Histology (Menoufia University) PDF

Menoufia University Faculty of dentistry Histology By Staff Members of Histology & Cell Biology Department 2024 - 25 1 VISION: To be academically accredited college with local, regional, and international reputatio...

Menoufia University Faculty of dentistry Histology By Staff Members of Histology & Cell Biology Department 2024 - 25 1 VISION: To be academically accredited college with local, regional, and international reputation for having a leading role in the field of medical education and health care provision. MISSION: The faculty of dentistry, Menoufia University is committed to graduate a physician in accordance to the National Academic Reference Standards, who is able to meet the needs of local and regional market, skilled in conducting scientific researches that participate in developing the profession and the provided health care, and keen on continuous training and education to support the service provided to community and surrounded environment in the frame of commitment to the ethics of the profession 2  Contents Index Topic Page Overall aims of the course Intended Learning Outcomes The Cell Cytogenetic Epithelial Tissue Connective Tissue Cartilage Bone Muscular Tissue Blood 3 Overall aims of the course: Acquire an appropriate functional background of cells, tissues, organs &systems. Intended Learning Outcomes: Enumerate histological structure of the cell Define different functions of cell organelles Integrate basic anatomical and histological data. Clarify cytogenetics and explain cell division Clarify the structural characteristics of the two basic tissue types (epithelium and Connective tissue). Understand histological structure of cartilage and its types Identify histological structure of bone and its types Know different types of skeletal muscle fibers Identify component of blood 4 HISTOLOGY ❖ It is the science that deals with the microscopical study of normal tissues. ("Histo" means tissue and "logia" means study). THE CELL 5 General characteristic It is the structural and functional unit of all living tissues (plants and animals) capable of independent existence. Structure: The cell is a mass of protoplasm that consists of two major components: The cytoplasm. Karyoplasm (Nucleus). The cytoplasm is the viscid colloidal mass containing organelles and inclusions. a-Organelles: are differentiated metabolically active units of living matter, essential for vital processes of the cell (respiration, digestion, secretion, excretion, growth... etc.). b- Inclusions (Cytoplasmic Deposits): They are inert cell products or metabolites that are usually temporary components, not essential for vitality of cells. They may be present or absent. CYTOPLASMIC ORGANELLES They are either membranous or non-membranous. Membranous Organelles: ▪ They are permanent structures in nucleated cells they include the following organelles. 6  1. Cell membrane 2. Mitochondria 3. Golgi complex 4. Lysosomes 5. Peroxisomes 6. endoplasmic reticulum (rough and smooth) 7. Coated vesicles. Non- Membranous Organelles: ▪ They are not enclosed by membranes they are. 1. Ribosomes 2. centrioles 3. Cytoskeleton (microtubules, microfilaments and micro trabecular lattice). MEMBRANOUS ORGANELLES Diagram showing a cell containing various structures as seen with electron microscope (E/M) 7 THE CELL MEMBRANE (PLASMALEMMA) I- Structure: Light microscope (LM): It is very thin, elastic and difficult to be seen. It appears dark brown by silver stain. Electron microscope (E/M): It appears as two dark layers, separated by a light one, (trilaminar membrane). a- Chemical composition (Molecular biology): The cell membrane is made of lipoprotein (lipids, proteins, glycolipids, and carbohydrates). ❖ The Lipid Component: It consists of three major classes of lipids (phospholipids, glycolipids and cholesterol). Phospholipids are arranged into a double layer. Each molecule has two ends, polar and non-polar. ▪ The polar ends (heads): are hydrophilic, charged and directed outwards and appear dark (dense) layers in electron microscope as a result of deposition of osmium used in E/M preparation. ▪ The non-polar ends (tails): are hydrophobic, non-charged and directed inwards. Thus, the phospholipid bilayer is formed of two parallel layers of phospholipid molecules lying tail to tail. Ultrastructure & Molecular organization of cell membrane 8 9  ❖ The Protein Component: arranged as ▪ Extrinsic protein (Peripheral proteins): It is loosely attached protein molecules, on both surfaces of cell membrane. ▪ Intrinsic protein (Integral proteins): It consists of small or large protein molecules, firmly embedded in the lipid bilayer. Some large integral proteins called transmembrane proteins extend the entire width of the plasmalemma (lipid bilayer) and protrude from both membrane surfaces. They are called one-pass or multipass transmembrane proteins. ❖ The cell Coat (glycocalyx): It is a layer of glycoprotein or glycolipid, on the external surface of the cell membrane. It plays a role in immunological specificity, contains blood group antigens, has receptor sites, holds the cells together, shares in the formation of the basement membrane of epithelial tissues and acts as a protective mechanical barrier. II- Specializations or Modifications of Cell Surfaces: 1- Lateral Surfaces: Junctional complex and interdigitations are finger like projections that interlock adjacent epithelial cells. 2- Basal Surface: Flagella form the tails of sperms, helping their movement. 3- Apical Surface: Microvilli are finger-like projections of epithelium that extend into the lumen 10 and increase the absorptive surface area. Cilia are present on the surface of respiratory tract epithelium to push particles or fluids in one direction. 4- Around the Surface: Myelin Sheath surrounds the nerve fibers and insulates nerve impulses. III- Functions of the cell membrane: 1- Simple transport (diffusion): Gases and water can pass into the cell. 2- Active transport: Large molecules as sugar need energy to enter the cell. 3- Selective Permeability: The cell membrane has the power to select the entering material. This is carried through specific receptors on the cell surface. It explains how drugs & hormones act on specific cells or organs. 4- Sodium-Potassium Pump: The cell membrane always keeps the Na concentrated outside the cell, while the K is kept concentrated inside the cell membrane. 5- Phagocytosis: It is the power of the cell membrane to pass a solid particle, forming a phagosome. 6- Pinocytosis: It is the power of the cell membrane to enclose & pass a driblet of fluid, forming a pinocytic vesicle. 7- Exocytosis: It is the power of the cell membrane to extrude waste products, outside the cell. 8- Cell Coat (Glycocalyx) and its function. 11 MITOCHONDRI  Structure of Mitochondria 1- Site & size: They are membranous cytoplasmic organelles. They vary in number and size. They can move, divide & fuse. Their number in a cell depends on its energy requirements. 2- Structure: a- Light microscope (LM): They appear as rods, granules or filaments, after staining with Iron Hx.or Janus green. b- Electron microscope (E/M): ▪ Mitochondria are enclosed by two membranes, each has a trilaminar substructure. ▪ The outer membrane is smooth, while the inner one forms incomplete alternating shelves (cristae), which extend in the interior of the mitochondrion. ▪ The cavity is filled with mitochondrial matrix rich in oxidative enzymes together with dense granules. 3- Chemical composition (Molecular biology): ▪ Mitochondria consist of lipids, proteins, carbohydrates, vitamins, minerals, and all the types of RNA, DNA and oxidative enzymes (enzymes of kreb’s cycle). ▪ The matrix granules are formed of phospho-lipo-proteins binding Ca and Mg.  Functions: 1-They are considered as the respiratory apparatus of the cell, concerned with the release of energy due to their content of oxidative enzymes (powerhouse of the cell). 2-They can form proteins for themselves, as they contain DNA and RNA and are capable of self- replication (division). 2- They are concerned with concentration of ions as ca. 3- They are strongly related to heat production in the brown fat of newborn. GOLGI BODY (GOLGI COMPLEX) - Site: It is a membranous cytoplasmic organelle, which is considered as the Secretory apparatus of the cell. ▪ It is always located between the nucleus and periphery of cell. Structure: a- Light microscope (LM): It appears as a network of fibrils, after staining with silver. In Hx and E. preparations, its site appears as an unstained area (negative Golgi image). b- Electron microscope (E/M): It is formed of three shapes of membranous components. ✓ Flattened vesicles (Cisternae): consisting of elongated parallel sacs piled one upon the other to form stacks. Each has an inner, concave surface (mature), facing the cell surface and an outer convex surface (immature) facing the cell base. They are the sites of protein concentrations. ✓ Transfer vesicles (microvesicles): They carry the formed protein from the rough endoplasmic reticulum (RER) to outer convex immature surface of the flatted vesicles (cis face). ✓ Macrovesicles (Condensing Vacuoles): They are large distended vesicles that separate from the periphery of mature face of flattened vesicles. They either discharge their enzymes outside the cell (zymogen granules) or remain in the cell as lysosomes.   