Which substances are reabsorbed by nephrons

Solutes move across the membranes of the collecting ducts, which contain two distinct cell types, principal cells and intercalated cells.

A principal cell possesses channels for the recovery or loss of sodium and potassium. An intercalated cell secretes or absorbs acid or bicarbonate. As in other portions of the nephron, there is an array of micromachines pumps and channels on display in the membranes of these cells.

Regulation of urine volume and osmolarity are major functions of the collecting ducts. If the blood becomes hyperosmotic, the collecting ducts recover more water to dilute the blood; if the blood becomes hyposmotic, the collecting ducts recover less of the water, leading to concentration of the blood. Another way of saying this is: If plasma osmolarity rises, more water is recovered and urine volume decreases ; if plasma osmolarity decreases, less water is recovered and urine volume increases.

This function is regulated by the posterior pituitary hormone antidiuretic hormone vasopressin. With mild dehydration, plasma osmolarity rises slightly. This increase is detected by osmoreceptors in the hypothalamus, which stimulates the release of antidiuretic hormone from the posterior pituitary.

If plasma osmolarity decreases slightly, the opposite occurs. When stimulated by antidiuretic hormone, aquaporin channels are inserted into the apical membrane of principal cells, which line the collecting ducts.

As the ducts descend through the medulla, the osmolarity surrounding them increases due to the countercurrent mechanisms described above. If aquaporin water channels are present, water will be osmotically pulled from the collecting duct into the surrounding interstitial space and into the peritubular capillaries.

Therefore, the final urine will be more concentrated. If less antidiuretic hormone is secreted, fewer aquaporin channels are inserted and less water is recovered, resulting in dilute urine. By altering the number of aquaporin channels, the volume of water recovered or lost is altered. This, in turn, regulates the blood osmolarity, blood pressure, and osmolarity of the urine. Aldosterone is secreted by the adrenal cortex in response to angiotensin II stimulation.

As an extremely potent vasoconstrictor, angiotensin II functions immediately to increase blood pressure. By also stimulating aldosterone production, it provides a longer-lasting mechanism to support blood pressure by maintaining vascular volume water recovery. In addition to receptors for antidiuretic hormone, principal cells have receptors for the steroid hormone aldosterone. Intercalated cells play significant roles in regulating blood pH. This function lowers the acidity of the plasma while increasing the acidity of the urine.

The kidney regulates water recovery and blood pressure by producing the enzyme renin. It is renin that starts a series of reactions, leading to the production of the vasoconstrictor angiotensin II and the salt-retaining steroid aldosterone.

Water recovery is also powerfully and directly influenced by the hormone antidiuretic hormone. Even so, it only influences the last 10 percent of water available for recovery after filtration at the glomerulus, because 90 percent of water is recovered before reaching the collecting ducts.

Mechanisms of solute recovery include active transport, simple diffusion, and facilitated diffusion. Most filtered substances are reabsorbed. Urea, NH 3 , creatinine, and some drugs are filtered or secreted as wastes. Movement of water from the glomerulus is primarily due to pressure, whereas that of peritubular capillaries and vasa recta is due to osmolarity and concentration gradients.

The proximal convoluted tubule is the most metabolically active part of the nephron and uses a wide array of protein micromachines to maintain homeostasis—symporters, antiporters, and ATPase active transporters—in conjunction with diffusion, both simple and facilitated. Almost percent of glucose, amino acids, and vitamins are recovered in the proximal convoluted tubule.

Bicarbonate HCO 3 — is recovered using the same enzyme, carbonic anhydrase CA , found in erythrocytes. The recovery of solutes creates an osmotic gradient to promote the recovery of water. The collecting ducts actively pump urea into the medulla, further contributing to the high osmotic environment.

The vasa recta recover the solute and water in the medulla, returning them to the circulation. Nearly 90 percent of water is recovered before the forming urine reaches the distal convoluted tubule, which will recover another 10 percent. Calciumrecovery in the distal convoluted tubule is influenced by parathyroid hormone and active vitamin D. In the collecting ducts, antidiuretic hormone stimulates aquaporin channel insertion to increase water recovery and thereby regulate osmolarity of the blood.

Answer the question s below to see how well you understand the topics covered in the previous section. Skip to main content. Module 9: The Urinary System. Search for:.

Tubular Reabsorption Learning Objectives By the end of this section, you will be able to: Describe how the renal tubules reabsorb useful solutes from the glomerular filtrate and return them to the blood. Describe how the nephron regulates water excretion.

Explain the role of aldosterone and of atrial natriuretic factor in sodium and water balance. Describe the mechanism that maintains the medullary osmotic gradient.

Figure 4. Countercurrent Multiplier System. Watch this video to learn about the countercurrent multiplier system. Critical Thinking Questions Which vessels and what part of the nephron are involved in countercurrent multiplication? Give the approximate osmolarity of fluid in the proximal convoluted tubule, deepest part of the loop of Henle, distal convoluted tubule, and the collecting ducts.

Show Answers The vasa recta and loop of Henle are involved in countercurrent multiplication. Licenses and Attributions. CC licensed content, Original.

The DCT will recover another 10—15 percent before the forming urine enters the collecting ducts. Peritubular capillaries receive the solutes and water, returning them to the circulation. Finally, calcitriol 1,25 dihydroxyvitamin D, the active form of vitamin D is very important for calcium recovery.

