Comprehensive Skin & Cell Junctions: Structure, Function, and Diseases

What are the five main types of cell junctions in the body?

Tight Junctions, Adherens Junctions, Desmosomes, Hemidesmosomes, Gap Junctions.

What is the primary function of tight junctions?

To seal off passageways between adjacent cells, preventing leakage of substances.

Where are tight junctions commonly found in the body?

In epithelial tissues lining the stomach, intestines, and urinary bladder.

What do adherens junctions contain that helps them connect cells?

Plaque, which attaches to membrane proteins and microfilaments of the cytoskeleton.

What role do adherens junctions play in epithelial tissues?

They help resist separation during contractile activities, such as food movement in the intestines.

How do desmosomes differ from adherens junctions?

Desmosomes attach to intermediate filaments instead of microfilaments and provide spot-weld-like connections.

In which types of cells are desmosomes commonly found?

Epidermal cells and cardiac muscle cells.

What is the function of hemidesmosomes?

To anchor cells to the basement membrane rather than to adjacent cells.

What proteins are involved in hemidesmosomes?

Integrins on the inside attach to keratin filaments, while on the outside they attach to laminin.

What is the main function of gap junctions?

To allow communication and the transfer of ions and small molecules between neighboring cells.

What proteins form the fluid-filled tunnels in gap junctions?

Connexins, which create connexons.

What is the significance of gap junctions in avascular tissues?

They facilitate the transfer of nutrients and wastes.

How do gap junctions contribute to muscle and nerve function?

They enable rapid spread of nerve or muscle impulses, crucial for normal operation of the nervous system and muscle contraction.

What is the primary role of epithelial tissue?

To cover body surfaces, line hollow organs, body cavities, ducts, and form glands.

What is the structure of tight junctions?

They consist of weblike strands of transmembrane proteins that fuse adjacent plasma membranes.

What are the components of desmosomes?

Plaque and transmembrane glycoproteins called cadherins.

What is the role of plaque in adherens junctions?

It forms a dense layer that connects to both membrane proteins and cytoskeletal microfilaments.

What type of filaments do desmosomes attach to?

Intermediate filaments, specifically those made of keratin.

What is the difference between hemidesmosomes and desmosomes?

Hemidesmosomes anchor cells to the basement membrane, while desmosomes link adjacent cells.

What is the intercellular gap in gap junctions?

A very narrow space separating the plasma membranes of connected cells.

What types of tissues rely on gap junctions for communication?

Tissues such as cardiac muscle and certain parts of the nervous system.

What is the significance of cadherins in adherens junctions and desmosomes?

Cadherins are transmembrane glycoproteins that join cells together.

What is the function of epithelial membranes?

To cover and protect body surfaces and line cavities.

What are the main functions of epithelial tissue?

Protection, absorption, filtration, secretion, and excretion.

What distinguishes the apical layer from the basal layer in epithelial tissue?

The apical layer is the most superficial layer of cells, while the basal layer is the deepest layer.

How does epithelial tissue receive nutrients if it is avascular?

Epithelial tissue has its own nerve supply but lacks a blood supply, relying on diffusion from underlying tissues.

What is the basement membrane and what are its two layers?

The basement membrane is a thin extracellular layer consisting of the basal lamina and reticular lamina.

What is the function of the basal lamina?

The basal lamina is closer to the epithelial cells and contains proteins such as laminin and collagen.

What is the role of the reticular lamina?

The reticular lamina is closer to the underlying connective tissue and contains collagen produced by fibroblasts.

What is the significance of high cell division rates in epithelial tissue?

High cell division rates allow epithelial tissue to constantly renew and repair itself.

What are the two main types of epithelium?

Covering & lining epithelium and glandular epithelium.

What is simple epithelium and its primary function?

Simple epithelium is a single layer of cells that functions in diffusion, osmosis, filtration, secretion, or absorption.

What is stratified epithelium and where is it typically found?

Stratified epithelium consists of two or more layers of cells that protect underlying tissues in areas of wear and tear.

What characterizes pseudostratified epithelium?

Pseudostratified epithelium appears to have multiple layers due to varying cell nucleus levels but is actually a simple epithelium.

What are squamous cells and their function?

Squamous cells are thin and arranged like floor tiles, allowing for rapid passage of substances.

What are cuboidal cells and their role?

Cuboidal cells are as tall as they are wide, may have microvilli, and function in secretion or absorption.

What are columnar cells and their characteristics?

Columnar cells are taller than they are wide, protect underlying tissues, and may have cilia or microvilli for secretion and absorption.

What are transitional cells and their function?

Transitional cells change shape as organs stretch and collapse, such as in the urinary bladder.

Describe simple squamous epithelium.

It consists of a single layer of flat cells with a centrally located nucleus.

Where is simple squamous epithelium located?

It lines the heart, blood vessels, lymphatic vessels, air sacs of lungs, and forms serous membranes.

What are the functions of simple squamous epithelium?

Filtration, diffusion, osmosis, and secretion in serous membranes.

What is the role of epithelial tissue in forming boundaries?

Epithelial tissue forms boundaries between the body's organs and between the body and the external environment.

Why is epithelial tissue subject to physical stress and injury?

Epithelial tissue is exposed to various external factors and must withstand wear and tear.

How does epithelial tissue repair itself?

Through a high rate of cell division that allows for the sloughing off of dead or injured cells.

What is the significance of microvilli and cilia on epithelial cells?

Microvilli increase surface area for absorption, while cilia help in movement of substances across the epithelial surface.

What is the simple squamous epithelium that lines the heart and blood vessels called?

Endothelium.

What type of simple squamous epithelium forms the epithelial layer of serous membranes?

Mesothelium.

What is the description of simple cuboidal epithelium?

