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Fluid and Electrolyte Homeostasis
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Fluids and Electrolytes Homeostasis
Ionic Bonds - Some atoms, such as metals tend to lose electrons to make the outside ring or rings
of electrons more stable and other atoms tend to gain electrons to complete the outside ring.
An ion is a charged particle. Electrons are negative. The negative charge of the electrons can
be offset by the positive charge of the protons, but the number of protons does not change in a
chemical reaction. When an atom loses electrons it becomes a positive ion because the
number of protons exceeds the number of electrons. Non-metal ions and most of the
polyatomic ions have a negative charge. The non-metal ions tend to gain electrons to fill out the
outer shell. When the number of electrons exceeds the number of protons, the ion is negative.
The attraction between a positive ion and a negative ion is an ionic bond. Any positive ion will
bond with any negative ion. They are not fussy. An ionic compound is a group of atoms
attached by an ionic bond that is a major unifying portion of the compound. A positive ion,
whether it is a single atom or a group of atoms all with the same charge, is called a cation,
pronounced as if a cat were an ion. A negative ion is called an anion, pronounced as if Ann
were an ion. The name of an ionic compound is the name of the positive ion (cation) first and
the negative (anion) ion second.
Major positive ions (cations):
Na+ (Sodium ion) it is the major positive ion of extracellular fluid
K+ (Potassium ion) it is the major positive ion of intracellular fluid
Ca2+ (Calcium ion)
Mg2+ (Magnesium ion)
Major negative ions (anions):
Cl- (Chloride ion) it is the major negative ion of extracellular fluid
HCO3- (Bicarbonate ion)
HPO42- (Phosphate ion) it is one of the major negative ions of intracellular fluid
H2PO4- (Phosphate ion) it is one of the major negative ions of intracellular fluid
SO2/4- (Sulfate ion)
Organic acids
Proteins it is one of the major negative ions of intracellular fluid
Within a fluid compartment, the total number of positive charges must be equal to the total
number of negative charges. Even though the number of positive and negative ions may differ,
the number of each charge must be equal.
Cofactors – positive ions or organic molecules which are required for the activity of some ions.
Ca2+ , Mg2+ and Zn2+ (zinc) can serve as cofactors for enzymes.
Enzymes – A protein that acts as a biological catalyst to speed up a chemical reaction.
Carbonic anhydrase - An enzyme that converts carbon dioxide and water into carbonic acid in
a reversible reaction.
Seven major functions of electrolytes:
1. Cofactors for enzymes (ex., H2O + CO2 + Carbonic anhydrase+Zn2+  H2CO3- (carbonic
acid)
2. Action potentials in neuron and muscle cells (Na+ and K+)
3. Secretion and action of hormones and neurotransmitters (Ca2+)
4. Acid/Base balance (HCO3- [bicarbonate], HPO42-, H2PO4-, and proteins)
5. Secondary active transport (Na+ / K+ pump + ATP)
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6. Osmosis
Osmosis - The movement of water across a selectively permeable membrane from the side that
has more water (less solute) to the side that has less water (more solute).
Isotonic – Two solutions with the same concentration on nonpenetrating solutes, separated by a
selectively permeable membrane. Water moves freely back and forth across the membrane in
both directions at the same rate.
Hypertonic – A solution with a higher concentration of nonpentrating solutes. Water will move
out of cells. The cells will crenate.
Hypotonic – A solution with a higher concentration of nonpentrating solutes. Water moves into
cells and the expand.
Water always follows solutes.
Tonicity – A measure of the ability of a solution to cause a change in cell shape by promoting
flow of water due to osmosis.
Osmotic pressure – The pressure required to prevent the movement of solvent (e.g., water) into a
solution containing solutes when the solutions are separated by a selectively permeable
membrane. It is the external pressure applied to the top of the fluid to prevent osmosis from
occurring. The greater the number of solute particles dissolved in solution the higher the osmotic
pressure.
Water Homeostasis
The body maintains a balance of water intake and output by a series of negative feedback
loops involving the endocrine system and autonomic system.
Antidiuretic Hormone (ADH) – Posterior pituitary hormone that regulates (increases) water
reabsorption in the kidneys. Also called vasopressin.
