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The blood–thymus barrier regulates exchange of substances between the circulatory system and thymus, providing a sequestered environment for immature T cells to develop. The barrier also prevents the immature T cells from contacting foreign antigens (since contact with antigens at this stage will cause the T cells to die by apoptosis).
- Blood–air barrier – Membrane separating alveolar air from blood in lung capillaries
- Blood–brain barrier – Semipermeable membrane that separates blood from the brain
- Blood–ocular barrier – A physical barrier between the local blood vessels and most parts of the eye itself
- Blood–retinal barrier – Part of the blood–ocular barrier that prevents certain substances from entering the retina
- Blood–testis barrier – A physical barrier between the blood vessels and the seminiferous tubules of the animal testes