NIU Patho Chapter 8 Porth

Carbon dioxide is the end product of aerobic metabolism. What are 3 ways it is transported in the circulation?

1. As a dissolved gas (i.e., PCO2). 2. As the bicarbonate ion (HCO3-). 3. As carbaminohemoglobin in CO2 bound to hemoglobin. Collectively, dissolved CO2 and HCO3- account for approximately 77% of the CO2 that is transported in the extracellular fluid. The remaining CO2 travels as carbaminohemoglobin.

What are some manifestations of hyperparathyroidism?

(Remember that secretion/ presence of PTH triggers calcium to be mobilized from bones...). Primary hyperparathyroidism is a leading cause of hypercalcemia in the outpatient department. It is seen more commonly after 50 years of age and is more common in women than men. Primary hyperparathyroidism causes an elevation in ionized serum calcium and increased urinary excretion of both calcium and phosphorus. This increased urinary concentration provides the potential for dev. of kidney stones.

Serum potassium levels are largely regulated through which 2 mechanisms?

1. Renal mechanisms that conserve or eliminate potassium. 2. A transcellular shift between the ICF and ECF compartments.

How many mEq daily dietary intake of potassium is needed to maintain potassium balance in healthy individuals?

50-100 mEq. Additional amounts of potassium are needed during periods of trauma and stress.

Normally, how long does it take to eliminate 50% of potassium intake?

6 to 8 hours. To avoid an increase in ECF potassium levels during this time, excess potassium is temporarily shifted into red blood cells and other cells such as those of muscle, liver, and bone. This movement is controlled by the function of the Na+/ K+-ATPase membrane pump and the permeability of ion channels in the cell membrane.

What is the normal range of extracellular body fluid pH?

7.35 to 7.45. This balance is maintained through mechanisms that generate, buffer, and eliminate acids and bases.

What percentage of body potassium is contained within body cells? What is the intracellular concentration of potassium in mEq/L?

98%; 140 to 150 mEq/L (140 to 150 mmol/ L). Because potassium is an intracellular ion, total body stores of potassium are related to body size and muscle mass.

What is a sign of hypocalcemia?

A total serum calcium level of less than 8.5 mg/dL and an ionized calcium level of less than 4.6 mg/dL

Describe how serum osmolality affects intracellular/ extracellular distribution of potassium.

Acute increases in serum osmolality cause water to leave the cell. The loss of cell water produces an increase in intracellular potassium, causing it to move out of the cell and into the ECF.

Total serum calcium is significantly altered by serum levels of what?

Albumin

What hormone plays an essential role in regulating potassium elimination in the distal tubule of the kidney?

Aldosterone. In the presence of aldosterone, Na+ is transported back into the blood and K+ is secreted in the tubular for elimination in the urine.

What is the definition of an acid? A base?

An acid is a molecule that can dissociate and release a hydrogen ion (H+). For example, HCl dissociates in water to form H+ and Cl- ions. A base is an ion or molecule that can accept or combine with H+. For example, the bicarbonate ion (HCO3-) is a base because it can combine with H+ to form carbonic acid (H2CO3). Most of the body's acids and bases are weak acids and bases, the most important being H2CO3, which is a weak acid derived from carbon dioxide (CO2) and bicarbonate (HCO3), which is a weak base.

What percentage of potassium is in muscle?

Approximately 65-75%. Total body potassium content declines with age, mainly as a result of a decrease in muscle mass.

How do acids and bases exist?

As buffer pairs or systems -- a mixture of a weak acid and its conjugate base or a weak base and its conjugate acid. When an acid (HA) is added to water, it dissociates reversibly to form H+ and its conjugate anion (A-).

How much potassium intake is needed to compensate for obligatory urine losses?

At least 40-50 mEq per day. Potassium intake is often inadequate in persons on fad diets and those who have eating disorders. Elderly persons are particularly likely to have potassium deficits.

Describe how insulin and beta-adrenergic stimulation affects intracellular/ extracellular distribution of potassium.

Both insulin and the catecholamines (e.g., epinephrine) increase cellular uptake of K+ by increasing the activity of the Na+/ K+-ATPase membrane pump. Insulin produces an increase in cellular uptake of potassium after a meal. The catecholamines, particularly epinephrine, facilitate the movement of potassium into muscle tissue during periods of physiologic stress. Beta-adrenergic agonist drugs, such as pseudoephedrine and albuterol, have a similar effect on potassium distribution.

