USMLE® Step 1 style questions USMLE
USMLE® Step 2 style questions USMLE
A 45-year-old woman comes to the emergency department because of nausea and vomiting for the past hour. Past medical and family histories are noncontributory. Temperature is 37.2°C (99°F), pulse is 90/min, respirations are 16/min, blood pressure is 165/105, and oxygen saturation is 96% on room air. Laboratory test show a serum potassium level of 4.9 mEq/L, increased plasma aldosterone concentration, and decreased plasma renin activity. Magnetic resonance imaging shows:
Which of the following is the most likely diagnosis?
Content Reviewers:Rishi Desai, MD, MPH
Contributors:Tanner Marshall, MS
Now, there are two adrenal glands, one above each kidney, and each one has an inner layer called the medulla and an outer layer called the cortex which is subdivided into three more layers, the zona glomerulosa, zona fasciculata, and the zona reticularis.
The outermost layer is the zona glomerulosa, and it’s full of cells that make the hormone aldosterone.
Aldosterone is part of a hormone family or axis which work together and are called the renin-angiotensin-aldosterone system.
Together these hormones decrease potassium levels, increase sodium levels, and increase blood volume and blood pressure.
Aldosterone is secreted in response to elevated levels of renin, and it’s role is to bind to receptors on two types of cells along the distal convoluted tubule of the nephron.
First it stimulates the sodium/potassium ion pumps of the principal cells to work even harder.
These pumps drive potassium from the blood into the cells and from there it flows down its concentration gradient into the tubule to be excreted as urine.
At the same time, the pumps drive sodium in the opposite direction from the cell into the blood, which allows more sodium to flow from the tubule to the cell down its concentration gradient.
Since water often flows with sodium through a process of osmosis, water also moves into the blood, which increases blood volume and therefore blood pressure.
The other function of aldosterone is to stimulate the ATPase pumps in alpha-intercalated cells which causes more protons to get excreted into the urine.
Meanwhile, ion exchangers on the basal surface of the cell move the negatively charged bicarbonate ion into the extracellular space, causing an increase in pH.
Hyperaldosteronism can happen due to primary causes which is where the adrenal gland itself is responsible for the excess production of aldosterone.
The most common primary cause is called idiopathic hyperaldosteronism, because the zona glomerulosa has an increase in the number of cells secreting aldosterone, but it’s not really clear why this happens.
The second most common cause is called Conn syndrome and this is where an adenoma or tumor in the glandular epithelial cells secretes too much hormone.
A third cause is familial hyperaldosteronism, and this is a genetic condition that runs in families, and it’s when the zona glomerulosa cells inappropriately make aldosterone in response to adrenocorticotropic hormone which is secreted by the pituitary gland, and this is in addition to responding to renin as normal.
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- "First Aid for the USMLE Step 1 2017" McGraw-Hill Education / Medical (2017)
- "Principles of Anatomy and Physiology" Wiley (2014)