Curriculum

17 Sections
1548 Lessons
100 Days

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U01.01 Biochemistry
This biochemistry review for USMLE Step 1 covers essential topics including metabolism, enzymology, and molecular biology.
126
U01.02 Immunology
Prepare for USMLE Step 1 Immunology with a comprehensive review covering foundational concepts, immune system mechanisms, and key disorders to solidify your understanding and boost exam readiness.
42
U01.03 Microbiology
Review essential microbiology topics for the USMLE Step 1, covering key pathogens, mechanisms of disease, and antimicrobial principles critical for mastering infectious disease concepts.
172
U01.04 General Pathology
Explore key concepts in general pathology essential for the USMLE Step 1. This review covers fundamental principles, disease mechanisms, and clinical correlations to help you excel in your medical exam.
35
U01.05 Pharmacology
Master key pharmacology concepts for the USMLE Step 1 with a focus on drug mechanisms, therapeutic uses, adverse effects, and interactions essential for high-yield exam performance.
43
U01.06 Public Health Sciences
Review essential Public Health Sciences topics for the USMLE Step 1, covering epidemiology, biostatistics, health policy, and ethics to strengthen your understanding of foundational public health principles.
53
U01.07 Cardiovascular system
Comprehensive review of essential cardiovascular system topics to help you excel in the USMLE Step 1 exam, covering key concepts from anatomy to pathology.
73
U01.08 Endocrine system
Master essential concepts of the endocrine system for USMLE Step 1, covering hormone regulation, feedback mechanisms, and key disorders to boost your exam readiness.
51
U01.09 Gastrointestinal system
Review key topics in the gastrointestinal system for the USMLE Step 1, covering essential concepts in anatomy, physiology, pathology, and pharmacology to reinforce your understanding and test readiness.
131
U01.10 Hematology and Oncology
This review covers essential Hematology and Oncology topics for the USMLE Step 1, including hematopoiesis, coagulation, anemias, leukemias, lymphomas, and neoplastic syndromes.
148
U01.11 Musculoskeletal, Skin, and Connective Tissue
Review essential topics for the USMLE Step 1 Musculoskeletal, Skin, and Connective Tissue systems, covering anatomy, physiology, pathology, and pharmacology fundamentals critical for exam success.
178
U01.12 Neurology and Special Senses
Master the foundational concepts of Neurology and Special Senses with our USMLE Step 1 review, covering essential topics like neuroanatomy, neurophysiology, and sensory pathways.
143
U01.13 Psychiatry
Psychiatry for the USMLE Step 1 focuses on understanding the pathophysiology, diagnosis, and treatment of psychiatric disorders, with an emphasis on key concepts like neurotransmitter imbalances, mental health disorders, and pharmacology.
83
U01.14 Renal System
The Renal System review for USMLE Step 1 covers key concepts including renal physiology, nephron function, acid-base balance, electrolyte regulation, and renal pathology, crucial for understanding both normal and abnormal kidney functions.
81
U01.15 Reproductive System
The USMLE Step 1 Reproductive System review covers key concepts in human reproduction, including anatomy, physiology, endocrinology, and common pathologies affecting both male and female reproductive health.
124
U01.16 Respiratory System
The Respiratory System review for the USMLE Step 1 covers key concepts in anatomy, physiology, pathophysiology, and pharmacology essential for understanding respiratory diseases and treatments.
61
U01.17 Rapid Review
he USMLE Step 1 Rapid Review covers essential topics across multiple disciplines, providing a concise, high-yield overview to reinforce key concepts and optimize your exam preparation.
5

U01.02.028 Hypersensitivity types

Hypersensitivity reactions are classified into four types (ABCD):

Type I: Anaphylactic and Atopic
Type II: AntiBody-mediated
Type III: Immune Complex-mediated
Type IV: Delayed (cell-mediated)

Types I, II, and III involve antibodies, whereas Type IV is mediated by T cells. Below is a detailed explanation with examples, tests, and mechanisms.