Functions of the Golgi apparatus: 1- Concentration of the secretory products 2- Discharge of secretory products (secretion). 3- It adds carbohydrates to its protein content to form glycoprotein 4- Formation and maintenance of cell membrane and cell coat. 5- Formation of lysosome  LYSOSOMES 1-Site & origin: They are membranous rounded vesicles (organelles), considered as the digestive apparatus of the cell. Lysosomes are numerous in the phagocytic cells. They originate from the Golgi apparatus and their enzymes are formed in the rough endoplasmic reticulum (RER). 2-Structure: a- Light microscope (LM): They can be demonstrated by special histochemical methods. b-Electron microscope (E/M): 1.Primary lysosomes: appear as homogenous vesicle surrounded by single membrane 2.Secondary lysosomes or End lysosomes: ▪ Heterolysosomes: formed by fusion of primary lysosomes with phagosomes (endosomes), containing exogenous substrates, as bacteria (Heterophagic vacuole). ▪ Autolysosomes: formed by fusion of primary lysosomes with phagosomes (endosomes), containing endogenous substrates as mitochondria (Autophagic vacuole). ▪ Multivesicular bodies: formed by fusion of primary lysosomes with pinocytic vesicles. 3-Residual bodies: They contain remains of indigestible material or debris.  c- Chemical composition: ▪ Lysosomes contain hydrolytic enzymes, active at an acidic pH (acid hydrolases) as lipase and acid phosphatases D-Functions of lysosomes: 1- Digestion of nutrients. 2- Defensive mechanism against bacterial and viruses. 3- Digestion of fluid droplets: The cell membrane surrounds fluid, forming pinocytic vesicles that fuse in the cytoplasm forming multivesicular bodies. 4- Autophagocytosis: Lysosomes can get rid of degenerated organelles as dead mitochondria. 5- In the thyroid gland: Lysosomes help the release of the active thyroid hormones. 6- During fertilization: They help the sperm to penetrate the ovum. 7- Removal of dead cells and autolysis after death. 8- Residual bodies play important role in the aging process. Diagram representing Autophagy & Heterolysosome  ENDOPLASMIC RETICULUM General Characteristics: There are two types: Rough (Granular) & Smooth (Agranular) due to the presence or absence of Ribosomes on the outer surface. Differences between rough and smooth endoplasmic reticulum Items Granular or Rough Endoplasmic Agranular or Smooth Reticulum (GER, RER) Endoplasmic Reticulum (SER) Site Abundant in protein forming cells Abundant in lipids and steroid (plasma cells) hormones forming cells ▪ Ribosomes are attached to its ▪ No ribosomes are found on its outer surface. surface. L/M ▪ Appear as basophilic areas. ▪ Can not be demonstrated. ▪ A system of sheets & cavities ▪ Branching anastomosing Structure (cisternae) bounded by tubules and vesicles without E/M membranes. cisternae. ▪ Ribosomes attached to their ▪ No ribosomes on the outer outer surfaces. surfaces. 1. Segregation of the protein, 1. Synthesis and storage of formed by the ribosomes on the fats. surface. 2. Synthesis of steroid Functions 2. Transfer of the protein to hormones as testosterone. the 3. Glycogen formation in liver Golgi vesicles. &muscle. 3. Protection of the 4. Formation of Hcl in stomach cytoplasm from the effect of the cells. contained enzymes. 5. It helps muscular 4. It provides a site for contraction, by acting as a attachment of ribosomes. calcium pump. 6. Detoxification of drugs and hormones.  MEMBRANOUS ORGANELLES RIBOSOMES & POLYSOMES Site & origin: Ribosomes are formed in the nucleolus from different cytoplasmic proteins & nucleoproteins and pass to the cytoplasm through the pores of the nuclear membrane to perform their functions in cytoplasm. o Structure: They are made of ribonucleic acid (RNA) combined with a protein, present in two forms: free and attached Small subunit mRNA Large subunit Polysomes Free Attached  Free ribosomes (not attached to membranes) are small, dense, rounded basophilic granules (due to content of RNA) distributed freely in mitochondrial matrix or in cytoplasm of all kinds of cells (except mature red blood cells). Attached ribosomes are small, dense, rounded basophilic granules (due to content of RNA) linked to membranes of endoplasmic reticulum (ER) & nucleus by their large subunit, while the small subunit projects in the cytoplasm. Attached ribosomes cause localized basophilia as in Nissl granules of nerve cells. o Electron microscope (E/M): Ribosomes seen by EM are non-membranous, small electron dense bodies formed of 2 subunits, a large and a small one. Polysomes (polyribosomes): Polysomes (polyribosomes), are groups of free ribosomes, connected together by a messenger RNA (mRNA) common in rapidly growing cells as cancer cells & developing red blood cells. o Function: 1- Free ribosomes are concerned with synthesis of protein for the cell growth while 2- attached ribosomes are concerned with synthesis of secretory.  CENTRIOLES Site: They are usually located near the nucleus o Structure: 1- Light microscope (LM): ▪ There are pair of centrioles that appear as two small bodies, after staining with iron Hx, near the nucleus. 2- Electron microscope (E/M): ▪ They appear as 2 cylinders, perpendicular to each other. ▪ The wall of each centriole is made of nine peripheral bundles of microtubules (9+0). ▪ Each bundle is made of three fused microtubules (triplets), arranged as A, B& C microtubules from inwards outward. Thus the wall is formed of twenty seven microtubules. The inner microtubule (A) is a complete ring consisting of 13 protofilamments, while B &C microtubules having a C shaped appearance B C A A B C A B C Diagram of Centriole (TS)  o Functions of the centriole: 1- Initiation of cell division and spindle formation. 2- Formation of cilia and flagella. 3- They may determine the direction of cell migration and cell polarity. o Modifications of the Centrioles: 1- Cilia: They are present on the free surfaces of some epithelial cells, as in the respiratory tract, to help the movement of particles or fluids in one direction. Structure of Cilia (E/M): ▪ Each cilium is covered by a plasmalemma and consists of basal body, axoneme (shaft) and rootlet. ▪ Basal Body has the same structure as the centriole. The wall of which consists of nine triplet microtubules (9+0). ▪ Axoneme is a protoplasmic core of cytoplasm containing twenty microtubules. Nine peripheral pairs of fused microtubules (the doublets A "complete rings of 13 protofilamments" & B " incomplete C-shaped of 10- 11 protofilamments") forming a ring around a central pair of individual microtubules (9+2). The two central singlets (each 13 protofilaments) of axoneme are surrounded by central sheath. ▪ Radial projections (spokes) extend from the doublets to central pair of microtubules. ▪ Rootlets are anchoring microtubules from the basal body to the cytoplasm to fix the cilia. Function: The cilia beat in one direction (sliding mechanism) and help in creating current pushing mucus and other materials away. a. Flagella: They form the tails of sperms. They are similar to cilia, in structure but longer and larger.  CYTOSKELETON General Characteristics: ▪ It is the structural framework of the cell, maintains cell shape, stabilizes cell attachments and plays a role in motility. ▪ It includes microtubules, microfilaments and filaments. FILAMENTS I- Structure: -Cytoplasmic filaments are usually found in most cells either singly or ingroups And appear as fine threads, after staining with silver. They are of three types. ❖ Thin filaments (micro filaments): -They are of small size, made of protein actin. -They are the contractile element present in the striated muscle cells. -They are present in the cores of microvilli, terminal web, blood platelets and play an important role during cell division as they form the mitotic spindle. ❖ Thick filaments: - They are thicker made of protein myosin. - They are contractile element similar to actin filaments present in the striated muscle cells (myocytes). - They are present also as actin filaments in the cores of microvilli, terminal web and blood platelets. ❖ Intermediate filaments include: They are intermediate in size between thick filaments and thin filaments as Desmin filaments and Vimentin filaments  THE CELL INCLUSIONS (CYTOPLASMIC DEPOSITS) They are the non-living contents of the cytoplasm, which may be present or absent. They include stored food, pigments, secretory granules or crystals. 