cytology 1

What is a cell

basic structural & functional unit of living body

size

Varies from 4 um (as granular cells of cerebellum) to 150 um (as ovum)

shap

CYTOPLASM

Formed of cytosol, Organelles and Inclusions

Cytosol

fluid component of

Lipids, proteins, carbohydrates, minerals, ions, water

Organelles

Organelle vs inclusions

Organelles Inclusions

Living & permanent Non-living & temporary

• Essential Not essential

• Active Inert

• Have vital functions

results from cell

activity

Membranous

Cytoplasmic Organelles Classified based on

Covered by membrane contain enzyme

CELL MEMBRANE

Definition

limiting membrane that envelopes all the cell

Lm

Difficult to be seen as it is very thin (7.5:10 nm)

• stained with: Silver (Ag) or PAS stains

Em

Two dark lines Separated by light one, So, it is called: tri-laminar membrane =

unit membrane.

• There is a fuzzy layer found only on the outer Side of the cell membrane, which

represent the Cell coat (Glycocalyx)

Molecular structure of the cell membrane

Lipid (bilayer) 2.Protein 50:60% 3. carbohydrates

Lipid (bilayer

Phospholipid bilayer:

Head (PHOSPHATE)

• Towards aqueous

• Outwards

2 tails (fatty acids)

Away aqueous

function:

Selective permeability

• 1. permeable to certain substances

• 2.impermeable to ions & polar molecules

• 3.Barrier between external and internal environmen

Cholesterol site

SITE: Between hydrophobic tails (fatty acids

function

1. Restircting phospholipid movement (Membrane stabilization)

• 2. Modulate membrane fluidity prevent too fluidity and too rigidity

Protein form of the cell membrane mass

50% 60%

present in two forms:

1

Peripheral and integral

Peripheral proteins

Small molecules forming a non-continuous layer outside the lipid bilayer.

• Loosely attached

• On both surfaces of the cell membrane

2

Integral and its two types

2) integral (transmembrane) proteins:• Embedded in the lipid bilayer.

Two types are present:

• channels proteins for transport of ions & water.

• carrier proteins for transport of small polar molecules as glucose and ions as

Na K pum

Protein function

specific transport of ions and polar molecules.

carbohydrates Site

at the external surface formed

Two types

Glycolysis and glycoprotein

Define both

oligosaccharide attached to protein molecules

2

Cell coat (glycocalyx):

Formed of molecules of glycoproteins & glycolipids.

• Present on the external surface of cell membrane.

• It includes receptors for drugs, hormones, bacteria & viruses

Function

They are important in adhesion

• cell immunity

• identification (Receptor) & protection

Functions of cell Membrane

Endo and eco

Endocytossi

Endocytosis: bulk movement of substances into the cell by forming

vesicles. 3

3 process

Phage pino and receptor mediated

Phagocytic define exemplify

cell engulfs solids.

• (pseudopodia) extend and fuse, enclosing the solid particle in vacuole

(phagosome) which fuse with lysosomes for digestion of its contents.

• Example: WBCs engulfing bacteria

Pinocytosis (cell drinking):

•

cell engulfs fluids.

• membrane (invaginations) enclose the fluid forming (pinocytic vesicles).

• Then fuse with lysosomes for digestion of its contents.

• Example: colloid in thyroid cells.

Receptor-mediated endocytosis

Attachment of the ligand (e.g. hormone) to a receptor.

• Accumualtion of cathrin protein on the cytoplasmic surface forming

(coated pit). coated pit Pinched off pits forming coated vesicles.

• Example: uptake of GH by the cel

Exocytosis define and explain

bulk movement of substance from inside to outside the cell

by forming vesicles

vesicles fuse with the cell membrane & discharge their contents into

the extracellular space without affecting continuity of cell membrane

•

MITOCHONDRIA

Defin

Membranous organelles, responsible for aerobic respiration and energy (ATP Power house of cell

sites

area of most activity (eg. Apical in ciliated cells)

Number

Numbers

More in active cells as liver cell 1000 mitochondria/ cell.

• increase in number by simple division

LM

H&E: acidophilic structures.

• By special stains: appear as oval, rod or filamentous:

• dark blue with Iron HX.

• green with Janus green.

EM

EM

appear as rounded or oval membranous vesicles

• Surrounded with two-unit membranes separated by inter membranous

space

Outer membrane

outer membrane: Outer membrane

Ribosomes

• Permeable to small molecules Intermembrane

Innor membrane

space y

• Smooth Cristao

• Contains porins (transmembrane protein

Inner

Less permeable (selective).

• It projects into the matrix forming shelves called cristae.

• Increase number of cristae = more energy production.

• Cristae Increase surface area for elementary particles

Elementary particles

globular structures connected to the inner membrane by stalk.

• contain enzymes for ATP production & oxidative phosphorylation

Mitochondrial Matrix: composed

Oxidative enzymes of citric acid (Krebs) cycle

• Electron dense granules rich in Cat+ act as a catalysts for mitochondrial

enzymes.

• Circular molecules of DNA

• 3 types of RNA (mRNA, tRNA & rRNA

Functions

Energy production & Cell respiration

Most of this energy is stored as ATP molecules by oxidative phosphorylation and

some is dissipated as heat to maintain body temp.

2. Synthesize some of its proteins as it contains its own DNA.

Clinical

Cytology 8

ENDOPLASMIC RETICULUM

• communicating membranous channels and sacs (cisternae).

