Histology 1 (PTBA 1103) 2023/2024 Horus University PDF

Horus University in Egypt Faculty of Physical Therapy Department of Basic Science HISTOLOGY 1 PTBA 1103 Frist Edition 2023/2024 Level 1/Semester 1 2024/2025  Vision The Faculty of Physical Therapy at Horus University strives to be a local and r...

Horus University in Egypt Faculty of Physical Therapy Department of Basic Science HISTOLOGY 1 PTBA 1103 Frist Edition 2023/2024 Level 1/Semester 1 2024/2025  Vision The Faculty of Physical Therapy at Horus University strives to be a local and regional competitor in educational programs, distinguished by scientific research that supports sustainable development and community service. Mission The aim of the faculty of Physical Therapy at Horus University is to prepare competent graduates in the field of physical therapy, capable of providing high quality competitive healthcare through the provision of an excellent academic environment and advanced educational programs that encourage self-learning, continuous learning, and systematic scientific research; thereby contributing to development and solving societal problems. Strategic goals 1. Improving institutional performance efficiency to ensure quality performance. 2. Achieving excellence in the educational program and enhancing graduate competitiveness. 3. Enhancing the scientific research system and supporting excellence and innovation. 4. Providing exceptional community services and contributing to environmental development for sustainable development. 5. Qualifying the faculty for accreditation according to the standards of the National Authority for Quality Assurance and Accreditation in Education 1  Contents Subject Page  Introduction 1  Body Tissues 8  Epithelium 9 - Covering epithelium…………………………. 10 - Glandular epithelium……………..………….. 16 - Neuroepithelium……………..………………. 20  Connective tissue 23 - Connective tissue fibers……………………... 23 - Connective tissue cells………………………. 25 - Connective tissue matrix…………………….. 29 - Types of connective tissue proper…………… 30  Cartilage 35 - Hyaline cartilage…………………………….. 35 - Yellow elastic fibro-cartilage………………... 37 - White fibro-cartilage………………………… 38  Bone 40 - Compact bone………………………………... 43 - Cancellous bone……………………………... 44 - Ossification…………………………………... 46  Muscle tissue 53 - Skeletal muscle fibers……………….……….. 53 - Cardiac muscle fibers…………………….….. 59 - Smooth muscle fibers………………………... 60  Nervous tissue 65 - Neuron……………………………………….. 65 - Nerve trunk…………………………………... 71 - Degeneration and regeneration of nerve fibers. 72 - Ganglia………………………………………. 75 2  Chapter 1: CELL STRUCTURE INTRODUCTION To study Histology, we have to answer three important questions: What is Histology? It is the science which deals with the microscopic structure of the cell (structural and functional unit of the body), different body tissues, organs and systems. It also correlates structural and functional relationship. Why do we study Histology? We study Histology to get knowledge about:  The structure and the behavior of the structural unit of the body (cell) Cell Biology  How the cells are organized together to form tissues (organized cells) General Histology  How the tissues are organized together to form organs (organized tissues) Special Histology Cells → Tissues → Organs → Systems → Body How do we study Histology? MICROTECHNIQUES They are steps by which we prepare a stained sample for examination. Sectioning Staining Obtaining a tissue section formed of Staining the section to make contrast monolayer of cells from the sample as tissues are colourless -1-  Chapter 1: CELL STRUCTURE I- SECTIONING  In order to obtain monolayer from a sample, it has to be hard enough to be cut into very thin sections. To make the sample hard we either:  Infiltrate the sample with a substance having liquid and solid phases (Paraffin technique) or  Freeze the sample rapidly (Freeing technique). A- Paraffin technique Advantages of paraffin sections: 1- Very thin sections (5-10 μm). 2- Serial sections. Disadvantages of paraffin sections: 1- Not suitable for studying lipids as used xylene dissolves lipids. 2- Not suitable for histochemical studies as heat destroys enzymes. B- The Freezing technique Advantages of Freezing Technique: 1- Very rapid method as the specimens are rapidly frozen and sectioned in cryostat, so it is used for rapid diagnosis. 2- Lipids and enzymes in the tissues are preserved. Disadvantages of Freezing Technique: 1- Thick sections. 2- Doesn’t give serial sections. -2-  Chapter 1: CELL STRUCTURE II- STAINING  Some cells in the body are coloured without being stained like RBCs and melanocytes in the skin. All other cells are colourless and have to be stained to make a contrast for examination by the microscope.  To stain the section, a reaction has to occur between the stain and the intracellular components.  The routine staining method is done by hematoxylin and eosin.  Stains which identifies specific components are termed specific stains. A- Hematoxylin and Eosin staining Hematoxylin and eosin staining is done in two steps starting with hematoxylin followed by eosin. It is considered as the routine staining method. Hematoxylin Eosin Basic (carry +ve charges) Acidic (carry -ve charges) Gives blue colour Gives pink colour Reacts with acidic strctures inside Reacts with basic strctures inside the cell (basophilic structures). the cell (acidophilic structures). -3-  Chapter 1: CELL STRUCTURE B- Other methods of staining (specific stains)  Carbohydrates: Periodic acid Schiff’s reaction (PAS) Magenta colour.  Glycogen: PAS reaction Magenta colour & Best's carmine red colour.  Lipids: Sudan III orange colour. Sudan black black colour. Osmic acid black colour. 7- EM stains Staining of ultrathin sections to produce contrast by reflection or passage of electrons through the sample to study the fine structures of cells:  Dark areas electron dense.  Light areas electron lucent. -4-  Chapter 1: CELL STRUCTURE MICROSCOPY A- Ordinary Light Microscope 1. Objective lenses: near the object, on a revolving nosepiece with different magnification powers 4X, 10X, 20X, 25X, 40X and 100X (oil-immersion lens). N.B.: When oil-immersion lens is used it has to be immersed in a drop of Cedar oil put on the slide glass cover overlying the object to be examined. This will replace the air gap between the lens and the glass cover. 2. Eye piece: near the eye, with different magnification powers 5X, 10X and 15X.  The magnification of LM is the product of magnification power of objective lens by the magnification power of eye piece. -5-  Chapter 1: CELL STRUCTURE B- Electron Microscope  The magnification of EM is up to 200000.  There are 2 types of electron microscopes: 1. Transmission Electron Microscope (TEM): for detection of intracellular details e.g., organelles and inclusions. 