Answer to Question #330380 in Human Anatomy and Physiology for Sonia

Question

1. Define the Glomerular filtration rate (GFR) and state what are normal values
2. What are the important factors that determine GFR?
3. Define alkalosis, pH and carbon dioxide and bicarbonate values
4. Use the Davenport diagram to explain alkalotic disorders and give examples of the primary disorders- metabolic and respiratory 

Answer 1

1)Glomerular filtration rate

    

Glomerular filtration rate (GFR) is a test used to check how well the kidneys are working. Specifically, it estimates how much blood passes through the glomeruli each minute. Glomeruli are the tiny filters in the kidneys that filter waste from the blood.

According to the National Kidney Foundation, normal results range from 90 to 120 mL/min/1.73 m2. Older people will have lower than normal GFR levels because GFR decreases with age. Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples

2)How the Test is Performed

A blood sample is needed.

The blood sample is sent to a lab. There, the creatinine level in the blood sample is tested. Creatinine is a chemical waste product of creatine. Creatine is a chemical the body makes to supply energy, mainly to muscles.

The lab specialist combines your blood creatinine level with several other factors to estimate your GFR. Different formulas are used for adults and children. The formula includes some or all of the following:

• Age
• Blood creatinine measurement
• Ethnicity
• Sex
• Height
• Weight

According to the National Kidney Foundation, normal results range from 90 to 120 mL/min/1.73 m2. Older people will have lower than normal GFR levels because GFR decreases with age. Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples.

3)Alkalosis    

Alkalosis is a condition in which the body fluids have excess base (alkali). This is the opposite of excess acid (acidosis).

Causes

The kidneys and lungs maintain the proper balance (proper pH level) of chemicals called acids and bases in the body. Decreased carbon dioxide (an acid) level or increased bicarbonate (a base) level makes the body too alkaline, a condition called alkalosis. There are different types of alkalosis. These are described below.

Respiratory alkalosis is caused by a low carbon dioxide level in the blood. This can be due to:

• Fever
• Being at a high altitude
• Lack of oxygen
• Liver disease
• Lung disease, which causes you to breathe faster (hyperventilate)
• Aspirin poisoning

Metabolic alkalosis is caused by too much bicarbonate in the blood. It can also occur due to certain kidney diseases.

Hypochloremic alkalosis is caused by an extreme lack or loss of chloride, such as from prolonged vomiting.

Hypokalemic alkalosis is caused by the kidneys' response to an extreme lack or loss of potassium. This can occur from taking certain water pills (diuretics).

Compensated alkalosis occurs when the body returns the acid-base balance to near normal in cases of alkalosis, but bicarbonate and carbon dioxide levels remain abnormal.

4)

DAVENPORT DIAGRAMS:

• Davenport diagrams are graphic displays of acid-base states.
• They illustrate the dynamic relationships between arterial blood pH, bicarbonate and non-bicarbonate buffers, and the partial pressure of carbon dioxide.
• An isopleth represents all possible combinations of bicarbonate and pH values at a given carbon dioxide partial pressure.

Graph Features:

• The x-axis tracks pH; the healthy homeostatic arterial blood value = 7.4
• Values less than this reflect acidosis; values higher reflect alkalosis.
• The y-axis tracks bicarbonate concentration; the healthy homeostatic value 24 millimolar.
• Recall that, as bicarbonate concentration increases, pH becomes more alkaline.
• Isopleth for a partial pressure of carbon dioxide of 40 mmHg.
• A straight line to represent the combination of all non-bicarbonate buffer titration curves.

Graph Features:

• The x-axis tracks pH; the healthy homeostatic arterial blood value = 7.4
• Values less than this reflect acidosis; values higher reflect alkalosis.
• The y-axis tracks bicarbonate concentration; the healthy homeostatic value 24 millimolar.
• Recall that, as bicarbonate concentration increases, pH becomes more alkaline.
• Isopleth for a partial pressure of carbon dioxide of 40 mmHg.
• A straight line to represent the combination of all non-bicarbonate buffer titration curves.

Disorders that cause the blood to become more acidic.

• Metabolic acidosis occurs when the reduction in bicarbonate concentration lowers the pH.
• Notice that, because this is a non-respiratory disorder, PaCO2 is unaffected.
• Respiratory acidosis occurs when the lungs retain excess carbon dioxide, so the partial pressure of carbon dioxide is elevated above normal, which lowers the pH. - Recall that respiratory acidosis produces an elevated bicarbonate concentration, which is reflected in our graph.

Disorders that cause the blood to become alkalotic (aka, basic).

• Metabolic alkalosis occurs when bicarbonate concentration is elevated.
• As in metabolic acidosis, the PaCO2 remains on the 40 mmHg isopleth.
• Respiratory alkalosis occurs when the lungs release too much carbon dioxide
• Lowers the PaCO2 and increases pH.

Compensatory Mechanisms

• The lungs and kidneys respond to acid-base disorders via compensatory mechanisms that bring pH back to normal.

When metabolic acidosis triggers release of carbon dioxide from the lungs, PaCO2 falls and pH increases.

• Thus, our point of interest lies lower and to the right than on our original graph.
• Shaded area represents all possible outcomes of partial compensation for metabolic acidosis; the extent of the original disturbance and the magnitude of compensation determine the specific blood outcome.

When respiratory acidosis triggers increased renal excretion of hydrogen ions and conservation of bicarbonate, pH increases.

• The partial pressure of carbon dioxide remains elevated until the source of the disorder is treated, because the lungs are unable to expel CO2.

When metabolic alkalosis triggers respiratory and renal mechanisms to conserve hydrogen ions, pH lowers.

• However, because the respiratory component of compensation requires conservation of carbon dioxide, its partial pressure remains elevated.

When respiratory alkalosis triggers renal mechanisms that conserve hydrogen ions, pH lowers.

• But, until the source of the disorder is treated, the partial pressure of carbon dioxide will remain below 40 mmHg.

Perfect Compensation - Blood pH returned to 7.4

• The blood profile end-states reflect both the original disorders and the compensatory mechanisms.

If the original disorder was metabolic acidosis or respiratory alkalosis, both the bicarbonate concentration and the partial pressure of carbon are reduced (isohydric hypocapnia).

• In the case of metabolic acidosis, this new state is accounted for by:
• The cause of the disorder, which was a low concentration of bicarbonate
• relative to hydrogen ions.
• The respiratory component of compensation, which required increased release
• of carbon dioxide.
• In the case of respiratory alkalosis, this new state is accounted for by:
• The cause of the disorder, which was the excessive release of carbon dioxide, and,
• Renal compensatory mechanisms that excreted bicarbonate.

If the original disorder was respiratory acidosis or metabolic alkalosis, both the bicarbonate concentration and the partial pressure of carbon dioxide are elevated above normal (isohydric hypercapnia).

• In the case of respiratory acidosis, this is state is accounted for by:
• The cause of the disorder, which was over-retention of carbon dioxide, and,
• Renal compensatory mechanisms that conserved bicarbonate.
• In the case of metabolic alkalosis, this state is accounted for by:
• The cause of the disorder, which was an increased bicarbonate to hydrogen ion ratio
• The respiratory component of compensation, which required increased carbon
• dioxide retention in the lungs.

Compound Disturbances:

• If both metabolic and respiratory acidosis are in play, pH is reduced more so than if just one disorder was influencing pH; the shaded area shows the range of possible values that could result.
• When alkalosis results from both metabolic and respiratory origins, pH is elevated more so than if only one disorder was present.
• Be aware that while this information can tell us if there are one or two sources of the pH disturbance, it cannot tell us which preceded the other.