Epithelial Tissue Functions and Features

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Questions and Answers

What is one principal function of epithelial tissue?

Energy production

Hormone synthesis

Absorption (correct)

Neural signal transmission

Which cell shapes are characteristic of epithelial cells?

Triangular, rectangular, or oval

Flat, round, or star-shaped

Cylindrical, spheroidal, or pear-shaped

Columnar, cuboidal, or squamous (correct)

What is a function of the basement membrane?

Facilitates blood flow

Filters substances reaching epithelial cells (correct)

Stores nutrients

Stores waste products

What type of junction forms a seal between adjacent epithelial cells?

Tight junctions Signup and view all the answers

Which feature is associated with the apical cell surface in epithelial tissue?

Microvilli Signup and view all the answers

What does the basal lamina help to maintain in epithelial cells?

Cell polarity Signup and view all the answers

How do adherent junctions function in epithelial tissue?

They provide sites for strong cell adhesion. Signup and view all the answers

Which of the following features does not describe the basement membrane?

Facilitates neural transmission Signup and view all the answers

What is the primary structural component of cilia?

Microtubules Signup and view all the answers

Which type of epithelium is characterized by layers of cells that can change shape?

Transitional Epithelium Signup and view all the answers

What is the length and diameter of cilia on average?

5-10 µm long, 0.2 µm in diameter Signup and view all the answers

Which type of epithelial cell is specialized for secretion and production of macromolecules?

Secretory (Glandular) Epithelia Signup and view all the answers

What structural feature distinguishes stereocilia from microvilli?

Stereocilia are longer and specialized. Signup and view all the answers

What is the main function of the primary cilium found in epithelial cells?

Signal transduction Signup and view all the answers

Which type of glandular epithelium produces lipids?

Sebaceous Glands Signup and view all the answers

What is the composition of the axoneme structure in cilia?

9 peripheral microtubule doublets surrounding 2 central microtubules Signup and view all the answers

Study Notes

Principal Functions of Epithelial Tissue

Covers, lines, and protects surfaces (e.g., epidermis)
Absorbs substances (e.g., intestinal lining)
Secretes substances (e.g., parenchymal cells of glands)

Characteristic Features of Epithelial Cells

Cells range in shape from columnar, cuboidal, to squamous
Cell nuclei vary in shape: elliptic (oval), spherical, or flattened
Epithelial cells are typically adjacent to connective tissue containing blood vessels
Epithelial cells exhibit polarity: organelles and membrane proteins are unevenly distributed within the cell

Basement Membranes

Thin, extracellular, felt-like sheet of macromolecules
Acts as a semipermeable filter for substances reaching epithelial cells from below
Composed of two layers:
- Basal lamina: thin, electron-dense, sheet-like layer of fine fibrils
- Reticular lamina: more diffuse and fibrous layer beneath the basal lamina

Functions of Basement Membranes

Filters substances reaching epithelial cells from below
Provides structural support for epithelial cells
Attaches epithelia to underlying connective tissue
Mediates cell-to-cell interactions involving epithelia
Marks routes for cell migration along epithelia
Serves as a scaffold for epithelial repair and regeneration
Helps organize integrins and other proteins in the plasma membrane of epithelial cells
Maintains cell polarity
Localizes endocytosis, signal transduction, and other activities

Intercellular Adhesion & Other Junctions

Tight/Occluding junctions: seal between adjacent cells
Adherent/Anchoring junctions: sites of strong cell adhesion
Gap junctions: channels for communication between adjacent cells

Specializations of the Apical Cell Surface

Microvilli:
- Uniform length, densely packed
- Visible as a brush or striated border projecting into the lumen (e.g., small intestine)
- Approximately 1 µm long and 0.1 µm wide
- Increase surface area by 20-30 fold
- Contain bundled actin filaments capped and bound to the plasma membrane by actin-binding proteins
Stereocilia:
- Longer and less motile than microvilli
- Specialized mechanosensory function in cells (e.g., inner ear)
- Involved in absorption (e.g., male reproductive tract - epididymis)
Cilia:
- Long, highly motile, larger than microvilli
- Contain internal arrays of microtubules
- Most epithelial cells have at least one primary cilium (non-motile, enriched with receptors and signal transduction complexes)
- Abundant on cuboidal or columnar cells
- 5-10 µm long and 0.2 µm in diameter

Cilia Structure

Axoneme: consists of 9 peripheral microtubule doublets arrayed around 2 central microtubules (9+2 assembly of microtubules)
Basal Bodies: apical cytoplasmic structures below the cell membrane, similar to centrioles, consisting of 9 microtubular triplets

Types of Epithelia

Covering or lining epithelia
Secretory (glandular) epithelia

Covering (Lining) Epithelia

Simple squamous epithelium
Simple cuboidal epithelium
Simple columnar epithelium
Stratified epithelium
Transitional epithelium (Urothelium)
Pseudostratified epithelium

Secretory (Glandular) Epithelia

Epithelial cells that produce and secrete macromolecules through glands
Secreted macromolecules include:
- Proteins (e.g., pancreas)
- Lipids (e.g., adrenal, sebaceous glands)
- Carbohydrate and protein complexes (e.g., salivary glands)
- Proteins, lipids, and carbohydrates (e.g., mammary glands)
- Water and electrolytes (e.g., sweat glands)
Scattered secretory cells (unicellular glands) are common in simple cuboidal, simple columnar, and pseudostratified epithelia.

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Description

This quiz explores the principal functions and distinctive characteristics of epithelial tissue, including its types of cells and the role of basement membranes. Learn how epithelial tissue covers, lines, and protects surfaces while also engaging in absorption and secretion. Test your knowledge of these essential biological components.