2. Scanning Electron Microscope (SEM): for examination of a whole fixed sample coated with gold chloride to study surface features e.g., microvilli & receptors. -6-  Chapter 1: CELL STRUCTURE QUESTIONS A. Choose the correct answer: 1. Ultrathin sections are: a. 50 - 100 nm sections. b. 5 - 10 µm sections. c. 50 - 100 µm sections. d. 5 - 10 nm sections. 2. Special stain for lipids: a. Hematoxylin. b. Histochemical techniques. c. Silver. d. Osmic acid. B. Complete: 1. ……………………………… technique gives serial sections. 2. Acidophilic structures are stained by ……………………………… stain. 3. Carbohydrates can be stained by ………………………………………… stain. C. Mention: 1. One advantage of freezing technique ( ……….…….………… ) 2. A specific stain for carbohydrates ( ……….…….………… ) -7-  Chapter 2: EPITHELIUM THE BODY TISSUES How body tissues are formed?  One sperm fertilizes an ovum single undifferentiated cell termed zygote.  Zygote undergoes successive mitotic divisions morula blastocyst having an inner cell mass (blastomere) and outer trophoblast.  The undifferentiated blastomere undergoes proliferation and differentiation to give rise to the differentiated cells of:  Ectoderm (skin & nervous tissue).  Mesoderm (muscle, connective tissue, bone, cartilage & blood).  Endoderm (respiratory & gastrointestinal systems).  Genito-urinary ridge (genital & urinary systems). -8-  Chapter 2: EPITHELIUM  The human body is composed of four basic tissues; each of them has its own structure and function. These tissues are: 1) Epithelial tissue: covers the body and lines its cavities from inside. 2) Connective tissue: connects, mainly, other tissues together. 3) Muscular tissue: responsible for movement. 4) Nervous tissue: responsible for transmission of nervous impulse. EPITHELIUM Epithelium is one of the four basic tissues of the human body responsible for covering it from outside and lining its cavities from inside. General characters:  It is formed of closely aggregated cells with little intercellular substance.  The epithelial cells rest on and are tightly adherent to a thin membrane (basement membrane) which separates them from the underlying connective tissue.  No blood vessels enter between the cells but nerves ramify between them.  Epithelium is subjected to continuous degeneration and regeneration. -9-  Chapter 2: EPITHELIUM Classification: Epithelium is classified according to its function into: 1) Covering Epithelium: covers the body and lines its cavities. 2) Glandular epithelium: specialized in production of secretions. 3) Neuroepithelium: specialized in perception of sensory stimuli. (I) Covering Epithelium  It is one type of the epithelial tissue which covers the body surface from outside and lines its cavities from inside.  It can be classified according to the number of cell layers into: Simple Stratified  Formed of one layer of cells lying  Formed of many layers of cells, the on the basement membrane. first lie on the basement membrane. Simple Epithelium (1) Simple squamous epithelium  Formed of one layer of flat cells (like squams) with flat bulging nuclei.  Is found in the lining of the:  Blood vessels and heart.  Lung alveoli.  Small ducts of exocrine glands. (2) Simple cubical epithelium  Formed of a single layer of cubical shaped cells with central rounded nuclei.  It is found in the lining of the:  Renal tubules.  Medium sized ducts of exocrine glands. - 10 -  Chapter 2: EPITHELIUM (3) Simple columnar epithelium  Formed of a single layer of tall cells (like columns) with basal oval nuclei.  This type can be further sub-classified into: A- Non-modified simple columnar epithelium: The columnar cells aren’t modified e.g. lining of large ducts of exocrine glands. B- Modified simple columnar epithelium: The columnar cells acquire some modifications to perform additional functions. Simple columnar secretory epithelium:  Specialized in production of mucous secretion.  The cytoplasm is vacuolated due to dissolution of mucin granules.  Example → lining of the stomach. Simple columnar absorptive epithelium:  Specialized in absorption of soluble molecules at the cell surface.  The apical surface of the columnar cells is provided with microvilli (brush border by L/M) to increase its surface area.  Example → lining of the intestine. - 11 -  Chapter 2: EPITHELIUM Simple columnar ciliated epithelium:  Cilia project from the free surface of the cells.  Example lining of the fallopian tube and uterus. (4) Pseudostratified columnar epithelium  Formed of a single layer of cells which were crowded during development.  As a result of crowding, some cells became short and squeezed between the bases of the tall ones.  The nuclei appeared to be arranged in more than one level, so there is a false appearance for this epithelium to be stratified.  This type of epithelium can be sub-classified into: Pseudostratified columnar non-ciliated epithelium: The surface of the tall columnar cells is not provided with cilia e.g.:  Lining of large ducts of exocrine glands. Pseudostratified columnar ciliated epithelium: The surface of the tall cells is provided with cilia e.g.:  Lining of the nasal sinuses.  Lining of the trachea, bronchi. N.B: Some of the columnar cells in this type may be modified into mucous secreting cells shaped like goblets (goblet cells) pseudostratified columnar ciliated epithelium with goblet cells. - 12 -  Chapter 2: EPITHELIUM Stratified Epithelium (1) Stratified squamous epithelium  This type is formed of about 30 layers of cells.  The cells are arranged as follows: Basal layer  Formed of columnar cells with basal oval nuclei.  The cells are tightly adherent to a wavy basement membrane.  Responsible for regeneration of the other cell layers. Middle layers  From the main thickness of the epithelium.  Formed of polyhedral cells with central rounded nuclei.  The cells are tightly adherent to each other. Top layer  Formed of squamous cells. - 13 -  Chapter 2: EPITHELIUM  Stratified squamous epithelium can be sub-classified into: Stratified squamous keratinized epithelium  The top layer of cells is covered by layers of horny scales (dried cells filled with keratin)  It covers the dry body surface i.e. epidermis of skin. Stratified squamous non-keratinized epithelium  The top layer is not covered by horny scales.  Lines the wet surface of all body openings which lead to skin: - Mouth cavity. - External auditory canal. - Oesophagus. - Ear drum. (2) Transitional epithelium  A type of stratified epithelium formed of about 6-8 layers of cells.  The cells lie on a thin, ill-defined straight basement membrane (to allow their sliding).  The cells are arranged as follows: Basal layer: formed of low columnar cells with basal oval nuclei. Middle layers: formed of polyhedral cells with rounded nuclei. Superficial two layers:  The top layer: formed of large cubical (cuboidal) cells with convex surface and concave base. These cells may be binucleated and are covered by a protective mucous like substance.  