The Fluid, Electrolyte and Acid-Base Balance (Pt. 2) Flashcards
What are the three main body fluid compartments that contain different concentrations of electrolytes and protein ions?
Blood plasma, interstitial fluid, and intracellular fluid
What is the main difference between blood plasma and interstitial fluid in terms of protein content?
Blood plasma contains many protein ions, while interstitial fluid contains only a few
Why does interstitial fluid have fewer proteins than blood plasma?
Because most capillary membranes are not permeable to proteins; only a few plasma proteins can leak out of blood vessels into the interstitial fluid
What physiological mechanism is created by the difference in protein concentration between blood plasma and interstitial fluid?
Blood colloid osmotic pressure (oncotic pressure)
True or False: Capillary membranes freely allow proteins to pass between blood plasma and interstitial fluid
False. Most capillary membranes are not permeable to proteins, with only a small amount of plasma proteins able to leak through
What is the relationship between protein concentration and blood colloid osmotic pressure?
The difference in protein concentration between blood plasma (high) and interstitial fluid (low) creates blood colloid osmotic pressure
What is the most abundant cation in extracellular fluid?
Sodium (Na⁺), accounting for 90% of extracellular cations
What is the normal blood concentration range for sodium?
136-148 mEq/L
What are the three main functions of sodium in the body?
- Fluid and electrolyte balance 2. Impulse transmission in neurons 3. Muscle contraction
What are the three hormones that control sodium levels?
- Aldosterone 2. Antidiuretic hormone (ADH) 3. Atrial natriuretic peptide (ANP)
What is hyponatremia?
Low blood sodium levels (<135 mEq/L)
What is hypernatremia?
High blood sodium levels (>148 mEq/L)
What does aldosterone do to sodium levels?
Increases sodium reabsorption in the kidneys
What happens when sodium levels are too high (hypernatremia)?
ANP is released to increase sodium excretion through the kidneys
What happens when sodium levels are too low (hyponatremia)?
ADH release stops, increasing water loss to restore sodium levels
Which organ is primarily responsible for regulating excess sodium?
The kidneys, through excretion or conservation
What is the main anion in extracellular fluid?
Chloride ions (Cl⁻)
What is the normal blood concentration range for chloride?
95–105 mEq/L
How does chloride move between compartments in the body?
It moves easily through leakage channels and antiporters in cell membranes.
What role does chloride play in maintaining anion balance?
It helps balance anions between fluid compartments, especially during the chloride shift related to carbon dioxide levels.
What important substance does chloride form in the stomach?
Hydrochloric acid (HCl)
Which hormones regulate chloride balance in body fluids?
Aldosterone and antidiuretic hormone (ADH)
How does sodium reabsorption affect chloride reabsorption?
Changes in sodium reabsorption influence chloride reabsorption through Na⁺–Cl⁻ symporters.
What is the most abundant cation in intracellular fluid?
Potassium ions (K⁺), with a concentration of 140 mEq/L.
What key roles does potassium play in the body?
Establishing resting membrane potential, repolarization of action potentials, maintaining fluid volume, and regulating pH.
What is the normal blood plasma concentration for potassium?
3.5–5.0 mEq/L.
Which hormone primarily regulates potassium levels in the blood?
Aldosterone.
What happens when blood plasma potassium levels are high?
More aldosterone is secreted, leading to increased potassium excretion by the kidneys.
What occurs when blood plasma potassium levels are low?
Aldosterone secretion decreases, resulting in less potassium excretion.
What condition is characterized by elevated potassium levels in the blood?
Hyperkalemia.
Why can abnormal potassium levels be dangerous?
Low or high potassium levels can disrupt nerve impulse conduction and potentially lead to conditions like ventricular fibrillation.
What is bicarbonate (HCO3−)?
A major plasma ion and key component of the body’s acid-base buffer system.
What is the normal concentration of bicarbonate in systemic arterial blood?
