Histology PDF - General Histology I

Introduction to Histology Microtechniques Histology: involved the study of the microscopic structure of the cells, tissue and organs. The Cells: are bound together to form different tissues. The Tissues: are combined together to form different organs. Several Organs: having correlated functions ar...

Introduction to Histology Microtechniques Histology: involved the study of the microscopic structure of the cells, tissue and organs. The Cells: are bound together to form different tissues. The Tissues: are combined together to form different organs. Several Organs: having correlated functions are grouped to form Systems.  Histological study A) Tissue preparation “Mirotechniques” The aim is: PRESERVATION & HARDENING of tissue B) Staining The aim is: to make GOOD CONTRAST between different tissue parts B) Examination by microscope The aim is: MAGNIFIED and DETAILED image  Slicing of the sample Obtaining the sample Fixation Embedding Tissue Block  Method of tissue preparation for LM Paraffin Technique Advantages of the paraffin technique: Takes short time. Gives very thin serial sections. Sections can be stained easily. Disadvantages of the paraffin technique: Fat cannot be demonstrated because fat dissolves in xylol. Not used in histo-chemistry as enzymes are destroyed by heat. 66 Paraffin technique Paraffin block 77  Types of stains 1. Acidic stain: as Eosin stain, Orange G. and Acid Fuscin. They stain the alkaline structures of the cytoplasm (as proteins) with red color. 2. Basic stain: as Hematoxylin, Toluidine blue and Methylene blue. They stain the acidic structures of cytoplasm and the nucleus with a blue color. The cytoplasm is usually alkaline in reaction in non- secretory cells, so it takes the acidic stain as Eosin. Thus it is acidophilic in staining (it likes the acidic stains). The nucleus is rich in nucleic acids, thus it is constantly acidic in reaction, so the nucleus takes the basic stains as Hematoxylin. It is basophilic in staining (it likes the basic stains).  MICROSCOPY To use an instrument to see objects too tiny for the naked eye. Microscopic means invisible to the eye unless aided by a microscope. 2222  Types of Microscopes 1. Light Microscope (L/M) 2. The Transmission Electron Microscope (E/M) 3. The scanning Electron Microscope  Microscope The microscope is an instrument used to Magnification power Magnify the tissue Resolution power View its detailed structures clearly THE MAGNIFICATION POWER AND THE RESOLUTION POWER For the LM: Magnification power: The LM is from 1000 to 2000. The resolution power of the LM is 0.2 um. For the EM: Magnification power: The EM is from 2000 to 100,000. The resolution power of the EM is 0.2 nm. Electron Microscope (EM) This type of microscope uses invisible light source which is the high energy electron beam Types of EM: 1. Transmission electron microscope (TEM): visualizes the internal structure of the cell. 1. Scanning electron microscope (SEM): visualizes the surface of cells (three dimensional image on the screen) as microvilli and cilia. 2828 Transmission Electron Microscope 3232 Tongue surface showing filliform and fungiform papillae with coloured scanning EM LM Microvilli TEM SEM  LM EM Day light or sub- Source of energy: Beam of Electrons stage lamp Thin sections (5-8 um) Sections Ultrathin (50-80 nm) Staining Ordinary stains Heavy metal stain Magnification power: From 2000 to Up to 1000 100,000 Resolution power: 0.2 um 0.2 nm o By eye through o On - fluorescent eye piece screen Image received: 40 Cytology The Cell  The Cell Definition: The cell is the structural and functional unit of the body organs. The cells are bound together to form tissues. The tissues are combined to form organs. Functions of cells: The cells in the body perform many functions as: secretion, excretion, respiration, absorption, conduction, contraction, sensation and regulation of the other body functions. Size of cells: The different body cells vary in size. Some cells are very small as certain cells of the cerebellum, while others are very large as the muscle cells. The majority of body cells are medium-sized. Shape of cells: The different body cells vary in shape. Some cells are rounded others are oval, flat, cubical or columnar in shape. Structurally the cell is formed of: Cell membrane that separates the external environment from the protoplasm. The protoplasm is formed of: The cytoplasm. The nucleus.  THE CYTOPLASM SUSPENDED CYTOSOL BODIES ORGANELLES INCLUSIONS MEMBRANOUS NON MEMBRANOUS The cytoplasm 1. Cytoplasmic matrix or Cell sap: It is a colloidal gel-like solution of proteins, lipids, carbohydrates, minerals, enzymes, small molecules and ions. 2. Cytoplasmic Organelles (cell organoids): They are of two types: a. Membranous cytoplasmic organelles: They are small permanent organs which are enclosed in membranes. b. Non-membranous cytoplasmic organelles: They are special cell components which are not enclosed in membranes. Cell organelles  3. Cytoplasmic inclusions (cell inclusions): They are temporary components of certain cells. They are usually an accumulation of stored food as: glycogen and fat or an accumulation of pigments as: carbon and melanin. I. Cell organelles The term organelle means small organ, each organelle performs certain functions which are essential for the life and metabolism of each cell. The cell organelles are also called organoids. They are classified into: 1. The membranous cytoplasmic organelles which are characterized by: a. They are enclosed in membranes b. They are present in all nucleated cells c. They are permanent components of the cytoplasm d. They contain enzymes that participate in cellular metabolic activities. The membranous cell organelles are 1. The cell membrane or plasma membrane. 2. The mitochondria. 3. The Golgi apparatus. 4. The lysosomes. 5. The endoplasmic reticulum (rough and smooth types). 6. Peroxisomes. 2- The non-membranous cytoplasmic organelles: They are not covered by membranes as: Ribosomes, centrioles, microtubules,microfilaments (cytoskeleton) cilia and flagella. The membranous cell organelles 1. The cell (plasma) membrane Definition: It is the outermost covering of the cytoplasm. It is also named Plasmalemma or Plasma membrane. With the light microscope (L/M): Staining: Stained red by PAS stain. With the electron microscope (E/M): It appears as if it is formed of three layers, tri-lamellar membrane. Its outer and inner layers appear as 2 dark lines, while its middle layer appears as a light area. The molecular composition of cell membrane PHOSPHOLIPIDS LIPIDS CHOLESTEROL INTEGRAL PROTEINS PROTEINS PERIPHERAL PROTEINS GLYCOLIPIDS CARBOHYDRATES GLYCOPROTEINS Molecular structure of the cell membrane: It is formed of lipids, proteins and carbohydrates molecules covered by cell receptors. 1. The lipid molecules (30%) They form 2 layers (bilayer) arranged in 2 rows inside the cell membrane. The lipid content is formed of: Phospholipid and cholesterol molecules  1) Each phospholipid molecule is formed of two parts: a. The hydrophilic charged part of the phospholipid molecule: It forms the heads of the phospholipid molecules. It is called hydrophilic because it has a great affinity for aqueous solutions (it likes water). It is composed of charged lipid and is called Polar Region. It is present near the outer and inner surfaces of the cell membrane.  