Aldosterone – Hormone secreted by the adrenal cortex which promotes sodium reabsorption
and potassium secretion by the kidneys.
Total Body Water – The average adult body content of 40 liters of water. It remains fairly constant
under normal circumstances.
Water Input Per Day, Average
2300 mL – Intake of H2O via food and drink
200 mL – Water generated by cell metabolism
2500 mL – Total intake of water
Water Output Per Day, Average
1500 mL – Kidneys (urine)
600 mL- Skin
300 mL – Lungs (water vapor in exhaled air)
(skin and lungs are referred to as Insensible Loss because we are unaware of them)
100 mL – GI tract
2500 mL – Total output of water
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Disturbances of H20 homeostasis usually involved both of the following:
Gain or loss of extracellular fluid
Gain or loss of solute
Hypervolemia – Occurs when too much water and solute are taken in at the same time.
Although extracellular fluid volume increases, plasma osmolarity (total concentration of all solute
particles in solution) may remain normal. (infusion of isotonic intravenous fluid)
Hypovolemia – Occurs when water and solute are lost at the same time. This condition primarily
involves loss of plasma volume. Plasma osmolarity usually remains normal even though volume is
low. (blood loss)
Overhydration – Occurs when too much water is taken in without solute. Volume increases, but
because solute is not present, plasma osmolarity decreases. (drinking too much water)
Dehydration – Occurs when water, but not solute, is lost. It involves a loss of volume but, because
solute is not lost in the same proportion, plasma osmolarity increases. (sweating)
The Kidney: Filtration & Reabsorption
The kidneys are the major way that we regulate water loss from the body.
Glomerular filtration – water and solutes from plasma, forming urine.
Reabsorption – water and solutes are removed from urine and reabsorbed into plasma (usually
in the PCT)
Secretion – water and solutes are removed from the plasma back into the DCT
4 Mechanisms of Fluid Homeostasis
1. ADH (also called vasopressin)
2. Thirst mechanism
3. Aldosterone (hormone secreted by the adrenal cortex which promotes Na+ reabsorption
and K+ secretion by the kidney)
4. Sympathetic Nervous System (SNS) – fight or flight, increases rate and force of heartbeat
Effects of ADH
Increased solute concentration in the plasma (e.g., from sweating).
1. Osmoreceptors in the hypothalamus detect the increased concentration of
solutes (osmolarity) in the interstitial fluid, which reflects the increased osmolarity in
the plasma [WHERE DOES THE OSOMORECPTORS GET THIS INFORMATION?]
2. ADH is released into the plasma by the posterior pituitary
3. ADH targets the collecting ducts (looks like the DCT). They become permeable to
water only in the presence of ADH. ADH promotes the addition of water channels
into the cells of the collecting duct allowing water to move from the filtrate into
the plasma through osmosis.
4. The plasma becomes more dilute, increasing plasma volume and decreasing
osmolarity. Urine has decreased volume and increased osmolarity.
All the effects of ADH help to prevent further fluid loss. ADH will probably be secreted until the
water is replaced, usually by drinking. This intake of water will decrease the plasma osmolarity to
normal, returning the secretion of ADH to baseline levels.
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Thirst Mechanism
The primary regulator of water intake. It involves hormonal and neural input as well as voluntary
behaviors.
Three reasons dehydration leads to thirst:
1. Impulses go from the dry mouth and throat (due to lack of saliva) to the thirst center in
the hypothalamus
2. Plasma osmotic pressure increases, stimulating osmoreceptors in the thirst center of the
hypothalamus
3. Decreased blood volume and pressure stimulates baroreceptors and cause the release
of renin. Renin causes angiotensinogen to convert to angiotensin I (be aware of the role
of vasoconstriction), which stimulates the thirst center
As a result of the fluid intake:
1.
2.
3.
4.
Dryness of mouth and throat are relieved
Stretch receptors in the stomach and intestine send inhibitory signals to the thirst center
Normal fluid osmolarity is restored, relieving dehydration
Dehydration is relieved and the thirst center is no longer stimulated.
Effects of Aldosterone
Hypovolemia (loss of water and solutes, e.g., blood loss, which also causes a decrease in blood
pressure)
A decrease in blood pressure leads to a release of renin by the kidneys.