22–26 mEq/L.
What is the normal concentration of bicarbonate in systemic venous blood?
23–27 mEq/L.
How do the kidneys regulate bicarbonate levels?
By reabsorbing it when levels are low and excreting it in urine when levels are high.
What happens to bicarbonate levels in systemic capillaries?
Bicarbonate levels increase as CO2 from cells forms carbonic acid, which dissociates into H+ and HCO3−.
What happens to bicarbonate levels in pulmonary capillaries?
Bicarbonate levels decrease as CO2 is exhaled.
Where is bicarbonate primarily found in the body?
Mostly in extracellular fluid, with smaller amounts in intracellular fluid.
What is the role of chloride in bicarbonate balance?
Chloride exchanges with bicarbonate to help maintain ion balance in fluids.
What is the most abundant mineral in the body?
Calcium
What is the normal blood concentration range for calcium?
4.5-5.5 mEq/L
What percentage of calcium is found in bones and teeth?
98%
List four main functions of calcium in the body.
- Blood clotting 2. Neurotransmitter release 3. Muscle tone maintenance 4. Excitability of nerves and muscles
Which two hormones regulate calcium levels in plasma?
Parathyroid hormone (PTH) and calcitonin (CT)
What are the three main actions of PTH?
- Increases bone resorption to release calcium 2. Enhances calcium reabsorption in kidneys 3. Increases calcitriol production for calcium absorption from food
What is the role of calcitonin in calcium regulation?
It lowers blood calcium levels by:
- Inhibiting osteoclast activity
- Accelerating calcium deposition in bones
Where is calcium combined with phosphates?
In bones and teeth, forming a crystal lattice of mineral salts
What is calcitriol and what does it do?
It’s the active form of vitamin D that acts as a hormone and increases calcium absorption from food in the digestive system
In what form does phosphate primarily occur in the body?
As calcium phosphate salt
What is the normal intracellular fluid concentration of phosphate?
100 mEq/L
What is the normal blood concentration range for phosphate?
1.7-2.6 mEq/L
What percentage of phosphate is stored in bones and teeth?
85%
What is the main buffer form of phosphate in body fluids?
HPO4²⁻ (hydrogen phosphate)
List three organic molecules that phosphate binds to in the body.
- Lipids (forming phospholipids)
- Nucleic acids (DNA and RNA)
- ATP (adenosine triphosphate)
What three hormones regulate phosphate levels?
- Parathyroid hormone (PTH)
- Calcitriol
- Fibroblast growth factor 23 (FGF 23)
What are the effects of PTH on phosphate?
- Increases phosphate release from bones
- Inhibits phosphate reabsorption in kidneys
- Increases urinary excretion of phosphate
What is the role of calcitriol in phosphate regulation?
It promotes phosphate absorption from the digestive system
How does FGF 23 affect phosphate levels?
It decreases blood phosphate levels by:
- Increasing kidney excretion
- Decreasing absorption from digestive system
What type of ion is magnesium and where does it rank in abundance inside cells?
It’s an intracellular cation and is the 2nd most common.
How is magnesium distributed in the body (percentages)?
- 54% in bone matrix as magnesium salts
- 45% in intracellular fluid
- 1% in extracellular fluid
What is the normal intracellular fluid concentration of magnesium?
35 mEq/L
What is the normal blood concentration of magnesium?
1.3-2.1 mEq/L
What is magnesium’s role as a coenzyme?
It’s involved in carbohydrate and protein metabolism.
List four important functions of magnesium in the body.
- Neuromuscular activity
- Synaptic transmission
- Myocardial function
- Operation of sodium-potassium pump
What hormone requires magnesium for its secretion?
Parathyroid hormone (PTH).
Which organ regulates magnesium levels?
The kidneys, through controlling excretion rates.
List four factors that increase magnesium excretion by the kidneys.
