Tissue Types and Epithelial Tissue

TISSUE

• Tissue are group of similar cells that perform similar functions in the body.

TYPES OF TISSUE

1. Epithelial tissue
2. Connective Tissue
3. Muscle Tissue
4. Nervous Tissue

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1. EPITHELIAL TISSUE

• Composed of closely packed cells with minimal intercellular space.
• Epithelial tissue covers both internal and external surfaces of the body, such as outer layer of skin, lining of the digestive tract.
• Forms the functional part of glands.

Functions

• Protection: Acts as a barrier to protect from physical damage, pathogens.
• Secretion: Produces and releases substances like mucus, hormones, and enzymes.
• Excretion: Helps in the removal of waste products, particularly in kidney tubules and skin.
• Absorption: Facilitates the absorption of nutrients in the intestines.
• Sensory functions (e.g., taste buds).

TYPES OF EPITHELIAL TISSUE

I. Simple epithelium

1. Simple squamous epithelium
2. Simple cuboidal epithelium
3. Simple columnar epithelium

II. Stratified epithelium

1. Stratified squamous epithelium
2. Stratified cuboidal epithelium
3. Stratified columnar epithelium
4. Transitional epithelium
5. Pseudo-stratified epithelium

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I. Simple epithelium

1. Simple squamous epithelium

Structure

• Composed of a single layer of flat, thin cells resting on basement membrane.
• With flat nucleus.

Location

• Lung Alveoli
• Lining of blood vessels
• Mesothelium Pleura, pericardium
• Kidneys

Function

• Rapid exchange of substance like air, nutrition.
• Filtration of substances in organs like the kidneys.
• Lubrication (reduce friction).

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2. Simple cuboidal epithelium

Structure

• Made up of a single layer of cube-shaped cells.
  
• Cells are roughly equal in height and width.

Location

• Kidney Tubules
• Ducts of Glands: like the thyroid, salivary glands, and pancreas.
• Surface of Ovaries

Function

• Secretion: Produces and releases hormones, enzymes, and other substances.
• Absorption: absorption of water, electrolytes, and nutrients, particularly in the kidneys.
• Protection

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3. Simple columnar epithelium

Structure

• Composed of a single layer of tall columnar cells resting on basement membrane.
• With oval shaped nucleus.
• If cilia is present known as Simple columnar ciliated epithelium.

Location

• Lining of the Stomach and Intestines
• Uterine Tubes: Ciliated cells help move the egg toward the uterus.
• Gallbladder: Plays a role in bile absorption.

Function

• Secretion: Produces mucus and digestive enzyme.
• Absorption: Facilitates the uptake of nutrients in the digestive tract.
• Movement (like the egg in the uterine tubes).

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II. Stratified / Compound epithelium

1. Stratified squamous epithelium

Structure 

• Basal cells are columnar in shape.
• Intermediate cells are polygonal in shape.
• Superficial cells are flat squamous cells which may be nucleated or non nucleated.

Types of Stratified squamous epithelium

i. Keratinized Stratified Squamous Epithelium: 

Structure

• Basal cells are columnar in shape.
• Intermediate cells are polygonal in shape.
• Superficial cells are flat squamous cells which are non nucleated (keratin).

Location

• Found in areas exposed to friction and moisture loss.
• Skin, hair & nails.

Function

• Protection
• Water Retention

ii. Non-keratinized stratified squamous epithelium 

Structure

• Basal cells are columnar in shape.
• Intermediate cells are polygonal in shape.
• Superficial cells are flat squamous cells which are nucleated.
• The surface remains moist due to the presence of mucus or other fluids.

Location

• Oral Cavity
• Esophagus
• Vagina
• Anus
• Eye cornea, conjunctiva

Function

• Protection
• Lubrication: The moist surface aids in reducing friction.
• Secretion, Sensory Function.

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2. Stratified cuboidal epithelium

Structure

• Consisting of multiple layers of cube-shaped (cuboidal) cells.
• The nuclei are usually centrally located within the cells.

Location

• Found in sweat glands, mammary glands, and larger ducts of some glands.

Function

• Protection
• Secretion

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3. Stratified columnar epithelium

Structure

• Composed of two or more layers.
• The basal layer is composed of cuboidal or columnar cells.
• Outermost layer consisting of columnar cells.

Location

• Conjunctiva of the Eye.
• Present in some ducts of large glands.
• Male Urethra.

Function

• Protection
• Secretion
• For example, in the conjunctiva, it helps maintain moisture and protects delicate eye.

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4. Transitional epithelium

Structure

• Consists of three to four layers of cells.
• The basal layer contains cuboidal or columnar cells.
• Intermediate layer consists pear shaped cells.
• The superficial layer features umbrella shaped cells.

Location

• Urinary Bladder
• Ureters
• Urethra

Function

• Helps in stretching when bladder fills with urine.
• When it stretched, it is not damaged and appears to be thinner with cells become flattened.

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5. Pseudo-stratified epithelium

Structure

• Single layer but appears multi-layered because tall cells of different height the nuclei are at different levels.
• It can contain ciliated cells.

Location

• Lining of the trachea and bronchi.
• Lining of the nasal passages, helping to filter and humidify air.
• Present in parts of the male reproductive system, such as the epididymis.

Function

• Protection: Acts as a protective layer.
• Mucus secretion
• Movement: Cilia help move mucus and debris out of the airways.

 

 

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