Cytology IICytology II

Cell organelles: peroxisome, centrioleCell organelles: peroxisome, centriole

Cell inclusionsCell inclusions

CytoskeletonCytoskeleton

Modifications of cell surfaceModifications of cell surface

PEROXISOMES (MICROBODIES)PEROXISOMES (MICROBODIES) (are similar to the primary lysosomes, but they (are similar to the primary lysosomes, but they

contain another category of enzymes)contain another category of enzymes)

membrane bound vesicles membrane bound vesicles (diameter 0.1(diameter 0.1-- 0.5 µm) containing 0.5 µm) containing enzymes involved in the production enzymes involved in the production or destruction of hydrogen peroxide or destruction of hydrogen peroxide (oxidases and catalase) (oxidases and catalase)

in EM, their content is of fine in EM, their content is of fine granular or homogeneous granular or homogeneous appearance with a dense center appearance with a dense center (crystalloid or nuleoid)(crystalloid or nuleoid)

function: to keep the low level of function: to keep the low level of hydrogen peroxide in a cell (toxic to hydrogen peroxide in a cell (toxic to cells), some types of oxidative cells), some types of oxidative reactionsreactions

occurrence: cells of liver and kidney occurrence: cells of liver and kidney (in other cells (in other cells –– microperoxisomes, microperoxisomes, 0.150.15--0.20 µm, without nucleoid)0.20 µm, without nucleoid)

CENTRIOLECENTRIOLE

located near the nucleuslocated near the nucleus

in most cells during in most cells during

interphase are two interphase are two

bodies = diplosome (they bodies = diplosome (they

are situated at right are situated at right

angle to each other) angle to each other)

area of cytoplasm area of cytoplasm

surrounding the surrounding the

centrioles = centrosomecentrioles = centrosome

structure: short cylinder 0.3structure: short cylinder 0.3--0.5 µm 0.5 µm long, 0.15 µm in diameterlong, 0.15 µm in diameter

the wall consists of nine microtubule the wall consists of nine microtubule triplets (the microtubules of each triplets (the microtubules of each triplet are designated A,B,C subfibrils, triplet are designated A,B,C subfibrils, A is the most central)A is the most central)

pericentriolar material (proteins pericentriolar material (proteins forming dense granules) attached to forming dense granules) attached to the centriole (microtubule organizing the centriole (microtubule organizing center center –– MTOC)MTOC)

occurrence: in all cells (except occurrence: in all cells (except erythrocytes and ovum)erythrocytes and ovum)

function: 1. function: 1. cell divisioncell division (they are (they are duplicated during Sduplicated during S--phase of cell phase of cell cycle, in mitosis cycle, in mitosis -- the two centriolar the two centriolar pairs move to opposite poles of a cell pairs move to opposite poles of a cell and serve as the organizing center of and serve as the organizing center of the mitotic spindle), 2. the mitotic spindle), 2. development development of ciliaof cilia and flagella (they replicate, and flagella (they replicate, pass to cell surface and form basal pass to cell surface and form basal bodies from which cilia develop)bodies from which cilia develop)

CELL INCLUSIONSCELL INCLUSIONS

„nonliving“ components of the cell (passive, „nonliving“ components of the cell (passive, they do not exploit energy) they do not exploit energy) -- metabolites, metabolites, cell products or exogenous materials, cell products or exogenous materials, which are stored in the cytoplasmwhich are stored in the cytoplasm

1. Food materials: carbohydrates (glycogen)1. Food materials: carbohydrates (glycogen)

lipidslipids

proteinsproteins

2. Pigments (display colour without 2. Pigments (display colour without staining): exogenous, endogenousstaining): exogenous, endogenous

3. Secretory granules3. Secretory granules

secretory granulessecretory granules

in glandular cellsin glandular cells

different size and chemical different size and chemical

compositioncomposition

spherical bodies limited by a spherical bodies limited by a

membrane, they develop from membrane, they develop from

the vacuoles of GAthe vacuoles of GA

three stages of the three stages of the

development: development:

1. immature homogeneous 1. immature homogeneous

(pale content)(pale content)

2. immature heterogeneous 2. immature heterogeneous

(center dark, periphery pale)(center dark, periphery pale)

