What ring-shaped structure forms the lower portion of the larynx?

The cricoid cartilage is the ring-shaped structure that forms the lower portion of the larynx. It is located below the thyroid cartilage and serves as a crucial structural support for the larynx and the airway. Its completeness in forming a ring around the trachea distinguishes it from the other types of cartilage found in the larynx, which are typically more open or U-shaped.

The cricoid cartilage is also involved in protecting the airway, and it is the only complete circular cartilage in the respiratory tract, which is notable during intubation and other medical procedures involving the airway. Understanding the anatomy and function of the cricoid cartilage is essential for EMTs and other healthcare providers, especially in emergency situations where airway management may be required.