Physiology 6: The distal convoluted tubule

Question 1

the distal convoluted tubule is within

Answer 1

the renal cortex

Question 2

how much filtered water actually reaches the distal convoluted tubule

Answer 2

20%

Question 3

how much filtered sodium reaches the distal convoluted tubule

Answer 3

10%

Question 4

osmolarity of fluid entering th distal convoluted tubule

Answer 4

is between 120-200osmol/litre

Question 5

the distal convoluted tubule is split into the

Answer 5

early and late distal convoluted tubule

Question 6

in the early distal convoluted tubule

Answer 6

• there are sodium/Potassium ATP pumps on the basolaterlal membrane
• sodium then flows down its concentration gradient into the cell which takes chloride with it via the sodium/chloride symporter
• the chloride then exits the cell through a specialised channel on the basolaterla membrane

Question 7

out of the 10% of sodium entering the distal convoluted tubule

Answer 7

5% is re-absorbed in the early distal convoluted tubule so only 5% remains

Question 8

also on the distal convoluted tubule there are PTH receptors on the basolatelra membrane

Answer 8

PTH binds to them resulting in the production of protein kinase A which adds a phosphate onto the calcium modulated channels which causes calcium to be re-absorbed

• when calcium is within the cell it is in a lower concentration than in the blood therefore, to enter the blood it has to flow agaist its concentration gradient so there are proteins on the basolateral memebrna which move calcium out of the cell and sodium into the cell via secondary active transport (as sodium just flows down its concentration gradient)
• there is also another mechasnim which pumps calcium out and brings hydrogen in chichis an ATP dependant process so is primary active transport

Question 9

thiazide diuretics inhibit

Answer 9

the Na+/Cl- symporter in the distal convoluted tubule

Question 10

aldosterone is produced by the cells of the bona glomerulosa in response to

Answer 10

low blood volume AND IN RESPONSE TO LOW SODIUM LEVELS AND HIGH POTASSIUM LEVELS IN THE BLOOD

Question 11

aldosterone is a

Answer 11

steroid hormone so it passes through the lipid bailer of the cell and activates transcription factors resulting in th production of NA+/K+ ATPase pumps, 3 sodium ions are pumped into the cell and 2 potassium ions are pumped out of the cell, so sodium then flows dos its concentration gradient from the distal convoluted tubule into the blood and as potassium concentration increases in the cell potassium then moves down its concentration gradient into the distal convoluted tubule to be excreted by the urine

Question 12

also in the distal convoluted tubule anti-diuretic hormone stimulates

Answer 12

aquaporins to bring water into the cell and into the blood which increases blood pressure

Question 13

intercalated A and interrelated b cells are present in

Answer 13

the distal convoluted tubules and the collecting ducts

Question 14

intercalated A cells are for

Answer 14

• acidotic conditions, if there are high levels of CO2 in the blood, the CO2 gets into the intercalated cells and combines with water to form carbonic acid via carbonic anhydrase
• the carbonic acid then dissociates into protons and bicarbonate, the protons travel into the tubule via the HYDROGEN/ POTASSIUM ATP transporter, potassium is pumped into the cell and hydrogen is pumped out of the cell into the tubule

Question 15

also in acidotic conditions

Answer 15

ammonia gets secreted from the blood into the urine, when ammonia is excreted it combines with hydrogen ions in the tubule to form ammonium which is excreted out

Question 16

the bicarbonate within the intercalated A cell

Answer 16

is then pumped out of the cell in order to correct the pH, with bicarbonate leaving chloride ions enter the intercalated A cells

Question 17

intercalated B cells are for

Answer 17

alkalotic conditions the reverse of whats happening in the A cells occurs, bicarbonate is secreted into the urine and chloride is taken up via a bicarbonate/chloride transporter, the protons are then moved from the cell into the blood and potassium is moved into the cell via a potassium/hydrogen ATP pump which decreases the pH

Question 18

intercalated A and B cells are found

Answer 18

in the late part of the distal convoluted tubule and in the collecting ducts

Question 19

also in the distal convoluted tubule

Answer 19

drugs and creatinine are excreted

Question 20

anti-diuretic hormone (vasopressin)

Answer 20

is released from the supra-optic nucleus of the hypothalamus and stored in the posterior pituitary, it is released in response to increase in plasma osmolarity, increase in angiotensin II, low blood volume and hypotension

Question 21

ADH IS RELEASED AND

Answer 21

binds to vasopressin receptors on the basolateral membrane on the principal cells of the collecting ducts which activates a G stimulatory protein which activates protein kinase A, which phosphorylates pre-formed vesicles which have aquaporin 2 channels in their membrane after they have been phosphorylated the pre-formed vesicles fuse with the apical membrane of the collecting ducts and water flows through aquaporin 1 into the cell and into the blood which increases the blood volume and increases blood pressure while reducing serum osmolarity

Question 22

when we become over-hydrated there is r

Answer 22

reduced expression of aquaporins so the aquporin 2 channels get internalised and there is reduced water re-absorption

Question 23

vasopressin also

Answer 23

increases total peripheral resistance by causing vasoconstriction

Question 24

alcohol and ecstasy inhibit

Answer 24

Anti-diuretic hormone secretion and people taking lithium commonly get nephrogenic diabetes insipidus