A&P II : Urinary System & Acid/Base Balance

You've counseled Mr. Boulard about how to prevent recurrence of his hypokalemia. Which of the statements he makes indicates a need for further instruction?

"There's lots of potassium in regular table salt, so I'll just use more." Table salt is NaCl, not KCl. So ingesting it will not help prevent hypokalemia.

A nonfasting urine sample from an individual who had previously ingested donuts and a soft drink showed the presence of sugar (glucose). Which of the following statements explains the presence of glucose in the urine?

The individual exceeded the transport maximum

Calculate the net filtration pressure if blood pressure in the glomerulus is unusually high, around 68 millimeters of mercury (mm Hg). Assume the colloid osmotic pressure and capsular hydrostatic pressure are normal.

23 mm Hg Net filtration pressure is calculated by subtracting the inward pressures from the outward pressures: (HPgc) − (HPcs + OPgc).

Calculate the net filtration pressure if capillary hydrostatic pressure is 60 mm Hg, capillary osmotic pressure is 25 mm Hg, and capsular hydrostatic pressure is 10 mm Hg.

25 mm Hg

Which hormone(s) is/are required for facultative water reabsorption in the collecting ducts?

ADH

An increase in blood CO2 levels leads to __________.

A drop in blood pH An increase in CO2 results in the formation of more carbonic acid, which leads to an increase in acidity, or a drop in pH.

The bicarbonate buffer system is one of the chemical buffer systems of the body. How would the bicarbonate buffer system work if sodium hydroxide were added to a solution?

A hydrogen on carbonic acid would dissociate and join the hydroxyl group on the base to form water and sodium bicarbonate. Yes, a strong base (sodium hydroxide) would be converted to a weak base (sodium bicarbonate).

What is the juxtaglomerular complex?

A system that regulates the rate of filtration formation and systemic blood pressure

Through the tubuloglomerular feedback mechanism, how would an increase in filtrate NaCl concentration affect afferent arteriole diameter?

Afferent arteriole diameter would decrease

The myogenic mechanism of renal autoregulation primarily involves smooth muscle in which blood vessels?

Afferent arterioles

Urinary incontinence may occur if a person has ______.

An overactive detrusor muscle

Which of the following homeostatic imbalances is indicative that glomerular blood pressure may be too low to cause filtration?

Anuria

Which of the following substances is not normally found in filtrate?

Blood cells and large particles

Which of the following are mechanisms of intrinsic control of glomerular filtration (renal autoregulation)?

Myogenic mechanism and tubuloglomerular feedback

Which of the following is not an electrolyte?

Carbohydrate Excellent! Carbohydrates are held together by covalent bonds, whereas electrolytes are held together by ionic bonds.

The respiratory system is one of the three systems that regulate acid-base balance in the body. How does it work to decrease an acidosis?

Carbonic acid is broken down into water and CO2; the CO2 is then exhaled. Yes, CO2 can be blown off, thus decreasing acidity.

What is the function of the renal pelvis?

Collects newly formed urine Correct. The minor calyces of the renal pelvis collect newly formed urine as it exits the renal papillae.

Identify the correct direction of urine flow from formation to exiting the kidney.

Cortex, medulla, renal pelvis, ureter Correct. Filtration occurs in the renal cortex, processing of the filtrate occurs within the renal tubules. Urine exits the renal pyramids into the renal pelvis, where it will be conveyed to the urinary bladder by the ureter.

Name the strong transparent covering that encases the kidney.

Fibrous capsule Correct. The fibrous capsule is a thin strong sheet of connective tissue that encapsulates the kidney.

Suppose that a patient has a failing liver and is unable to make normal levels of albumin for the blood plasma. If all other factors remain the same, what would be the effect on the amount of filtrate produced?

Filtrate production would increase. If the liver were making insufficient levels of albumin, which is the most important contributor to the blood's osmotic pressure, the blood's osmotic pressure would drop, leading to a rise in filtrate production.

Which of the following is NOT part of the filtration membrane?

Extraglomerular mesangial cells

The net filtration pressure (NFP) is the chief force pushing water and solutes out of the blood and across the filtration membrane. True or false?

