Selective reabsorbtion occurs in the PCT (proximal convoluted tubule). The PCT
is highly permeable meaning it is easy for molecules to diffuse through it
.
How does reabsorption occur in the proximal convoluted tubule?
Fluid in the filtrate entering the proximal convoluted tubule is reabsorbed into the peritubular capillaries. This is driven by
sodium transport from the lumen into the blood
by the Na
+
/K
+
ATPase in the basolateral membrane of the epithelial cells. Sodium reabsorption is primarily driven by this P-type ATPase.
How is the proximal convoluted tubule adapted for selective reabsorption?
The proximal convoluted tubule is used for selective re-absorption of glucose, water, peptides and other nutrients from the tubule fluid back into the blood. The cells lining this tubule are
ciliated
, to ensure maximum surface area for reabsorption.
Why the process in proximal convoluted tubule is called as reabsorption not absorption?
It is called reabsorption (and not absorption) both because
these substances have already been absorbed once
(particularly in the intestines) and because the body is reclaiming them from a postglomerular fluid stream that is well on its way to becoming urine (that is, they will soon be lost to the urine unless they are …
What is reabsorbed at the proximal convoluted tubule?
The proximal convoluted tubule avidly reabsorbs
filtered glucose
into the peritubular capillaries so that it is all reabsorbed by the end of the proximal tubule. The mechanism for glucose reabsorption was described in Chapter 7.4. The proximal tubule is the only site for glucose reabsorption.
What happens if proximal convoluted tubule is removed?
Therefore, the removal of the proximal convoluted tubule (PCT) will result in
the formation of highly dilute(more water) urine
. The PCT secretes organic acids and bases such as bile salts, oxalate, and catecholamines (waste products of metabolism).
What is the difference between proximal and distal convoluted tubule?
| PROXIMAL CONVOLUTED TUBULE DISTAL CONVOLUTED TUBULE | PCT regulates excretion of urine by absorbing excess water from primary urine. In DCT, water and salts are secreted. | FUNCTION |
|---|
Which of the following is completely absorbed in PCT?
The PCT accounts for only 15-25% of absorbed
magnesium
, and the distal convoluted tubule (DCT), for another 5-10%. There is no significant reabsorption of magnesium in the collecting duct. Inherited disorders of magnesium transport, although rare, may present through an array of underlying biochemical abnormalities.
Is reabsorption active or passive?
Most of the reabsorption of solutes necessary for normal body function, such as amino acids, glucose, and salts, takes place in the proximal part of the tubule. This reabsorption
may be active
, as in the case of glucose, amino acids, and peptides, whereas water, chloride, and other ions are passively reabsorbed.
Which of the following is not reabsorbed by proximal convoluted tubule?
D)
creatinine
is the right answer.
What happens if reabsorption fails?
If there will be no tubular reabsorption in nephrons the
useful things would get off from the body with urine (urea and water formed urine)
. Selective reabsorption allows useful materials to get into capillaries again and the body will use them for further processes.
Where is most water reabsorbed?
Most water reabsorption takes place in
the proximal convoluted tubules, part of the nephrons in the kidney
. Water is reabsorbed by a process called osmosis; the diffusion of water from an area of high water potential to an area of low water potential through a partially permeable membrane.
What percentage of water is reabsorbed by the kidneys each day?
| Compound Filtered Load Percent Reabsorbed | Water 180 L/day 99% | Glucose 180 g/day 100% | Lipids 1080 g/day 99.99% | Sodium 630 g/day 99.5% |
|---|
What happens to the glucose in the filtrate when it reaches the proximal convoluted tubule?
The proximal convoluted tubule
avidly reabsorbs filtered glucose into the peritubular capillaries
so that it is all reabsorbed by the end of the proximal tubule. If the filtered load of glucose overwhelms the proximal tubule transport mechanisms, glucose escapes to the loop of Henle.
What happens to the glomerular filtrate as it passes through the proximal convoluted tubule?
In the proximal convoluted tubules,
all the glucose in the filtrate is reabsorbed, along with an equal concentration of ions and water (through cotransport)
, so that the filtrate is still 300 mOsm/L as it leaves the tubule.
Why does the concentration of sodium remain constant along the length of the proximal convoluted tubule?
Epithelial Transport
Transport capacity is well above what is needed for normal plasma concentrations to ensure that adequate absorption occurs and that there is little/no wastage. As sodium,
chloride and water are reabsorbed at the same rate
, the filtrate concentrations remains the same along the proximal tubule.
