The
Proximal convoluted tubule (PCT) is the first part of the nephron where
absorption of other solutes from the filtrate take place. This process of
selective reabsorption is called tubular reabsorption and solutes from the
filtrates are selectively reabsorbed back into the bloodstream, through the
surrounding blood capillaries or known to be more specific the peritubular
capillaries. The process of tubular reabsorption is a selective transepithelial
process that begins as soon as the filtrates enter the PCT. For the reabsorbed
substances to reach the blood, the substances follow either the transcellular or
paracellular route. If the reabsorbed substance were to take the transcellular
route then it would firstly transport the substance across the luminal membrane,
diffuse through the cytosol, then have to transport across the basolateral
membrane and finally movement through the intestinal fluid surrounding the
peritubular capillary and then entering the capillary and back into the
bloodstream (refer to the above diagram). Movement of substances in the
paracellular route between the tubule cells is limited because these cells are
connected by tight junctions. These tight junctions within the PCT area allow
some important ions to pass through back into the bloodstream.
Obligatory
reabsorption of water is caused by the removal of molecules, this is because in
a continuously water permeable environment of the PCT the removal of molecules
and ions from the filtrate cause the PCT to be 'obliged' to absorb water
regardless of its state whether it be over or under hydration. This water flow
is referred to Obligatory water reabsorption, that is essentially caused due to
the reabsorption of molecules and ions from the PCT.
Proximal convoluted tubule (PCT) is the first part of the nephron where
absorption of other solutes from the filtrate take place. This process of
selective reabsorption is called tubular reabsorption and solutes from the
filtrates are selectively reabsorbed back into the bloodstream, through the
surrounding blood capillaries or known to be more specific the peritubular
capillaries. The process of tubular reabsorption is a selective transepithelial
process that begins as soon as the filtrates enter the PCT. For the reabsorbed
substances to reach the blood, the substances follow either the transcellular or
paracellular route. If the reabsorbed substance were to take the transcellular
route then it would firstly transport the substance across the luminal membrane,
diffuse through the cytosol, then have to transport across the basolateral
membrane and finally movement through the intestinal fluid surrounding the
peritubular capillary and then entering the capillary and back into the
bloodstream (refer to the above diagram). Movement of substances in the
paracellular route between the tubule cells is limited because these cells are
connected by tight junctions. These tight junctions within the PCT area allow
some important ions to pass through back into the bloodstream.
Obligatory
reabsorption of water is caused by the removal of molecules, this is because in
a continuously water permeable environment of the PCT the removal of molecules
and ions from the filtrate cause the PCT to be 'obliged' to absorb water
regardless of its state whether it be over or under hydration. This water flow
is referred to Obligatory water reabsorption, that is essentially caused due to
the reabsorption of molecules and ions from the PCT.