False

The medullary pyramids contain collecting tubules (ducts) that travel towards the renal cortex, carrying urine to exit the kidney. True or false?

False Correct. The medullary pyramids contain collecting tubules that travel towards the renal papillae, carrying urine to exit the kidney.

The fibrous capsule is a layer of adipose tissue that surrounds the kidney. True or false?

False The fibrous capsule is a strong sheet of dense fibrous connective tissue. There is a layer of adipose tissue superficial to the fibrous capsule, called the perirenal fat capsule.

Capsular hydrostatic pressure is the chief force pushing water and solutes out of the blood and across the filtration membrane. True or false?

False When the forces directed out of the capillary (glomerulus) exceed the forces directed into the capillary, net filtration pressure is positive, and filtration occurs. Glomerular hydrostatic (blood) pressure is the chief (outward directed) force pushing water and solutes out of the blood and across the filtration membrane.

GFR regulation mechanisms primarily affect which of the following?

Glomerular hydrostatic pressure (HPg)

Which of these cells is located interspersed between the capillaries of the glomerulus?

Glomerular mesangial cells Glomerular mesangial cells cover some of the glomerular capillaries and function in filtration and support.

Which cells of the juxtaglomerular apparatus secrete renin?

Granular cells

Where does the ureter penetrate the kidney?

Hilum Correct. The ureter, renal blood vessels and nerve supply all enter the kidney at the hilum.

What is the chief force pushing water and solutes out of the blood and across the filtration membrane of the glomerulus?

Hydrostatic pressure in glomerular capillaries (HPgc)

What is the primary driving force (pressure) that produces glomerular filtration?

Hydrostatic pressure of blood (blood pressure)

If the efferent arteriole constricts while the afferent arteriole remains unchanged, the glomerular filtration rate __________.

Increases

Which age group most commonly has fluid, electrolyte, and acid-base balance issues?

Infants Several factors work together to cause myriad problems in infants.

Which of the following does NOT serve as a source of acids in the body?

Ingesting of bicarbonate

All of the following would stimulate the release of renin from granular cells, EXCEPT __________.

Inhibition by the macula densa cells

What does a high concentration of NaCl in the renal tubule at the juxtaglomerular apparatus (JGA) most likely indicate?

Insufficient NaCl reabsorption due to high GFR

Which of the following is the only logical explanation for why hypocalcemia increases neuromuscular excitability and causes muscle tetany?

Low plasma calcium ion concentration increases the permeability of neuron membranes to sodium ions, thereby causing depolarization that in turn increases the likelihood of action potentials being generated. Sodium and calcium are cations, and so loss of positive charge in the extracellular fluid would increase membrane permeability to all cations, including sodium. Recall that the influx (inward movement) of sodium causes depolarization.

A patient is admitted to the hospital with the following plasma values: pH = 7.2, pCO2 = 25 mmHg, and HCO3 −− = 18 mEq/L. What is the acid base imbalance?

Metabolic acidosis with respiratory compensation Yes, the low bicarbonate indicates this is a metabolic acidosis. Since CO2 is below the normal range, this indicates there is a respiratory compensation.

Starvation would cause which of the following acid-base conditions? Also, determine what type of compensation (metabolic or respiratory) there would be.

Metabolic acidosis with respiratory compensation Yes, this is known as a ketosis (due to the breakdown of fat for metabolism), and the respiratory system would increase respiration to compensate for the excess hydrogen ions.

Diarrhea can lead to which acid/base disturbance? Assuming compensation, would it be a metabolic or respiratory compensation?

Metabolic acidosis with respiratory compensation Yes, with the loss of bicarbonate ions, this is a metabolic acidosis. If compensated, it would be a respiratory compensation.

Ingesting too much antacid would cause which of the following acid-base disturbances?

Metabolic alkalosis Yes, ingestion of an antacid would increase the bicarbonate, causing a metabolic alkalosis.

Vomiting will cause which type of acid-base disturbance?

Metabolic alkalosis Yes, loss of HCL acid from the stomach would cause a metabolic alkalosis.

A patient is admitted to the hospital with the following plasma values: pH = 7.5, pCO2 = 45 mmHg, and HCO3 −− = 30 mEq/L. What is the acid-base imbalance?

