Lecture 3 - Reabsorption Of Na+ Along The Tubule Flashcards
What is the Normal plasma levels of glucose?
2.5 - 5.5mmol/L
The body wants to reabsorb all glucose, where in the nephron does most of the glucose get reabsorbed?
Proximal Convoluted Tubule
What type of transport is the glucose reabsorbed by in the PCT?
Secondary active transport
What 3 transporters are responsible for the reabsorption of glucose into the peritubular capillaries from the PCT?
SGLT2 or SGLT1
Na+/K+ ATPase
GLUT2
Describe how SGLT/2/1, Na+/K+ATPase and GLUT 2 work to reabsorb glucose into the peritubular capillaries from the PCT:
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
What is Tm?
Maximum tubular resorption capacity for a solute (like glucose)
Why will glycosuria occur if plasma glucose rises above 10mmol/L? (Diabetes)
SGLT1/2 get fully saturated so glucose reabsorption back into blood limited so some glucose stays in filtrate and ends up in urine
How are all amino acids reabsorbed in the PCT?
Secondary active transport
Symported with Na+ driven by Na+/K+ ATPase
What are the main things reabsorbed from the PCT back into the peritubular capillaries?
Glucose
Amino acids
Phosphates
Organic s
Some water
Describe the processes occurring in the PCT of the nephron.
Look at the Neil The Nephron slide
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
What is trans cellular transport?
When solutes reabsorbed through the cell
What is paracellular transport?
Reabsorption of solutes between cells
What is solvent drag?
When the movement of water drags ions with it
Why is reabsorption of in the PCT considered to be isoosmotic?
And why is it isoosmotic?
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
How does the permeability of the loop of Henle change as it goes from descending to ascending limb?
Descending limb is permeable to water
Ascending limb is impermeable to water
What gets reabsorbed at the ascending limb of the LOH?
Na+, K+ and Cl-
Describe how reabsorption occurs in the loop of Henle:
Look at the Neil the nephron slide
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
What is reabsorbed in the DCT?
Na+
Cl-
Water
Describe how reabsorption occurs in the DCT:
Look at Neil the nephron slide
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
What is the main job of the collecting duct?
Water reabsorption
Describe reabsorption across the collecting duct:
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
What is central diabetes Insipidus?
Patients hypothalamus doesn’t produce ADH
Can be due to brain injury, tumour, aneurysm, sarcoidosis
What happens as a result of Central diabetes Insipidus/too little ADH?
Large vol dilute urine
Since water isn’t reabsorbed from collecting duct as well
How is Central Diabetes Insipidus treated?
Administer ADH (desmopressin)
What is Nephrogenic diabetes Insipidus?
Acquired insensitivity of the kidney to ADH
so ADH is made by kidney doesn’t respond to it
What can cause Nephrogenic diabetes Insipidus?
Mutated Vasporessin 2 (V2) receptors
Chronic pyelonephritis
Polycystic kidneys
Drugs like lithium
How can Nephrogenic diabetes Insipidus be managed?
Low salt low protein diet reducing urine output
Thiazide (increases Na+ excretion)
What is SIADH (Syndrome of inappropriate anti diuretic hormone secretion)?
Excessive ADH release from posterior pituitary gland (or other source)
How does Syndrome of inappropriate ADH secretion present?
Excess ADH
Very dilute plasma / low plasma [Na+]\dilutionallll hyponatremia
Total body fluid increase
Very conc urine
What can lead to inappropriate ADH secretion?
CNS disorders
Malignancy
Lung disease
Drugs like opiates
Metabolic disease (porphyria, hypothyroidism)