- Hypercalcemia
- Hypermagnesemia
- Increases in extracellular fluid volume
- Decreases in PTH/acidosis
True or False: Most magnesium in the body is found in bone matrix.
True - 54% of magnesium is found in bone matrix as magnesium salts.
What is the normal pH range of arterial blood?
7.35 to 7.45
What are the three main mechanisms for maintaining acid-base balance?
- Buffer systems 2. Exhalation of carbon dioxide 3. Kidney excretion of H+
What is the function of buffer systems in acid-base balance?
They temporarily bind excess H+ ions to stabilize pH (but don’t remove H+ from the body)
How does breathing help regulate pH?
Increasing breathing rate and depth removes more CO2, reducing carbonic acid and raising blood pH
What effect do high-protein diets have on blood pH?
They tend to make blood more acidic due to increased acid production during metabolism
Which mechanism is the slowest but most effective at removing non-carbonic acids?
Kidney excretion of H+
Why is pH balance important for the body?
It’s essential for normal cellular function and proper protein structure/function
What do buffer systems do?
They stabilize pH by converting strong acids and bases into weak ones, preventing drastic pH changes.
What are buffer systems made of?
A weak acid and its salt, which acts as a weak base.
Why do strong acids and bases have a greater effect on pH than weak ones?
Strong acids and bases release or absorb H+ ions more readily, causing larger pH changes.
What are the main buffer systems in the body?
- Protein buffer system
- Carbonic acid–bicarbonate buffer system
- Phosphate buffer system
What is the most abundant buffer system in cells and plasma?
The protein buffer system.
How do proteins help in buffering pH?
They contain carboxyl groups (—COOH) that release H+ when pH rises, acting as acids.
What happens to free H+ in a buffered solution?
Free H+ can react with OH– (bases) to form water, neutralizing the solution.
What happens when pH falls (becomes more acidic)?
There are too many H+ ions in solution, and the amino group (NH₂) of proteins acts as a base by combining with excess H+ ions to form NH₃⁺
How does the amino group (NH₂) act as a buffer?
It acts as a base by absorbing H+ ions when the solution becomes too acidic, converting NH₂ to NH₃⁺
Why can proteins function as both acids and bases?
Because they contain:
- Amino groups (NH₂) that can accept H+ (act as base)
- Carboxyl groups (COOH) that can donate H+ (act as acid)
What role do amino acid side chains play in buffering?
Some side chains can also act as buffers by releasing or absorbing H+ ions, depending on their chemical nature
What makes proteins effective buffers?
Their dual ability to either:
- Give up H+ ions when solution is too basic
- Accept H+ ions when solution is too acidic
What is the chemical formula for the reaction when pH falls?
NH₂—C—COOH + H⁺ → ⁺NH₃—C—COOH
What is the main purpose of the protein buffer system?
To prevent large, rapid changes in pH by maintaining stable conditions in cells and blood through H+ regulation
What happens to carbon dioxide (CO2) in blood capillaries?
CO2 enters red blood cells and combines with water (H2O) to form carbonic acid (H2CO3).
What does carbonic acid (H2CO3) dissociate into?
It dissociates into hydrogen ions (H⁺) and bicarbonate ions (HCO3⁻).
What happens to oxyhemoglobin (Hb–O2) in red blood cells?
It releases oxygen (O2) to tissues and becomes deoxyhemoglobin (Hb).
How does deoxyhemoglobin act as a buffer?
Deoxyhemoglobin binds to free hydrogen ions (H⁺), forming Hb–H, which helps stabilize pH.
What’s the overall role of hemoglobin in red blood cells?
Hemoglobin acts as a buffer by picking up excess hydrogen ions from the blood.
What is the carbonic acid–bicarbonate buffer system?
It’s a system that uses bicarbonate ions (HCO3⁻) as a weak base and carbonic acid (H2CO3) as a weak acid to maintain pH balance.
What role does bicarbonate (HCO3⁻) play in the buffer system?