3. mature (electron dense 3. mature (electron dense ––

dark dark –– content)content) GERGER

GolgiGolgi

apparatusapparatus

secretorysecretory

granulesgranules

Lipid inclusions = fat dropletsLipid inclusions = fat droplets

Content: neutral fats, cholesterol, fatty acidsContent: neutral fats, cholesterol, fatty acids

morphology: spherical (about 1 µm) with or morphology: spherical (about 1 µm) with or

without membrane, homogeneous content without membrane, homogeneous content

of low or high electron density (depending of low or high electron density (depending

upon the fixation method upon the fixation method –– osmium tetroxide osmium tetroxide

stains lipids black stains lipids black –– and composition), the and composition), the

lipids may be extracted by solvents used in lipids may be extracted by solvents used in

the preparation of the specimen the preparation of the specimen –– in this case in this case

lipid droplets appear as clear (empty) areaslipid droplets appear as clear (empty) areas

lipid inclusions

Glycogen:Glycogen:

polymer of glucose polymer of glucose

in the EM it appears as electron dense in the EM it appears as electron dense

particles often lying among particles often lying among

tubules of AERtubules of AER

ββ--particles (15particles (15--30 nm) 30 nm)

αα--particles = complexes of βparticles = complexes of β--particles particles

(50(50--100 nm) 100 nm)

it is mostly stored in the liver cells and it is mostly stored in the liver cells and

muscle cellsmuscle cells

for LM is stained by the PASfor LM is stained by the PAS--reaction)reaction)

glycogenglycogen

ββ--granulesgranules

glycogen, glycogen, αα--granulesgranules

glycogen in light microscope (in hepatocytes)glycogen in light microscope (in hepatocytes)

Proteins Proteins ––

crystals crystals

(Leydig cells)(Leydig cells)

PigmentsPigments

Exogenous Exogenous -- pass into organism from environment pass into organism from environment (carotens (carotens –– pigments of vegetables are fatsoluble, pigments of vegetables are fatsoluble, carbon carbon –– in lymph nodes of lung, minerals in lymph nodes of lung, minerals –– lead, lead, silver)silver)

Endogenous Endogenous -- are formed in organism:are formed in organism:

hemoglobin and its breakdown products hemoglobin and its breakdown products (hemosiderin (hemosiderin –– contains iron, hematoidin and contains iron, hematoidin and bilirubin bilirubin –– ironiron--free)free)

melanin melanin –– dark brown, in the skin and eyesdark brown, in the skin and eyes

lipofuscin lipofuscin –– yellowishyellowish--brown, (granules of lipofuscin brown, (granules of lipofuscin are in fact indidestible rests of lysosomal activity are in fact indidestible rests of lysosomal activity –– residual bodies), its amount increases with age (in residual bodies), its amount increases with age (in longlong--living cells: neurons, cardiomyocytes)→ living cells: neurons, cardiomyocytes)→ lipofuscin is also called „wear and tear“ pigmentlipofuscin is also called „wear and tear“ pigment

CytoskeletonCytoskeleton 1. microfilaments1. microfilaments (5(5--7 nm) 7 nm) –– actin, attached actin, attached

to the plasma membrane, important in to the plasma membrane, important in defining the surface morphology of the celldefining the surface morphology of the cell

2. microtubules 2. microtubules (22(22--25 nm) 25 nm) –– hollow tubes hollow tubes from tubulin subunits, they are bound to from tubulin subunits, they are bound to other cytoskeletal elements and other cytoskeletal elements and organelles, function organelles, function –– determine cell determine cell architecture, movement of organelles and architecture, movement of organelles and substrates, motile activities substrates, motile activities –– cilia, mitotic cilia, mitotic spindlespindle

3. intermediate filaments3. intermediate filaments (8(8--11 nm) 11 nm) –– 5 classes 5 classes (tissue specific) (tissue specific) ––

tonofilaments (tonofilaments (keratin) in epithelia,keratin) in epithelia,

neurofilaments in neurons, neurofilaments in neurons,

vimentin in cells of mesenchymal origin,vimentin in cells of mesenchymal origin,

desmin in muscle cells, desmin in muscle cells,

GFAP (glial fibrillar acidic protein) in glial cellsGFAP (glial fibrillar acidic protein) in glial cells

nonnon--contractile, provide cells with mechanical contractile, provide cells with mechanical strenght (resistance in the traction and pressure)strenght (resistance in the traction and pressure)

stable (they do not polymerize and depolymerize)stable (they do not polymerize and depolymerize)

tissue specifity is maintained also after tissue specifity is maintained also after dediferentiation during tumour development dediferentiation during tumour development –– important for diagnoseimportant for diagnose and therapyand therapy

freefree

laterallateral

basalbasal

modifications ofmodifications of

cell surfacecell surface

Cell surfacesCell surfaces 1. the 1. the freefree surface: microvilli, surface: microvilli,

stereocilia, cilia (kinocilia)stereocilia, cilia (kinocilia)

