what type of cell contributes to the blood-brain barrier in the central nervous system
Blood–brain barrier The blood–brain barrier (BBB) is a highly selective semipermeable border that separates the circulating blood from the brain and extracellular fluid in the central nervous system (CNS).[1] The blood–brain barrier is formed by endothelial cells of the capillary wall, astrocyte end-feet ensheathing the capillary, and pericytes embedded in the capillary basement membrane.[2] This system allows the passage of water, some gases, and lipid-soluble molecules by passive diffusion, as well as the selective transport of molecules such as glucose and amino acids that are crucial to neural function. Specialized structures participating in sensory and secretory integration within neuronal networks – the circumventricular organs and choroid plexus – do not have a blood–brain barrier.
Adrenal medulla Because the ANS, specifically the sympathetic division, exerts direct control over the chromaffin cells the hormone release can occur rather quickly. In response to stressors such as exercise or imminent danger, medullary cells release the catecholamines adrenaline and noradrenaline into the blood. Adrenaline composes about 85% of the released catecholamines, and noradrenaline the other 15%.[2]
Antigen Antigen presenting cells present antigens in the form of peptides on histocompatibility molecules. The T cell/T lymphocyte (a subtype of white blood cell), of the adaptive immune system, selectively recognize the antigens. Depending on the antigen and the type of the histocompatibility molecule, different types of T cells will be activated. For T-Cell Receptor (TCR) recognition, the peptide must be processed into small fragments inside the cell and presented by a major histocompatibility complex (MHC).[5] The antigen cannot elicit the immune response without the help of an immunologic adjuvant.[3] Similarly, the adjuvant component of vaccines plays an essential role in the activation of the innate immune system.[6][7]
Rate equation k is the first order rate constant, which has units of 1/s or sâˆ’1.