1- STORED FOOD: Carbohydrates: They are stored in the form of glycogen, as in the liver and muscle. E/M: Glycogen granules are either alpha granules and represent groups of very electron dense granules (rosettes) in liver cells, or beta granules, which are irregular electron dense single granules found in muscles. Fats: They are stored in fat cells as small droplets or large globules. Fat dissolves in Hx & E preparations, so the cells appear as a thin ring of cytoplasm surrounding large vacuole (signet-ring appearance). 2- PIGMENTS: (endogenous or exogenous) Endogenous pigments: They are formed inside the body. a- Melanin is present in skin & eye, to protect against ultraviolet rays. b- Hemoglobin is the most important and essential pigment in the body, presents in RBCs to carry O2 and CO2. c- Lipofuscin is found in nerve cells and heart muscle, representing waste products. It increases with age, representing end product of lysosomal activity. Exogenous pigments: They come from outside the body. a- Dust and carbon particles, in dust cells of lung. b- b- Tattoo marks, in skin. c- Carotene ingested with food as carrots and tomatoes. Carotenemia (yellow color of skin as a result of too much ingestion of carrots). d- Minerals: as silver and lead. 3- SECRETION GRANULES: include mucous, serous secretion, proteins etc... 4- CRYSTALS: as crystals of CaCo3  The Nucleus Number: cells that possess nuclei are called eukaryotic. While, that possessing no nucleus is called prokaryotic (e.g. R.B. Cs). Usually, a cell has one nucleus mononucleated. cells possessing two nuclei are called binucleated (e.g. some liver cells). Cells are described as multinucleated when they have more than two nuclei (e.g. osteoclast). Size: the nucleus may be small, medium-sized or large. Shape: The nucleus may be rounded, oval, flattened, rod- shaped bilobed, lobulated, kidney- shaped (indented) horseshoe- shaped. Position: The nucleus may be central, eccentric, peripheral or basal. Appearance: The nuclei are sometimes described as: a) Vesicular (or open face) type: Details of its components could be seen inside (e.g. nuclei of. liver cells, nerve cells). b) Condensed (or deeply stained) type: no details could be seen within it (e.g. nucleus of a lymphocyte). The nucleus of interphase cell (non-dividing cell) consists of: 1. Nuclear envelope. 2. Chromatin. 3. Nucleolus. 4. Nuclear sap. ❖ Nuclear Membrane (Envelope) -With the LM: It appears surrounding the nucleus as a single basophilic line (due to the presence of peripheral chromatin on its inner side). - With the EM: It is formed of two thin membranes (8 nm thick) separated by a perinuclear space (25 nm wide). -The outer membrane is continuous with the membranes of the endoplasmic reticulum in the cytoplasm. -The inner membrane shows chromatin granules (peripheral chromatin). Nuclear pores (about 30-100 nm in diameter) interrupt the nuclear- membrane at intervals. At the pore, the two layers of the membrane fuse together, forming a Nuclear Pore Complexes (NPCS) which allows the exchange of chemical molecules between the nucleus and the cytoplasm.  ❖ Chromatin The nucleus of any somatic (body) cell contains chromosomes (the gene carriers), made of a nucleoprotein, composed of a protein histone conjugated with an important nucleic acid called deoxyribonucleic acid (DNA). The chromosome, is a long, thread- like structure called chromosomal thread or s- chromosomes It is too thin to be visible with LM, However, along its length, parts of it are tightly coiled and folded and thus become dense enough to be seen as granules. With the LM: Chromatin appears as basophilic granules called chromatin granules which represent those parts of the chromosomal threads which are tightly coiled. The granules are described as coarse or fine depending of their size. The fact that they contain acid explains why they are basophilic. With the EM: Two types are present: 1. The condensed Chromatin (heterochromatin, or the inactive type). - It appears as aggregations of electron-dense granules (coiled parts). They appear as string of beads called nucleosomes. It is distributed within the nucleus as: (a) Peripheral chromatin aggregated close to the inner nuclear membrane. (b) Nucleolus-associated chromatin aggregated into a crust around the nucleolus. (c) Chromatin islands aggregated into clumps in the nuclear sap. - The genes present in these condensed chromatin segments are inactive (i.e. they do not direct any protein synthesis). - Under certain conditions of cellular activity, the condensed chromatin becomes extended and active.  2. The Extended Chromatin (euchromatin or the active type) - These are the extended (uncoiled) parts of the chromosomal threads. - They are invisible with L.M because they are very thin, but can be seen with EM, only if higher magnification is used. - Euchromatin is the active parts of the chromosomal threads in which genes are functioning (i.e. engaged in directing protein synthesis) Functions of Chromatin: 1. It directs and guides the synthesis of protein so as to produce the proper specific proteins required by the cell to perform specialized function. 2. It contains the genetic material, which directs all cellular activities and regulates cellular structure. ❖ Nucleolus Nucleolus is round, dense, well-defined structure, it has no limiting membrane. There are l- 4 nucleoli per cell nucleus; more active cells have more nucleoli, Nucleoli are rich in rRNA and proteins, they disappear during cell division. By EM, nucleolus consists of: I. Nucleolar organizer DNA: consists of DNA coding for rRNA. II. Pars fibrosa: are the sites of rRNA synthesis. III. Pars granulose: consists of maturing subunits of ribosomes. Functions of nucleolus: Nucleolus is the site of synthesis of rRNA and ribosomes.  ❖ Nuclear matrix Nuclear matrix, karyoplasms, or nucleoplasm, is a semifluid substance occupying the space between chromatin particles and nucleolus. It consists of fibrogranular network, metabolites, ions and fibrous lamina.  CYTOGENETICS THE LIFE CYCLE OF THE CELL It is the period that includes an interphase and a complete cell division.The interphase; is the period between two cell divisions. It is divided into three phases: Gl-phase(Gap or presynthesis): is the phase in which the cell restores its normal size after mitosis, forms RNA and protein, needed for its growth. S-phase(DNA synthesis): is the phase during which, duplication of DNA & centrioles take place. G2-phase(Post DNA duplication): is the phase in which the cell produces the energy needed for the next cell division. Cells vary according to their ability to divide and renew into: Cells that cannot divide Nerve cells. Cells unable to divide but after degeneration are replaced by stem cells of the same family Cells of small intestine. Cells that divide only at time of need-- Cells of liver and endocrine gland cells HUMAN CHROMOSOMES General Characteristics Chromosomes are the carriers of genetic information, as they contain the genes, which are the units of heredity. They are formed of macro-molecules of DNA, in the form of two strands, twisted on each other, in the form of double helix.  Male cells contain XY sex chromosomes, while female cells contain XX ❖ Chromosomal abnormalities: Definition: It is disturbance in chromosomal structure and number. Types: I- Abnormalities of structure: These are changes in morphology of chromosomes. 1-Deletion, is loss of a part of one or more chromosome. 2-Breaks of chromosomes & ring formation. 3- Inversion, is wrong reattachment of broken segments Of chromosomes. 4- Translocation is the transfer of segments between chromosomes. 5- Isochromosomes, is abnormal transverse division of the centromere separating the two arms instead of longitudinal division separating individual chromatids. II- Abnormalities of number: These are changes in number by addition or loss of one or more of chromosomes. 1- Polyploidy, is abnormal duplication of haploid number of chromosomes. Normally the number of chromosomes in somatic cells is double the haploid number (2n), in Triploid it is 3 times the haploid number (3n), in Tetraploidy it is 4 times the haploid number (4n). These numerical aberrations are incompatible (impossible to continue) with life & cause miscarriage (loss of pregnancy). 