b. The hydrophobic non-charged part of the phospholipid molecule: It is formed of the 2 tails of the phospholipid molecule. It is called hydrophobic because it has no affinity for aqueous solutions (it dislikes water). It is formed of non-charged lipid and it called Non Polar Region. The hydrophobic ends of the lipid molecule are directed inwards, they face each other in the central part of the cell membrane. The cholesterol molecules: )2 They are mainly present in the inner cytoplasmic aspect of the cell membrane. Functions: The lipids facilitate enterance of fat- soluble materials into the cell. The protein molecules (60%).2 present in the cell membrane in these forms: Extrinsic or peripheral protein: )1 It is formed of protein molecules which are present on both surfaces of the cell membrane. It forms a non-continuous layer floating outside the lipid molecules. Intrinsic or integral protein: )2 a. Small intrinsic protein molecules Which are present as small collections of protein distributed among the lipid molecules. They contain enzymes. b. Large intrinsic protein molecules: They are present as large masses of protein. They are called trans membrane protein. They contain channels through which ions and water- soluble molecules can pass. The carbohydrate molecules (10%).3 They are present only on the outer surface of the cell membrane. They are either linked to the protein molecules forming Glycoproteins or linked to the lipid molecules forming Glycolipids. The glycoproteins and the glycolipids form the Cell Coat on the outer surface. The Cell Coat = Glycocalyx The cell coat is a layer of glycoproteins and glycolipids which are present on the external surface of the cell membrane. It is called also Glycocalyx. It may be very thick or very thin according to the type and function of each cell. The cell coat can be stained with PAS stain. It is very rich in Cell Receptors.  Functions of cell membrane: A- Maintain the structural integrity of the cell B- Conduction of nerve impulses: In nerve and muscle cells, the cell membrane facilitates conduction of nerve impulses from one cell to another. C- Functions of cell coat: It is very rich in Cell Receptors D- Exchange of substances: (Transport) Bulk transport including: Endocytosis: a - i- Phagocytosis of solid particles ii- Pinocytosis of fluid particles iii- Receptor mediated endocytosis b- Exocytosis: (Membrane trafficking) Expulsion of secretory elements and the residual bodies out of the cell. 2. Mitochondria Definition: They are membranous cell organelles present in all nucleated cells. They contain enzymes. They are concerned with the production of energy. Site: Mitochondria vary in location in the cytoplasm from one cell to another. Structure: They are formed of: protein, lipid, DNA, RNA, Zinc, calcium, magnesium and oxidative enzymes. Shape: The mitochondria word means: Mitos = thread + chondros = granules With the light microscope (L/M): 1− They appear as rods, granules or filaments. 3− The mitochondrial matrix is rich in: oxidative enzymes. With the electron microscope (E/M): Each mitochondrion appears as a vesicle surrounded by two membranes: The outer membrane is smooth, while the inner membrane is rough because it projects into the cavity of the mitochondrion forming shelves called cristae. Number of mitochondria: It varies from one cell to another. About 1000 mitochondria are present in liver cell, but no mitochondria are present in red blood corpuscles. Staining of mitochondria: 1− They stain black with iron hematoxylin and green with Janus green stains. 2− Mitochondria can divide to increase their number. 3− They contain DNA which carries some genetic characters. Functions of mitochondria they are considered as the power house of the cell. Energy production through formation of ATP by oxidative phosphorylation 3. Endoplasmic Reticulum Definition: They are membranous cell organelles formed of communicating wide and narrow tubules. The two types of endoplasmic reticulum A. Granular or Rough Endoplasmic Reticulum Definition: It is formed of communicating flat tubules (cisternae) with rough surfaces. Its surface is covered by ribosomes. Position: It extends between nuclear membrane and cell membrane. It is present in great amounts in protein forming cells as: Fibroblast, Osteoblast, plasma cells and pancreatic cells. By the (E/M): They are formed of communicating flat tubules (cisternae) covered by ribosomes. Staining: They stain blue with hematoxylin. They are basophilic due to presence of ribosomes.  Functions of Rough Endoplasmic Reticulum: 1. The rough endoplasmic reticulum and the attached ribosomes form protein. 2. They store formed protein. 3. They package the formed protein. The packaged proteins travel through the cytoplasm as transfer vesicles to fuse with Golgi apparatus. 4. They form the protein needed for the formation of lysosomal enzymes.  B. Non-Granular Smooth Endoplasmic reticulum Definition: They are membranous cell organelles, formed of anastomosing narrow tubules with smooth walls. Position: It extends between the nuclear membrane and cell membrane. It is present in great amounts in the cells which synthesize lipid and carbohydrate as: liver and endocrine cells. By the light microscope: It cannot be demonstrated with hematoxylin stain. By the electron microscope: it appears as fine anastomosing tubules with smooth walls. There are no ribosomes on their outer surfaces. Functions of smooth endoplasmic reticulum Synthesis of lipid..1 Synthesis of glycogen..2 Synthesis of Steroid hormones...3 Regulation of muscular contraction 4 through the release of calcium ions.  4. Golgi Apparatus Definition: Golgi apparatus is a membranous cell organelle. Position: In nerve and liver cells, it surrounds the nucleus. In secretory cells, it is present between the nucleus and the free border of the cell. Stain: It stains brown with silver stain. It is not stained with Hx and E. Its position is indicated by a non-stained area called Negative Golgi image. Shape: With light microscope, it appears as a network. Golgi apparatus with the electron microscope appears in the following three forms: 1-Flat vesicles or Golgi Saccules: They are formed of small flat sacs. The sacs are arranged above each other forming stacks. Each stack has a concave mature surface called Trans Face and a convex immature surface called Cis Face.  Transfer or Micro Vesicles: They are small rounded sacs (vesicles) filled with protein. These transfer vesicles originate from the rough endoplasmic reticulum. They fuse with the flat vesicles of Golgi apparatus where their contents are transformed into Secretory Vesicles. 3-Secretory or Macro Vesicles: In Golgi apparatus the entered proteins are collected, concentrated and enveloped by membranes to be transformed into the following vesicles: a. secretory vesicles.that discharge their content to the outside (exocytosis) b. Lysosomal vesicles: They carry inside them the lysosomal enzymes. These lysosomal vesicles remain in the cytoplasm as primary lysosomes. Functions of Golgi apparatus 1. Golgi apparatus is responsible for collecting, concentrating and packaging the secretory products of the cells. 2. Golgi apparatus and the endoplasmic reticulum share in the formation of lysosomes and the secreted hormones and enzymes.  