98 Questions
What is the normal hematocrit value in men?
0.40
What is the normal hematocrit value in women?
0.36
What is the fraction of the blood composed of red blood cells?
40%
What causes the hematocrit to fall to as low as 0.10?
Severe anemia
What causes polycythemia, leading to a rise in hematocrit to 0.65?
Excessive production of red blood cells
What is the main difference between plasma and interstitial fluid?
$60 ext{%}$ protein content in plasma
Why does plasma have a slightly greater concentration of positively charged ions than interstitial fluid?
Due to the Donnan effect caused by plasma proteins
What separates plasma and interstitial fluid?
Highly permeable capillary membranes
What fills the semicircular ducts and the ampulla?
Endolymph
What structure has a small crest called a crista ampullaris?
Ampulla
What causes the cupula to bend to one side?
Inertia of the fluid in the semicircular ducts
How are the three semicircular ducts arranged?
At right angles to one another
What happens when a person's head rotates in any direction?
Fluid flows through the duct and ampulla, bending the cupula
What excites the sensory organ of the ampulla?
Flow of endolymph through the ampulla
What is located on top of the small crest called a crista ampullaris?
Cupula
What causes fluid to flow from the duct and through its ampulla?
Inertia of the fluid in the semicircular ducts
What is the main reason for the higher concentration of negatively charged ions (anions) in interstitial fluid compared with plasma?
Repulsion by the negative charges of plasma proteins
Why does the intracellular fluid contain only small quantities of sodium and chloride ions?
Selective permeability of the cell membrane
What determines the relative amounts of extracellular fluid distributed between the plasma and interstitial spaces?
Balance of hydrostatic and colloid osmotic forces across the capillary membranes
Why do intracellular compartments have a different distribution of fluids compared to extracellular compartments?
Mainly due to the osmotic effect of smaller solutes acting across the cell membrane
What makes cell membranes highly permeable to water but relatively impermeable to even small ions?
Selective permeability of the cell membrane
Which constituents have low concentrations in extracellular fluid but large amounts in intracellular fluid?
Potassium and phosphate ions
What is the primary factor determining the distribution of fluids between intra and extracellular compartments?
Osmotic effect of smaller solutes acting across the cell membrane
What causes the higher concentration of anions in interstitial fluid compared with plasma?
Repulsion by the negative charges of plasma proteins
What is the main purpose of the body fluid buffers?
To neutralize the acids produced by the body
How much H+ is ingested or produced each day by metabolism?
About 80 milliequivalents
Which buffer system is quantitatively the most important in the extracellular fluid?
Bicarbonate buffer system
What two ingredients make up the bicarbonate buffer system?
Carbon dioxide and water
Where is carbonic anhydrase enzyme especially abundant?
In the walls of lung alveoli
What reaction forms H2CO3 in the body?
$CO_2 + H_2O \rightarrow H_2CO_3$
Where does CO2 react with H2O to form H2CO3?
In the walls of lung alveoli
What would happen without buffering in relation to acids produced by the body each day?
$H^+$ concentration in body fluids would cause lethal changes
What happens to H2CO3 formation if carbonic anhydrase is not present?
$H_2CO_3$ formation decreases
What are the main components of the bicarbonate buffer system?
$NaHCO_3$ and $H_2CO_3$
What is the most common form of muscular dystrophy?
Duchenne muscular dystrophy
Which gene mutation is responsible for Duchenne muscular dystrophy?
Mutation in the gene encoding dystrophin
What effect does abnormal dystrophin have on muscle cells?
Increases membrane permeability to calcium
Which metabolic system is NOT important for understanding the limits of physical activity?
Krebs cycle system
What is the source of energy used to cause muscle contraction?
ATP
Which bonds in ATP are designated as high energy bonds and are removed successively to release energy?
~ between the second and third phosphate radicals
What happens when the first phosphate from ATP is removed?
ADP is formed
What happens when the second phosphate from ATP is removed?
$AMP$ is formed
Which of the following best describes a strong base?
A base that reacts rapidly and strongly with H+
What is the normal blood H+ concentration?
40 nEq/L
In the context of acid–base regulation, which molecule is considered a weak base?
HCO3−
What term refers to the excess removal of H+ from the body fluids?
Alkalosis
What is a characteristic of weak acids in terms of releasing H+?
They are less likely to dissociate their ions and release H+ with less vigor
What happens under extreme conditions to the blood H+ concentration?
It can vary from as low as 10 nEq/L to as high as 160 nEq/L without resulting in death
What is the main reason for referring to alkalosis as the excess removal of H+ from body fluids?
