Renal System - Renal Regulation of H+

Question 1

What is a chemical buffer?

Answer 1

A chemical buffer can bind to H+ and remove it as its concentration increases or release H+ as its concentration decreases

Question 2

What is a protein buffer system?

Answer 2

carboxyl and amino groups can bind to H+, present in ICF and ECF

Question 3

What is a bicarbonate buffer system?

Answer 3

important in regulation of pH in the kidneys
In this system carbonic acid (H2CO3) is formed from a reaction between CO2 and H2O in presence carbonic anhydrase enzyme
H2CO3 can then dissociate to form H+ and HCO3-

Question 4

What is a physiological buffer?

Answer 4

A physiological buffer is a system that stabilises body fluid pH by controlling the excretion of acids or bases
As they get rid of excess ions they have a much greater buffering capacity than chemical buffers

Question 5

What are the 2 different types of physiological buffers?

Answer 5

Renal system - greatest buffering capacity excreting H+, takes hours/ days to have a significant effect
Respiratory system - less buffering capacity than renal system, but acts much quicker than respiratory

Question 6

Describe the buffering of H+ ions into urine

Answer 6

• Tubular secretion of H+ ions occurs when there is a concentration gradient favoring them.
• High H+ in tubular cell and low H+ in tubular fluid.
• If the pH drops below 4.5, H+ secretion stops, known as the limiting pH.
• Some H+ combines with HCO3-, but free H+ persists.
• To avoid this, the body combines H+ with NH3 and Cl- to form ammonium chloride (NH4Cl), a weak acid.
• The pH of urine in a normal healthy individual can vary from 4.5 to 8

Question 7

What is the renal correction of alkalosis ?

Answer 7

More HCO3- needs to be excreted
More H+ retained
pH > 7.45

Question 8

What is the renal correction of acidosis

Answer 8

pH of body fluid may be more acidic than normal so to correct this H+ secretion increases and more HC03- is added to the ECF
pH < 7.35

Question 9

Describe HCO3 filtration and reabsorption as a physiological buffer.

Answer 9

• HCO3- is not directly reabsorbed due to its inability to penetrate the luminal side of the tubular cell membrane.
• HCO3- is created within the tubular cell from H2O and CO2 from the tubular fluid and renal interstitial fluid.
• These HCO3- ions diffuse across the cell membrane and reach the peritubular capillaries.
• Filtered HCO3- ions can combine with H+ ions to form H2CO3.
• At normal acid base balance, HCO3- enters the blood, causing H+ ions to be lost but HCO3- not.

Question 10

Describe H+ secretion as a physiological buffer.

Answer 10

• It’s the Na+,H+ exchanger which secretes H+ ions into the tubular fluid
• H+ is produced within the tubular cells by the combination of CO2 and H2O to form H2CO3, which then dissociates to release H+
• Once the H+ ions have been secreted, they can combine with filtered HCO3- to form CO2 and H2O,
• some of which will be excreted in the urine

Question 11

What is the micturition reflex ?

Answer 11

Involuntary component of micturition
When the bladder contains about 200 mL of urine, stretch receptors in the bladder wall send afferent impulses to the sacral region of the spinal cord via parasympathetic fibres, these fibres are conveyed by the pelvic nerves
Results in contraction of the bladder detrusor muscle and relaxation of the internal urethral sphincter

Question 12

How is the micturition reflex controlled by higher centres ?

Answer 12

Sensory signals to the sacral region of the spinal cord also stimulate ascending pathways to the micturition centre of the pons
Integrates the information from stretch receptor with the cerebrum to establish appropriateness of urinating at that time