It is used to stain a living structure inside a living animal such as staining of phagocytic cells using trypan blue or India ink.  2 5) Supravital stain: It can stain a living cell outside a living person e.g. Brilliant Cresyl blue which stains reticulocytes (immature RBCs) in a blood film. 6) Metachromatic stain: It will give a new color after staining which is different from its original color. The new color develops as result of a chemical combination between the stain & certain structures within the cell e.g. toluidine blue stains granules within mast cell with a violet color. Changing the original color of the stain at the end of staining process is called metachromasia. 2-The cell  The cell is the functional & structural unit of all living tissues.  The cell is the smallest living structure which has vital properties such as growth, secretion, excretion, digestion, contraction, respiration & reproduction.  The cells of the body are variable in shape, size& functions but they are similar in composition: I- Cytoplasm. II- Nucleus. I. Cytoplasm: It is formed of: 1) Cytoplasmic matrix: It is a colloidal solution containing proteins, carbohydrates, lipids, minerals & enzymes. 2) Cytoplasmic organelles: They are permanent minute living structures that are essential for the vital processes of all cells e.g., respiration, secretion, digestion. 3) Cytoplasmic inclusions: They are non- living temporary structures, not essential for the vitality of the cell. They are no more than substances stored within some cells e.g. glycogen, fat & pigments.  3 Cytoplasmic Organelles They are classified according to presence or absence of surrounding membranes into: A) Membranous cell organelles 1. Cell membrane. 2. Mitochondria. 3. Endoplasmic reticulum (rough & smooth). 4. Golgi apparatus. 5. Lysosomes. 6. Peroxisomes. B) Non membranous cell organelles 1. Ribosomes 2. Cytoskeleton: a. Microtubules (centrioles & cilia) b. Filaments (Thin, intermediate& thick) A-Membranous cell organelles 1-Cell membrane Definition: It is an ultra- thin membrane that surrounds the cell i.e. it forms an envelope or a cover for the cell. L.M.: It is invisible by L.M as it is very thin (8-10 nm) but can be stained by Ag or PAS. E.M.: It appears as three parallel lines, two dark layers separated by a light one i.e. it is a Trilamellar membrane. The cell membrane has an outer covering rich in carbohydrates called cell coat.  4 Molecular structure of the cell membrane: (Fig1)  5 The cell membrane is composed of lipids, protein & carbohydrate: 1. Lipids component: Cell membrane has two types of lipids: a) Phospholipid molecules b) Cholesterol molecules. The lipid component of the cell membrane allows passage of fat-soluble substances through it. 2. Protein component: Cell membrane contains two types of protein: a) Intrinsic protein ( integral protein): Intrinsic protein is present in the form of:  Small particles  A large globule which extends along the whole thickness of the cell membrane & acts as a pathway for water soluble substances. b) Extrinsic protein: It is represented by small molecules which are loosely attached to both surfaces of the cell membrane forming a non-continuous layer. 3. Carbohydrate component:  They are oligosaccharides.  They are either attached to protein molecule & form glycoprotein  OR to lipid and from glycolipid.  Glycolipid & glycoprotein are known as the cell coat or glycocalyx.  Cell receptors are present among the cell coat; they are responsible for entrance of drugs, hormones & bacteria to the cell. Functions of cell membrane: a- It keeps the internal composition of the cell. b- Cell coat as a part of the cell membrane is responsible for cell adhesion, cell recognition, cell protection &cell immunity (functions of cell coat). c- It allows passage of substance through it by:- 1) Passive diffusion: (e.g. gases & water) 2) Facilitated diffusion: e.g. glucose. 3) Active transport: e.g. Na pumps outside the cell. 4) Selective permeability: By presence of receptors 5) Bulk transport (vesicular transport): Macromolecules enter & leave the cell by vesicular transport that involves changes in plasma membrane at a localized site  6 & formation of vesicles from the cell membrane or fusion of vesicles with the cell membrane. Vesicular transport may be one of two processes: * Exocytosis: in which substances leave the cell to outside. * Endocytosis: in which substances enter the cell. If the substance that enters the cell is solid the process is called phagocytosis. Entrance of fluid is called pinocytosis.