Circulus arteriosus major

1. Circulus Arteriosus Major

The **Circulus Arteriosus Major**, also known as the Circle of Willis, is a critical arterial structure located at the base of the brain. It is a circulatory anastomosis that supplies blood to the brain and surrounding structures. The Circle of Willis is named after Thomas Willis, an English physician who described it in the 17th century.

Anatomy

The Circle of Willis is formed by the following arteries:

• Anterior cerebral artery (ACA)
• Anterior communicating artery
• Internal carotid artery
• Posterior cerebral artery (PCA)
• Posterior communicating artery

These arteries create a circular network that provides multiple pathways for blood to supply the brain, which is crucial in maintaining cerebral perfusion even if one part of the circle is compromised.

Function

The primary function of the Circle of Willis is to ensure consistent blood flow to the brain. It acts as a safety mechanism, allowing for collateral circulation. This means that if one part of the circle becomes blocked or narrowed (such as in the case of a stroke), blood can still reach the brain through alternative routes.

Clinical Significance

The Circle of Willis is significant in the context of cerebrovascular diseases. Conditions such as aneurysms, strokes, and transient ischemic attacks (TIAs) often involve the arteries of the Circle of Willis. Anomalies in the structure of the Circle of Willis can predispose individuals to these conditions.

Aneurysms

Aneurysms are bulges in the wall of an artery that can occur in the Circle of Willis. They are particularly dangerous because they can rupture, leading to a subarachnoid hemorrhage, a type of stroke that can be life-threatening.

Strokes

Strokes can occur when there is an interruption of blood flow in the Circle of Willis. This can be due to a clot (ischemic stroke) or a bleed (hemorrhagic stroke). The Circle of Willis can sometimes compensate for a blocked artery, reducing the severity of a stroke.

Variations

There are several anatomical variations of the Circle of Willis, which can affect its function. Some individuals may have a complete circle, while others may have one or more segments that are hypoplastic or absent. These variations can influence the risk and severity of cerebrovascular events.

See Also

• Cerebral circulation
• Cerebrovascular disease
• Neuroanatomy

References

Keith L.,

 Clinically Oriented Anatomy, 
  
 Wolters Kluwer, 
 2018, 
  
  
 ISBN 978-1496347213,

Willis, Thomas,

 Cerebri Anatome, 
 , 
 1664,

External Links

• [Circle of Willis - Wikipedia](https://en.wikipedia.org/wiki/Circle_of_Willis)