Editing Hemorrhoid (section)

==Pathophysiology==
[[File:Gross pathology of hemorrhoids.jpg|thumb|[[Gross pathology]] of hemorrhoids, showing engorged blood vessels]]
Hemorrhoid cushions are a part of normal human anatomy and become a pathological disease only when they experience abnormal changes.<ref name=World09 /> There are three main cushions present in the normal [[anal canal]].<ref name=Review09 /> These are located classically at left lateral, right anterior, and right posterior positions.<ref name=Kaidar2007 /> They are composed of neither [[arteries]] nor [[veins]], but blood vessels called [[sinusoids]], [[connective tissue]], and [[smooth muscle]].<ref name=Beck2011 />{{rp|175}} Sinusoids do not have [[muscle tissue]] in their walls, as veins do.<ref name=World09 /> This set of blood vessels is known as the [[hemorrhoidal plexus]].<ref name=Beck2011 />

Hemorrhoid cushions are important for [[fecal incontinence|continence]]. They contribute to 15–20% of anal closure pressure at rest and protect the [[internal anal sphincter|internal]] and [[external anal sphincter]] muscles during the passage of stool.<ref name=World09 /> When a person bears down, the intra-abdominal pressure grows, and hemorrhoid cushions increase in size, helping maintain anal closure.<ref name=Kaidar2007 /> Hemorrhoid symptoms are believed to result when these vascular structures slide downwards or when venous pressure is excessively increased.<ref name=AFP2006 /> Increased [[internal anal sphincter|internal]] and [[external anal sphincter]] pressure may also be involved in hemorrhoid symptoms.<ref name=Kaidar2007 /> Two types of hemorrhoids occur: internals from the [[superior hemorrhoidal plexus]] and externals from the inferior hemorrhoidal plexus.<ref name=Kaidar2007 /> The [[pectinate line]] divides the two regions.<ref name=Kaidar2007 />