(Fig.2) 2- Mitochondria (Fig.3)  7 Definition: -It is a membranous cell organelle. -It is the powerhouse of the cell. -It is responsible for cell respiration & energy production. Number: varies according to cell activity e.g. liver cells contain 1000- 2000/ cell N.B. They are present in all cells except RBCs. Site: at site of the most activity e.g. apical part in ciliated cells. L M.:  Mitochondria appear as granules, rods or filaments.  They can be stained dark blue by iron hematoxylin & green by Janus green stain. EM:  Mitochondrion appears as a vesicle rounded or oval in shape.  It is covered with double membranes, separated by an inter-membranous space.  Outer membrane is smooth while the inner one shows incomplete folds, shelves or cristae.  Mitochondrial matrix fills the internal cavity of mitochondria.  The matrix contains lipids, protein, carbohydrates, Ca & Mg as well as DNA & RNA.  Oxidative enzymes are attached by heads to the cristae. Functions: 1. Mitochondria are the Powerhouse of the cell. They produce energy stored in the form of ATP & released at time of need. 2. They can form their own protein & can divide, as they contain DNA & RNA.  8 3- Endoplasmic Reticulum (Fig.4) Definition:  It is a membranous organelle formed of flattened communicating vesicles & tubules that form reticulum [network] inside the cytoplasm.  It is classified according to presence or absence of ribosomes into two types: a. Rough (granular) E.R. b. Smooth (agranular) E.R. Rough endoplasmic reticulum r Smooth endoplasmic reticulum ER s ER Site Protein forming cells e.g. Lipid forming cells e.g. liver & cells of pancreas, plasma cells, fibroblasts some endocrine glands. LM A basophilic (blue) structure due It cannot be seen. If it is abundant the to presence of ribosomes cytoplasm becomes acidophilic EM -A network of parallel flattened -Branching & anastomosing tubules & communicating vesicles & tubules vesicles. called cisternae. -It has no ribosomes. It is covered with ribosomes. -It is continuous with r ER Functions 1- Synthesis of protein by the 1- Lipid synthesis. help of the ribosomes 2- Steroid hormones synthesis. 2- Condensation & packing of the 3- Formation & storage of glycogen. protein e.g. in liver & muscles. 3- Budding of the packed protein 4- It helps muscle contraction by Ca in the form of transfer vesicles. pump. 4- It acts as intracellular pathway 5- Detoxification of drugs & hormones in 5 - It shares in the formation of liver. Lysosomes, by formation & 6- Acts as intracellular pathway. segregation of their hydrolytic enzymes.  9 4-Golgi Apparatus (Fig.5) Definition:  It is a membranous organelle.  It is considered as the secretory system of the cell.  It is well developed in protein forming cells and secretory cells. LM: It is demonstrated by (Ag) stain. It appears as a dark brown network & fibrils around the nucleus (perinuclear) in nerve cell or between the nucleus & secretory pole (supranuclear) in secretory cell. e.g. pancreas. N.B. In sections stained with H&E. the area occupied by Golgi apparatus appears as unstained, area & so it is called negative Golgi Image.(Fig6) Negative Golgi Image  10 EM: It is formed of saucer-shaped flattened saccules stacked over each other forming a stack. Each stack has two faces:- 1- Immature convex surface, which is the forming surface (cis surface) that receives the transfer vesicles which carry protein from r E.R. 2- Mature concave surface from which secretory vesicles come out carrying condensed & modified protein. Also, other vesicles containing hydrolytic enzymes will come out &these are called Lysosomes Functions: 1- Concentration of protein formed by r E.R. 2- Modification of protein by adding sulphates or carbohydrates. 3- Discharge of secretion in the form of secretory vesicles 4- Isolation and packaging of hydrolytic enzymes in the form of lysosomes. 5- Formation & maintenance of cell membrane & cell coat. 5- Lysosomes (Fig.7) Definition:  Membranous organelles rich in hydrolytic enzymes  They are considered as the digestive system of the cell. Number: They are numerous in phagocytic cells e.g. white blood cells. Origin: The hydrolytic enzymes are formed in rER &carried in transfer vesicles to Golgi apparatus &come out as primary lysosomes LM: They can be demonstrated by using a special stain for the enzymes present within them, e.g. acid phosphates enzyme. EM: E.M picture of Lysosomes depends on their types. 