Renin to Aldosterone
1. Granular cells release renin into the blood stream
2. It converts angiotensinogen to agiotinsen I
3. As angiotinsen I travels through the lungs and capillaries, Angiotensin Converting Enzyme
(ACE) converts it to angiotinsen II
4. Angiotinsen II stimulates the adrenal gland to secret aldosterone. Angiotinsen II also has a
vasoconstrictor effect which helps to increase BP
High K+ Concentrations
This can also cause a release of aldosterone.
Aldosterone exerts if effect by inserting channels in the DCT and collecting duct of the kidneys
that allows Na+ to move from the filtrate into the plasma and K+ to move from the plasma into
the filtrate.
If ADH is also present, water will follow the Na+ into the plasma by osmosis.
The flow of Na+ and water into the plasma causes the BP to increase, completing the negative
feedback loop.
Synpathetic Stimulation
A decrease in blood volume and, therefore, a decrease in BP, stimulates the SNS.
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When BP is low, baroreceptors in the aortic arch and carotid arteries send information to the
medulla. This information will cause an increase in the sympathetic impulses to the kidneys.
Smooth muscle cells in the afferent arteriole constrict causing a decrease in blood flow into the
glomerulus.
Less urine forms, causing less water to leave the body.
Sympathetic stimulation will also cause the release of renin which, by stimulating aldosterone
secretion, will increase the reabsorption of Na+.
As a result, blood volume and BP may stabilize. However, they have not returned to normal. The
baroreceptors will continue to be stimulated to prevent further loss of blood volume.
In order to achieve homeostasis, the person will have to increase the blood volume by drinking
fluids. This is why people are encourage to drink juice after giving blood, which will increase their
blood volume.
Acid/Base Homeostasis
Chemical buffers, the respiratory system and the urinary system work together to ensure that the
pH of body fluids remain within a specific narrow limit.
Acids – Chemical substances that donate hydrogen ion (H +)
Bases – Chemical substances that accept hydrogen ion (H+)
When H+ , acidity  and pH 
When H+ , acidity  and pH 
A pH unit is a change in a factor of 10.
pH of Body Fluids and Exocrine Secretions
Arterial blood:
Venous blood:
Iterstitial fluid:
Intracellular fluid:
7.35 – 7.45
7.35 (because of the presence of more carbonic acid)
7.35
7.0 (organelles have different pHs)
Gastric juices:
Small intestine:
Urine:
1.2 – 2.0 (pH increases after a meal, food acts as a buffer)
8.0 (because of presence of bicarbonate ions)
4.5 – 8.0
If the pH of a body fluid changes too much, enzymes and hormones will no longer function and
clinical will result.
Strong acids – Acids that release all of their H+ when dissolved in water. HCL is the only one in the
body. pH 1.
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Weak acids – Acids that release only some of their H+ when dissolved in water. H 2CO3 (carbonic
acid) is an example. pH 4.5.
Strong and Weak bases – Only weak bases are found in the body.
A neutral solution has a pH of 7 because the H+ concentration and OH- (hydroxide)
concentration are equal.
Electrolytes normally found in plasma can act as weak bases in the body:
• HCO3- Bicarbonate
• HPO42- Hydrogen Phosphate
• SO42- Sulfate
• Anions of organic acids
Acids
• H2PO4- Dihydrogen Phosphate
Proteins have acidic and basic side groups.
Globular Proteins – Proteins which are coiled upon themselves to form a particular shape, which
determines the function of that protein. They cannot function at an altered pH.
Enzymes are proteins that have active sites with specific functions. If the shape of the enzyme
changes, it can no longer function. Clinical symptoms will result. For example, when lactic acid is
generated in large quantities in a muscle, muscles can no longer perform at their maximum.
Enzymes that work within the cytoplasm of cells function best in a pH of 7.
Proteins have many positive and negative charges that impact the shape, or tertiary structure,
of the protein. These positive and negative charges are present because of acidic and basic
amino acid side chains.
Buffers
Buffer – A chemical substance or a system that minimizes changes in pH by releasing or binding
hydrogen ions.
3 ways the body maintains a normal pH range:
1. Chemical buffer systems
2. Respiratory controls
3. Renal mechanisms
Chemical Buffers
Act in seconds.