Metabolic alkalosis with no compensation Yes, since HCO3¯ is 30 (above the normal range of 22 to 26 mEq/L), this is definitely a metabolic alkalosis. There is no respiratory compensation since CO2 is within the normal range.

A friend has acid indigestion after eating a big meal. Which of the following would act as a buffer and help ease his pain?

Milk of magnesia, with a pH of 10 Excellent! Excess acid can be buffered by the addition of an alkaline or base.

The most important factor affecting the glomerular filtration rate is __________.

Net filtration pressure

Which pressure accounts for the other three?

Net filtration pressure

If the osmotic pressure in the glomerular capillaries increased from 28 mm Hg to 35 mm Hg, would net filtration increase or decrease?

Net filtration would decrease

Which part of the brain controls the micturition reflex?

Pons

Which substance would be found in higher concentration if the membrane were damaged?

Protein

Where in the nephron does most solute reabsorption occur?

Proximal convoluted tubule

All of the following are layers of the filtration membrane in the glomerular membrane, EXCEPT the __________.

Renal capsule The renal capsule is not considered part of the filtration membrane in the glomerulus.

Which structure is found separating the renal pyramids?

Renal columns Correct. The renal columns are extensions of cortical tissue located in between the renal pyramids.

The glomerular (Bowman's) capsule and glomerulus make up the __________.

Renal corpuscle

Where does the kidney filter the blood?

Renal corpuscle Correct. The renal corpuscle is an interface between the blood supply and the kidney. It consists of the glomerulus, which is a capillary bed, and the glomerular (bowman's) capsule, which is part of the nephron. Filtration is the exit of small substances from the blood in the glomerulus into the glomerular capsule of the nephron.

Where does filtration of the blood occur within the kidneys?

Renal cortex Correct. Filtration takes place within the renal corpuscles located in the renal cortex.

Which of the following regions of the kidney is in contact with the fibrous capsule?

Renal cortex Correct. The fibrous capsule encloses the kidney. It is in contact with the renal cortex.

Which region of the kidney is the most superficial?

Renal cortex Correct. The renal cortex is the most superficial region of the kidney. Renal corpuscles are found in the renal cortex. They are microscopic structures, so they can't be observed on a kidney specimen. The renal corpuscles are responsible for the bumpy texture of the renal cortex that can be visualized.

Where are the renal columns located?

Renal medulla Correct. The renal columns are located between the renal pyramids in the renal medulla.

A major calyx is a component of which of the following anatomical structures?

Renal pelvis Correct. The major branches of the renal pelvis are the major calyces, and the smaller branches that contact the renal papillae are the minor calyces.

Of the three buffering mechanisms in the body, which is the strongest?

Renal system Yes, although slow, the renal system is the strongest buffering system in the body. By altering the reabsorption and excretion of hydrogen ions and bicarbonate ions, the kidneys control the pH of body fluids.

Granular cells of the juxtaglomerular apparatus (JGA) regulate GFR indirectly through which mechanism?

Renin-angiotensin mechanism

What is the effect of hypoventilation on pH?

Respiratory acidosis Hypoventilation causes decreased CO2 exhalation. With higher blood CO2, there is more carbonic acid formed, so the patient goes into acidosis.

A patient is admitted to the hospital with the following plasma values: pH = 7.2, pCO2 = 55 mmHg, and HCO3 −− = 30 mEq/L. What is the acid base imbalance?

Respiratory acidosis with metabolic compensation Yes, this is a respiratory acidosis with metabolic compensation. Since pCO2 is above the normal range, it is the cause of the acidosis. HCO3 −− is increased to compensate, which is a metabolic compensation.

Emphysema can lead to which acid/base disturbance? What would be the compensation?

Respiratory acidosis; kidneys will retain more HCO3 -- and excrete H+ Yes, a patient with emphysema would retain CO2, leading to a respiratory acidosis. The kidneys would compensate by retaining HCO3 −− and excreting H+.

Severe anxiety would cause which type of acid-base disturbance? What would be the compensation?

