BS - Bleaching and Recycling - Week 10 Flashcards
(43 cards)
What are RPE cells and where are they located?
Monolayer of pigmented cells located between choricapillaris and photoreceptors
Name 6 functions of RPE cells.
- Absorption of light, heat
- Transport of nutrients, waste (glucose, omega 3, retinal, lactic acid)
- BRB
- Phagocytosis of shed OS (outer segment)
- Interacts with BM - for barrier function and selective transport
- Involved in photopigment recycling (interacting with photoreceptors)
How many photoreceptors does each RPE cell form a functional unit with?
Around 23 photoreceptors
What are the 2 components of photopigments, and where are they synthesised?
Opsin and chromophore
Consider the components of a photopigment. What is the origin of each?
Chromophore - not made in the body, is derived from the diet.
Opsin - synthesised in the inner segment
What are the 2 isomeric forms of retinal? And what causes them to change to the other?
11-cis and all-trans - converts to all-trans in response to light
All-trans is a straighter molecule
What are some source of vitamin A?
B-carotene and vitamin A precursors from diet
Red/yellow vegetables, fish, dairy, eggs
What is a retinoid?
Any derivative of vitamin A.
What are the three active forms of vitamin A?
Retinal, retinol, and retinoic acid.
In what form is vitamin A stored?
Retinyl ester.
What two forms of retinoids can be readily interconverted?
Retinal and retinol.
Where are retinyl esters typically found (2)?
Rich in the liver, also found in circulating chylomicrons
What are retinyl esters complexed with in the bloodstream?
Transthyretin
What happens if you eat a polar bear liver?
Le khod
What happens to beta-carotene when eaten, and how? What does it form?
It is solubilised by bile salts and lipolytic enzymes into retinol.
When beta-carotene is eaten, how is it transported out of the intestines?
Once converted to retinol, it binds to cellular retinol binding protein, CRBP, and is transported out.
What form of retinoid can be found in chylomicrons? Where do these eventually end up, and are they a major source of retinoid for this structure?
Retinyl esters are incorporated into chylomicrons.
They can bind to the RPE, but is a minor source.
In what 3 forms are retinoids stored in the liver?
Chylomicrons
Retinyl esters
Retinol palmitate
Is vitamin A susceptible to oxidation or reduction?
Oxidation
When not in retinyl ester form, what are retinoids always bound to?
Retinoid binding protein RBP
How do retinoids avoid being filtered by the kidneys?
Retinoids and RBP complex with transthyretin
Where do retinol-transthyretin complexes end up?
They bind to retinoid binding protein receptors on the RPE.
What are the two sources of retinoids for the RPE, and which is major/minor?
Major - retinol-transthyretin complex binding to receptors on the RPE.
Minor - retinyl esters in chylomicrons reaching the RPE through the bloodstream.
In what form is vitamin A within the RPE?
Retinyl ester.