The underlying layer: formed of flask shaped cells lying in the concavity of the top ones. - 14 -  Chapter 2: EPITHELIUM  Transitional epithelium lines the:  Pelvis of kidney.  Urinary bladder.  Ureter.  Prostatic urethra.  Transitional epithelium is present in two forms: When the bladder is empty: it has its full thickness as described above. When the bladder is full: gliding the cells over each other takes place and the epithelium become formed of two cell layers:  Basal cubical cells.  Top flat cells. Empty bladder Full bladder - 15 -  Chapter 2: EPITHELIUM (II) Glandular Epithelium Glandular epithelium is a modified type of epithelial tissue specialized in production of secretions. Formation of glands:  The epithelial cells of the covering epithelium proliferate and penetrate the underlying connective tissue.  When these cells remain connected to the surface epithelium → an exocrine gland is formed. The cord of cells which connects the gland with the surface forms the duct.  When the cells lose their connection which the surface → an endocrine gland is formed. - 16 -  Chapter 2: EPITHELIUM Classifications of Glandular Epithelium I. According to presence or absence of duct: A. Exocrine glands: possess ducts e.g. salivary glands. B. Endocrine glands: have no ducts e.g. thyroid, pituitary and adrenal glands. C. Mixed glands: have the two types e.g. pancreas and liver. II. According to duct and secretory part: A. Simple glands: characterized by having:  Single unbranched duct.  Single unbranched secretory part. 1) Simple tubular glands Have tubular secretory parts. 2) Simple alveolar glands Have alveolar secretory parts. 3) Simple tubulo-alveolar glands Have tubulo–alveolar secretory part. B. Simple branched glands: characterized by having:  Single unbranched duct.  Branched secretory units. 1) Simple branched tubular glands Have tubular secretory units. 2) Simple branched alveolar glands Have alveolar secretory units. 3) Simple branched tubulo–alveolar glands Have tubulo–alveolar secretory units. - 17 -  Chapter 2: EPITHELIUM C. Compound branched glands: characterized by having:  Branched duct system.  Branched secretory units. 1) Compound branched tubular glands: Have tubular secretory units. 2) Compound branched alveolar glands: Have alveolar secretory units. 3) Compound branched tubulo-alveolar glands: Have tubulo-alveolar secretory units. III. According to secretion: A. Nature of secretion: 1) Mucous glands: produce viscid mucous poor in enzymes e.g. goblet cells and minor salivary glands. 2) Serous glands: produce watery solution rich in enzymes e.g. parotid glands and pancreas. 3) Mucoserous glands: produce both types of secretions e.g. submandibular and sublingual glands. - 18 -  Chapter 2: EPITHELIUM 4) Sweat glands: of skin produce watery secretion containing some enzymes and waste products. 5) Oily glands: secrete fatty secretion e.g. sebaceous and tarsal glands. 6) Waxy glands: secret waxy secretion e.g. ceruminous glands of the external canal. B. Method (mode) of secretion: 1) Merocrine glands: the secretory cells are not destroyed during secretion e.g. salivary glands. 2) Apocrine glands: the apical part of the cells is destroyed during secretion e.g. mammary glands. 3) Holocrine glands: the whole cell is destroyed during secretion e.g. sebaceous glands. MEROCRINE APOCRINE HOLOCRINE - 19 -  Chapter 2: EPITHELIUM (III) Neuroepithelium Definition: A modified type of epithelial tissue specialized in perception of sensory stimuli. Structure: The epithelial cells are modified to form a neuroepithelial structure formed of: A. Sensory cells:  Tall cells with hairlets on their free borders.  Their cytoplasm contains vesicles of chemical transmitters.  Their bases are surrounded by free sensory nerve endings. B. Supporting cells:  Tall cells which support the sensory ones. C. Basal cells:  Small pyramidal cells lying on the basement membrane between the bases of the tall cells.  Regenerate the above types. Sites: 1) Taste buds (tongue) 2) Olfactory epithelium (roof of the nose) - 20 -  Chapter 2: EPITHELIUM QUESTIONS A. Choose the correct answer: 1. Epithelium is characterized by: a. Rest on cell membrane which separates it from the underlying connective tissue. b. Blood vessels enter between the cells but nerves do not. c. Has little intercellular substance. d. Not subjected to regeneration. 2. Simple cubical epithelium is characterized by: a. Has no basement membrane. b. Lines trachea. c. Lines medium sized ducts of glands. d. Formed of one layer of flat cells with flat bulging nuclei. 3. Fallopian tubes are lined by: a. Pseudostratified columnar ciliated epithelium. b. Simple cubical epithelium. c. Simple columnar ciliated epithelium. d. Simple squamous epithelium. 4. Simple columnar secretory epithelium: a. Provided with cilia. b. Lines stomach. c. Nuclei arranged at more than one level. d. Covered with keratin. 5. Stratified squamous epithelium: a. Formed of 30 layers. b. Lines trachea. c. The top layer is columnar. d. The middle cells are squamous. - 21 -  Chapter 2: EPITHELIUM 6. Type of epithelium that changes its cellular arrangement on distension: a. Transitional. b. Simple squamous. c. Stratified squamous keratinized. d. Stratified squamous non-keratinized. 7. Simple branched tubular glands: a. Are endocrine gland. b. Have branched ducts. c. Have branched secretory portions. d. Are present in liver. 8. Neuroepithelium: a. Its sensory cells show free nerve endings at its lower border. b. Is found in the lining of external auditory canal. c. Its basal cells are supportive cells. d. Is specialized in production of secretions. B. Write true (√) or false (X): 1. Lung alveoli are lined by simple squamous epithelium ( ) 2. Esophagus is lined by transitional epithelium ( ) 3. Glandular epithelium is specialized in production of secretions. ( ) 4. Compound gland has unbranched duct. ( ) - 22 -  Chapter 3: CONNECTIVE TISSUE CONNECTIVE TISSUE General characters:  The connective tissue (C.T.) supports and connects various tissues and organs.  Consists of cells, fibers and intercellular substance (matrix).  It is rich in blood vessels and nerves. Types: 1) Connective tissue proper (soft). 3) Bone (hard). 2) Cartilage (rigid). 4) Blood (fluid). CONNECTIVE TISSUE PROPER A- Connective Tissue Fibers There are three types of C.T. fibers, each has its own structure, characters & distribution 1- White Collagenous Fibers Characters:  Formed of collagen.  Strong & resist stretch.  White in fresh state.  Form wavy bundles.  Bundles branch, but single fiber doesn’t branch.  Digested by pepsin and collagenase enzyme.  Converted into gelatin by boiling. - 23 -  Chapter 3: CONNECTIVE TISSUE LM: H&E: acidophilic. Van Gieson's stain: red. Mallory trichrome: blue. Types & sites: Type I: in white fibrocartilage and bone. Type II: in hyaline cartilage & elastic fibrocartilage. Type III: reticular fibers. 2- Yellow Elastic Fibers Characters:  Elastic in nature.  Yellow in fresh state.  Thin, long and highly refractile.  