A single layer of cube-shaped cells with a centrally located nucleus.

Where is simple cuboidal epithelium located?

It covers the surface of the ovary, lines the anterior surface of the lens capsule, forms the pigmented epithelium at the posterior surface of the eye, lines kidney tubules, and makes up the secreting portion of some glands.

What are the primary functions of simple cuboidal epithelium?

Secretion and absorption.

What are the two forms of simple columnar epithelium?

Non-ciliated simple columnar epithelium and ciliated simple columnar epithelium.

What types of cells are found in non-ciliated simple columnar epithelium?

Microvilli and goblet cells.

What is the function of microvilli in non-ciliated simple columnar epithelium?

They increase the surface area of the plasma membrane, enhancing absorption.

What do goblet cells in non-ciliated simple columnar epithelium secrete?

Mucus.

Where is non-ciliated simple columnar epithelium located?

It lines the gastrointestinal tract, ducts of many glands, and the gallbladder.

What is the function of non-ciliated simple columnar epithelium?

Secretion and absorption.

What is the main characteristic of ciliated simple columnar epithelium?

It contains columnar epithelial cells with cilia at the apical surface.

What is the function of cilia in ciliated simple columnar epithelium?

They move mucus and foreign particles toward the throat.

Where is ciliated simple columnar epithelium located?

It lines some bronchioles, uterine tubes, uterus, efferent ducts of the testes, and parts of the central nervous system.

What is the description of pseudostratified columnar epithelium?

It is not a true stratified tissue; nuclei are at different levels, and all cells are attached to the basement membrane.

Where is pseudostratified columnar epithelium located?

It lines the airways of the upper respiratory tract and larger ducts of many glands.

What is the function of pseudostratified columnar epithelium?

Secretion and movement of mucus by ciliary action.

What is the description of stratified squamous epithelium?

It has several layers of cells; cuboidal to columnar shape in deep layers, with squamous cells forming the apical layer.

Where is keratinized stratified squamous epithelium found?

It forms the superficial layer of the skin.

What is the function of nonkeratinized stratified squamous epithelium?

Protection, lining wet surfaces such as the mouth and esophagus.

What is keratin and its role in keratinized stratified squamous epithelium?

Keratin is a tough, fibrous protein that helps protect the skin and underlying tissues.

What type of epithelium forms the superficial layer of the skin?

Keratinized stratified squamous epithelium.

Where is non-keratinized stratified squamous epithelium found?

Lining the mouth and esophagus.

What is a key characteristic of non-keratinized stratified squamous epithelium?

It does not contain keratin in the apical layer and remains moist.

What is the structure of stratified cuboidal epithelium?

Two or more layers of cells with cube-shaped cells in the apical layer.

Where can stratified cuboidal epithelium be found?

In ducts of adult sweat glands, esophageal glands, and part of the male urethra.

What are the functions of stratified cuboidal epithelium?

Protection and limited secretion and absorption.

What describes the structure of stratified columnar epithelium?

Several layers of irregularly shaped cells with only the apical layer being columnar.

Where is stratified columnar epithelium located?

Lines part of the urethra, large excretory ducts of some glands, and small areas in the anal mucous membrane.

What is the function of stratified columnar epithelium?

Protection and secretion.

What is the appearance of transitional epithelium?

Variable; cells in the apical layer range from squamous (when stretched) to cuboidal (when relaxed).

Where is transitional epithelium found?

Lines the urinary bladder and portions of the ureters and urethra.

What is the function of transitional epithelium?

Permits distension.

What is the primary function of glandular epithelium?

Secretion.

What are the two classifications of glands in the body?

Endocrine and exocrine.

What is connective tissue known for?

Being one of the most abundant and widely distributed tissues in the body.

List some functions of connective tissue.

Binds, supports, and strengthens other tissues; protects and insulates organs; serves as a transport system; stores energy reserves; and is the main source of immune responses.

What constitutes an epithelial membrane?

A combination of an epithelial layer and an underlying connective tissue layer.

What are the principal types of epithelial membranes?

Mucous membranes, serous membranes, and cutaneous membranes.

What is a mucous membrane?

A membrane that lines a body cavity opening directly to the exterior.

Where do mucous membranes line?

The entire digestive, respiratory, and reproductive tracts, and much of the urinary tract.

What is the structure of a serous membrane?

It has two layers: the parietal layer lining the cavity wall and the visceral layer covering the organs.

What is the function of the mesothelium in serous membranes?

Secretes serous fluid, a lubricant allowing organs to glide easily.

What does the cutaneous membrane consist of?

A superficial portion called the epidermis and a deeper portion called the dermis.

What type of tissue makes up the epidermis?

Keratinized stratified squamous epithelium.

What types of connective tissue are found in the dermis?

Areolar connective tissue and dense irregular connective tissue.

What does the synovial membrane line?

Structures that do not open to the exterior.

What distinguishes synovial membranes from mucous, serous, and cutaneous membranes?

Synovial membranes lack an epithelium and are not classified as epithelial membranes.

What are the two main components of synovial membranes?

A discontinuous layer of cells called synoviocytes and a layer of connective tissue.

What is the function of synovial fluid?

It lubricates and nourishes cartilage at movable joints and contains macrophages that remove microbes and debris.

What are the major functions of the skin?

Physical permeability barrier, protection from infectious agents, thermoregulation, sensation, UV protection, wound repair, and outward appearance.

What are the major regions of the skin?

Epidermis, Dermis, and Hypodermis.

What is the thickness range of the epidermis?

0.4 to 1.5 mm.

What is the deepest layer of the epidermis called?

Stratum Basale, also known as Stratum Germinativum.

What are the primary cell types in the epidermis?

Keratinocytes, which make up 80-90% of the total cells.