Because it involves the rapid removal of H+ from body fluids
What is a distinguishing factor between strong and weak acids?
Weak acids are more likely to dissociate their ions and release H+ with less vigor
What is the primary function of the kidneys in preventing the loss of bicarbonate in the urine?
Reabsorption of HCO3− and excretion of H+ through the process of H+ secretion
In alkalosis, what happens to the extracellular fluid H+ concentration?
It increases towards normal
What effect does acidosis have on the kidneys' secretion and reabsorption processes?
The kidneys secrete more H+ and reabsorb all the filtered HCO3−
What is the consequence of reducing the extracellular fluid H+ concentration back toward normal in alkalosis?
Addition of more H+ to the extracellular fluid
What is the role of secreted H+ in the process of reabsorbing filtered HCO3−?
React with filtered HCO3− to form H2CO3 before its reabsorption
What happens to the excretion of bicarbonate in alkalosis?
It increases
How do the kidneys respond in acidosis?
Secrete additional H+ and produce new bicarbonate to reduce extracellular fluid H+ concentration back toward normal
What reaction must occur to enable reabsorption of filtered bicarbonate?
HCO3− must react with a secreted H+ to form H2CO3 before it can be reabsorbed
What happens when a strong acid like HCl is added to the bicarbonate buffer solution?
The H+ released from the acid reacts with HCO3− to form H2CO3, leading to increased CO2 and H2O production
What occurs when a strong base like NaOH is added to the bicarbonate buffer solution?
The OH− from NaOH combines with H2CO3 to form additional HCO3−
What is the effect of adding a strong acid to the bicarbonate buffer solution on the production of CO2 and H2O?
Increased production of CO2 and H2O
What reaction forms additional HCO3− when a strong base like NaOH is added to the bicarbonate buffer solution?
NaOH + HCO3− → NaHCO3 + OH−
How does a strong acid like HCl affect the H+ concentration in the extracellular fluid?
Increases the H+ concentration
What is the result of a strong base like NaOH being added to the bicarbonate buffer solution?
Increases the concentration of HCO3−
How is the increased CO2 from strong acid addition eliminated from the extracellular fluid?
Greatly stimulates respiration, which eliminates the excess CO2
What does the weak dissociation of H2CO3 result in?
Extremely low H+ concentration
How does a strong base like NaOH affect the formation of additional HCO3−?
Forms additional HCO3−
How is increased CO2 eliminated from the extracellular fluid after strong acid addition?
Greatly stimulates respiration, which eliminates excess CO2
What is the net result of the decrease in H2CO3 concentration in the blood?
A tendency for CO2 levels in the blood to decrease
How is the rise in blood HCO3− concentration compensated for?
By decreased renal excretion of HCO3−
Why are proteins plentiful buffers in the body?
Because of their high concentrations in the cells
In what proportion does the pH of cells change in relation to extracellular fluid changes?
Directly proportional
What happens when a strong base like NaOH is added to the bicarbonate buffer solution?
It affects the formation of additional HCO3−
What occurs with the diffusion of H+ and HCO3− through the cell membrane?
Requires several hours to reach equilibrium with the extracellular fluid
Why does the decreased CO2 in the blood inhibit respiration?
As a result of decreased CO2 expiration rate
What is the primary purpose of the phosphocreatine system in muscle cells?
To provide instant energy for muscle contraction
In terms of energy content, how does the bond in phosphocreatine compare to that in ATP?
The bond in phosphocreatine has more energy than that in ATP
How long can the combined amounts of cell ATP and phosphocreatine provide maximal power for muscle contraction?
8-10 seconds
What is the main function of the glycogen-lactic acid system in muscle cells?
To provide energy by splitting stored glycogen into glucose
What is the immediate source of energy for muscle contraction during short bursts of maximal power?
Phosphocreatine system
What happens to phosphocreatine in order to release large amounts of energy?
It decomposes to creatine and a phosphate ion
Why is the amount of phosphocreatine important for muscle power?
It provides instant energy for muscle contraction
What happens when a hypertonic solution is added to the extracellular fluid?
The extracellular osmolarity increases, causing osmosis of water out of the cells and into the extracellular compartment.
What is the main effect of adding isotonic saline to the extracellular fluid compartment?
An increase in extracellular fluid
What occurs when a hypotonic solution is added to the extracellular fluid?
The osmolarity decreases, and some of the extracellular water diffuses into the cells until both have the same osmolarity.
Which solution is widely used for intravenous administration when people cannot ingest enough nutrition?
Glucose solutions
What is the effect of adding a hypertonic solution to the extracellular fluid on intracellular and extracellular volumes?
