For discussing the functions of different structures of all organisms.
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My question is, can immune cells get into our brain?
Microglia are kind of immune cells (?), in terms of they phagocyte in the nervous tissue, but are there actual immune cells in our brain, outside the blood vessels?
Which materials can actually freely pass the blood-brain barrier? Does it only depend on their sizes? (naturally, rules that apply for general biological membrane transports are also true here, but on top of those general things, any specific rule to it)?
This is a brief overview of the structure and function of the blood brain barrier. Detailed information can be found in the related websites section.
Nowhere in the body is there more need for homeostasis than in the brain. The mechanism for maintaining this barrier function lies in the capillary network supplying blood to the brain. Ion concentration levels in plasma may fluctuate abruptly. The blood- brain barrier protects the brain against surging fluctuations in ion concentrations.
The concept of the blood brain barrier was first introduced by Paul Ehrlich. He found that intravenous injection of dyes into the bloodstream stained all the tissues in most organs except the brain. Using electron microscopy and electron- dense tracers such as horseradish peroxidase (HRP) a group of scientists demonstrated that the blood- brain barrier is located in endothelial cells of capillaries of the brain.
These endothelial cells of capillaries in the brain are different to those found in peripheral tissues in various ways:
1. Brain endothelial cells are joined by tight junctions of high electrical resistance providing an effective barrier against molecules.
2. In peripheral endothelial cells there is good transcellular movement of molecules. There is no such movement in brain endothelial cells.
3. Brain capillaries are in contact with foot processes of astrocytes which essentially separate the capillaries from the neurones.
The answer to your question is yes. Normally, the b-b barrier cannot be passed by the immune cells. When infection occurs such as meningitis or encephalitis, because of the inflammation caused by bacterial toxins, destroyed neurons and endogenous substances, the endothelial cells become more permeable (the cell junctions loosen), and immune cells can enter the brain.
Only lipo soluble substances can pass through the b-b barrier.
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