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Embryology USMLE Step1 @doctordc_online
Researchers study kidney development in mouse embryos. When the ureteric bud is surgically removed, the metanephric mesenchyme fails to form nephrons. When the metanephric mesenchyme is removed, the ureteric bud fails to branch into collecting ducts. Each tissue needs signals from the other to develop.
This same type of signaling interaction also occurs between which of the following?
6 hours ago | [YT] | 3
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Anatomy USMLE Step1 @doctordc_online
A 45-year-old man notices tender lumps in his right groin and behind his right knee. Examination shows enlarged, tender right superficial inguinal lymph nodes and enlarged right popliteal lymph nodes. The rest of the examination is normal.
Which of the following lesions best explains this pattern of lymphadenopathy?
1 day ago | [YT] | 2
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Physiology USMLE Step1 @doctordc_online
A 26-year-old healthy man from sea level travels to a mountain town at 4,000 m. He has headache and mild breathlessness for the first few days. After 2 weeks he feels better.
Arterial blood gas (room air, day 14): pH 7.45, PaO₂ 52 mm Hg, PaCO₂ 29 mm Hg, HCO₃⁻ 19 mEq/L.
Which physiologic change has most likely occurred?
2 days ago | [YT] | 5
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Cardiology USMLE Step1 @doctordc_online
A 1-day-old girl has puffy hands and feet. Examination shows a short neck with loose skin folds at the back, a broad chest with widely spaced nipples, and nonpitting edema of the dorsa of the hands and feet. Blood pressure is 88/60 mm Hg in the right arm and 60/40 mm Hg in the right leg.
Labs: Serum albumin 3.6 g/dL (normal); urinalysis negative for protein.
What is the most likely cause of the edema?
3 days ago | [YT] | 7
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Anatomy USMLE Step1 @doctordc_online
A 24-year-old rugby player is tackled from behind and develops severe pain in the left lower back that worsens with deep breathing. He is tachycardic. There is bruising and point tenderness over the left posterior lower chest wall. CT shows an isolated fracture of the left 12th rib.
Which organ is most likely injured by the fractured rib?
4 days ago | [YT] | 4
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Pathology USMLE Step1 @doctordc_online
A 5-day-old boy develops a generalized seizure. He has a harsh murmur, low-set ears, a short philtrum, and a cleft palate. Chest x-ray shows absence of the thymic shadow. Echocardiogram shows truncus arteriosus.
Labs: Calcium 6.6 mg/dL (normal 8.5–10.5), phosphorus elevated, PTH low; CD3⁺ T cells low.
Which mechanism most likely explains this condition?
5 days ago | [YT] | 6
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Neurology USMLE Step1 @doctordc_online
A 4-year-old boy is evaluated for infantile spasms that began at 8 months, now generalized seizures, and developmental delay. Examination shows several oval hypopigmented macules on the trunk (seen better under a Wood lamp) and small reddish papules over the nose and cheeks.
Image description: Axial MRI of the brain showing multiple small nodules lining the walls of the lateral ventricles (subependymal), some of them calcified, and cortical/subcortical areas of abnormal signal (cortical tubers).
What is the most likely nature of these brain lesions?
6 days ago | [YT] | 6
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Embryology USMLE Step1 @doctordc_online
A 46,XY newborn has ambiguous genitalia with a small phallus, bifid scrotum, and a blind-ending vaginal pouch. Serum testosterone is normal for age, but the testosterone:dihydrotestosterone ratio is markedly increased. Which of the following internal structures would most likely be found?
Testes Vas deferens / epididymis Uterus
A. Absent Absent Present
B. Present Absent Absent
C. Absent Present Absent
D. Present Present Absent
1 week ago | [YT] | 4
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Physiology USMLE Step1 @doctordc_online
An 84-year-old woman is admitted after a fall with a hip fracture and significant blood loss. Blood pressure is 92/58 mm Hg and pulse is 96/min. Despite ongoing bleeding, her heart rate does not rise much further, and her blood pressure continues to fall.
Which age-related change most likely limits her ability to compensate for this stress?
1 week ago | [YT] | 8
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Pathology USMLE Step1 @doctordc_online
A 38-year-old farmer is treated with polyvalent equine antivenom after a snakebite. Nine days later he develops fever, a pruritic urticarial rash, and painful swelling of the knees, wrists, and MCP joints.
Labs: ESR 68 mm/h; C3 and C4 decreased; urinalysis shows 1+ protein. Joint aspirate: neutrophil-predominant fluid, no crystals, Gram stain negative.
Which of the following mediators is most responsible for the neutrophil recruitment and increased vascular permeability in the affected joints?
1 week ago | [YT] | 7
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