Why is hypocalcemia a common problem with acute pancreatitis?

Because fat necrosis and precipitation of calcium soaps produce a decrease in serum calcium.

In renal failure, what happens to serum calcium levels in the presence of phosphate?

Because of their inverse relationship, serum calcium levels fall as phosphate levels rise (in renal failure). Hypocalcemia and hyperphosphatemia occur when the glomerular filtration rate falls to less than 25 to 30 mL/ minute (normal is 100 to 120 mL/ minute).

What are ionized calcium levels inversely affected by?

Blood pH. (pH rises, ionized calcium serum level falls). To illustrate, when the arterial pH increases due to alkalosis, more calcium becomes bound to protein. Although the total serum calcium remains unchanged, the ionized portion (the portion free to leave the vascular compartment and participate in cellular functions) decreases.

How is Chvostek sign elicited?

By tapping the face just below the temple at the point where the facial nerve emerges. This causes spasm of the lip, nose, or face when the test result is positive.

How is Trousseau sign tested?

By using an inflated blood pressure cuff. The cuff is inflated 10 mm Hg above systolic blood pressure for 3 minutes. Contraction of the fingers and hands indicates the presence of tetany.

Because it is almost impossible to measure H2CO3, what is measured and commonly used when calculating pH (e.g., of the blood)?

CO2. The H2CO3 content of the blood can be calculated by multiplying the partial pressure of CO2 (PCO2) by its solubility coefficient, which is 0.03. This means that the concentration of H2CO3 in the arterial blood, which normally has a PCO2 of ~ 40 mm Hg, is 1.20 mEq/L (40 x 0.03 = 1.20), and that for venous blood, which normally has a PCO2 of ~ 45 mm Hg, is 1.35 mEq/L.

What is the major divalent (having a valence of 2) cation in the body?

Calcium

Three major divalent ions in the body.

Calcium, phosphorous, and magnesium .

What 2 factors strongly influence potassium balance?

Dietary intake & urine output.

The reaction that generates H2CO3 from CO2 and water is catalyzed by which enzyme?

Carbonic anhydrase. Carbonic anhydrase is present in large quantities in red blood cells, renal tubular cells, and other tissues in the body. The rate of the reaction between CO2 and water is increased ~ 5000 times by the presence of carbonic anhydrase.

Describe a major bone-related manifestation of primary hyperparathryoidism.

Chronic bone resorption (as seen in primary hyperparathyroidism), which may produce diffuse mineralization, pathologic fractures, and cystic bone lesions.

What does hypoparathyroidism reflect? What does it result in?

Deficient PTH secretion. It results in low serum levels of IONIZED calcium.

How is hyperparathyroidism diagnosed?

Diagnostic procedures include serum calcium, intact PTH levels, and imaging studies of the parathyroid area.

How do volatile and nonvolatile (fixed) acids exit the body?

Volatile acids leave the body by way of the lungs. Nonvolatile acids are buffered by body proteins or extracellular buffers, and then eliminated by the kidney.

What is another factor (besides serum osmolality, acid-base disorders, insulin, and beta-adrenergic stimulation) that can produce compartmental shifts in potassium?

Exercise. Repeated muscle contraction releases potassium into the ECF. Although the increase usually is small with modest exercise, it can be considerable during exhaustive exercise. Even the repeated clenching and unclenching of the fist during a blood draw can cause potassium to move out of cells and artificially elevate serum potassium levels.

Although CO2 is a gas and not an acid, a small percentage of the gas combines with water to form what?

H2CO3

What does secondary hyperparathyroidism involve?

Hyperplasia of the parathyroid glands; it occurs primarily in persons w/ chronic kidney disease. In early stages of chronic kidney disease, an increase in PTH results from decreased serum calcium and activated vit. D levels. As the disease progresses, there is a decrease in vit. D and calcium receptors, making the parathyroid glands more resistant to feedback regulation by serum calcium and vit. D levels. At this point, elevated phosphorous levels induce hyperplasia of the parathyroid glands independent of calcium and vit. D levels. The bone disease seen in persons with secondary hyperparathyroidism due to chronic kidney disease is knows as renal osteodystrophy.