2. the 2. the laterallateral surface: surface:

interdigitationsinterdigitations

cell junctions:cell junctions:

occluding (zonula occluding (zonula occludens)occludens)

adhering (zonula adhering (zonula adherens, macula adherens, macula adherens = desmosome)adherens = desmosome)

communicating (nexus = communicating (nexus = gap junction)gap junction)

3. the 3. the basalbasal surface: basal surface: basal labyrinth (deep infoldings), labyrinth (deep infoldings), hemidesmosomeshemidesmosomes

MicrovilliMicrovilli fingerfinger--like projections from cell surface like projections from cell surface

containing the cytoplasm and actin containing the cytoplasm and actin microfilaments (they interact with a horizontal microfilaments (they interact with a horizontal network of other filaments network of other filaments –– terminal web)terminal web)

number and lenght: differentnumber and lenght: different

function: increasing of the surface area function: increasing of the surface area (correlation with the absorptive capacity of a (correlation with the absorptive capacity of a cell)cell)

Regular and parallel microvilli extend from the Regular and parallel microvilli extend from the surface of cells with principal absorptive surface of cells with principal absorptive function: so called „striated border“ of intestinal function: so called „striated border“ of intestinal cells or „brush border“ of kidney tubule cellscells or „brush border“ of kidney tubule cells

StereociliaStereocilia –– extremely long and branched extremely long and branched microvilli (epithelial cells of ductus epididymidis) microvilli (epithelial cells of ductus epididymidis)

microvilli =microvilli =

striated border striated border

(enterocytes)(enterocytes)

brush border brush border

(proximal tubule (proximal tubule

of nephron)of nephron)

Cilia (kinocilia)Cilia (kinocilia)

hairhair--like processeslike processes

numerous (several hundred) or singlenumerous (several hundred) or single

in cross section in cross section -- axonema: nine doublets of axonema: nine doublets of microtubules and two central microtubulesmicrotubules and two central microtubules

at the base of cilium: the central paar terminates, at the base of cilium: the central paar terminates, each of peripheral doublets is continuous with a each of peripheral doublets is continuous with a triplet of basal body (=modified centriole)triplet of basal body (=modified centriole)

strands of fibrous material extending into strands of fibrous material extending into cytoplasm, so called striated rootletcytoplasm, so called striated rootlet

movement of cilia: rapid forward beat with slower movement of cilia: rapid forward beat with slower recovery stroke (transport of materials along the recovery stroke (transport of materials along the surface)surface)

ciliacilia

axonemaaxonema

dynein armsdynein arms

cilia andcilia and

microvillimicrovilli

axonemaaxonema

basal bodybasal body

striated rootletstriated rootlet

cilia and microvilli in SEMcilia and microvilli in SEM

CELL JUNCTIONS:CELL JUNCTIONS: zonula occludenszonula occludens (tight junction):(tight junction):

at the most apical part of the lateral surfaceat the most apical part of the lateral surface

ring (circumferential band = zonula) of plasma membrane union between ring (circumferential band = zonula) of plasma membrane union between cells, the outer leaflets of the plasma membranes fuse at some intervalscells, the outer leaflets of the plasma membranes fuse at some intervals

junction obliterating (occluding) the intercellular spacejunction obliterating (occluding) the intercellular space

zonula adherens zonula adherens

circumferential band below the z. occludenscircumferential band below the z. occludens

intercellular space (15intercellular space (15--20 nm) is occupied by a material of low electron 20 nm) is occupied by a material of low electron densitydensity

electron dense material along the cytoplasmic side of the membrane of electron dense material along the cytoplasmic side of the membrane of neighbouringneighbouring cells is associated with actin microfilamentscells is associated with actin microfilaments

function: mechanical attachmentfunction: mechanical attachment

macula adherens (desmosome)macula adherens (desmosome)

discoid structure at different levels along the lateral surfacediscoid structure at different levels along the lateral surface

intercellular space (20intercellular space (20--30 nm) filled with filamentous material with 30 nm) filled with filamentous material with intermediate lineintermediate line

electron dense plaques on the cytoplasmic side of the plama membranes electron dense plaques on the cytoplasmic side of the plama membranes to which tonofilaments are attachedto which tonofilaments are attached

function: strong attachmentfunction: strong attachment

hemidesmosomes: one half of desmosome on the basal surface of epithelial hemidesmosomes: one half of desmosome on the basal surface of epithelial cells which are in contact with basal laminacells which are in contact with basal lamina

zonula occludenszonula occludens

zonula adherenszonula adherens

desmosomedesmosome

(macula adherens)(macula adherens)

