Skip to ContentGo to accessibility page

Key Terms

blood urea nitrogen (BUN)
a blood test that measures the amount of urea nitrogen in the blood; elevated levels can indicate decreased renal function
Bowman’s capsule
part of the nephron that contains the glomerulus
cortical nephrons
comprise a majority of the functional units of the kidney located in the outer renal cortex
fenestrated capillaries
small blood vessels in the glomerulus that filter waste
glomerular filtration
initial step in making urine involving the filtering of excess fluid and waste products from blood
glomerular filtration rate (GFR)
the rate at which the kidneys filter the blood, calculated using the results of blood tests that measure renal function
glomerulus
located in nephrons, a tuft of capillaries surrounded by the Bowman’s capsule that filters blood
hilum
indentation on the medial side of the kidney that allows blood vessels, lymphatic vessels, and nerves to enter and exit
juxtamedullary nephrons
nephrons with longer loops of Henle that extend into the medulla
loop of Henle
part of the nephron that contributes to absorption of sodium
mesangial cells
cells that increase the body surface area for glomerular filtration by limiting the size of molecules that can be filtered
micturition
the process through which urine is released from the bladder
nephrons
the functional units of the kidney that produce urine
renal colic
acute pain associated with kidney stones
renal cortex
outermost layer of the internal areas of the kidney containing nephrons
renal medulla
inner part of the kidney containing structures essential for regulating urine concentration
renal pelvis
funnel-shaped area of the kidney that collects urine and is connected to the ureter
tubular necrosis
damage to the tubule cells of the kidney typically resulting from reduced blood flow or chemical exposure
vasa recta
long, hairpin-shaped blood vessels that run parallel to the loops of Henle and facilitate water reabsorption
vesicoureteral reflux
abnormal backflow of urine from the bladder up through the ureters
Citation/Attribution
Reuse and redistribution of this content in digital or print format:
  • This book may not be used in the training of large language models or otherwise be ingested into large language models or generative AI offerings without OpenStax's prior written permission.
  • This book uses the Creative Commons Attribution-NonCommercial-ShareAlike License, which means that you can reuse and modify the material only for noncommercial purposes, must attribute OpenStax, and must distribute any derivative works under the same license.
  • Any commercial printing of this textbook, including using a local or custom printer, must be approved by OpenStax, and proper citation provided.
  • OpenStax-copyrighted images, activities, assessments, and similar components of this book are subject to the same licensing – CC-BY-NC-SA. They can be used for noncommercial purposes with attribution. Commercial use requires permission.
  • Permission requests: Anyone who intends to incorporate this content (including text, images, and other components) into large language models, use it in AI offerings, use it commercially (including in print), and/or has questions about another use case is welcome to complete our reuse request form.
Attribution information
  • If you are redistributing all or part of this book in a noncommercial print format, then you must include on every physical page the following attribution:

    Access for free at https://openstax.org/books/pharmacology/pages/1-introduction

  • If you are redistributing all or part of this book in a noncommercial digital format, then for every page that includes OpenStax content, you must license the derivative work under the same CC-BY-NC-SA license as the original, and include on every digital page view the following attribution:

    Access for free at https://openstax.org/books/pharmacology/pages/1-introduction

Citation information

The information below includes the information needed to generate citations in most major styles (APA, MLA, etc.); you must reformat and organize the information as needed to fit the requirements of the style. Use the information below to generate a citation. We recommend using a citation tool such as this one.

© Apr 23, 2026 OpenStax. Textbook content produced by OpenStax is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike License. The OpenStax name, OpenStax logo, OpenStax book covers, OpenStax CNX name, and OpenStax CNX logo, and Rice University name, and Rice University logo trademarks, or wordmarks are not subject to the Creative Commons license and may not be reproduced without the prior and express written consent of Rice University.