Fibers branch and may form elastic membranes (wall of the aorta).  Digested by elastase enzyme.  Not affected by boiling. LM: H&E: acidophilic. Van Gieson's stain: yellow. Ver-Hoff's stain: black. Sites: 1. Walls of arteries. 2. Trachea. 3. Ligaments of the back. - 24 -  Chapter 3: CONNECTIVE TISSUE 3- Reticular Fibers Characters:  Very thin.  Branch and anastomose to form network. LM: H&E: not stained Silver: black. Sites: stroma of organs e.g. Liver, spleen & lymph nodes. B- Connective Tissue Cells There are eight types of C.T. cells: I. Rounded or oval cells: 1. Fat cells (adipocytes). 3. Mast cells. 2. Plasma cells. 4. Blood leucocytes. II. Branched cells: 5. Fibroblasts. 7. Pigment cells. 6. Macrophages. 8. Undifferentiated mesenchymal cells (UMCs). 1- Fat cells (adipocytes) Origin: U.M.Cs. Site: adipose and loose C.T. LM: Shape: oval. Nucleus: flattened & peripheral. Cytoplasm: large fat globule pushing the nucleus at one side. - 25 -  Chapter 3: CONNECTIVE TISSUE Stain: H&E: signet ring. Sudan black: black. Sudan III: orange. Osmic acid: black. Functions: 1) Storage of energy. 2) Heat insulation. 2- Plasma cells Origin: activation of B lymphocytes by specific antigen plasmablasts plasma cells. Site: lymphatic organs. LM: Shape: oval. Nucleus: rounded, eccentric & cart-wheel (special arrangement of its chromatin). Cytoplasm: deep basophilic & negative Golgi image. Function: secretion of antibodies (humoral immunity). 3- Mast cells Site: mucosa of the GIT & respiratory tract. LM: Shape: oval. Nucleus: rounded & central. - 26 -  Chapter 3: CONNECTIVE TISSUE Cytoplasm: Large basophilic granules: 1- Protein (histamine). 2- Sulfated glycosaminoglycans (heparin). Stain: Toluidin blue: (metachromatic) purple (sulfated glycosaminoglycans). Functions: 1) Secretion of histamine (allergy). 2) Secretion of heparin (anti-coagulant). 4- Blood leucocytes Blood leucocytes leave the blood and appear in the C.T. in certain conditions, e.g.: 1) Eosinophils: in allergy. 2) Neutrophils: in acute infections. 3) Monocytes & lymphocytes: in chronic infections. 5- Fibroblasts Origin: Pericytes which develop from U.M.Cs. Site:  Most common type of C.T. cells.  Very numerous in the loose C.T. LM: Shape: Branched spindle-shaped. - 27 -  Chapter 3: CONNECTIVE TISSUE Nucleus: oval and eccentric. Cytoplasm: basophilic with negative Golgi image. Functions: 1) Synthesis of nearly all types of C.T. fibers (fiber-forming cells). 2) Synthesis of C.T. matrix. 3) Growth of C.T. and healing of wounds. 6- Macrophages Origin: blood monocytes. LM: Shape: large, branched with pseudopodia. Nucleus: eccentric may be oval or kidney shaped. Cytoplasm: not clear. Stain: trypan blue (vital stain). Functions: 1) Phagocytosis of foreign bodies (bacteria). 2) Fuse to form foreign body giant cell for large foreign body. 3) Secrete collagenase & elastase enzyme. - 28 -  Chapter 3: CONNECTIVE TISSUE 7- Pigment cells They are melanin containing C.T. cells found in skin and eye. 8- Undifferentiated mesenchymal cells (UMCs) Mother cell of all types of C.T. cells. LM: Shape: branched cell. Nucleus: large and oval. Cytoplasm: basophilic. C- Connective Tissue Matrix  Matrix of C.T. proper is a soft material in which cells and fibers lie.  It is formed: 1) Organic (amorphous) component (secreted by fibroblast):  Proteins.  Glycoproteins (protein and monosaccharides).  Proteoglycans (GAGs) (protein and disaccharides). 2) Fluid component (derived from blood): About 60-70% water.  If increased oedema.  If decreased dehydration. - 29 -  Chapter 3: CONNECTIVE TISSUE Types of CT Proper 1 - Loose (ordinary) connective tissue Sites: widely distributed: 1) Around blood vessels. 2) Submucosa of GIT. Structure: Fibers: Collagenous & elastic. Cells: Fibroblasts, fat cells & macrophages. Matrix: Rich in hyaluronic acid. 2 - White fibrous connective tissue Regular Irregular Sites: 1) Cornea 1) Sclera 2) Tendons 2) Perichondrium & periosteum Structure: Fibers: Regular collagenous bundles Irregular Cells: Fibroblasts Stains: Mallory trichrome stain: blue Van Gieson's stain: red - 30 -  Chapter 3: CONNECTIVE TISSUE 3 - Yellow elastic connective tissue Sites: 1) Walls of arteries. 2) Trachea. 3) Ligaments of the back. Structure: Fibers: regular elastic fibers. Cells: fibroblasts. Stains: Ver Hoff's stain: black. Van Gieson's: Yellow. 4 - Mucoid connective tissue Sites: 1) Umbilical cord. 2) Pulp of the teeth. Structure: Cells: young fibroblasts. Matrix: soft, rich in mucin & hyaluronic acid. 5- Reticular connective tissue Sites: stroma of liver, spleen & lymph node. Structure: Fibers: reticular fibers. Cells: reticular cells (modified fibroblast). - 31 -  Chapter 3: CONNECTIVE TISSUE 6 - Adipose connective tissue White adipose C.T. Brown adipose C.T. Colour: White Brown Bl. supply: Less More Sites: Majority of adipose C.T. in adults: In newborn infants 1) Subcutaneous tissue In adults: 2) Perinephric fat 1) Mediastinum 2) Between 2 scapulae Structure: Lobules of fat cells separated by loose C.T. Fat cell: Large Small Fat: Single large fat globule Numerous fat droplets Nucleus: The large fat globule pushes the Central and rounded nucleus to one side signet ring EM: Few cell organelles Numerous mitochondria Functions: 1) Storage of energy (fat) Rapid heat production on 2) Heat insulation exposure to cold - 32 -  Chapter 3: CONNECTIVE TISSUE QUESTIONS A. Choose the correct answer: 1. Fat cells: a. Store lipids. b. Secrete antibodies. c. Secrete heparin. d. Perform phagocytosis. 2. Healing and growth of C.T. is a function of: a. Mast cells. b. Plasma cells. c. Fibroblasts. d. Reticular cells. 3. White collagenous fibers: a. Are stretchable. b. Are stained yellow with Van Gieson's stain. c. Are digested by pepsin. d. Form membranes in wall of arteries. 4. Yellow elastic fibers are stained yellow by: a. Mallory stain. b. Van Gieson’s stain. c. H & E stain. d. Silver stain. 5. Matrix of C.T. proper: a. Contains glycoproteins. b. Is firm in consistency. c. Contains phospholipids. d. Secreted by chondroblasts. - 33 -  Chapter 3: CONNECTIVE TISSUE 6. Plasma cells: a. Originate from pericyte. b. Are present in lymphatic organs. c. Secrete heparin. d. Have deep acidophilic cytoplasm with negative Golgi image. 7. Which cell is derived from blood monocyte? a. Macrophage. b. Fibroblast. c. Mast cell. d. Chondrocyte. 8. Reticular connective tissue: a. Formed of adipocytes. b. Has soft matrix which is rich in mucin. c. Can be stained by Ver Hoff's stain. d. Present in the stroma of spleen. B. Write true (√) or false (X): 1. Yellow elastic fibers form wavy bundles ( ) 2. C.T. proper matrix is rigid. ( ) 3. Mast cells produce histamine. ( ) 4. Brown adipose C.T. has less blood supply than white adipose C.T. ( ) - 34 -  Chapter 4: CARTILAGE CARTILAGE It is a type of C.T. poor in blood supply with firm or rubbery matrix. 1- Hyaline Cartilage Characters:  Rigid with some degree of flexibility (chondroitin sulphate).  