In this lecture, I am going to discuss about tight junctions or septate junctions. Main points of the lesson are discs, large and urexin, cladins, advantage of tight junctions. Tied junctions are also known as septate junctions. There is a trans-mimbrane protein that is called cladins. Join the plasma membrane by layer of two cells to create a barrier. That limits our boundary, the diffusion of ions and salutes between the cells. Tight junctions is a belt-like adhesive seal that selectively limits the diffusion of water, ions and large salutes between the epithelial cells. This allows the epithelial cells to separate the interior of the body from external world. As we know that plasma membrane has sodium potassium pump, calcium pump, carrier proteins for transport of ions and molecules. But tight junctions, this separates different pumps, carriers and receptors in the plasma membrane. So, there is no exchange of materials takes place through tight junctions. Tight junctions are literally areas of tight connections between the membranes of adjacent cells and these connections are so tight that no space remains between the cells and substances cannot leak between them. In russophila, the proteins include discs, large and urexin. Tight junctions are unique to vertebrates and they contain a protein that is called cladins. Because of their ability to occlude, our block substances from passing between the cells, this form of junction between the cells act as a wall within that issue and keeping the molecules on one side. Tight junctions, cells connected by tight junctions, seal of the body cavities. For example, tight junctions between the cells lining the intestine prevent substances, prevent digested food in the intestine from passing between the cells. So, digested food directly entering the blood. The sheet of cells does act as a selective barrier and food substances must be transported across the plasma membranes through the intestinal cells and they enter into the bloodstream. This arrangement helps to prevent toxins and unwanted materials from entering the blood directly and also prevents nutrients from leaking out of the intestine. Tight junctions are also present between the cells that line capillaries in the brain. They form the blood brain barrier which prevents many substances in the blood from passing into the brain. The purpose of tight junction is to keep the liquid from escaping between the cells and it allows a layer of cells to act as impermeable barrier. For example, tight junctions which are present between the epithelial cells that lining the urinary bladder, it prevent urine from leaking out into extra cellular space.