The human respiratory system is a complex network of organs and tissues working together to facilitate breathing. This intricate system allows the body to take in oxygen from the air and release carbon dioxide, a waste product. It includes various specialized structures, each performing a specific function to ensure efficient gas exchange.
What Is the Carina?
The carina is an anatomical landmark within the respiratory tract. It is a sagittally-oriented cartilaginous ridge that represents the inferior termination of the trachea, also known as the windpipe. The carina is primarily composed of cartilage. Its presence marks a significant division within the airway.
Precise Location within the Respiratory System
The carina is situated at the lower end of the trachea, where this single airway divides into two separate passages. This division point, known as the tracheal bifurcation, is where the trachea branches into the right and left main bronchi, leading directly into the lungs. This cartilaginous ridge lies slightly to the left of the midline and extends from front to back. In most adults, the carina is found at the level of the fourth or fifth thoracic vertebra (T4-T5) in the upper back, aligning with the sternal angle. Its exact position can shift by one or two vertebral levels with changes in breathing or body position.
Why the Carina Is Important
The carina is important for directing airflow into the lungs. Its position ensures air entering the trachea is efficiently distributed to both the right and left main bronchi, allowing for proper ventilation. This structure is also one of the most sensitive areas for triggering the cough reflex. Specialized nervous tissue in its mucous membrane is highly responsive to irritation, initiating a forceful cough to expel foreign particles or excess mucus and protect the lower airways.
Knowing the precise location of the carina is important in various medical procedures. During a bronchoscopy, a procedure to visualize the airways, the carina serves as a landmark for navigating the respiratory tree and examining the main bronchi. In endotracheal intubation, which involves inserting a tube into the trachea to assist breathing, the carina acts as a guide for correct tube placement. The tip of the endotracheal tube is ideally positioned a few centimeters above the carina to prevent it from entering only one lung, a condition known as single-lung intubation.