Скачать или смотреть 18. Urea Cycle | Steps, Regulation & Disorders | Nitrogen Metabolism | Medical Biochemistry USMLE

𝐒𝐮𝐛𝐬𝐜𝐫𝐢𝐛𝐞 𝗙𝐨𝐫 𝗠𝐨𝐫𝐞 𝗜𝐧𝐟𝐨𝐫𝐦𝐚𝐭𝐢𝐨𝐧 𝐨𝐧 𝗛𝐞𝐚𝐥𝐭𝐡 👩‍⚕‍ 𝐚𝐧𝐝 𝗠𝐞𝐝𝐢𝐜𝐢𝐧𝐞💉🩺💊
📌𝗜𝗻𝘀𝘁𝗮𝗴𝗿𝗮𝗺 :   / clinical.learning  

Urea Cycle | Steps, Regulation & Disorders | Nitrogen Metabolism | Medical Biochemistry | MBBS | USMLE Step 1

👋 Hey future doctors and biochem learners! Have you ever wondered how the body gets rid of the toxic ammonia generated during amino acid breakdown? ☠️ The answer lies in the Urea Cycle (also called the ornithine cycle) — the liver’s special pathway to detoxify nitrogen and excrete it as urea in urine. 💧

Understanding the steps, regulation, and clinical disorders of the urea cycle is essential for MBBS, NEET PG, FMGE, and USMLE Step 1, as it links biochemistry with clinical medicine. 🧬📚

🌟 Steps of the Urea Cycle (Ornithine Cycle)

1️⃣ Carbamoyl phosphate formation

Ammonia + CO₂ + 2 ATP → Carbamoyl phosphate

Enzyme: Carbamoyl phosphate synthetase I (CPS-I) (rate-limiting, requires N-acetylglutamate as activator).

2️⃣ Citrulline formation

Carbamoyl phosphate + Ornithine → Citrulline

Enzyme: Ornithine transcarbamylase (OTC).

3️⃣ Argininosuccinate formation

Citrulline + Aspartate → Argininosuccinate

Enzyme: Argininosuccinate synthetase (uses ATP).

4️⃣ Arginine formation

Argininosuccinate → Arginine + Fumarate

Enzyme: Argininosuccinate lyase.

5️⃣ Urea release

Arginine → Urea + Ornithine

Enzyme: Arginase (found only in the liver).

Ornithine re-enters cycle to continue the process.

⚙️ Regulation of Urea Cycle

N-acetylglutamate (NAG) is the allosteric activator of CPS-I.

Increased protein intake or fasting → ↑ urea cycle activity.

Tightly linked with TCA cycle (fumarate) and aspartate shuttle (for nitrogen entry).

🩺 Clinical Correlations

Hyperammonemia: due to urea cycle enzyme defects or liver failure → confusion, vomiting, cerebral edema, coma.

Ornithine Transcarbamylase (OTC) Deficiency: most common urea cycle disorder (X-linked).

Argininosuccinate synthetase deficiency (Citrullinemia), Argininosuccinate lyase deficiency, Arginase deficiency → characteristic lab findings (↑ specific metabolites).

Management: protein restriction, nitrogen scavenger drugs (sodium benzoate, sodium phenylbutyrate), and in some cases, arginine supplementation.

🎯 Exam Integration

Location: mitochondria + cytosol (partly).

Key enzyme: CPS-I (rate-limiting, NAG required).

Major concept: Urea cycle detoxifies 2 nitrogen atoms — one from free NH₃, one from aspartate.
👉 High-yield in both recall questions (steps, enzymes, location) and clinical case vignettes (hyperammonemia, OTC deficiency).

👉 Don’t forget to Subscribe and hit the 🔔 bell so you never miss our high-yield biochemistry lectures!

👍 If this lecture helped you, please like and share with your classmates. Your support keeps us motivated to produce simplified, exam-focused content. 🙌

❓Got questions about nitrogen metabolism or want us to cover Urea Cycle Disorders (UCDs) in detail? Drop your request in the comments below — we’d love to help! 😊

#UreaCycle #OrnithineCycle #NitrogenMetabolism #Hyperammonemia #CPS1 #OTCDeficiency #MedicalBiochemistry #USMLEStep1 #MBBSLectures #FMGE #NEETPG #Argininosuccinate #Arginase #CarbamoylPhosphate #BiochemistryLecture #MedicalStudents