What can cause pseudohypocalcemia?

Hypoalbuminemia. This results in a decrease in protein-bound, rather than ionized, calcium and usually is asymptomatic.

What are some cardiovascular effects of acute hypocalcemia?

Hypotension, cardiac insufficiency, cardiac arrhythmias (particularly heart block and ventricular fibrillation), and failure to respond to drugs such as digitalis, norepinephrine, and dopamine that act through calcium-mediated mechanisms.

How is H+ concentration commonly expressed?

In terms of pH. pH represents the negative logarithm (log10) of the H+ concentration expressed in mEq/L. Thus, a pH value of 7.0 implies an H+ concentration of 10 raised to the negative 7, or 0.0000001 mEq/L. Since the pH is inversely related to the H+ concentration, a low pH indicates a high concentration of H+ and a high pH a low concentration of H+.

Where is 99% of calcium found, and what is its function here?

In the bone, where it provides the strength and stability for the skeletal system and serves as an exchangeable source to maintain extracellular calcium levels.

What is the major action of the activated form of vitamin D?

Increase the ABSORPTION of CALCIUM from the intestine.

What causes hyperparathryoidism?

Increased levels of PTH. Hyperparathryoidism can manifest as a primary disorder caused by hyperplasia (the enlargement of an organ or tissue caused by an increase in the reproduction rate of its cells, often as an initial stage in the development of cancer; 15% of cases), an adenoma (a benign tumor formed from glandular structures in epithelial tissue; 85% of cases), and rarely carcinoma of the parathyroid glands (fewer than 5% of cases) or as a secondary disorder seen in persons with chronic renal failure or chronic malabsorption of calcium. Parathyroid adenomas and hyperplasia can occur in several distinct familial diseases (including multiple endocrine neoplasia [MEN] types 1 and 2a).

What are 2 main signs of large or abrupt changes in ionized calcium?

Increased neuromuscular excitability and cardiovascular effects.

How is hypocalcemia diagnosed?

Initially diagnosed based on serum calcium levels and signs of increased neuromuscular excitability. Additionally, Chvostek and Trousseau tests can be used to asses for increased neuromuscular excitability that is associated with hypocalcemia.

What are some factors that can increase intestinal absorption of calcium?

Intake of excessive doses of vit. D or as a result of a condition called the milk-alkali syndrome, which is caused by excessive ingestion of calcium (often in the form of milk) and absorbable antacids. Discontinuance of the antacid repairs the alkalosis and increases calcium elimination.

Describe pseudohypoparathyroidism.

It is a rare familial disorder characterized by target tissue resistance to PTH. It is characterized by hypocalcemia, increased parathyroid function, and a variety of congenital defects in the growth and development of the skeleton, incl. short stature and short metacarpal and metatarsal bones. There are variants in the disorder, with some persons having the pseudohypoparathyroidism along w/ the congenital defects and others having the congenital defects with normal calcium & phosphorus levels. The manifestations of the disorder are due primarily to chronic hypocalcemia.

How is hypoparathyroidism diagnosed?

It is based on history, including a history of neck surgery; physical examination to assess for signs of neuromuscular irritability due to hypocalcemia; and lab measurements of serum total and ionized calcium, albumin, phosphorus, magnesium, vit. D levels, and intact PTH (intact 84-amino-acid hormone).

How is the ionized form of calcium filtered and circulated?

It is filtered from the plasma into the glomerulus and then selectively reabsorbed back into the blood.

What is the normal concentration of ECF potassium?

It is normally precisely regulated at about 4.2 mEq/L (4.2 mmol/L). Precise control is necessary because many cellular functions are sensitive to even small changes in ECF potassium levels. An increase in potassium of as small an amount as 0.3 to 0.4 mEq/L can cause serious cardiac arrhythmias and even death.

What causes hypoparathyroidism?

It may occur because of a congenital absence of all of the parathyroid glands, or because of an acquired disorder due to inadvertent removal or irreversible damage to the glands during thyroidectomy, parathyroidectomy, or radical neck dissection for cancer. Additionally, a transient form of PTH deficiency may occur after thyroid surgery owing to parathyroid gland suppression. It may also have an autoimmune origin. Anti-PTH antibodies have been detected in some persons with hypoparathyroidism, esp. those w/ multiple autoimmune disorders such as type I diabetes mellitus or Graves disease. Still other causes include heavy metal damage such as occurs with Wilson disease and metastatic tumors. Finally, functional impairment of parathyroid function occurs with magnesium deficiency.

