Urea cycle
Read the topic background here, then explore the labeled visual and structured learning explanations on this page.
Read explanation on this page ↓ See diagram ↓Urea cycle — on-site reading
An introductory overview for this topic. The article introduction is reproduced here, so you do not need to leave MedAtlas to read it. It may not match the latest official medical guidance.
The urea cycle (also known as the ornithine cycle) is a cycle of biochemical reactions that produces urea (NH2)2CO from ammonia (NH3). Animals that use this cycle, mainly amphibians and mammals, are called ureotelic.
The urea cycle converts highly toxic ammonia to urea for excretion. This cycle was the first metabolic cycle to be discovered by Hans Krebs and Kurt Henseleit in 1932, five years before the discovery of the TCA cycle. The urea cycle was described in more detail later on by Ratner and Cohen. The urea cycle takes place primarily in the liver and, to a lesser extent, in the kidneys.
How this connects to Biochemistry
To study this topic responsibly, identify its normal structure or function, distinguish the main mechanism from its observable consequences, and ask which data can test a competing explanation. The subject foundations below outline these connections without pretending to be a specialist textbook chapter.
Text credit: Wikipedia contributors, “Urea cycle”, original article · authors & revision history · CC BY-SA 4.0. Unmodified opening extract, accessed 24 September 2026. This Wikipedia-derived section is provided under CC BY-SA 4.0; the independent MedAtlas notes and design are separate works.
Urea cycle · visual study map
Scalable vector illustration. Labeled conceptual map, not a precise anatomical, histological or diagnostic image.The wording in this learning map is adapted from the attributed Wikipedia background section below (CC BY-SA 4.0).
What the underlying subject studies
Biochemistry explains biological function through molecules, enzymes, energetic coupling and regulation. Map the principal substrates and products of a reaction, identify the relevant cellular compartment, and distinguish direct energy output from energy transferred to cofactors.
How mechanisms and evidence connect
Metabolic pathways form a network rather than isolated cycles. A pathway’s flux depends on enzyme activity, substrate availability, hormonal signals, cell type and the body’s nutritional or disease state. Single reaction diagrams intentionally simplify complex regulation.
How to develop a sound explanation
For study, draw input → key steps → output. Mark where energy is invested or recovered, identify irreversible or regulated steps, and relate abnormal biomarkers to possible processes without using them alone to diagnose a patient.
References and verification (optional)
All reading material on this page appears above. The links below are for checking the primary syllabus, research or source attribution, not requirements for opening this lesson.
NMC official CBME Curriculum 2024 and current regulations index ↗