Questions & Answers
These are questions submitted by students as they study histology. New questions will be added at the top of the list, as they are submitted. Click on a question to see the answer or explanation.
3. What part of the connective tissue is affected by Marfan's syndrome, and is there a certain area that is damaged more severely?
2. Where can I learn about urinary casts?
1. Is there fenestrated endothelium in lungs? Do capillaries in the lung have fenestrations to provide transport of O2 and CO2, or is this done by channels and diffusion?
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(Also see Introductory Unit Question & Answer.)
3. How does Marfan's syndrome affect connective tissue? Is there a certain area that is damaged more severely? Marfan's syndrome is caused by a defect in the gene FBN1, which affects the connective tissue matrix protein fibrillin-1. A major consequence is aortal aneurysm, due to damage of the vessel lining and weakening of its wall. For additional physical findings, see Center for Marfan Syndrome Research at Johns Hopkins.
According to current understanding (based on a mouse model of fibrillin-1 deficiency), fibrillin is needed for maintenance of elastic fibers and for regulating (inhibiting) the function of transforming growth factor beta (TBF beta). For more information, see a research summary at www.marfan.org, by researcher Hal Dietz, M.D. Also see recent research news (from marfan.org), and Marfan FAQ (from Johns Hopkins).
2. Where can I learn about urinary casts? Begin with the WebPath tutorial on urinalysis. Some additional general information may be found here, here, and here.
1. Is there fenestrated endothelium in lungs? No. CO2 and O2 both diffuse freely through cell membranes, so neither fenestrations nor special "transport mechanisms" are necessary. As an adaptation to faciliate diffusion, the gas-exchange membrane in lung is as thin as possible -- just simple squamous alveolar epithelium + capillary endothelium, together with associated basement membranes.
Furthermore, controlling fluid leakage from the capillaries into lungs is just as important as efficient gas exchange, so fenestrations would be a bad idea. We do NOT want fluid to pass freely out of capillaries, or else the alveoli would fill up with water. Therefore, alveolar capillaries are continuous, NOT fenestrated.
Incidently, the brain also has a high need for rapid oxygen exchange (out from blood, rather than into blood), but here also diffusion is adequate. The only molecules which cross the blood-brain barrier (which is established by tightly-sealed continuous capillary epithelium) are those that either can diffuse through cell membranes or else have dedicated channels to allow them to pass.
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SIUC / School
of Medicine / Anatomy / David
Last updated: 5 September 2006 / dgk