11: Physiology 7 Flashcards
What is the equation for pH?
pH = 1 / [H+]
or
pH = -log[H+]
What is the average pH of blood?
7.4
Why is the pH of venous blood slightly more acidic than the pH of arterial blood?
Venous blood has more CO2
A pH of 7.4 is equal to which concentration of H+?
40 x 10-9 M
Small changes in pH reflect (small / large) changes in [H+].
large changes in [H+]
Acidosis causes ___ of the CNS.
Alkalosis causes ___ of the CNS.
acidosis - depression
alkalosis - excitability
What
a) sensory
b) motor
symptoms are caused by alkalosis?
a) Pins and needles
b) Spasticity
Which important proteins do changes in [H+] have an effect on?
Enzymes
What happens to potassium ion concentration in acidosis?
Why?
[K+] increases
As [H+] is secreted by kidneys to compensate, K+ is reabsorbed
What is constantly added to the blood by metabolism?
H+
What endocrine disease can cause a metabolic acidosis?
What endocrine disease can cause a metabolic alkalosis?
Diabetes
Conn’s syndrome
What solutions in the blood resist changes in pH
Buffers
What is the equation for the pH at which a buffer system is at equilibrium?
Henderson Hasselbalch
go over principles
What does carbon dioxide form when it combines with water?
Carbonic acid
Is carbonic acid a strong or weak acid?
Weak acid
so dissociates in solution
Which organs regulate
a) [CO2]
b) [HCO3-]?
a) Lungs
b) Kidney
For Henderson Hasselbalch
pH = pK + log (kidneys/lungs)
i. e bicarbonate over carbon dioxide
i. e base over acid
Which organs regulate bicarbonate concentration?
Kidneys
How do you calculate rate of filtration?
ROF = [substance]plasma x GFR
Which enzyme converts carbon dioxide and water to carbonic acid?
Carbonic anhydrase
How is bicarbonate reabsorbed by the proximal tubules?
Bicarbonate ions in filtrate combine with hydrogen ions pumped out of tubular cells to form CARBONIC ACID
Carbonic anhydrase converts carbonic acid to CARBON DIOXIDE and WATER
That enters cell, carbonic anhydrase converts it back to CARBONIC ACID
Carbonic acid dissociates into HYDROGEN AND BICARBONATE
H+ pumped out, HCO3- reabsorbed into capillaries
What effect does an increase in CO2 have on
a) H+ secretion
b) HCO3 reabsorption?
Increases both
The rate of ___ ___ is greater than the rate of ___ ___.
Rate of hydrogen secretion
is GREATER THAN
Rate of bicarbonate reabsorption
What does H+ bind with in the absence of bicarbonate?
When might this occur?
Phosphate
Metabolic acidosis
In severely acidotic patients, where all bicarbonate and phosphate has been used up, what combines with H+ ions?
Ammonia
to form ammonium ions
In a patient who is severely acidotic, what is excreted in their urine?
Ammonium ions (NH4+)
What can be measured in the urine when a patient’s H+ is combining with
a) phosphate
b) ammonia?
a) Titratable acid
b) Ammonium ions
Why is bicarbonate ion reabsorption described as unorthodox?
Because the bicarbonate ion found in the filtrate isn’t the one being reabsorbed at the end
Converted to carbonic acid > carbon dioxide + water and back again first
reabsorption of bicarbonate
THEN
excretion of acid phosphate
THEN
excretion of ammonium
as acidosis worsens
H+ secretion drives ___ ___ to prevent acidosis.
bicarbonate reabsorption
What is excreted in the urine to prevent acidosis if bicarbonate stores are used up?
Acid phosphate (titratable acid)
THEN
Ammonium ions
