Cytology Lec

C

Cell

The smallest and basic unit structure of a protoplasm that can exist independently

Metabolism

The sum of all chemical reactions occurring within the cell

Anabolism

is a reaction resulting from the synthesis of new molecular components essential for growth, maintenance and repair

Catabolism

is a reaction resulting to the degradation of cellular components with the release of energy

Secretion

Ability of the cell to elaborate useful new substances.

• Examples are secretion of the hepatocytes of bile, pancreatic juice by the pancreas.

Excretion

Ability of the cell to get rid of the waste product of metabolism.

• Examples are urine by the kidney, feces by the GIT.

Contractility

• The ability of the cell to shorten along their long axes

• Special property of muscle

Irritability

The ability of the cell to respond to stimuli in their environment

Conductivity

• Ability of the cell to transmit impulses along their cell membrane

• Special property of nerve cells

Endocytosis

• process by which materials gain access to the cell either by diffusion or pinocytosis (“pinching off of the cell” membrane) in case of fluids; or phagocytosis (engulfment and uptake of particulate matter).

Exocytosis

The exit of materials from the cell

• Cellular contact

• Pressure

• Inherent ability of the cell to alter shape

Cell shape are influenced by several factors such as:

Golgi apparatus

is juxtanuclear in position

• Cell Membrane

• Nucleus

• Cytoplasm

Cell components

Nucleus

• Controls and mediates cellular activities (metabolism, synthesis, reproduction and homeostasis) within the cell

• Number varies from 1, 2 or several to none at all as in the case of mammalian RBC

• Shape also varies from round, crescent shape or lobulated as in the case of some WBC

• Position varies also from central, paracentral to eccentrical location

Nuclear Membrane/envelope

• Porous double membrane separated by a

perinuclear space or cisterna

• Outer membrane are continuous with the RER

KARYOPLASM/ NUCLEOPLASM/ KARYOLYMPH/ NUCLEAR SAP

Amorphous ground substance of the nucleus suspending the DNA

Nucleolus

• The center for the synthesis of RNA

• May occur singly or more in the cell and this determines the malignancy of a cell

Chromatin

•Any area in the nucleus suspected to contain DNA and its bound proteins

• Heterochromatin

• Euchromatin

Euchromatin

The dispersed form that stains lightly and metabolically active

Heterochromatin

The condensed form of chromatin which stains deeply with basic dyes and is metabolically inert

Barr body

a distinguishable heterochromatin believed to contain the X chromosome, a distinct feature in female

• ground substance/ hyaloplasm/ cytoplasm matrix

• organelles

• inclusion bodies

Cytoplasm is composed of three major constituents:

Ground substance

is an admixture of H2O, CHON,CHO, organic and inorganic salts

Cell organelles

Are classified into membranous and non-membranous

Ribosomes

The only non-membranous cell organelles

• Cell membrane/plasma membrane/ plasmalemma and cell coat

• Endoplasmic reticulum (smooth & rough)

• Golgi apparatus

• Mitochondria

• Lysosomes

The membranous organelles are

Ribosomes

RNA containing bodies in the nucleus and cytoplasm of the cell.

Polyribosomes or Polysomes

While in the cytoplasm, they occur as free ribosomes individually or in groups called

Leaflet theory

States that a cell membrane has a sandwich appearance in which 2 protein layers are laid upon a layer of lipid (protein-lipid-protein).

Globule theory

Makes use of the Fluid Mosaic Model which is a bimolecular layer of phospholipids with their hydrophilic (polar) ends directed outwardly and their hydrophobic ends inwardly

Cell coat

• Glycocalyx

• The outer most covering of the cell membrane composed of glycoproteins, glycolipids and polysaccharides wherein sialic acid predominates

• Cellular recognition

• Absorption

• Adhesion and attachment

• Protection (Igs)

Functions of cell coat

Endoplasmic reticulunm

A system of hollow structures either tubules or flattened vesicles (cisterna) extending throughout the cytoplasm.

