Cell Junction | Physiology

                                 

                                                Cell Junction

This article discusses different types of cell junctions present in humans. Here, learn about the site of junctions, structure, functions, and more about junctions.

Keywords: Claudin| zona occluding| collagen | laminin | fibronectin | Nexus|

 | E-cadherin | Catenin | Vineutin | desmosomes | Hemidesmosomes | keratin |

Table of contents

1.	Introduction
2.	Types
3.	Structure
4.	Location
5.	Links

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 Introduction

The cells and the basement membrane are attached using the following methods.

1. Tight junction: In a tight junction, the membrane of two adjacent cells becomes opposed, and the outer layers of the cell membranes fuse strongly.

Structure of the tight junction: One cell's cell membrane has a specific protein called 'Claudin,' which extends in the cell. Its inner side has another protein called 'zona occludin.' Many filaments, e.g., Actin, spread into the cell from zona occludins.

                          This Photo is by Sandhya Prasad, Licensed under CCBY.

 The cell membrane of an adjacent cell has another specific protein called 'Occludin, ' which extends into the cell. In addition, its inner side has another protein called 'zona occluding.' From zona occludins, many filaments, like Actin, spread into the cell.'

A tight junction obliterates the space between the cells in the epithelium.

Tight junctions are present along the apical margins of cells and form a barrier to the movement of ions and other molecules.

Tight junctions are present in the Blood-brain barrier, choroid plexus, intestinal mucosa, renal tubules, etc.

2. Adherens junction: 

In adherens, two cell membranes are joined by dense proteins on both membrane surfaces extending from the cytoplasmic surface of each membrane into the cell. The protein is E-cadherin, which extends towards adjacent cells and is attached to Vineutin and Catenin on its inner side.' From vineutin and catenin, many filaments, like Actin, spread into the cell. E-cadherin is Ca++ dependent.

Adherens junction and types of the main protein involved in this junction.

                             This photo was taken by Sandhya Prasad, licensed under CCBY.

 These adherens junctions are in the middle of the cell membrane and hold adjacent cells together. So, these junctions are present where stretching and abrasive forces are more common, e.g., the gastrointestinal tract, respiratory tract skin, and others.

3. Desmosomes: In desmosomes, two cell membranes are joined by dense proteins on both membrane surfaces extending from the cytoplasmic surface of each membrane into the cell. The protein is cadherins (calcium ion-dependent) attached to desmoplakin (plaque protein) towards the cell. From the desmoplakin's intermediate filaments, keratin extends into the cell.

                         

                   This photo was taken by Sandhya Prasad, licensed under CCBY.

These desmosome junctions are in the middle of the cell membrane and hold adjacent cells firmly together. So these junctions are present in the areas where high tensile stretching and abrasive forces act, e.g., heart, gastrointestinal tract, respiratory tract

skin and others.

4. Hemidesmosomes: Hemidesmosome junctions are present on the basal side of the cells. These junctions join the cell with the basal lamina, which contains many proteins like collagen, laminin, and fibronectin.

Integrin is present in the basal cell membrane, which joins the basal lamina proteins. On the inner side, it is attached to intermediate fibers, such as keratin.

The Hemidesmosomes provide strength and stability to the cell. This is present in all tissues.

 

                                                       Hemidesmosomes

                             This photo was taken by Sandhya Prasad, licensed under CCBY.

 5. A gap junction is also known as a Nexus. In gap junctions, densely packed particles are present between two cell membranes. The densely packed particles are 'connexons,' one on each side. Six connexins make a connexion. In the connexons, a gap is present.

Intracellular calcium ions, pH, and voltage regulate the diameter of the channels.

Gap junctions permit the rapid propagation of electrical potential changes and the direct transfer of ions and other small molecules between cells.

It is present in cardiac muscles, smooth muscles, etc.,

                                    Gap  junction and proteins forming the junction

                             This photo was taken by Sandhya Prasad, licensed under CCBY.

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Different types of cell junctions
This photo was taken by Sandhya Prasad, licensed under CCBY.

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Hashtags: Claudin #  zona occluding #  collagen # laminin # fibronectin # Nexus #

 E-cadherin # Catenin #Vineutin | desmosomes #Hemidesmosomes #

Internal link: https://blog.totalphysiology.com/2021/06/normal-respiration.html

            https://blog.totalphysiology.com/2023/10/lymph-neglected-body-fluid.html

           https://blog.totalphysiology.com/2023/10/capillaries.html

External link: https://en.m.wikipedia.org/wiki/Cell _junction