Metabolic alkalosis - causes, symptoms, diagnosis, treatment, pathology
Summary
TLDRMetabolic alkalosis occurs when blood pH rises above 7.45 due to increased bicarbonate concentration. It can result from loss of hydrogen ions through vomiting or excess aldosterone, or from primary bicarbonate gain via kidney reabsorption or antacid ingestion. Hypokalemia often accompanies it, affecting the body's compensatory mechanisms, including cellular ion transport and respiratory rate adjustments. The kidneys eventually correct the imbalance by retaining hydrogen ions and reducing bicarbonate reabsorption.
Takeaways
- 📝 Metabolic alkalosis is a condition where blood pH rises above 7.45 due to an increase in bicarbonate (HCO3-) concentration.
- 📝 Blood pH is maintained between 7.35 and 7.45, and deviations indicate an imbalance in the body's acid-base regulation.
- 📝 The condition can arise from two main causes: loss of hydrogen ions or gain of bicarbonate ions, often a combination of both.
- 📝 Loss of hydrogen ions can occur through the gastrointestinal tract, such as during vomiting, or through the kidneys.
- 📝 Excess aldosterone, possibly due to an adrenal tumor, can lead to increased reabsorption of bicarbonate and loss of hydrogen ions in the urine.
- 📝 Primary gain of bicarbonate can be caused by increased reabsorption from the kidneys, stimulated by factors like volume contraction or hypokalemia.
- 📝 Hypokalemia, or low potassium levels, can trigger the renin-angiotensin-aldosterone mechanism, leading to metabolic alkalosis.
- 📝 Excess bicarbonate ions can also come from external sources, such as the ingestion of large amounts of antacids like sodium bicarbonate.
- 📝 Metabolic alkalosis often leads to hypokalemia, as the body tries to maintain pH balance by shifting potassium and hydrogen ions.
- 📝 The body compensates for increased bicarbonate levels by using ion transporters in cells and adjusting respiratory rates.
- 📝 If not caused by renal issues, the kidneys can eventually correct the imbalance by retaining hydrogen ions and reabsorbing less bicarbonate.
Q & A
What is metabolic alkalosis?
-Metabolic alkalosis is a condition where blood pH is raised above 7.45 due to an increase in bicarbonate (HCO3-) concentration in the blood.
What is the normal range for blood pH?
-The normal range for blood pH is between 7.35 and 7.45.
How can loss of hydrogen ions lead to metabolic alkalosis?
-Loss of hydrogen ions, which can occur from the gastrointestinal tract during vomiting or through the kidneys due to excess aldosterone, leads to a relative increase in bicarbonate ions, thus causing metabolic alkalosis.
Why does vomiting lead to loss of hydrogen ions?
-Vomiting leads to loss of hydrogen ions because gastric secretions, which are acidic and rich in hydrogen ions, are expelled from the body. Additionally, the pancreas may not secrete bicarbonate to neutralize the acid in the intestines, leading to a buildup of bicarbonate in the blood.
How does aldosterone contribute to the loss of hydrogen ions?
-Aldosterone stimulates the kidneys to excrete more hydrogen ions and reabsorb more bicarbonate, leading to a more acidic urine and a more basic blood pH.
What is the role of diuretics in causing metabolic alkalosis?
-Diuretics, especially loop and thiazide diuretics, can cause volume contraction and excessive loss of extracellular fluid, which can stimulate the kidneys to reabsorb more bicarbonate, leading to metabolic alkalosis.
How does hypokalemia (low potassium levels) relate to metabolic alkalosis?
-Hypokalemia can trigger the renin-angiotensin-aldosterone mechanism, leading to increased reabsorption of bicarbonate by the kidneys and thus contributing to metabolic alkalosis.
What is contraction alkalosis?
-Contraction alkalosis is a type of metabolic alkalosis that occurs due to volume contraction or excessive loss of extracellular fluid, often as a result of diuretic use or severe dehydration.
How do antacids contribute to metabolic alkalosis?
-Antacids, such as sodium bicarbonate, are used to neutralize stomach acid. Excessive use can lead to an excess of bicarbonate ions being absorbed into the blood, increasing the blood pH.
What are the body's mechanisms to counteract metabolic alkalosis?
-The body counters metabolic alkalosis through cellular ion transporters that exchange hydrogen for potassium ions, respiratory adjustments that retain carbon dioxide, and renal mechanisms that retain hydrogen ions and reduce bicarbonate reabsorption.
