Cytology PDF

Chapter 1 Cytology Histology is the subject dealing with the microscopical structure of normal tissues. The aim of the histology course is to help the student to understand the microanatomy of cells, tissues & organs & to correlate structure with fu...

Chapter 1 Cytology Histology is the subject dealing with the microscopical structure of normal tissues. The aim of the histology course is to help the student to understand the microanatomy of cells, tissues & organs & to correlate structure with function. The study of histology is carried out by using microscopes of different types, the commonly used types of microscopes are: 1. Light microscope (L.M) 2. Electron microscope (E.M.). ▪ Light microscopes & Electron microscopes differ in their optical resolution & magnification. Optical resolution means the least distance at which two points appear separate from one another - If the distance is less the two points will appear as one. - This distance is About 0.2 mm in eye About 0.2 μm by L.M About 0.2 nm by E.M. Maximum magnification power in case of L.M. is about X1000 while an E.M. has a greater magnification more than X100.000. Common stains used for Light microscopy Cells are colourless and usually indistinguishable by L.M. unless stained. 1. Acidic stain: e.g. eosin, it can stain basic structures, so these structures are acidophilic. 2. Basic stain: e.g. hematoxylin which stains acidic structures so these structures are basophilic. 3. Neutral stains: e.g. Leishman’s stain is a combination of an acidic & a basic stain for staining of blood cells. 4. Vital stain: It is used to stain a living structure inside living animal such as staining of phagocytic cells using trypan blue or India ink. 5. Supravital stain: It can stain a living (cell) outside a living person e.g. brilliant cresyl blue which stains reticulocytes (immature RBCs) in a blood film. 6. Metachromatic stain: it will give a new color after staining which is different from its original color. The new color develops as a result of a chemical combination between the stain & certain structures within the cell e.g. toluidine (blue stains granules within mast cell with a violet color changing of the original color of the stain at the end of staining process is called metachromatic. 7. Orcein stain for elastic fibers, they take brown color. 8. Silver stain: It can stain reticular fibers with brown or black color, it is also used to demonstrate Golgi apparatus in the cell. 9. Osmic acid: It stains myelin sheath with black colour. 10. Histochemical & cytochemical stain: These stains localize & demonstrate certain substances within a tissue or a cell depending on a biochemical reaction: a) Glycogen can be stained red by Best’s carmine. 1 b) Lipids (fat) can be stained (black) with Sudan black & orange with Sudan III. c) Enzymes can also be stained using special methods e.g. alkaline phosphatase enzymes. The cell It is the functional & structural unit of all living tissues. It is the smallest living structure which has vital properties such as growth, secretion, excretion, digestion & reproduction. The cells of the body are variable in shape, size& functions but they are similar in composition. Any cell in the body, except RBC’s& Platelets, is composed of: - Cytoplasm - Nucleus I. Cytoplasm It is formed of: 1- Cytoplasmic Matrix: It is a colloidal solution contains proteins, carbohydrates, lipids, minerals & enzymes. 2- Cytoplasmic organelles: They are permanent minute living structured that are essential for the vital processes of all cells e.g. respiration, secretion, digestion………. 3- Cytoplasmic inclusions: They are non-living temporary structures, not essential for the vitality of the cell. They are no more than stored substances within some cells e.g. glycogen, fat & pigments. Cytoplasmic organelles They are classified according to presence or absence of membranes into: - Membranous cell organelles Non membranous cell organelles: 1. Cell membrane. 1. Ribosomes. 2. Mitochondria. 2. Cytoskeleton: 3. Endoplasmic reticulum (Rough & a. Microtubules Smooth). (Centrioles & Cilia). 