Most buffers are composed of weak acid and weak base pairs, sometimes called conjugated
acid/base pairs.
Conjugated acid/base pairs – Weak acid and weak bases that can be converted to one to the
other by the removal or addition of a hydrogen ion.
3 Important Buffer Systems
• The carbonic acid / bicarbonate system; H2CO3 / HCO3-
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•
The phosphate system; H2PO4- Dihydrogen / HPO42- Hydrogen Phosphate
Protein buffers
Carbonic Acid / Bicarbonate System
Weak acid: H2CO3 Carbonic Acid
Weak base: HCO3- Bicarbonate
Phosphate Buffer System
Weak acid: H2PO4Weak base: HPO42H2PO4- is an acid as compared to HPO42- because it has more hydrogen
Proteins
They can tolerate some addition of acids or bases, but if the number of H+ in solution increases
too much, they will cease to function (i.e., become denatured).
Respiratory Control of pH
When we breathe more quickly and deeply, more CO2 leaves the body.
Carbonic Anhydrase – An enzyme that converts carbon dioxide and water into carbonic acid in
in red blood cells. It is a reversible solution.
CO2 + H2O  H2CO3 (carbonic acid)
It is a reversible reaction. The reaction can take place outside of cells without the enzyme, but it
is slower.
Another reaction that forms carbonic acid, hydrogen + bicarbonate form carbonic acid:
H+ + HCO3-  H2CO3
CO2 + H2O  H2CO3  HCO3- + H+
Effect of Hypoventilation
IF RR then CO2 and pH
If RR then CO2 and pH
Volatile acid – An acid which can freely turn into a gas and be eliminated from the body via the
lungs. Carbonic acid (H2CO3)is considered a volatile acid because it can freely turn into carbon
dioxide.
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Renal Control of pH
3 renal processes:
1. Glomerular filtration
2. Tubular reabsorption
3. Tubular secretion
Glomerular Filtration
The following are filtered out in the glomerular capsule and affect pH
• H+ (hydrogen ions – acid)
• HCO3- (bicarbonate ions – base)
• CO2 (carbon dioxide ions )
• HPO42-, H2PO4- (phosphate ions - bases)
• Other fixed acids (metabolic acids generated in the body that are eliminated in urine.
Carbonic acid is not a fixed acid because it can be eliminated via the lungs.)
Renal tubules selectively reabsorb and secrete these acids and bases to fine-tune the pH of the
plasma.
Renal mechanisms
• The slowest ways of regulating pH. They make take hours or days
• Allow for the elimination fixed acids [generated by metabolic acids]
Alkalosis
If plasma pH is too high [i.e., too basic,  7.45, alkalosis], HCO3- (bicarbonate, a base) is filtered
at the glomerulus, but is not reabsorbed. HCO3- goes into the urine and is eliminated, causing
the pH to  [plasma becomes more acidic].
Acidosis
If the plasma pH is too low [i.e., too acidic,  7.35, acidosis], there are three ways the kidney
tubules regulate the pH of body fluids; combat acidosis:
1. Reabsorption of HCO3- (bicarbonate ions – base)
2. Generation of HCO3- (bicarbonate ions – base) by the kidney tubule cells
3. Secretion of H+ [hydrogen ions – acid] tied to the generation of HCO3Reabsorption [i.e., conserving] of HCO3- (bicarbonate ions – base) in PCT:
1. CO2 arrives at the kidney tubule in the PCT from filtrate, plasma or metabolic processes in
the tubule cell
2. The more CO2 in the plasma [i.e., respiratory acidosis] the more CO2 enters the tubule cell
3. Within the PCT tubule cell, CO2 + H2O  H2CO3, a reaction catalyzed by carbonate
anhydrase (CA) [an enzyme that converts carbon dioxide and water into carbonic acid
in a reversible reaction.]
4. The H2CO3 then splits into H+ and HCO3- [H2CO3  H+ + HCO3-]
5. The H+ moves into the filtrate in exchange for Na+ [which moves out of the filtrate and
into the cell] to maintain electrical neutrality through the Na+ - H+ antiport transport
protein1
A membrane-bound protein that will transport one substance in one direction in exchange for another
specific substance moved in the other direction using the energy of the concentration gradient of one the
substances. It is a form of secondary active transport.
