Epithelial Tissue Overview
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Questions and Answers

Which type of epithelium is characterized by a single layer of thin, flattened cells and is involved in filtration?

  • Simple columnar epithelium
  • Simple cuboidal epithelium
  • Stratified squamous epithelium
  • Simple squamous epithelium (correct)

What is the primary function of simple cuboidal epithelium?

  • Transport of oxygen
  • Transpiration of moisture
  • Protection against abrasion
  • Absorption, secretion, or excretion (correct)

Which structure is responsible for binding the cell membrane to the basement membrane in epithelial cells?

  • Microvilli
  • Folds of plasma membrane
  • Hemidesmosomes (correct)
  • Cilia

What is a distinguishing feature of pseudostratified epithelium?

<p>Has a varying cell shape and height (A)</p> Signup and view all the answers

Which epithelial type commonly features microvilli to increase its surface area for absorption?

<p>Simple columnar epithelium (D)</p> Signup and view all the answers

What are the primary characteristics used to classify lining epithelia?

<p>Number of layers, cell shape, and surface specializations (B)</p> Signup and view all the answers

Which component of the hemidesmosome attaches to intermediate filaments in the epithelial cell?

<p>Dense plate (A)</p> Signup and view all the answers

Stratified squamous epithelium is best suited for which of the following functions?

<p>Protection against abrasion (A)</p> Signup and view all the answers

What is the primary function of microvilli?

<p>To increase the surface area for absorption (D)</p> Signup and view all the answers

Which structure is primarily responsible for the rhythmic movement that helps move substances in the respiratory tract?

<p>Cilia (C)</p> Signup and view all the answers

In which part of the body would you primarily find stereocilia?

<p>Epididymis and inner ear (A)</p> Signup and view all the answers

What is a primary function of epithelial tissue?

<p>Secretion of glandular products (D)</p> Signup and view all the answers

What role does keratin play in epithelial cells?

<p>Provides rigidity and protection (A)</p> Signup and view all the answers

Which type of cellular junction forms a continuous band around the perimeter of epithelial cells?

<p>Zonula (C)</p> Signup and view all the answers

Which domain of epithelial cells faces the external environment?

<p>Apical domain (C)</p> Signup and view all the answers

What is a key characteristic of lining epithelia?

<p>Cells are tightly joined by junctional complexes (B)</p> Signup and view all the answers

How are epithelial cells primarily nourished?

<p>From underlying connective tissue (A)</p> Signup and view all the answers

What are microvilli primarily involved in?

<p>Transport and absorption (B)</p> Signup and view all the answers

How do adherent junctions differ from occlusive junctions?

<p>Adherent junctions allow for some space between membranes (D)</p> Signup and view all the answers

What characteristic is unique to epithelial tissue?

<p>High mitotic rate (A)</p> Signup and view all the answers

What happens to keratin filaments after the epithelial cell dies?

<p>They remain to provide protection until replaced (B)</p> Signup and view all the answers

Which type of apical specialization is NOT typically found in epithelial cells?

<p>Neurotransmitters (A)</p> Signup and view all the answers

What important structural feature separates epithelial tissue from underlying connective tissue?

<p>Basement membrane (C)</p> Signup and view all the answers

Which of the following is NOT a function of epithelial tissue?

<p>Storage of lipids (C)</p> Signup and view all the answers

What proteins primarily facilitate the sealing action of tight junctions?

<p>Occludins and Claudins (C)</p> Signup and view all the answers

Which junction type allows for the passage of ions and small molecules between cells?

<p>GAP junctions (D)</p> Signup and view all the answers

What is the main structural characteristic of desmosomes?

<p>They leave an intercellular space of about 30 nm. (A)</p> Signup and view all the answers

What is the primary function of adherens junctions?

<p>To provide mechanical stability to tissues. (B)</p> Signup and view all the answers

Where are cadherins primarily located within adherens junctions?

<p>In the space between cell membranes. (C)</p> Signup and view all the answers

Which type of junction is found randomly distributed across the plasma membrane?

<p>GAP junctions (B)</p> Signup and view all the answers

What kind of proteins form the transmembrane channels in GAP junctions?

<p>Connexins (B)</p> Signup and view all the answers

What distinguishes the basement membrane from other junctions discussed?

<p>It separates epithelia from connective tissue. (C)</p> Signup and view all the answers

What is the primary function of stratified squamous keratinized epithelium?

