Renal And Acid Base

Question 1

What is the most important method of secreting H+ out of tubular cells?

Answer 1

Na+/H+ counter transport

Question 2

What is the maximal H+ gradient to pump acid into the lumen?

Answer 2

4.5 I.e. a conc of H+ 1000x that of plasma and this is normally reached in the collecting ducts

Question 3

Why do you need buffers in the urine?

Answer 3

To keep the gradient and enable H+ to be secreted into the lumen

Question 4

What is the most important buffer system in the body?

Answer 4

The bicarbonate buffer system

Question 5

Where does H+ mainly bind with HPO4?

Answer 5

Distal tubule and collecting ducts because phosphate is maximally concentrated here.

Question 6

What is the titratable acidity of urine?

Answer 6

The amount of alkali that is added to urine to return the pH to 7.4, the pH of glomerular filtrate

Question 7

Why does the phosphate system play a major role in H+ buffering in the tubules?

Answer 7

Because the phosphate buffer system has a pK suited to the pH of the tubular fluid

Question 8

What else contributes to phosphate being an effective buffer in the tubules?

Answer 8

1. Composed of HPO and HPO4 and are poorly reabsorbed and become conc in a/w water reabsorption
2. Their pK of 6.8 also makes these active buffers as the urine becomes concentrated through the tubules and the pH falls to about 6

Question 9

Where are hydrogen ions actively secreted?

Answer 9

In the proximal, distal tubules and the collecting ducts

Question 10

Can H+ be secreted against a concentration gradient?

Answer 10

Yes until the urine has a pH of 4.5. Therefore a urine pH of <5 is normal.

Question 11

Is the secretion of H+ in the nephron anything to do with K+?

Answer 11

No, it is exchanged with Na+

Question 12

What happens to H+ secretion in the presence of aldosterone?

Answer 12

Na reabsorption is the aim with aldosterone, therefore H+ is secreted in increased amounts in the distal tubule

Question 13

Can H+ ions directly stimulate the respiratory centre?

Answer 13

Yes

Question 14

How is H+ secreted in the urine?

Answer 14

By combining with urinary buffers
In the PCT- HCO3-
When heaps to be excreted mostly with ammonium salts
Urine pH of <5 contains more H2PO4 than HPO4

Question 15

Does H2CO3 appear in the urine in acidosis?

Answer 15

No, only very small amounts because most of it will rapidly dissociate into H+ and HCO3-

Question 16

What are the characteristics of a urine with a pH of less than 5? (4)

Answer 16

1. It is within normal limits
2. Contains more H2PO4 than HPO4
3. Contains more than normal NH4+
4. Does not contain HCO3- in greater than normal concentration

Question 17

What is elevated serum bicarbonate associated with?

Answer 17

1. Chronic emphysema
2. Duodenal ulcer with obstruction
3. Milk-alkali syndrome
4. Hyperaldosteronism

Question 18

Does total parenteral nutrition lead to elevated serum bicarbonate?

Answer 18

NO

Question 19

Where is K+ reabsorbed?

Answer 19

PCT, predominantly secreted at other sites

Question 20

What are the 3 most important buffer systems in the body?

Answer 20

Bicarbonate (most important), phosphate, proteins

Question 21

Why is phosphate a good buffer?

Answer 21

PK of 6.8 which is near plasma pH, but it has low concentration compared with bicarbonate

Question 22

Why are proteins a good buffer?

Answer 22

PK close to physiological pH but most are within the cells

Question 23

Why is bicarbonate the most important buffer?

Answer 23

Has a pK of 6.1 which is far from ideal, but it is abundant and can be easily controlled: CO2 at lungs, HCO3 at kidneys. Thus most important buffer in ECF

Question 24

How does urine get from renal pelvis to bladder?

Answer 24

Regular peristaltic contractions 1-5x per minute

Question 25

What is the main muscle responsible for micturition?

Answer 25

Detrusor muscle

Question 26

At what volume is the urge to void first felt?

Answer 26

150mL

Question 27

When is fullness of th ebladder felt?

Answer 27

400mL

Question 28

Which nerves innervate the bladder?

Answer 28

Inferior hypogastric nerves, inferiro mesenteric ganglion, pelvic nerves from sacral plexus

Question 29

Which nerve innervates the external urethral sphincter?

Answer 29

Pudendal nerve

Question 30

How is continence maintained via the internal urethral sphincter?

Answer 30

The urethral pressure being higher than the bladder pressure

Question 31

What type of reflex is the micturition reflex?

Answer 31

Autonomic spinal cord reflex

Question 32

What is the role of the hypogastric nerves on the bladder?

Answer 32

Acts via noradrenaline on B3 and A1 receptors to relax the bladder and excites the urethra and fills the bladder (sympathetic, S= storage)

Question 33

What is the role of the pelvic nerves from the sacral plexus on the bladder?

Answer 33

Act via Acth on M3 receptors and cause contraction of detrusor and relaxation of the internal sphincter