How does hypokalemia act as both a cause and a result of metabolic alkalosis?
-Hypokalemia can be both a cause, by triggering increased bicarbonate reabsorption, and a result of metabolic alkalosis, as aldosterone can cause potassium excretion in the urine.
Outlines
🌡️ Metabolic Alkalosis Explained
Metabolic alkalosis is a condition where blood pH rises above 7.45 due to an increase in bicarbonate (HCO3-) concentration. It can occur from loss of hydrogen ions or gain of bicarbonate ions. Loss of hydrogen ions typically happens through vomiting, which leads to a lack of stomach acid and reduced bicarbonate secretion by the pancreas, or through increased aldosterone levels, which can be caused by adrenal tumors. Gain of bicarbonate ions can be due to increased reabsorption by the kidneys in response to volume contraction or hypokalemia. Hypokalemia can be both a cause and a result of metabolic alkalosis. The body responds by using ion transporters to move hydrogen ions into the blood and potassium ions into cells, which can contribute to hypokalemia. Another response is the respiratory system's adjustment to decrease the respiratory rate and depth, leading to a buildup of carbon dioxide and a decrease in pH.
💨 Respiratory Response to Metabolic Alkalosis
The respiratory system plays a crucial role in managing metabolic alkalosis. Chemoreceptors in the carotid arteries and aortic arch detect increased pH and signal the brain stem to reduce the respiratory rate and depth. This results in decreased minute ventilation, slowing the expulsion of carbon dioxide and increasing its partial pressure, which in turn lowers the pH. If metabolic alkalosis is not due to renal issues like diuretic use or volume contraction, the kidneys can correct the imbalance over several days by retaining hydrogen ions and reabsorbing less bicarbonate, facilitating its excretion in urine. The paragraph concludes with a recap that metabolic alkalosis is caused by an elevated bicarbonate ion concentration, leading to a pH above 7.45, and is most commonly due to loss of hydrogen ions from vomiting or adrenal tumors, or less commonly from bicarbonate gain due to antacids or volume contractions.
Mindmap
Keywords
💡Metabolic Alkalosis
💡Bicarbonate
💡pH
💡Hydrogen Ions
💡Aldosterone
💡Vomiting
💡Diuretics
💡Hypokalaemia
💡Renin-Angiotensin-Aldosterone System
💡Antacids
💡Respiratory Compensation
Highlights
Metabolic alkalosis is a condition where blood pH rises above 7.45 due to an increase in bicarbonate concentration.
Blood pH is normally maintained between 7.35 and 7.45, balancing bases and acids.
Metabolic alkalosis can occur from loss of hydrogen ions or gain of bicarbonate ions.
Vomiting can lead to loss of hydrogen ions as stomach acid is expelled and bicarbonate is not secreted by the pancreas.
Excess aldosterone from adrenal tumors can cause loss of hydrogen ions through urine.
Primary gain of bicarbonate is often due to increased reabsorption by the kidneys.
Volume contraction or excessive loss of extracellular fluid can stimulate kidneys to reabsorb more bicarbonate, leading to alkalosis.
Hypokalemia, or low blood potassium, can trigger renin-angiotensin-aldosterone mechanism, increasing bicarbonate reabsorption.
Excess bicarbonate intake from antacids can also cause metabolic alkalosis.
Hypokalemia can be both a cause and a result of metabolic alkalosis.
The body compensates for increased bicarbonate by shifting hydrogen ions into the blood and potassium into cells.
Respiratory system responds to alkalosis by decreasing respiratory rate and depth, retaining carbon dioxide.
Kidneys can correct metabolic alkalosis by retaining hydrogen ions and reabsorbing less bicarbonate if not caused by renal problems.
Metabolic alkalosis is frequently caused by vomiting or adrenal tumors, and less commonly by antacids or volume contractions.