Pale blue & translucent. Sites: 1) Long bone of foetal skeleton. 2) Cartilage of respiratory passages. 3) Costal cartilage. 4) Articular cartilage. Structure:  Perichondrium: vascular C.T. membrane which covers cartilage. Structure: 1) Outer fibrous layer: white fibrous C.T. rich in blood vessels. Functions:  Attachment of muscles.  Blood supply and nourishment. 2) Inner chondrogenic layer: contain chondroblasts (flat cells). Functions: They secret matrix, then change into chondrocytes during growth & healing. - 35 -  Chapter 4: CARTILAGE  Chondrocytes: Young Mature Site Under the perichondrium Deep in the cartilage Shape Flat Rounded Nucleus Oval Rounded Cytoplasm Basophilic Pale basophilic Lacunae Singly in flat lacunae Singly or in cell nests (2,4,8) as they can divide Hyaline cartilage  Matrix:  Firm or rubbery in consistency.  Non-vascular & allows diffusion of nourishment and O2 form perichondrium to chondrocytes. Components: 1) Tissue fluid. 2) Collagenous fibers: type II. - 36 -  Chapter 4: CARTILAGE 3) Amorphous substances:  Proteoglycan (chondroitin sulphate).  Protein.  Glycoprotein. Stain: H&E: homogenous basophilic (chondroitin sulfate). 2- Yellow Elastic Fibro-cartilage Characters:  More elastic.  Yellow. Sites: 1) Ear pinna. 2) External auditory canal. Structure:  Perichondrium  Chondrocytes  Matrix: very rich in elastic fibers. Stain: Ver Hoff's stain: black. - 37 -  Chapter 4: CARTILAGE 3- White Fibro-cartilage Characters:  Less elastic.  White. Sites: 1) Intervertebral discs. 3) Semilunar cartilage of knee. 2) Symphysis pubis. Structure:  Matrix: contain parallel bundles of collagenous fibers. Stain: H&E: acidophilic.  No perichondrium (nourishment & O2 from blood vessels of the surrounding collagenous bundles).  Chondrocytes: Rows of chondrocytes (single or in pairs) inside lacunae in between collagenous bundles. - 38 -  Chapter 4: CARTILAGE QUESTIONS A. Choose the correct answer: 1. Cartilage: a. Is rich blood supply. b. Is a type of C.T. proper. c. Has firm matrix. d. Surrounded by periosteum. 2. Chondrocytes receive their nutrition from: a. Lacunae. b. Canaliculi. c. Periosteum. d. Perichondrium. 3. Matrix of hyaline cartilage: a. Is highly vascular. b. Contains collagenous fibers type I. c. Is stained acidophilic. d. Contains chondroitin sulphate. 4. Yellow elastic fibro-cartilage is present in: a. Long bones of foetal skeleton. b. Ear pinna. c. Semilunar cartilage of the knee. d. Shaft of long bones. B. Write true (√) or false (X): 1. Hyaline cartilage is pale blue and translucent. ( ) 2. White fibro-cartilage is present in semilunar cartilage of knee. ( ) - 39 -  Chapter 5: BONE BONE  Calcified osteoid tissue with hard matrix and rich in blood vessels.  It is formed of periosteum, endosteum, bone matrix, and bone cells. I - Periosteum Definition: Vascular C.T. membrane which covers the bone. Structure: 1) Outer fibrous layer: white fibrous C.T. rich in blood vessels. Functions:  Attachment of muscles.  Blood supply and nourishment of osteocytes. 2) Inner osteogenic layer: osteogenic cells Functions: New bone formation during growth or healing of fracture by changing into osteoblasts to form bone tissue. II - Endosteum Definition: Vascular C.T. membrane which lines the internal surface of the bone. Structure: Similar in structure to the inner layer of the periosteum. - 40 -  Chapter 5: BONE III - Bone Matrix  Hard in consistency.  Rich in blood vessels (vascular).  Arranged in bone lamellae separated by osteocytes in lacunae. Components: A. Organic components: 1) Collagenous fibers: type I 2) Amorphous substances:  Proteoglycan (chondroitin sulphate) few.  Protein (osteocalcin).  Glycoprotein. B. Inorganic components (salts):  Calcium and phosphorus in the form of "Hydroxy apatite" crystals.  Small amounts of citrate, sodium, magnesium & iron. N.B.: Hardness of matrix is due to:  Hydroxy apatite crystals.  Collagenous fibers. Stain: acidophilic (collagen). IV - Bone Cells 1- Osteogenic Cells Origin: pericyte. Site: periosteum & endosteum. LM: Shape: flat. Nucleus: central, flat. Cytoplasm: pale basophilic. Function: give rise to osteoblasts during growth & healing. - 41 -  Chapter 5: BONE 2- Osteoblasts Origin: osteogenic cell. Site: activated periosteum & endosteum. LM: Shape: oval, branched with few cytoplasmic processes. Nucleus: eccentric, oval. Cytoplasm:  Deep basophilic cytoplasm with negative Golgi image. Functions: 1) Synthesis of organic component of bone matrix. 2) Help calcification. 3- Osteocytes Origin: mature osteoblasts. Site: single inside lacunae in between bone lamellae. LM: Shape: oval, branched. Nucleus: central, oval. Cytoplasm: slightly basophilic. EM: Processes pass through canaliculi inter-communicate by gap junctions electrolyte exchange. Functions: maintain the integrity of the bone matrix. - 42 -  Chapter 5: BONE 4- Osteoclasts Origin: fusion of many blood monocytes. Site: Howships Lacuna at inner surface of bone. LM: Size: large. Shape: irregular with brush border facing bone surface. Nucleus: multinucleated. Cytoplasm: foamy. Functions: bone resorption during ossification & after healing by:  Secretion of carbonic acids.  Secretion of collagenase. Types of bone 1- Compact (Ivory) Bone Characters: solid with no holes. Sites: 1) Shaft of long bones. 2) Outer covering of the vertebrae & ribs. 3) Outer & inner plates of flat bones of the skull. Structure: A. Periosteum: see before. B. Endosteum: lines medullary cavity. - 43 -  Chapter 5: BONE C. Bone matrix: regular lamellae: 1) Outer circumferential lamellae: under and parallel to periosteum. 2) Inner circumferential Lamellae: under and parallel to endosteum. 3) Concentric bone lamellae: in Haversian system. 4) Interstitial Lamellae: irregularly arranged between Haversian systems. D. Bone cells: see before. Haversian system (Osteon): structural & functional unit of compact bone.  Haversian Canal:  Parallel to the longitudinal axis of bone.  Contains loose C.T., rich in blood vessels.  Concentric lamellae: 4-20 lamellae around Haversian canal. Volkmann’s canals:  Transverse or oblique canals.  Connect Haversian canals together and with periosteum or endosteum. 2- Cancellous (Spongy) Bone Characters: many holes filled with bone marrow. Sites: 1) Epiphysis of long bones. 3) Bodies of vertebrae & ribs. 2) Central part of flat bones. 4) Young embryonic bone. Structure: A. Endosteum: lines bone marrow cavities. B. Bone matrix: irregular bone lamellae in the form of branching and anastomosing trabeculae separated by bone marrow spaces. - 44 - - 45 - (Haversian) (Volkmann’s) Chapter 5: BONE  Chapter 5: BONE Ossification (1) Intramembranous Ossification: Definition: Method by which a membrane of mesenchymal connective tissue is transformed into spongy bone. Sites: Flat bones (skull, face & clavicle). Stages:  At primary ossification center, UMCs osteoblasts bone matrix formation & calcification branched trabeculae join spongy bone.  