Epithelium Tissue Structure and Function

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Questions and Answers

What is the main characteristic of epithelium?

It is composed of scattered polyhedral cells and a lot of extracellular matrix.

It is composed of scattered polyhedral cells and very little extracellular matrix.

It is composed of closely aggregated polyhedral cells and a lot of extracellular matrix.

It is composed of closely aggregated polyhedral cells and very little extracellular matrix. (correct)

What is the function of basement membrane?

To separate epithelium from underlying connective tissue (correct)

To provide nutrition to epithelial cells

To facilitate sensory reception

To protect epithelial cells from infection

What is the characteristic of avascular epithelium?

It has a rich blood supply

It has no blood vessels (correct)

It has a variable blood supply

It has a limited blood supply

What is the function of glands?

To secrete substances Signup and view all the answers

What type of epithelium lines the inner surface of body cavities?

Covering epithelium Signup and view all the answers

What is the main function of simple cuboidal epithelium?

Covering and secretion Signup and view all the answers

What is the characteristic of simple squamous epithelium?

It has a single layer of flattened cells Signup and view all the answers

What is the function of endothelium?

Transport of materials Signup and view all the answers

What is the characteristic feature of pseudostratified ciliated columnar epithelium?

Presence of four types of cells Signup and view all the answers

What is the function of simple squamous epithelium in the human body?

To protect underlying tissues Signup and view all the answers

Where is simple squamous epithelium commonly found?

In the lining of body cavities Signup and view all the answers

Where is stratified squamous epithelium found?

Skin and mucosa Signup and view all the answers

What is the function of transitional epithelium?

Stretching and accommodating varying amounts of urine Signup and view all the answers

What is the shape of nucleus in simple cuboidal epithelium?

Spherical Signup and view all the answers

What is the function of goblet cells in pseudostratified ciliated columnar epithelium?

Producing mucus Signup and view all the answers

What is unique about transitional epithelium?

It is flexible and can change shape Signup and view all the answers

What type of epithelium is found in the conjunctiva?

Stratified columnar epithelium Signup and view all the answers

What is the function of microvilli?

To increase the surface area of the cell Signup and view all the answers

What is the structure of a cilium?

Microtubules, 9×2+2, dynein, and cell membrane Signup and view all the answers

Where are stereocilia found?

Sensory cells of the ear Signup and view all the answers

What type of epithelium is found in the urinary bladder?

Transitional epithelium Signup and view all the answers

What is the function of cilia?

Produce a forward-moving wave Signup and view all the answers

Where are microvilli found?

Intestinal epithelial cells and proximal renal tubule Signup and view all the answers

What is the function of intercellular junctions?

Hold adjacent cells together Signup and view all the answers

What is the thickness of the lamina lucida?

10-50 nm Signup and view all the answers

What is the primary function of tight junctions?

To seal the space between cells Signup and view all the answers

What is the main function of reticular lamina?

Support and connection Signup and view all the answers

What is the function of plasma membrane infolding in epithelial cells?

Increase the basal surface area Signup and view all the answers

What is the characteristic feature of the structure of desmosomes?

A plate or spot-shaped structure with a 20-30 nm gap Signup and view all the answers

What is the function of hemidesmosomes?

Bind epithelial cells to the subjacent basal lamina Signup and view all the answers

What is the function of gap junctions?

To provide a pathway for communication between cells Signup and view all the answers

What is the characteristic of exocrine glands?

Maintain contact with the surface and discharge secretion through a duct system Signup and view all the answers

What is the composition of the basal lamina?

A layer of amorphous ground substance produced by epithelial cells Signup and view all the answers

What is the characteristic of endocrine glands?

Release secretion directly into blood stream Signup and view all the answers

What is the characteristic feature of the structure of intermediate junctions?

A plaque of electron-dense materials with microfilaments Signup and view all the answers

What is the role of the basement membrane?

To separate epithelial cells from underlying connective tissue Signup and view all the answers

Where are plasma membrane infoldings mainly found?

Proximal and distal renal tubule Signup and view all the answers

What is the composition of reticular lamina?

Reticular fibers and ground substance Signup and view all the answers

What is the characteristic feature of the structure of tight junctions?

Point-like fused structures arranged in 2-4 thread-like structures Signup and view all the answers

What is the term used to describe the complex of four types of junctional structures?

Junctional complex Signup and view all the answers

Study Notes

Epithelium Characteristics

Composed of closely aggregated polyhedral cells with little extracellular matrix
Cells cover body surfaces, line body cavities, and constitute glands
General features:
- Contain more cells and less extracellular ground substance
- Polarity: free surface faces air or other substances, basal surface faces underlying CT, and lateral surface faces adjacent cells
- Avascularity, but innervation: no blood vessels, but rich in nerve terminals
- Functions: protection, secretion, absorption, excretion, and sensory reception

Classification of Epithelium

Covering epithelium: covers body surface or lines inner surface of body cavities, tubes, and sacs
Glandular epithelium: main function is secretion
Sensory epithelium: has special sensory function

Covering Epithelium Classification

Simple epithelium:
- Simple squamous epithelium: one layer of flattened cells, found in mesothelium, endothelium, alveoli, and parietal layers of renal capsule
- Simple cuboidal epithelium: one layer of cells with same height and width, found in renal tubule, thyroid, and some ducts of many glands
- Simple columnar epithelium: one layer of columnar cells, found in respiratory tract, digestive tract, and glands
- Pseudostratified ciliated columnar epithelium: one layer of columnar cells with cilia, found in respiratory tract
Stratified epithelium:
- Stratified squamous epithelium: multiple layers of cells, found in skin, mouth, pharynx, esophagus, urethra, and vagina
- Stratified cuboidal epithelium: multiple layers of cells, found in sweat glands and developing ovarian follicles
- Stratified columnar epithelium: multiple layers of cells, found in conjunctiva

Epithelial Specializations

Specialization of free surface:
- Microvilli: increase cell surface area, found in intestinal epithelium and proximal renal tubule
- Cilia: move substances or particles stuck to the epithelium, found in respiratory tract
- Stereocilia: increase cell surface area, found in epididymis, ductus deferens, and sensory cells of the ear
Specialization of lateral surface:
- Intercellular junctions:
  - Tight junction (zonula occludens): seal the space between cells
  - Intermediate junction (zonula adherens): adhere and keep cell shape
  - Gap junction (communicating junction): provide a pathway between cells
  - Desmosome (macula adherens): firmly connect cells
Specialization of basal surface:
- Basement membrane: a sheet of amorphous material between epithelial cells and underlying CT
- Plasma membrane infolding: increase basal surface area and facilitate passage of water and ions, found in proximal and distal renal tubule
- Hemidesmosomes: bind epithelial cells to the subjacent basal lamina

Glandular Epithelium and Gland

Glandular epithelium: specialized for secretion
Gland: organs composed mainly of glandular epithelium
Classification of glands:
- Exocrine gland: maintain contact with the surface, discharge secretion through a duct system
- Endocrine gland: do not maintain contact with the surface, release secretion directly into blood stream
Formation of glands from covering epithelia: epithelial cells proliferate and penetrate connective tissue

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Description

Learn about the characteristics and functions of epithelial tissue, including its structure, junctions, and polarity. Understand the role of epithelium in covering body surfaces, lining cavities, and forming glands.