2- Aneuploidy is the addition (Triosomy) or loss (Monosomy) of a chromosome and may affect autosomes or sex chromosomes. a- Autosomes:  Triosomy is the presence of an additional chromosome to the usual pairs. It has been reported in all autosomes except chromosome number 1. The commonest is trisomy 21, which means the presence of 3 of chromosome (21) in Down’s syndrome or Mongolism. Monosomy is the missing of one chromosome from the usual pairs and monosomy of autosomes is lethal. a- Sex chromosomes: Triosomy is presence of an additional sex chromosome (usually X). Normally, males have X & Y sex chromosomes and need both for sex differentiation, while female cells possess double X chromosomes, one is inactive called sex chromatin or Barr body, and so females are positive for sex chromatin, while males are negative. Klinefilter syndrome: In this disease males have positive sex chromatin (47, XXY) presenting with poor musculature, underdeveloped genitalia, infertility and gynecomastia. They have higher risk for breast cancer. Monosomy of X chromosome is detected in females (45, X) in Turner syndrome. Turner syndrome or gonadal dysgenesis is a common abnormality, where one X chromosome is missing. Barr body is absent. In this disease females have primary amenorrhea, underdeveloped genitalia and secondary sex characters, infertility, together with renal and cardiac anomalies. There are four main tissues of the body: 1- Epithelial Tissue 2- Connective Tissue 3- Muscular Tissue 4 – Nervous Tissue  Epithelial Tissue General Characters of Epithelial Tissue: 1. Crowded cells with minimum intercellular substance 2. Cells are resting on a basement membrane (B.M.) 3. Polarity of cells with distinct apical, lateral &basal surfaces. 4. Avascular tissue (No blood or lymph vessels can penetrate epithelial tissue). 5. It receives nutrition by diffusion from underlying connective tissue ((C.T.) 6. It is penetrated by nerve fibers which carry sensations or control secretion. 7. It has a high power of regeneration. Classification of Epithelial Tissue: I. Surface epithelium: formed of continuous sheets of epithelial cells which cover surfaces or line cavities. It is classified according to number of layers into: Simple (one layer) & Stratified (more than one layer). II. Glandular epithelium: formed of epithelial cells modified to give secretion III. Neuroepithelium: formed of epithelial cells modified to receive stimuli. IV. Myoepithelium: formed of epithelial cells modified to be contractil  Surface Epithelium It is named according to: 1- Number of layers ▪ Simple epithelium : one layer ▪ Stratified epithelium : several layers 2- Shape of cells on the top layer ▪ Squamous ▪ Cubical ▪ Columnar 3- Surface specializations Keratinized or not (with stratified squamous) Ciliated or not (with columnar) Type of epithelium Shape 1. Simple Squamous Formed of one layer Forms thin sheets & epithelium of flat cells with flat looks like scales of nuclei resting fish from on basement top view : membrane a) Lining heart & blood and lymphatic vessels (Endothelium) b) Lining serous membranes (Mesothelium) c) Lining alveoli of lungs (Pneumocytes I) d) Lining Bowman’s capsule of kidney & thin loop of Henle 2. Simple Cubical Formed of one a) epithelium layer of cube- like cells with central rounded nuclei resting on basement membrane 3. Simple Formed of one a) stomach Columnar layer of tall cells epithelium with basal oval b) Small & large nuclei resting on intestines basement membrane c) Gall bladder & large bile ducts 4. Simple Formed of one ▪ Uterus & Fallopian tubes Columnar layer of tall cells ciliated ▪ Bronchioles provided with epithelium cilia & have basal oval nuclei. The cells are resting on basement membrane. 5. Pseudo-stratified Formed of : ▪ Membranous columnar non ciliated Crowded cells, all are urethra epithelium: resting on the same Large ducts of BM, so it is simple epithelium. salivary glands Some cells are tall with central nuclei reaching the surface & other cells are short with basal nuclei and not reaching the surface Nuclei of cells appear at more than one level giving false impression  of stratification (Pseudo = false) 6.Pseudo-stratified The stereocilia Male genital system: are found to be columnar ciliated ▪ Vas deferens long microvilli with ▪ Epididymis non-motile cilia (stereocilia) 7. Pseudo-stratified The cilia are true Respiratory system: columnar ciliated &motile with ▪ Trachea Goblet cells are motile cilia & goblet ▪ Bronchi mucous cells: secreting cells B. Stratified Epithelium: ❖ It is formed of more than one layer of cells, the basal layer resting on B.M. ❖ The function of stratified epithelium is protection. ❖ It is divided according to shape & structure of cells in the top layer into: Type of epithelium Shape Sites 1. Stratified squamous Formed of 5-30 layers A. Lines & covers of epithelium: cells resting on clear & moist body surfaces & wavy B.M. openings on the skin: divided into 2 subtypes Basal cell layer is o Cornea columnar with basal oval o Oral cavity nuclei o Esophagus Intermediate layers are o Anal canal polygonal crowded cells o Vagina A. Non keratinized with o Tip of urethra minimal intercellular StratifiedSquamous substance. epithelium Top layer is formed of flat cells with flat nuclei. This type of epithelium may be keratinized or not. In case of the keratinized type: The top layer is covered with keratin scales. B. keratinized Stratified Squamous epithelium B. Present all over the body on the skin& lining dry openings on the skin: ▪ Epidermis of skin ▪ External ear ▪ Nasal orifices 2. Stratified Formed of 2-3 layers of ▪ Ducts cubical of cubical cells epithelium: sweat glands 3. Transitional epithelium: o It is a highly specialized Urinary system: type of stratified cuboidal ▪ Pelvis of ureter epithelium ▪ Ureter o It is capable of a great degree of stretch ▪ Urinary bladder to be suitable for lining ▪ Prostatic the urinary tract male urethra passages o This type can change its thickness according to State of stretch of urinary bladder: Empty bladder: 4-8 layers of cells resting on non-clear - non wavy B.M Basal cells are low columnar or cuboidal Intermediate layers are polygonal with wide intercellular spaces containing mucous like substance, allowing gliding of cells Superficial cells are large, rounded with convex free border & may be binucleated Full bladder ▪ Becomes 2-3 layers only due to gliding of cells over each other ▪ Cells is Superficial & intermediate layers become flattened. 4. Stratified columnar Similar to stratified squamous epithelium: epithelium, but with few layers& the top layer is formed of columnar cells, which may be ciliated or not. divided into 2 subtypes A. Stratified columnar non ciliated epithelium Recto-anal junction Penile male urethra large ducts of glands B. Stratified columnar ciiated epithelium ▪ Fetal esophagus ▪ Soft palate  II. Glandular Epithelium Glandular epithelium is formed of epithelial cells modified to give secretion Glandular epithelium can be classified according to: 1) Presence or absence of ducts 2) Number of cells forming the gland 3) Nature (type) of secretion 4) Mode (mechanism) of secretion 1) Presence or absence of ducts: Exocrine Endocrine Mixed glands glands glands Formed of 2 portions: Formed of 2 Formed of 2 a- Secretory units components: parts:exocrine part structure forming the secretion with duct system a- Groups of secretory &endocrine part which b- duct system to carry cells pour their the secretion from is ductless secretion into secretory units outside the gland b- Blood capillaries To reach blood stream & go to target tissues No duct system  Salivary glands Thyroid gland Pancreas Sweat glands Suprarenal glands liver Examples  2) Number of cells forming the gland Unicellular gland Multicellular gland Structure Formed of one cell Formed of several cells Example Goblet cell : All glands e.g. Salivary glands Unicellular mucous secreting cells Thyroid gland Scattered in the epithelial lining of the Digestive & respiratory Systems Flask shaped with slender base containing the nucleus and organelles &expanded apical part  3) Nature (type) of secretion: Nature (type of secretion) Example 1 Watery secretion Sweat gland 2 Serous secretion Parotid gland & pancreas 3 Mucous secretion Sublingual salivary gland & goblet cells 4 Mucoserous secretion Submandibular salivary Gland 5 Fatty secretion Sebaceous gland 6 Waxy secretion Glands of external ear 7 Cellular secretion Ovary & testis III. Neuroepithelium It is a specialized type of epithelial tissue, formed of cells modified to receive stimuli It consists of 3 types of cells: hair cells for perception of stimuli, provided at its base with nerve endings, sustentacular cells for support &basal cells acting as stem cells. Sites: 1-Tongue ---------- Taste buds 2-Nose----------- Olfactory epithelium 3-Inner ear------------ Organ of Corti  IV. Myoepithelium It is a specialized type of epithelial tissue, formed of cells modified to be contractile (contain abundant actin filaments in the cytoplasm). They are present around secretory cells, between the base