Histology

Prepared by
DR. lUBNA JAMIL
Lecturer of histology
 Cytology

YTHE CELL
 The cell is the functional & structural unit of all living tissues. The cell is the smallest living structure which has vital properties such as growth, secretion, excretion, digestion,

contraction, respiration &reproduction. Any cell in the body, except RBCs.

 is composed of:
 Cytoplasm Nucleus

I -Cytoplasm
 It is formed of:
 Cytoplasmic Matrix Cytoplasmic organelles Cytoplasmic inclusions

II- Nucleus:
 Nuclear membrane Chromatin Nucleolus Nuclear sap.
 Nucleic acids
 DNA RNA
 Membranous cell organelles

 Cell membrane

 Definition:

 It is a thin outer limiting membrane that forms the outer cover of the cell.

 Light Microscope (LM):

 It is ultra-thin membrane that can’t be seen, but can be stained by silver (Ag) or PAS.

 Electron Microscope (EM):

 It is a tri-lamellar membrane. It appears as three parallel lines,

 two dark layers separated by a light one. The cell membrane has an outer covering rich in

 carbohydrates called cell coat.

 Molecular structure of the cell membrane:-

 The cell membrane is composed of lipids, protein & carbohydrate.

 Lipids component (30%):


 Cell membrane has two types of lipids:

 Phospholipid molecules b) Cholesterol molecules.
 Phospholipid molecules composed of:-
 Hydrophilic polar end: the head of hydrophilic end [has affinity to H2O].
 Hydrophilic non polar end: the tail hydrophilic end [No affinity to H2O].

 Cholesterol molecules:
 They are present in between tails of the phospholipids molecules to restrict their movement.




1. Protein component (60%)

Cell membrane contains two types of protein:

a) Intrinsic (integral) Protein: present in the form;

*Small molecules embedded in the lipid bilayer.

*Large globules which extend along the whole thickness of the cell membrane & act as
pathway for water soluble substances.

b) Extrinsic Protein:

Small molecules which form a non- continuous layer loosely attached to surfaces of the cell
membrane.
 1. Carbohydrate component (10%):

They are oligosaccharides attached to protein molecule &form glycoprotein or to lipid

one and from glycolipid.

Cell coat or glycocalyx:

Glycolipid & glycoprotein molecules found on the external surface of the cell membrane.
It contains specific receptors to allow the entrance of drugs, hormones and bacteria to the
cell.
Functions of cell membrane:-

a) Cell coat functions

1. Cell protection cell adhesion,
2. Cell recognition & cell immunity

a) Substances pass into or out of the cell through the cell membrane by different
methods:
1) Passive diffusion: (e.g. water & gases ions).The molecules cross according to
concentration gradient.
2) Facilitated diffusion: (e.g. glucose & amino acids) needs the help of intrinsic
protein which acts as a carrier.
3) Active transport: This process needs energy & takes place against the
concentration gradient e.g. Na+ /K+ pump.
4) Selective permeability: By presence of receptors in the cell coat that allow
certain substance only to into the cell, so it is also called receptor- mediated
endocytosis.
5) Bulk transport (vesicular transport): Large molecules enter & leave the cell by
one of two processes:
*Exocytosis: in which substances leave the cell to outside.

*Endocytosis: in which substances enter the cell. If the substance that enters the cell is solid
the process is called Phagocytosis. If the substance that enters the cell is fluid the process is
called pinocytosis.
 MITOCHONDRIA


 Definition:
 It is a membranous cell organelle. It is the power house of the cell responsible for cell
respiration & energy production (ATP).
 Light microscope (L.M.):
 Mitochondria appear as granules, rods or filaments. They need a special stain to be
demonstrated e.g. iron hematoxylin (dark blue) & Janus (green).
Electron Microscope (E.M.):

Each mitochondrion appears as a vesicle rounded or oval in shape & covered with
double membranes. Separated by inter- membranous space. The outer membrane is
smooth while the inner one shows folds or shelves called cristae.

Mitochondrial matrix: fills the internal cavity of mitochondria. It contains protein,

Ca & Mg as well as DNA &RNA. Oxidative enzymes are also present attached by
heads to the cristae.

Functions:

Mitochondria are the Power House of the cell. This energy is stored in the form of
ATP or produce heat to maintain body temperature.
3 – ENDOPLASMIC RETICULUM (ER)
Definition:
It is a membranous organelle. It is formed of flattened communicating vesicles & tubules that form reticulum inside the cytoplasm.
Types:
a) Rough (Granular) ER b) Smooth (agranular) ER

Site: in protein forming cells: In lipid forming cells:

e.g. fibroblasts, pancreas &plasma cells e. g. liver & cells in some endocrine glands.

