What are Sinuses? - Anatomy & Types

Instructor: Kelly Robson

Kelly has taught High School Science and Applied Communications. She holds an Education Specialist Degree in Ed. Leadership.

Sinuses are usually only noticed when they are infected. However, they have some great value. They even help us to hold our heads up high. In this lesson, you will learn about what sinuses are, what they do, and the different infections related to them.

What Are Sinuses Good For?

Paranasal sinuses is a group of connected hollow sacks of air surrounding our nasal area. 'Paranasal sinuses' is the long technical name. We usually just call them 'sinuses.' Each sinus is lined with soft pink tissue called mucosa. Normally the sinuses are empty except for a thin layer of mucus. The mucus is there to protect the tissue of the sinuses from drying out.

Sinuses have many functions, including protecting the face from trauma. You can think of them like those air pillows that are used to protect fragile items during shipping. The sinuses act as protection for the face and help protect the vital bones and other facial features from trauma just like the air pillows protect the fragile objects.

Along with protecting our facial bones from trauma, our sinuses also help to lighten the weight of our heads. The average human brain weighs 2.86-3lbs. The human skull weighs around 2 lbs. That is a lot of weight for our spine to hold up. Our sinuses help to alleviate some of this weight off of our spines. They are also thought to help with our breathing by humidifying and heating the air we inhale.

Types of Sinuses

Sinuses are found in our skull bones. Each sinus is named for the bone in which the sinus can be found.

Types of Sinues

Maxillary sinuses are the largest (max/maximum) of the sinuses. They are shaped like pyramids and are found in your cheekbones just under your eyes. The thinnest part of the maxillary sinuses is located just above the canine tooth. This allows easy access for viruses or bacteria to enter and cause infection in the sinus cavity.

Frontal sinuses are located in the low center of the forehead. They are in the frontal bone above the eyes right around the eyebrows. Unlike the maxillary sinuses, the frontal sinuses are shaped more like funnels.

Sphenoid sinuses are found in the center of the head. They are located in the sphenoid bone. This bone is behind the nasal cavity.

Ethmoid sinuses form tiny air cells that can be found at the bridge of the nose right between the eyes. They are found in the ethmoid bone.

Side view of sinues

Sinus Issues and Infections

Sinuses always seem to be linked to infections and annoyances, like runny noses. This is because the sinuses drain through the middle meatus, a small drainage pathway that leads to the nose. The sinuses surround and are connected to the nasal cavities. Therefore, sinus and nasal infections go hand-in-hand with each other.

Acute sinusitis, or a sinus infection, occurs when a virus or bacteria enters and infects a sinus cavity. If these infections become persistent, they may cause the sinuses to become inflamed. A persistent sinus infection is a condition known as chronic sinusitis.

Allergies can also cause the sinuses to become irritated. When the body detects allergens, it sets off a series of defenses, such as increased mucus. Sometimes the body overreacts and can cause allergic rhinitis. Allergic rhinitis causes extra mucus to form and the nasal cavity to stiffen. Sneezing and itching can also take place during this infection.

Nasal polyps are small growths that are found inside the nasal cavity due to inflammation. These can be caused by multiple infections, asthma, and allergic rhinitis.

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