Identify the amino acid that is the major contributor to the transport of nitrogen destined for excretion as urea:
Alanine
Glycine
Lysine
Glutamine
Ornithine
The Correct Answer is D
Nitrogen metabolism involves the safe transport of potentially toxic ammonia from peripheral tissues to the liver for neutralization. Ammonia is converted into organic forms to prevent neurotoxicity during transport in the blood. The urea cycle in the liver then converts this nitrogen into urea for renal excretion. Specific amino acids serve as specialized "carriers" to move nitrogen across the body's metabolic compartments.
Rationale:
A. Alanine is a significant nitrogen carrier, specifically from skeletal muscle to the liver via the glucose-alanine cycle. While important, it primarily handles nitrogen generated during muscle protein catabolism. It is not the "major" contributor to total systemic nitrogen transport compared to the more versatile and high-capacity glutamine pathway.
B. Glycine is the simplest amino acid and participates in many biosynthetic pathways, including heme and creatine synthesis. While it contains nitrogen, it does not function as a dedicated carrier for the transport of excess ammonia for excretion. Its role in the urea cycle is indirect and not related to systemic transport.
C. Lysine is an essential amino acid and is purely ketogenic. It does not participate in the transamination reactions that are central to nitrogen transport and urea cycle priming. Therefore, it cannot serve as a vehicle for moving excess nitrogen from peripheral tissues to the hepatocyte for processing into urea.
D. Glutamine is the major contributor to systemic nitrogen transport. It carries two ammonia groups in a non-toxic form (as the amide of glutamate). Most tissues convert free ammonia into glutamine via glutamine synthetase for safe passage to the liver and kidneys, making it the most abundant amino acid in human plasma.
E. Ornithine is a key intermediate within the urea cycle itself. It combines with carbamoyl phosphate to form citrulline inside the mitochondria. While essential for the production of urea, it acts as a catalytic carrier within the hepatocyte rather than a vehicle for transporting nitrogen through the systemic circulation.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is A
Explanation
Zestoretic is a fixed-dose combination antihypertensive medication designed to manage systemic hypertension through synergistic pathways. It combines an angiotensin-converting enzyme (ACE) inhibitor with a thiazide diuretic to reduce vascular resistance and extracellular fluid volume. This pharmacological approach is highly effective for patients who require multi-modal therapy to reach their target blood pressure goals, particularly when monotherapy has failed to provide adequate cardiovascular protection.
Rationale:
A. Zestoretic is the brand name for the combination of lisinopril and hydrochlorothiazide. Lisinopril acts as an ACE inhibitor, preventing the conversion of angiotensin I to angiotensin II, which is a potent vasoconstrictor. Hydrochlorothiazide is a diuretic that inhibits sodium reabsorption in the distal convoluted tubules. Together, they provide superior blood pressure control by addressing both hormonal and fluid-related mechanisms of hypertension.
B. Enalapril combined with hydrochlorothiazide is marketed under the brand name Vaseretic. While enalapril is also an ACE inhibitor, it is a prodrug that must be converted in the liver to enalaprilat, unlike lisinopril. Vaseretic and Zestoretic are therapeutically similar but are distinct brand entities with different active ACE-inhibitor molecules, making this choice incorrect.
C. Losartan combined with hydrochlorothiazide is known by the brand name Hyzaar. Losartan is an angiotensin II receptor blocker (ARB) rather than an ACE inhibitor. ARBs work further down the renin-angiotensin-aldosterone system by blocking the receptor sites directly. Because Zestoretic specifically contains an ACE inhibitor, this ARB combination does not match the requested generic profile.
D. Amlodipine combined with hydrochlorothiazide does not have a single common brand name as a dual-combination pill; amlodipine is often paired with an ACE inhibitor or ARB in triple-therapy agents like Exforge HCT. Amlodipine is a calcium channel blocker, which works through a completely different mechanism than lisinopril. Therefore, this combination is not the generic equivalent of the brand Zestoretic.
Correct Answer is E
Explanation
The nephron is the functional unit of the kidney, responsible for filtering blood and maintaining homeostatic balance. Through filtration, reabsorption, and secretion, the renal system controls the composition of extracellular fluid. This involves complex interactions with the endocrine and cardiovascular systems. The kidneys ensure that the internal environment remains stable despite fluctuations in dietary intake and metabolic waste production.
Rationale:
A. The kidneys regulate blood pressure through the Renin-Angiotensin-Aldosterone System (RAAS) and the control of blood volume. By adjusting the excretion of sodium and water, the renal system directly influences cardiac preload and systemic vascular resistance. This is a critical mechanism for the long-term management of arterial blood pressure.
B. Blood solute concentrations, or osmolality, are regulated by the kidneys via the action of antidiuretic hormone (ADH) on the collecting ducts. The renal system can produce urine that is either highly concentrated or dilute to maintain a stable plasma osmolality (typically 285-295 mOsm/kg). This protects cells from osmotic shrinking or swelling.
C. The renal system is involved in hormone secretion, including erythropoietin for red blood cell production and renin for pressure regulation. Additionally, the kidneys perform the final activation of Vitamin D into its active form, calcitriol. These endocrine functions are vital for systemic health and are directly performed by specialized renal cells.
D. Blood pH is maintained by the kidneys through the reabsorption of bicarbonate and the secretion of hydrogen ions. While the respiratory system provides rapid pH adjustments, the renal system provides the long-term, definitive compensation for acid-base imbalances. This ensures that the blood pH remains within the narrow physiological range of 7.35-7.45.
E. Blood temperature is not directly regulated by the renal system. Thermoregulation is primarily controlled by the hypothalamus and involves mechanisms such as vasodilation/vasoconstriction in the skin, sweating, and shivering. The kidneys do not have a specialized physiological mechanism for adjusting or maintaining core body temperature.
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