Eyes: Difference between revisions
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Tear production system | Tear production system | ||
The protection of tears has three separate layers: the lipid layer, the aqueous layer, and the mucous layer. The outermost lipid layer contains oils produced by the meibomian glands. It is a thin layer (0.1-0. | The protection of tears has three separate layers: the lipid layer, the aqueous layer, and the mucous layer. The outermost lipid layer contains oils produced by the meibomian glands. It is a thin layer (0.1-0.2µm and hydrophobic surface, so it reduces evaporation of water. The temperature in meilbomain gland lipids has the low melting point range 19-32C depending on the degree of fatty acids unsaturation. The meibomain gland lipids allow lipid get through the meibomian gland ducts and excretion to the tear film. | ||
The aqueous layer is a tear film including water and proteins produced by the lacrimal gland. The middle layer of the lacrimal gland is the thickest (7- | The aqueous layer is a tear film including water and proteins produced by the lacrimal gland. The middle layer of the lacrimal gland is the thickest (7-8µm) and produces 0.9% saline tears. It functions delivery the main nutrients such as oxygen to the cornea and carrying waste products away from the cornea | ||
The innermost mucous layer ( | The innermost mucous layer (30µm) contains mucin produced by goblet cells. Its thin layer of hydrophilic surface can make even on the corneal surface to spread water. (1,3,4 and 5) | ||
Many species of bacteria are found in the eyelid and conjunctiva as symbiotic relationships. These are Staphylococcus aureus (S. aureus), Staphylococcus epidermidis, Streptococcus, Corynebacterium, Propionibacterium, and Propionibacterium acnes. These bacteria produce lipase that harm to the tear film lipid layer especially, S. epidermidis and S. aureus produce triglyceride lipase and cholesterol and wax esterase. Accumulated cholesterol is used for the growth of certain ocular bacteria. Increased bacteria are regulated by anti-microbial peptides from the lacrimal gland and conjunctiva. (6) | Many species of bacteria are found in the eyelid and conjunctiva as symbiotic relationships. These are Staphylococcus aureus (S. aureus), Staphylococcus epidermidis, Streptococcus, Corynebacterium, Propionibacterium, and Propionibacterium acnes. These bacteria produce lipase that harm to the tear film lipid layer especially, S. epidermidis and S. aureus produce triglyceride lipase and cholesterol and wax esterase. Accumulated cholesterol is used for the growth of certain ocular bacteria. Increased bacteria are regulated by anti-microbial peptides from the lacrimal gland and conjunctiva. (6) | ||
Revision as of 01:28, 27 August 2008
Description of Niche
Where located?
Physical Conditions?
What are the conditions in your niche? Temperature, pressure, pH, moisture, etc.
Influence by Adjacent Communities (if any)
Is your niche close to another niche or influenced by another community of organisms?
Conditions under which the environment changes
Do any of the physical conditions change? Are there chemicals, other organisms, nutrients, etc. that might change the community of your niche.
Tears
Tears Tears are secretion from tear glands to lubricate and protect eyes from infection. The tear film allows gas exchange between the air and the epithelium and also keeps the cornea wet. The substance of the tear film is retinol to provide the transparent nature of the epithelium. (1) Tears are composed of water, electrolytes, proteins (albumin, globulin, and lysozyme), lipid, mucins and others. They are weak base. (2)
Tear production system The protection of tears has three separate layers: the lipid layer, the aqueous layer, and the mucous layer. The outermost lipid layer contains oils produced by the meibomian glands. It is a thin layer (0.1-0.2µm and hydrophobic surface, so it reduces evaporation of water. The temperature in meilbomain gland lipids has the low melting point range 19-32C depending on the degree of fatty acids unsaturation. The meibomain gland lipids allow lipid get through the meibomian gland ducts and excretion to the tear film. The aqueous layer is a tear film including water and proteins produced by the lacrimal gland. The middle layer of the lacrimal gland is the thickest (7-8µm) and produces 0.9% saline tears. It functions delivery the main nutrients such as oxygen to the cornea and carrying waste products away from the cornea The innermost mucous layer (30µm) contains mucin produced by goblet cells. Its thin layer of hydrophilic surface can make even on the corneal surface to spread water. (1,3,4 and 5)
Many species of bacteria are found in the eyelid and conjunctiva as symbiotic relationships. These are Staphylococcus aureus (S. aureus), Staphylococcus epidermidis, Streptococcus, Corynebacterium, Propionibacterium, and Propionibacterium acnes. These bacteria produce lipase that harm to the tear film lipid layer especially, S. epidermidis and S. aureus produce triglyceride lipase and cholesterol and wax esterase. Accumulated cholesterol is used for the growth of certain ocular bacteria. Increased bacteria are regulated by anti-microbial peptides from the lacrimal gland and conjunctiva. (6)
Who lives there?
Which microbes are present?
You may refer to organisms by genus or by genus and species, depending upon how detailed the your information might be. If there is already a microbewiki page describing that organism, make a link to it.