RER and SER

Two types of ER

Smooth endoplasmic reticulum

Not studded with ribosomes, thus has no distinct staining characteristics; less extensive than RER except in certain cells like hepatocytes

Rough endoplasmic reticulum

Continuous with the nuclear membrane studded with ribosomes (appears basophilic due to ribonucleoproteins )

RER

• Protein synthesis destined for secretion ( e.g. digestive enzyme)

• Glycogen biosynthesis

• Prod’n of degrative enzymes (e.g. glucose-6-PO4)

SER

• Participates in glycogen metabolism, synthesis

• Participates in ion concentration, distribution and detoxification of certain substances

• Believed to contribute to the formation of Golgi apparatus

Golgi apparatus

Has a lamellated profile (4 or more) usually dilated sacks or cisternae

Chromophobic thus it can not be stained routinely

• convex face or immature/ formative/cis face

• concave or mature/ open/ trans face

2 faces of golgi apparatus

Convex face or immature/ formative/cis face

closely associated with transfer vesicle from RER

Concave or mature/ open/ trans face

intimately associated with secretory vesicles in various stages of condensation and maturation

JANUS GREEN B

Mitochondria appears as thread or granules which could be stained specifically with special stain called

Mitochondria

appears as double membrane structure composed of outer and inner walls

Mitochondrial cristae

Mitochondria Inner wall forms plate like or tubular folds called

Mitochondrial matrix

Cristae are separated by

Mitochondria

• Site of Kreb’s citric acid cycle

• Contains enzymes for oxidative phosphorylation and fatty acid oxidation

• Contains DNA & RNA thus possessing some genetic and protein synthetic potentials

Acid hydrolases

Lysosomes are membrane bound particles contain hydrolytic enzymes collectively called

• Intracellular digestion of materials taken in by the cells

• Responsible for autolysis

• Responsible for post-mortem degeneration

Lysosome functions

Phagolysosomes or heterophaagic vacoule

Lysosome unite with phagosomes to form secondary or active lysosome referred as

Multivesicular body

Lysosome may unite with pinocytic or fluid vesicle and become a

Primary lysosomes

After completion of digestion, multivesicular body is converted into

Autophagic vacoule or cytolysosome

Lysosome may ingest degenerative cellular components and become - which later become a residual body

Centrioles

Small bodies contained within an area of the cytoplasm known as CENTROSPHERE

• Ultrastructurally, are seen as two cylindrical unit oriented to each other

• Important in mitosis by forming spindle fibers

Nine groups of three tubules

Each cylinder of centrioles is composed of —

Basal bodies

• Structurally similar to centrioles but are associated with cilia

• Ultrastructurally, the cilia are similar with that of the centriole except each cylinder is composed of nine groups

Perixisomes

• Intracellular vesicles containing a mixture of enzymes, namely, oxidases and catalases.

• Smaller than lysosomes

• Hydrogen peroxide is produced within the peroxisome as a result of enzymatic action.

Cytoskeleton

Serves the cell’s structural framework.

• Microfilaments

• Intermediate filaments

• Microtubules

Three types of filamentous proteins

Microfilaments

• The thinnest structures of the cytoskeleton.

• Composed of the protein actin

• Are most prevalent on the peripheral regions of the cell membrane.

Intermediate filaments

• Thicker than microfilaments

Keratin

epithelial cells

Vimentin filaments

many mesenchymal cells

Desmin filaments

smooth and striated muscles

Neurofilament proteins

nerve cells and their processes

Glial filaments

astrocytic glial cells of the nervous system

Lamin intermediate filaments

inner layer of the nuclear membrane

Microtubules

• The largest elements of the cytoskeleton

• Composed of the two-protein subunit, α- and β-tubulin.

• All microtubules originate from the microtubule-organizing center, the centrosome in the cytoplasm, which contains a pair of centrioles.

Microtubules

• Maintain cell shape

• Significant in the motility of cilia, flagella, spermatid

• Serves as transport medium for secretory products and axoplasm of neurons