Ciliary Body and Production of Aqueous Humor

Will the introduction of aqueous humor play a role in how many immune cells live in the tissue?

As we increase aqueous humor, we can reduce the MHC-II presentation. It ACTIVELY shuts down dendritic cells to keep the tissue immune privileged.

What is the advantage of the blood-aqueous barrier?

-Proteins cause turbidity and cause light to scatter. The plasma also contains growth factors and lots of cytokines that could be harmful. Possible antigens that are in the bloodstream can't get into the aqueous.

What two physiological characteristics of the anterior segment can cause a difference between plasma and aqueous humor?

1. Blood-aqueous barrier 2. active transport of the various organic and inorganic substances by the ciliary epithelium.

What are the three major histological structures?

1. Ciliary epithelium: bilaminar epithelium, pigmented epithelium, non-pigmented epithelium 2. Ciliary body stroma 3. Ciliary muscle

List some properties of aqueous humor and its production:

1. Clear colorless liquid that fills anterior and posterior chambers. Clear because it is protein free (less than 1% usually found in plasma). It does have a high ascorbate concentration which protects the eye from UV-light damage. 2. Formed from blood plasma and actively secreted by the non-pigmented epithelium at 2-4 microliters/minute but is produced at about half that rate during sleep. 3. Aqueous humor provides a medium of refractive index of 1.33, which makes it optically important. 4 Helps generate outward pressure to maintain structural integrity of the eye. 5. Provides nutrient to transparent structures in the front of the eye since there aren't many blood vessels in other places in the eye. 6. Can remove metabolic waste 7. Facilitates immune quiescence in anterior segment.

What are three hypothesized mechanisms for aqueous humor production?

1. Diffusion: flowing concentration gradient. Eg. lipid soluble stuff. 2. Ultrafiltration: involves the bulk flow of substances across a membrane related to either hydrostatic or osmotic pressures on either side. 3. Active transport: accounts for 80-90% -Sodium potassium pump -Carbonic anhydrase:

What are the three bundles of ciliary muscles and how do they come together?

1. Longitudinal 2. Radial 3. Circular They work as one unit. These muscles insert into the scleral spur and the contraction distend trabecular network spaces:

What are the two anatomical zones of the ciliary body?

1. Pars plicata: anterior 1/3 which includes 70 ciliary processes, lots and lots of surface area, thus lots of interaction (secretion and absorption), BUT zonules don't attach here 2. Pars plana: posterior 2/3- long and smooth. This is where the zonules would attach.

List the three roles of the ciliary bodies

1. control of accommodation 2. production of aqueous humor 3. production of zonules, virtual collagen, bit real hyaluronic acid

How does the aqueous humor get produced?

Blood flows from the stroma of the ciliary body to the epithelium into the processes. Here, there are fenestrated (leaky) capillaries that leak fluids, ions, and proteins to provide a reservoir to be secreted by the ciliary epithelium. The nutrients and fluid are then taken up by the pigmented epithelium and transferred to the non pigmented epithelium with the use of gap junctions. The non-pigmented epithelial cells secret nutrients, fluid, etc. to posterior chamber.

What does an accommodated lens look like?

Ciliary muscles in action: pulling zonules tight upward to cause the inflation of the lens.

Where is the ciliary body?

It's the middle part of the uveal tract between the iris and choroid. It is a 5 to 6 mm wide ring along the inner wall of the globe with a triangular shape in cross-section. This is also the site of zonular fiber attachment. Limbal function: aqueous outflow

What do ciliary bodies at rest look like?

Muscles relaxed, back down, lens flattened.

Describe the ciliary epithelium.

Pigmented epithelium is on the inside of the process. Non pigmented is closest to the surface. The fibrovascular core makes the extended processes. *RPE continuous with the process- explains the pigmented section- probably not important.

What does the flow of aqueous humor look like?

The ciliary bodies produce the aqueous humor into the posterior chamber. It then travels through to the anterior chamber and will go to Schlemm's canal through the trabecular meshwork.

How are the ciliary bodies innervated?

The long and short ciliary nerves accompany those arteries. They are a target of glaucoma drugs.

Describe the double layer epithelium and how it creates the blood-aqueous barrier.

The pigmented and non pigmented are apical-apical and so there are TWO basement membranes covering the basal side of each layer. Two operate layers are JOINED by gap junctions for nutrient transport but NPE forms TIGHT JUNCTIONS which prevent macromolecules from passing into the posterior chamber.

Describe some characteristics of the ciliary processes.

They are delicate finger-like protrusions, with highly vascularized loose connective tissue covered by a "bilaminar epithelium," pigmented epithelium, and non-piglet epithelium. The radial orientation attach to the zonules.

What is required of the blood supply to ciliary muscles?

We need a high rate of blood flow, 7%, which is pretty high considering the eyes have neural tissue that connect to brain function. -Arterial Supply: long posterior ciliary artery, anterior ciliary artery -Venous return: vortex vein, anterior ciliary veins. The capillaries must be fenestrated such that proteins up to 150kD can enter the stromal compartment. Pigmented epithelium picks up the proteins, send them to non pigmented, add electrolytes. These regulate aqueous hour formation via the osmotic pressure created.

What does accommodation look like?

https://www.youtube.com/watch?v=1yIpyitm6eE