Fungal Infestation of the Eye Niche
The warm and moist environment of the eye is subject to mycotic infections from fungi such as Fusarium, Aspergillus, Acremonium, and the Candida species of yeasts. Due to the preferences for moisture-rich environments and warm weather, the prevalence of fungal infections of the eye is higher in tropical areas and in areas with large agrarian communities. Despite the relatively sterile environment of the eye, factors such as eye “trauma (generally with plant material), chronic ocular surface diseases, contact lens usage, corneal anesthetic abuse and immunodeficiencies” can result in infection of the eye by filamentous fungi or yeasts. Fusarium solani, a species of fungi that is associated with contact lens wearers, normally inhabits warmer climates in soil and organic matter. Invasion of the inner layers of contact lenses and transfer to the surface of the eye is possible due to the ability of Fusarium solani to reside in the water-rich inner matrix of soft contact lenses.
Fungal infections, such as fungal keratitis, can occur on the anterior surface of the eye or the cornea, and may also infect the posterior of the eye as a result of mycosis. Fungi that inhabit the eye produce proteases that are specific for the surface on which they grow. As a result, protein catabolism by fungal proteases results in tissue damage to the eye, ulceration as well as an inflammatory response around the infected area. Aggregation of fungal microbes into hyphae enlarges the infected region and prevents host inflammatory cells from ingesting the fungi. As a result of the pattern of fungi to join together and form hyphae, fungi that inhabit the eye may extend throughout the entire depth of the cornea, and tend to grow parallel to the lamellae of the cornea. As a result of catabolic degradation of the eye environment by the fungi, an inflammatory response by the host is accompanied by coagulative necrosis of the surrounding eye tissues.
Fungal infection of the eye may occur as a result of fungal growth on contact lenses. Due to tendency of fungi to inhabit moisture-rich locations, contact lens cases and the soft inner matrix of contact lenses are subject to fungal growth. Fungi have the ability to degrade hydrophilic polymers of contact lenses, and may be transferred from contaminated lenses to the anterior surface of the eye, often causing the implantation of fungi into the anterior regions of the eye or the cornea and result in fungal keratitis.
Do the microbes that are present interact with each other?
Describe any negative (competition) or positive (symbiosis) behavior
Do the microbes change their environment?
Do they alter pH, attach to surfaces, secrete anything, etc. etc.
Do the microbes carry out any metabolism that affects their environment?
Do they ferment sugars to produce acid, break down large molecules, fix nitrogen, etc. etc.
Defense Mechanisms of the Eye
Barely any microbes live in the eye. This stems from the fact that each section within the eye has mechanisms that defend against infection and microbe colonization.
Blink Reflex
The blink reflex is a mechanical defense against particles in the air or trauma. Eyelashes and the sensitive cornea both participate in this reflex. Tears, debris, allegans, microbes, etc. are moved over to the lacrimal excretory system with the motion from the eyelid.
Barriers
The orbital septum, cornea and conjunctiva all provide a protective barrier against pathogens. The orbital septum divides the orbit from the eyelid into pre and postseptal spaces which allows for a physical barrier against infections. The various layers of the cornea limit permeability of items into the eye. Also, native flora of the lids and mucosal surface limit possible pathogenic colonization.
Tears
Tears provide a mechanical defense via flushing of foreign particles from the surface of the eye and transporting antimicrobial agents to the surface as defensive measures.
Immune Response
The cornea, due to lack of a vascular system, contains limited immune defenses. Immune defenses are provided by Langerhans cells and immunoglobulins. Langerhans cells modify B and T cell in the cornea Glycocalx coupled with a mucous glycoprotein layer covers the corneal surface for added protection.
Langerhans cells have receptors for immunoglobulins, antigen, and complement. They work like macrophages to destroy foreign invaders. The B and T cells that are modified by Langerhans cells work in conjunction with lymphocytes, resulting in a strong immune reponse.
Leukocyte Defense Leukocytes consume and destroy microorganisms via and oxygen-dependent pathway and oxygen-independent pathway. The oxygen-dependent pathway uses oxygen radicals while the oxygen-independent pathway utilizes defensins, which are antimicrobial proteins consisting of peptides that have broad antimicrobial activity, destroying gram-positive and gram-negative bacteria, some fungi, and various pathogens in the eye.
Current Research
Enter summaries of the most recent research. You may find it more appropriate to include this as a subsection under several of your other sections rather than separately here at the end. You should include at least FOUR topics of research and summarize each in terms of the question being asked, the results so far, and the topics for future study. (more will be expected from larger groups than from smaller groups)
References
(1) http://physiologyonline.physiology.org/cgi/content/full/13/2/97
(2) http://www.nature.com/eye/journal/v17/n8/full/6700566a.html
(3) http://www.tedmontgomery.com/the_eye/cornea.html
(4) http://www.lea-test.fi/en/eyes/lidsncha.html
