Lecture 11/12 Flashcards
The regulation of H+ is most important where? Why?
Intracellularly –> where most protein enzymes are located
The extracellular plasma H+ is mostly regulated by what two organs?
Kidneys & Lungs
What induces strong shifts in K+?
Weak shifts in K+?
- HCL/KCl –> mineral acids!
- Organic Acids
- lactic acidodis (metabolic acidosis)
- hypercarbia (respiratory acidosis)
- hypocarbia (respiratory alkalosis)
What are the three major systems responsible for maintaining Arterial Plasma [H+]?
- Chemical Buffering
- Renal System (slow responding)
- Respiratory System (rapidly responding)
Describe the 3 Chemical Buffering systems in the kidney. (3)
- Phosphate Buffer system
- Protein Buffers (hemoglobin, intracellular proteins)
- Bicarbonate Buffer
Describe how the Renal system is responsible for maintaining Arterial plasma H+.
- Kidney excretes 50 mol of H+ per day as H+, NH4+, and H2PO4 (urine is acidic)
- Kidney reabsorbs 5500 mol of HCO3- per day (bicarbonate is at renal plasma threshold)
Describe how the Respiratory system is responsible for maintaining Arterial plasma H+.
- Lung Ventilates off 12,000 mol of CO2 per day
2. Lung has 150 times the capacity of the kidney (13,000 - 5500)/50mmol
What is the bronzed lowry concept of acids and bases?
Acid (HA): is a proton donor
Base (A-) is a proton acceptor
If the Kd is small is this a weak or strong acid? If the Kd is large?
Kd is small = weak acid (dissociates poorly, therefor weak proton donor)
Kd = large –> strong acid & donates proton easily
pKd = -log (Kd)
What is more critical, the acid base ratio or the concentrations of acid or base?
Acid base ratio
What is the most important blood borne protein buffer?
Hemoglobin
- classified as extracellular despite the fact that it is intracellular and located within RBC’s
At a ph below the pKd, the acid is in its dissociated or undissociated state?
At pH ABOVE the pkd?
Undissociated –> still in acidic form
Dissociated –> in basic form
What is the equation for pH in the kidney/lung?
pH = 6.1 + log (kidney/lung)
CO2 in lung = acid
HCO3- = base –> kidney
pH = 6.1 + log (HCO3- / CO2)
What are the values of CO2 in the lung? Of HCO3- in the kidney?
CO2 in the lung = 0.3 mM * PaCO2
(PaCO2 in arterial blood = 40)
HCO3 - in the kidney = 24mM
Base/Acid = HCO3-/CO2 = 24mM/1.2mN = ratio of 20:1!!!
What is the importance of the bicarbonate buffer system?
3
- It is an open system
- CO2 is directly linked to the environment via the lungs (ventilation)
- H+ is directly linked to environment via the kidneys (excretion)
What does it mean that CO2 and H+ are in a steady state balance?
CO2 and H+ are continuously removed from the body at rates that match production
- they do not normally build up in body fluids
What is the isohydric principle?
Multiple acid/base pairs in solution will be in equilibrium with one another, tied together by their common reagent: H+ ion!
What will dictate the ratio of concentrations of a buffer’s base and weak acid forms at a given pH?
pKd for the buffer!
If a condition changes the balance of one buffer system, the other buffer systems are ALSO affected. True or False?
TRUE!
- the buffer systems actually buffer one another by shifting hydrogen ions back and forth from one to the other
Changing the H+ concentration can lead to changes in what? Specifically in regards to what aspects of this?
H+ are highly reactive cations that change the charge distribution on proteins
H+ + COO- ↔COOH and H+ + NH2 ↔NH3+
◆ altered charge distributions lead to protein conformational changes and
modified reaction rates
What are located intracellularly and function within very specific pH ranges?
protein enzymes
What compensates for the low pKd of the bicarbonate buffer system?
its OPEN nature!
- CO2 and H+ are continuously removed from the body at rates that exactly match production (“steady state” balance)
- normally, [CO2] and [H+] do not build up in body fluids
pathologically, [CO2] and [H+] can increase or decrease in body
fluids (respiratory and metabolic acidosis or alkalosis)
(constantly removed and reformed = steady state)
Answer the paradox as to why the quantitative assessment of a single buffer
system is adequate despite the presence of multiple buffer systems.
ISOHYDRIC PRINCIPLE
Any condition that changes the balance of one of the buffer systems, also changes
the balance of all the others because the buffer systems actually buffer one
another by shifting hydrogen ions back and forth from one to the other.
Because there are multiple buffer systems, which must be specifically examined to understand the H+ in plasma?
Which buffer system is MOST important?
only one buffer system needs to be closely examined to
understand the [H+] in the plasma space
This is possible because all buffer systems are linked
together through a common H+ (isohydric principle)
For biomedical purposes, the bicarbonate buffer system is
of primary importance: [H+] = 24 • (PaCO2)/[HCO3-]