<p>Protection against abrasion (D)</p> Signup and view all the answers

Where can pseudostratified columnar epithelium predominantly be found?

<p>Respiratory tract (B)</p> Signup and view all the answers

Which type of epithelial cells is characterized by multiple layers of cuboidal cells?

<p>Stratified cuboidal epithelium (A)</p> Signup and view all the answers

Which type of epithelium is primarily involved in lining and protecting various internal surfaces?

<p>Stratified squamous epithelium (B)</p> Signup and view all the answers

Which type of glands does not possess an excretory duct?

<p>Endocrine glands (B)</p> Signup and view all the answers

What unique characteristic does urothelium (transitional epithelium) exhibit?

<p>Its cells can flatten when the bladder is full (B)</p> Signup and view all the answers

What is the function of stratified columnar epithelium?

<p>Absorption and secretion (D)</p> Signup and view all the answers

Which feature distinguishes glandular epithelia from other epithelial types?

<p>Originating from surface epithelial cells (C)</p> Signup and view all the answers

Which type of gland releases secretion products through exocytosis?

<p>Merocrine glands (A)</p> Signup and view all the answers

What classification is based on the shape of the secretory part of exocrine glands?

<p>Tubular, acinar, alveolar (B)</p> Signup and view all the answers

Which of the following is NOT a characteristic of endocrine glands?

<p>They have a duct and a secretory part (D)</p> Signup and view all the answers

Which type of gland secretes a product that includes cell components along with the secretion?

<p>Apocrine glands (C)</p> Signup and view all the answers

How are follicular endocrine glands organized?

<p>In hollow spherical structures called follicles (D)</p> Signup and view all the answers

What type of secretion is associated with goblet cells?

<p>Mucous (A)</p> Signup and view all the answers

Which of the following describes the role of cordonal endocrine glands?

<p>They are organized in cords or groups (A)</p> Signup and view all the answers

Which type of gland contains both exocrine and endocrine functions in the human body?

<p>Pancreas (D)</p> Signup and view all the answers

Flashcards

Microvilli

Finger-like projections extending from the apical surface of epithelial cells, increasing surface area for absorption.

Enterocytes

Specialized epithelial cells in the small intestine responsible for nutrient absorption.

Cilia

Hair-like structures that extend from the surface of epithelial cells, involved in movement of fluids and particles.

Stereocilia

Modified microvilli that serve as sensory receptors, found in the male reproductive system and inner ear.

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Keratin

A fibrous protein produced by epithelial cells, providing rigidity and protection to the epithelium.

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Zonula

Junctions that form a continuous band around the cell, connecting adjacent cells.

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Macula

Junctions that form small, localized points of contact between adjacent cells.

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Occlusive junctions

Junctions that seal the space between membranes of adjacent cells, preventing leakage.

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Epithelial tissue: Key function

Epithelial tissue covers internal and external body surfaces, lines cavities, and forms glands. Cells are tightly connected with little space between them, relying on the underlying connective tissue for nourishment.

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Epithelial tissue: Avascularity

Epithelial tissue lacks blood vessels (avascular). Instead, it receives nutrients from the underlying connective tissue.

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Epithelial tissue: Basement membrane

Epithelial tissue is separated from the underlying connective tissue by a thin, non-cellular layer called the basement membrane.

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Epithelial cell: Apical Domain

Apical domain faces the lumen or external environment, responsible for secretion and absorption.

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Epithelial cell: Basal Domain

Basal domain attaches to the basement membrane, responsible for cell adhesion and signaling.

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Epithelial cell: Lateral Domains

Lateral domains face adjacent cells, responsible for cell-to-cell communication and adhesion.

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Microvilli: Function

Microvilli are finger-like projections increasing surface area for absorption and transport. Abundant in the small intestine and renal tubules.

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Cilia: Function

Cilia are hair-like structures that move fluids and particles across epithelial surfaces.

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Exocrine Glands

Glands that release their secretions through ducts. These secretions can be used for various functions like digestion, lubrication, or protection.

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Simple Exocrine Gland

Exocrine gland that has one duct.

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Compound Exocrine Gland

Exocrine gland with multiple ducts branching out from a main duct.

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Branched Exocrine Gland

Exocrine gland with one duct serving multiple secretory units.

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Tubular Exocrine Gland

Gland with a tube-shaped secretory part.

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Acinar Exocrine Gland

Gland with a sac-shaped secretory part.

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Alveolar Exocrine Gland

Gland with a rounded secretory part.

