WGU D236 pathophysiology OA Exam Study Guide 2025
Questions and Answers
What is Starling's Law of Capillary forces?
How does this explain why a nutritionally deficient child would have edema?
- Starling's Law describes how fluids move across the capillary membrane. There are two major
opposing forces that act to balance each other, hydrostatic pressure (pushing water out of the
capillaries) and osmotic pressure (including oncontic pressure, which pushes fluid into the capillaries).
Both electrolytes and proteins (oncontic pressure) in the blood affect osmotic pressure, high
electrolyte and protein concentrations in the blood would cause water to leave the cells and
interstitial space and enter the blood stream to dilute the high concentrations.
On, the other hand, low electrolyte and protein concentrations (as seen in a nutritionally deficient
child) would cause water to leave the capillaries and enter the cells and interstitial fluid which can lead
to edema.
,How does the RAAS (Renin-Angiotensin-Aldosterone System) result in increased blood volume and
increased blood pressure?
- A drop in blood pressure is sensed by the kidneys by low perfusion, which in turn begins to
secrete renin.
Renin then triggers the liver to produce angiotensinogen, which is converted to Angiotensin I in the
lungs and then angiotensin II by the enzyme
Angiotensin-converting enzyme (ACE). Angiotensin II stimulates peripheral arterial vasoconstriction
which raises BP.
Angiotensin II is also stimulating the adrenal gland to release aldosterone, which acts to increase
sodium and water reabsorption increasing blood volume, while also increased potassium secretion in
urine.
How can hyperkalemia lead to cardiac arrest?
- Normal levels of potassium are between 3.5 and 5.2 mEq/dL. Hyperkalemia refers to
potassium levels higher that 5.2 mEq/dL.
,A major function of potassium is to conduct nerve impulses in muscles. Too low and muscle weakness
occurs and too much can cause muscle spasms.
This is especially dangerous in the heart muscle and an irregular heartbeat can cause a heart attack
The body uses the Protein Buffering System, Phosphate Buffering System, and Carbonic Acid-
Bicarbonate System to regulate and maintain homeostatic pH, what is the consequence of a pH
imbalance
- Proteins contain many acidic and basic group that can be affected by pH changes. Any
increase or decrease in blood pH can alter the structure of the protein (denature), thereby affecting its
function as well
Describe the laboratory findings associated with metabolic acidosis, metabolic alkalosis, respiratory
acidosis and respiratory alkalosis. (ie relative pH and CO2 levels).
- Normal ABGs (Arterial Blood Gases) Blood pH: 7.35-7.45 PCO2: 35-45 mm Hg PO2: 90-100 mm
Hg HCO3-: 22-26 mEq/L SaO2: 95-100%
Respiratory acidosis and alkalosis are marked by changes in PCO2. Higher = acidosis and lower =
alkalosis
, Metabolic acidosis and alkalosis are caused by something other than abnormal CO2 levels. This could
include toxicity, diabetes, renal failure or excessive GI losses.
Here are the rules to follow to determine if is respiratory or metabolic in nature. -If pH and PCO2 are
moving in opposite directions, then it is the pCO2 levels that are causing the imbalance and it is
respiratory in nature.
-If PCO2 is normal or is moving in the same direction as the pH, then the imbalance is metabolic in
nature.
The anion gap is the difference between measured cations (Na+ and K+) and measured anions (Cl- and
HCO3-), this calculation can be useful in determining the cause of metabolic acidosis.
Why would an increased anion gap be observed in diabetic ketoacidosis or lactic acidosis?
- The anion gap is the calculation of unmeasured anions in the blood.
Lactic acid and ketones both lead to the production of unmeasured anions, which remove HCO3- (a
measured anion) due to buffering of the excess H+ and therefore leads to an increase in the AG.
Questions and Answers
What is Starling's Law of Capillary forces?
How does this explain why a nutritionally deficient child would have edema?
- Starling's Law describes how fluids move across the capillary membrane. There are two major
opposing forces that act to balance each other, hydrostatic pressure (pushing water out of the
capillaries) and osmotic pressure (including oncontic pressure, which pushes fluid into the capillaries).
Both electrolytes and proteins (oncontic pressure) in the blood affect osmotic pressure, high
electrolyte and protein concentrations in the blood would cause water to leave the cells and
interstitial space and enter the blood stream to dilute the high concentrations.
On, the other hand, low electrolyte and protein concentrations (as seen in a nutritionally deficient
child) would cause water to leave the capillaries and enter the cells and interstitial fluid which can lead
to edema.
,How does the RAAS (Renin-Angiotensin-Aldosterone System) result in increased blood volume and
increased blood pressure?
- A drop in blood pressure is sensed by the kidneys by low perfusion, which in turn begins to
secrete renin.
Renin then triggers the liver to produce angiotensinogen, which is converted to Angiotensin I in the
lungs and then angiotensin II by the enzyme
Angiotensin-converting enzyme (ACE). Angiotensin II stimulates peripheral arterial vasoconstriction
which raises BP.
Angiotensin II is also stimulating the adrenal gland to release aldosterone, which acts to increase
sodium and water reabsorption increasing blood volume, while also increased potassium secretion in
urine.
How can hyperkalemia lead to cardiac arrest?
- Normal levels of potassium are between 3.5 and 5.2 mEq/dL. Hyperkalemia refers to
potassium levels higher that 5.2 mEq/dL.
,A major function of potassium is to conduct nerve impulses in muscles. Too low and muscle weakness
occurs and too much can cause muscle spasms.
This is especially dangerous in the heart muscle and an irregular heartbeat can cause a heart attack
The body uses the Protein Buffering System, Phosphate Buffering System, and Carbonic Acid-
Bicarbonate System to regulate and maintain homeostatic pH, what is the consequence of a pH
imbalance
- Proteins contain many acidic and basic group that can be affected by pH changes. Any
increase or decrease in blood pH can alter the structure of the protein (denature), thereby affecting its
function as well
Describe the laboratory findings associated with metabolic acidosis, metabolic alkalosis, respiratory
acidosis and respiratory alkalosis. (ie relative pH and CO2 levels).
- Normal ABGs (Arterial Blood Gases) Blood pH: 7.35-7.45 PCO2: 35-45 mm Hg PO2: 90-100 mm
Hg HCO3-: 22-26 mEq/L SaO2: 95-100%
Respiratory acidosis and alkalosis are marked by changes in PCO2. Higher = acidosis and lower =
alkalosis
, Metabolic acidosis and alkalosis are caused by something other than abnormal CO2 levels. This could
include toxicity, diabetes, renal failure or excessive GI losses.
Here are the rules to follow to determine if is respiratory or metabolic in nature. -If pH and PCO2 are
moving in opposite directions, then it is the pCO2 levels that are causing the imbalance and it is
respiratory in nature.
-If PCO2 is normal or is moving in the same direction as the pH, then the imbalance is metabolic in
nature.
The anion gap is the difference between measured cations (Na+ and K+) and measured anions (Cl- and
HCO3-), this calculation can be useful in determining the cause of metabolic acidosis.
Why would an increased anion gap be observed in diabetic ketoacidosis or lactic acidosis?
- The anion gap is the calculation of unmeasured anions in the blood.
Lactic acid and ketones both lead to the production of unmeasured anions, which remove HCO3- (a
measured anion) due to buffering of the excess H+ and therefore leads to an increase in the AG.