5. Lysosomes Definition: Lysosomes are membranous cell organelles present in all kind of cells. They contain hydrolytic enzymes for the intracytoplasmic digestion of nutritive substances, and removal of foreign bodies. Number: Their number varies from one cell to another. They are more present in phagocytic (eating) cells. Shape and size: They are spherical in shape, their diameters vary from 0.2 to 0.4 micron. With the electron microscope; lysosomes appear in these 2 forms: 1. Primary lysosomes: appear as homogenous rounded vesicles, surrounded by single membranes. 2. Secondary lysosomes: appear as heterogenous rounded bodies because they contain the digested elements. Enzymatic contents: They contain hydrolytic enzymes as: Proteases, nucleases, lipases, glycosidases and are rich also in acid phosphatase enzymes. Steps of formation of lysosomes 1. The lysosomal enzymes are protein in nature; they are synthesized in the Rough Endoplasmic Reticulum. 2. These lysosomal enzymes migrate to Golgi apparatus as transfer vesicles. 3. In Golgi apparatus, the enzymes are phosphorylated in the Trans Golgi Network and then are concentrated and enveloped to transformed into lysosomes. 4. The newly-formed lysosomes are budded off from Golgi apparatus to enter the cytoplasm and now are called Primary Lysosomes. Fate of Primary Lysosomes 1. Primary lysosomes may circulate in the cytoplasm and remain as such if they are not fused with any cytoplasmic foreign bodies or nutritive elements. 2. Primary lysosomes may fuse with foreign bodies or with nutritive materials with old mitochondria to be changed into secondary lysosomes. Types of Secondary Lysosomes a. Hetero-Lysosomes: formed by fusion of primary lysosomes with exogenous substances as bacteria. b. Autophagic Lysosomes: formed by fusion of primary lysosomes with the endogenous residual bodies of old organelles as old mitochondria. c. Multi-vesicular bodies: formed by fusion of primary lysosomes with engulfed liquid elements which are called pinocytic vesicles. d- Residual Bodies Whatever is left over after the digestion of either the heterolysosomes or the multivesicular body becomes known as Residual bodies. Fate of residual bodies of lysosomes a. Residual bodies may be excreted from the cell by Exocytosis process. b. Old residual bodies may accumulate in cardiac muscles and in nerve cells to form lipofuscin granules or age pigments. Function of lysosomes 1. Lysosomes during life are concerned with intracytoplasmic digestion of nutritive materials. 2. Lysosomes play an important role in defending the body against invading organisms; they can kill bacteria and viruses. 3. They can digest old mitochondria before their disposal outside the cell.  3. Lysosomes are concerned with the post-mortem changes in the body after death. When cells approach death as in oxygen deficiency, lack of blood supply or in cell infection, the escaped lysosomal enzymes will destroy the whole cells after death. Lysosomes are sometimes called Suicidal Bags.  6. Peroxisomes or Microbodies Membranous organelle contain OXIDATIVE enzymes and catalase enzyme. Look like lysosome but less dense. Synthesized by free ribosomes and completed in Golgi. Function: lipid metabolism as oxidation of long chain fatty acid  The Non-membranous Cell Organelles 1. The Ribosomes Definition: They are rounded or oval cytoplasmic organelles formed of ribo- nucleoprotein (RNA + Protein). Site of their formation: They are formed in the nucleolus. They pass through the nuclear pores to reach the cytoplasm. Staining: They can be stained with basic stains. example basophilic granular area in nerve cells are called Nissl’s granules. Different forms of Ribosomes in different cells 1. Free ribosomes: They are scattered freely in the cytoplasm. Their number may increase in: growing cells, secretory cells, cancer cells and during cell division. 2. Attached ribosomes: They are attached to the outer surface of the rough endoplasmic reticulum and are called ribosomal RNA.  3. Polysomes: Ribosomes may be attached to each other by messenger RNA to form rosettes or spiral structures called Polysomes. E/M picture: 1- Each ribosome is composed of 2 subunits, one of which is twice the size of the other. 2- The large subunit of the ribosome is formed of 2 parts; between these two parts a polypeptide chain is present. 3- The formed proteins are segregated from this polypeptide chain and then pushed into rough endoplasmic reticulum. Functions of Ribosomes: Factories of protein synthesis Free ribosomes form proteins used within the cytoplasm attached ribosomes form the secreted protein by the cell as hormones.  The Nucleus Definition: It plays an important role in heredity, in cell division and in controlling all cellular function Blood RBCs and blood platelets have no nuclei. Number: Usually each cell contains one nucleus. Two nuclei may be present in some liver cells and some superficial cells of the transitional epithelium, while many nuclei are present in skeletal muscle cells. Size: The nucleus may be small, medium sized or large. Shape: There are various shapes for the nuclei Position: They may be central, eccentric, peripheral or basal in position. Staining: The nucleus is a basophilic structure. It can be stained with basic stain as hematoxylin because it is rich in nucleic acids (DNA + RNA). Structure of nucleus The nucleus consists of the following 4 components: 1. Nuclear membrane or nuclear envelope. 2. Nuclear Sap or nuclear matrix. 3. Nucleolus. 4. Nuclear chromatins are of 2 types: Euchromatin and Heterochromatin.  1-Nuclear Envelope or Membrane It is dark basophilic membrane which surrounds the nucleus. L/M: It appears as single dark membrane. E/M: It is formed of the following 2 thin membranes: a. Inner fibrillar membrane: rich in chromatin fibres on its inner aspect. b. Outer granular membrane: rich in ribosomes on its outer surface. It is continuous with the rough endoplasmic reticulum.  2. The Nuclear sap or Nuclear Matrix (Karyolymph) It is a protein solution present between the condensed chromatin.  The Nucleolus. By L/M: it appears as rounded dark basophilic mass rich in nucleic acids and surrounded with chromatin. By E/M: The nucleolus is formed of light and dark areas: a. The light areas are very rich in nuclear sap. b. The dark areas is it is formed of mature ribosomal RNA Functions of the Nucleolus It forms the ribosomal RNA (Ribosomes) Which pass through the nuclear pores to the cytoplasm  3-The chromatin material Structure: Chromatin materials are formed mainly of nucleoprotein which is formed of DNA bound to basic proteins called Histones. Staining: They are basophilic in staining due to presence of DNA. With L/M: The chromatin materials appear as darkly stained basophilic granules or lightly- stained filaments. With E/M: The darkly-stained chromatin (Heterochromatin) is distributed within the nucleus are: 1. Peripheral chromatin: which lies close to the inner side of the nuclear membrane. 2. Chromatin islands: which are the condensed scattered masses between the nuclear membrane and the nucleolus. 3. Nucleolus associated chromatin: which are the condensed chromatin materials present around the nucleolus. There are two types of chromatin: Euchromatic and heterochromatin. a- The Euchromatin or the extended chromatin is characterized by: 1- They are not visible by the light microscope because they are very thin threads. 2- They represent the extended (uncoiled) parts of the chromosomal threads. 3- They stain very lightly with the basic stains. 4- They are the most active chromatin. 