Concentration of the urine is controlled by?

Appeared in: NHM UP Staff Nurse - 2016

Explanation

Antidiuretic Hormone (ADH) is the primary hormone responsible for regulating the concentration of urine.
ADH acts on the collecting ducts of the kidneys, increasing their permeability to water.
This action allows more water to be reabsorbed from the filtrate back into the blood, resulting in a smaller volume of more concentrated urine.
The secretion of ADH is regulated by plasma osmolarity; high osmolarity stimulates ADH release to conserve water, while low osmolarity inhibits it to excrete excess water.

Option A: Melanocyte-stimulating hormone (MSH) is primarily involved in skin pigmentation by stimulating melanin production. It has no direct role in regulating urine concentration.
Option C: Oxytocin's main functions are stimulating uterine contractions during labor and milk ejection. While it can have a very weak antidiuretic effect, it is not the primary hormone controlling urine concentration.
Option D: Adrenocorticotropic hormone (ACTH) stimulates the adrenal glands to release cortisol, a stress hormone. It is part of the hypothalamic-pituitary-adrenal (HPA) axis and does not directly control urine concentration.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Hormonal regulation of renal function and urine concentration as background academic context rather than a clinical decision trigger.
Understanding ADH function is crucial for diagnosing and managing conditions like Diabetes Insipidus (DI) and the Syndrome of Inappropriate ADH Secretion (SIADH).
In DI, a deficiency of ADH or the kidneys' response to it leads to the excretion of large volumes of dilute urine (polyuria) and intense thirst (polydipsia).
In SIADH, excessive ADH secretion causes excessive water retention, leading to dilutional hyponatremia (low sodium levels in the blood) and concentrated urine.

How to Approach the Question

First, identify the key physiological process in the question: 'Concentration of the urine'.
Recall the major endocrine glands and the hormones they produce that are related to kidney function and water balance. The posterior pituitary is a key player here.
Systematically evaluate the function of each hormone listed in the options.
Eliminate the options whose primary functions are unrelated to the kidneys or water balance (e.g., MSH for skin, Oxytocin for uterus/breasts, ACTH for adrenal cortex).
Confirm that the remaining option, ADH (Antidiuretic Hormone), directly matches the function described. The name 'antidiuretic' itself means 'against urination', which is a strong clue.

Concept Tested & Keywords

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E6 Physiology Guyton 4SAE Part 2B pp. 40-41, 41-43

Practise the full NHM UP Staff Nurse - 2016

Attempt every question from this paper in a timed mock, then review the full solution for each one.