Chapter 24: Fluid, Electrolyte, and Acid-Base Balance

Why can the kidneys neutralize more acid or base than any other buffer in the human body?

Only the kidneys actually expel H+ from the body.

If a local imbalance between the intracellular and extracellular fluid occurs, water movement called -- restores the balance. This depends on the relative concentration of solutes in each compartment.

Osmosis

Match each type of water loss with its description.

Insensible water loss: water loss through the breath and cutaneous transpiration. Obligatory water loss: water loss through minimal urine formation; expired air; cutaneous transpiration; fecal moisture. Sensible water loss: water loss through urine and visible sweating.

Match each fluid compartment with the percentage of the body water that it contains.

Intracellular fluid (ICF): 65% Tissue (interstitial) fluid: 25% Blood plasma and lymph: 8% Transcellular fluid: 2%

Anthony is really thirsty after mowing his lawn in the hot sun, so he drinks a large glass of water. How long will it take for long-term thirst satitation responses to take effect?

30 minutes.

Which of the following would be considered a normal pH value for arterial blood?

7.4

Which of the following has the largest effect on plasma sodium concentration?

ADH

Most magnesium is found in intracellular fluid complexed with --.

ATP

Examples of a fluid state imbalance.

Abnormal distribution such as in edema. Abnormal volume such as in hemorrhage. Abnormal concentration such as in hypotonic hypovolemia.

A tissue fluid pH below 7.35 is defined as a state of --.

Acidosis

Which regulate sodium homeostasis?

Aldosterone Antidiuretic hormone Natriuretic peptides

Respiratory -- results from hyperventilation, in which CO2 is eliminated faster than it is produced.

Alkalosis

Which statements are true concerning the protein buffer system?

Amino groups (-NH2) bind buffer decreases in pH. The protein buffer system is especially important in the ICF. Carboxyl groups (-COOH) release H+ and buffer increases in pH.

A person is in a state of fluid -- when daily gains and losses are equal. We typically gain and lose about 2,500 mL/day.

Balance

-- systems are composed of a weak acid and a weak base.

Buffer

Which is a cation that lends strength to the skeleton, activates muscle contraction, serves as a second messenger for some hormones and neurotransmitters, and is an essential factor in blood clotting?

Calcium

Which of the following are means by which water can move from one fluid compartment to another?

Capillary filtration Osmosis

List the components of transcellular fluid.

Cebrebrospinal, synovial, peritoneal, pleural, and pericardial fluids. Vitreous and aqueous humors of the eye. Bile and fluid in the digestive, urinary, and respiratory tracts.

What are possible causes of hypernatremia?

Edema Water retention Hypertension

True or False: during dehydration, the kidneys restore blood volume by the formation of metabolic water.

False

True or False: most of the water (65%) is found in the extracellular compartemnt.

False

Which statements are true regarding acid-base imbalances?

Fluid imbalances can cause pH imbalances. Electrolyte imbalances can cause pH imbalances. pH imbalances can cause electrolyte imbalances.

Which of the following are possible causes of hypokalemia?

Heavy sweating, chronic vomiting or diarrhea. Aldosterone hypersecretion. Alkalosis. Excessive use of laxatives.

The pH of a solution is determined solely by the concentration of which ion?

Hydrogen

A plasma concentration of calcium greater than 5.8 mEq/L is called --.

Hypercalcemia

The condition called -- is a dangerously high plasma potassium conentration greater than 5.5 mEq/L.

Hyperkalemia

Which are important functions of sodium?

It is involved in generating body heat via the Na-K pump. It participates in cotransport of glucose, K+ and Ca+. It participates in muscle and nerve depolarization.

Match the pH disorder with its cause.

Metabolic acidosis: excess production of organic acids i.e. diabetes mellitus and starvation; hyperkalemia; chronic diarrhea; excessive alcohol consumption; aspirin; laxatives. Metabolic alkalosis: rare but can result from chronic vomiting; overuse of antacids; aldosterone hypersecretion. Respiratory acidosis: hypoventilation; apnea. Respiratory alkalosis: hyperventilation due to pain or emotions such as anxiety.

-- acidosis can result from increased production of organic acids, such as lactic acid in anaerobic fermentation and ketone bodies in alcoholism and diabetes mellitus.

Metabolic.

Which are fast-acting stimuli that cause a temporary, short-term of thirst?

Moistening the mouth. Cooling the mouth. Distension of the stomach.

What are possible effects of hypokalemia?

Neurons become hyperpolarized and are less excitable. Electrical activity of the heart becomes irregular. Reflexes may become depressed.

Match the type of fluid replacement with the ideal case in which it could be used.

