U01.01.029 Cilia structure

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Learning Objectives

  • Distinguish between the Axoneme and Basal Body microtubule arrangements.
  • Identify the role of Axonemal dynein in ciliary movement.
  • Contrast Motile vs. Nonmotile (Primary) cilia and their clinical correlations.
  • Explain the importance of Gap Junctions in ciliary coordination.

1. Ciliary Microtubule Anatomy

Cilia are hair-like projections from the cell surface. Their internal structure differs depending on whether you are looking at the shaft or the base.

  • Axoneme (The Shaft): Consists of a 9 doublet + 2 singlet arrangement of microtubules.
  • Basal Body (The Base): Located just below the cell membrane. It consists of 9 microtubule triplets with no central microtubules.

2. The Mechanics of Movement

Motile cilia move in a rhythmic, whip-like fashion to clear mucus or move cells (e.g., sperm).

  • Axonemal Dynein: An ATPase protein that links the peripheral 9 doublets. It causes the cilium to bend by facilitating the differential sliding of these doublets.
  • Gap Junctions: These intercellular channels allow for electrical and chemical coupling, enabling a coordinated, synchronized beating pattern across a field of cilia.

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3. Motile vs. Nonmotile (Primary) Cilia

Type Function Clinical Significance of Dysgenesis
Motile Movement (Mucociliary escalator, fallopian tubes). Infertility, Bronchiectasis, Situs inversus (Kartagener).
Nonmotile (Primary) Chemical/Signal sensors; cell growth control. Polycystic Kidney Disease (PKD), Retinal degeneration, Mitral Valve Prolapse.

4. Clinical Correlation: Kartagener Syndrome

A primary ciliary dyskinesia caused by a dynein arm defect. This leads to immobile cilia and flagella.

  • Triad: 1. Situs inversus (organs on the wrong side), 2. Chronic sinusitis, 3. Bronchiectasis.
  • Fertility: Leads to infertility in males (immotile sperm) and decreased fertility in females (dysfunctional fallopian tube cilia).

 

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