Dr. Maher Hadidi, University of Jordan 1

Tissues

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TypesTissues are classified into 4 types according to their

structure and function:

1. Epithelial tissues

2. Connective tissues

3. Muscular tissues

4. Nervous tissue

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1. Epithelial tissues

• Cover body surfaces and line hollow organs, body cavities, and forms glands.

• Allow body to interact with its internal and external environments.

• Form of tightly packed cells with little intercellular space.

• Its cells arranged in sheets, single or multiple layers.• Rich in nerve supply.• It is avascular but receive blood from the nearby CT.

Major functions:1. Act as a selective barriers that limit

or aid the transfer of substances into and out the body.

2. Produce secretions on their free surfaces.

3. Has high capacity for renewal, since its cells has high rate of cell division.

(Healing of wounds?)

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1. Epithelial tissues

Divided into two types:

A. Covering and lining epithelium.

B. Glandular epithelium.

They forms the secreting part of glands.

A. Covering and lining epithelium are classified according to two characters:

1. Shapes of cells.

2. The arrangement of cells into layers.

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Shapes and layers of cells

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1. Shapes of cells

This classification is based on the shape of the cells

at the apical (apex / Top) surface.

a. Squamous cells (flat): Are thin, allow rapid passage of substances through them.

b. Cuboidal cells: shaped like cubes, may have microvilli and function in either secretion or absorption.

c. Columnar cells: like columns, may have cilia or microvilli.

d. Transitional cells: Able to change their shape, from squamous to cuboidal and back e.g.. urinary bladder.

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2. Layers of cells

Cells arranged in one or more layers depending on

their function:

a. Simple epithelium:

Cells arranged in one layer.

b. Pseudostratified epithelium: (pseudo= false)

• Tissue appears to be several layers but is really a single layer. Cells nuclei lie at different levels and cells appears to have multiple layers.

• All its cells rest on the base but not all of them reach the surface.

c. Stratified epithelium:

Cells arranged in two or more layers.

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Classification of epithelial tissue

When the we combine the 2 characters (cell shapes

of and number of layers), epithelial tissue has the

following types:

I. Simple epithelium

a. Simple squamous.

b. Simple cuboidal.

c. Simple columnar (nonciliated and ciliated)

d. Pseudostratified columnar (nonciliated and ciliated)

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Classification of epithelial tissue

II. Stratified epithelium

a. Stratified squamous.

b. Stratified cuboidal epithelium.

c. Stratified columnar epithelium.

d. Transitional epithelium.

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a. Simple squamous epithelium

Form of single layer of flat cells.

Locations: Peritoneum, pleura, pericardium.

Functions:

– Filtration

– Diffusion

– Secretion

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b. Simple cuboidal

Form of a single

Layer of cube-shaped

cells.

Locations:

– Line kidney tubules.

– Surface of ovary.

– Ducts of pancreas.

Functions:

– Secretion

– Absorption.

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c. Simple columnar nonciliated

• Form of single layer of nonciliated column like cells.

Contain cells with microvilli and Goblet ( كأس، قدح) cells.

• location: lines Gastrointestinal Tract.

• Functions: High capacity of secretion and absorption.

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d. Simple columnar ciliated

Form of single layer of ciliated column like cells with Gobletcells in between.

Locations:• lines (Bronchioles of lung) small tubes.• lines Uterine tubes and Uterus.Functions:• Move mucus and foreign particles toward throat.• Move Ovum toward uterus.

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e. Pseudostratified columnarAppears to have several layers since nuclei located at various levels.1. Ciliated: Form of cells with cilia and Goblet cells. • Locations: Lines airways of most of upper respiratory tract.• Functions: Secretes mucus that traps foreign particles.2. Nonciliated: Contains cells without cilia and lack goblet cells.• Locations: Lines larger ducts of many glands & epididymis.• Functions: Absorption and protection.

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II. Stratified epithelium

Types:

a. Stratified squamous

• keratinized

• Nonkeratinized.

b. Stratified cuboidal epithelium.

c. Stratified columnar epithelium.

d. Transitional epithelium.

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a- Stratified squamous epithelium

• Forms of several layers of cells.

• Cells in apical layer and some layers deep to it are squamous (Flat).

• Cells move gradually from deep to superficial away from blood vessels then die and slough (fall off).

• Found mainly in places subject to attrition (wear and tear) as skin, mouth, esophagus, vagina).

Two types:

• Keratinized (dry).

• Nonkeratinized (wet).

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Keratinized stratified squamous :• Covers dry surfaces such as epidermis of skin (superficial

layer of the skin). Form tough layer of keratin (tough protein)between surface cells.

• Functions:Protect skin and underlying tissues from heat, microbes, chemicals and

water loss.

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Nonkeratinized stratified squamous

• Surface layers contain small amount of keratin and always wet.• Location: Lines wet surfaces as Mouth and Esophagus.• Function: Protection against scratch, water loss, ultraviolet radiation, and

foreign invasion.• Both types form first line of defense against microbes.

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d. TRANSITIONAL EPITHELIUM

• Show variable appearance.

• The form of these cells changes according to the degree of distention of the organ.

• Locations: Urinary bladder, ureter.

• Functions:Allow the organ to stretch and protection from rupturing.

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B. Glandular Epithelium

• A gland may consist of a single epithelial cell or a group of cells adapted for secretion.

• Normally found as:– Unicellular glands as Goblet cells.– Multicellular glands group of cells

as Salivary glands.

• All glands of the body are classified into:– Exocrine (Exo=outside, crine=secretion): Secrete substances

onto a surface by ducts.– Endocrine: Secrete hormones into the blood.– Mixed (exocrine and endocrine): e.g.. Pancreas

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Exocrine multicellular glands

• Most exocrine glands are multicellular glands, form of a group of cells, e.g.. Sweat and salivary glands.

• Each gland has a secretory part and ducts.

Divided according to two conditions:

• Branching pattern of its duct.– Simple glands duct not branched.

– Compound glands the duct branches.

• Shape of its secretory part.– Tubular tubular glands.

– Rounded alveolar glands.

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Functional classification of exocrine glands

• The ER and Golgi complex works together to form secretory vesicles.

• Based on the releasing mode of their secretions and whether the secretion is a product of a cell or consists whole or a partof the cell.

1. Merocrine glands (mero=a part):

2. Apocrine glands (apo=from).

3. Holocrine glands (holo= entire).

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Functional classification of exocrine glands

Merocrine glands

(mero=a part):

• Secretions are released via exocytosis.

• Most exocrine glands of the body are merocrine glands.

Apocrine glands

(apo= from):

• Secretion collected at the apical part of the cell then pinched off by exocytosis.

Holocrine glands

(holo= entire):

• Secretion collected in their cytosol.When cell matures, it ruptures andbecomes the secretory product.

e.g. sebaceous gland.

Dr. Maher Hadidi, University of Jordan 32