zonula occludenszonula occludens

(tight junction):(tight junction):

at the most apical part at the most apical part of the lateral surfaceof the lateral surface

ring (circumferential ring (circumferential band = zonula) of band = zonula) of plasma membrane plasma membrane union between cells, the union between cells, the outer leaflets of the outer leaflets of the plasma membranes fuse plasma membranes fuse at some intervalsat some intervals

junction obliterating junction obliterating (occluding) the (occluding) the intercellular spaceintercellular space

zonula adherens zonula adherens

circumferential band below the z. occludenscircumferential band below the z. occludens

intercellular space (15intercellular space (15--20 nm) is occupied by 20 nm) is occupied by a material of low electron densitya material of low electron density

electron dense material along the electron dense material along the cytoplasmic side of the membrane of cytoplasmic side of the membrane of neighbouring cells is associated with actin neighbouring cells is associated with actin microfilamentsmicrofilaments

function: mechanical attachmentfunction: mechanical attachment

macula adherens (desmosome)macula adherens (desmosome)

discoid structure at different levels along the discoid structure at different levels along the lateral surfacelateral surface

intercellular space (20intercellular space (20--30 nm) filled with 30 nm) filled with filamentous material with intermediate linefilamentous material with intermediate line

electron dense plaques on the cytoplasmic electron dense plaques on the cytoplasmic side of the plama membranes to which side of the plama membranes to which tonofilaments are attachedtonofilaments are attached

function: strong mechanical attachmentfunction: strong mechanical attachment

hemidesmosomes: one half of desmosome on the basal hemidesmosomes: one half of desmosome on the basal

surface of epithelial cell which surface of epithelial cell which isis in contact with basal laminain contact with basal lamina

gap junction (nexus in smooth and cardiac muscle)gap junction (nexus in smooth and cardiac muscle) a hexagonal array of particles (short hollow cylinder with a central canal)a hexagonal array of particles (short hollow cylinder with a central canal)

intercellular space (2intercellular space (2--3 nm)3 nm)

permits direct cellpermits direct cell--toto--cell interchangecell interchange

in EM: intercellular space is not visible (plasma membranes come into contact)in EM: intercellular space is not visible (plasma membranes come into contact)

function: exchange of metabolites and ions, transmission of electrical impulses, synchronization function: exchange of metabolites and ions, transmission of electrical impulses, synchronization

of activityof activity

basement membrane (lamina)

ENDOENDO-- AND EXOCYTOSISAND EXOCYTOSIS

substances enter and leave a cell:substances enter and leave a cell:

a) without change in configuration of a) without change in configuration of

the plasma membrane (diffusion, the plasma membrane (diffusion,

pumps, channels)pumps, channels)

b) with change in configuration of the b) with change in configuration of the

plasma membrane at localised sites plasma membrane at localised sites --

endocytosis and exocytosis are visible endocytosis and exocytosis are visible

in EMin EM

EndocytosisEndocytosis

1. 1. phagocytosisphagocytosis (ingestion of (ingestion of

particulate material)particulate material)

2. 2. pinocytosispinocytosis (ingestion of fluids)(ingestion of fluids)

plasma membrane invaginates to form plasma membrane invaginates to form

pits and vesicles, which separate from pits and vesicles, which separate from

plasma membraneplasma membrane

pinocytotic vesicles are numerous in pinocytotic vesicles are numerous in

the endotheliumthe endothelium

Exocytosis Exocytosis

the reverse process the reverse process –– movement of a movement of a

membranemembrane--limited structure (secretory limited structure (secretory

granule) to the plasma membrane, granule) to the plasma membrane,

fusion with plasma membrane, fusion with plasma membrane,

opening and releasin of the content.opening and releasin of the content.

3 Cytology II

Ultrastructure of cell organelles (peroxisomes, and the centriol). Cell inclusions.

The arrangement of cell surfaces: apical, lateral, and basal ones.

Intercellular junctions: adhering, occluding, and communicating ones.

Atlas of Electron Micrographs (snaps are numbered from 1 to 58):

(Snaps recommended to the study are in brackets)

Peroxisomes (17, 18, and 19)

Centrioles (20, 21)

Glycogen (8, 13, 14, 17, 22, and 53)

Microvilli (20, 27, 28, 30, 38, 40, and 45)

Kinocilia (26, 29, and 30)

Flagellum of the sperm (31)

Pinocytotic vesicles (33)

Phagocytosis (34)

Adhering junctions - desmosomes (9, 13, 24, 26, 27, and 28)

Tonofilaments (24)

Occluding (tight) junction (26)

Communicating (gap) junction (25)