1- Primary Lysosomes:  These are the newly formed lysosomes coming from Golgi apparatus.  They appear as small rounded homogenous vesicles.  11 2- Secondary Lysosomes:  They result from fusion of primary Lysosome with phagocytic vesicle.  They appear as heterogonous vesicles.  They are of different types: a) Heterolysosomes: They result from fusion of a primary lysosome with a phagocytic vesicle containing food or bacteria. b) Multivesicular bodies: They result from fusion of primary lysosomes with pinocytic vesicle containing fluid droplets. c) Autolysosomes: They result from fusion of primary lysosomes with vacuoles containing old organelles. d) Residual bodies: These are no more than secondary lysosomes containing the undigested remnants. They are either discharged outside the cell or accumulated within the cell as lipofuscin granules as in long lived cells e.g. cardiac muscle or nerve cell. Functions: 1- Digestion of nutrients within the cell. 2- Defensive function, destruction of any bacteria or virus. 3- Removal of any degenerated old organelles. 4- Lysis of the cells & all the body after death. 5- Change of inactive hormone into active one. e.g. in thyroid gland. 6- Help the sperm to penetrate the ovum. Nucleus - Definition: In all cells except (RBCs) and (platelets) (not true cells) - Number: Usually one, two in liver cell, more than 2 (osteoclasts, skeletal muscle cell). - Position: Central, eccentric, basal or peripheral. – Stains: Hx, methylene blue (basic stains) dark blue (due to DNA & RNA).  12 Structure: 1. Nuclear membrane (nuclear envelope): Light microscopy: Basophilic line (inner chromatin and outer ribosomes). Electron microscopy: Double wall interrupted by nuclear pores. Outer membrane: Granular (ribosomes) continuous with rER. Inner membrane: Fibrillar (peripheral chromatin). - Nuclear pores: Outer and inner membranes fuse. 2. Nuclear sap: Colloid solution between chromatin and nucleolus. Formed of nucleoproteins, enzymes, sugars, Ca, K, P. Function: Transport of RNA which pass through pores to the cytoplasm. 3. Chromatin: Formed of nucleoprotein (DNA + histones) Light microscopy: Basophilic particles and threads. 2 types: Euchromatin: Extended, active, not visible, the nucleus appears pale. It is formed of extended chromosomes with active genes responsible for protein synthesis. Heterochromatin: Condensed, inactive, dark. It is formed of coiled chromosomes with inactive genes. Electron microscopy: Euchromatin: fine granules. Heterochromatin: Arranged as: 1. Peripheral chromatin related to inner nuclear membrane. 2. Chromatin islands in nuclear sap. 3. Nucleolus associated chromatin  13 Function: Genetic information (DNA). Formation of rRNA, mRNA, tRNA. Protein synthesis. 4. Nucleolus: Light microscopy: Rounded, basophilic (rich in nucleic acid). Electron microscopy: Spongy, not limited by membrane: Dark areas & Light areas Function: rRNA formation that attach to protein and leave through the nuclear pores to cytoplasm to form ribosomes.  14 Tissues of the Body  There are four main tissues in the body, these are: 1- Epithelial tissue 2- Connective tissue 3- Muscular tissue 4- Nervous tissue I-Epithelial Tissue This tissue is called epithelial tissue because it can cover surfaces or line cavities all over the body. o General characters of epithelial tissue: 1- It may develop from ectoderm, mesoderm or endoderm. 2- The epithelial cells rest on a basement membrane (B.M.) which may be clear or not clear. 3- No blood vessels can enter in between epithelial cells, but nerves can, so epithelial tissue is avascular tissue. 4- Epithelial tissue receives nutrition by diffusion from the underlying connective tissue. 5- Epithelial tissue consists of numerous crowded cells with minimal intercellular substance between the cells that form continuous sheets, which cover surfaces or line cavities &is called surface epithelium. 6- Epithelial tissue may be modified to give secretion & is called glandular epithelium. 7- Epithelial tissue may modify to receive sensation & is called neuroepithelium & may acquire a contractile function & is called myoepithelium. 8- Epithelium can regenerate in a short time i.e. there is a continuous process of regeneration.  