Normal saline isotonic (0.9%): patients with extensive blood loss. Ringer's lactate solution: patients with acidosis. Potassium chloride: patients with alkalosis (with no renal failure) and close monitoring of blood pH. Plasma volume expanders (i.e. mannitol): patients with seizures or coma (in order to combat hypotonic hydration). Isotonic 5% dextrose: patients who cannot eat (for example after severe trauma).

Which is the same in the ICF and in the blood plasma?

Osmolarity

Fluid intake is governed by thirst and it is regulated by a group of hypothalamic neurons called --, which respond to angiotensin II and to rising osmolarity of the ECF.

Osmoreceptors

Which triggers the release of ADH?

Osmoreceptors detect the increase in osmotic pressure of body fluids and signal the posterior pituitary.

A pH below 6.8 or above 8.0 is which of the following?

Quickly fatal

Which are effects of dehydration?

Reduced salivation. Increased blood osmolarity. Reduced blood pressure.

A buffer can be generally defined as a mechanism that does which of the following?

Resists changes in pH.

-- acidosis occurs in hypoventilation, when carbon dioxide accumulates in the ECF and lowers its pH.

Respiratory

The addition of CO2 to the body fluids raises H+ concentration and lowers pH, while the removal of CO2 has the opposite effect. This the basis for the strong buffering capacity of which system?

Respiratory

Prolonged, heavy work increases which of the following?

Respiratory loss Perspiration

Which physiological buffer system exerts an effect within a few minutes but cannot alter the pH as much as the urinary system?

Respiratory system

Which of the following are functions of chloride ions?

They are important in osmotic balance. They play a major tole in the regulation of body pH. They contribute to formation of stomach acid. They participate in the chloride shift in that accompanies carbon dioxide loading and unloading.

Which is an important function of electrolytes in the ECF?

They control the movement of water between fluid compartments.

True or False: a newborn baby's weight is as much as 75% water, whereas obese and elderly people's weight is as little as 45% water.

True

True or False: in cases of volume depletion, total body water declines but fluid osmolarity is normal.

True

As compared to hydroxide (OH-), bicarbonate (HCO3-) binds a relatively small amount of the available H+ and therefore has less of an effect on pH. Because of this, bicarbonate is classified as?

Weak base

Slight deviations from the body's normal -- range can shut down metabolic pathways as well as alter the structure and function of other macromolecules. Buffer systems help to avoid this.

pH

Using this figure as a guide, order the events during neutralization of hydrogen ions in the kidney from the moment H2CO3 forms until HCO3- returns to blood. Begin with the formation of H2CO3 in the blood.

1. H+ in blood reacts with HCO3- to form H2CO3. 2. H2CO3 decomposes into H2O and CO2, which enter the tubule cell. 3. Tubule cells contain CO2 from blood, and tubular fluid. 4. CAH combines H2O and CO2 to re-form H2CO3. 5. H2CO3 ionizes to form HCO3- (which returns to the blood) and H+.

The most important buffer system in the blood is a solution of carbonic acid and -- ions.

Bicarbonate

Cells maintain a very low intracellular calcium concentration to avoid crystallization of calcium phosphate. Which mechanisms maintain intracellular calcium concentrations low?

Cells sequester Ca2+ in the smooth E.R. and release it only when needed. Cells actively pump Ca2+. Cells often have a protein called calsequestrin, which binds the stored Ca2+ and keeps it chemically unreactive.

Which factors can lead to volume depletion (hypovolemia), in which proportionate amounts of water and sodium are lost?

Chronic vomiting Diarrhea Hemorrhage

In -- transpiration, water diffuses through the epidermis and evaporates.

Cutaenous

Which term is used to refer to the ions that participate in important metabolic and physiological processes?

Electrolytes

Match the steroid hormones below with their effects on Na+ homeostasis.

Estrogen: mimics the effect of aldosterone and causes women to retain water during pregnancy and part of the menstrual cycle. Progesterone: reduce sodium reabsorption and has a diuretic effect. Glucocorticoid: promotes sodium reabsorption and edema.

The following electrolyte imbalances may all be caused by acidosis. Match each type of imbalance to the explanation of how it may be caused by acidosis.

Hyperkalemia: H+ diffuses into cells and displaces K+ (as K+ leaves the ICF, K+ concentration in the ECF rises). Hypochloremia: More Cl- is excreted as NH4Cl to buffer the excess acid in the renal tubules, leaving less Cl- in the ECF. Hypercalcemia: Acidosis causes more Ca2+ to bind to plasma protein and citrate ions, lowering the concentration of free, ionized Ca2+.

A plasma concentration of chloride less than 95 mEq/L is called -- and it is usually a side effect of hyponatremia.

Hypochloremia

The potassium imbalance known as -- is a plasma concentration of potassium less than 3.5 mEq/L.