These binding proteins are also important for the movement of calcium inside the cell and aid in exocytosis of calcium across the basolateral membrane. Solutes move across the membranes of the collecting ducts, which contain two distinct cell types, principal cells and intercalated cells.

A principal cell possesses channels for the recovery or loss of sodium and potassium. An intercalated cell secretes or absorbs acid or bicarbonate.

As in other portions of the nephron, there is an array of micromachines pumps and channels on display in the membranes of these cells. Regulation of urine volume and osmolarity are major functions of the collecting ducts. If the blood becomes hyperosmotic, the collecting ducts recover more water to dilute the blood; if the blood becomes hyposmotic, the collecting ducts recover less of the water, leading to concentration of the blood.

Another way of saying this is: If plasma osmolarity rises, more water is recovered and urine volume decreases; if plasma osmolarity decreases, less water is recovered and urine volume increases. This function is regulated by the posterior pituitary hormone ADH vasopressin. With mild dehydration, plasma osmolarity rises slightly. This increase is detected by osmoreceptors in the hypothalamus, which stimulates the release of ADH from the posterior pituitary.

If plasma osmolarity decreases slightly, the opposite occurs. When stimulated by ADH, aquaporin channels are inserted into the apical membrane of principal cells, which line the collecting ducts.

As the ducts descend through the medulla, the osmolarity surrounding them increases due to the countercurrent mechanisms described above. If aquaporin water channels are present, water will be osmotically pulled from the collecting duct into the surrounding interstitial space and into the peritubular capillaries.

Therefore, the final urine will be more concentrated. If less ADH is secreted, fewer aquaporin channels are inserted and less water is recovered, resulting in dilute urine. By altering the number of aquaporin channels, the volume of water recovered or lost is altered.

This, in turn, regulates the blood osmolarity, blood pressure, and osmolarity of the urine. Aldosterone is secreted by the adrenal cortex in response to angiotensin II stimulation. As an extremely potent vasoconstrictor, angiotensin II functions immediately to increase blood pressure.

By also stimulating aldosterone production, it provides a longer-lasting mechanism to support blood pressure by maintaining vascular volume water recovery. In addition to receptors for ADH, principal cells have receptors for the steroid hormone aldosterone.

Intercalated cells play significant roles in regulating blood pH. This function lowers the acidity of the plasma while increasing the acidity of the urine. The kidney regulates water recovery and blood pressure by producing the enzyme renin.

It is renin that starts a series of reactions, leading to the production of the vasoconstrictor angiotensin II and the salt-retaining steroid aldosterone. Water recovery is also powerfully and directly influenced by the hormone ADH. Even so, it only influences the last 10 percent of water available for recovery after filtration at the glomerulus, because 90 percent of water is recovered before reaching the collecting ducts. Mechanisms of solute recovery include active transport, simple diffusion, and facilitated diffusion.

Most filtered substances are reabsorbed. Urea, NH 3 , creatinine, and some drugs are filtered or secreted as wastes. Movement of water from the glomerulus is primarily due to pressure, whereas that of peritubular capillaries and vasa recta is due to osmolarity and concentration gradients. The PCT is the most metabolically active part of the nephron and uses a wide array of protein micromachines to maintain homeostasis—symporters, antiporters, and ATPase active transporters—in conjunction with diffusion, both simple and facilitated.

Almost percent of glucose, amino acids, and vitamins are recovered in the PCT. Bicarbonate HCO 3 — is recovered using the same enzyme, carbonic anhydrase CA , found in erythrocytes.

The recovery of solutes creates an osmotic gradient to promote the recovery of water. The collecting ducts actively pump urea into the medulla, further contributing to the high osmotic environment. The vasa recta recover the solute and water in the medulla, returning them to the circulation.

Nearly 90 percent of water is recovered before the forming urine reaches the DCT, which will recover another 10 percent. In the collecting ducts, ADH stimulates aquaporin channel insertion to increase water recovery and thereby regulate osmolarity of the blood.

Answer the question s below to see how well you understand the topics covered in the previous section. Skip to main content. Module 9: The Urinary System. Search for:. Tubular Reabsorption Learning Objectives By the end of this section, you will be able to: List specific transport mechanisms occurring in different parts of the nephron, including active transport, osmosis, facilitated diffusion, and passive electrochemical gradients List the different membrane proteins of the nephron, including channels, transporters, and ATPase pumps Compare and contrast passive and active tubular reabsorption Explain why the differential permeability or impermeability of specific sections of the nephron tubules is necessary for urine formation Describe how and where water, organic compounds, and ions are reabsorbed in the nephron Explain the role of the loop of Henle, the vasa recta, and the countercurrent multiplication mechanisms in the concentration of urine List the locations in the nephron where tubular secretion occurs.

Figure 1. Locations of Secretion and Reabsorption in the Nephron. Figure 2. Figure 3. Regulated reabsorption, in which hormones control the rate of transport of sodium and water depending on systemic conditions, takes place in the distal tubule and collecting duct. Even after filtration has occured, the tubules continue to secrete additional substances into the tubular fluid. This enhances the kidney's ability to eliminate certain wastes and toxins.

It is also essential to regulation of plasma potassium concentrations and pH. See Fluid and electrolyte balance.