Transcript Acid-Base Balance Chapter 24 Overview – Cellular metabolism produces many acidic substances • • • CO2- produced when metabolism proceeds in presense of oxygen Lactic acid - produced when.

Acid-Base Balance
Chapter 24
Overview
– Cellular metabolism produces many acidic
substances
•
•
•
CO2- produced when metabolism proceeds in presense of
oxygen
Lactic acid - produced when metabolism proceeds in
absence of oxygen
Ketones- produced when fats and proteins are metabolized
– Normal plasma pH: 7.35–7.45
•
This is possible because of a balance between the acids
and bases of the body
– Acid-base balance disruptions include:
•
•
Acidosis- there is more acid than base – pH drops below
7.35 and the blood becomes acidic
Alkalosis- there is more base than acid- pH is raised above
7.45 and the blood becomes basic
To maintain normal blood
pH the hydrogen (acid)
and the bicarbonate
(base) must stay in
balance.
Blood will become basic if there is
more bicarbonate than hydrogen. To
restore to normal the body must
(1) Obtain more hydrogen ions
(2) Slow down the resupply of the
bicarbonate ions
Blood will become acidic if there is
more hydrogen then bicarbonate. To
restore to normal the body must
(1) Get rid of excess hydrogen ions
(2) Resupply additional bicarbonate
ions
Systems Regulating Acid-Base Balance
• The three systems work together to maintain
the normal physiological pH of the blood
– Cardiovascular- blood buffers - resist the change
in pH by neutralizing acid or resupplying acid
– Respiratory- regulate the amount of CO2 (acid)
present in the body
– Renal- remove hydrogen and resupply
bicarbonate to the blood
Buffer system
1.
Carbonic acid–bicarbonate buffer system
•
Most important in extracellular fluid and blood
•
The reaction is catalyzed by carbonic anhydrase enzyme.
•
If there is more CO2 than H+ and HCO3-, the reaction will result in
production of more H+ and HCO3-., adding acid (H+). This will decrease
the pH.
•
If there is more H+ and HCO3-, the reaction will result in production of
more CO2, getting rid of acid (H+). This will increase the pH.
Carbonic
Anhydrase
CO2 + H2O  H2CO3  HCO3– + H+
1.
Phosphate buffer system
•
Buffers pH of intracellular space and urine
3. Protein buffer systems
•
Buffers pH of intracellular space and urine
Respiratory System
• If pH is low- Increased levels of H+ increase
the respiratory rate (Hyperventilation) to get
rid of CO2 (acid) thus decreasing the acidity
of the blood
• If pH is high- decreased levels of H+ decrease
the respiratory rate (Hypoventilation) to
retain CO2 (acid), thus increasing the acidity
Renal System
•
The renal tubules indirectly
– Secrete H+
– Reabsorb HCO3-
•
The process proceeds as following:
1.
2.
3.
4.
5.
CO2 enters the renal tubule
Combines with water to produce
carbonic acid. This reaction is
catalyzed by carbonic anhydrase
(CA)
The carbonic acid dissociates into
hydrogen and bicarbonate ions
Hydrogen enters into the filtrate in
exchange for sodium. Hydrogen is
secreted
Bicarbonate enters into the
interstitial fluid (EFC) and then into
the blood along with sodium.
Bicarbonate is reabsorbed.
The systems work together!
• In case of acidosis
– Renal system supplies the body with bicarbonate and secretes
H+
– The buffer system uses this bicarbonate to neutralize H+ (acid)
and to produce CO2
– CO2 produced by the buffer system is expelled by the lungs
• In case of alkalosis
– Renal system slows down the reabsorption of bicarbonate and
secretion of hydrogen
– The respiratory rate slows down to retain CO2
– The buffer system converts CO2 into H+ ions
Response to Acidosis
Response to Alkalosis
Types of Acid-Base Disorders
• Acidosis is more prevalent than alkalosis
• Respiratory Acidosis- decreased blood pH caused by
inefficient riddance of CO2 by the respiratory system
• Respiratory Alkalosis- elevated blood pH caused by
excessive expulsion of CO2 by the respiratory system
• Metabolic Acidosis- accumulation of acids or depletion
of bases in the blood caused by a system other than
respiratory
• Metabolic Alkalosis- accumulation of bases or
depletion of acids in the blood caused by a system
other than respiratory
Respiratory Acidosis
•
•
Any condition that decreases CO2 clearance will cause respiratory acidosis
Factors important for proper CO2 clearance
1.
