U01.01.027 Cilia structure

Cilia are hair-like structures protruding from the surface of many cells. They may seem small, but they play a crucial role in various bodily functions. Here’s a breakdown of their structure, how they move, and a related disease:

Structure:

Cilia have a core structure called the axoneme, which is a complex arrangement of microtubules:
- 9 Peripheral Doublets: Each doublet consists of two microtubules arranged side-by-side.
- Central Pair: Absent in cilia, unlike flagella (a similar structure with a 9+2 arrangement).
The base of the cilium is anchored within the cell by the basal body, which has a different microtubule organization:
- 9 Microtubule Triplets: Unlike doublets, triplets have three microtubules arranged in a triangular pattern.

Movement:

Cilia bend and sway due to a protein called axonemal dynein.
Dynein acts as an ATPase (enzyme that uses ATP for energy) and is located between the outer microtubules of each doublet.
By causing a “sliding” movement between adjacent doublets, dynein generates the force for ciliary bending.

Coordinated Movement:

In some tissues, cilia work together in a coordinated fashion.
Gap junctions connect neighboring cells, allowing for the synchronized beating of cilia.

Kartagener Syndrome:

This autosomal recessive disorder affects cilia due to a defect in dynein arms.
Immotile cilia lead to various problems:
- Infertility: Sperm lack the ability to move effectively, and fallopian tube cilia can’t transport eggs properly.
- Respiratory issues: Impaired mucus clearance in the airways can lead to bronchiectasis (lung damage), recurrent sinusitis, and chronic ear infections.
- Hearing loss: Cilia dysfunction in the ear can contribute to conductive hearing loss.
- Situs inversus (rare): In some cases, internal organs may be reversed (e.g., dextrocardia – heart on the right side).
Diagnosis: Reduced nasal nitric oxide levels can be a screening test for Kartagener syndrome.

Analogy:

The provided analogy is quite creative! Imagining Kartagener syndrome as a restaurant where cilia can’t “dine in” due to dynein arm defects, resulting in “take-out only” (immobile sperm and egg transport issues) is a memorable way to understand the disease.

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U01.01.027 Cilia structure

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