4. Golgi apparatus. b. Filaments 5. Lysosome's. (Thin, Intermediate & Thick) 2  a- Membranous cell organelles 1- Cell membrane Definition: It is an/ultra-thin membrane that surrounds the cell i.e. it forms an envelope or a cover for the cell. LM: It is invisible by L.M as it is very thin 8-10 nm but can be stained by Ag or PAS. E.M.: It appears as three parallel lines, two dark layers separated by a light one i.e. it is a trilamellar membrane. The cell membrane has an outer covering rich in carbohydrates called cell coat. Molecular structure of the cell membrane: - The cell membrane is composed of lipids, protein & carbohydrate: 1. Lipids component (30%): o Cell membrane has two types of lipids: a) Phospholipid molecules b) Cholesterol molecules. a)- Phospholipid molecules: - - They are arranged into two layers. 3  - Each molecule has a polar end & a non-polar end: Polar end: It forms the head of the phospholipid molecule. It is directed to outside & carry charges. It is also called the hydrophilic end [Has affinity to H2O]. Nonpolar end: It forms the tail of the phospholipid molecule directed to the center of the cell membrane. It is the noncharged end; it is also called the hydrophobic end [no affinity to H2O]. b)- Cholesterol molecules: - They are present in between tails of the phospholipid’s molecules. - Lipid component of the cell membrane allows passage of fat-soluble compounds through it. 2. Protein component: - Cell membrane contains two types of protein: a) Intrinsic protein (Integral protein): is present in the form of: o Small particles that extend for some distance within the thickness of the cell membrane. o Large globules which extend along the whole thickness of the cell membrane & act as a pathway for water soluble substances. b) Extrinsic protein: is represented by small molecules which are loosely attached to the extracellular & intracellular surfaces of the cell membrane forming a non-continuous layer. 3. Carbohydrate component (10%): - They are polysaccharides. - They are either attached to protein molecules & form glycoprotein or to lipid one and from glycolipid. - Glycolipid & glycoprotein are known as the cell coat or glycocalyx. - Cell receptors are present among the cell coat; they are responsible for entrance of drugs, hormones & bacteria to the cell. Functions of cell membrane: a. It keeps the internal composition of the cell. b. Cell coat as a part of the cell membrane is responsible for cell adhesion, cell recognition, Protection & cell immunity functions of cell coat. c. It allows passage of substance through it by: 1) Passive diffusion: (e.g. gases & water) The molecules cross according to concentration gradient. 2) Facilitated diffusion: This diffusion needs the help of intrinsic protein which acts as a carrier e.g. glucose) 3) Active transport: This process needs(energy) & takes place against the concentration gradient e.g. Na pump outside the cell. 4) Selective permeability: By presence of receptors which are present in the cell coat, they allow certain substance only to enter the cell, so it is also called receptor mediated endocytosis. 5) Bulk transport (vesicular transport): - Macromolecules enter & leave the cell by vesicular transport that involves changes in plasma membrane at a localized site & formation of vesicles from the cell membrane or fusion of vesicles with the cell membrane: - Vesicular- transport may be one of two processes: 4  Exocytosis: in which substances leave the cell to outside. Endocytosis: in which substances enter the cell. If the substance that enters the cell is solid the process is called phagocytosis. If the substance that enters the cell is fluid the process is called pinocytosis. 2- Mitochondria Definition: It is a membranous cell organelle. It is the powerhouse of the cell. It is responsible for cell respiration & energy production. Number: varies according to activity e.g. liver cells contain 1000 – 2000 cell N.B. They are present in all cells expect RBCs. Site: at site of most activity e.g. apical in ciliated cells. L.M.: appear as granules, rods or filaments. They need special stains to be demonstrated e.g. iron hematoxylin stains them black while Janus green stains them green. E.M.: - Each mitochondrion appears as a vesicle rounded or oval in shape - It is covered with double membranes, which are separated by a narrow space which is called inter-membranous space. ▪ The outer membrane is smooth ▪ The inner one is thrown into incomplete folds, which are called shelves or cristae. - Mitochondrial matrix is substance, which fills the internal cavity of mitochondria. It contains lipids, protein, carbohydrate Ca & Mg as well as DNA & RNA/Oxidative