What causes hypercalcemia?

It occurs when calcium movement into the circulation overwhelms calcium regulatory hormones or the ability of the kidney to remove excess calcium ions. The two most common causes are increased bone resorption due to neoplasms and hyperparathyroidism. Additionally, hypercalcemia is a common complication of malignancy, occurring in appr. 20-30% of persons with advanced disease. A number of malignant tumors, including carcinoma of the lungs, have been associated with hypercalcemia. Some tumors destroy the bone (thereby releasing Ca++), while others produce humoral agents that stimulate bone resorption or inhibit bone formation.

What are some functions of ionized calcium?

It participates in many enzyme reactions; exerts an important effect on membrane potentials and neuronal excitability; is necessary for contraction in skeletal, cardiac, and smooth muscle; participates in the release of hormones, NTs, and other chemical messengers; influences cardiac contractility and automaticity by way of slow calcium channels; and is essential for blood clotting. (Calcium is required for all but the first two steps of the intrinsic pathway for blood coagulation).

What is the function (general; non-patho) of ionized calcium?

It stabilizes neuromuscular excitability, thereby making nerve cells LESS sensitive to stimuli. Therefore, nerves exposed to LOW ionized calcium levels show decreased thresholds for excitation, repetitive responses to a single stimulus, and, in extreme cases, continuous activity.

What are loop diuretics? What are they used primarily for?

Loop diuretics act on the ascending loop of Henle in the kidney, and are used primarily to treat hypertension and edema (due to congestive heart failure or renal insufficiency, for example). Thiazide diuretics are more effective in patients with normal kidney function, whereas loop diuretics are more effective in patients with impaired kidney function.

Is the concentration of H+ in body fluids HIGH or LOW compared with other ions?

Low. For example, the Na+ is present at a concentration approximately 3.5 million times that of H+.

What is the second most abundant ICF cation?

Magnesium

Besides calcium, what other electrolyte affects the synthesis and release of PTH from the parathyroid gland?

Magnesium, which serves as a cofactor in the generation of cellular energy and is important in the function of second messenger systems. Magnesium's effects on the synthesis and release of PTH are thought be mediated through these mechanisms. Because of its function in regulating PTH release, severe and prolonged hypomagnesemia can markedly INHIBIT PTH levels.

What is the main function of PTH?

Maintain the calcium concentration of the ECF. It performs this function by promoting the release of calcium from the bone, increasing the activation of vitamin D as a means of enhancing intestinal absorption of calcium, and stimulating calcium conservation by the kidney while increasing phosphorus elimination.

Potassium is critical to many body functions. Give some specific examples.

Maintenance of the osmotic integrity of cells, acid-base balance, and the kidney's ability to concentrate urine. Potassium is necessary for growth and it contributes to the intricate chemical reactions that transform carbohydrates into energy, change glucose into glycogen, and convert amino acids to proteins. Potassium also plays a critical role in conducting nerve impulses and controlling the excitability of skeletal, cardiac, and smooth muscle.

What are 3 body processes/ systems that depend on pH being regulated within a narrow physiologic range to function in an optimal way?

Membrane excitability, enzyme systems, and chemical reactions. Many conditions, pathologic or otherwise, can alter acid-base balance.

What can cause falsely elevated levels of calcium?

Prolonged drawing of blood with an excessively tight tourniquet. Increased serum albumin levels may also elevate total serum calcium but not affect ionized calcium.

What are the signs and symptoms of calcium excess?

Neural excitability, alternations in cardiac and smooth muscle function, and exposure of the kidneys to high concentrations of calcium. There may be a dulling of consciousness, stupor, weakness, and muscle flaccidity due to a decrease in neural excitability.

What is the treatment for chronic hypocalcemia?

Oral intake of calcium. Oral calcium supplements of carbonate, gluconate, or lactate salts may be used. Long-term treatment may require the use of vitamin D preparations, especially in individuals with hypoparathyroidism and chronic kidney disease. (The active form of vit. D is administered when the liver or kidney mechanisms needed for hormone activation are impaired. Also, synthetic PTH can be administered by subcutaneous injection as replacement therapy in hypoparathyroidism.

