**Question:** Structurally the connexons are:

A. Gap junctions
B. Hemichannels
C. Channels
D. Pores

**Correct Answer:** B. Hemichannels

**Core Concept:**
Hemichannels are water-soluble protein channels formed by connexin proteins, which are integral components of the connexin protein family. They are involved in the formation of gap junctions and play a crucial role in intercellular communication. Gap junctions, on the other hand, are formed by the fusion of two hemichannels to create a continuous channel between adjacent cells.

**Why the Correct Answer is Right:**
Hemichannels are the building blocks of gap junctions. They are comprised of connexin proteins, which are expressed in various tissues and cells depending on the specific connexin isoform present. When two connexin hemichannels come together, they form a complete gap junction channel allowing direct communication between cells, facilitating the exchange of ions, small molecules, and second messengers. This process is essential for physiological functions such as cell growth, differentiation, and tissue homeostasis.

**Why Each Wrong Option is Incorrect:**
A. Gap junctions are composed of hemichannels coming together, not gap junctions themselves.
C. Channels refer to the whole gap junction, not the protein component hemichannels.
D. Pores refer to the entire structure of a gap junction, not the protein component hemichannels.

**Clinical Pearl:**
Understanding the structural components of connexins and their role in forming gap junctions is crucial for grasping cellular and tissue communication processes. This knowledge is essential in various medical fields, including pharmacology, pathology, and internal medicine, especially when studying the effects of drugs on cell signaling pathways.