Growing blood vessels and additional UMCs invade the tissue between bone trabeculae bone marrow.  Remaining Mesenchymal tissue at the surface periosteum. - 46 -  Chapter 5: BONE (2) Endochondral (intra-cartilaginous) ossification: Definition: method by which a hyaline cartilaginous model is transformed into bone. Sites: long bones. Stages: A. Primary ossification center: Develops at the diaphysis of the cartilaginous model by the following sequence of events:  Transformation of chondrogenic cells in perichondrium (future periosteum) to osteogenic cells, then osteoblasts which secrete bone matrix deep to the periosteum forming subperiosteal bone collar.  Chondrocytes within the center of the cartilaginous model undergo hypertrophy and initiate matrix calcification by releasing alkaline phosphatase.  The calcified cartilage matrix prevents diffusion of nutrients, causing death of the chondrocytes with matrix break down, so neighboring lacunae become confluent, producing an increasingly large cavity.  Osteoclasts create perforations in the bone collar that let the blood vessels, osteogenic cells, and mesenchymal cells to enter the newly formed spaces in the cartilaginous model.  Newly developed osteoblasts secrete bone matrix on the surface of the calcified cartilage, forming a basophilic calcified cartilage surrounded by acidophilic calcified bone. B. Secondary ossification centers: Appear later at the epiphyses of the cartilaginous model and develop in a similar manner except a bone collar is not formed. - 47 -  Chapter 5: BONE When the epiphyses are filled with bone tissue, cartilage remains in two areas: 1. Articular cartilage which normally persists through adult life between long bones within joints. 2. Epiphyseal cartilage (epiphyseal plate)  It connects epiphysis to diaphysis and allows longitudinal bone growth.  It disappears upon completion of bone development at adulthood.  Epiphyseal closure occurs at various times with different bones and by about age 20 is complete in all bones.  Epiphyseal plate shows distinct zones of cellular activity starting with the cartilage farthest from the diaphysis: i. Zone of reserve (resting) cartilage: - It is formed of small, resting chondrocytes embedded in their matrix. - It acts as reserve for cartilage cells. ii. Zone of proliferation: - The resting chondrocytes divide and give large number of chondrocytes. - They are arranged in rows parallel to the longitudinal axis of the bone. - 48 -  Chapter 5: BONE iii. Zone of maturation and hypertrophy: - The chondrocytes grow in size compressing the matrix into thin bars. iv. Zone of calcification: - The chondrocytes secrete alkaline phosphatase enzyme and osteocalcin to begin calcification. - The matrix become impermeable cut off nutrient to chondrocytes death of the cells leaving empty lacunae. - 49 -  Chapter 5: BONE v. Zone of ossification: - The previous empty spaces are invaded by blood vessels and osteogenic cells. - Osteoblasts settle over the calcified cartilage matrix and secrete osteoid forming basophilic calcified cartilage surrounded by acidophilic calcified bone. - This bone is then remodeled into lamellar bone and mature Haversian systems are formed. - 50 -  Chapter 5: BONE QUESTIONS A. Choose the correct answer: 1. Bone: a. Is poor in blood supply. b. Is a type of C.T. proper. c. Has firm matrix. d. Is surrounded by periosteum. 2. Periosteum is formed of: a. Outer fibrous layer and inner chondrogenic layer. b. Outer elastic layer and inner osteogenic layer. c. Outer osteogenic layer and inner bone resorping layer. d. Outer fibrous layer and inner osteogenic layer. 3. Osteocytes: a. Have deep basophilic cytoplasm with negative Golgi image. b. Are present inside Howships lacunae. c. Have long processes that pass through canaliculi. d. Synthesize organic component of bone matrix. 4. Inner circumferential lamellae of compact bone are present in: a. Under the periosteum. b. Near the endosteum. c. Around the Haversian canal. d. Between the osteons. 5. Cancellous bone is characterized by: a. Solid with no holes. b. Formed of regular lamellae. c. Its structural unite is Haversian system. d. Is present in young embryonic bone. - 51 -  Chapter 5: BONE B. Write true (√) or false (X): 1. Bone matrix contains type I collagenous fibers. ( ) 2. Osteoblasts are responsible for bone resorption. ( ) 3. Haversian system is the structural unit of compact bone. ( ) C. Complete: 1. Inner osteogenic layer of periosteum contains ………….……….…….…....… 2. Origin of osteocyte is ……….………..……...……..……… 3. Function of osteoclast is ……….………..……...……..……… - 52 -  Chapter 6: MUSCLE TISSUE MUSCLE TISSUE  One of the four basic tissues of the body responsible for the different types of movements.  It is formed of elongated cells called muscle fibers. I. Skeletal Muscle Fibers General characters:  Striated (show transverse dark and light bands).  Voluntary (under control of will).  Do not branch. Sites: 1) All muscles attached to the skeleton. 2) Eye muscles. 3) Pharynx & larynx. LM:  L.S.: Length: variable (from few mm up to 30 cm). Diameter: 100 µm. Shape: single elongated cell. Nuclei: multiple, peripheral, flattened oval. Sarcoplasm: acidophilic with transverse striation. - 53 -  Chapter 6: MUSCLE TISSUE  T.S.: Shape: polyhedral. Nuclei: only seen in some fibers. Sarcoplasm: acidophilic with myofibrils. EM: 1) Myofibrils. 4) Glycogen granules. 2) Mitochondria. 5) sER (sarcoplasmic reticulum). 3) Myoglobin pigment. 6) Ribosomes. Myofibrils Definition: Contractile elements which are longitudinally arranged in the sarcoplasm of the skeletal muscle fiber. Structure:  The myofibril shows alternating light (I-band) and dark (A-band).  The dark band of one myofibril is present beside those of adjacent myofibrils giving the cross striation seen by light microscope.  Each dark band is divided at its center by a light disc called H-zone.  Each light band is divided at its center by a dark line called Z-line. - 54 -  Chapter 6: MUSCLE TISSUE Sarcomere Definition: Area between the two Z-lines & represents the functional contractile unit of skeletal myofibrils. Structure:  Includes a whole A band and two halves of I band on either side.  Contains minute structure called myofilaments. Myofilaments Definition: Thread-like filaments which are longitudinally arranged in the myofibrils. Types: Thin Filaments (Actin) Thick filaments (Myosin) Extension: From Z-line to the border In A-band only of H-zone interdigitating in the free ends of the thin filaments Ends: One is free and the other Both ends are free is attached to the Z-line Length: 1 µm 1.5 µm - 55 -  Chapter 6: MUSCLE TISSUE Triad of Tubular System This triad is formed of: 1. One transverse tubule (T.T): Sarcolemma (cell membrane of muscle fiber) sends narrow tubular invagination called transverse tubules (T.T.) into the fibers to encircle the sarcomeres like collars. 