What are some less common causes of hypercalcemia?

Prolonged immobilization (and lack of weight bearing cause demineralization of bone and release calcium into the bloodstream), increased intestinal absorption of calcium, excessive doses of vit. D, or the effects of drugs such as lithium and thiazide diuretics.

What 3 forms does extracellular calcium exist in (give percentages of each)? Which of these forms is free to leave the vascular compartment and participate in cellular functions?

Protein bound (mostly albumin; 40%); complexed (chelated; 10%) and ionized (50%). Ionized calcium.

What stimulates calcium reabsorption in the distal convoluted tubule?

PTH and possibly vit. D

What are two electrolytes parathyroid hormone (PTH) has major sway over?

PTH is a major regulator of serum calcium and phosphorus. PTH is secreted (no surprise here) by the parathyroid glands. To review, there are 4 parathyroid glands located on the dorsal surface of the thyroid gland. PTH is synthesized as a preprohomrone (a preprohormone is the precursor protein to one or more prohormones, which are in turn precursors to peptide hormones) in the parathyroid gland and cleaved first to a prohormone with 90 amino acids, then to the PTH with 84 AAs, and finally packaged into secretory granules for release into the circulation.

Levels of what hormone affect the ability of the body to mobilize calcium from bone?

PTH levels

What does hypoparathyroidism reflect a deficiency of?

PTH secretion.

In what ways can increased neuromuscular excitability manifest?

Paresthesias (tingling around the mouth and in the hands and feet), tetany (i.e., muscle spasms of the muscles of the face, hands, and feet), and, in severe hypocalcemia, laryngeal spasm and seizures.

What is the second most abundant cation in the body and the major cation in the ICF compartment?

Potassium

Describe the action of potassium filtration in the kidney.

Potassium is filtered in the glomerulus, reabsorbed along with sodium and water in the proximal tubule and with sodium and chloride in the thick ascending loop of Henle, and then secreted into the late distal and cortical collecting tubules for elimination in the urine. This latter mechanism serves to "fine-tune" the concentration of potassium in the ECF.

What inhibits./ suppresses PTH levels?

Primary or secondary forms of hypoparathyroidism, elevated levels of vit. D, magnesium deficiency (inhibits PTH release and impairs the action of PTH on bone resorption.

What is hypokalemia.

Refers to a decrease in serum potassium levels below 3.5 mEq/L (3.5 mmol/L). Because of transcellular shifts, temporary changes in serum levels can occur as the potassium moves between the ECF and ICF compartments.

What is the dominant regulator of PTH secretion?

Serum calcium concentration. A unique calcium receptor on the parathyroid cell membrane (extracellular calcium-sensing receptor) responds rapidly to changes in serum calcium levels. When the serum calcium level is high, the secretion of PTH is INHIBITED, and serum calcium is deposited in the bones. When the level is low, PTH secretion is INCREASED, and calcium is mobilized from the bones and released into the blood.

What are some factors that alter the intracellular/ extracellular distribution of potassium?

Serum osmolality, acid-base disorders, insulin, and beta-adrenergic stimulation.

What has major influence/ control over the rate of aldosterone secretion by the adrenal cortex?

Serum potassium levels. As illustration, an increase of less than 1 mEq/L of potassium causes aldosterone levels to triple. The effect of serum potassium on aldosterone secretion is an example of the powerful feedback regulation of potassium elimination.

What are some of the general signs & symptoms of primary hyperparathyroidism?

Signs & symptoms of the disorder are related to skeletal abnormalities, exposure of the kidney to high calcium levels, and elevated serum calcium levels. Most patients with primary hyperparathyroidism manifest an asymptomatic disorder that is discovered in the course of routine biochemical testing. However, these patients may experience nonspecific constitutional symptoms such as fatigue, weakness, anorexia, and bone pain.

What are some manifestations of hypoparathyroidism?