Respiratory alkalosis; kidneys would excrete HCO3 Yes, during hyperventilation caused by severe anxiety, carbonic acid is excreted from the lungs in the form of CO2, thus causing an alkalosis. Kidneys would compensate by excreting HCO3.

Approximately 80% of the energy used for active transport is devoted to the reabsorption of __________.

Sodium

Mr. Boulard's blood pressure is quite high. How would this affect his nephron function? Choose the statement below that is most accurate.

The heart releases atrial natriuretic peptide that reduces sodium reabsorption at the kidney when blood pressure increases. Atrial natriuretic peptide is released by the heart in response to high blood pressure. It targets the nephron where it reduces the reabsorption of sodium, which leads to less water being reabsorbed. More water is lost in urine, reducing the blood volume and blood pressure.

The lab results of a newly admitted patient indicate renal impairment. How might this affect the dosing regimen of drugs that are excreted by the kidney?

The dosage or the dosage interval may need to be reduced. If the renal clearance of the drug is reduced by kidney disease, then drugs eliminated by the kidney may need to be given less often, in smaller amounts, or both. This appropriate regimen is often found in information provided by the drug manufacturer.

In a respiratory acidosis the kidney would do which of the following?

The kidney would reabsorb bicarbonate and secrete hydrogen ions. Yes, when the kidney secretes hydrogen ions it also generates a bicarbonate ion, which further aids in decreasing the acidity of the plasma.

The frequency of cystitis in men is lower than in women because ______.

The male urethra is longer than the female urethra

Hypersecretion of aldosterone results in hypokalemia, which causes hyperpolarization of neurons; this in turn results in ______.

The need for a stronger than normal stimulus in order to trigger an action potential To trigger an action potential cells must reach threshold (critical electrical value required to open voltage-gated ion channels). If the membrane potential is hyperpolarized and falls below normal resting membrane potential, then more cations must enter the cytoplasm for the cell to reach threshold.

Which of the following best describes glomerular filtration rate (GFR)?

The volume of filtrate created by the kidneys per minute

Which of the following is true of electrolytes?

They are ionic compounds. Excellent! Electrolytes dissociate, or come apart, in water, releasing ions, which have electrical charges—hence the term "electrolyte."

Which of the following is NOT a hormone involved in water and electrolyte balance?

Thyroxine

In situations where there is an extreme change of blood pressure (e.g., mean arterial pressure of less than 80 mm Hg), extrinsic controls take precedence over intrinsic blood pressure controls. True or false?

True

The ureter, blood vessels, and nerves penetrate the kidney on its medial surface. True or false?

True Correct. The ureter, blood vessels, and nerve supply penetrate the kidney at its concave medial surface at the hilum.

Glomerular capillaries are drained by efferent arterioles whose diameter is smaller than the afferent arterioles that feed them; this creates the high blood pressure that drives filtration. True or false?

True The blood pressure in the glomerulus is extraordinarily high (approximately 55 mm Hg compared to an average of 26 mm Hg or so in other capillary beds) and it remains high across the entire capillary bed. This is because the glomerular capillaries are drained by a high resistance efferent arteriole whose diameter is smaller than the afferent arteriole that feeds them. As a result, filtration occurs along the entire length of each glomerular capillary and reabsorption does not occur as it would in other capillary beds.

Macula densa cells of the juxtaglomerular apparatus (JGA) regulate GFR through which intrinsic mechanism?

Tubuloglomerular feedback

Since most patients with renal failure produce little or no urine, hemodialysis often involves removal of water from the blood. However, side-effects may develop if too much fluid is removed from the blood. Which of the following is NOT one of the potential side-effects?

Vasoconstriction of afferent arterioles

Which of the following is NOT a cause of anuria?

Vasodilation of afferent arterioles Vasodilation of the afferent arterioles occurs during times of low systemic blood pressure. This reflexive response raises glomerular blood pressure and helps maintain normal glomerular filtration rates. Anuria is an abnormally low urine output (<50 ml/day).

If a person exercises for a long time, lactic acid will start to build up in his or her muscles. Which of the following would you expect to happen as the lactic acid first starts to be formed?

Weak bases in the muscles will act as buffers and resist or minimize any pH change. Excellent! Bases buffer acids, and acids buffer bases.