58 Questions
What is the function of the lipid layer in the tear film?
Preventing tear evaporation
Which of the following is NOT a component of the lipid layer in tear film?
Proteins
During tear-film breakup time, the subsequent blink is stimulated by:
Film stabilization
Which gland secretes Meibum, a crucial component of the tear film lipid layer?
Meibomian gland
The aqueous layer of tear film contains which of the following components?
Dissolved salts
In tear film formation, when substances are transported in opposite directions, it is an example of:
Antiport
What is the major component of the lipid layer of the precorneal tear film?
Waxes
Which of the following is derived from eicosanoic acids and includes examples like prostaglandins and leukotrienes?
Eicosanoids
What is the main characteristic of glycolipids?
Found in nervous, ocular, and other tissues
What is the basic structure that binds glycolipids?
Sphingosine
In which glycolipid is phosphocholine esterified to a ceramide?
Sphingomyelin
What is the function of lipid esters found in tear film?
Help the lipids adhere to the eyelid skin and act as a barrier to the aqueous layer
What is a possible cause contributing to meibomian gland dysfunction?
Increased cholesterol and appearance of ceramides
What is the advantage of high fluidity of the photoreceptor disc membrane?
Allows for rotational and lateral movements of rhodopsin needed for phototransduction
To what class of lipids does Vitamin A belong?
Isoprenoid
What is the role of Vitamin E in the retina?
Absorbs free radicals
What are the chemical forms of Vitamin A and their roles?
Retinyl ester: storage; Retinol: transport; Retinal: visual transduction; Retinoic acid: synthesis
What process involves the transport of 3 sodium ions out of the cell and 2 potassium ions into the cell by hydrolyzing 1 molecule of ATP?
Antiport
Which type of transport involves substances being transported in the same direction, such as glucose transport in kidney tubules?
Symport
What is the primary function of the lipid layer in tear film?
To stabilize the tear film
Which components are present in the anterior/superficial lipid layer of tear film?
Cholesteryl esters and waxes
In tear-film formation, when substances are transported simultaneously, it is an example of:
Cotransport
Which gland secretes Meibum, a crucial component of the tear film lipid layer?
Meibomian gland
What is the result of tear-film breakup time?
Stimulation of the next blink
What is the composition of the aqueous layer in tear film?
Dissolved salts and proteins
What is the significance of the protein to lipid ratio in a membrane?
Helps gauge the role of membrane – transport, metabolism, and signal transduction
What is simple diffusion and provide an example?
Movement from lower to higher concentration without energy, example: movement of glucose using GLUT-1
How does facilitated transport differ from active transport?
Facilitated transport occurs against the concentration gradient, while active transport occurs down the gradient
What is the role of glycolipids in cell membranes?
Serve as biological bridges and bonding agents in membranes
Which membrane has a protein to lipid ratio of 3:1?
Mitochondrial inner membrane
What is the primary function of glycoproteins in cell membranes?
Function as molecular bridges between cells
Which type of transport is limited by the ability of proteins or enzymes to perform the task?
Facilitated transport
Give an example of a process that requires enzyme catalysis for energy to operate a pump moving molecules against their concentration gradient.
Active transport
What is one of the functions of lipid esters found in the tear film?
Help the lipids form a film over the aqueous layer and maintain contact with it
Which is a possible cause contributing to meibomian gland dysfunction?
Detachment of epithelial cells from the gland blocking lipid flow to the tear film
Why is high fluidity crucial for the photoreceptor disc membrane?
Enables rotational and lateral movements required for phototransduction
To which class of lipids does Vitamin A belong?
Isoprenoid
What happens in the retina in the absence of Vitamin E?
Free radicals attack membrane fatty acids, breaking them into fragmentary aldehydes
What is a role of retinol among the chemical forms of Vitamin A?
Transport and hormonal function
Which statement describes a function of Vitamin E in the retina?
Absorption of free radicals
What are common dietary sources of Vitamin A apart from animal sources?
Carrots, sweet potatoes
What is a common adverse effect of high daily intake of Vitamin A?
Blurred vision
Where do gangliosides mainly reside in the body?
Nervous tissue
What is the characteristic physical feature of Tay-Sachs disease?
Accumulation of gangliosides in nerve tissues
What enzyme deficiency leads to Tay-Sachs disease?
Hexosaminidase A
In which region of the eye is the characteristic cherry-red spot observed due to Tay-Sachs disease?
Macular region
What is the primary impact of ganglioside accumulation in the retina?
Degeneration of ganglion cells
How does Tay-Sachs disease affect the lifespan of affected individuals?
Causes early childhood death
What are some common symptoms experienced with high Vitamin A intake?
Irritability and abdominal pain
What is the main role of Chylomicra in the body?
Incorporate hydrophobic lipids
How is retinol conveyed from the liver to target cells?
Mobilization after binding to prealbumin
What happens to retinol after it enters target cells?
Released and transported via a receptor protein
Which proteins are involved in mobilizing retinal for transport to target cells?
Prealbumin and retinol binding protein
What are the three disorders of the eye caused by Vitamin A deficiency?
Nyctalopia, xerophthalmia, keratomalacia
What does Keratomalacia involve?
Degeneration of corneal epithelium and corneal perforation
Which process occurs after all-trans retinal is converted to 11-cis-retinal in the retina?
Esterification and isomerization
What is Xerophthalmia primarily characterized by?
Dry eyes due to hardening of corneal conjunctiva
Which type of lipids are found on the surface of chylomicra transport complexes?
Hydrophilic lipids
This quiz covers the definitions of uniport, cotransport, symport, and antiport in the context of cellular transport mechanisms. Examples such as GLUT-1 for uniport and glucose transport in kidney tubules for symport are discussed.
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