Tetany with muscle cramps, carpopedal spasm, and convulsions; paresthesias, such as tingling of the circumoral area (around the mouth) and in the hands & feet are almost always present. Low calcium levels may cause prolongation of the QT interval (the QT interval represents electrical depolarization and repolarization of the left and right ventricles; a lengthened QT interval is a biomarker for ventricular arrhythmias), resistance to digitalis, hypotension, and refractory heart failure. Symptoms of chronic PTH deficiency include lethargy, an anxiety state, and personality changes. There may be blurring of vision b/c of cataracts, which develop over a number of years. Extrapyramidal signs, such as those seen with Parkinson disease, may occur b/c of calcification of the basal ganglia. Teeth may be defective if the disorder occurs during childhood.

Describe how acid-base disorders can affect intracellular/ extracellular distribution of potassium.

The H+ and K+ ions, which are positively charged, can be exchanged between the ICF & ECF in a cation shift. In metabolic acidosis, for example, H+ moves into body cells for buffering, causing K+ to leave and move into the ECF.

What is the effect of severe hyperkalemia on the resting membrane potential?

The RMP approaches the threshold potential, causing sustained subthreshold depolarization with a resultant INactivation of the sodium channels and net DECREASE in excitability. The rate of repolarization (return of the membrane potential toward its resting potential so it can undergo another action potential) also varies with serum potassium levels. It is more rapid in hyperkalemia and delayed in hypokalemia.

What causes hypokalemia? (What are the 3 categories?)

The causes of potassium deficit can be grouped into 3 categories: 1. Inadequate intake. 2. Excessive GI, renal, and skin losses. 3. Redistribution between the ICF & ECF compartments.

What determines whether an acid or a base is a strong or weak acid'/ base?

The degree to which an acid dissociates and acts as an H+ donor determines whether it is a strong or weak acid. Strong acids, such as sulfuric acid, dissociate completely, whereas weak acids, such as acetic acid, dissociate only to a limited extent. The same is true of a base and its ability to dissociate and accept a H+.

What is an important regulatory site for controlling the amount of calcium that enters the urine?

The distal convoluted tubule.

What are two situations or factors that alter the ratio of protein-bound to ionized calcium calcium, which can subsequently produce signs of hypocalcemia?

The first is situations where an increase in pH that occurs with alkalosis produces a decrease in ionized calcium. For example, hyperventilation sufficient to cause respiratory alkalosis can produce a decrease in ionized calcium sufficient to cause tetany. The second is free fatty acids, which can increase protein binding, causing a reduction in ionized calcium. Elevations in free fatty acids sufficient to alter calcium binding may occur during stressful situations that cause elevations of epinephrine, glucagon, growth hormone, and adrenocorticotropic hormone levels.

What is the main source of potassium loss?

The kidneys. ~ 80-90% of potassium losses occur int he urine, with the remainder being lost stools and sweat.

What causes hypocalcemia?

The most common causes are abnormal losses of calcium from the kidney, impaired ability to mobilize calcium from bone due to hypoparathyroidism, and increased protein binding or chelation such that greater proportions of calcium are in the NON-ionized form. Another cause is renal failure, in which decreased production of activated vitamin D and hyperphosphatemia both play a role.

What is a major difference between potassium and other electrolytes with regard to the regulation of elimination?

Unlike other electrolytes, the regulation of potassium elimination is controlled by SECRETION FROM the blood into the tubular filtrate rather than through REABSORPTION from the tubular filtrate INTO the blood.

What reflects the body's required precise regulation of acid-base balance?

The pH of the ECF.

What ratio determines the resting membrane potential?

The ratio of ECF to ICF potassium concentration. A DECREASE in the ECF potassium concentration (hypokalemia) causes the RMP to become MORE negative, moving it further from the threshold for excitation. Thus, it takes a greater stimulus to reach the threshold potential and open the sodium channels that are responsible for the action potential. An INCREASE in serum potassium (hyperkalemia) has the opposite effect; it causes the RMP to become MORE positive, moving it closer to the threshold.

Besides thiazide diuretics, what is another factor that influences calcium reabsorption by the kidney?

The serum concentration of phosphorus. An INCREASE in serum phosphorus stimulates PTH, which increases calcium reabsorption by the renal tubules, thereby reducing calcium excretion. (The opposite occurs with a reduction in serum phosphorus levels... PTH is inhibited, and a a decrease in calcium reabsorption by the renal tubules and an increase in calcium excretion occurs).

What are some factors that affect the severity of manifestations of low ionized calcium levels?

The underlying cause, rapidity of onset, accompanying electrolyte disorders, and extracellular pH.