5- They control protein synthesis. b. The Heterochromatin or the condensed chromatin characterized by: 1- They are visible by light microscope as coarse granules. 2- They stain dark with the basic stains. 3- They are inactive chromatin. 4- They do not direct any protein synthesis. Functions of the nucleus 1. controls cell. the function 2. carries genetic information. 3. The nucleus regulates the processes of cell division. 4. formation of different types of RNA. Epithelial tissue  Tissues of the body The human body organs are formed of the following 4 types of tissues 1. Epithelial tissue 2. Connective tissue 3. Muscular tissue 4. Nervous tissue  General characteristics of epithelial tissue Blood vessels do not penetrate between epithelial cells except in endocrine glands but nerve fibres can penetrate between the epithelial cells. 1. Epithelium rests on a basement membrane which may be clear or non clear. 2. Epithelium can degenerate (destroyed) and can rapidly regenerate (renewed). 3. Epithelium has a little intracellular substance but the epithelial cells may be connected with each other by different types of cellular junctions. 4. Epithelial tissue covers a surface or lines a cavity or forms a gland. 5. Epithelial cells may act as special receptors for taste and equilibrium. Epithelial tissue  Functions of epithelial tissues 1. Protection against injuries, bacteria, chemicals and water as epithelium of skin 2. Secretion as glandular epithelium of,salivary glands. 3. Absorption as the cells of intestine 4. Sensation as the taste buds 5. Covering surfaces (as skin) or lining cavities (as stomach). 6. Respiration as the epithelium of lung alveoli. The basement membrane: It binds epithelium to the underlying C.T. It permits the passage of blood and nutrition to the epithelium. Types of epithelial tissue a. Simple epithelium (formed of one layer of cells) b. Stratified epithelium (formed of many layers of cells one above the other) c. Glandular epithelium (cells are collected to form glands) d. Neuro-epithelium (epithelial cells act as receptors) e. Myoepithelium (cells are modified to contract) 1. Simple Epithelium a. Simle squamous epithelium It is formed of one layer of flat cells with flattened nuclei Sites: a. It forms a thin smooth lining to blood vessels to allow easy passage of blood. The endothelium of heart and blood vessels. b. The mesothelium of serous membranes as pleura (around the lung) pericardium (around the heart) and peritoneum (around the intestine) to facilitate the movements of viscera. c. Present in the alveoli of lung.  b. Simple Cubical Epithelium Simple cubical is formed of one layer of cubical cells with central rounded nuclei Sites: 1. Lining the thyroid follicles they secrete thyroid hormones. 2. The kidney c. Simple Columnar Epithelium (Non-ciliated or Ciliated) It is formed of one layer of tall columnar cells with basal oval nuclei. Sites: a. In the stomach, simple columnar cells secrete mucin, b. In the intestine, they have a surface covered with microvilli to facilitate absorption processes. Simple Columnar Ciliated Epithelium It is formed of simple columnar cells with basal oval nuclei. The free surfaces of these cells are covered with cilia. Sites: a.Fallopian tube and uterus (some of their lining cells are ciliated to facilitate movements of menstrual blood and ova). b. Outer part of Eustachian tube.  d. Pseudo – Stratified Columnar (Ciliated and Non-ciliated) It is a simple type of epithelium formed of one layer of columnar cells  1-The columnar cells of this type of epithelium are crowded over each other, 2-Their nuclei are arranged at different levels forming false rows. 3- All the cells reach the basement membrane but some of them may fail to reach the surface. 4- The surface may be ciliated or non-ciliated. 5- Goblet cells may be present between the columnar cells, they secrete mucus secretion.  Sites: 1.Pseudo-Stratified columnar ciliate epithelium with goblet cells and motile cilia a-The upper respiratory passages as: nasal air sinuses, nasopharynx, larynx, trachea and bronchi. b. Eustachian tube (in its inner part). 2. Pseudo Stratified Columnar Ciliated Epithelium but the Cilia are non-motile the epididymis. 3. Pseudo-Stratified columnar non-ciliated epithelium: a. Vas deferens and male urethra. 2. Stratified Epithelium Stratified epithelium is formed of many layers of cells (3 or more layers). Types The stratified epithelium is named according to the most superficial cells, 1. Stratified squamous epithelium 2. Stratified cubical epithelium 3. Stratified columnar epithelium 4. Transitional epithelium (the superficial cells are broad a. Stratified squamous epithelium The number of layers ranges from 5 to 30 layers of cells resting on a clear wavy basement membrane. The basal cells are well nourished and are formed of columnar cells with oval basal nuclei, from these basal cells, the other layers are renewed. The intermediate layers are polygonal cells (have many sides) with desmosomes between their cell boundaries The superficial layers are formed of flat squamous cells with flattened nuclei. They are not well-nourished and they are exposed to air so they are gradually shed off. The surface may be covered with fresh non-keratinizing squamous cells. In other areas, the epithelium is covered with keratin layer and the epithelium is named keratinizing stratified squamous. Sites: 1. Keratinizing stratified squamous epithelium a. Epidermis of skin. b. Openings upon the skin External ear, external nose, outer surface of the lip and the anal orifice. 2. Non-keratinizing stratified squamous epithelium a. Oral cavity, b. Oesophagus, c. Cornea d. Vagina e-anal canal. b. Stratified cuboidal epithelium the free surface is covered with cuboidal cells, Sites. 1-In the ducts of sweat glands, 2-In the testis. c. Stratified columnar epithelium It is similar in structure to stratified squamous epithelium Its layers are less in number. The superficial cells are columnar cells. Sites: 1. Male urethra. 2. Recto-anal junction. glands.  d. Transitional epithelium It is stratified type of epithelium which is present in the urinary tract. The epithelium rests on thin basement membrane. The superficial cells are cuboidal in shape. Some of the superficial cells may contain two nuclei. These superficial cells are called Dome-like cells. The basal cell layer is high cuboidal cells. The intermediate cells ,between the basal and superficial layers are polyhedral cells and are separated from each other by mucous-like substance in their intercellular spaces. The transitional epithelium can be considered as a stratified cuboidal epithelium. The mucous substance between the cells, facilitate gliding of cells on each other, so the transitional epithelium may be formed of 3 to 4 layers only in full distended urinary bladder or 6 to 8 layers in an empty bladder. Sites: Pelvis of the ureter, 1-the ureter and the urinary bladder. bladder part of 2. Glandular epithelium It is the type of epithelium which is specialized to produce secretion. The glands are formed of collections of secretory epithelial cells  3. Neuro-Epithelium In this type, the epithelial cells act as sensory receptors for special stimuli. Sites: a. Taste buds in the tongue. b. Organ of Corti in internal ear (for hearing). 4. Myo-epithelium or Basket cells 1-They are epithelial cells 2-They are rich in actin and myosin filaments. 