Epithelial Tissue Characteristics Quiz

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Questions and Answers

What are the characteristics of primary cilia?

Responsible for rapid beating patterns

Non-motile and consist of a 9 + 0 pattern of microtubules (correct)

Highly motile structures with a 9 + 2 pattern of microtubules

Abundant in respiratory epithelium and sperm cells

Which type of epithelium is responsible for producing and secreting macromolecules?

Secretory epithelium (correct)

Covering epithelium

Simple columnar epithelium

Stratified epithelium

What distinguishes cilia from microvilli?

Cilia are involved in absorption, whereas microvilli are not

Cilia have a 9 + 2 arrangement of microtubules, while microvilli do not (correct)

Cilia are typically shorter and less motile than microvilli

Cilia are organized into layers, while microvilli are singular structures

What type of epithelial tissue is classified as simple?

It has only one cell layer Signup and view all the answers

What is the main function of stereocilia found in inner ear sensory cells?

Detecting light and motion Signup and view all the answers

What is the primary role of parenchyma in an organ?

Performing specialized functions Signup and view all the answers

Which layer of the basement membrane is primarily made up of Type IV collagen?

Basal lamina Signup and view all the answers

What are the functions of the basement membrane?

Organizing proteins and providing structural support Signup and view all the answers

Which of the following correctly describes the polarity of epithelial cells?

They have a basal pole and an apical pole Signup and view all the answers

What is the primary function of tight junctions in epithelial cells?

Preventing leakage of substances between cells Signup and view all the answers

Which type of collagen is primarily found in the reticular lamina?

Type III collagen Signup and view all the answers

What type of cells form the cellular sheets of epithelial tissue?

Closely aggregated polyhedral cells Signup and view all the answers

Which of the following statements about the stroma is correct?

It has a supporting role in organs Signup and view all the answers

Which transmembrane proteins are primarily involved in the formation of tight junctions?

Claudins and occludins Signup and view all the answers

What role do desmosomes play in epithelial tissue?

Provide cellular adhesion and strength Signup and view all the answers

How do hemidesmosomes attach epithelial cells to the basal lamina?

With the help of integrins Signup and view all the answers

What is the primary purpose of gap junctions in epithelial tissues?

Facilitate intercellular communication Signup and view all the answers

What structural feature characterizes microvilli on epithelial cells?

Are covered with glycocalyx Signup and view all the answers

What is the typical diameter of the hydrophilic pore in connexons formed by connexins?

1.5 nm Signup and view all the answers

Which of the following best describes stereocilia?

Found primarily in the male reproductive system Signup and view all the answers

What is a characteristic of unicellular glands?

They consist of a single secretory cell such as a goblet cell. Signup and view all the answers

How do endocrine glands differ from exocrine glands?

Endocrine glands lose their connection to the epithelium. Signup and view all the answers

Which type of gland secretion involves total destruction of the secretory cell?

Holocrine Signup and view all the answers

What characterizes serous glands?

They contain a high amount of rough endoplasmic reticulum. Signup and view all the answers

Which of the following glands is classified as a mixed gland?

Salivary glands Signup and view all the answers

What morphology describes glands with ducts that are not branched?

Simple Signup and view all the answers

What is the primary method of renewal for epithelial cells?

Mitotic activity and stem cell populations Signup and view all the answers

Which type of secretion results in partial destruction of the secretory cell?

Apocrine Signup and view all the answers

Study Notes

Epithelial Tissue/Epithelium

Epithelial tissue is composed of closely aggregated polyhedral cells that adhere strongly to one another and to a thin layer of extracellular matrix (ECM).
The cells form cellular sheets that line the cavities of organs and cover body surfaces.
They line all external and internal surfaces of the body and all substances that enter or leave an organ.

Main Characteristics of Tissue Types

Epithelial: Aggregated polyhedral cells, small amount of extracellular matrix, lining of surfaces, body cavities, and glandular secretion.
Connective: Several types of fixed and wandering cells, abundant extracellular matrix, support and protection of tissues/organs.
Muscle: Elongated contractile cells, moderate amount of extracellular matrix, strong contraction, body movements.
Nervous: Elongated cells with extremely fine processes, very small amount of extracellular matrix, transmission of nerve impulses.

Parenchyma and Stroma

Parenchyma: Cells responsible for an organ's specialized functions.
Stroma: Supporting role in the organ; always connective tissue except in the brain and spinal cord.

Epithelial Tissues

Composed of closely aggregated polyhedral cells adhering strongly to one another and to a thin layer of ECM.
Forms cellular sheets lining cavities of organs and covering body surfaces.
Lines all external and internal body surfaces and substances entering/leaving organs.

Principal Functions of Epithelial Tissues

Covering, lining, and protecting surfaces (e.g., epidermis).
Absorption (e.g., intestinal lining).
Secretion (e.g., parenchymal cells of glands).
Includes myoepithelial cells and specialized sensory cells.

Characteristic Features of Epithelial Cells

Shapes and dimensions vary, ranging from tall columnar to cuboidal to low squamous cells.
Epithelial cell nuclei vary in shape, elliptic (oval), spherical, or flattened, corresponding roughly to cell shape.
Most epithelia are adjacent to connective tissue containing blood vessels.
Lamina propria underlies the epithelia lining organs of digestive, respiratory, and urinary systems.