1
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6. The concentration of Na+ in the tubule cell is kept low by the Na+ - K+ ATPase pump2 on
the surface of the cell facing the plasma. Na+ moves out of the cell and into the plasma.
The low concentration of Na+ in the cell drives the pump.
7. In the filtrate, H+ combines with filtered HCO3- to form H2CO3 [H2CO3  H+ + HCO3-]
8. Carbonic anhydrase, which may be attached to the microvilli of the tubule cell, then
breaks up the H2CO3 into CO2 and H2O [CO2 + H2O  H2CO3]
9. The CO2 diffuses into the tubule cell from the filtrate, removing HCO3- from the filtrate.
HCO3- can’t move into the cell as HCO3-; it must be moved back in the form of CO2.
10. The CO2 can reform HCO3- within the tubular cell and the process repeats.
11. Much of the water generated also gets reabsorbed
12. The HCO3- generated within the tubule cell diffuses into the plasma by combining with
Na+ via the symport transport protein3. The diffusion of Na+ out of the cell maintains the
cell’s electrical neutrality
Result:
1. HCO3- is absorbed back into the plasma. Typically, 80 – 90% of the HCO3- is
reabsorbed in the PCT
2. More Na+ is reabsorbed back into the plasma
3. In severe acidosis, this process continues until all of the HCO3- is reabsorbed into
the filtrate
Bicarbonate Generation in the Intercalcalated cells in the Cortical Collecting Ducts:
1. To combat acidosis, the cells of the collecting duct generate HCO3-, which is taken back
into the plasma.
2. At the same time, H+ is secreted into the filtrate.
3. The H+ attaches to buffers and is eliminated from the body.
Process:
1. CO2 arrives at the kidney tubule cell (of the PCT) in the collecting duct from the plasma
or from metabolic reactions within the cell
2. In the cell, CO2 and H2O form H2CO3. The reaction is catalyzed by carbonic anhydrase
[CO2 + H2O  H2CO3]
3. H2CO3 splits into H+ and H2CO3. [H2CO3  H+ + H2CO3]
4. H+ goes into the filtrate via primary active transport4 through the H+ pump [on the lumen
side of the tubular cell, with the assistance of ATP]
5. ATP is used up. H+ Is secreted against the gradient and there can be 1000 times more H +
in the filtrate than in the plasma
6. H2CO3 is scarce in the filtrate at this point because it is reabsorbed in the PCT
7. The H+ will combine with a buffer such as HPO42- [hydrogen phosphate, the most
important buffer in urine] forming H2PO4- [HPO42- + H+  H2PO4-]
8. The resulting H2PO4- is unable to go back into the cell and is trapped in the filtrate and is
excreted
ATP – Adenosine TriphosPh ate, an organic molecule that stores and releases chemical energy within a cell;
composed of adenine, ribose sugar, and three phosphate groups
ATPase – A cellular enzyme that binds to ATP and hydrolyses ATP into ADP (Adenosine DiPhosphate) and
inorganic phosphate, liberating the energy within the high-energy phosphate bond.
3
Symport Transport Protein – A membrane-bound protein that will transport two different substances in the
same direction using the energy of the concentration gradient of one of the substances. A form of secondary
transport.
4
Primary Active Transport – The active transport process in which the energy liberated from ATP is transferred
directly to the carrier molecule participating in the transport, moving the substance across the membrane from
lower to higher concentration.
2
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9. By attaching the H+ to HPO42- the pH of the filtrate is kept above 4.5
10. Elimination H+ will stop if the pH goes below 4.5
11. The newly formed HCO3- moves into the plasma via the antiport transport protein on the
cell wall facing the interstitial fluid. Cl- (sodium chloride) moves into the cell at the same
time to maintain electrical neutrality
12. By adding new HCO3- to the plasma, H+ is used up and the pH increases
Result:
1. Newly generated HCO3- is added to the plasma, increasing the pH of the plasma
and adding new buffering power to it
2. H+ is secreted into the filtrate [via the H+ pump with the assistance of ATP] and is
eliminated from the body.
