The human respiratory system works in combination with the circulatory system. It supplies oxygen to the body's cells and removes carbon dioxide in the process. Respiratory system is composed of the respiratory tract which is divided into an upper and a lower part and lungs. The upper part of the tract consists of the nose, nasal cavity, pharynx (throat), and larynx (voice box). The lower part consists of the trachea (windpipe), bronchi, and bronchial tree. Common respiratory diseases are asthma, bronchitis, common cold, croup cough, etc. Croup occurs due to viral infection and results in swelling of larynx and trachea. Home care measures are best to treat the majority of cases of croup and it takes three to six days for it to cure itself.

The above image of an X-ray of the neck in a child with croup shows steeple sign, narrowing of the trachea. Inflammation of the larynx and trachea due to a viral infection results in croup. The visual diagnosis of croup indicates redness and swelling in the upper part of the respiratory areas. X-ray scan is used for initial imaging of the neck or chest to diagnose and confirm croup. In patients of croup, X-ray scan shows a tapering or narrowing of the airway below the vocal cords in an inverted V pattern (steeple sign). Distension of the hypopharynx is also a sign of croup. [Image used under Creative Commons License from Wikimedia]

Croup is an infection due to virus in respiratory system. Croup causes swelling around the vocal cords which generally lasts for five to seven days. The upper respiratory system involves the upper airways of the lungs (bronchial tubes), vocal cords (larynx), and windpipe (trachea). Common symptoms of croup are typical cold symptoms like sneezing and runny nose, fever, barking cough, heavy breathing, hoarse voice, etc. In croup, lining of the throat, trachea and larynx (voice box) becomes red and swollen and therefore it is also known as croup laryngotracheitis.

The larynx is also known as the voice box. It is a 2 inches (5cm) long tube in adults. It is loacted above the windpipe (trachea) in the neck and in front of the food pipe. The food pipe in the upper part of the neck is called the pharynx.

CROUP COUGH: The image shows a normal lumen of the bronchus and an inflamed lumen containing mucus, in case of bronchial asthma.

The voice box is present in front of the neck and contains the vocal cords. The larynx is responsible for sound production and swallowing. It is also the entrance to the windpipe, and plays a critical role in the airway.

Croup leads to irritation in the upper airways and cause them to swell. As the airway below the vocal cords become narrow, it becomes difflicult to breath. Your breathing will become noisy and you will experience a high-pitched cough. This occurs due to narrowing of lumen due to thickened smooth muscles linning the airways.