What are some drugs that can elevate calcium levels?

The use of lithium to treat bipolar disorders has been shown to cause hyperparathyroidism and hypercalcemia. The thiazide diuretics increase calcium reabsorption in the distal convoluted tubule of the kidney. Although the thiazide diuretics seldom cause hypercalcemia, they can unmask hypercalcemia from other causes such as underlying bone disease and conditions that increase bone resorption.

Acids are continuously generated as by-products of metabolic processes. Physiologically, these acids fall into 2 groups. What are they?

The volatile H2CO3 acid and all other nonvolatile or fixed acids. The difference between the 2 types of acids arises because H2CO3 is in equilibrium with CO2, which is volatile and leaves the body by way of the lungs. Therefore, the H2CO3 concentration is determined by the lungs and their capacity to exhale CO2. The fixed or nonvolatile acids (e.g., sulfuric, hydrochloric, phosphoric) are NOT eliminated by the lungs. Instead, they are buffered by body proteins or extracellular buffers, such as H2CO3-, and then eliminated by the kidney.

Calcium, phosphorus, and magnesium are all directly or indirectly regulated by, among other factors, these 2 "hormones."

Vitamin D & PTH (Vitamin D acts like a hormone)

What type of diuretics exert their effects in the distal convoluted tubule and enhance calcium reabsorption?

Thiazide diuretics

What are the three types of diuretics?

Thiazide, loop and potassium-sparing

How does potassium play a role in conducting nerve impulses and controlling the excitability of skeletal, cardiac, and smooth muscle?

This involves potassium's regulation of: 1. The resting membrane potential. 2. The opening of the sodium channels that control the flow of current during the action potential. 3. The rate of membrane repolarization. Changes in nerve and muscle excitability are particularly important in the heart, where alterations in serum potassium levels can produce serious cardiac arrhythmias and conduction defects. Changes in serum potassium levels also affect the electrical activity of skeletal muscles and smooth muscle in the blood vessels and GI tract.

How does calcium enter the body, and under the influence of what? Where is it stored? How is it excreted?

Through the GI tract. Calcium is absorbed from the intestine under the influence of vit. D. It is stored in bone and is excreted by the kidney.

What are the goals of hypoparathyroidism therapy?

To control symptoms while minimizing complications. Acute hypoparathyroidism tetany is treated with intravenous calcium gluconate followed by oral administration of calcium salts and vit. D. Magnesium supplementation is used when the disorder is caused by magnesiujm deficiency. Persons w/ chronic hypoparathyroidism are treated w/ oral calcium and vit. D. Levels of serum calcium, phosphorus, and creatinine (to check kidney function) are monitored at regular intervals as a means of maintaining serum calcium w/in a slightly low but asymptomatic range.

What are some treatment protocols for hyperparathyroidism?

Treatment includes resolving the hypercalcemia with increased fluid intake. Parathyroidectomy may be indicated in persons with symptomatic PRIMARY hyperparathyroidism. Whenever possible, the underlying cause of secondary hyperparathyroidism should be removed. The goal of medical management is to normalize calcium levels. Calcitriol and other vit. D analogs may be used to control parathyroid hyperplasia in chronic kidney disease (these analogs "trick" the parathyroid gland into inhibiting PTH secretion due to high "calcium" levels). Persons with chronic kidney disease may also need phosphate binders to decrease HYPERphosphatemia and prevent the skeletal disorders associated w/ the osteodystrophies. Additionally, calcimimetic agents (these mimic the action of calcium on tissues), which act through the calcium-sensing receptor in the parathyroid gland, may be used to decrease PTH production in primary and secondary hyperparathyroidism.

True or False. Acute hypocalcemia is an emergency situation.

True; prompt treatment is required, which includes administering an IV infusion containing calcium (calcium gluconate, calcium chloride) when tetany or acute symptoms are present b/c of a decrease in the serum calcium level.

Describe the potassium/ hydrogen exchange mechanism in the cortical collecting tubules of the kidney.

When serum potassium levels INCREASE, K+ is secreted into the urine and H+ is reabsorbed into the blood, producing a DECREASE in pH and causing metabolic ACIDOSIS. Conversely, when potassium levels are low, K+ is reabsorbed and H+ is secreted in the urine, leading to metabolic alkalosis.