Glutamine Metabolism
[a second and more important process for generating HCO3- and secreting H+ in the tubular cell]
Glutamine is an amino acid that is metabolized in the tubule cells. The product of its metabolism
is NH3 [ammonia] and HCO3- [bicarbonate].
1. NH3 combines with H+ inside the cell to form NH4+ [ammonium]
2. The NH4+ then travels from the cell to the filtrate in exchange for Na + via the antiport
transfer protein
3. The Na+ concentration is kept low inside the cells by the Na+ - K+ ATPase pump [moves
Na+ out of the cell and into the plasma and K+ out of the plasma and into the cell]
4. The NH4+ [ammonium] is eliminated in the urine
5. The HCO3- leaves the cell together with Na+ and goes into the plasma
Result
1. Newly generated HCO3- is added to the plasma, increasing the pH of the plasma
and adding new buffering power to it
2. H+ is eliminated from the body in the form of NH4+ [ammonium]
Summary
Acidosis and Alkalosis
3 mechanisms the body uses to maintain pH
1. Chemical buffers, they act within minutes
2. Respiratory controls
a. Starts acting within seconds
b. Compensates for metabolic acidosis5 or metabolic alkalosis6
c. Permits the elimination of the volatile acid H2CO3
3. Renal Mechanisms
a. Act within hours or days
b. Compensates for respiratory acidosis and respiratory alkalosis
c. Eliminate fixed acids
Metabolic Acidosis – A condition in which the pH or arterial blood falls below 7.35 due to a non-respiratory
cause. Plasma bicarbonate levers decrease.
6
Metabolic Alkalosis – A condition in which the pH or arterial blood increases above 7.35 due to a nonrespiratory cause. Plasma bicarbonate levers decrease.
5
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Effect of Plasma Proteins of pH
Normal arterial pH is between 7.35 and 7.45.
Most proteins in plasma have an optimum pH of 7.4.
When respiratory acidosis or alkalosis occurs, the problem lies within the respiratory system.
Because the respiratory system cannot correct the problem, the renal system compensates for it.
Metabolic Acidosis
Metabolic acidosis occurs when there is an excess of any body acid, except H 2CO3 [carbonic
acid].
Caused by excess acid production or loss of base.
Excess acid production can be caused by:
• Diabetic ketoacidosis7
• Starvation ketosis8
• Lactic acidosis [lack of oxygen]
• Kidney disease
• High extracellular K+ [as excess K+ moves into the cells, H+ comes out]
Loss of base can occur because of:
• Diarrhea [causes the loss of bicarbonate which is plentiful in intestinal fluid.]
Symptoms of Diabetic Ketoacidosis
• CNS depression [plasma pH of 6.9 causes brain stem dysfunction, closely followed by
death]
• Heart dysrhythmias
• Decreased cardiac contractility
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Eat a lot but losing weight
Thirst, drinking lots of water
Frequent urination
Difficult to wake
Skin is warm, dry and flushed
Deep and rapid breathing
Diabetic ketoacidosis is the first sign of Type 1 diabetes,
In normal cell metabolism, insulin is released from beta cells in the pancreas and allows glucose
transport across the cell membrane of some cells.
When insulin is absent [which is the case in Type 1 diabetes], fat breakdown occurs and
production of keto acids by the liver increases until the body’s buffer systems become
overwhelmed and ketoacidosis ensues.
Compensation for Metabolic Acidosis
Ketoacidosis – A type of metabolic acidosis brought about by a production of acidosis ketones [fatty acid
metabolites; strong organic acids
8
Ketosis – The production of ketone bodies by the liver which occurs during starvation, diabetes, or a low
carbohydrate diet.
7
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The carbonic acid / bicarbonate buffer system [H2CO3 / HCO3- ] will come into action
Because more H+ is being generated in the body, the excess H+ will combine with HCO3to form CO2. The HCO3- level will decrease.
The respiratory system will compensate in order to bring the pH level back to normal
Because of the increased acid, the respiratory centers in the brain will be stimulated and
the person will hyperventilate [breath fast and deeply]
Hyperventilation allows the body to reduce the overall amount of acid by exhaling
H2CO3 in the form of CO2 and H2O.
The kidneys may respond to the decreased pH by excreting more H+. This response may
take several days to occur.
These mechanisms compensate only. They do not correct the underlying problem.
