Primary or Basic Tissue. Introduction

A tissue is composed of similar cells that are specialized to

perform a common function (s).

Four adult primary types of tissues form the "fabric" of the

human organism:

1. Epithelial tissues (ET; covering/lining);

2. Connective tissues (CT; support);

3. Muscle tissues (MT; movement);

4. Nervous tissues (NT; control).

Are derived from three embryonic germ layers:

1. Ectoderm (outside) gives rise to ET and NT;

2. Mesoderm (middle) gives rise to ET, CT and MT;

3. Endoderm (inside) gives rise to ET.

The Four Basic Tissues

Epithelium

Lining or glandular, less or no intercellular space,

junctions, avascular

Connective tissue

Has intercellular space, vascularized

Muscle tissue

Elongated cells specialized for contraction (smooth,

skeletal, cardiac)

Nervous tissue

Elongated cells specialized to receive & send signals

(neurons)

Glial supportive cells

Stomach as an Organ Within Digestive System

Epithelium

Epi → above

Thelium → nipple like

Most of the epithelial organs of the body are derived from

Ectoderm and Endoderm germ layers

Few organs containing epithelia that arise from Mesoderm

e.g.

Kidney, male and female reproductive system, lining of

vessels and body cavities

Common features of epithelia

Cells are connected to one another providing a lining for a surface

or a hollow organ or tube

Sit on a layer of fine filaments, called a "basal lamina".

Form a boundary between the external environment and the

remainder of the organ.

Control movement of substances into and out of that organ.

General Structural Characteristics1. Cellularity: ETs show tightly packed sheet (s) of cells with

little intercellular material between them.2. Polarity:

a. Always have a free surface (apical surface) which opens to the outside or to an internal space (lumen);

b. Free surface may possess modifications → microvilli, cilia

3. Basement Membrane:"basal surface" anchored to underlying CT by a basement

membrane4. Specialized contacts include:

a. Tight junctions (zipper-like junctions that prevent intercellular leakage)

b. Desmosomes (hold adjacent cells).c. Gap junctions

5. Avascularity: a. no blood vessels.b. nourished with nutrients by diffusion.

6. Regeneration: high regeneration capacity, due to rapid cell division

General Structural Characteristics

7. Locations: ETs cover us and line us:

a. Coverings:

body (i.e. epidermis)

b. Linings:

Internal spaces (i.e. lumen of the intestine),

line body cavities (i.e. Visceral & parietal

membranes),

line ducts of exocrine glands (i.e. sweat

glands).

Functions:

a. Protection (i.e. epidermis)

b. Absorption (i.e. lining of intestine)

c. Secretion (i.e. glands)

d. Excretion (i.e. G.I.T and kidney)

e. Filtration. (i.e. lining of kidney capillaries)

f. Sensory perception ( i.e. skin, G.I.T)

Epithelium

Definition

Type of tissue formed by collection of cells in the form of layer (s),

with or without very little intercellular space, whose main function

is to cover and protect body surfaces but can also form ducts and

glands or be specialized for secretion, excretion, absorption and

lubrication.

Classified according to the;

1. NUMBER OF CELL LAYERS

Simple epithelium; composed of a single layer of cells

Stratified epithelium; contains several layers.

2. SHAPE OF THE APICAL CELLS.

Squamous, (flat cells → scale-like, or leaf like)

Cuboidal ( cube-shaped )

Columnar ( tall, elongated ) .

To correctly identify the type of epithelium, requires three words

(e.g., simple columnar epithelium, stratified squamous epithelium,

etc.)

