October 17, 2010

Q&A: Concerning Aqueous Humour

The aqueous humour is a transparent watery fluid similar to plasma, but containing low protein concentrations. It is secreted from the ciliary body, a structure supporting the lens. It fills both the anterior and the posterior chambers of the eye, and is not to be confused with the vitreous humour, which is located in the space between the lens and the retina, also known as the posterior cavity or vitreous chamber.

This article is for Medical Students & Professionals
This is a Question & Answer revision article designed for medical students and professionals preparing for the PLAB, MRCP or USMLE examinations. They are based on actual questions from these examinations. You may find the Anatomy Of The Eye article more useful, or one of our many articles on Diseases & Conditions, Medical Syndromes, Health & Wellness or Home Remedies.
In this article:
Composition and function of aqueous humour
MCQ: clinical scenario
MCQ: answer
MCQ: explanation

Composition and function of aqueous humour

The aqueous humour is composed of amino acids, 98% water, electrolytes (sodium, potassium, calcium, magnesium, chloride, HCO3, phosphate, and with Osm of 304), ascorbic acid, glutathione, and immunoglobulins.

It functions to maintain the intraocular pressure inflating the globe of the eye, thus generating the hydrostatic pressure which keeps the eyeball in a roughly spherical shape and the walls of the eyeball taut. It provides nutrition (e.g. amino acids and glucose) for the avascular ocular tissues; posterior cornea, trabecular meshwork, lens, and anterior vitreous. The aqueous humour may serve to transport ascorbate in the anterior segment to act as an antioxidant agent. Presence of immunoglobulins in it indicate a role in immune response to defend against pathogens. It provides inflation for expansion of the cornea and thus increased protection against dust, wind, pollen grains and some pathogens. It achieves refractive index, and prevents eye dryness

MCQ: clinical scenario

The aqueous humour of the eye may be divided into an anterior chamber and a posterior chamber. What mostly tends to separate these chambers?

a) lens
b) cornea
c) iris
d) limbus
e) ciliary processes

MCQ questions & answers on medicalnotes.info

MCQ: answer

The correct answer is C

MCQ: explanation

The iris is an annular membrane dividing the aqueous humour into the anterior chamber, nearer the cornea, and the posterior chamber, towards the lens. The inner portion of the iris, the pupillary zone, is separated from the ciliary zone by the zig-zagging collarette. The colour of eyes is determined by the amount of pigment in the iris. With no pigment the eyes appear blue; with increasing amounts of pigment the colour tends towards grey, brown and black.

See also the separate article, Anatomy of the Eye, for more information.

Reference(s)
1). Dee Unglaub Silverthorn. Human Physiology. An Integrate approach. 5th edition.
2). WebMD. Eye Anatomy. Available online: http://www.webmd.com/eye-health/tc/eye-anatomy-and-function-topic-overview?page=2

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