4-They contract to squeeze the acini to secrete their products. 5-They are present on the outer surfaces of the acini of sweat, salivary and mammary glands. Connective tissue Characteristics: 1- Formed of Widely separated cells with large amount of ground substance (matrix), unlike other tissue types (epithelium, muscle and nerves which consist mainly cells. 2- Penetrated by Blood vessels, nerves and lymphatic vessels. Functions of connective tissue: Connect, support and protect other tissues and organs The tissue fluid in its intracellular substances acts as a medium for diffusion of O2 and nutrients from nearby blood vessels to the surrounding tissue cells.  Types of Connective Tissue: According to the rigidity and chemical composition of its intercellular substance, connective tissue is classified into three types, 1) C.T. proper with a soft intercellular substance. 2) Cartilage with a rigid (rubbery) intercellular substance. 3) Bone with a solid (stony hard) intercellular substance.  The C.T proper The intercellular substance of c.t proper formed of (jelly like )component (jelly like )component: composed of tissue fluid +macromolecules responsiple for the softness of c.tproper  1) Connective tissue proper Connective tissue proper is a type of connective tissue characterized by its soft intercellular substance. Structure of connective tissue proper Connective tissue proper is composed of cells widely separated by a good amount of soft intercellular substance. This intercellular substance is penetrated by blood vessels, lymphatics and nerves, and is separated from other tissues by a basement membrane.  The fibers of the C.T. proper: The C.T. proper contains 3 types of fibers: white collagenous fibers, yellow elastic fibers and reticular fibres: a) The white collagenous fibers: □ colourless, when present singly, but on condensation, they are white in colour. □ made of collagen protein. □ affected by boiling, enzymes, acids and alkalies □ give tissue strength and rigidity b) The yellow elastic fibers: □ yellow on condensation. □ They are made of elastin protein □ thin branching fibers. □ resist acids and alkalies □ specially stained by orcein (brown) □ They provide the tissue with the power of stretch and elasticity. c) The reticular fibers: □ formed of a delicate network of fibers. □ made of collagen protein(type III). □ demonstrated by silver stain (argyrophilic). □ They form the stroma of organs  The cells of C.T. proper C.T. cells are classified into: Fixed: 1. Undifferentiated Mesenchymal Cell (UMC) & Pericyte 2. Fibroblasts & Fibrocytes 3. Reticular cells 4. Fat Cells: Unilocular & Multilocular 5. Fixed Macrophage  Free: 1. Free macroghages 2. Mast cells 3. Plasm cells 4. White blood cells (WBCs) 1) Undifferentiated mesenchymal cells (UMC): - Branched cells. - Nucleus is large, pale(vesicular) and oval. -Cytoplasm is basophilic (good content of free ribosomes. Function: a. They can differentiate to give the different cells of all types of connective tissue (C.T. proper,cartilage and bone). b. They also give the origin of blood elements, endothelial cells and muscle cells. c. Some cells remain after birth around blood capillaries (pericytes). 2) Fibroblasts: - Most common, found in all types of C.T. proper. - Flat branched cells (spindle –shaped in side view). - Nucleus is large, pale and oval with prominent nucleolus. - Cytoplasm is scanty and basophilic, with well developed Golgi apparatus, rough endoplasmic reticulum (rER), many ribosomes and mitochondria (Characters of protein-secreting cells). - The inactive fibroblasts (fibrocytes) smaller with fewer processes. the nucleus is smaller and darker.The cytoplasm contains less rough endoplasmic reticulum (less basophilic), non dividable cell. They maintain the C.T. Function: 1)- Synthesis of protein that form collagen, reticular and elastic fibers. 2)- Production of the ground substance. 3)- Production of growth factors that influence cell growth and differentiation. 4)- Healing of the connective tissue after injury. 3)Reticular cells: (Considered as specialized type of fibroblast) 4) Fat cells (Adipocytes): a) Unilocular fat cells: □ Abundant in white adipose connective tissue. □ Large spherical cells. □ Nucleus is peripheral and flattened. □ Cytoplasm forms a thin film around a single large fat droplet. □ Lipid droplets are removed by the alcohol and xylol used in routine histological techniques, so thecells appear as large vacuoles (signet –ringappearance). □ Fat is stained with Sudan III or Sudan black. Unilocular fat cells Function:(function of white fat) 1- Storage of energy and release at time of need (tissue starvation). 2- heat insulation 3-supportive pads to some organs e.g. (kidney). 4-give the body its characteristic contour. b) Multilocular fat cells: □ Found in brown adipose connective tissue. □ Cells are smaller than the Unilocular. □ Contain many fat droplets of various sizes. □ Nucleus is central and rounded. Function is heat production. Multilocular fat cells 5) Macrophages (Histiocytes): Originate: from blood monocytes. shape: L.M large irregular cells which send broad irregular processes called pseudopodia. nucleus :eccentric, kidney-shaped and deeply stainednucleus.  E.M. the cytoplasm appears to contain a good amount of lysosomes, phagosomes as well as rER, Golgi apparatus and mitochondria. function: They play an important role in the body defence mechanism by: 1) Phagocytosis. 2) Antigen presenting function. 6) Mast cells: Site: Abundant in loose connective tissues, along the blood vessels. Shape: Oval or rounded in shape. Cytoplasm: is basophilic granular. Granules contain heparin and histamine. Function: a) Secretion of heparin (anticoagulant). b) Secretion of histamine which initiate allergic reaction. c) Secretion of eosinophil chemotactic factor (which attracts eosinophils). N.B. Note the similarity between mast cells and basophil leucocytes. 7) Plasma cells: - Abundant in lymphoid tissues. - Develop from B-lymphocytes. - Oval in shape. - Nucleus is eccentric with a cart-wheel (clock-face) appearance. - The cytoplasm is basophilic non-granular, rich in rough endoplasmic reticulum, mitochondria contains a well developed Golgi apparatus (- ve golgi image).(characteristics of protein – secreting cells). Function: Secretion of antibodies (humoral immunity) 8) Leucocytes (WBCs):BLOOD  Types of connective tissue proper There are 7 types: 1) Loose (areolar) connective tissue. 2) Adipose connective tissue. 3) Mucoid connective tissue. 4) White fibrous connective tissue. 5) Yellow elastic connective tissue. 6) Reticular connective tissue. 7) Pigmented connective tissue.  1.Dense C.T (White collagenous C.T) White collagenous fibers are predominate (arranged in bundles) with fibroblast & fibrocytes There are 2 types: a. Regular type: in cornea. b.Irregular type: found in sclera of eye Dense regular C.T Dense irregular C.T  2) Loose (areolar) connective tissue: - the most common type. - Has potential cavities (areolae), which can accommodate large amounts of fluids or gas. - It contains all the types of fibers and cells (most common cells are fibroblast, fibrocytes and macrophages). Site: - It is found everywhere in the body, except in central nervous system (CNS). 