胃溃疡和胃癌的发病机理

长了点医学知识

 

 

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胃溃疡和胃癌的发病机理

via People's Republic of Desire on 3/7/07

Barry Marshall and Robin Warren 2人于2005年因"发现螺旋幽门杆菌是导致胃溃疡和胃癌的直接原因"而获得NOBLE医学奖

十几年的探索之路中关键点是：由于该杆菌只在人类中发源和归宿，而当时普遍认为的导致胃溃疡的原因是压力和抑郁产生过多胃酸，从而破坏胃壁，发生炎症；而在100年前就有德国人发现胃溃疡患者的胃黏膜上含有螺旋幽门杆菌，而在这100年中，人们都想当然认为是因为胃壁先被破坏，随后导致感染，才会产生螺旋幽门杆菌，而不像Barry Marshall and Robin Warren2人认为的相反：是螺旋幽门杆菌导致了胃溃疡。所以无人愿意在该理论未被支持的情况下做活体试验，Barry Marshall自己将提取并培养出来的螺旋幽门杆菌浓缩液喝下肚，亲自观察自己胃中的变化。随后的5天，Barry Marshall发生了剧烈呕吐和呼吸困难，并最终患上了胃溃疡，随后通过广普抗生素治疗，迅速恢复了胃溃疡。从而一举推翻了医学界原由的关于胃溃疡产生机制及其疗法的观点，并因此获得2005年NOBLE医学奖。

Diagram 1: The immune system responds to the invasion

H. pylori use a specialised system to inject a
toxin called Cag A into epithelial cells. The cells
signal to the white blood cells of the immune system to
produce destructive oxygen compounds. H. pylori is
protected from these compounds by enzymes that break
them down and render them inactive. H. pylori strains that
do not make Cag A are less virulent than H. pylori that do.
Infection with Cag A strains also increases the risk of
developing cancer. This, and other genetic differences in
H. pylori strains, could explain why most people infected
with H. pylori do not develop ulcers or cancers.

The programmed cell death of epithelial cells -- also called
apoptosis -- that results from infection with H. pylori is
thought to be the main reason for the development
of cancer.

Diagram 2: H. pylori invades epithelial cells

H. pylori are able to attach to the epithelial cells
of the stomach and duodenum which stops them from
being washed out of the stomach. Once attached, the
bacteria start to cause damage to the cells by secreting
degradative enzymes, toxins and initiating a
self-destructive immune response.

Diagram 3: The protective mucus layer of the stomach

H. pylori make an enzyme called urease, which
degrades urea to produce bicarbonate and ammonia. The
ammonia neutralises the acid in the area, increasing the
pH in the mucus to about seven. But the ammonia is also
toxic to the cells lining the stomach and, along with other
toxins made by the bacteria, causes the cells to become
inflamed or to die. Inflammation is caused by the body's
immune system trying to defend itself against invasion
by the bacteria.

 

 

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