An increase in extracellular volume and a decrease in intracellular volume
Which type of solution causes a decrease in osmolarity when added to the extracellular fluid?
Hypotonic solution
What happens if a person cannot ingest enough nutrition?
Intravenous administration of glucose solutions may be used
What is the physiological effect of impairment of lung function on CO2 elimination?
Decreased CO2 elimination leading to a buildup of CO2 in the extracellular fluid and/or respiratory acidosis
How do the kidneys respond to metabolic acidosis?
By excreting acidic urine to reduce the amount of acid in extracellular fluid
What happens if more H+ is secreted than HCO3- is filtered by the kidneys?
There will be a net loss of acid from the extracellular fluid
What is the primary mechanism for removal of nonvolatile acids from the body?
Renal excretion
How are large amounts of HCO3- filtered continuously into the tubules used by the kidneys?
To remove base from the blood if excreted into the urine
What is a distinguishing feature of nonvolatile acids?
They are not H2CO3 and cannot be excreted by the lungs
What is the role of renal control in acid–base balance?
By excreting acidic or basic urine to regulate extracellular fluid pH
How does impairment of lung function affect the ability to respond to metabolic acidosis?
Prevents reductions in Pco2 that would normally occur by increased ventilation
Why does excreting acidic urine reduce the amount of acid in extracellular fluid?
It removes excess acid from extracellular fluid
Study Notes
Hematocrit Values
- Normal hematocrit value in men: 0.40-0.54
- Normal hematocrit value in women: 0.37-0.48
- Hematocrit is the fraction of the blood composed of red blood cells
Causes of Hematocrit Changes
- Hematocrit can fall to as low as 0.10 due to anemia or blood loss
- Polycythemia can lead to a rise in hematocrit to 0.65
Plasma and Interstitial Fluid
- Main difference between plasma and interstitial fluid: concentration of ions
- Plasma has a slightly greater concentration of positively charged ions than interstitial fluid
- Capillary wall separates plasma and interstitial fluid
Semicircular Ducts and Ampulla
- Semicircular ducts and ampulla are filled with endolymph
- Crista ampullaris is a small crest in the ampulla
- Cupula bends to one side due to the flow of endolymph
- Three semicircular ducts are arranged at right angles to each other
- When a person's head rotates, the fluid in the ducts lags behind, causing the cupula to bend
- The sensory organ of the ampulla is excited by the bending of the cupula
Body Fluid Compartments
- Intracellular fluid contains only small quantities of sodium and chloride ions
- Extracellular fluid is distributed between the plasma and interstitial spaces
- Cell membranes are highly permeable to water but relatively impermeable to ions
- Constituents with low concentrations in extracellular fluid but large amounts in intracellular fluid: potassium, magnesium, and phosphate
- The primary factor determining the distribution of fluids between intra and extracellular compartments is the concentration of ions
Body Fluid Buffers
- The main purpose of body fluid buffers is to maintain a stable pH
- 50-100 mmol of H+ is ingested or produced each day by metabolism
- The bicarbonate buffer system is the most important in the extracellular fluid
- The bicarbonate buffer system consists of carbonic acid (H2CO3) and bicarbonate ions (HCO3-)
- Carbonic anhydrase enzyme is especially abundant in red blood cells
- The reaction that forms H2CO3 in the body is: CO2 + H2O → H2CO3
- Without buffering, the concentration of H+ would increase, leading to acidosis
Muscular Dystrophy
- The most common form of muscular dystrophy is Duchenne muscular dystrophy
- Duchenne muscular dystrophy is caused by a mutation in the gene that codes for dystrophin
- Abnormal dystrophin leads to muscle cell degeneration and weakness
Muscle Contraction
- The source of energy used to cause muscle contraction is ATP
- The bonds in ATP that are designated as high energy bonds are the phosphate bonds
- When the first phosphate from ATP is removed, energy is released
- When the second phosphate from ATP is removed, more energy is released
Acid-Base Regulation
- A strong base is a compound that completely dissociates in water
- The normal blood H+ concentration is 0.00004 mmol/L
- Weak acids, such as bicarbonate, release H+ slowly
- Under extreme conditions, the blood H+ concentration can increase or decrease
- Alkalosis is characterized by an excess removal of H+ from the body fluids
- The kidneys play a crucial role in preventing the loss of bicarbonate in the urine
- In alkalosis, the extracellular fluid H+ concentration decreases
- In acidosis, the kidneys increase secretion and reabsorption of H+ and HCO3-
Test your knowledge of fluid compartments and ion concentrations with this quiz. Explore the differences in ion concentrations between interstitial fluid, plasma, and intracellular fluid.
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