Blood-lumen barrier

ABC transporter proteins are crucial elements in the detoxication process as they pump potentially toxic chemicals out of cells and tissues. Thus the transporters in the intestine pump chemicals back into the lumen of the gut, those in the brain form part of the blood-brain barrier, keeping chemicals out of the organ, as also occurs in the placenta where transporters move chemicals out of the fetal bloodstream and back into the maternal bloodstream. 

Yoshikawa, H., K. Takada, and S. Muranishi. 1984. Molecular weight dependence of permselectivity to rat small intestinal blood-lymph barrier for exogenous macromolecules absorbed from lumen. J Pharmacobiodyn 7 1. 

Q6 Loperamide hydrochloride is an opioid. The starting dose will be 4 mg, which can be reduced to 2 mg, three times a day for five days if necessary. Opioids act on // opiate receptors in the myenteric plexus of the intestine and may modulate acetylcholine release to reduce peristalsis. They trigger mucosal transport of ions and water out of the lumen and cause a reduction in secretion. The absorption of fluid and electrolytes is increased since the stool remains in the colon for a longer period. Loperamide does not produce sedation or other central effects associated with opiates, since it does not cross the blood-brain barrier. 

Sertoli cells are epithelial cells that line the seminiferous tubules of the testes. At their basal aspects, these cells form the basement membrane and tight junctions that make up the highly selective blood-testes barrier, which normally prevents entry of immune cells into the lumen. 

For polarized epithelial cells to carry out their functions as barriers and mediators of selective transport, extracellular fluids surrounding their apical and basolateral membranes must be kept separate. The tight junctions between adjacent epithelial cells are usually located just below the apical surface and help establish and maintain cell polarity (see Figures 6-1 and 6-5). These specialized regions of the plasma membrane form a barrier that seals off body cavities such as the intestine, the stomach lumen, the blood (e.g., the blood-brain barrier), and the bile duct in the liver. 

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