Type I Hypersensitivity

Mechanism

Immediate phase (minutes):
- Antigen crosslinks preformed IgE on mast cells → degranulation → release of histamine and tryptase.
Late phase (hours):
- Chemokines (e.g., eosinophil attractants) and leukotrienes mediate inflammation and tissue damage.

Key Features

Mnemonic: First (Type) and Fast (anaphylaxis).
Tests:
- Skin test or ELISA for allergen-specific IgE.

Examples

Anaphylaxis: Food, drug, or bee sting allergies.
Allergic asthma: Triggered by environmental allergens.

Component	Role
Allergen	Triggers the reaction.
IgE	Sensitizes mast cells.
Mast cell degranulation	Releases histamine and mediators.

Type II Hypersensitivity

Mechanism

Antibodies bind to cell-surface antigens →

Cellular destruction:
- Opsonization → Phagocytosis or complement activation.
- NK cell-mediated killing (ADCC).
Inflammation:
- Antibody binding → Complement activation → Inflammation.
Cellular dysfunction:
- Antibody binding to receptors → Abnormal function (e.g., blockade or activation).

Key Features

Direct Coombs test: Detects antibodies on RBCs.
Indirect Coombs test: Detects unbound serum antibodies.

Examples

Mechanism	Examples
Cellular destruction	Autoimmune hemolytic anemia, ITP, transfusion reactions, hemolytic disease of the newborn.
Inflammation	Goodpasture syndrome, rheumatic fever, hyperacute transplant rejection.
Cellular dysfunction	Myasthenia gravis, Graves disease, pemphigus vulgaris.

Type III Hypersensitivity

Mechanism

Antigen-antibody (IgG) complexes form → Complement activation → Neutrophil recruitment → Tissue damage via lysosomal enzymes.

Key Features

Associated with vasculitis and systemic manifestations.
Mnemonic: Think of 3 things stuck together: Antigen–Antibody–Complement.

Examples

Example	Description
Serum sickness	Antibody-antigen complexes form 1–2 weeks after antigen exposure → fever, urticaria, arthralgia.
Arthus reaction	Local immune complex reaction (e.g., booster vaccine reaction).
Diseases	SLE, polyarteritis nodosa, poststreptococcal glomerulonephritis.

Type IV Hypersensitivity

Mechanism

Mediated by T cells:

CD8+ cytotoxic T cells: Directly kill target cells.
CD4+ T cells: Release cytokines → Activate macrophages → Induce inflammation.

Key Features

Does not involve antibodies (vs Types I, II, and III).
Mnemonic: 4 T’s → T cells, Transplant rejection, TB test, Touching (contact dermatitis).

Examples

Test/Mechanism	Examples
PPD test	Tuberculosis screening.
Patch test	Contact dermatitis (e.g., poison ivy, nickel allergy).
Graft-versus-host disease	Immune response in transplant recipients.

Quick Mnemonics for Hypersensitivity Types

Type	Key Mnemonic
I	First and Fast (Anaphylaxis).
II	Antibodies attack directly.
III	Immune Complexes → 3 things together.
IV	Fourth and Last (Delayed by T cells).

Points to Remember for USMLE

Type I: Immediate allergy tests.
Type II: Coombs test for antibody-mediated conditions.
Type III: Complex-driven systemic manifestations.
Type IV: T cell-mediated delayed reactions.

USMLE Step 1 Review Series

Curriculum

U01.02.028 Hypersensitivity types

Type I Hypersensitivity

Mechanism

Key Features

Examples

Type II Hypersensitivity

Mechanism

Key Features

Examples

Type III Hypersensitivity

Mechanism

Key Features

Examples

Type IV Hypersensitivity

Mechanism

Key Features

Examples

Quick Mnemonics for Hypersensitivity Types

Points to Remember for USMLE

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