Download Ch. 27 – Fluid, Electrolyte, and Acid

Ch. 27 – Fluid, Electrolyte,
and Acid-Base Balance
• These notes are a brief
overview of the main
themes of Ch. 27 only
• The new information in
these notes and in Ch. 27 is
FYI only, and will not be fair
game for the Final Exam
• While Ch. 27 repeats a
lot of information we
have discussed during
the past 5 months, it
does a nice job of tying
these topics together
under the umbrella
concept of homeostasis
Fluid (water) balance
•
•
•
Water gain must = water loss
Water ≈ 50-60% of our body weight
There are no active transporters for water molecules, just water channels
(aquaporins)
•
Major players in the maintenance of fluid balance: the renin-angiotensinaldosterone system (RAAS), ADH, aldosterone, natriuretic peptides,
baroreceptors in the heart and blood vessels, and the thirst center in the
hypothalamus
– “Water follows salt” by osmosis
Fig. 27-3, p. 1022
1
Electrolyte balance
• Electrolyte gain must = electrolyte loss
• Electrolytes = ions released when soluble
inorganic compounds dissociate; they can
conduct an electrical current in solution
– So essentially, electrolytes = ions in solution
– E.g. Na+, K+, Cl-, Ca2+, etc.
• Electrolytes are lost and gained in most (but
not all) of the same ways as water
– In (gain): diet
– Out (loss): urine, feces, and sweat
Some important electrolytes in body fluids
Fig. 27-2, p. 1019
2
Acid-base balance
•
production must = H+ loss
• Normal body fluid pH = 7.35-7.45
• Major players in the maintenance of acid-base
balance:
H+
– The kidneys via the reabsorption and/or secretion of H+
and HCO3-
• HCO3- = bicarbonate, which acts with carbonic acid (H2CO3) as a
buffer system: H2O + CO2 ↔ H2CO3 ↔ H+ + HCO3-
– The elimination of CO2 via external respiration and
exhalation at the lungs
• Since most of the CO2 in the blood is carried as bicarbonate,
exhaling CO2 drives the above equation to the left, ↓ H+ (which
↑ pH)
– Other buffer systems…
• See the next slide for examples of buffer systems including and in
addition to the carbonic acid-bicarbonate buffer system
Buffer systems in body fluids
Fig. 27-10, p. 1032
3
How an amino acid (and thus a
protein) can act as a buffer
Fig. 27-11, p. 1033
Acid-base imbalances
Table 27-4, p. 1045
• Severe acidosis causes ↓ neuron excitability (which can lead
to disorientation, coma, and death)
• Severe alkalosis causes ↑ neuron excitability (which can lead
to nervousness, muscle spasm, convulsions, and death)
4
Respiratory
acidosis
and
alkalosis
• Respiratory
acidosis is the
most common
type of acidbase imbalance
• Respiratory
alkalosis is
relatively rare
Fig. 27-15, p. 1040
Metabolic
acidosis
• This is the 2nd most
common type of
acid-base imbalance
– E.g. lactic acidosis
and ketoacidosis
Fig. 27-16, p. 1042
5
Metabolic alkalosis
• Is relatively rare
• The loss of HCl via severe vomiting is the most common cause
Fig. 27-17, p. 1043
A diagnostic
chart for
acid-base
disorders
Fig. 27-18, p. 1044
6