Transcripts
with metabolic alkalosis alkalosis
refers to a process that raises blood pH
above 7.45
and metabolic refers to the fact that
it's caused by an increase in the
concentration of bicarbonate or hco3
minus in the blood
normally blood pH depends on the balance
or ratio between the concentration of
bases mainly bicarbonate which increases
the ph and acids which decrease the pH
the blood pH needs to be constantly
between 7.35 and 7.45
now metabolic alkalosis can typically
happen from two main causes
loss of hydrogen ions and gain of
bicarbonate ions or most often a
combination of these two
loss of hydrogen ions can happen either
from the gastrointestinal tract or from
the kidneys
the first case most commonly happens
during vomiting because the gastric
secretions are very acidic meaning that
they have lots of hydrogen ions
on top of that normally as gastric
secretions flow into the pancreas
they're met with bicarbonate secretions
which neutralize the acid so that the
various pancreatic enzymes like trypsin
and chymotrypsin can work effectively
so during vomiting not only is the
stomach acid lost but in addition the
pancreas doesn't secrete bicarbonate
into the intestines and so it builds up
in the blood instead
another way that hydrogen ions can be
lost is through the urine in the context
of having too much of the hormone
aldosterone
this can happen when there's an adrenal
tumor that secretes excess aldosterone
the aldosterone makes the alpha
intercalated cells to the distal
convoluted tubule and collecting duct
dump out hydrogen ions and reabsorb more
bicarbonate
the result is that the urine becomes
more acidic and the blood becomes more
basic
now the second cause a primary gain of
bicarbonate is usually caused by an
increased reabsorption of bicarbonate
from the kidneys
there are various things that could
stimulate the kidneys to do this one of
them is volume contraction or excessive
loss of extracellular fluid which can
happen with Loop Diuretics and thiazide
diuretics as well as in cases of severe
dehydration
the resulting alkalosis is called a
contraction alkalosis
sometimes dehydration happens in
combination with other causes of
metabolic alkalosis like prolonged
vomiting
another stimulus is hypokalemia or
decreased levels of potassium in the
blood which can be due to excessive loss
from the gastrointestinal tract like in
diarrhea or from the kidneys due to
diuretic use
in any case When there's less volume or
less potassium in the extracellular
space it triggers the renin Angiotensin
aldosterone mechanism
as a result Angiotensin II and
aldosterone levels rise and the kidneys
start to retain water and reabsorb more
bicarbonate in the proximal convoluted
tubule
in addition the alpha intercalated cells
of the distal convoluted tubule and the
collecting ducts secrete more hydrogen
ions into the urine but most importantly
they also make new bicarbonate ions
which will again get reabsorbed
now in other cases excess bicarbonate
ions don't come from within our bodies
at all but are ingested in large amounts
usually in the form of antacids like
sodium bicarbonate
these are typically used to neutralize
stomach acid and relieve indigestion
excess use of antacids though can result
in more bicarbonate ions than hydrogen
ions in the stomach and the excess
bicarbonate ions can get absorbed into
the blood
all these processes have a net result of
increasing the bicarbonate ion
concentration in the blood which
increases blood pH
but in addition there's often a
hypokalemia
in vomiting for example potassium ions
in the gastric secretions are lost
in other situations there's an increase
in aldosterone like during a contraction
alkalosis or when there's an adrenal
tumor
the aldosterone can affect principal
cells which line the distal convoluted
tubule and collecting ducts making them
excrete potassium into the urine
so essentially hypokalemia can be both a
cause and a result of metabolic
alkalosis
now if there's an increase in the
bicarbonate concentration in the blood
the body has a few important mechanisms
to help keep the pH in balance
first cells throughout the body have a
special type of ion transporter that
exchanges hydrogen ions for potassium
ions across the cell membrane
using this transporter the cells can
shift hydrogen ions out of the cells and
into the blood and in exchange pull
potassium ions out of the blood and into
the cells
and this can contribute to the
hypokalemia
another mechanism involves a respiratory
system and starts with chemoreceptors
that are located in the walls of the
carotid arteries and in the wall of the
aortic Arch
these chemoreceptors fire less often
when the pH Rises and that notifies the
respiratory centers in the brain stem
that they need to decrease the
respiratory rate and depth of breathing
as the breathing becomes slow and
shallow the minute ventilation decreases
and that's the volume of air that moves
in and out of the lungs in a minute
the decreased ventilation slows down how
much carbon dioxide leaves the body
increasing the partial pressure of
carbon dioxide in the body which
decreases the pH
a final mechanism is that of metabolic
alkalosis isn't caused by some renal
problem like the use of diuretics or
extracellular fluid volume contraction
then several days later the kidneys
usually correct the imbalance
the kidneys retain more hydrogen ions
while also reabsorbing less bicarbonate
ions so that it's more easily dumped
into the urine
alright as a quick recap metabolic
alkalosis is caused by an increased
bicarbonate ion concentration in the
blood
that elevates blood pH above 7.45
this most frequently results in loss of
hydrogen ions due to vomiting or adrenal
tumors
and less commonly from a gain of
bicarbonate ions from antacids or volume
contractions
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