Lecture 3 - Reabsorption Of Na+ Along The Tubule

Question 1

What is the Normal plasma levels of glucose?

Answer 1

2.5 - 5.5mmol/L

Question 2

The body wants to reabsorb all glucose, where in the nephron does most of the glucose get reabsorbed?

Answer 2

Proximal Convoluted Tubule

Question 3

What type of transport is the glucose reabsorbed by in the PCT?

Answer 3

Secondary active transport

Question 4

What 3 transporters are responsible for the reabsorption of glucose into the peritubular capillaries from the PCT?

Answer 4

SGLT2 or SGLT1
Na+/K+ ATPase
GLUT2

Question 5

Describe how SGLT/2/1, Na+/K+ATPase and GLUT 2 work to reabsorb glucose into the peritubular capillaries from the PCT:

Answer 5

Na+/K+ ATPase actively transports 3Na+ from PCT cell into the peritubular capillary setting up a Na+ gradient so [Na+] in cell is low
So SGLT2 Cotransport/symports Na+ with a glucose from lumen into PCT cell or SGLT1 Cotransport/symports 2Na+ with a glucose from the lumen into the PCT cell

Glucose travels across GLUT2 from inside PCT cell into peritubular capillary

Question 6

What is Tm?

Answer 6

Maximum tubular resorption capacity for a solute (like glucose)

Question 7

Why will glycosuria occur if plasma glucose rises above 10mmol/L? (Diabetes)

Answer 7

SGLT1/2 get fully saturated so glucose reabsorption back into blood limited so some glucose stays in filtrate and ends up in urine

Question 8

How are all amino acids reabsorbed in the PCT?

Answer 8

Secondary active transport
Symported with Na+ driven by Na+/K+ ATPase

Question 9

What are the main things reabsorbed from the PCT back into the peritubular capillaries?

Answer 9

Glucose
Amino acids
Phosphates
Organic s
Some water

Question 10

Describe the processes occurring in the PCT of the nephron.
Look at the Neil The Nephron slide

Answer 10

Na+/K+ ATPase establishes low [Na+] in PCT cell
Glucose, AA, Phosphates and organics symported with Na+ into cell then into blood
Need to reabsorb HCO3- to regulate pH
HCO3- combines with H+ to make Carbonic acid (H2CO3) H2CO3 then breaks down to H20 and CO2 with help of carbonic anhydrase
CO2 diffuses into cell which then combines with water to form carbonic acid (H2CO3) this then breaks down to H+ and HCO3-
HCO3- then reabsorbed into capillary along with Na+
The H+ produced from this process antiported back into tubule lumen and Na+ brought into cell
Aquaporins reabsorb water from PCT lumen all the way to the blood
Antiport of Cl- and base occurs with Cl- entering cell and Base returning to PCT lumen

Question 11

What is trans cellular transport?

Answer 11

When solutes reabsorbed through the cell

Question 12

What is paracellular transport?

Answer 12

Reabsorption of solutes between cells

Question 13

What is solvent drag?

Answer 13

When the movement of water drags ions with it

Question 14

Why is reabsorption of in the PCT considered to be isoosmotic?

And why is it isoosmotic?

Answer 14

Osmolality at the start and end of the PCT is the same (300 milliosmoles)

Ions are being reabsorbed but Osmolality doesn’t change since water is also being reabsorbed

Question 15

How does the permeability of the loop of Henle change as it goes from descending to ascending limb?

Answer 15

Descending limb is permeable to water

Ascending limb is impermeable to water

Question 16

What gets reabsorbed at the ascending limb of the LOH?

Answer 16

Na+, K+ and Cl-

Question 17

Describe how reabsorption occurs in the loop of Henle:

Look at the Neil the nephron slide

Answer 17

Na+/K+ ATPase establishes Na+ gradient

NKCC cotransporter transporters a Na+ a K+ and 2Cl- into the LOH cell from the lumen

K+ diffuses into blood via transporter
Cl- diffuse into blood via transporter

K+ and Cl- Cotransport/symported into blood

ROMK allows K+ in LOH cell to return to lumen of LOH so theres K+ available for the NKCC transporter

As the lumen gets more and more positively charged it repels cations like Mg2+ and Ca2+ into the vasa recta via paracellular transport

Question 18

What is reabsorbed in the DCT?

Answer 18

Na+
Cl-
Water

Question 19

Describe how reabsorption occurs in the DCT:

Look at Neil the nephron slide

Answer 19

To remember what happens here think ENAC and calcium

Na+/K+ ATPase establishes Na+ gradient

Na+ and Cl- cotransported into DCT cell from DCT lumen

ENAC (Epithelial Na+ channel) transports Naa+ into DCT cell

Ca2+ actively transported by Ca2+ ATPase from DCT cell into peritubular capillaries
Sets up Ca2+ gradient so Ca2+ can move into DCT cell

K+ moves across into peritubular capilaries
Cl- moves into peritubular capilaries

Question 20

What is the main job of the collecting duct?

Answer 20

Water reabsorption

Question 21

Describe reabsorption across the collecting duct:

Answer 21

Think what affect aldosterone has

Na+/K+ ATPase establishes Na+ gradient
ENAC reabsorbs Na+ from lumen (ENAC upregulated by aldosterone, aldosterone also] upgregulates ROMK channels)

ROMK channels allow K+ to leak back into lumen to maintain electro neutrality

ADH binds to V2 receptors increasing aquaporin translocation allowing more water to be reabsorbed

ANP produced when BP high reducing ENAC expression so less Na+ and therefore water reabsorbed

Question 22

What is central diabetes Insipidus?

Answer 22

Patients hypothalamus doesn’t produce ADH
Can be due to brain injury, tumour, aneurysm, sarcoidosis

Question 23

What happens as a result of Central diabetes Insipidus/too little ADH?

Answer 23

Large vol dilute urine
Since water isn’t reabsorbed from collecting duct as well

Question 24

How is Central Diabetes Insipidus treated?

Answer 24

Administer ADH (desmopressin)

Question 25

What is Nephrogenic diabetes Insipidus?

Answer 25

Acquired insensitivity of the kidney to ADH
so ADH is made by kidney doesn’t respond to it

Question 26

What can cause Nephrogenic diabetes Insipidus?

Answer 26

Mutated Vasporessin 2 (V2) receptors
Chronic pyelonephritis
Polycystic kidneys
Drugs like lithium

Question 27

How can Nephrogenic diabetes Insipidus be managed?

Answer 27

Low salt low protein diet reducing urine output

Thiazide (increases Na+ excretion)

Question 28

What is SIADH (Syndrome of inappropriate anti diuretic hormone secretion)?

Answer 28

Excessive ADH release from posterior pituitary gland (or other source)

Question 29

How does Syndrome of inappropriate ADH secretion present?

Answer 29

Excess ADH
Very dilute plasma / low plasma [Na+]\dilutionallll hyponatremia
Total body fluid increase

Very conc urine

Question 30

What can lead to inappropriate ADH secretion?

Answer 30

CNS disorders
Malignancy
Lung disease
Drugs like opiates
Metabolic disease (porphyria, hypothyroidism)