15 Epithelial tissue is classified into: I- Surface epithelium. II- Glandular epithelium. III- Neuro-epithelium IV- Myo-epithelium. I- Surface epithelium Surface epithelium is classified according to its number of layers into: a) Simple epithelium. b) Stratified epithelium. a- Simple Epithelium Definition: It is formed of one layer of cells resting on basement membrane. It is divided according to shape of cells into: 1- Simple squamous epithelium 2- Simple cubical epithelium 3- Simple columnar epithelium 4- Simple columnar ciliated epithelium 5- Pseudo-stratified columnar epithelium  16 4-Simple 1-Simple squamous 2-Simple cubical 3-Simple columnar epithelium columnar ciliated  Shape  Flat  Cube-like -Tall cells Tall cells of cells  Flat nucleus  Central carry rounded -Basal oval cilia nucleus nucleus -Basal oval nucleus  Functi  Smooth surface  Secretion Secretion Movement ons (easy movement)  Reabsorpti Absorption of  Thin surface on (microvilli particles (gas &fluid e.g. intestine) or fluids exchange) over the surface  Sites  Mesothelium[pleu  Thyroid -Stomach -Lung ra, pericardium follicle -Intestine bronchiole &peritoneum]  Small -Goblet cells s  Endothelium[hear ducts of [secrete t &blood vessels] salivary g. mucous -Uterus  Lung alveoli  Renal which  Bowman's convoluted accumulates -Fallopian capsule of kidney tubules in its apex] tubes Hanaa.AK  17 5- Pseudostratified Columnar Epithelium:  It is actually a simple epithelium as all the cells rest on the B.M.  It is formed of crowded cells.  Nuclei are present at more than one level; this gives the epithelium a false appearance of being stratified. POC a-Pseudostratified b-Pseudostratified c-Pseudostratified columnar non-ciliated columnar ciliated columnar ciliated with motile cilia with non-motile &goblet cells cilia  Sites 1- male genital system Respiratory epithelium  Epididymis  Nose (vas deferens).  Larynx 2- Membranous part of  Trachea male urethra  Bronchi Hanaa.AK. Pseudostratified columnar epith. b- Stratified Epithelium: Definition: Epithelium is formed of more than one layer, the basal layer resting on the B.M. It is classified according to shape of the top layer into:- 1- Stratified squamous epithelium. 2- Transitional epithelium [stratified cuboidal]. 3- Stratified columnar epithelium. 4- Stratified cubical epithelium.  18 Function: The main function of stratified epithelium is protection. 2- Transitional 1- Stratified Squamous Epithelium Epithelium  Number of 5-30 6-8 [empty bladder] 3-4 [full layers bladder]  Basement Clear & wavy Non-clear, non-wavy membrane  Basal cell Columnar with basal oval nuclei High cuboidal cells with rounded layer  Intermediate  Crowded polygonal cells with  polyhedral with rounded layers central rounded nuclei nuclei  Minimal intercellular substance.  wide intercellular spaces  Cells are held together with containing mucous like desmosomes. substance which helps gliding  They gradually decrease in size of the cells over each other.  NO desmosomes  Cells become flat in full bladder  Top layer Flat cells with flat nuclei.  Cells are dome shape with upper convex, lower concave surface & have rounded nuclei,  Some cells are binucleated.  The top layer is covered with mucous to protect against the action of urine.  Types Non-Keratinized Keratinized One type: In full bladder the cells of the top change in number of layers is due layer gradually to gliding of cells help of mucus die& change present between the cells so the into keratin number of layers decrease & the scales. surface area increase.  Sites Line any wet Skin & dry Urinary bladder, ureters, some surface opening opening over it parts of urethra, renal calyces and over the skin 1-Epidermis of renal pelvis 1-Oral cavity skin. 2-Oesophagus 2- External ear. 3- Cornea. 3- Nasal orifices.  Functions Protection Protection &accommodation (distensibility)  19 3- Stratified Columnar Epithelium: Like stratified squamous epithelium , but the number of layers is fewer & the top layer is formed of columnar cells which may be ciliated or not ciliated: - a- Stratified columnar ciliated epithelium:(Fig15) Sites: Fetal esophagus (a rare type). Fig:15- Stratified columnar ciliated epithelium b- Stratified columnar non ciliated epithelium:(Fig 16) Sites: 1- Recto-anal junction. 2- Large ducts of glands. 3- Male urethra (penile part). Fig16: Stratified columnar non ciliated epithelium:  20 4- Stratified Cubical Epithelium: (Fig17) Fig17 It is a rare type of epithelium which is formed of few layers of cells, may be onlytwo layers of cubical cells as in ducts of sweat glands.