enzymes are also present attached beheads to the cristae. Functions: 1. Mitochondria are the powerhouse of the cell as they contain oxidative enzymes which produce energy. This energy is stored in the form of A TP & released at time of need. 2. They can form their own protein & can divide as they contain DNA & RNA. 5  3- Endoplasmic Reticulum It is a membranous organelle formed of flattened communicating tubules that form reticulum inside the cytoplasm. It is classified according to. Presence or absence of ribosomes into two types: a) Rough (granular) E.R. b) Smooth (agranular) E.R. Rough endoplasmic reticulum (rER) Smooth endoplasmic reticulum (sER) Site: in protein forming cells e.g. pancreas, plasma Site: in lipid forming cells e.g. liver cell, fibroblasts. muscle& cells of endocrine glands. L.M: It appears as a basophilic (blue) structure L.M: cannot be seen by L.M. when due to presence of ribosomes = rRNA. abundant cause acidophilic of cytoplasm E.M.: E.M.:- - It appears as a network of parallel flattened - It is formed of branching & anastomosing communicating tubules called cisternae with tubules. It is surrounded with a smooth its outer surface covered with ribosomes. membrane which has no ribosomes Functions: Functions: 1. Synthesis of protein by the help of the 1. Lipid synthesis. ribosomes attached to it 2. Steroid hormones synthesis. 2. Condensation of the protein 3. Formation & storage of glycogen e.g. 3. Budding of the packed protein at one end of r in liver ER in the form of transfer vesicle. 4. Detoxification of drugs & hormones 4. It acts as an intracellular pathway. in liver. 5. It shares in the formation of Lysosomes by 5. It helps muscle contraction by Ca formation of their hydrolytic enzymes. pump 6. Acts as intracellular pathway. 4- Golgi Apparatus Definition: It is a membranous organelle. It is considered as the secretory system of the cell. Site: it is well developed in protein forming cells and secretory L.M. - In sections stained with H&E.: The area occupied by Golgi apparatus appears as unstained area & so it is called negative Golgi Image. - It is demonstrated by (Ag) stain. It appears as a dark brown network fibrils a) Around the nucleus (perinuclear) in nerve cell b) Between the nucleus & secretory pole (supranuclear) in secretory cell. e.g. pancreas. 6  E.M.: - It is formed of saucer-shaped flattened saccules stacked over each other. - Each stack has two faces: - o Immature convex surface→, which is the forming surface (cis surface)→ that receives the transfer vesicles which carry protein budding from rE.R. o Mature concave surface→ from which secretory vesicles come out carrying condensed & modified protein. Also, other vesicles containing hydrolytic enzymes will formed &these are called Lysosomes. Functions: - 1. Concentration of protein formed by r E.R. 2. Modification of protein by adding sulphates or carbohydrates. 3. Discharge of secretion in the form of secretory vesicles 4. Isolation and packaging of hydrolytic enzymes in the form of Lysosomes. 5. Formation & maintenance of cell membrane & cell coat. 5- LYSOSOMES Definition: They are membranous organelles rich in hydrolytic enzymes. It is considered as the digestive system of the cell. Site: they are numerous in phagocytic cells e.g. white blood cells. L.M: demonstrated by using a special stain for the enzymes present within them e.g. acid phosphates enzyme. E.M.: The picture of Lysosomes depends on their types. a) Primary Lysosomes: - - These are the newly formed Lysosomes. 7 - They appear as small rounded homogenous vesicles. b) Secondary Lysosomes: - Result from fusion of primary Lysosomes with intracellular macromolecules. - They appear as heterogonous vesicles. ❖ Types of secondary lysosomes: a) Heterolysosome: Primary lysosome +a phagocytic vesicle containing food or bacteria. b) Multi vesicular bodies: Primary lysosomes + Pinocytic vesicle containing fluid droplets. c) Autolysosomes: Primary lysosomes + Vacuoles containing old organelles. d) Residual bodies: These are no more than secondary lysosomes containing the undigested remnants which are secreted outside the cell or accumulated within the cell as lipofuscin granules as in long lived cells e.g. cardiac muscle or nerve cells. Function of lysosomes- 1. Digestion of nutrients within cell. 2. Defensive function, destruction of any bacteria or virus. 3. Removal of any degenerated old organelles. 