HCO3⁻ acts as a weak base that removes excess H+ ions when pH is low.
What happens when bicarbonate (HCO3⁻) binds with hydrogen ions (H+)?
It forms carbonic acid (H2CO3).
What does carbonic acid (H2CO3) break down into?
It breaks down into water (H2O) and carbon dioxide (CO2).
How is carbon dioxide (CO2) handled in the body?
CO2 is exhaled from the lungs.
What do the kidneys do in relation to the bicarbonate buffer system?
The kidneys synthesize and reabsorb bicarbonate (HCO3⁻) to maintain the buffer system.
What happens in the carbonic acid–bicarbonate buffer system if pH rises?
Carbonic acid (H2CO3) acts as a weak acid and releases H+ ions, lowering the pH.
What does carbonic acid (H2CO3) break down into?
It dissociates into hydrogen ions (H⁺) and bicarbonate ions (HCO3⁻).
What does the carbonic acid–bicarbonate system depend on?
It relies on carbon dioxide (CO2) and water (H2O) combining to form carbonic acid (H2CO3).
Why can this buffer system fail during respiratory problems?
If there is an excess or shortage of CO2, the system cannot regulate pH properly because it depends on CO2 to form carbonic acid.
What is the role of carbon dioxide (CO2) in this buffer system?
CO2 combines with water to create the carbonic acid needed for pH regulation.
What is the phosphate buffer system?
A pH regulation system that works similarly to the carbonic acid-bicarbonate system, using phosphate ions to maintain pH balance.
What are the two main components of the phosphate buffer system?
- Dihydrogen phosphate (H2PO4⁻) - acts as a weak acid
- Monohydrogen phosphate (HPO42⁻) - acts as a weak base
Where are phosphates primarily found in the body?
- Major anions in intracellular fluid (inside cells)
Minor anions in extracellular fluid (outside cells)
How does dihydrogen phosphate (H2PO4⁻) act as a buffer?
It acts as a weak acid and can neutralize strong bases (OH⁻) by converting them to water and monohydrogen phosphate.
What is the chemical equation for the phosphate buffer neutralizing a strong base?
OH⁻ + H2PO4⁻ → H2O + HPO42−
What is the main function of the phosphate buffer system?
To stabilize pH changes by converting strong acids and bases into weaker ones, especially in intracellular fluid.
What role does the monohydrogen phosphate ion (HPO42⁻) play in the phosphate buffer system?
It acts as a weak base that buffers hydrogen ions (H⁺) released by strong acids like hydrochloric acid (HCl).
What is formed when H⁺ combines with HPO42⁻?
Dihydrogen phosphate (H2PO4⁻) is formed.
Where does the phosphate buffer system primarily regulate pH?
It primarily regulates pH in the intracellular fluid (cytosol) of cells.
How does the phosphate buffer system function in urine?
In kidney tubules, excess H⁺ combines with HPO42⁻ to form H2PO4⁻, which is excreted in the urine.
What is one way the kidneys help maintain blood pH?
By excreting H⁺ ions in the urine as part of the phosphate buffer system.
What is the overall function of the phosphate buffer system?
To buffer acids in the cytosol and urine, helping to regulate and maintain pH balance.
How does increased CO2 affect pH in body fluids?
It raises H⁺ concentration, making the pH lower (more acidic).
What happens when CO2 is exhaled?
CO2 mixes with water to form carbonic acid (H2CO3).
What is the negative feedback loop for pH regulation?
A system where breathing rate and depth automatically adjust to maintain blood pH balance by controlling CO2 levels.
What happens when blood becomes too acidic?
- Receptors detect increased acidity 2. Breathing becomes faster and deeper 3. More CO2 is exhaled 4. Blood pH returns to normal
What happens when blood becomes too basic?
- Respiratory center is inhibited 2. Breathing becomes slower and shallower 3. CO2 builds up in blood 4. Blood pH returns to normal
Which receptors detect changes in blood pH?