Insulin must be administered to restore normal metabolism.
Metabolic Alkalosis
Caused by a deficit of any acid in the body, except H2CO3.
Causes
• Too much base by ingesting too much HCO3• Loss of acid through vomiting of stomach contents, which contains hydrochloric acid
• Hypokalemis – An excess of K+ in the extracellular fluid [plasma] causes K+ to come
out of cells in exchange for H+
PH will rise indicating a loss of H+.
Symptoms
• Initially nerve cell membranes become irritable and muscle spasms and convulsions
occur.
• In severe alkalosis, CNS depression occurs, confusion, lethargy and coma ensue.
• Death occurs when plasma pH reaches about 7.8
Compensation
• The carbonic acid / bicarbonate buffer system [H2CO3 / HCO3- ] will come into action
• CO2 + H2O  H2CO3  HCO3- + H+. Because there is less H+ in the body, the reaction will
shift to the right and more H+ and HCO3- will form.
• The respiratory centers in the brain will become inhibited and the person will
hypoventilate, bringing in/retaining CO2 and, therefore, H2CO3
• The loss of Cl-, fluid volume and acid combine to prevent the kidneys from excreting
excess base.
Respiratory acidosis
This occurs when there is an excess of CO2, and, therefore, an increase in H2CO3 in the body.
Any condition that impairs the elimination of CO2 may result in respiratory acidosis.
Causes:
• Impaired gas exchange in the lungs
• Impaired activity of the diaphragm muscle
• Impaired respiratory control in the brain stem
Symptoms
• Headache
• Cardiac dysrhythmias
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Blurred vision
Dizziness
Disorientation
Lethargy
CO2 + H2O  H2CO3  HCO3- + H+. Because there is an increase in CO2 the reaction shifts to the
right to achieve equilibrium. Acid levels rise.
Compensation
• Because the problem is in the respiratory system, it cannot compensate
• The kidneys will excrete H+
Respiratory Alkalosis
It is a deficit of CO2 and occurs as a result of hyperventilation. During hyperventilation
[excessively deep and fast breathing] H2CO3 is excreted from the lungs in the form of CO2.
Causes
• Low levels of O2 in the plasma
• Stimulation of the brainstem, for example, in the case of meningitis
• Head injury
• Anxiety
Symptoms
• Numbness and tingling in fingers and around the mouth
• Dizziness and confusion
• Cerebral vasoconstriction
• Seizures
• Coma
CO2 + H2O  H2CO3  HCO3- + H+. The reaction proceeds to the left because with each
exhalation more H2CO3 is eliminated from the lungs as CO2.
H+ will decrease because it is combining with HCO3- to form CO2.
Because this is an acid/base disturbance of the respiratory origin, the kidneys will excrete HCO 3,
a base, to compensate for the loss of acid. Often this never happens because if the
hyperventilation is caused by anxiety, breathing will return to normal after the anxiety is
alleviated.
Respiratory
Metabolic
Fluid and Electrolyte Homeostasis
Page 14 of 14
Acidosis
Cause: Generation of H+ or loss of
base from body
H2CO3 falls
Compensation: Respiratory System,
hyperventilation. The increased H+
stimulates the respiratory centers,
increasing ventilation, decreasing CO2
Alkalosis
Cause: Loss of H+ or a gain of base in the body
CO2 + H2O  H2CO3  HCO3- + H+
Reaction moves to the left
Cause: Defective exchange of gases
in the lungs.
CO2 + H2O  H2CO3  HCO3- + H+
Reaction moves to the right
CO2 rises
Compensation: Renal System will
generate or reabsorb HCO3-, or
excreting H+, which may take several
hours or days for complete
compensation to occur.
CO2 + H2O  H2CO3  HCO3- + H+
Reaction moves to the right
Cause: Hyperventilation
H2CO3 falls
Compensation: Respiratory System,
hypoventilation. This conserves CO2, and, therefore
H2CO3.
CO2 + H2O  H2CO3  HCO3- + H+
Reaction moves to the left
CO2 falls
Compensation: Renal System will excrete excess
HCO3- [base], which may take several hours or days
for complete compensation to occur.
The causes of respiratory alkalosis are often short
lived and are usually alleviated before
compensation can occur.