UWorld 090324

• Proximal humerus and glenohumeral joint receive their blood supply via the anterior and posterior circumflex humeral arteries, which are branches of the axillary artery that form an anastomosis at the neck of the humerus
• Humeral neck fractures can disrupt the blood flow, leading to avascular necrosis of the humeral head
• Radial nerve & deep brachial artery are damaged by fractures posterior to the midshaft of the humerus
• Supracondylar fracture injures the brachial artery & median nerve as they pass ant. to distal humerus
• A 16-year-old boy is brought to the office by his father after he was found smoking marijuana in his room. The father states that although the patient "swears this was the first time," he cannot trust him. He says that his father "has always had high expectations" and frequently compares him to his older sister, who was valedictorian of her class. When asked about substance use, the patient says, "No matter what I say, I know you're going to judge me. I'm not like your other patients who do everything right." What type of response? Transference.
• In undoing, patients attempt to manage shame and repair relationships by making excessive qualifications for or acting in a manner opposite of an offense
• Patient developed erythema and pruritus on the scalp, face, and neck 2 days after reexposure to hair dye, which is Allergic Contact Dermatitis (ACD), a type IV hypersensitivity (delayed type) reaction
• Initial phase of ACD

  Cutaneous Langerhans cells take up haptens, present them to naive CD4+ and CD8+ T cells in regional lymph nodes, resulting in T cell proliferation; 10-14 days; DOES NOT RESULT IN CUTANEOUS LESIONS
• Reexposure phase of ACD

  Sensitized T cells [CD8+] are recruited to skin, release cytotoxins (eg, perforin, granzymes) and express Fas ligand to induce keratinocyte apoptosis; occurs 2-3 days following reexposure
• Type I Hypersensitivity reaction results in wheals of urticaria that resolve within 24 hours
• Immunoglobulins produced by plasma cells are involved in type II and III hypersensitivity reactions
• Nitrites cause poisoning by inducing the conversion of heme iron to the oxidized ferric (Fe3+) state, leading to the formation of methemoglobin
• Turner’s Syndrome is most often caused by meiotic nondisjunction during gametogenesis
• Meiotic nondisjunction refers to failed separation of homologous chromosomes (meiosis I) or sister chromatids (meiosis II), resulting in a gamete with an abnormal number of chromosomes (eg, 22, 24)
• Heterophile IgM antibodies react with antigens on horse erythrocytes and are specific for EBV infection
• Cryoglobulins, cold-precipitable serum proteins containing Igs, are most commonly associated with HCV infection
• Influenza and Parainfluenza viruses are associated with hemadsorption
• Tzanck smear for HSV or VZV involves examining epithelial cells scraped from the ulcer base for multinucleated giant cells and intranuclear inclusions
• Transverse tubules (T-tubules) are tiny tunnels in the membrane of muscle cells, found near the storage sites for calcium in striated muscles like the heart and skeletal muscles
• During muscle contraction, T-tubules allow the depolarization impulse to rapidly propagate through the interior of the muscle fiber
• Heart and skeletal muscles

  • Contain voltage-gated L-type calcium channels (dihydropyridine receptors) adjacent to the ryanodine receptors on the terminal cisterns
• Muscle contraction


  1. tubules allow the depolarization impulse to rapidly propagate through the interior of the muscle fiber, ensuring uniform calcium release from the sarcoplasmic reticulum throughout the fiber for synchronized contraction of myofibrils in each muscle cell
• Decremental force generated on repeated stimulation characterizes myasthenia gravis
• McArdle disease is characterized by impaired ATP production due to a failure of muscle glycogen breakdown
• A mutation in troponin C may block its response to intracellular calcium and prevent muscle contraction
• Tranexamic acid (TXA) is an antifibrinolytic medication that stabilizes blood clots by inhibiting plasmin formation, preventing fibrin degradation and clot dissolution, used for PPH
• Maternal hemostasis after placental delivery

  Includes uterine contraction to constrict bleeding placental bed vessels, activation of coagulation pathways, and clot formation at the former placental attachment site
• Coagulation after placental delivery


  Prothrombotic substances in the decidua activate the extrinsic coagulation cascade, generating thrombin that converts fibrinogen into fibrin, forming a clot. The fibrinolytic pathway is also activated
• Prothrombin complex concentrate (PCC) increases vitamin K–dependent coagulation factor levels
• Misoprostol, a PG analogue, induces prostaglandin-mediated smooth muscle contraction
• Oxytocin rapidly increases intracellular calcium levels in the uterine myometrium
• Desmopressin promotes endothelial release of vWF
• Failed fusion of the medial nasal prominences to form the intermaxillary segment is associated with severe midline defects, such as holoprosencephaly
• Hyperplasia of the frontonasal prominence leads to hypertelorism, broad forehead, and wide nasal bridge
• Hypoplasia of the mandibular prominence causes micrognathia, seen in Pierre Robin sequence
• A cleft palate can develop from failed fusion of the palatine shelves, thin sheets of tissue derived from the maxillary prominences that grow medially, fuse, and form the secondary palate
• Norepinephrine stimulates alpha-1 receptors for peripheral vasoconstriction, increasing systemic vascular resistance and blood pressure, triggering a baroreceptor–mediated reflexive decrease in heart rate
• Stimulation of alpha-2 receptors in the CNS decreases sympathetic output, causing peripheral vasodilation, decreased heart rate, and reduced blood pressure
• Stimulation of dopamine-1 receptors causes renal arteriolar vasodilation and increases renal blood flow
• Patient with numerous fleshy, dome-shaped, and pedunculated lesions has neurofibromatosis type 1 (NF1) with cutaneous neurofibromas, Lisch nodules, and potential optic pathway gliomas