• Extend from nucleus to cell membrane

• They There are two types: a) Rough b) Smooth.

Rough definition site lm em function

Membranous organelle considered with

protein synth. protein forming cells e.g.

* plasma cell localized diffuse Parallel, regular flattened cisternae.

* covered with electron-dense particle

(ribosomes).

* Ribosomal large subunit attached

to rER by specific receptors

(Ribophorins).

* Pores are present under the receptor

for passage of proteins to cisternae Protein synthesis.

• Protein segregation

• Protection (in cisternae) Cytoplasm

from hydrolytic enzymes

• Protein glycosylation (initial) By

adding monosaccharides

• Protein packing

Smooth definition site lm em function

Membranous organelle considered with lipid & steroid synth.

lipid & steroid forming cells, e.g. liver cells

when abundant → acidophilia

• branching & anastomosing variable shaped tubules continuous with rER.

• No ribosomes.

• Synthesis Phospholipid of cell membrane.

• Synthesis Steroid hormones
  (Cortisone & testosterone)

• Breakdown (Liver)

Glycogen ---- glucose

Drugs, hormones & alcohol (Detoxification)

• Contraction (muscle) Ca release (pump)

Golgi Apparatus

Definition

• Membranous organelles, responsible for secretion.

sites

Site

well developed in secretory cells

Lm

&E stained sections, (in deeply basophilic cytoplasm as in plasma cells),

seen as unstained area near the nucleus called "negative Golgi image".

• Silver (Ag), seen as a network of brown granules & fibrils.

• Apical: between the nucleus and the pole of the cell, e.g. Secretory cells.

• Perinuclear: completely surrounds the nucleus, e.g. in nerve cells.

EM

is formed of membranous saccules.

• Each saccule is flat, curved, has a narrow lumen & expanded ends, filled with

low electron-dense material.

• Saccules are inter-connected with each other.

• 3-10 parallel saccules forming stacks, Each stack has 2 faces

Two face of each stack explain

Entry (CiS) Face:

• They receive transfer vesicles, that arise from rER carrying proteins.

2 - Exit (Trans) Face:

vesicles that bud off from this face are either:

a -secretory vesicle that discharge their contents b exocytosis

b- lysoso

Functions of Golgi Apparatus

Packing, concentration & storage of protein received from rER.

• Chemical modification of proteins & lipids by addition of carbohydrate.

• Formation of Lysosomes, secretory vesicles.

• Discharge of secretory products as hormones in secretory vesicles.

• Renewal and maintenance of cell membrane & providing it with integral

proteins from membrane of secretory vesicles

Lysosomes

Definition:

•

membranous vesicles enclosed by single membrane responsible for

intracytoplasmic digestion.

• Contain hydrolytic enzymes ( protease, sulfatase

Origin:

•

Enzymes of lysosomes are proteins which are formed in rER then transferred

to the Golgi apparatus as transfer vesicle & arise from of Golgi apparatus as

lysosomes.

Numbers

abundant in phagocytic cells (macrophages, neutrophils

LM:

•

histochemical stain that detect the enzymes inside them

EM

Em

Primary lysosomes:

• They are newly released from Golgi apparatus.

• Enzymes inactive

• By EM appear EM homogeneous moderate electron-dense

2- Secondary Iysosomes:

• Primary lysosome + phagosome, pinocytic vesicle or autophagic vesicle.

Enzymes inactive

•Enzymes active

• By EM appear heterogenous

Types of secondary Iysosomes

Hetero lysosomes: primary lysosome + phagosome to digest its content

(bacteria, viruses)

2- Multivesicular bodies: primary lysosome +pinocytic vesicle.

3- Autolysosomes: primary lysosome + autophagic vesicle (vesicle containing mitochondria or rER

Residual bodies:

Digested nutrients diffuse back to the cytoplasm through lysosomal

membrane.

• undigested materials remain in vesicles & called residual bodies.

Fate

Fate of residual bodies

discharge their contents outside the cell by exocytosis (cytostool).

• accumulate in the cells as lipofuscin granules (age pigments) as in long-lived

cells (nerve cells and heart muscles)

Functions

Functions of Lysosomes

Digest nutrients, bacteria & viruses.

• Maintain cell health by removal of nonfunctional organelles.

• postmortem autolysis by digestion of the whole cell after death due to

rupture of lysosomes.

• fertilization by helping the head of sperm to penetrate the ovum.

• Activation of thyroid hormones by hydrolysis of bond between the

hormone and protein

PEROXISOMES (MICROBODIES)

Definition:

•

membranous organelles enclosed by single membrane, containing oxidases

and catalase enzyme

origin

Origin

membranous vesicles bud off from rER.

• Enzymes are formed in free polysomes.

Numbers:

•

more in liver & kidney cells

• Increased in response to diet & drugs.

• They divide by simple division (fission)

LM

Lm

demonstrated by histochemical method.

EM

Em

small (0.5 um) in diameter.

• spherical to ovoid organelle bound by a single membrane of moderate

density.

Functions o

Functions of Peroxisomes

• B-oxidation of long chain fatty acid by oxidases will produce :

a) energy that comes out as heat

b) hydrogen peroxide (H202) which is a toxic product. H202 breakdown by

catalase into H2O + Oz.

• oxidases are important in liver cells in detoxification of alcohol and some

drugs.