25.6 Tubular Reabsorption 25.6 Tubular Reabsorption

how many L of fluid does the nephrons of the kidney filter per day

180 L

what structures reabsorb most of the 180 L of fluid

PCT, loop of henle, DCT, and collecting ducts

much of reabsorption and secretion is reabsorbed based on what

concentration gradients

what is tightly regulated

the amount of water that is reabsorbed or lost

what hormones control the regulation of water in the kidneys

ADH (antidiuretic hormone), aldosterone, and indirectly renin

where is most water recovered

PCT, loop of henle, and DCT

how much fluid reaches the collecting ducts

10% or 18 L

what is the collecting duct under the influence of

ADH (antidiuretic hormone)

what does under the influence of ADH mean

more concentrated urine is produced and the body conserves water

what does the collecting ducts do

can recover almost all of the water passing through them

what cases does the collecting duct work under

cases of dehydration or almost none of the water, and over-hydration

Glucose

Almost 100 percent reabsorbed in the PCT by secondary active transport with sodium

Oligopeptides proteins amino acids

Almost 100 percent reabsorbed in the PCT using symport with sodium

Vitamins

Reabsorbed in the PCT - V

Lactate

Reabsorbed in the PCT - L

Creatinine

Secreted in the PCT

Urea - PCT

50 percent reabsorbed by diffusion in the PCT

Urea - loop

Secreted and diffuses in the descending limb of the loop of Henle

Urea - collecting

Reabsorbed by diffusion in the medullary collecting ducts

Sodium - pct

65 percent actively reabsorbed in the PCT

sodium - loop

25 percent reabsorbed in the thick ascending limb of the loop of Henle

sodium - dct

5 percent reabsorbed in the DCT through active transport

sodium - collecting

5 percent reabsorbed in the collecting ducts stimulated by aldosterone through active transport

Chloride - pct

Reabsorbed in the PCT with sodium via symport and diffusion

chloride - loop

Reabsorbed in the thin and thick ascending limbs by diffusion

chloride - dct

Reabsorbed in the DCT by diffusion

chloride - collecting

Reabsorbed in the collecting ducts via symport

Water - pct

67 percent reabsorbed in the PCT by osmosis

water - loop

15 percent reabsorbed in the descending limb of the loop of Henle by osmosis

water - dct

8 percent reabsorbed in the DCT by osmosis if ADH is present

water - collecting

Variable reabsorption in the collecting ducts controlled by ADH by osmosis

Bicarbonate ion (HCO3−) - pct

80 to 90 percent reabsorbed in the PCT by symport with sodium

Bicarbonate ion (HCO3−) - looop

Reabsorbed in the loop of Henle via symport with sodium and antiport with chloride in the ascending limb

Bicarbonate ion (HCO3−) - collecting

Reabsorbed in the collecting ducts via antiport with chloride

Hydrogen ions (H+) - pct

Secreted in the PCT by diffusion

Hydrogen ions (H+) - dct

Secreted in the DCT and collecting ducts by active transport

Ammonium (NH4+)

secreted in the PCT DCT and collecting ducts by diffusion

Some drugs

Secreted in the PCT DCT and collecting ducts via active transport

Potassium - pct

65 percent reabsorbed in the PCT by diffusion

Potassium - loop

20 percent reabsorbed in the thick ascending limb of the loop of Henle via symport

Potassium - dct

Secreted in the DCT by active transport

Potassium - collecting

Secreted in the collecting ducts by active transport controlled by aldosterone

Calcium - pct

Reabsorbed in the PCT by diffusion

Calcium - loop

Reabsorbed in the thick ascending limb of the loop of Henle by diffusion

Calcium - collecting

Reabsorbed in the collecting ducts if parathyroid hormone is present by active transport

Magnesium - pct

Reabsorbed in the PCT and thick ascending limb by diffusion

Magnesium - dct

Reabsorbed in the DCT

Phosphate - pct

85 percent reabsorbed in the PCT by diffusion inhibited by parathyroid hormone

Phosphate - dct

Reabsorbed in the DCT by diffusion

what is the mechanisms of recovery

by which substances move across membranes for reabsorption or secretion include active transport, diffusion, facilitated diffusion, secondary active transport, and osmosis

whaat is active transport

utilizes energy, usually the energy found in a phosphate bond of ATP, to move a substance across a membrane from a low to a high concentration.

what is a characteristic of active transport

It is very specific and must have an appropriately shaped receptor for the substance to be transported.

what is an example of active transport

the active transport of Na⁺ out of a cell and K⁺ into a cell by the Na⁺/K⁺ pump. Both ions are moved in opposite directions from a lower to a higher concentration.

what is simple diffusion

diffusion moves a substance from a higher to a lower concentration down its concentration gradient

what is a characteristic of simple diffusion

It requires no energy and only needs to be soluble.

what is facilitated diffusion

moves a substance down its concentration gradient and requires specific membrane receptors or channel proteins for movement.

what is an example of facilitated diffusion

The movement of glucose and, in certain situations, Na⁺ ions

what is mediated transport

two different substances share the same channel protein port; these mechanisms are described by the terms symport and antiport.

what is symport

mechanisms move two or more substances in the same direction at the same time

what is antiport

mechanisms move two or more substances in opposite directions across the cell membrane.

what does both symport and antiport mechanism utilize

utilize concentration gradients maintained by ATPase pumps.

what is secondary active transport

when active transport powers the transport of another substance in this way

what mechanism reabsorbs glucose

Glucose reabsorption in the kidneys is by secondary active transport.