L.M. basophilic cytoplasm Cannot be seen by L.M.

E.M. parallel communicating membranous - branching & anastomosing tubules with no ribosomes.
tubules = cisternae covered with ribosomes

Functions: 1. Synthesis of phospholipids of the cell membrane.

2. Synthesis of steroid hormones e.g. cortisol & testosterone
1. Synthesis of protein by the attached
3. Storage & breakdown of glycogen e.g. in liver & muscle.
ribosomes.
4. Detoxification of drugs e.g. in liver
2. Segregation of the formed protein
5. Muscle contraction by pumping of CA.
3. Packing of protein which travel as
6. Intracellular pathway.
transfer vesicles to be delivered to the
Golgi apparatus
4. Protect the cytoplasm from the action of
its hydrolytic enzymes
5. Intracellular pathway
 4-Golgi Apparatus

Definition:

It is a membranous organelle concerned with secretion secretory cells.

L.M.:

1. In sections stained with H&E. the area occupied by Golgi apparatus appears as unstained area & so it is called negative Golgi Image.

2. With (Ag) stain. It appears as a dark brown network & fibrils around the nucleus

Site: (perinuclear) e.g. in nerve cell or (supranuclear) between the nucleus & secretory pole in secretory cell. e.g. Pancreas.

E.M: it consists of flattened saccules (small sacs).

1. Immature convex surface, which is the forming surface (cis surface) that receives
the transfer vesicles which carry protein from r E.R.

2. Mature concave surface from which secretory vesicles come out carrying
condensed & modified protein. Also other vesicles containing hydrolytic enzymes will
come out & these are called Lysosomes
Functions:-

1. Concentration of protein formed by r E.R.

2. Modification of protein by adding sulphates or carbohydrates.

3. Discharge of secretion in the form of secretory vesicles

4. Isolation and package of hydrolytic enzymes in the form of Lysosomes.

Formation & maintenance of cell membrane & cell
 5- LYSOSOMES

Definition: They are membranous organelles rich in hydrolytic enzymes and considered
as the digestive system of the cell as they contain hydrolytic enzymes.

L.M.: The site of lysosome can be seen in the cell by using histochemical test.

E.M.:
1- Primary Lysosomes: These are the newly formed Lysosomes, not yet engaged in any digestive
process. They appear as small rounded homogenous vesicles.

1. Secondary Lysosomes: They result from fusion of primary Lysosomes with intracellular
molecules. They appear as heterogonous vesicles. They are of different types:

a) Heterolysosome: It results from fusion of a primary lysosome with a phagocytic vesicle

containing food or bacteria.

b) Multivesicular bodies: they result from fusion of primary lysosomes with pinocytic vesicle
containing fluid droplets.

c) Autolysosomes: They result from fusion of primary lysosomes with vesicles containing old
organelles.

d) Residual bodies: These are secondary lysosomes containing the undigested remnants fate.
a) They either discharge their contents outside the cell or accumulate within the cell as
lipofucsin granules as in long lived cells e.g. cardiac muscle or nerve cell.

Functions:

1. Digestion of nutrients & fluid droplets.

2. Defensive function, destruction of any bacteria or virus.

3. Removal of any degenerated old organelles.

4. Lysis of the cells as a whole after death.

5. Change of inactive hormone into active one. e.g. in thyroid gland.

6. Help the sperm to penetrate the ovum.

 NUCLEUS

Shape: Rounded, oval, flat, horse- shoe, kidney shaped, segmented or lobulated.

Site: Central, eccentric, peripheral & may be basal in position.

Number: Single (mononucleated), two nuclei (binucleated), or many nuclei (multinucleated).

L.M. The nucleus appears as a prominent basophilic structure within the cell as it contains nucleic
acids (DNA & RNA), it may be:

1- Vesicular nucleus: Pale stained as it has extended chromatin.

2- Condensed nucleus: Darkly stained due to its condensed chromatin.

E.M.: The nucleus is composed of:

1. Nuclear membrane. 2. Nuclear chromatin.

3. Nuclear sap. 4. Nucleolus.

Classification of chromatin according to site:

1. Peripheral chromatin adherent to nuclear membrane.

2. Nucleolus associated present around the nucleolus.
3. Chromatin Island scattered between the nucleolus & nuclear membrane.

Functions of nucleus:

4. It is responsible for cell division as it contains chromosomes which carry the

genetic information.
5. It controls all the vital processes within the cell, as protein formation.
6. It forms the different types of RNA (mRNA, tRNA, rRNA).
Thank you