NucleusDefinition: Contains genetic material (DNA of chromosomes)Directs protein synthesis (RNA)In all cells except (RBCs) & (platelets) (un truecells).

Number: Usually one, two in liver cell, more than 2 (osteoclasts, skeletal muscle cell).

Position: Central, eccentric, basal.

Stains : Hx, methylene blue (basic stains) dark blue (due to DNA & RNA).

Shape: Rounded, oval,flat, horseshoe,kidney shaped,segmented or or lobulated.

LM: basophilic (DNA& RNA).1-vesicular: pale (open face) in nerve cells. (active cells).2- condensed: dark (closed face) in lymphocyte. (inactive cells).

NucleusEM:1.Nuclear membrane (nuclear envelope):

LM: Basophilic line (inner chromatin and outer ribosomes)

EM: Double wall interrupted by nuclear pores.Outer membrane: Granular (ribosomes attached to rER). Inner membrane: Fibrillar (peripheral chromatin).Nuclear pores: Outer and inner membranes fuse. Covered with diaphragm. for passage of substances between nucleus & cytoplasm.

2.Nuclear sap:Colloid solution between chromatin and nucleolus.Formed of nucleoproteins, enzymes, sugars, Ca, K, P.Transport of RNA through pores to the cytoplasm. 22

3. Chromatin: Formed of nucleoprotein (DNA + histones) & forms the chromosomes.

LM: Basophilic particles and threads. 2 types:Euchromatin: Extended, active, pale. (invisible) It is formed of extended chromosomes with active genes responsible for protein synthesis.

Heterochromatin: Condensed, inactive, dark. (visible) It is formed of coiled chromosomes with inactive genes.

EM:Euchromatin: electron lucent fine granules.Heterochromatin: electron dense masses Arranged as:• Peripheral chromatin at inner nuclear membrane.• Chromatin islands in nuclear sap.• Nucleolus associated chromatin related to nucleolus.

Function:• Genetic information (DNA).• Formation of rRNA, mRNA, tRNA.• Protein synthesis. 23

4. Nucleolus:LM: Rounded, basophilic(rich in ribonucleic acid).The nucleus may contain one 0r two or noNucleoli (activity).

EM: Spongy, not limited by membrane.-Nucleolar organiser: DNA.-Pars fibrosa : newly formed strands of rRNA-Pars granulosa: mature rRNA (granules)

Function: Formation of ribosomal RNA.rRNA passes through nuclear pores to the cytoplasm to form ribosomes.

Functions of the nucleus:1- cell division , carries the genetic information2-It control all vital processes.3- It forms all types of RNA (mRNA,rRNA,tRNA) 24

EPITHELIAL TISSUEGeneral Characters

• Arise from the three germ layers (Ectoderm = skin endoderm = lining GIT, mesoderm = endothelium & mesothelium)

• Crowded cells.minimal intercellular spaces.

• Avascular, but richly innervated • Resting on a basement membrane• Receive nutrition from the underlying CT• .High power of regeneration.Types:• Surface epithelium: Covers surfaces &

lines cavities (simple & stratified).

• Form glands (glandular epithelium) or act as receptors (neuroepithelium) or have a contractile function (myoepithelium).

I. Simple Epithelium 1- Simple Squamous:

One layer of flat cells with flat nuclei. Resting on BM. It gives smooth surface for easy

movement & thin surface that help exchange of gases & fluids.

– Endothelium (lining the CVS).– Alveoli of lung. (gas exchange).– Mesothelium (as pleura,

peritonium & pericardium).– Parietal layer of Bowman’s

capsule. (filtration of blood).

2- Simple Cubical:

One layer of cubical cells with central rounded nuclei.

– Thyroid follicles.– Convoluted tubules of kidney.– Acini & small ducts of exocrine

glands eg. Salivary glands.

– Function: reabsorption & secretion.

I. Simple Epithelium 3-Simple Columnar:

-One layer of columnar cells with basal oval nuclei.

Function : secretion & absoptionSites:Digestive system, lining the stomach (secretion). intestine (absorption) with

microvilli., gall bladder , pancreatic & bile

ducts

• Goblet cells:• Modified columnar

cell.• Secrete mucus.• Site: small & large

intestine.• Vacuole.

4-Simple columnar Ciliated:

+ cilia on the free surface.- Uterus.- Fallopian tubes...help movement of ova.- Bronchioles of lung.....move secretion to upper part of respiratory tract.

I. Simple Epithelium 5- Pseudo-Stratified

Columnar: A- Non ciliated

One layer of crowded columnar cells. Some cells don’t reach the free surface.male genital tract:

(membranous urethera & vas deferens)

- Large ducts of glands

B- Pseudo-Stratified Columnar Ciliated:

+ cilia & goblet cells.Upper respiratory tract ( nasal cavity, trachea & bronchi).

C- Pseudo-Stratified Columnar Ciliated (nonmotile cilia):

epidedymis

• B) Stratified Epithelium: Several layers of cells for protection.1-Stratified squamous epith:• 5-30 layers. • Clear wavy basement membrane.• Basal cells tall columnar with basal oval nuclei attached to basement membrane by hemidesmosomes. Basal layer acts as germinal layer (mitotically active).

Intermediate layers polygonal , central rounded nuclei, attached together by desmosomes. Cells smaller near surface. Superficial layers squamous with flat nuclei.

Types:Non keratinizing:. In oral cavity, esophagus,cornea

Keratinizing: In skin,external ear and nose.

• 2-Transitional epithelium: • In urinary passages (renal pelvis, ureter, urinary bladder, urethra) so called urothelium. • Relaxed state: Passages are empty it is formed of 6-8 layers. • Nonclear, nonwavy b.membrane.• Basal cells are low columnar. • Intermediate cells are polygonal. Mucin like substance in intercellular Space--- gliding of cells over each other. • Superficial cells large cuboidal with convex surface, may contain 2 nuclei.

• Stretched state: Passages are full of urine

it is formed of 2 to 3 layers of squamous

cells. So it is called transitional for

its ability to change its thickness as its cells can stretch and flatten to increase the internal volume of the organ

Neuro-epithelium

Epithelial cells act as receptors, formed of

sensory cells & supporting cells sensory cells have hairs at their free surfaces . Their bases are surrounded with sensory nerve fibers.

Sites:

Tongue: Taste buds (taste).