of cells & the basement membrane Function: help secretory cells to squeeze & evacuate the secretion &are called basket cells. Sites: salivary & mammary glands  CONNECTIVE TISSUE PROPER Connective tissue is the tissue which binds & connects organs together & tissues in the same organ together. it is composed mainly of fibers, ground substance and cells. Ground substance Ground substance is a colorless and transparent substance presents between cells and fibers which binds them together. It is mixture of polysaccharides: glycoproteins and proteoglycans. These polysaccharides are secreted by fibroblasts. Ground substance also contains water and mineral salts. There is a very small quantity of fluid, called tissue fluid that is similar to blood plasma in its content of ions. Fibers of connective tissue: Collagen fibers: - Are flexible and have a high tensile strength. - In the light microscope they are stained pink with Eosin. When examined in the EM, collagen fibers appear as bundles of fine collagen fibrils. - Collagen fibrils are made of protein molecules, tropocollagen. The fibrils have cross striation (a banding pattern) under E/M - Collagen is a key element of all connective tissues & is the most abundant protein in the human body representing 30% of its dry weight. - Collagens are secreted by fibroblasts and several other cells - There are many types of collagens the most important of which are: Collagen type I: represent 90% of body collagen, present in skin, bone, tendons, ligaments. Collagen type II: in hyaline and elastic cartilage, 44  Collagen type III: forms reticular fibers. Reticular fibers -Reticular fibers consist mainly of collagen type III and glycoprotein. -These fibers are characteristically stained black by silver stain so, they are termed argyrophilic. -It provides a supporting framework for the cells of various tissues i.e. liver, spleen, lymph nodes & kidney. Yellow elastic fibers - Elastic fibers have physical properties similar to those of rubber, allowing tissues to be stretched or distended and return to their original shape & size. -They are thin wavy branching fibers, yellow in color in fresh state, made of elastin protein. They are present in the wall of large blood vessels, as aorta, also present in ligamentum nuchae. - Elastic fibers are stained yellow by van Gasion stain. CONNECTIVE TISSUE CELLS: 1. Fixed: fibroblasts – fibrocytes, undifferentiated mesenchymal cells, pericytes, endothelial cells, reticular, fat cells and histiocytes (fixed macrophages). 2. Free: free macrophages, plasma cells, pigment cells, mast cells, and leucocytes 45 Fixed connective tissue cells: 1- Fibroblasts: Fibroblasts synthesize and secrete collagen and elastin, as well asthe ground substance.. Irregular shape, many short and sharp cytoplasmic processes Pale, oval nucleus, rich in euchromatin & prominent nucleolus Basophilic cytoplasm rich in rER and Golgi apparatus and many ribosomes. Fibrocytes: spindle shaped cells, smaller than fibroblasts, cytoplasm poor in organelles, with less rough endoplasmic reticulum. 46 2- Undifferentiated Mesenchymal Cells (UMCS): They are similar to fibroblasts, but smaller and are found in the embryonic CT. They act as stem cells can differentiate to give the other types of CT cells. 3- Reticular cells: star shaped cells with long processes by which they are interconnected, synthesize collagen type III which forms reticular fibers. Together with reticular fibers, they form the background of organs. 4- Adipocytes (fat cells): they are two types 1- unilocular 2- Multilocular Unilocular adipocytes: Spherical cells with one large fat vacuole fill the cytoplasm. Each cell appears with thin ring of cytoplasm & eccentric flattened nucleus surrounding the vacuole dissolved lipid droplet in hematoxylin and eosin section giving signet ring appearance. Multilocular adipocytes: Polygonal cells, smaller than unilocular. Spherical nucleus usually in the center of the cell. In the cytoplasm, many fat vacuoles of different size. 47  Present in brown adipose tissue in newborns and hibernating animals. Produce heat to warm the body, on exposure to cold (the energy not stored in ATP form during beta oxidation of fatty acids). 5- Macrophages -Macrophages are characterized by their phagocytic ability and removal of dead cells, tissue debris, or other particulate material, present in the connective tissue of most organs and are often referred to as “histiocytes”. - They have a characteristic irregular surface, acidophilic cytoplasm & an eccentrically located, oval or kidney- shaped nucleus. -In the E/M, macrophages are shown. They have a well- developed Golgi apparatus and many lysosomes. - Macrophages are derived from bone marrow precursor cells (monocytes) that circulate in the blood. 48 Free connective tissue cells: 1- Plasma cell - Plasma cells are derived from B- lymphocyte. They are antibody- producing cells. - These large, ovoid cells have basophilic cytoplasm due to their richness in rER. - The nucleus of the plasma cell is generally spherical but eccentrically placed with the appearance of a clock face or cart wheel. - Function: Synthesis of immunoglobulins (antibodies). 2- Mast cell: Mast cells are oval or irregularly shaped connective tissue cells. - The cytoplasm is filled with basophilic secretory granules. - The nucleus is spherical centrally situated and often obscured by abundant secretory granules. -Mast cells function: Secretion of heparin which is an anticoagulant Secretion of histamine which initiates allergic reactions  3- Pigment cells (melanocytes): They have oval cell body with long cytoplasmic processes. Their cytoplasm contains granules with melanin pigment. Function: Protection against UV – rays 4- Free Macrophages: They are wandering cells, derived from blood monocytes, which enter the connective tissue upon need. They are phagocytic cells that participate in the immunological responses. 5- leucocytes (white blood cells): discussed later in blood. Types of CT 1- Connective tissue proper: a. loose connective tissue b. Dense connective tissue (regular – irregular) 2- Connective tissue with special properties a. Elastic b. reticular c. Adipose d. embryonic (mesenchymal, mucous)  3- Specialized CT a. Cartilage. b. Bone tissue. c. Blood. d. Lymphatic tissue 1- Connective tissue proper: a- Loose connective tissue: it contains potential areolae (spaces). It is soft flexible and distributed widely in the body. It supports other body tissues. b- Dense connective tissue: It consists of the same component of loose connective tissue but there are fewer cells and a clear predominance of collagen fibers. Its less flexible and more resistance to stress than its loose connective tissue. It has two types: - Regular - Collagen fibers are regularly arranged - Tendons are the most common example of this tissue. - Irregular - collagen fibers are arranged in bundles without a definite orientation and provide resistance to stress in all directions e.g. sclera of eye 2- Connective tissue with special properties: a- Elastic connective tissue: - Elastic connective tissue is composed of bundles of thick, parallel elastic fibers. - They are present in yellow ligaments of vertebral column. b- Reticular: - It is a special type of loose connective tissue that provides the architectural framework of organs.  c- Embryonic (mesenchymal or mucous): - Mucous tissue has abundance of ground substance composed chiefly of hyaluronic acid. It is a jelly- like tissue containing very few fibers. - The cells in this tissue are mainly fibroblasts with UMC. Mucous tissue is the principle component of the umbilical cord. It is referred to as Wharton’s jelly. It is present also in pulp of growing teeth. d- Adipose connective tissue: Adipose connective tissue is a special type of connective tissue in which adipose (fat) cells predominate. - It represents 15- 20% of body weight in normal weight men and 20- 25% of body weight in normal weight women. Classification: there are two types of adipose tissue Unilocular type Multilocular Type Structure unilocular adipocyte type multilocular adipocyte type Sites Mammary gland & Subcutaneous tis In new- born & hibernating animals Function Storage of fat and insulation of heat On exposure to cold, it releases he Support of soft organs. to warm body. Colour Whitish in colour Brownish in colour N.B. - The multilocular type is called brown fat due to the large number of blood capillary in their tissues and numerous mitochondria in their cells. -No One of adipose tissue is transformed into another.  