1- dermis of the skin 2- submucosa of gastro-intestinal tract (GIT) 3- serous membranes (peritoneum, pleura and pericardium). Loose (areolar) connective tissue:  3. Adipose Connective Tissue: It is a type of C.T in which fat cells predominate. There are 2 types: 1-white Fat 2- BROWN Fat origin: UMC→ accumulate small fat droplets in its cytoplasm→fuse together and form a single large fat droplet (unilocular fat cell). Some other cells accumulate fat as small multiple, non –fused fat globules (multilocular fat cells).  WHITE FAT(white adipose c.t) Structure: □ Fat cells are large (Unilocular). □ Each cell contains a large single fat droplet. □ Poor blood supply, affected by dietatory state. Sites: □ Mammary gland. □ Subcutaneous tissue. □ (around the kidney). Function: □ Storage of fat. □ Insulation of heat. □ Support of soft organs. □ Gives the body its smooth curves, especially in females.  Brown Fat Structure: □ Smaller fat cells (Multilocular). □ Each contains many fat droplets. □ Rich blood supply and high content of mito with their cytochrome oxidase enzyme (has iron in it stucture) (cause of brown colour ) Sites: □In new born infants: Around the aorta, and in the axilla Function: □ On exposure to cold, it releases heat, to warm the body. 4. Yellow Elastic Connective Tissue: Elastic fibres predominate + fibroblast &fibrocyte. It is found in: □ Aorta and large blood vessels. □ Trachea  Reticular Connective issue: ormed of network of delicate reticular bers and reticular cells *(specialized broblasts),. eticular connective tissue forms the troma of all organs ( lymph node, pleen, liver and kideny).  Mucoid Connective Tissue Wharton’s Jelly): t consists of UMC + few collagenous bres, embedded in a large amount of ucoid ground substance here are called ucoid cells. : it is an embryonic type of C.T ites: Umbilical cord. Muscular tissue Tissues of the body  Character of muscle Origin: mesodermal The functional unite of muscular tissue is muscle cell (muscle fibre). Each muscle fibre surrounded by delicat c.t that provides them with a rich bl supply. The cytoplasm of the ms fibre is called (sarcoplasm) containing contractile structures The ms cell (fibre) is surrounded by a cellmembrane called “sarcolemma” The sarcolemma is thick & covered by a basement membrane (external lamina). Muscular tissue is specialized for producing movement.  Types of Muscle Tissue Skeletal Attach to skeleton striated voluntary in action Cardiac: only in the wall of the heart Cells are striated Contractions are involuntary. Smooth: walls of hollow organs no striations Contractions are involuntary) Skeletal ms fibres (sk myofibres) Origin : - In prenatal (embryonic)----- fusion of multiple myoblast - In post natal life-----satellite cell (residual myoblasts for repair).  General appearance Site & shape: 1‐ They are present in muscles attached to the skeleton (hence their name).they also present in the upper part oF GIT (pharynx and upper third of the oesophagus). 2‐ They are non banching except in the muscles of the tongue and the face. 3‐ They are long cylindrical cells of large size & uniform diameter. L.M: in (LS) sections, they show cross striations of alternating light band & dark band Between the sarcolemma of the sk ms fibre and its basement membrane, there are mono- nucleated flattened cells called “the satellite cells” In a tansverse section (T.S) the myofibres appear rounded or polygonal in shape and have an equal diameter. Between the sarcolemma of the sk ms fibre and its basement membrane, there are mono- nucleated flattened cells called “the satellite cells” L.S & T.S OF skeletal muscles Nuclei: Multiple (up to 100), rode like or oval & peripheral in position. Cytoplasm (sarcoplasm): Deeply acidophilic, contain organoids &inclusion especially for its contractile function. E.M. Picture: Sarcoplasm contains: -Parallel myofibrils -Numerous mitochondria rod-shaped, arranged in rows between the myofibrils. -Well developed smooth endoplasmic reticulum(sarcoplasmic reticulum). -Golgi vesicles and ribosomes. -Glycogen and myoglobin. a)- The myofibrils: - each myofibre contain plenty of myofibrils which are thread-like structures present in bundles - They are contractile (organelles), Numerous, parallel & organized longitudinal to each other and to long axis of the ms fibre. Each myofibril shows alternate dark and light bands. The corresponding bands of the adjacent myofibrils are arranged at the same level, causing the transverse striations of the muscle fibres.   Myofilaments The myofibrilis made of myofilaments: 1)-Thick (myosin)------forming the (A) band of sarcomere 2)- Thin (actin)-----forming the (I) band, They extend from the Z line and other end is free and proceeding inbetween and interdiditating with myosin filament. The (A) band is dark because it contains both myosin and actin except its paler H-zone (formed of myoin filament). The (I) band are light because they have only one type of myofilaments (actin).  The TRIAD or the tubular system ByE.M, the sarcolemma sends transverse invaginations into the sarcoplasm, the T-tubules. They form collars around the myofibrils at the level of the junctions between the A and I bands. On the other hand, the sarcoplasmic reticulum forms transverse wider cisternae on either surface of the T-tubule. The 2 cisternae of the sarcomplasmic reticulum and the T-tubule in- between form the triad tubular system, which plays an important role during muscle contraction. The TRIAD SYSTEM Regeneration of sk ms Sk ms can not divide. After trauma or any disease, satellite cells stimulate to divide and differentiate into myoblast-----then multiple myoblast are fused together tor form new sk ms fibres large ms defect are filled by fibrous tissue scars.  Differences between the three types of muscle. Skeletal muscle Cardiac muscle Smooth muscle Intercalated discs Absent Present Absent Unit of contraction Regular Irregular sarcomeres No sarcomeres sarcomeres Tubular system Triad system Diad system No tubular system Regeneration Satellite cells Cannot regenerate By mitosis Modification Muscle spindle Purkinje fibers ------------ Origin Myoblast Myoblast Undifferetiated mesenchymal cells  Skeletal ms Cardiac ms Smooth ms Nervous tissue CNS: brain & spinalcord. -PNS: nerve fibres, ganglia & nerve endings. The nervous tissue →ectodermal in origin -Two cell types: *Neurons → functioning cells *Glial cells →supporting tissue  NEURONS General apperance:  branching cell,with variable shape &size  Compsed of cell body (perikaryon) and (processes).  Neuronal cell processes (2 types): a) axon b)dendrites Classification of Neurons: According to number of processes, it classifid into: 1- Unipolar: only in embryo. 2- Pseudo-Unipolar: single process → T shape. 3- Bipolar: 1 dendrite & 1 axon. 4- Multipolar: Many dendrites & 1 axon. a- Stellate b- Pyramidal c- Pyriform Structure of neurons: 1- Perikaryon (cell body): -Nucleus: large rounded central Vesicular (open face) nucleus with prominent nucleolus. -Cytoplasm: Mild basophilic & containg : Nissl bodies LM → basophilic granules → in cell body & dendrites but Not in axon or in axon hillock EM → rER & polyribosomes (EM).  Golgi → around the nucleus. Mitochondria: large amount Centrosome → absent (no division).  Intermediatfilaments → Bundled together forming neurofibrils → structural support → stained by Ag. → in cell body, dendrite & axons. Microtubules → in cell body, dendrite & axon. → for intracellular transport. Inclusions: → Lipofuscin pigments (↑ with age). → Melanin (eg. In nerve cell of substatia nigra). → Lipid droplets & glycogen.  