This article is in response to the request made by a reader in the comment section. Today, we will try to simplify the biliary tree cancers. Classification of Cholangiocarcinoma Second-order bile ducts act as the separation point between intrahepatic and extrahepatic cholangiocarcinoma. A. Inhtrahepatic – 10 to 20% B. Extrahepatic…
PGMEE, MRCS, USMLE, MBBS, MD/MS 
Most Important Urinary Buffer: Phosphate or Ammonia?
There are multiple choice questions (mcq) which asks: What is the most important urinary buffer? And the choices include both the phosphate and ammonia. Different textbooks on physiology and biochemistry have different opinions. Some say that the most important is Phosphate and the others say Ammonia is more important. So,…
PGMEE, MRCS, USMLE, MBBS, MD/MS 
Rosettes in Pathology
Rosette refers to a decoration or pattern resembling a rose. In pathology, rosette refers to aa halo or “spoke-wheel” arrangement of cells around a central structure especially in neoplasms of neuroblastic or neuroectoderma origin. The central structure can be: a. Empty lumen: True ependymal rosette Well differentiated ependymomas (minority of cases)…
PGMEE, MRCS, USMLE, MBBS, MD/MS 
DNA Replication Explained With Zipper Model
Imagine DNA as a zipper Prokaryotic DNA as a zipper with single slider (single origin of replication) and Eukaryotic DNA as a zipper with two sliders (multiple origin of replication). Zipper teeth: Purines and pyrimidine bases Complementary teeth pair: Complementary base pairs attached by hydrogen bonds Top stops: Origin of…
PGMEE, MRCS, USMLE, MBBS, MD/MS 
Purine and Pyrimidines : Structure, Synthesis and Metabolism
Purines and Pyrimidines Bases Purines = 2 rings Adenine Guanine Hypoxanthine (Deaminated Adenine) Adenine to Hypoxanthine deamination is mediated by Adenosine deaminase which is decreased in Autosomal recessive SCID. Accumulated dATP inhibit ribonucleotide reductase leading to deficient synthesis of other deoxyribonulceotide precursors for DNA synthesis. Xanthine (Deaminated Guanine) Mnemonics: Pure…
PGMEE, MRCS, USMLE, MBBS, MD/MS 
Trinucleotide Repeat Disorders and Anticipation Mnemonics
Anticipation in genetics refers to an increase in severity and decrease in age of onset in successive generations, most likely due to increased size of trinucleotide repeats. Paternal anticipation: Huntington’s disease, Friedreich’s Ataxia Maternal anticipation: Myotonic dystrophy, Fragile X syndrome Diseases Trinucleotide Repeat Affected gene Chromosome Fragile X syndrome CGG…
PGMEE, MRCS, USMLE, MBBS, MD/MS 
Solving Pedigree Analysis in 3 steps
First: Look for Mitochondrial Inheritance Female transmits disease to all the offsprings (both males and females). Male doesn’t transmit the disease and only the females transmit the disease. If Mitochondrial inheritance is absent, go to second step. Second: Look if the gene is Dominant, Recessive Dominant: Atleast one member in…
PGMEE, MRCS, USMLE, MBBS, MD/MS 
Lysosomal Storage Disorders Made Easy
Among the common lysosomal storage disorders: Two of them are Mucopolysaccharidoses (Hunter and Hurler syndrome) Pompe’s disease is Glycogen Storage Disease. Others are Sphingolipidoses. Inheritance of Lysosomal Storage Diseases All are inherited as Autosomal Recessive (AR) condition except: Hunter syndrome (X-linked recessive) Fabry’s disease (X-linked recessive) Higher risk in Ashkenazi…