Special Connective Tissues CARTILAGE Cartilage is an avascular specialized fibrous connective tissue. It has a firm extracellular matrix to bear mechanical stress. Types of cartilage The three types of cartilage according to matrix components and type and amount of fibers in the matrix into: hyaline cartilage, elastic cartilage, and fibrocartilage 1-Hyaline cartilage Hyaline cartilage is the most abundant and typical structure of cartilage in the body.  1- Sites: 1- Costal cartilage 2- Articular cartilage 3- Cartilage of nose, larynx and trachea 4- Most skeleton of the fetus 5- Epiphyseal plates of long bones 2- Structure: a. Perichondrium Is a layer of dense, irregular connective tissue that surrounds hyaline cartilage except at articular surfaces, It consists of: - Outer fibrous layer containing type I collagen, fibroblasts, and blood vessels. - Inner cellular layer containing chondrogenic cells and chondroblasts. It provides the nearest blood supply to the avascular cartilaginous tissue. b. Cartilage cells 1. Chondroblasts Origin: derived from mesenchymal chondrogenic cells, which present within the inner layer of the perichondrium. L/M: ovoid, when located deeper they are more spherical in shape and surrounded by the matrix. Deep basophilic cytoplasm and flat to ovoid pale nucleus. It can divide. E/M: these cells contain an extensive Golgi complex, abundant rough endoplasmic reticulum (rER), lipid droplets, and glycogen. Functions: -They form the cartilage matrix & fibers (collagen type II). -Growth of cartilage from outside. 2. Chondrocytes: are mature cartilage cells that are embedded within lacunae in the matrix. Origin: They arise from chondroblasts. Once these cells become totally trapped by matrix and imprisoned in spaces called lacunae, they are referred to as chondrocytes. L/M: Superficial chondrocytes are oval while deeper ones are rounded with pale basophilic cytoplasm and dark stained nucleus. They are located with their longitudinal axis parallel to the cartilage surface. Those located deeper occur in groups of four to eight cells (isogenous groups) or (cell nest). E/M: They contain abundant rER, extensive Golgi complex and mitochondria. The cytoplasm is rich with glycogen and fat. Function: they maintain the cartilage matrix by secretion of matrix and fibers around them. c. Cartilage Matrix & Fibers 1- Ground substance is composed of an amorphous substance containing mainly sulfated glycosamines: hyaluronic acid, chondrotin sulfate and keratin sulfate. It is basophilic. 2- Fibers which is type II collagen, is embedded in the matrix but not appear by the L/M as it is very thin and has the same refractive index of the matrix. 2.Elastic cartilage Elastic cartilage has yellowish color in fresh state It is covered by a perichondrium. It is similar to hyaline cartilage with a network of elastic fibers together with type II collagen fibers. It is located in areas where flexible support is required: -Ear pinna -Eustachian tube External auditory meatus -Epiglottis  3. Fibrocartilage -It is not covered with perichondrium. -It is a tough cartilage important in bone relation. -It has characters between dense connective tissue and hyaline cartilage, so it is called fibrocartilage. Structure: It is formed of alternating rows of chondrocytes surrounded By scanty matrix and thick parallel bundles of type I collagen fibers. Site: Fibrocartilage is in areas where support and strength are required. -Intervertebral disks -Symphysis pubis. -Lips of the glenoid & acetabular cavities. -Sternoclavicular joint  BONE It is a type of specialized CT characterized by hard matrix (calcified type). It is not traversed by blood vessels, nerves, or lymphatics, and entirely nourished by diffusion through canaliculi. Bone is composed of: 1- Bone Matrix 2- Bone cells 3– Periosteum 4- Endosteum Bone Matrix It forms the bulk of bone and composed of: I. The inorganic (calcified) portion of the bone matrix: It represents about 65%of the dry weight of bone matrix. It consists mainly of calcium and phosphorus II. The organic portion of the bone matrix: It represents about 35%of the dry weight of bone matrix. It consists mainly of: a) Type I collagenous fibers It forms with hydroxyapatite crystals the bone lamellae (i.e. layers of calcified collagenous fibers). The lamellae are separated by lacunae which intercommunicate by canaliculi. b) The ground substance formed of: - Mucopolysaccharides (chondroitin sulphate and keratin sulphate). Glycoproteins of bone: osteocalcin, osteopontin and osteonectin.  Bone cells 1- Osteogenic cells or osteoprogenitor cells: Origin: from embryonic mesenchymal cells and pericytes around the capillaries. Site: in the inner osteogenic layer of periosteum and in the endosteum. L/M: These are flat cells with flattened nuclei and pale basophilic cytoplasm. E/M: Rich in rER, ribosomes, Golgi apparatus and mitochondria. Function: in times of need e.g. bone fracture or growth they can divide and differentiated into osteoblast. 2-Osteoblasts (The bone forming cells) Origin: derived from osteogenic cells. Sites: on bony surfaces, inner osteogenic layer of periosteum and in the endosteum. L/M: cuboidal or ovoid cells with few cytoplasmic processes with oval vesicular eccentric nuclei and deeply basophilic cytoplasm with -ve Golgi image. EM: They show plenty of ribosomes, rER, mitochondria and well-developed Golgi apparatus.  Functions of osteoblast: a) They are the bone forming cells form organic components & deposit inorganic components by alkaline phosphatase enzyme. e) They converted into osteocytes when their activity declines. 3- Osteocytes (Mature bone cells-bone preserving cell) Origin: derived from osteoblasts. Sites: singly in the bony lacunae (can’t divide) in bone matrix. L/M: small, branched cells with multiple cytoplasmic processes passing through canaliculi, the cellular processes of osteocytes connected together by gap junctions. They have central oval deeply stained nuclei and lightly basophilic cytoplasm. E/M: Few free ribosomes, rER, small Golgi and mitochondria. Functions: a) They preserve the bone matrix by continuous deposition of calcium salts by their alkaline phosphatase enzyme. b) They may be playing a role in mobilization of calcium from the bone to the blood in times of need. 4- Osteoclasts (Bone Destroyers) Origin: derived from fusion of blood monocytes. Site: inside a depression in the matrix known as Howship’s lacuna found on the bone surfaces. L/M: irregular cell with brush border (striated border facing bone surface). It is multinucleated cell (up to 50 nuclei) with acidophilic foamy cytoplasm. E/M: - rich in lysosomes. -Functions: Bone resorption (osteolysis during ossification and healing).  Periosteum Definition: It is a vascular non- calcified connective tissue membrane covering the bone on its external surfaces except at synovial articulations. It is formed of two layers: 1. Outer fibrous layer: formed of dense irregular C.T. with abundant collagenous fibers, few elastic fibers, fibroblasts, fibrocytes and blood vessels and nerves. 2. Inner cellular osteoprogenitor (osteogenic) layer formed of loose C.T, blood vessels, osteogenic cells and osteoblasts when stimulated during growth or fracture they can divide and differentiate into bone cells. Perforating fibers of Sharpey: Definition: These are type I collagen fibers (calcified or non-calcified) attaches the periosteum to the bone surface. They fixed the periosteum to the bone, Endosteum -It is a thin specialized C.T. that lines the bone marrow cavities. -It is made of one layer of osteogenic cells and osteoblasts. specially at attachment site of a tendon, ligaments, or muscle. Classification of Bone There are two main types of bone a- Compact (Dense) bone. b- Cancellous (Spongy) bone a- Compact (Dense) bone: appears solid. 1- Sites: a- Shafts of long bones b- Outer and inner tables of flat bones of skull c- Outer covering of flat bones (e.g. ribs, sternum), short bones (e.g. phalanges) and  irregular bones (e.g. vertebrae). 2- Collagen fibers & osteocytes are arranged regularly in the form of lamella. Structure: a- Periosteum b- Endosteum c- Organization of bone lamellae in compact bone: are deposited in a regular pattern: 1- Outer or external circumferential lamellae: They are subperiosteal and parallel to the outer circumference of the bone 2- Haversian system (osteon): a- They are the structural units of compact bone. b- They are long cylindrical structures that run parallel to the longitudinal axis of the bone.Each is formed of 5-20 circular lamellae, osteocytes in their lacunae are present between lamellae. These lacunae are connected together by canaliculi, through which they get their nutrition. d- These lamellae surround a central canal (Haversian canal). e- Haversian canals contain loose C.T. rich in vessels (blood and lymphatics) and nerves. They are lined by osteogenic and osteoblasts. f- The Volkmann's canals are transverse and oblique canals connecting the Haversian canals together and with the periosteum and bone marrow cavity. They have the same contents of the Haversian canals. 