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Epithelial Tissues and Their Functions

Epithelial Tissues and Their Functions

Epithelial tissues are large sheets of cells covering all of the surfaces of the body. These surfaces can be internal or external, for example, skin, airways, the digestive tract, the urinary system, and the reproductive system. Hollow organs and body cavities that do not connect to the body's exterior, including blood vessels and serous membranes, are lined by epithelial tissue known as the endothelium.
Epithelial tissues provide the body's first line of protection from physical, chemical, and...

Integrins

Integrins

Animal and protozoan cells do not have cell walls to help maintain shape and provide structural stability. Instead, these eukaryotic cells secrete a sticky mass of carbohydrates and proteins into the spaces between adjacent cells. This network of proteins and molecules is called an extracellular matrix or ECM.
Some ECM proteins assemble into a basement membrane to which the remaining components adhere. Proteoglycans typically form the bulk of the ECM while fibrous proteins, like collagen,...

Anchoring Junctions

Anchoring Junctions

Anchoring junctions are multiprotein complexes that help cells connect to other cells and the extracellular matrix. Anchoring junctions are present on the lateral and basal surfaces of cells, providing strong and flexible connections. Focal adhesions are often formed due to cell interactions with the ECM substrata, which initiate signal transduction via kinase cascades and other mechanisms. Together, they provide stability and tissue integrity. There are three types of anchoring junctions:...

Classification of Epithelial Tissues: Overview

Classification of Epithelial Tissues: Overview

Epithelial tissues are classified according to the shape of the cells and the number of cell layers formed. Cell shapes can be squamous (flattened and thin), cuboidal (square-like, as wide as it is tall), or columnar (rectangular, taller than it is wide). Additionally, the nucleus shape helps identify the type of epithelial cells. Squamous cells have flattened disc-shaped nuclei, cuboidal cells have spherical nuclei, and columnar cells have elongated nuclei.
Based on the number of cell layers,...

Classification of Epithelial Tissues: Simple Epithelium

Classification of Epithelial Tissues: Simple Epithelium

Simple epithelium consists of a single layer of cells that lines body cavities and blood vessels. The shape of the cells in the epithelium reflects the function of the tissue. Cells in simple squamous epithelium appear as thin scales with flat, elliptical nuclei that mirror the form of the cell.
Because of the thinness of the cells, simple squamous epithelium is present where the rapid passage of chemical compounds is observed. For example, the endothelium that lines the capillaries and vessels...

Classification of Epithelial Tissues: Glandular Epithelium

Classification of Epithelial Tissues: Glandular Epithelium

The glandular epithelium is made of one or more epithelial cells modified to synthesize and secrete chemical substances. Glandular epithelia can be classified based on cell number. Unicellular glands have individual secretory cells scattered across the epithelial monolayer. In contrast, multicellular glands consist of a hollow tubular duct attached to the cluster of secretory cells located in the deep pockets.
Multicellular glands are formed during early development when epithelial budding...

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Related Experiment Video

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Characterizing Epithelial Wound Healing In Vivo Using the Cnidarian Model Organism Clytia hemisphaerica

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Epithelia and integration in sponges.

Sally P Leys¹, Scott A Nichols, Emily D M Adams

¹*Department of Biological Sciences, University of Alberta, Edmonton, AB, Canada T6G 2E9; Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720, USA.

Integrative and Comparative Biology

|June 15, 2011

Summary

Sponges possess true epithelia, challenging previous notions. This finding helps connect sponge biology to other metazoans, highlighting their evolutionary significance.

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Area of Science:

Zoology
Evolutionary Biology
Cell Biology

Background:

Epithelia are crucial for metazoan body plan development, integrity, and function.
Sponges, simple metazoans, have historically been considered to lack true epithelia.

Purpose of the Study:

To investigate the presence and characteristics of epithelia in sponges.
To assess the homology between sponge and bilaterian epithelia.
To understand the evolutionary implications of sponge epithelia.

Main Methods:

Review of historical studies on sponge epithelia.
Analysis of ultrastructural data from electron micrographs of sponge tissues.
Examination of gene families involved in epithelial development and function.

Main Results:

Adherens-type junctions are present in sponges, though often less prominent than in other metazoans.
Collagenous sheets underlie epithelia in all sponges; distinct basal laminae are found in Homoscleromorpha.
Most gene families associated with epithelial function are present in sponges, suggesting homology with bilaterian epithelia.

Conclusions:

Sponge epithelia share key features and likely homology with bilaterian epithelia.
The presence of differentiated epithelia in sponges suggests specialized physiological roles.
Recognizing sponge epithelia reframes their biological complexity and evolutionary position within Metazoa.