Histology - Menoufia University Faculty of Dentistry - PDF

# Histology ## Menoufia University Faculty of Dentistry ## Histology ### First Year By Staff Members of Histology & Cell Biology Department 2024 - 25 ## Vision To be academically accredited college with local, regional, and international reputation for having a leading role in the field of medi...

# Histology ## Menoufia University Faculty of Dentistry ## Histology ### First Year By Staff Members of Histology & Cell Biology Department 2024 - 25 ## Vision To be academically accredited college with local, regional, and international reputation for having a leading role in the field of medial 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. ## Contents ### Index | Topic | Page | |---|---| | Overall aims of the course | | | Intended Learning Outcomes | | | The Cell | | | Cytogenetic | | | Epithelial Tissue | | | Connective Tissue | | | Cartilage | | | Bone | | | Muscular Tissue | | | Blood | | ## 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). * Undersand 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 ## Histology It is the science that deals with the microscopical study of normal tissues. ("Histo" means tissue and "logia" means study). ## The Cell * A diagram shows the following parts of a cell: Lysosome, Smooth endoplasmic reticulum, Free ribosome, Centriole, Cytoplasm, Mitochondrion, Rough endoplasmic reticulum, Plasma membrane, Cell coat, Nucleus, Nucleolus, Chromatin, Nuclear pore, Nuclear envelope, Golgi body, Ribosome ## 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. ### Organelles: Are differentiated metabolically active units of living matter, essential for vital processes of the cell (respiration, digestion, secretion, excretion, growth ... etc.). ### 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. 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 * A diagram showing a cell containing various structures as seen with electron microscope (E/M): Macrovesicles (secretory vesicles), Peroxisomes, Lipid, SER, Ribosomes, Mitochondria, Glycogen, Microfilament, Microtubules, Microvilli, Lysosomes, Junctional Complex, Centrioles, Cell membrane, Golgi complex, Microvesicles, Nucleus & nucleolus, Mitochondria ## The Cell Membrane (Plasmalemma) ### 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). ### 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. * A diagram shows the ultrastructure & molecular organization of a cell membrane.  ### 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. ## 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 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. ## 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.** ## Mitochondria * A diagram shows the following parts of a Mitochondria: Inner membrane, Matrix, Outer membrane, Cristae, F1 particle, DNA, Ribosome, Inter membrane space ### Structure of Mitochondria: * 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. * Structure: * Light microscope (LM): They appear as rods, granules or filaments, after staining with Iron Hx.or Janus green. * 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. ### 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). 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: * 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). * 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. * A diagram shows the following parts of Golgi complex: Endoplasmic reticulum, EXOCYTOSIS, Cell membrane, Lysosome, Endosome, Golgi, Transport vesicle, ENDOCYTOSIS. ### Functions of the Golgi apparatus: * Concentration of the secretory products * Discharge of secretory products (secretion). * It adds carbohydrates to its protein content to form glycoprotein * Formation and maintenance of cell membrane and cell coat. * Formation of lysosome ## Lysosomes * 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). ### Structure: * Light microscope (LM): They can be demonstrated by special histochemical methods. * Electron microscope (E/M): * Primary lysosomes: appear as homogenous vesicle surrounded by single membrane * 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. * Residual bodies: They contain remains of indigestible material or debris. ### Chemical Composition: * Lysosomes contain hydrolytic enzymes, active at an acidic pH (acid hydrolases) as lipase and acid phosphatases ### Functions of lysosomes: * Digestion of nutrients. * Defensive mechanism against bacterial and viruses. * Digestion of fluid droplets: The cell membrane surrounds fluid, forming pinocytic vesicles that fuse in the cytoplasm forming multivesicular bodies. * Autophagocytosis: Lysosomes can get rid of degenerated organelles as dead mitochondria. * In the thyroid gland: Lysosomes help the release of the active thyroid hormones. * During fertilization: They help the sperm to penetrate the ovum. * Removal of dead cells and autolysis after death. * Residual bodies play important role in the aging process. * A diagram shows the following parts of lysosome: Fluid molecules, Foreign matter being phagocytosed, Phagosome, Endosome, Pinocytotic vesicle, Multivesicular body, Phagolysosome, Primary lysosome or Golgi hydrolase vesicle, Secondary lysosome or endolysosome, Golgi complex * A diagram shows the following parts of a cell: Endoplasmic reticulum, Mitochondrion, Autophagosome, Bacterium, Phagosome, Phagolysosomes, Lysosome ## Endoplasmic Reticulum * General Characteristics: There are two types: Rough (Granular) & Smooth (Agranular) due to the presence or absence of Ribosomes on the outer surface. * A