4. Lysis of the cells &the body after death. 5. Change of inactive hormone into active one. e.g. in thyroid gland. 6. Help the sperm to penetrate the ovum. b- Non Membranous organelles 1- Ribosomes Definition: Non membranous cell organelles. They are formed within the nucleolus; their chemical composition is ribonucleoprotein= rRNA + protein. L.M.: very minute structures (15-20nm) which are difficult to be seen by L.M. They appear as basophilic structures when stained by H. E.M.: Ribosome appears as small electron dense particle formed of two subunits, one is large & the other is small both are connected by m RNA. The large subunit has a central groove which is occupied by the newly formed polypeptide chain. There are three forms of ribosomes: - 8 a) Free ribosomes are diffusely scattered in the cytoplasm. This form is common in immature cells, e.g. embryonic & stem cells. b) Polyribosomes: the ribosomes are connected by m-RNA in a spiral or rosette form. c) Attached ribosomes: The ribosomes are attached ribosomes are attached by means of their large subunits to rER. Functions of Ribosomes: Ribosomes provide the intracellular site where amino acids are linked together forming polypeptide chains i.e. They are the site for protein synthesis. Protein formed by free ribosomes is used within the cell while that formed by rER is secreted & used outside the cell (transfer vesicle from rER → Golgi apparatus secretory vesicle → cell membrane → outside the cell). II. Nucleus Shape: Rounded, oval, flat, horse-shoe, kidney shaped, segmented or tabulated. Site: Central, eccentric, peripheral &may be basal in position. Number: Single (mononucleotide), two nuclei (binucleated), or many nuclei (multinucleated). L.M: It appears as a prominent basophilic structure within the cell as it contains nucleic acids (DNA & RNA), it may be: o Vesicular nucleus: pale stained as it has extended chromatin. o Condensed nucleus: Darkly stained due to its condensed chromatin. E.M.: The nucleus is composed of: 1. Nuclear membrane. 2. Nuclear chromatin. 3. Nuclear sap. 4. Nucleolus. 1- Nuclear membrane: L.M.: it appears as a blue line because of the presence of chromatin on its inner surface & ribosomes on its outer surface. E.M.: it consists of a double walled membrane. Its two layers are separated by a perinuclear space. 9  Nuclear pores are present at intervals along the nuclear membrane where the two layers are fused together & they are covered by diaphragms. They are the pathway through which substances pass in between the nucleus & cytoplasm in both directions. 2- Nuclear chromatin: Definition: it consists of nucleoprotein (DNA+ protein) & forms the chromosomes of the cell. L.M.: Chromatin appears as a basophilic substance which fills the nucleus. E.M.: There are two types according to the activity of the cell: Euchromatin Heterochromatin It is the extended type of chromatin. It is present in a condensed form (Large masses of chromatin It is invisible by L.M. the nucleus appears pale The nucleus with condensed chromatin is in staining. darkly stained It carries the active genes It carries inactive genes. Present in Active cell has a pale nucleus with Present in Inactive cell has a dark nucleus extended chromatin. with condensed ❖ Classification of chromatin according to site: 1- Peripheral chromatin adherent to nuclear membrane. Nucleolus associated present around the nucleolus. 2- Chromatin island scattered between the nucleolus & nuclear membrane. 3- Nucleolus: LM: appears as dark basophilic structure within the nucleus. The nucleus may contain one, two or no nucleoli according(to) activity. EM: it contains: a) Light area: nuclear sap. b) Dark area: formed of: o Granular part: ribosomal RNa (rRNA). o Fibrillary part: new filaments of rRNa around DNA filaments. o Nucleolus associated chromatin. Functions: Formation of rRNa which is responsible for protein synthesis, So, Protein forming cells have well defined one or two nucleoli. 4- Nuclear sap: It is the fluid filling areas between nucleolus & chromatin islands. It acts as a transport medium to carry ribosomes from the nucleus to cytoplasm. Functions of nucleus: - 1. It is responsible for cell division as it contains chromosomes which carry genetic information. 2. It controls all the vital processes within the cell as protein formation. 3. It forms the different types of RNA (m RNA, t RNA, r RNA) 10