Epithalial tissue pdf - د.ملاك الياور د.فردوس محمد د.هدى الخطيب د.زهراء قاسم

Epithelial Tissue

Lecturer: Dr.Firdous M. Jaafar

Department of Anatomy/Histology section

Lecture 1

Objectives

• 1- Define epithelial tissue, and describe its cell types.
• 2- Identify the intercellular adhesion and junctions, and

enumerate their types.

• 3- Enumerate the types of epithelial tissue.
• 4- Define basal lamina and basement membrane, and

recognize their functions.

• 5- Describe the specialization of epithelial cell surface;
• a- Define microvilli.
• b- Define stereocilia.

Introduction

• the human body is composed of only four basic types of

tissue

• Epithelial, connective, muscular, and nervous.

• These tissues, which are formed by cells and molecules of the

extracellular  matrix,  exist  not  as  isolated  units  but  rather  in
association  with  one  another  and  in  variable  proportions,
forming different organs and systems of the body.

Epithelial tissues

• are composed of closely aggregated

polyhedral cells

with very

little

extracellular substance

. These cells have strong

adhesions,    membrane  interdigitations,  and  intercellular
junctions. These features allow the cells to form cellular sheets
that  cover  the  surface  of  the  body  and  line  its  cavities  or  are
arranged as three-dimensional secretory units.

• They have

different shapes

; columnar, cuboidal, or squamous.

• They rest on

basal lamina

(

basement membrane

)

• The lateral membranes between adjacent cells exhibit

intercellular junctions

Epithelial tissues

• Epithelial cells are polyhedral in shape, ranging from

squamous, cuboidal, and columnar.

• Nuclear shape corresponds to the cell shape; ranging from flat,

cuboidal, to elongated, and their long axis is parallel to the
long axis of the cell.

• All epithelial cells rests on connective tissue layer to support

these cells.

• The lower part of epithelial cell is called

basal pole,

while the

upper part is called

apical pole or free surface.

Epithelial tissues

• The principal functions of epithelial tissues are
• 1- the covering and lining of surfaces (eg, skin,

intestines).

• 2-absorption (eg, intestines).
• 3- secretion (eg, glands),
• 4- sensation (eg, gustative and olfactory

neuroepithelium).

• 5- contractility (eg, myoepithelial cells).

Basal Lamina & Basement

Membrane

•

Most epithelial cells are separated from the connective tissue by a sheet of
extracellular material called the

basal lamina

. This structure is visible only with the

electron microscope, and it is called

basement membrane

when seen by LM

Structure of BM

• it appears as a dense layer, 20–100 nm thick, consisting of a delicate

network of very fine fibrils (

lamina densa

), and an electron-lucent layer on

one or both sides of the lamina densa, called

lamina rara

lamina lucida

Functions of basal lamina

• 1- structural functions as supporting the cells.
• 2- provide a barrier that limits or regulates the exchange of

macromolecules between connective tissue and cells of other
tissues.

• 3- influence cell polarity, regulate cell proliferation and

differentiation by binding with growth factors, influence cell
metabolism, and serve as pathways for cell migration.

• 4- contain the information necessary for certain cell-to-cell

interactions.

• 5-establishment of new neuromuscular junctions around

muscle cells.

Intercellular Adhesion & Junctions

• Several membrane-associated structures contribute to cohesion

and communication between cells.