Central chemoreceptors in the medulla oblongata
Peripheral chemoreceptors in aortic and carotid bodies
What role does the diaphragm play in pH regulation?
It contracts more forcefully and frequently when blood is acidic to help exhale more CO2.
How does CO2 affect blood pH?
More CO2 = more acidic (lower pH)
Less CO2 = more basic (higher pH)
What is the main job of kidneys in pH balance?
To remove excess acids from the body by filtering them into urine and maintaining blood pH balance.
What are the two main parts of the kidney that help control pH?
- Proximal Convoluted Tubule (PCT) 2. Collecting Duct
How does the PCT help control acid levels?
It trades sodium (Na⁺) for hydrogen (H⁺) - takes in sodium and pushes out acid.
What are intercalated cells and what do they do?
Special cells in the collecting duct that:
- Have pumps to push out acid
- Can make urine very acidic
- Help return bicarbonate to blood
Why is kidney pH control so important?
Without it, acids would build up in blood, which can be deadly. Healthy kidneys constantly adjust acid levels to maintain health.
How acidic can the kidneys make urine compared to blood?
Up to 1000 times more acidic than blood.
What happens if kidney pH control fails?
Acids build up in the blood, causing severe acid-base imbalances that can be life-threatening.
What causes respiratory disorders?
Changes in CO2 levels (partial pressures) in systemic arterial blood.
What causes metabolic disorders?
Changes in bicarbonate (HCO3⁻) concentrations in systemic arterial blood.
Explain respiratory acidosis:
- Too much CO2 retained in blood
CO2 + H2O forms H2CO3 (carbonic acid)
Leads to excess H⁺ (acid)
Blood pH drops
Common causes: poor breathing, lung diseases
Explain respiratory alkalosis:
- Too much CO2 lost through breathing
Caused by hyperventilation
Less CO2 means less acid formation
Blood pH rises
Common causes: anxiety, high altitude
Explain metabolic acidosis:
- Loss of bicarbonate (HCO3⁻) in blood
Less HCO3⁻ available to buffer acids
Blood pH drops
Common causes: severe diarrhea, kidney failure, diabetes
Explain metabolic alkalosis:
- Excess bicarbonate (HCO3⁻) in blood
Too much acid being buffered
Blood pH rises
Common causes: vomiting, excess antacids, dehydration
What is the normal blood pH range?
7.35 - 7.45
What are the two main chemical players in acid-base balance?
- CO2 (acts as acid when dissolved)
HCO3⁻ (acts as base to neutralize acids)
What are the key differences in fluid distribution between infants and adults?
Infants: Higher total body water (65-80%), Larger extracellular fluid volume. Adults: Lower total body water (about 50%), More stable fluid distribution.
What are the five main factors that influence fluid distribution?
- Metabolic rate 2. Functional development of the kidneys 3. Body surface area 4. Breathing rate 5. Ion concentrations
How does metabolic rate affect fluid balance in infants vs. adults?
Infants: Higher metabolic rate, faster fluid turnover. Adults: More stable metabolic rate, steadier fluid balance.
How do kidneys differ between infants and adults?
Infants: Kidneys still developing, less efficient regulation. Adults: Fully developed kidneys, better fluid and electrolyte control.
Why is body surface area important for fluid balance?
Infants: Larger surface area relative to body mass = more fluid loss through skin. Adults: More proportionate surface area = more stable fluid loss.
What are the common fluid/electrolyte problems in older adults?
- Dehydration 2. Hypernatremia (high sodium) 3. Hypokalemia (low potassium) 4. Acidosis
Why are older adults more susceptible to fluid imbalances?
Declining kidney function, Reduced thirst sensation, Multiple medications, Chronic health conditions, Impaired ability to maintain balance.
How does breathing rate affect fluid balance?
Infants: Faster breathing rate = more fluid loss through respiration. Adults: More stable breathing rate = more consistent fluid loss.