Characteristic Features of Epithelial Cells — Contact Area

Contact area between tissues increased by small evaginations called papillae.
Covering of skin or tongue.
Epithelial cells demonstrate polarity: basal pole, apical pole, and lateral surfaces.

Basement Membranes

Basal surface of all epithelia rests on a thin extracellular, felt-like sheet of macromolecules.
A semipermeable filter for substances reaching epithelial cells from below.
Two parts on TEM: basal lamina and reticular lamina.

ECM Components of Basal Lamina

Type IV collagen
Laminin (glycoprotein), attach to integrins
Nidogen and perlecan (CHON and proteoglycan, respectively).

ECM Components of Reticular Lamina

Type III collagen
Type VII collagen

Functions of Basement Membrane

Filter
Structural Support
Organize proteins
Maintain cell polarity
Cell-to-cell interactions
Scaffold allowing rapid epithelial repair and regeneration

Intercellular Adhesion & Other Junctions

Epithelial cell junctions, major structural features and functions. (Table provided).

Tight Junction (Zonula Occludens)

Forms a band completely encircling each cell.
Most apical of the junctions.
Band of branching strands in the membrane around each cell's apical end.
Seals between membranes due to tight interactions between claudin and occludin proteins.
Restricts movements of membrane lipids and proteins.

Adherent Junction (Zonula Adherens)

Encircles epithelial cells, usually immediately below the tight junction.
Firmly anchors cells to neighbors.
Mediated by cadherins and catenins.
Forms a "terminal web."

Desmosome (Macula Adherens)

Resembles a single "spot-weld"; does not form a complete belt.
Disc-shaped structures.
Contains members of the cadherin family (desmogleins and desmocollins).
Provides firm cellular adhesion and strength.

Hemidesmosome

On the basal epithelial surface, cells attach to the basal lamina by anchoring junctions.
Structurally resembles a half-desmosome.
Integrins primarily bind to laminin molecules in the basal lamina.

Gap Junction (Nexus)

Mediates intercellular communication.
Transmembrane proteins (connexins) form hexameric complexes (connexons) with central pore (~1.5nm).
Permits intercellular exchange of small molecules (< 1.5 nm) allowing coordinated cellular function in many tissues.

Specializations of the Apical Cell Surface

Microvili: Seen on apical cell surfaces of absorption-specialized epithelia (e.g., brush border of small intestine).
Increase surface area (20-30 fold).
Covered with glycocalyx.
Contain bundled actin filaments.

Stereocilia

Less common, typically longer and less motile than microvilli.
Found in absorptive epithelial cells lining the male reproductive system (e.g., epididymis).
Increase surface area, facilitating absorption.
Important for motion-detecting functions in inner ear sensory cells.

Cilia

Long, highly motile apical structures containing internal arrays of microtubules.
Primary cilium: not motile, involved in detecting light, odors, and fluid flow.
Motile Cilia: typical cilia, abundant on cuboidal/columnar cells.
Axoneme: 9 + 2 assembly of microtubules.
Basal bodies: structure similar to centrioles, exhibit rapid beating patterns.
Found in respiratory epithelium and sperm cells.

Types of Epithelia

Covering/Lining Epithelia: Organized into one or more layers covering surfaces or lining cavities. Classified by layer number (simple or stratified) and cell shape (squamous, cuboidal, columnar). (Table provided).
Secretory/Glandular Epithelia: Function mainly to produce and release macromolecules (proteins, lipids, carbohydrates). Classified by cell number (unicellular or multicellular) (e.g. goblet cells) or secretion method (exocrine, endocrine). (Table provided).

Review of Naming

Step 1: Number of layers (simple, stratified, pseudostratified, transitional).
Step 2: Cell shape (squamous, cuboidal, columnar).
Optional: Special features (microvilli, cilia, stereocilia, goblet cells, keratinized, non-keratinized).

Renewal of Epithelial Cells

Epithelial tissues are relatively labile, renewed continuously by mitotic activity and stem cell populations.
Rate of renewal varies widely.
In stratified tissues, stem cells and mitosis primarily occur in the basal layer in contact with the basal lamina.
Epithelia are capable of rapid repair and replacement.

Endocrine Glands

Will be discussed in another chapter.

Exocrine Glands

Organized as a continuous system of many small secretory portions and ducts.
Secretory units in both exocrine and endocrine glands are supported by a stroma of connective tissue
Classified by morphology (simple/compound; tubular/acinar/tubuloacinar). This is based of the formation of ducts from the secretory portion. (Table provided).

Classification (Based on Fate of Secretion)

Merocrine: Without destruction, (release protein via exocytosis) (e.g., sweat glands).
Holocrine: Total destruction (e.g., sebaceous glands).
Apocrine: Partial destruction (e.g., mammary glands).

Classification (Based on Type of Secretion)

Serous: Synthesize non-glycosylated proteins, with rough ER and Golgi complex. Heavily stained (e.g., acini of pancreas, parotid salivary glands).
Mucous: Contain glycosylated proteins (mucins), hydrophilic, lightly stained.
Mixed/Seromucous: Mixture of digestive enzymes and watery mucus (e.g., submaxillary/mandibular glands).

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Description

Test your knowledge on the various characteristics and functions of epithelial tissues. This quiz covers essential topics such as cilia, macromolecule secretion, and junction formation. Perfect for students studying histology or related biological sciences.