diagram shows the following parts of endoplasmic reticulum: Cell nucleus, Smooth ER, Rough ER, Rough ER in 3D, Transition vesicle, Ribosomes * A diagram shows the following parts of endoplasmic reticulum: Nuclear Pore, SER, RER, Ribosomes, Cisternal space, Cisternee ## Differences Between Rough and Smooth Endoplasmic Reticulum | Items | Granular or Rough Endoplasmic Reticulum (GER, RER) | Agranular or Smooth Endoplasmic Reticulum (SER) | |:---|:---|:---| | Site | Abundant in protein forming cells (plasma cells) | Abundant in lipids and steroid hormones forming cells | | L/M | Appear as basophilic areas. | Can not be demonstrated. | | Structure | A system of sheets & cavities (cisternae) bounded by membranes. Ribosomes attached to their outer surfaces. | Branching anastomosing tubules and vesicles without cisternae. No ribosomes on the outer surfaces. | | Functions | 1. Segregation of the protein, formed by the ribosomes on the surface. 2. Transfer of the protein to the Golgi vesicles. 3. Protection of the cytoplasm from the effect of the contained enzymes. 4. It provides a site for attachment of ribosomes. | 1. Synthesis and storage of fats. 2. Synthesis of steroid hormones as testosterone. 3. Glycogen formation in liver &muscle. 4. Formation of Hcl in stomach cells. 5. It helps muscular contraction, by acting as a calcium pump. 6. Detoxification of drugs and hormones. | ## Non-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. ### Structure: * They are made of ribonucleic acid (RNA) combined with a protein, present in two forms: free and attached. * A diagram shows ribosomes: Large subunit, Small subunit, mRNA, Polysomes, Free, Attached. * Free ribosomes (not attached to membranes) are small, dense, rounded basophilic granules (due to content of RNA) distributed freely in mitochondria 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. * 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. ### 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.  ### Structure:  * Light microscope (LM): * There are pair of centrioles that appear as two small bodies, after staining with iron Hx, near the nucleus. * 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. * A diagram shows a Centriole (TS): A, B, C ### 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. ## 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. ### Flagella: * They form the tails of sperms. They are similar to cilia, in structure but longer and larger. * A diagram shows a flagella: Outer fiber (doublet), Outer arm, Inner arm, Nexin bridge, Central fiber, Radial link head, Central sheath. * A diagram shows a flagella: Axoneme, Dyneins, Central pair, Spokes. * A diagram shows a flagella: Flagellar membrane, IFT, Cell membrane, Basal body ## 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 ### 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.  ### 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). ### Pigments: (endogenous or exogenous)  * **Endogenous pigments** They are formed inside the body.  * Melanin is present in skin & eye, to protect against ultraviolet rays. * Hemoglobin is the most important and essential pigment in the body, presents in RBCs to carry O2 and CO2. * 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. * Dust and carbon particles, in dust cells of lung. * Tattoo marks, in skin.  * Carotene ingested with food as carrots and tomatoes. Carotenemia (yellow color of skin as a result of too much ingestion of carrots). * Minerals: as silver and lead. ### Secretion Granules: * Include mucous, serous secretion, proteins etc... ### 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:  * Vesicular (or open face) type: Details of its components could be seen inside (e.g. nuclei of. liver cells, nerve cells). * 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. * A diagram shows the following showing parts of NUCLEUS: Euchromatin (EC), Peripheral chromatin (PC)(HC), Island of chromatin (IC), Nucleolus (NC), Nucleolus associated chromatin (NC), RER, Pore * A diagram shows the following showing parts of NUCLEUS: Nuclear lamina, Nuclear envelope, Ribosomes, EC, Hc, F, G. ### 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: * Peripheral chromatin aggregated close to the inner nuclear membrane. * Nucleolus-associated chromatin aggregated into a crust around the nucleolus. * 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 1- 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:  * Nucleolar organizer DNA: consists of DNA coding for rRNA. * Pars fibrosa: are the sites of rRNA synthesis. * 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, of DNA & duplication 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: * Abnormalities of structure: These are changes in morphology of chromosomes. * Deletion, is loss of a part of one or more chromosome. * Breaks of chromosomes & ring formation. * Inversion, is wrong reattachment of broken segments Of chromosomes. * Translocation is the transfer of segments between chromosomes. * Isochromosomes, is abnormal transverse division of the centromere separating the two arms instead of longitudinal division separating individual chromatids. * Abnormalities of number: These are changes in number by addition or loss of one or more of chromosomes. * 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). * Aneuploidy is the addition (Triosomy) or loss (Monosomy) of a chromosome and may affect autosomes or sex chromosomes. * 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. * 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.