4.0 (introduction) and 4.2 Epithelial tissue

Histology =

the microscopic study of tissues

Tissue =

a group of cells with similar structure and function

Tissues work together to form?

organs

The body has 4 major tissue types:

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1. Epithelial

2. Connective

3. Muscle

4. Nervous

What is epithelial tissue?

Sheet of cells that covers or lines to form boundaries, includes glands

Examples of epithelial tissues:

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• Skin

• Digestive tract lining

• Urinary tract lining

• Kidney tubules

• Blood vessel lining

Main functions of epithelial tissue:

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• Protection

• Absorption

• Filtration

• Excretion

• Secretion

• Sensory reception

Polarity is epithelial means?

Epithelial cells have different sides.

Apical surface

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• May have:

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• Faces the outside of the body or the inside of a hollow organ/lumen

• May have:

  • Microvilli

  • Cilia

Microvilli →

increase surface area for absorption

Cilia →

move substances along the surface

Basal surface is attached to?

basement membrane

basal surface-

sits on basal lamina made by epi cells

Why is polarity important?

It allows substances to move in a specific direction.

Epithelial cells are ________ connected.

tightly

specialized cell junctions

• Tight junctions →

• Desmosomes →

• Hemidesmosomes →

• Tight junctions → seal spaces between cells

• Desmosomes → attach cell to cell and provide strength

• Hemidesmosomes → attach cells to the basement membrane

Avascular =

Avascular = no blood vessels

Epithelial tissue does not

Instead:

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have its own blood supply.

Instead:

• Nutrients and oxygen diffuse from capillaries in the underlying connective tissue.

epithelial can regenerate_______

quickly (closes holes)

Epithelial tissue is frequently exposed to:

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• Friction

• Chemicals

• Microorganisms

• Other environmental damage

Epithelial cells have a _____________________ through _______

Epithelial cells have a high rate of regeneration through mitosis

Epithelial tissue sits on a

basement membrane

___________+ ______________ = basement membrane

Basal lamina + reticular lamina = basement membrane

Basal lamina

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• Closest to epithelial cells

• Made by epithelial cells

• Provides support and acts as a boundary

Reticular lamina

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• Below basal lamina

• Made by connective tissue cells

The basement membrane:

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• Supports the epithelium

• Helps attach epithelium to underlying connective tissue

• Provides strength

• Acts as a boundary

Epithelia are classified by:

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1. Number of layers

2. Shape of cells

Simple is?

• 1 layer

Stratified is?

• 2 or more layers

Pseudostratified

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• Looks like multiple layers

• Actually only 1 layer

• Every cell contacts the basement membrane

• Nuclei are at different heights, creating the appearance of multiple layers

Squamous

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• Flat

• Thin

• Scale like

Cuboidal

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• Approximately as tall as they are wide

• Box/square-shaped

Columnar

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• Taller than they are wide

• Tall/rectangular

Transitional

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• Cells change shape when stretched

Simple Squamous

Structure:

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Function:

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Structure:

• One layer of very thin, flat cells

Function:

• Diffusion

• Filtration

• Exchange

Locations of Simple Squamous

• __________→ ___________

• _________ →_____

• ________ → _______

• Alveoli of lungs → gas exchange

• Kidney glomeruli → filtration

• Blood vessels → endothelium

Simple Cuboidal

Structure:

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Function:

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Structure:

• One layer

• Cube-shaped cells

Functions:

• Absorption

• Secretion

Locations of Simple Cuboidal

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• Kidney tubules

• Glands/ducts

Simple Columnar

Structure

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May contain:

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Functions

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structure:

• One layer

• Tall cells

May contain:

• Microvilli

• Cilia

• Goblet cells

Functions

• Absorption

• Secretion

• Protection

Locations of Simple Columnar?

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• Digestive tract

• Stomach

• Small intestine

• Some respiratory/uterine structures

Microvilli =

increase surface area

Cilia =

move material

Goblet cells =

secrete mucus

Pseudostratified Columnar

Structure:

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Functions:

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Structure:

• Actually one layer

• Looks like multiple layers because nuclei are at different heights

• All cells contact the basement membrane

Functions:

• Protection

• Secretion

• Movement of material

Locations of Pseudostratified Columnar

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• Respiratory tract

• Nasal cavity

• Trachea

Stratified Squamous

Structure:

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Function:

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Structure:

• Multiple layers

• Surface cells are squamous

• Deeper cells are often cuboidal/columnar

Function:

• Protection from abrasion

Keratinized

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• Helps prevent:

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• Surface cells contain lots of keratin

• Surface cells are dead and lack nuclei

• Helps prevent:

  • Abrasion

  • Dehydration

  • Entry of pathogens

Location of Keratinized

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• Epidermis of skin

Nonkeratinized

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• Surface remains moist

• Protects against abrasion

Stratified Cuboidal

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• Example:

• Multiple layers

• Cuboidal cells at surface

• Relatively uncommon

• Often found in gland ducts

• Example: sweat and mammary ducts

Stratified Columnar

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• Multiple layers

• Columnar cells at surface

• Relatively uncommon

• Found in some glandular ducts and parts of the pharynx/urethra

Transitional Epithelium?

Cells can change shape when stretched.

Location of Transitional Epithelium

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• Urinary bladder

• Ureters

• Part of urinary tract

Example of Transitional Epithelium

When bladder fills:

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• Cells stretch

• Surface cells become flatter

• Epithelium becomes thinner

When bladder empties:

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• Cells return to a more rounded shape

Why are glands considered epithelial tissue?

Because glands are made of epithelial cells that specialize in secretion.

Two major gland types

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• Endocrine glands

• Exocrine glands

Endocrine glands- ______________

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Endocrine glands- internally secreting

• Ductless

• Picked up by blood

• Release products into the bloodstream

• Products are usually hormones

Examples of Endocrine glands

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• Thyroid

• Endocrine portion of pancreas

Exocrine glands-externally secreting

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• Use a duct

• Release products onto an epithelial surface or into a lumen

Examples of Exocrine glands:

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Examples:

• Sweat glands

• Salivary glands

• Gastric glands

Unicellular- ________

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scattered within epithelium

• One secretory cell.

  
  

Example of unicellular:

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• Goblet cell (produces mucus)

Multicellular- ____________

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Multicellular- invagination of epithelium into CT

• Many cells.

Multicellular Usually contain:

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• Duct

• Secretory portion

Exocrine Secretion Methods

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• Merocrine

• Apocrine

• Holocrine

Merocrine

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• Product released by exocytosis

• Cell remains intact

Apocrine

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• Part of the cell's apical portion pinches off

Holocrine

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• Entire cell breaks apart

• The cell becomes part of the secretion