Hypokalemia

Which are types of fluid deficiency?

Hypovolemia Dehydration

Match each form of fluid imbalance to its description.

Hypovolemia: total body water is reduced; ECF remains isotonic. Dehydration: total body water is reduced; ECF becomes hypertonic. Volume Excess: total body water is elevated; ECF remains isotonic. Hypotomic Hydration: total body water is elevated; ECF becomes hypotonic.

Which hormone plays a major role in calcium homeostasis?

Parathyroid hormone (PTH)

Which ions are important buffers that help stabilize the pH of body fluids?

Phosphate

A -- buffer is a system that stabilizes pH by controlling the body's output of acids, bases, or CO2 (i.e., the respiratory or urinary system).

Physiological

Which of the following can cause fluid sequestration?

Pleural effusion. Hemorrhage.

Imbalances in which ion are the most dangerous of all electrolyte imbalances?

Potassium

Which ion is the most abundant cation of the intracellular fluid and has the greatest impact on intracellular osmolarity and cell volume?

Potassium

Which statements are true regarding potassium homeostasis?

Potassium homeostasis is closely linked to that of sodium. Aldosterone stimulates renal secretion of potassium.

Rank the following electrolyte imbalances in terms of how dangerous they are.

Potassium imbalances. Calcium imbalances. Phosphate imbalances.

Which is the principal cation of the ECF, accounting for 90% to 95% of the osmolarity of the ECF?

Sodium

Which of the following may cause metabolic alkalosis?

Overuse of intravenous bicarbonate solutions or aldosterone hypersecretion.

-- exception represents the major route of water loss.

Urine

Which are the primary effects of aldosterone?

Urine has a lower pH. Urine contains more K+. Urine contains less NaCl.

Water output is primarily controlled through variations in which of the following?

Urine volume

Rank the following routes of normal water loss from largest volume to smallest volume.

Urine. Cutaneous transpiration. Expired breath. Feces. Sweat (at an ambient temperature of 20 C [68 F]).

Output through the expired air and cutaneous transpiration (but not including fecal moisture, urine, and sweat) is called -- water loss because we are not usually conscious of it.

Insensible

Which stimulate aldosterone secretion?

Hyperkalemia Hypotension Hyponatremia

Plasma concentrations of calcium less than 4.5 mEq/L are known as --.

Hypocalcemia

Fluid excesses are of two types: volume excess and -- hydration.

Hypotonic

What happens to ECF osmolarity during dehydration?

It increases

Which best describes how aldosterone acts as the "salt retaining hormone"?

It increases the number of Na+-K+ pumps in the nephron.

Which of the following are functions of potassium?

It plays a role in cotransport and thermogenesis via the Na+-K+ pump. It helps produce the resting membrane potentials and action potentials of nerve and muscle cells. It is an essential cofactor for protein synthesis and some other metabolic processes. It is the greatest determinant of intracellular osmolarity and cell volume.

How does blood plasma differ from the intracellular fluid?

K+ concentration is lower in plasma. Na+ concentration is higher in plasma. Ca2+ concentration is higher in plasma.

Water intake totals about 2500 mL/day. The combination of water from food (about 700 mL) and drink (about 1600 mL) is known as -- water.

Preformed.

The simplest cause of dehydration is a lack of drinking water. Which of the following can also cause dehydration?

Profuse sweating Cold or hot weather Overuse of diuretics Diabetes mellitus

The -- buffer system accounts for about three-quarters of all chemical buffering in the body fluids, especially in the ICF.

Protein

Match each type of potassium imbalance to its neurological effects.

Slow-Onset Hyperkalemia: voltage-gated sodium channels inactivate. this prevents the firing of action potentials. Hypokalema: the concentration gradient for K+ across the membrane becomes steeper, resulting in hyperpolarization. this makes neurons and muscle cells less excitable. Rapid-Onset Hyperkalemia: neurons and muscle cells depolarize suddenly and fire action potentials. synchronous activation of cardiac muscle cells can lead to cardiac arrest.

During dehydration, urine volume decreases and more body water is retained. This is often due to increased reabsorption --.

Sodium

The most abundant solute particles are electrolytes, especially potassium in the intracellular fluid (ICF) and -- in the extracellular fluid (ECF).

Sodium

Which of these ions are major cation electrolytes?

Sodium Calcium

Why are true imbalances in sodium concentration relatively rare?

Sodium excess or depletion is almost always accompanied by proportionate changes in water volume.

An acid such as hydrochloric acid (HCl) that ionizes freely, gives up most of its hydrogen ions, and can markedly lower the pH of a solution is known as what type of acid?

Strong

The hydroxide (OH-) is an example of a -- base, which has a great tendency to bind H+ and raise the pH.

Strong