Post on 01-Jun-2015
description
THE CELL
By: Dr. Sidra AhmadDepartment Of Anatomy
Amina Inayat Medical College
DEFINITION
Basic morphologic and functional unit of the body
Types:Somatic CellsSex Cells
Size:Approx 5-50(micron)Largest upto 120(micron)
Shape
• Shperical• Ovoid• Cuboidal• Columnar• Polygonal• Pyramidal• Cylindrical• Fusiform• Irregular
CELL ORGANELLESCell MembraneNucleusCytoplasmGolgi ApparatusMitocondriaRibosomesEndoplasmic ReticulumLysosomesPeroxisomesCentriolesCytoskeletonCytoplasmic Inclusions
CELL MEMBRANEDef;Limiting membrane also called plasma membrane or plasma lemmaCan be seen in highly magnifying electron micrograph (osmium tetra oxide fixative)
Thickness
Trileminar as seen in electron micrograph• Two electron dense lines (2.5-3 nm each)• Central electron lucent zone (3.4-4 nm) This Trileminar structure is also
known as UNIT MEMBRANE
STRUCTURE
Composition:•Lipids (phospholipids and cholestrol)•Protiens•Carbohydrates (oligosaccharides)
FLUID MOSAIC MODEL•Because the lipid bilayer is fluid in nature and the intercalated protiens have a mosaic disposition, this model of cell membrane is known as Fluid Mosaic Model•In the bimolecular layer hydrophilic heads of phospho lipids lie at the outer and inner faces of the membrane while the hydrophobic chains project towards middle of the bilayer
Protiens
Partially embedded Trans membrane (provide channels for
water soluble substances e.g ions)
Glycocalyx
The carbohydrate portion of the glyco protiens and glyco lipids of the cell membranes form a coating over the external surface called glycocalyx or cell coat
Thickness:• 2-20nm• Comprising highly branched oligosaccharides
and polysaccharides• Thickest over epithillium cells lining intestinal
mucosa
FUCNTIONSCell BoundaryBarrier b/w Cytoplasm and extra cellular fluidExchange of substancesTrans membrane protiens-ionsEndocytosis•Pinocytosis (Uptake of fluids)•Phagocytosis (Uptake of particulate matter )Exocytosis
Fucntions
Conduction of electrical impulse (e.g muscle cells)
Maintenance of cell shape
NUCLEUS
NUCLEUSContains genetic materialsInfluences metabolic activitiesAt least one in each cell except mature erythrocytes
Size:Diameter from 3-10 micronPosition in the cell:
CentralEccentric
NUCLEUS
Number:Usually one (most of the cells)Binucleate (some liver cells)Multinucleate (skeletal muscle cells)Non- nucleated (mature RBCs)
STRUCTURE
Nuclear EnvelopeNucleoliNuclear sapChromatin
NUCLEAR ENVELOPE
Thickness-40nm Consist of two closely apposed unit
membrane Nuclear Pores:
Dia 60nmExchange of materials
CHROMATINFine to course granules in routine H&E stained sections examined under L/MConsists of DNA
Chromosomes:Rod like structures made of DNA
Hetrochromatin:Quilled or crumpled chromosomes
Euchromatin:Extended chromatin relatively straight or incoilled chromosomes metabolically active
No.of Chromosomes
Diploid e.g, somatic cells having 46
chromosomes (23 pairs) Haploid Haplo- Greek word meaning single e.g,
sex cells (ova & sperms having 23 chromosomes)
Types of chromosomes
Autosomes (22 pairs) Sex chromosomes (23rd pair) X- chromosome (ova) Y-chromosome (sperm) Nucleus of female sometic cells
44 Autosomes Pair of X-chromosome 44 XX
Nucleus of male sometic cells 44 Autosomes 1X and 1 Y-chromosome 44 XY
Karyotype
The number and characteristics of chromosomes encountered in an individual
Barr Body: One of X-chromosome in females remains
condenced located either closed to nuclear membrane or near nucleolus
NUCLEOLI
Rounded dense well-defined bodies not circumscribed by a membraneComposition:
RNAProtiensNucleolonemaWith very high megnifications RNA is seen to be present in the form of a thick thread
MEDICAL APPLICATIONS
The study of sex chromatin discloses the genetic sex in patients whose external sex organs do not permit assignment of gender as in hermaphroditism and psudohermaphroditismSex chromatin helps the study of other anomalies involving the sex chromosomes e.g, kline felter syndromeThe study of karyotypes has revealed chromosomal alterations associated with tumors, leukemia and cellular types of genetic diseasesLarge nucleoli are encountered in embryonic cells during their proliferation, cells actively synthesizing proteins and rapidly growing malignant cells
CYTOPLASMDelimited by the cell membraneSurround the nucleusSite for most of the metalbolic processes
ZONES
Centrosome/ centrosphere:Close to the nucleus, contains centrioles Endoplasm:Zone that surround centrosomes ,contains most of the organellesEctoplasm:Occupies peripheral part of the cell beneath the cell membrane
