Retinal Pigment Epithelium Quiz

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Questions and Answers

What role do monocarboxylate transporters (MCT) play in cellular transport?

Creation of an electrochemical gradient across membranes

Active transport of ions against their gradient

Transport of waste products from retinal cells to blood (correct)

Facilitated diffusion of nutrients into cells

How is carbonic acid relevant to pH maintenance in the body?

It acts as a buffering agent (correct)

It directly increases hydrogen ion concentration

It reacts with bicarbonate to increase acidity

It facilitates oxygen transport in blood

What drives the movement of water through aquaporins in retinal pigment epithelium (RPE)?

Passive ion channels

Activated sodium-potassium pump

Concentration gradient of K+

Localized hypertonic solution (correct)

What is the primary driving force behind the Na+/K+ -ATPase activity in the RPE apical membrane?

Electrochemical gradient creation Signup and view all the answers

What occurs during the 'dark current' in retinal cells?

Na+ and Ca2+ ions flow inward through channels Signup and view all the answers

What is the function of NKCC cotransporters in RPE cells?

Using Na+ gradient to transport Cl- into cells Signup and view all the answers

How does the RPE maintain ion homeostasis in the subretinal space?

By buffering changes and providing K+ when needed Signup and view all the answers

What happens to gated ion channels upon exposure to light in retinal cells?

They close, reducing K+ outflow Signup and view all the answers

What structure forms part of the blood-retina barrier?

Retinal pigment epithelium (RPE) Signup and view all the answers

Which of the following functions does the RPE fulfill regarding light absorption?

Absorbs unreflected photons Signup and view all the answers

What mechanism does the RPE primarily use for the transport of glucose?

Facilitated transport through GLUT1 and GLUT3 Signup and view all the answers

What is a key characteristic of the epithelial transport performed by the RPE?

Prevents any paracellular movement of water or solutes Signup and view all the answers

How does the RPE contribute to the dissipation of heat energy?

Through transfer of heat to the choroidal blood supply Signup and view all the answers

What type of fatty acids does the RPE transport via simple diffusion?

Omega-3 fatty acids Signup and view all the answers

Which of the following statements accurately describes the role of RPE in immune privilege?

RPE forms barriers to maintain low immune activity in the retina Signup and view all the answers

What anatomical structure prevents the passage of fluid and solutes between photoreceptors and the choroid?

Basolateral membrane of RPE Signup and view all the answers

What is the primary effect of decreased K+ concentration in the apical RPE membrane?

It causes hyperpolarization of the apical RPE membrane. Signup and view all the answers

How does RPE respond to low subretinal K+ concentration?

By opening K+ channels to release K+. Signup and view all the answers

During phagocytosis of photoreceptor outer segments, what happens to the phagosome?

It fuses with an endosome and lysosome. Signup and view all the answers

When is the phagocytosis of photoreceptor outer segments primarily triggered?

In the morning, triggered by light. Signup and view all the answers

What role does the circadian rhythm play in the function of RPE?

It regulates the phagocytosis process of photoreceptor outer segments. Signup and view all the answers

Which process involves the digestion of phagolysosome contents in RPE?

Phagocytosis of outer segments. Signup and view all the answers

What is one of the consequences of sloughing off outer segment tips?

It enhances the recycling of digested molecules. Signup and view all the answers

What is hyperpolarization related to in relation to Na+ pumping in RPE?

Slowing down Na+ being pumped out of RPE cells. Signup and view all the answers

Study Notes

Learning Objectives

Locate the retinal pigment epithelium (RPE), photoreceptors, Bruch's membrane, and choriocapillaris on a diagram.

Functions of the RPE

Blood-Retina Barrier: Forms a tight-junction epithelium between the choroid and photoreceptor outer segments.
Prevents paracellular movement of water and solutes.
Isolates the inner retina from systemic influences at the choroidal side.
Efficiently absorbs light.
Absorbs photons not absorbed by rhodopsin preventing reflection, using melanin.
Dissipates heat generated from absorbed light and transports it away with the blood.
Transports nutrients.
Transports glucose (GLUT1 and GLUT3), metabolizes immediately, maintains low glucose photoreceptor levels.
Transports omega-3 fatty acids by simple diffusion.
Maintains membranes.

Ion Buffering in the Interphotoreceptor Matrix

Maintains ion homeostasis in subretinal space by epithelial transport of ions.
Buffers changes in ion concentration.

Dark Current

Influx of Na+ and Ca2+ through gated ion channels in the outer segment are counterbalanced by outflow of K+ in the inner segment.
Decrease in K+ concentration compensated by RPE.

Light

Light closes gated ion channels, decreasing K+ outflow in the inner segment
Increased subretinal K+ concentration due to decrease in K+ efflux.

Phagocytosis of Photoreceptor Outer Segments

Process: Microvilli surround and seal off phagosome →phagosome fuses with endosome, lysosome digests molecules, returns some to regenerate photoreceptors.
Timing: Occurs in the morning, regulated by circadian rhythm and coordinated by RPE and photoreceptors.
Outer segment tips are sloughed and phagocytosed by RPE due to light damage.
Duration: Outer segment replenishment ~2 weeks, 7-10% eliminated daily.
Function: Maintains photoreceptor excitability, providing nutrients and materials for new outer segments through ATP generation.

Secretion

Function: Prevents photoreceptor apoptosis from photooxidative damage through PEDF (pigment epithelium-derived factor) production, a neurotrophic factor.
Secretion of VEGF (vascular endothelial growth factor) for stabilization of choroid capillary fenestrations.

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Description

Test your understanding of the retinal pigment epithelium (RPE) and its functions. This quiz covers the anatomy of the RPE, its role in the blood-retina barrier, and the transport mechanisms involved in maintaining retinal health. Prepare to identify key structures and functions critical to vision.