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