Nerve cell Processes Dendrites Axon Usually numerous Single Short & tapering Thin & long cylinder Branching from the start Not branching except at the like a tree. end giving “terminal arborisations. beaded irregular diameter Has a uniform diameter although it arises by wide base (axon hillock) Contain Nissl granules No Nissl granules but &neurofibrils neurofibrils is present Carry nerve impulses to the Carries nerve impulses away cell body (centripetal. from the cell body(centrifugal.  Peripheral nervous system The nerve trunk is formed of bundles of peripheral nerve fibres (myelinated with neurolemma). 1- Epineurium →dense c.t surrounding whole nerve trunk. 2- Perineurium → dense c.t surrounding each bundle. 3- Endoneurium →loose c.t in between axons.  Nerve fiber in PNS: ► It is the axon (axolemma & axoplasm), arising at axon hillock. Types of nerve fibres: 1- Myelinated with myelin sheath and neurilemma: *In peripheral nerves (nerve trunk) 2- Unmyelinated With neurolemmal sheath: Surrounded by cell body of schwann cell * In autonomic nervous system 3- Naked: * Uncovered by sheath, present in the nerve endings (terminal part of the peripheral nerve).  Schwann cells -Forming the neurolemmal sheath → like sleeve around myelin. -Flat cells with flat nuclei & few organelles. Functions: -Essential for function of axon. -Formation of myelin. -Electric insulation. -Regeneration of axons.  Myelin Sheath ► Lipoprotein (layers of plasmalemma) → osmic acid (black). *In CNS → by oligodendroglia (many axons) *In PNS → by Schwann cell (one axon). ► Divided into segments (internodal segments) → by nodes of Ranvier  Schwann cell Unmyelinated axon with neurolemma in PNS oligodendroglia Myelinated axon with neurolemma in PNS Myelinated axon in CNS Functions of myelin sheath: -↑speed of nerve impulse. -Assuring continuity of conduction. -Nutrition of axon.  Ganglia Definition: Course of nerve fibres surrounded by c.t capsule. 2 Types:cells bodies and glial cells outside CNS aloCollection of nerve ng the Sensory (Spinal G.) Autonomic (Sympathetic or parasymp G.) NERVE CELL Pseudo-unipolar cells (rounded) Stellate multipolar(irreg ) Glomeruli No glomeruli Cells are variable in size Uniform Large & small cells Small ↑ satellite cells Few Cells in groups or rows Scattered Myelinated nerve fibres Unmyelinated fibres No synapse Synapse is present  Spinal G. Sympathetic G. The nerve fibres Thick & myelinated Thin &non myelinated The capsule Thick C.T. capsule & poorly vascular Thin & vascular synapses No synapse (the pre & post-ganglionic Synapse is present fibres are the same Spinal Sympathetic Blood  Blood Blood is a viscous fluid, formed of: Blood Plasma (55%) and blood cells (45%). Types of blood cells and their average number in the human body: 1. Red blood corpuscles or RBCs or Erythrocytes: about 4.5 to 5.5 million per cubic millimeter. 2. White blood cells or leucocytes: about 4000 to 11,000 per cubic millimeter. 3. Blood platelets or thrombocytes: about 150,000 to 400,000 per cubic millimeter. Red Blood Corpuscles = RBCs Number of RBCs In males: The number varies from 5 to 5.5 million per cubic millimeter. In females: The number varies from 4.5-5 millions per cubic millimeter. The number is less in females due to loss of blood during menstruation. Abnormalities in the number of RBCs: Decrease in the number of RBCs is known as Anaemia. Anaemia: It is either A- a decrease in the number of RBCs B- or due to a decrease in haemogolobin content of RBCs. Polycythaemia or increase in the number of RBCs above 6 million as in 1) hypoxia 2) in low oxygen tension as in high altitude, also in heart and lung disease. Shape of RBCs They are rounded, non-nucleated biconcave discs. In slow blood stream and in blood films, RBCs adhere together due to their surface tension showing a rouleaux appearance. Diameters of RBCs Normal diameter of an RBC is 7.5 microns and the normal thickness is 1.9 microns at the periphery and 1.1 microns at the center of RBC. Abnormalities in the diameters of RBCs 1. In macrocytic anaemias: there is increase in the diameters of RBCs. 2. In microcytic anaemias: there is a decrease in the diameters of RBCs. Structure of RBCs 1- RBCs are acidophilic in staining because their Hb is a basic protein. 2- RBCs have no nuclei and no organelles except their cell membranes. 3- RBCs have on their surfaces the antigens of blood groups and of Rh factor. 4- RBCs contain haemoglobin  Color of RBCs When the Hb% is normal, the red blood corpuscles are called Normochromic. Abnormal color of RBCs 1.RBCs with less Hb% than normal are pale are called hypochromic. 2. RBCs with more Hb% than normal are called hyperchromic Contents of RBCs They are not true cells; they have neither nuclei nor organoids. The RBCs are filled with haemogolobin (Hb).  Life span of RBCs RBCs can live for about 4 months. Old RBCs are destroyed by the phagocytic cells in the liver, spleen and bone marrow. Adaptation of the structure of RBCs in order to perform their functions 1. The cell membrane of RBCs is plastic. It allows RBCs to change their shape. RBCs are in the form of corpuscles with rounded edges which facilitate their passage inside narrow blood capillaries. 2. The biconcave surfaces of RBCs increase their surface areas, through these surfaces; gaseous exchange (O2 + CO2) takes place. 3. There are neither nuclei nor cell organoids in RBCs. Their absence also allows free space for haemoglobin. Blood Leucocytes  Leucocytes They are called also white blood cells. General characteristics of Leucocytes 1-They are true nucleated cells. 2- spherical cells 3-the cytoplasm is mild basophilic 4- They are 5 types of leucocytes: Neutrophil, Eosinophil, Basophil, Lymphocyte and Monocyte. N.B: the nucleus is of variable shape &size according to the type of WBC.  Number of leucocytes They vary in number from 4000 to 11,000 per cubic millimeter. Leucocytosis It is the increase in number of leucocytes above 12,000 per cubic millimeter Leucocytosis occur in: some infectious dis and serious bl disease as leukemia (up to 100,000cmm). Leucopenia: It is the decrease in number of leucocytes below 4,000 per cubic millimeter. This may occur afterexposure to X-ray or after taking certain antibiotics.  Types of Leucocytes According to the presence or absence of granules seen by LM in this cytoplasm, leucocyte are classified into: Granular leucocytes 1- Neutrophils 2- Eosinophils 3- Basophils Non-granular leucocytes 1- Lymphocytes 2- Monocytes  Granular Leucocytes 1. Neutrophils (50 – 70%) 1-They are called Polymorpho-nuclear leucocytes 2-Their diameter varies from 10 to 12 micron. 3-The nucleus is single but segmented, it is formed of 2 to 5 segments connected with each other by chromatin threads = polymorpho-nuclear. 4- Neutrophils have an amoeboid movement, they can form pseudopodia in order to engulf micro- organisms. The E/M of neutrophils shows few mitochondria, endoplasmic reticulum, glycogen granules  Two types of granules are present in Neutrophils: a. Azurophilic Granules: which are few in number and large in size. They are considered as lysosomes because they are very rich in hydrolytic enzymes. b. Specific granules: which are numerous and small in size. They contain: 1- collagenase enzyme, 3- lactoferrin enzymes which kill bacteria.  Functions of neutrophils 1. They are phagocytic to micro-organisms. 2. They secrete proteolytic enzymes to dissolve protein around bacteria. 3. They secrete trephone substances which help in healing of wounds. 