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Endocrine Glands

Glands that release their secretions directly into the bloodstream, typically producing hormones.

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Zonula occludens (tight junction)

The most apical junction between epithelial cells. It forms a continuous band around the cell, sealing the space between cells. It prevents the passage of molecules between cells.

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Occludins and Claudins

Transmembrane proteins that are essential for the formation of tight junctions. They help to seal the gap between cells, preventing the passage of molecules.

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Zonula Adherens (adherens junction)

A type of cell junction located next to tight junctions. It forms a belt around the cell, leaving a small space between the membranes. It helps to anchor cells together and allows for communication.

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Cadherins

The transmembrane proteins that are essential for the formation of adherens junctions. They help to bind cells together and connect to the cytoskeleton.

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Desmosomes (Macula adherens)

A type of cell junction that provides strong adhesion between cells, acting like 'spot welds'. They are located below zonula adherens and have a space between the membranes filled with cadherins.

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Folds

Invaginations of the plasma membrane that increase the cell's surface area. This allows for more contact points or enhanced transport through the membrane.

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Hemidesmosomes

Binding structures that connect the cell membrane to the basement membrane, found in the basal cells of the epithelium. They resemble half of a desmosome and have a dense plate attached to intermediate filaments inside the cell. Their extracellular part binds to the basement membrane via integrins.

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Communicating (GAP) junctions or nexus

A type of cell junction that allows for communication between cells. Circular union zones distribute across the membrane, allowing the passage of ions and small molecules through pores formed by connexins.

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Lining Epithelium

A type of epithelium classified by the number of cell layers (simple, stratified, pseudostratified), cell shape (squamous, cuboidal, columnar), and presence of specializations on the apical surface (microvilli, cilia, stereocilia, keratin).

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Basement membrane

A membrane located at the border between epithelia and the underlying connective tissue. It acts as a barrier and provides structural support.

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Connexins

Six proteins that bind together to form transmembrane channels in communicating junctions. These channels allow the passage of ions and small molecules between cells.

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Simple Squamous Epithelium

A single layer of thin, flattened cells. Its function is lining surfaces and filtering substances. It is found in the pulmonary alveoli, blood and lymphatic vessels, some renal tubules, and the mesothelium of the pleural, pericardial, and peritoneal cavities.

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Simple Cuboidal Epithelium

A single layer of cuboidal cells with a rounded nucleus in the center. Its function is absorption, secretion, or excretion. It is found in gland ducts, covering the ovary, and some renal tubules.

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Simple Columnar Epithelium

A single layer of tall, rectangular cells with an oval nucleus near the base. Its function is lining, transport, absorption, and secretion of substances. It is found in the digestive tract, gallbladder, and large gland ducts. It often has microvilli to increase surface area for absorption and can also have cilia, as seen in the oviducts, efferent ducts, or small bronchi.

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Stratified Squamous Epithelium

Several layers of cells with flattened apical cells, polygonal intermediate cells, and cuboidal or cylindrical basal cells. Only the deepest layer contacts the basement membrane.

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Stratified Squamous Keratinized Epithelium

A type of epithelium that lines surfaces exposed to friction or abrasion. It consists of multiple layers of flat cells with the most superficial layer being dead and filled with keratin.

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Stratified Cuboidal Epithelium

A type of epithelium composed of multiple layers of cuboidal cells. It is found lining the ducts of glands and is involved in absorption and secretion.

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Stratified Columnar Epithelium

A type of epithelium with multiple layers of cells, where the surface layer is cylindrical and the basal layers are polyhedral or cuboidal. It is found in areas like the eye and some gland ducts and contributes to lining, protection, absorption, and secretion.

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Pseudostratified Columnar Epithelium

A single layer of tall, columnar cells that appear stratified due to the varying heights of the cells. All cells contact the basement membrane, but only some reach the lumen. Usually contains cilia and is found in the respiratory tract, male reproductive system, and some gland ducts.

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Urothelium (Transitional Epithelium)

A type of epithelium found only in the urinary tract. Consists of one or multiple layers of cells with a pseudostratified appearance. The basal cells are cuboidal or cylindrical, and the apical cells are large and rounded. The epithelium can distend and flatten when the organ fills with urine.

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Mucosal Epithelium

Covers the walls of the mouth, oropharynx, esophagus, vocal cords, and vagina. These epithelia are usually protected by a mucous secretion that keeps them moist.