CONSTITUENTS
1. Cytosol2. Organelles3. Inclusions4. Cytoskeleton
CYTOSOL
oOccupies the spaces b/w organelles, inclusions and the elements of the cytoskeletonoContains soluble proteins, soluble enzymes, substrates, ions and products of different enzymatic reactionsoVery fine interconnected microtrabecular network holds the organelles in position and plays important role in their redistribution
ORGANELLES
Means little organ Specialized living structural components
of the cell Carry out various specialized functionsExamples:
• Mitocondria• Golgi Apparatus• Ribosomes• Endoplasmic reticulum• Lysosomes
MITOCONDRIA Under L/M Only by specialized staining method appear as
rods, filaments or granules Seems to be contracting and swelling React rapidly to temp, pH or osmotic change Under E/M Bounded by two unit membranes, Inner one thrown into folds called cristae Cristea are arranged perpendicular to long axis
mitochondrion Internal surface of inner membrane and cristae are
coated with small particles, elementary particles Interior is filled by finely granular matrix
containing calcium, DNA and RNA
MITOCONDRIAFunctions: Power house of the cell Transform chemical energy of metabolites
to available energy easily accessible to the cell, by catalytic activity of kreb’s cycle and is captured through oxidative phosphorilation
Concentrate Ca ions and maintain optimum Ca environment within cytoplasm
GOLGI APPARATUSUnder L/M:Appear as network confined in nucleus or throughout cytoplasmUnder E/M:Appear as curved stacks of closely packed membranous cisterns associated with small vesiclesDivide off ribosomesWell developed in actively secreting cells
GOLGI APPARATUS
Functions: Concentration and packing of the
secretory produc Assembly of poly saccharides Addition of carbohydrates and sulphates
to secretory proteins Combination of lipids and proteins to
form lipo proteins
RIBOSOMESComposition:•RNA 60%•Proteins 40%•Absent in mature RBCsUnder L/M:Only impart basophiliaUnder E/M:Roughly sphericalApprox 20nm diaTwo sub units (one large and one small)Either free or bound to RERUsually occur in groups or clusters, polysomes held by thread of mRNAFunctions:Site for proteins synthesis
ENDOPLASMIC RETICULUM
Structure:Extensive system of membrane bound canaliculi, expanded and locally into flat saccules called cisternsTypes:Rough endoplasmic reticulumSmooth endoplasmic reticulum
ROUGH ENDOPLASMIC RETICULUM
Numerous granules made of ribosomes are attached to outer surface of cisterns
At places show continuation with the nuclear envelope
Most abundant in the cell secreting proteins e.g., pancreatic acinar cells, fibroblasts and plasma cells
Functions: Synthesis of secretary proteins Synthesis of lysosomal enzymes
SMOOTH ENDOPLASMIC RETICULUM
Closed-meshed network of branching tubules
No ribosomes attachedFunctions: Synthesis of lipids (liver cells) Detoxification processes (liver cells) Synthesis and storage of cholesterol and
production of steroid hormones (adrenal cortex)
Concentration of chloride ions (gastric glands)
Released and sequestration of Ca ions (striated muscles)
LYSOSOMESBounded by single membraneApprox 0.25-0.8micron in dia found in all cells except RBCsContain hydrolyses which include proteases, glycosidase, phosphatases, nucleases, phospholipases and cellphatasesRER synthesizes lysosomal enzymes and pack into primary lysosomesWhen fused with a membrane bound vacuole called secondary lysosomesResidual bodies containing partially degraded lipid material converts to yellowish brown pigment, lipofuscin
LYSOSOMES
Functions: HetrophagyDegradation of material
taken into cell AutophagyDegradation of cells own
old and worn out organelles
AutolysisLysosomes rupture and
released enzymes to destroy the cell from within
PEROXISOMESMembrane bound0.3-0.6micron diaContain enzymes for production as well as destruction of hydrogen peroxide
CENTRIOLES Under L/M: Appear as diplosome Lie in centrosome May contain variable number of small dense
bodies called centriolar satellites or pericentriolar bodies from which microtubules arise
Under E/M:Appear as short rodDia; 200nmLength; 500nmArranged at right angle to each otherCross-section:
CENTRIOLESCross-section: 9 evenly spaced sub-units in the wall each of
which is a microtubule triplet running paralelly arranged at 40 deg to the tangent of the triplets forming a pin-wheel like arrangement
Named A B and C A microtubule has complete wall of 13
protofilaments of tubulin B&C share tubulin sub-units Number is doubled during S-phase of cell cycle Basal body of cilia has same structure