2. Two terminal cisternae of sarcoplasmic reticulum: The sarcoplasmic reticulum tubules terminate by two wide tubules called terminal cisternae (one on each side of the T.T.). Role of triad in contraction:  Nerve impulses are transmitted to the terminal cisternae through the T.T. of the triads.  The terminal cisternae release Ca++ ions into the myofibrils leading to muscle contraction. - 56 -  Chapter 6: MUSCLE TISSUE Skeletal Muscle Connective Tissue Skeletal Muscle Fibers Epimysium  Dense C.T. which surrounds the whole muscle. Perimysium  Dense C.T. which divides the muscle into bundles.  Each bundle contains a group of muscle fibers. Endomysium  Loose C.T. which separates the muscle fibers. Functions of C.T. component: 1) Connects muscle fibers together. 2) Carries blood vessels, nerves and lymphatics. 3) Attachment of muscle to tendons, ligaments, perichondrium and periosteum. - 57 -  Chapter 6: MUSCLE TISSUE Classification of Skeletal Muscle Fibers Red White Intermediate Contraction Slow Fast Fast Fatigue Not easy Easy Not easy Energy Oxidative Anaerobic Both phosphorylation glycolysis of fatty acids Mitochondria Numerous Fewer Intermediate Myoglobin Large amount Few amount Intermediate Bl. Supply Highly vascular Poor Intermediate Glycogen Less More Intermediate Development of Skeletal Muscle Fibers Skeletal muscle fibers are formed by fusion of mono nucleated cells called myoblasts. Regeneration of Skeletal Muscle Fibers  Satellite cells are mononucleated spindle-shaped cells considered to be inactive myoblasts that persist after muscle differentiation.  After injury, satellite cells become activated, proliferating and fusing to form new skeletal muscle fibers.  A similar activity of satellite cells occurs in muscle hypertrophy. - 58 -  Chapter 6: MUSCLE TISSUE II. Cardiac Muscle Fibers General characters:  Striated.  Involuntary.  Branching & anastomosing cut in various directions. Site: wall of the heart. LM: Length: 100 µm. Diameter: 25 µm. Shape: short cylindrical cells. Nuclei: large, central, oval, mono- or bi-nucleated. Sarcoplasm: acidophilic with transverse striation. EM: 1) Myofibrils. 4) Glycogen granules small amount. 2) Numerous mitochondria. 5) Lipid droplets. 3) Intercalated discs. 6) Lipochrome pigment (↑↑ with age). Intercalated discs Definition: Site where the cell membranes of two adjacent muscle cells interdigitate and are joined together. Functions: 1) Intercellular adhesion prevents separation of cells during contraction. 2) Intercellular communication allows free and rapid transmission of nerve impulses from one cell to another. - 59 -  Chapter 6: MUSCLE TISSUE III. Smooth Muscle Fibers General characters:  Non-striated.  Involuntary. Sites: 1) Walls of the blood vessels. 2) Viscera of various systems (GIT, respiratory system). Arrangement: 1) Bundles 2) Layers: circular, longitudinal, oblique or spiral LM: Length: 20 µm in blood vessels, and up to 500 µm in pregnant uterus. Diameter: 4-10 µm. Shape: spindle (fusiform). Nuclei: central, oval. Sarcoplasm: acidophilic, non-striated. - 60 -  Chapter 6: MUSCLE TISSUE EM: 1) Irregularly arranged thin & thick filaments (no sarcomeres or myofibrils). 2) Intermediate filaments are present. Functions: 1) Maintain partial tonic contractions for very long periods regulating luminal size in hollow organs. (digestive, respiratory, urinary, etc…). 2) Produce peristaltic movements e.g. digestive system. - 61 -  Chapter 6: MUSCLE TISSUE Skeletal Muscle Fibers Cardiac Muscle Fibers Smooth Muscle Fibers General  Voluntary  Involuntary  Involuntary characters:  Not branching  Branching & anastomosing  Not branching Sites: 1) Ms. attached to skeleton Wall of the heart 1) Wall of blood vessels 2) Eye muscles 2) Viscera (GIT, respiratory 3) Pharynx & larynx system) LM: Length: Few mm - 30 cm 100 µm 20 – 500 µm Diameter: 100 µm 25 µm 4-10 µm No. of cells/ fiber: Single cell Chain of cells Single cell Shape: Elongated Short cylindrical Spindle Nuclei: Multiple, peripheral, flattened oval Central, oval, mono- or bi-nucleated Central, oval Sarcoplasm: Striated Striated Non-striated EM: Thin & thick filaments forming Thin & thick filaments forming Thin, thick & intermediate sarcomeres sarcomeres filaments with no sarcomeres Intercalated discs: Absent Present Absent Regeneration: Satellite cells Fibrosis Mitosis - 62 -  Chapter 6: MUSCLE TISSUE QUESTIONS A. Choose the correct answer: 1. Myofibrils: a. Each light band is divided at its center by a light disc called H-zone. b. Formed of alternating light and dark band. c. Each dark band is divided at its center by a dark line called Z-line. d. Are contractile elements transversly arranged in skeletal muscle fiber. 2. Distance between two successive Z-lines in the myofibril is called: a. H zone. b. Centromere. c. Sacomere. d. I band. 3. The depolarization wave reaches the depth of the striated muscle fiber via: a. Sarcoplasmic reticulum. b. Sarcolemma. c. Transverse tubules. d. Mitochondria. 4. Intercalated discs are present in: a. Skeletal muscle fibers only. b. Cardiac muscle fibers only. c. Skeletal and cardiac muscle fibers. d. Smooth muscle fibers only. 5. Smooth muscle fibers: a. Are striated. b. Contain peripheral flattened oval nuclei. c. Show sarcomeres. d. Are fusiform in shape. - 63 -  Chapter 6: MUSCLE TISSUE B. Write true (√) or false (X): 1. Skeletal muscle fibers are involuntary. ( ) 2. Cardiac muscle fibers are branching and anastomosing. ( ) C. Complete: 1. The functional contractile unit of skeletal muscle is ………………………….. 2. In sarcomere, both ends of …………………….…………… filaments are free. - 64 -  Chapter 7: NERVOUS TISSUE NERVOUS TISSUE Central Nervous System Peripheral Nervous System Brain Spinal Cord Peripheral Nerves Ganglia Cranial Cerebro-spinal Autonomic Spinal Sympathetic Parasypathetic Neuron Structural and functional unit of the nervous tissue Cell Body Processes Axon Cell Membrane Nucleus Cytoplasm Very thin Large Dendrites Central Nissl Granules Rounded Golgi Apparatus Mitochondria Centriols Young cells only - 65 -  Chapter 7: NERVOUS TISSUE Processes Axon Dendrites Number: Single Multiple Size: Long, thin Short, thick Diameter: Constant Tapering Surface: Smooth Irregular Branching: At its terminal end only Extensive branching along their course Contents: No Nissl granules Nissl granules Conduction of nerve Centrifugal (away from the Centripetal (to the cell impulses: cell body) body) - 66 -  Chapter 7: NERVOUS TISSUE Types of Neuron According to the number of processes (polarity) Unipolar Pseudounipolar Bipolar Multipolar Polygonal Pyramidal Pyriform 1) Unipolar nerve cells: Shape: rounded. Number of processes: one. Site: mesencephalic nucleus of the trigeminal nerve. 2) Pseudounipolar nerve cells: Shape: rounded. Number of processes: single process which divides in inverted T-shaped manner into 2 branches, a dendrite and an axon. Site: spinal ganglion. 