What role does the Na+/K+ ATPase play in glucose reabsorption

Na+/K+ ATPase on the basal membrane pumps sodium out of the cell maintaining a strong electrochemical gradient for sodium to enter from the tubular lumen

Where is the Na+/K+ ATPase located in the tubular cell

It is located on the basal membrane or the side of the cell facing away from the tubular lumen

How do sodium and glucose enter the tubular cell

They enter together through a Na+/glucose symport protein located on the apical or luminal surface of the cell

How is glucose moved into the cell against its concentration gradient

Glucose is carried into the cell by the Na+/glucose symporter as sodium moves down its electrochemical gradient into the cell

What happens to glucose after it enters the tubular cell

It diffuses across the basal membrane by facilitated diffusion into the interstitial space and then into the peritubular capillaries

Why does glucose use facilitated diffusion to exit the cell

Because it moves down its concentration gradient from inside the cell to the interstitial space without the use of energy

Which substances must be reabsorbed by the nephron to maintain homeostasis

Calcium sodium glucose and amino acids must be reabsorbed to maintain stable plasma concentrations

Which substances are secreted into the filtrate as waste products

Urea potassium ammonia creatinine and some drugs are secreted into the filtrate to be excreted

How is acid base balance maintained in the body

It is maintained by both the lungs and the kidneys

How do the lungs help regulate acid base balance

The lungs help by removing hydrogen ions from the body

How do the kidneys help regulate acid base balance

The kidneys help by secreting or reabsorbing hydrogen ions and bicarbonate ions

What happens to urea in the proximal convoluted tubule

About 50 percent of urea is passively reabsorbed in the proximal convoluted tubule

Is more urea reabsorbed later in the nephron

Yes additional urea can be recovered in the collecting ducts if needed

What role does ADH play in urea reabsorption

ADH stimulates the insertion of urea transporters into the collecting duct cells to increase urea reabsorption

What other protein channels does ADH stimulate besides urea transporters

ADH also induces the insertion of aquaporin channels which allow water to be reabsorbed

What does the renal corpuscle do to the blood

It filters the blood to make a filtrate that does not contain cells or large proteins

What happens to the filtrate after it leaves the renal corpuscle

It is modified through secretion and reabsorption as it travels through the nephron

Where does the modification of filtrate first begin

In the proximal convoluted tubule or PCT

What does reabsorption mean in the context of the nephron

It means substances that were already absorbed from the digestive tract are being absorbed again from the filtrate back into the blood

What percentage of water and solutes must be reabsorbed

About 99 percent of water and most solutes must be reabsorbed

Where do reabsorbed water and solutes go

They are returned to the blood through the peritubular capillaries and the vasa recta

What is the difference between the glomerulus and peritubular or vasa recta capillaries

The glomerulus has high pressure for filtration while the peritubular capillaries and vasa recta are low pressure and help with reabsorption

How does the glomerulus maintain high pressure

It dilates the afferent arteriole and constricts the efferent arteriole to keep filtration pressure high

What influences the movement of water into the peritubular capillaries and vasa recta

Osmolarity and concentration gradients

How does sodium move from the PCT into the bloodstream

It is actively pumped into the space around the tubule and then diffuses into the peritubular capillaries

What happens to water when sodium is reabsorbed

Water follows sodium passively to maintain balance

What is this automatic movement of water called

It is called obligatory water reabsorption

Which part of the nephron moves the most substances across its membranes

The proximal convoluted tubule or PCT

What types of substances use symport to enter the PCT cells

Amino acids glucose chloride calcium and phosphate

What are other transport methods used in the PCT

Antiport, active transport, simple diffusion, and facilitated diffusion

What is the apical surface of a cell

It is the side that faces the inside or open space of the tubule

What is the basal surface of a cell

It is the side of the cell that faces the connective tissue base or basement membrane

What kind of cells line the PCT

Simple cuboidal epithelial cells

Are the types and number of pumps the same on both sides of the PCT cell

No, the apical and basal surfaces have different types and numbers of pumps and channels

Which substances are moved by symport with sodium on the apical membrane

Chloride calcium glucose amino acids and phosphate

How is sodium exchanged on the basal membrane

Sodium is actively exchanged for potassium using ATP on the basal membrane

How do most substances leave the cell after entering by symport

They leave by facilitated diffusion through the basal membrane