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Study Notes

Epithelial Tissue

  • Epithelial tissue covers internal and external body surfaces, lines cavities, and forms glands.
  • Cells are tightly connected by junctional complexes, minimizing extracellular space.
  • Nourishment comes from underlying connective tissue.
  • Separated from connective tissue by a basement membrane.

Functions of Epithelial Tissue

  • Delimitation: Forming surfaces and lining cavities (Lining Epithelium)
  • Protection: Protecting underlying structures
  • Diffusion: Regulating molecular exchange between compartments
  • Absorption: Taking in substances
  • Filtration: Separating substances
  • Excretion: Removing substances
  • Reception of stimuli: Detecting changes
  • Secretion: Producing and releasing glandular products (hormones, enzymes) - secretory glands

Epithelial Cell Polarity

  • Epithelial cells are polarized: structurally and functionally different domains.
  • Basal domain: Attaches to the basement membrane.
  • Apical domain: Faces the lumen (cavity) or external environment.
  • Lateral domains: Face adjacent cells.
  • Cell features vary depending on function in these domains.

Apical Membrane Specializations

  • The apical domain faces the lumen.
  • Contains numerous ion channels and transport proteins for secretion.
  • Specialized structures, like microvilli, cilia, and stereocilia, are present, related to its function.
  • Microvilli: Membrane-covered cytoplasmic extensions formed by actin filaments, increasing cell surface for absorption in the small intestine and renal tubules.
  • Cilia: Larger membrane extensions composed of microtubule doublets and a central pair; for movement of substances in the respiratory tract.
  • Stereocilia: Modified microvilli, sensory structures for movement in the male reproductive tract.
  • Keratin: Protein providing structural support and rigidity, making it resistant to damage. Fills dead cells in stratified squamous epithelium increasing resistance and impermeability.

Lateral Membrane Specializations

  • Cells are tightly joined by junctional complexes in lining epithelia.
  • Extracellular matrix is minimal
  • Tight Junctions (Zonula Occludens): Prevent substance passage between cells; seals space between cell membranes.
  • Adherens Junctions (Zonula Adherens): Attach cells together; anchor actin filaments to cytoskeleton to keep cells tightly joined.
  • Desmosomes (Macula Adherens): Provide strong adhesion between cells; intermediate filaments interact with dense plates within the cell.
  • Gap Junctions (Nexus): Channels forming pores between cells; allowing passage of small molecules (ions) between cytoplasm of adjacent cells.

Basal Membrane Specializations

  • The basal membrane is located at the base of epithelial cells and separates them from the underlying connective tissue.
  • Folds: Increases surface area for transport and contact with neighboring cells.
  • Hemidesmosomes: Bind epithelial cells to the basement membrane.
  • Provide structural support and anchoring strength. They incorporate intermediate filaments of keratin in their dense plates.

Classification of Epithelia

  • Two main types:
    • Lining Epithelia: Classified by cell layers (simple, stratified, pseudostratified) and cell shapes (squamous, cuboidal, columnar) and surface specializations (microvilli, cilia, stereocilia, keratin).
    • Glandular Epithelia (Glands): Produce and secrete substances. Classified by whether there are ducts (exocrine) or not (endocrine).

Number of Cells

  • Unicellular: Made of a single cell (ex: goblet cell).
  • Multicellular: Composed of multiple cells (ex: salivary glands).

Types of Secretion

  • Merocrine: Secretion released by exocytosis (most common).
  • Holocrine: Secretory cells disintegrate; releasing their contents (ex: sebaceous glands).
  • Apocrine: Secretory cell releases portion of cytoplasm in addition to the product (ex: mammary glands).

Nature of Secretion

  • Mucous: Secretion forms mucus
  • Serous: Secretes enzymes
  • Mixed: Contains both mucous and serous components.

Types of Glands

  • Exocrine: Secrete into ducts or the exterior
    • Classified according to duct structure (Simple, Compound, Branched) and secretory portion shape (Tubular, Acinar/Alveolar).
  • Endocrine: Secrete hormones directly into blood.
    • Classified into Cordonal (arranged in cords/groups) and Follicular (hollow structures).

Anficrins Glands

  • Some glands (e.g., pancreas, liver) have combined exocrine and endocrine properties.

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Description

This quiz explores the structure and functions of epithelial tissue, including cell polarity and the various roles it plays in the body. Test your knowledge on how epithelial cells protect, absorb, and secrete substances across different surfaces and cavities.

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