4. Neutrophils help blood monocytes to migrate to the inflamed areas. 5. During acute infections and in fever conditions, neutrophils stimulate bone barrow to develop more leucocytes. 6. Neutrophils secrete pyrogens which can elevate body temperature. Neutrophilia Neutrophilia = increased number of neutrophils. This occurs in acute infections which may produce pus (Pyogenic infection) as in tonsillitis, appendicitis and in any abscess formation. Neutropenia Neutropenia or Neutrophil leucopenia: It is the decrease in the number of neutrophils. It occurs in typhoid fever, T.B. Influenza  2. Eosinophil leucocytes (1 to 4%) 1- Their diameter varies from 10-14 microns. 2- The nucleus is bilobed and is called horse shoe-shaped nucleus.  3- By the electron microscope, the cytoplasm contains Few cell organoids. 4- The cytoplasm is rich in (specific granules)They contain the following enzymes:Histaminase enzyme: to destroy histamine substance.Sulphatase enzyme:to destroy sulphate substances which are secreted by mast cells. 5- Also it shows few (Azurophil) granules)  Functions of Eosinophils 1. They can destroy parasites through excretion of cytotoxic proteins. 2. Eosinophils can destroy allergic substances as histamine and heparin which are secreted by mast cells and by basophil leucocytes. 3. Eosinophils can phagocytose the antigen- antibody complex in allergic conditions. Life span of eosinophils: is about 8 hours in the circulating blood. Eosinophil can live about 8 days in the connective tissue. Eosinophilia = increase in the percentage of Eosinophils which occurs in: 1- Allergic diseases: as urticaria, eczema, and bronchial asthma 2. Parasitic diseases: as ascaris, Bilharzia and ankylostoma infestation. Eosinopenia = decrease in number of eosinophils  3. Basophil leucocytes (0 to 1%) Their diameter varies from 10-12microns. E/M of basophils: 1- They have few cell organoids and inclusions. 2- They are rich in (specific) granules that contain heparin, histamine and few azurophil granules. 3- They have twisted S-shaped nuclei.  Functions of basophils: 1. Production of histamineand heparin. 2. They play a role in allergic and parasitic diseases. Life span: from 10-15 days. Basophilia = An increase in the percentage of basophils. Occurs in: - Liver cirrhosis - small pox and - in allergic and parasitic diseases.  Non-Granular Leucocytes Lymphocytes Their percentage varies from 20% - 40% of the total number of blood leucocytes. According to the diameter of lymphocytes, they are classified into 1- small (7- 8 microns) Lymphocytes Represent 90% of blood lymphocytes 2- medium-sized (12microns) Lymphocytes - Represent 10% of blood lymphocytes Lymphocytes are highly mobile cells, they are present in blood, lymph and lymphatic tissues as spleen, lymph nodes and tonsils. Small Lymphocytes (90%) They represent about 90% of the circulating lymphocytes. Each lymphocyte is about 8 microns in diameter. The cytoplasm is scanty and it contains few organelles and many ribosomes. The nucleus is small, darkly stained and filling the whole cytoplasm. There are 3 types of small lymphocytes: a. T-lymphocytes (70%) b. B-lymphocytes (25%) c. Null-lymphocytes (5%)  Small T and B lymphocytes Their cytoplasm shows many free ribosomes, few endoplasmic reticulum and a pair of centroiles. Null-lymphocytes (5%): They develop in bone marrow, they have no surface markers, they are Natural killer cells to foreign and to viral infected cell. Classification of small lymphocytes According to the origin and function: The T-Lymphocytes (70%) They are termed as T-lymphocytes because they are thymus dependent lymphocytes. They differentiate in the Thymus. During childhood they require the presence of the thymus gland for their development They contain surface receptors for antigens. They have a long life span, they can live for years. Types and Functions of T- lymphocytes 1- T-killer cells (Natural killer cells) T- lymphocytes are responsible for cellular immunity. (Cell mediated immunity) Any foreign body or bacteria entering our body act as antigen. T-lymphocytes will come in contact with antigens and can destroy these antigens, this means that the T-lymphocytes can kill directly foreign cells and bacteria. 2- T-memory cells If foreign bodies (antigen) enter the body, they activate the newly formed T- lymphocytes which are then called T-memory cells. These memory cells in the future can defend the body against the same antigen if it enters the body again 3. Helper cells T-lymphocytes are considered as helper cells to B-lymphocytes. They can help B- lymphocytes to perform their immune response against foreign bodies. 4. T-suppressor cells: which suppress (stop) the immune reaction of B-lymphocytes against body antigens preventing autoimmune diseases. The B-lymphocytes (25%) They are derived from the stem cells of thebone marrow in animals. They are rich in surface immunoglobulin receptors. They have short life span (about 3months) Functions of B-lymphocytes 1. B-lymphocytes are responsible for the development of humoral immunity, as follows: If any antigen enters the body, it is first picked up by the T-lymphocytes which act as helper cells for B- lymphocytes. The antigen is then delivered from T-lymphocytes to activate B-lymphocytes. These activated B-lymphocytes are proliferated in order to form the following 2 types of cells a. Plasma cells which secrete immune bodies directly in the blood (Anti-bodies) forming Humoral immunity. This process is called primary immune response. b. B-memory cells which produce secondary immune response when they are exposed once again in the future to the same types of antigens. Lymphocytosis Increase in the percentage of lymphocytes in the circulating blood above 50% is called lymphocytosis. Causes of Lymphocytosis 1- Lymphocytosis occurs normally in children. Lymphocytosis occurs 2- in chronic diseases as in: - Whooping cough, - T.B. (Tuberculosis), - syphilis  Monocytes (3-8%) Their diameter varies from 14 to 18 microns. Their cytoplasm is non-granular and is not clear. (Frosted glass appearance) The cytoplasm is rich in many Lysosomes (Azurophil Granules), ribosomes and mitochondria. Mobility: they can penetrate the capillaries by their pseudopodia to go to C.T. Nucleus: The nucleus is pale, large, kidney shaped  Function of Monocytes: 1.They are highly phagocytic cells in the connective tissue. 2.They can be transformed into macrophage cells all over the body tissues and organs Life span: It is about 3 days in the blood and 3 months in the tissues. Monocytosis = increase number of monocytes as in Lymphomas, Leukaemia, and in chronic infections as in malaria, T.B., syphilis and glandular fever. Blood Platelets Shape: Blood platelets are not cells, they are small oval non nucleated bodies similar to plates, and are found in mammals. Number: of blood platelets varies from 150,000 to 400,000 per cubic millimeter. The average number = ¼ million per cubic millimeter. Diameter: Each has 2-5 microns and have no nuclei Life span of blood platelets is from 7 to 10 days. Functions of blood platelets Haemostasis (stop bleeding) They are important for blood clotting by 1- agglutination of blood. 2- Blood platelets release serotonin which is a vasoconstrictor substance to B.V. Purpura: It is a congenital disease which results from a decrease in the number of blood platelets. The bleeding time is prolonged in this disease.