3- Interstitial lamellae: They are consisted of irregularly arranged lamellae in between Haversian systems. 4-Inner or internal circumferential lamellae: it lines the bone  Cancellous (Spongy) Naked eye examination: it looks spongy, with many holes separated by irregular trabeculae. Sites: a- Epiphysis of long bones b- Diploe of flat bones of skull c- Young embryonic bone d- Bodies of flat bones (e.g. ribs, sternum), short bones (e.g. phalanges) and irregular bones (e.g. vertebrae). Structure: - It consists of interconnected branching and anastomosing bony trabeculae, surrounding irregular bone marrow cavities. - It has no Haversian system. - Osteocytes in their lacunae are irregularly arranged & nourished by diffusion through their canaliculi from marrow cavities. - Its outer surface is covered by periosteum, endosteum lines irregular marrow cavity.  Muscular Tissue General Characteristics of Muscles: The cell membrane of these muscle fibers is known as sarcolemma. The cytoplasm of these muscle fibers is known as sarcoplasm & contains all cell organoids and cell inclusions The cells contain contractile elements (myofibrils) formed of specially arranged myofilaments (thick, thin & intermediate) Muscle fibers are classified into 3 types according to structure & function: 1. Skeletal muscle: Striated & voluntary 2. Cardiac muscle: Striated & involuntary 3. Smooth muscle: Non-striated & involuntary Skeletal muscle Sites: ▪ The skeletal muscles are attached to the skeleton, they form the muscle of the limbs, neck and trunk. They are present also in the diaphragm, tongue, muscles of the face, of the eye ball, pharynx and upper third of esophagus. ▪ Skeletal muscles are voluntary muscles except those in the upper third of esophagus, some muscles of the pharynx and the cremasteric muscles of the spermatic cord. Shape and size: ▪ Skeletal muscle fibers (fiber=cell) are long cylindrical (1-40 mm length) & appear polygonal in cross sections (10-100 um diameter) ▪ Fibers don’t branch (except in tongue & face) ▪ ▪ The skeletal muscle fibers are arranged in bundles. Connective Tissue of skeletal muscle: ✓ Every skeletal muscle is surrounded from outside by a dense connective tissue sheath called the epimysium. ✓ The skeletal muscle fibers are arranged in bundles. ✓ The bundles of fibers are separated from each other by CT tissue sheath called the perimysium.  ✓ Each muscle fiber itself is surrounded by a delicate layer of CT called the endomysium composed mainly of basal lamina and reticular fibers The role of connective tissue is: Transmission of the forces generated by contracting muscle cells. It carries the blood vessels, nerves and lymph vessels to muscle fibers. C.T. also firmly attach the muscle bundles together Structure: 1- LM: ▪ Cell membrane (sarcolemma): is distinct ▪ Nuclei: are multiple, oval & peripheral in position. ▪ Cytoplasm (sarcoplasm): is acidophilic & shows clear transverse striations of alternating dark and light bands 2- Polarized Microscope The dark band is called anisotropic or A band because it doubly refractive to polarized light and appear dark in fresh state. The light band is called isotropic or I band because it singly refractive to polarized light and it is pale in fresh fibers. 3- EM: o The sarcoplasm contains all cell organoids and cell inclusions, mainly myofibrils and in-between minimal amount of cytoplasm: Membranous organelles: 1- Numerous Golgi bodies, 2- Well-developed modified SER named sarcoplasmic reticulum and associated with myofibrils, 3- Rows of mitochondria in-between myofibrils 4- Few RER. Non membranous organelles 1. Well-developed parallel longitudinally arranged myofibrils, composed of myofilaments (thick & thin) & show the banding pattern of alternating dark & light bands. 2. Few ribosomes Inclusions 1- Abundant myoglobin, which is an oxygen binding protein; like haemoglobin. It acts as oxygen - storing pigment which is necessary for the high oxidative phosphorylation level. Iit is responsible for the red color of muscles 2- numerous beta glycogen granules serves as a source of energy for muscle contraction 3- Intramyocellular lipids Myofibrils ❖ Definition: The myofibrils are the contractile threads which are arranged longitudinally in the sarcoplasm of each muscle fiber. Shape & Structure: The arrangement of myofibrils near each other shows transverse striations. The transverse striations in the muscle fibers are due to presence of alternating dark and light bands on each myofibril. Each dark band of one myofibril is present beside the dark band of the adjacent myofibril. These arrangements of dark and light bands give the muscle fiber the appearance of transverse striations. The myofibrils are formed of two types of myofilaments. 1- Thick filaments (15 nm) present in A dark band which are formed of protein known as myosin. 2- Thin filaments (5 nm) are formed of proteins: actin, troponin and tropomyosin present in the I light bands and extend for a short distance in the A dark bands. The light I band contains only thin actin myofilaments which are attached to zigzag dark Z line. The dark A band contains both thin actin and thick myosin myofilaments. In relaxed fiber the middle of the dark band is pale and contains only myosin and called (Hensen`s) H zone. Condensation of myosin in the middle of H zone forms dark (membrane) M line. At the site of overlapping of thick & thin filaments, one thick filament is surrounded by 6 thin filaments (hexagon). Desmin & vimentin intermediate filaments are responsible for linkage of sarcomeric units, and in particular the Z disk, transversely to other Z disks and to the plasma membrane Item Light band (I Dark band (A band) band) LM Pale Dark acidophilic acidophilic EM Light with Dark with central dark lighter H zone Z line & middle dark M line Polarized Singly Doubly microscop refractile refractile e Isotropic Anisotropic(Bir efringent) Molecular Only thin Both thick & structure myofilaments thin myofilaments The sarcomere: ▪ It is the functional and the structural unit of the muscle. ▪ It is the distance between two successive Z lines. ▪ Each sarcomere includes the whole dark band and half of the two light bands on both sides of the dark band. ▪ The region of the sarcomere which contain both actin and myosin filaments appears darker than the region which contains actin filaments only. ▪ The H band appears lighter because it has only myosin filaments.  ▪.When the sarcomere contracts, the actin filaments on either side of the H hand approaches each other to make the H band not seen from the other regions of the dark band. Sarcoplasmic reticulum: ✓ They are smooth endoplasmic reticulum. ✓ Each myofibril is surrounded by a network of sarcoplasmic reticulum formed of thin tubes and sacs which are interconnected with one anther. ✓ At the regions of the A-I junction the sacs are wider and are called the terminal cisternae. T- tubule: ✓ It is a transverse tubule between each 2 neighboring terminal cisternae. It is formed by the invagination of the sarcolemma. ✓ It extends transversely to encircle the sarcomeres like collars at the A-Ijunction. ✓ All the T- tubules of a muscle fiber are together called the T- system. The Triad tubular system: ▪ Formed of two terminal cisternae of sarcoplasmic reticulum with a T tubule in between. ▪ The terminal cistemae in successive triads are joined by smaller tubules of the sarcoplasmic reticulum forming fenestrated collars around the sarcomeres. ▪ It is present at the A-I junction. ▪ The role of Tubular System: The T-tubules and the surrounding Two Sarcoplasmic Tubules control muscular contractions by regulating the concentration of calcium ions within the myofibrils of skeletal muscles. Calcium ions facilitate the interaction between actin and myosin filaments. The triads play an important role in conducting the waves of excitation to the myofibrils Types of skeletal muscle fibers: According to the amount of myoglobin, the type of innervation and the mode of contraction, the muscle fibres of skeletal muscles are classified into: Type I fibers (Red fibers): hey have small diameter, contain large amount of mitochondria and myoglobin which is responsible for the red color of this type of fibers. They are highly vascular, contract slowly and can sustain contraction for a long time without fatigue. Their energy is derived from oxidation of fatty acids. Type IIa fibers (White fibers): They have large diameter, contain small amount of mitochondria and myoglobin and contract faster but they become easily fatigued.. Their energy is derived from glycolysis. Type IIb fibers (Intermediate fibers): They have intermediate characters between the previous 2 types. Skeletal muscles contain the three types of muscle