3) Bipolar nerve cells: Shape: fusiform or spindle-shaped. Number of processes: two processes, a dendrite and an axon. Site: Retina of the eye and olfactory epithelium of the nose. - 67 -  Chapter 7: NERVOUS TISSUE 4) Multipolar nerve cells: Number of processes: many dendrites and one axon. a) Polygonal or stellate shaped: Shape: star-shaped. Site: sympathetic ganglia. b) Pyramidal: Shape: pyramidal. Site: cerebrum. c) Pyriform: Shape: flask-shaped cells. Site: cerebellum. Polygonal Pyramidal Pyriform Nerve Fiber Definition: axon of a nerve cell. Types: A. Naked Fibers: (Non-myelinated without neurolemma) e.g. gray matter. B. Ensheathed fibers: 1. Myelinated with neurolemma: e.g. peripheral nerves. 2. Myelinated without neurolemma: e.g. nerve fibers in the white matter. 3. Non-myelinated with neurolemma: e.g. sympathetic nerve fibers. Axon Structure:  The axon is surrounded by a membrane called "axolemma".  Its cytoplasm is known as "axoplasm".  It contains neurofilaments and mitochondria but no Nissl granules. - 68 -  Chapter 7: NERVOUS TISSUE Diameter:  Thick fibers conduct impulses rapidly.  Thin fibers conduct impulses slowly. Myelin Sheath Histological appearance:  It is a white tubular covering of the axon.  It is interrupted at intervals by constrictions called "nodes of Ranvier".  The segment between two successive nodes is called "internodal segment". Chemical structure:  It is a lipoprotein sheath.  It appears in the form of concentric layers derived mainly from the lipid layer of the cell membrane of Schwann cell. - 69 -  Chapter 7: NERVOUS TISSUE Staining:  H&E: the fat of myelin dissolves in xylol and appears as an empty space.  Osmic acid: black. Function: insulation of the nerve impulses. Neurolemmal Sheath (Schwann Cells) Histological appearance:  It is formed of a chain of cells forming a tube around myelin sheath.  Each Schwann cell has a flat oval nucleus and corresponds to an internodal segment. Function: 1. Formation of myelin sheath. 2. Insulation of nerve impulses in non-myelinated nerve fibers. 3. Regeneration of peripheral nerve after injury. - 70 -  Chapter 7: NERVOUS TISSUE Nerve Trunk Connective Tissue Nerve Fibers Myelinated with neurolemma Epineurium Dense C.T. which surrounds the whole trunk. Osmic acid H&E Perineurium Black rings Axon: acidophilic of myelin Myelin: empty space Dense C.T. which surrounds the bundles of nerve fibers. Schwann cell: pink rim Endoneurium Loose C.T. which separates the individual nerve fibers. Peripheral Nerve Trunk - 71 -  Chapter 7: NERVOUS TISSUE Degeneration of Nerve Fibers Cutting of a nerve fiber by a knife, trauma or infection leads to: I. Retrograde Degeneration Changes that occur in the cell body after injury of the axon. 1- Cell body: swells, withdraws its processes & becomes globular in shape. 2- Cytoplasm: becomes vacuolated. 3- Nissl granules, neurofibrils & Golgi apparatus: → disintegration & finally disappearance. 4- Nucleus: becomes condensed, eccentric & gradually degenerates.  If the cutting is partial → the cell recovers after one or two weeks.  If the cutting is complete → death of the cell and no recovery occurs. II. Wallerian Degeneration Changes that occur in the peripheral part of the nerve fiber distal to the site of injury A. Changes in axon: After few hours: the neurofibrils become swollen at interrupted areas → beaded appearance. After few days: → segmentation. Finally: → disintegration of the neurofibrils into granules, which finally disappear. B. Changes in myelin sheath: (slower than axon) After few days: → nodes of Ranvier widen, myelin retracts and becomes irregular. After few weeks: → segmentation. Finally: → myelin is broken down into fat globules & fatty acids. - 72 -  Chapter 7: NERVOUS TISSUE C. Changes in neurolemma: Firstly: neurolemmal cells increase in size (hypertrophy). Then: they increase in number (mitosis) and extend slowly across the gap between the 2 cut ends to meet those from the distal stump and form a tube which is ready to receive the regenerating axon which will sprout from the proximal part of the cut nerve. Regeneration Factors improving regeneration: 1) Partial cutting of nerve fiber. 2) Small distance between the 2 cut ends. 3) Absence of infection at the site of injury. 4) Presence of neurolemma. - 73 -  Chapter 7: NERVOUS TISSUE Mechanism of regeneration:  After a temporary reaction in the cell body, regeneration starts in the nerve cell by resuming its normal shape and contents.  The cell resynthesizes axoplasm, which passes down to the central stump.  Several branches of the axoplasm called axon sprouts arise from the proximal stump and grow across the gap into the tube of neurolemmal cells.  Only the proper axon will reach the proper nerve ending and the others fail to do so.  The neurolemmal cells then form the myelin around the axon. - 74 -  Chapter 7: NERVOUS TISSUE Nerve Ganglia: collection of nerve cells and nerve fibers outside the C.N.S. Spinal ganglion Sympathetic ganglion Site: Dorsal roots of spinal nerves Sympathetic chain C.T. Capsule: Thick Thin Nerve cells: Type: Pseudounipolar Multipolar Number: Few Numerous Size: Small, medium & large All are small Arrangement: In groups or rows Scattered irregularly Nuclei: Central Eccentric Nerve fibers: Thickly myelinated Thinly or non-myelinated - 75 -  Chapter 7: NERVOUS TISSUE QUESTIONS A. Choose the correct answer: 1. Axon: a. Has extensive branching along its course. b. Carry impulse away from the cell body. c. Is short & rough. d. Has Nissle granules. 2. Pseudounipolar nerve cells are present in: a. Mesencephalic nucleus of the trigeminal nerve. b. Spinal ganglion. c. Retina of the eye. d. Sympathetic ganglia. 3. Myelin sheath is stained black with: a. Hematoxylin and Eosin stain. b. Silver stain. c. Osmic acid stain. d. Ver-Hoff’s stain. 4. Sympathetic nerve fibers are: a. Naked. b. Myelinated with neurolemma. c. Myelinated without neurolemma. d. Non-myelinated with neurolemma. 5. Perineurium: a. Surrounds the whole nerve trunk. b. Surrounds each nerve bundle. c. Surrounds the individual nerve fibers. d. Surrounds each Schwann cell. - 76 -  Chapter 7: NERVOUS TISSUE B. Write true (√) or false (X): 1. Pyramidal multipolar nerve cells are present in cerebrum, ( ) 2. Dendrites have irregular surface. ( ) 3. Function of myelin sheath is to insulate nerve impulse. ( ) C. Mention: 1. Example for myelinated nerve with neurolemma. (……….….…………… ) 2. Example for multipolar nerve cells. (……….….…………… ) - 77 -  References Cormack, D. H. (2001): Essential Histology. Second ed. Lippincott Williams & Wilkins. Philadelphia. Pennsylvania. Eroschenko, V. P. (2008): Di Fiore's atlas of histology with functional correlations. Eleventh ed. Lippincott Williams & Wilkins. Baltimore. Philadelphia. Fawcett, D. W. and Jensh, R. P. (2002): Bloom & Fawcettˊs Concise Histology, Liver and Gall bladder. Second ed. Arnold. London. New York. New Delhi. Gartner, L. P. and Hiatt, J. L. (2007): Colour Textbook of Histology. Third ed. 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