WBR0516

Author	[[PageAuthor::Gonzalo A. Romero, M.D. [1]]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Physiology
Sub Category	SubCategory::Renal, SubCategory::Vascular
Prompt	[[Prompt::A 32-year-old woman delivers a 38-week-old boy after a non-controlled pregnancy. She is known hypertensive and was taking enalapril to control her blood pressure before becoming pregnant. She assisted to her first trimester control, when the physician told her that it was necessary to stop her medication because it can cause many fetal problems. Regardless of medical advice, she continued taking enalapril. Upon delivery and physical examination, the newborn is suspected to have malformations and renal damage after the chronic in-utero exposure to this drug. Which of the following changes in an adult's kidney physiology occurs with the use of enalapril?]]
Answer A	AnswerA::Increase in FF, increase in GFR and decrease in RPF
Answer A Explanation	[[AnswerAExp::Incorrect. Corresponds to the AT-II functions]]
Answer B	AnswerB::Decrease FF, decrease GFR and increase RPF
Answer B Explanation	[[AnswerBExp::Correct. ACE inhibitor effect]]
Answer C	AnswerC::No change in FF, decrease in GFR and decrease in RPF
Answer C Explanation	[[AnswerCExp::Incorrect. Constriction of afferent arteriole]]
Answer D	AnswerD::Increase in FF, Increase in GFR and no change in RPF
Answer D Explanation	[[AnswerDExp::Incorrect. Corresponds to hypoalbuminemia]]
Answer E	AnswerE::Decrease in FF, decrease in GFR and no change RPF
Answer E Explanation	[[AnswerEExp::Incorrect. Corresponds to hyperalbuminemia]]
Right Answer	RightAnswer::B
Explanation	[[Explanation::* Enalapril is an ACE (angiotensin converting enzyme) inhibitor medication used to treat hypertension. ACE inhibitors and aldosterone receptor blockers are associated with many fetal malformations if used during pregnancy (teratogenic), especially renal damage. ACE inhibitors are associated with the following teratogenic effects: hypotension, renal dysplasia, anuria or oliguria, oligohydramios, intrauterine growth retardation (IUGR), pulmonary hypoplasia, patent ductus arteriosus (PDA), incomplete ossification of the skull, intrauterine neonatal death Physiology: normally angiotensin II (AT-II) constricts the glomerular efferent arteriole, which causes an increase in the hydrostatic pressure within the glomerulus increasing the glomerular filtration rate (GFR). AT-II by constricting the efferent arteriole, decreases the renal plasma flow (RPF). By decreasing RPF and increasing GFR, AT-II increases the filtration fraction (FF), which is GFR/RPF. ACE inhibitors such as enalapril, decrease AT-II which cause the inverse effect, therefore by inhibiting the production of angiotensin II (AT-II), it decreases the FF by dilating the efferent arteriole. With enalapril the hydrostatic pressure within the glomerulus decreases, which decreases GFR. By decreasing the resistance in the efferent arteriole, the renal plasma flow increases, which ultimately leads to decrease in filtration fraction. ACE inhibitors are contraindicated in patients with renal artery stenosis, because the blood flow decreases even more and the filtration fraction decreases, therefore the patient is prone to develop renal insufficiency. Educational Objective: AT-II constricts the efferent arteriole, increasing GFR, decreasing RPF, and increasing the FF ACE inhibitors → decrease AT-II → decrease GFR & increase RPF → FF decrease ACE inhibitors are teratogenic, causing fetal renal damage References: First Aid for STEP 1 2013, Renal-Physiology Chapter, page 516. Educational Objective: References: ]]
Approved	Approved::Yes
Keyword	WBRKeyword::Filtration fraction, WBRKeyword::GFR, WBRKeyword::ACE inhibitor, WBRKeyword::enalapril
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::