fibers, but the white fibers predominate. Diaphragm and muscles of mastication consist of red type of muscle fibers. SMOOTH MUSCLE It is non striated, involuntary muscle. Site: in the wall of the lower third of oesophagus, the wall of stomach, intestine, gall bladder and wall of salivary and pancreatic ducts. In the respiratory, Urinary, and genital systems and in arteries, veins, and larger lymphatic vessels, in the dermis  Shape: are elongated, spindle-shaped cells with oval central nucleus Size: they vary with location, being only 20 microns or less in length around small ducts and blood vessels, but reaching 500 micron in the pregnant uterus. At L/M level: The nucleus: is single, oval and central in position. The cytoplasm: is homogenous acidophilic. At E/M level Attachment plaques: Small darkly staining patches along the surface of plasmalemma and Dense bodies in the sarcoplasm. Cytoplasm is rich in mitochondria, few granular endoplasmic reticulum,free ribosomes, a small Golgi apparatus. glycogen, and a few lipid droplets also present. Sarcolemma shows vesicular caveoli (invaginations). T tubule sare not present in smooth muscles. No sarcomere. The sarcolemma: Is covered externally by a basal lamina. Sarcolemmae of adjacent cells form nexuses or gap junctions that permit rapid passage of an electrical impulse from one cell to another Myofilaments: 1- Thin myofilaments and thick myofilaments: -They do not show the regular arrangement seen in striated muscle. 2- The intermediate filaments 85 - Contain the protein desmin and vimentin and attach to the attachment plaques and dense bodies, forming a framework or skeleton in the cell.  Blood Blood, is a fluid that moves through the vessels of a circulatory system. In humans, it includes plasma (the liquid portion), blood cells (red and white varieties), and cell fragments called platelets. Formed elements of blood Erythrocytes (red blood corpuscles (RBCs) Shape: A red blood cell is a small and biconcave disc measure about 6 to 8 micrometers in diameter (average = 7-8 um) with an average thickness of 2 micrometers. Mature RBCs have no nuclei and possess no organelles but are filled with hemoglobin (Hb).Iron in the hemoglobin is responsible for its red appearance. Life span: The average life span of RBC is 120 days. Aged RBCs are destroyed by splenic, hepatic, and bone marrow macrophages. Number: The normal number of RBCs is: Male: 5 - 5.5 millions\mm³ blood Female: 4.5 - 5 millions\mm³ blood Function of R.B.Cs: Transport of CO2 and O2 to and from the tissues of the body. Variable abnormal erythrocyte morphology 1- Anisocytosis: great variation in the size of R.B.Cs. it may be: a- Microcytosis: RBCs smaller than the normal sizeas in iron deficiency anaemia and thalassemia. b- Macrocytosis: RBCs larger than the normal size as in megaloblastic anemia in vitamin B12 deficiency. 1-Variation in shape Spherocytes: RBCs lacks the biconcave shape and becomes more spherical as in hereditary spherocytosis. Ovalocytes: Oval shaped RBCs. 3-Variation in color -Hypochromic (lightly stained R.B.Cs): decrease amount of Hb as in iron deficiency anaemia. -Hyperchromic (darker R.B.Cs): increase amount of Hb 4-Variation in number: 1- Polycythemia: is the increase in number of RBCs above the normal range as in heart and lung diseases. 2- Anemia: is the decrease in number of RBCs below normal range as in as hemolytic anaemia. Or decrease in amount of HB as in iron deficiency anemia. Leukocytes (white blood cells) White blood cells (W.B.Cs), also called leukocytes, are true cells with normal nucleus and cytoplasmic organelles. They are involved in immune responses, recognizing and neutralizing invaders such as bacteria and viruses. Classifications: They are classified according to the presence or absence of granules and their type in the cytoplasm and shape of the nucleus into 2 groups. a- Granular leucocytes: Neutrophils, Eosinophils and Basophils. b- Agranular leucocytes: Lymphocytes and Monocytes. c- Total number of leucocytes\mm³ of blood d- Normal count: 4.000 – 11.000\mm³ of blood. e- *Leucocytosis: increase in the total leucocytic count above 11.000\mm³ Causes: 1-Physiological: as in pregnancy, after meals, newly born infant. 2-Pathological:as in acute bacterial infections. f- *Leukopenia: decrease in total leucocytic count below 4.000\mm³ g- Causes: irradiation, prolonged use of certain antibiotics. h- Granulocytes possess two major types of cytoplasmic granules: nonspecific granules which are lysosomes (appear only by electron microscpe) and specific granules that bind neutral, basic, or acidic stains (appear by both light & electron microscpe). i- Agranulocytes, have nonspecific granules (lysosomes) but they do not contain specific granules. The nucleus is spherical or indented but not lobulated. This group includes lymphocytes and monocytes. The differential count (percentage of all leukocytes) for each type of leukocyte is also presented in Table.  Granulocytes (granular leukocytes) 1- Neutrophils (Polymorphonuclear Leukocytes) -Percentage: 54- 62% of circulating leukocytes. -Size: neutrophils are 12-15 μm in diameter in blood smears. -Nucleus has 3- 5 lobes linked by thin chromatin threads. In females the nucleus of neutrophils, showing inactive X chromosome, which appears as a drumstick-like appendage on one of the lobes of the nucleus and called Barr body. -The cytoplasmic granules: are nonspecific granules (lysosomes) which appear as large, dense vesicles and specific granules which are smaller and less dense and stained faintly pink. - Life Span: Less than one week. -Function: microphage. 2- Eosinophils -Percentage:1- 3% of leukocytes. -Size: 12-15 μm in diameter. -Nucleus: bilobed or horse shoe. -The cytoplasmic granules: Nonspecific granules (lysosomes) and specific granules which are abundant, large granules stained red or dark pink. -Life Span: Less than two weeks. -Function: anti-parasitic activity - participating in immediate allergic reactions. Basophils cytoplasmic granules. -The cytoplasmic granules: Non-specific granules (lysosomes) and specific granules which are large (0.5 μm in diameter), irregularly shaped & stained dark blue. The strong basophilia of the granules is due to the presence of heparin. These granules also contain histamine.  3- Percentage: less than 1% of blood leukocytes and are therefore difficult to find in normal blood smears. 4- -Size: Basophils are also 12 - 15 μm in diameter. 5- -Nucleus: The nucleus is divided into two irregular lobes, which may be obscured by 6- Life Span: Very long 1 - 5 years 7- -Function: involved in allergic inflammation. Agranulocytes (non granular leukocytes) 1) Lymphocytes - Percentage: 25 -33% of total number of leucocytes. Lymphocytosis: increase number of lymphocytes. It occurs in some chronic infections e.g., tuberculosis, syphilis. - Life Span: Few days to many years - Size: according to the size there are small – medium &large lymphocytes.  Small lymphocytes Medium –Large lymphocytes Percentage: 92% 8% Size: 6 – 8 µm 10 – 18 µm Nucleus: single, rounded with Large with less indentation slight indentation at one side and lightly stained and deeply stained Cytoplasm: Thin rim of pale More amount of cytoplasm blue cytoplasm around the nucleus,. Types: T lymphocytes, B lymphocytes - Function: 1- T -lymphocytes: begins its development in bone marrow, then it completes the development in the thymus. It has different subtypes (T helper, T memory, T cytotoxic & T suppressor). Function: cell-mediated immune response (cellular immunity). 2-B- lymphocytes: develop in the bone marrow. Function: humeral immune response (production of antibodies)  2- Monocyte Percentage: 3- 8% of total number of leucocytes. Monocytosis: increase number of monocytes. It occurs in some chronic infections e.g., tuberculosis, syphilis. Size:12 - 20 µm in diameter (the largest leucocyte) Life Span: 3 days in the blood - In the C.T several months. Nucleus: Single large eccentric nucleus, pale stained, kidney-shaped or horse-shoe shaped. Cytoplasm: Large amount of cytoplasm, basophilic with a faint grayish stainability (frosted-glass appearance), rich in non-specific granules (Lysosomes). Platelets Platelets, also called thrombocytes, are cell fragments of a large cells called megakaryocytes & are involved in blood clotting. -Number: 250.000 – 400.000 \mm³ of blood. - -Size: 2 - 4µm in diameter. - Strucure: Platelets are roughly small disc-shaped non- nucleated structures. It consists of Two zones: Hyalomere: Peripheral pale clear zone which contains actin filaments, electron dense microtubules & vesicles in electron microscopy. Granulomere : basic central granular region which contains mitochondria, lysosomes, glycogen granules, calcium ions, ADP,ATP, and dense bodies. -Function: blood clotting Blood film