2.
3.
4.
•
Thickness of respiratory membrane
Lung perfusion- blood flow to the lungs
Large surface area
Alveolar ventilation
Causes:
– Pulmonary edema and lower respiratory tract infections (pneumonia, tuberculosis) affect the
respiratory membrane thickness
– Cancer can reduce surface area and decrease alveolar ventilation
– Asthma decreases alveolar ventilation
– Cardiovascular pathologies of pulmonary embolism can decrease lung perfusion
•
In all cases, the blood CO2 will increase and
1.
2.
3.
Respiratory rate will increase to rid of excess CO2
The renal system will reabsorb HCO3- and secrete H+
The buffer system will use the HCO3- to neutralize the excess H+ ions and to produce CO2
to be expelled through the lungs. However, this will not be very efficient because the lungs
are the source of the problem. So, the main system available to restore acid-base balance is
the renal system
Respiratory Alkalosis
• May be caused by a panic attack
• What happens to the respiratory rate during a
panic attack?
• What happens to the blood CO2 levels?
• How is the body going to fix this?
Metabolic Acidosis
• Causes:
– Renal damage –cannot secrete H+ and reabsorb bicarbonate because the
number of available nephrons is depleted
– Metabolism of fats and proteins produces ketones which are acidic
• Low carb diet- low sugar supply, the body starts to break down fats and then proteins
• Anorexia – no nutrient supply, the body starts to break down fats and then proteins
• Diabetes- cannot utilize sugar available, the body starts to break down fats and then
proteins
• Diarrhea- loss of bicarbonate in stool, the pancreas resupply bicarbonate to the small
intestine but place H+ into the blood
• In all cases, the blood pH will decrease
1.
2.
3.
Respiratory rate will increase to rid of excess CO2
The renal system will reabsorb HCO3- and secrete H+ (unless the renal
system is the source of the problem)
The buffer system will use the HCO3- to neutralize the excess H+ ions and
to produce CO2 to be expelled through the lungs.
Metabolic Alkalosis
• May be caused by severe, prolonged vomiting
– Stomach looses H+ and begins to produce more
H+. However, in the process, the cells of the
stomach deposit bicarbonate to the blood
• How is the body going to fix this?
– Renal
– Buffers
– Respiratory
Practice question 1
• Suzy is five month pregnant. She developed
gestational diabetes (underproduction of
insulin) during the third month of pregnancy.
– How will her blood pH be affected if she does not
control her blood sugar with insulin injections?
Explain your prediction.
– Will Suzy’s condition cause acidosis or alkalosis? Is
the condition respiratory or metabolic in origin?
– Describe the mechanisms that will be
implemented to maintain her acid-base balance
Practice question 2
• John, a patient with a history of diabetes was
complaining of shortness of breath and chronic nonproductive cough. Upon arrival to the hospital John
was hyperventilating. He was diagnosed with stage II
squamous cells carcinoma of the lung. Furthermore,
John’s blood sugar was severely elevated.
– Why is John hyperventilating
– Predict John’s blood pH and urine pH and explain your
prediction
– Is John experiencing acidosis or alkalosis?
– Is the condition respiratory or metabolic in origin?
Practice question 3
• Mrs. Mia Wallace found a stash of
heroin in Vincent Vega’s coat
pocket. Mistaking it for cocaine,
she snorts it and overdoses.
Heroin depresses respiratory and
cardiovascular rates.
– Predict Mia’s blood pH and urine
pH and explain your prediction
– Is Mia experiencing acidosis or
alkalosis?
– Is the condition respiratory or
metabolic in origin?
– Describe the mechanisms that
will be implemented to maintain
her acid-base balance
Review
• Explain the reasoning behind the following treatments for a hypertensive
person
– low Na+ diet - where will this treatment work? which process would it affect?
how would this decrease BP? what will be the effect on the urine output?
– ACE inhibitor- what is the target of the drug? ? which process would it affect?
how would this decrease BP? what will be the effect on the urine output?
– Angiotensin II receptor blockers- what are the targets of the drug? ? which
processes would it affect? how would this decrease BP? what will be the effect
on the urine output?
– Beta1-blockers- what are the targets of the drug? ? which processes would it
affect? how would this decrease BP? what will be the effect on the urine
output?
– Renin inhibitors- what is the target of the drug? which process would it
affect? how would this decrease BP? what will be the effect on the urine
output?