Key cell structures at each surface

Microvilli, Cilia,

Stereocilia

Specialized

junctions

(Cellular interdigitations)

Basal lamina + receptors

Epithelial Cell Types -

Nomenclature

SIMPLE – 1 cell layer thick

STRATIFIED – 2 or more cell layers thick

Squamous – cell width > height

(i.e., flat)

Cuboidal – width/depth/height ~same

Columnar – cell height >> width

Simple squamous epithelium

Squama → flat, leaf like or

scale like

A single layer of flat cells

Surface view, tile-like pattern

of closely adherent cells,

polygonal in outline ( eggs in

a fry pan )

Flat ( circular nucleus)

SIMPLE SQUAMOUS EPITHELIUM

endothelium, mesothelium

• In sections perpendicular to the plane of the epithelium →

• Cell are thin and fusiform or rectangular

Simple squamous epithelium

Simple cuboidal epithelium

In surface view,mosaic of

polygonal cell,

Outlines much smaller than

those of sq. epth.

Rounded nuclei in the centre

e.g Thyroid, ducts of various

glands, kidney tubules

SIMPLE CUBOIDAL EPITHELIUM

proximal and distal renal tubules

Duct

Simple cuboidal epithelium

Figure 4.4a

Simple cuboidal epithelium

Simple columnar epithelium

Cells have rectangular outlines

with their long axis

perpendicular to the basal

lamina

Height of the cells is more than

their width,

Tall and slender and, hence,

columnar in form,

Their nuclei tend to be aligned

at the same level ( usually

close to the base )

e.g. digestive tract, uterus,

Striated borderat apical surface

Basement membrane

A simple

columnar

epithelium

may have

more than

1 type cell

within it.

... with cilia

Simple columnar epithelium

STRATIFIED EPITHELIUM

Stratified Squamous epithelium

Cells on the basal lamina are

rounded (may be elongated)

Above this layer are irregularly

polyhedral cells

Becoming increasingly flattened

toward the surface,

Superficial layers they are thin

squamous cells.

Two types

Keratinized and Nonkeratinized

e.g. skin, esophagus,

Stratified squamous epithelium

Stratified squamous epithelium

Stratified Cuboidal Epithelium

Found only (typically) in the

ducts of sweat glands in the

adult and consists two layers of

cuboidal cells.

Cells of superficial layer are

usually smaller as seen in

cross section than those of the

basal layer.

Other locations (mammary

glands salivary glands

pancreas)

Figure 4.4b

Stratified Cuboidal Epithelium

Stratified Cuboidal Epithelium

Two (or more layers) of cells;

Secretes sweat; ovarian hormones & produces sperm

Found in sweat gland ducts; ovarian follicles & seminiferous

tubules

specialized epithelium = Seminiferous tubules (Germinal Epithelium)

Stratified columnar epithelium

Uncommon type of epithelium

Superficial cells are columnar and basal cells are cuboidal

One or more rows of polygonal cells may be lying between basal cells and the columnar cells

e.g. conjunctiva, pharynx, large excretory ducts of some glands

Ciliated stratified columnar epithelium → soft palate, larynx

Stratified columnar Epithelium

Pseudostratified columnar epithelium

All cells are in contact with the basal

lamina but all of them do not reach the

surface

Some cells are broad at their base but

narrow upward

Taller cells extend through the entire

thickness of epithelium, widest near the

free surface and narrow at basal lamina,

Nuclei are in wider part of cells of both

shapes,

Nuclei aligned at two levels in

the epith: creating a false

impression of cell stratification

hence,→ Pseudostratified epith:

e.g. urethra of male and in the

excretory duct of parotid gland,

Ciliated; Pseudostratified

columnar epithelium e.g. trachea

Pseudostratified columnar epithelium

Pseudostratified columnar epithelium

Transitional epithelium “Urothelium"Found in urinary tract

Appearance, in histological

sections, varies greatly depending

on its degree of distension

Empty, contracted bladder, it has

many cell layers ( usually 5 – 7)

Base have a cuboidal or low

columnar shape cells

Above, polyhedral cells, superficial

cells are very much larger, with a

characteristic rounded free surface

(dome shaped appearance)

Apical surface may appear “domed” (empty)

Transitional epithelium

Transitional Epithelium

empty bladder full bladder

from renal pelvis to

neck of urethra.

When the urinary bladder is full

(apical surface appear flattened)

Figure 4.4c

Transitional epithelium

specialized epithelium = Olfactory Epithelium