A 28-year-old woman presents to her primary care physician complaining of intense thirst and frequent urination for the past 2 weeks. She says that she constantly feels the urge to drink water and is also going to the bathroom to urinate frequently throughout the day and multiple times at night. She was most recently hospitalized 1 month prior to presentation following a motor vehicle accident in which she suffered severe impact to her head. The physician obtains laboratory tests, with the results shown below: Serum: Na+: 149 mEq/L Cl-: 103 mEq/L K+: 3.5 mEq/L HCO3-: 24 mEq/L BUN: 20 mg/dL Glucose: 105 mg/dL Urine Osm: 250 mOsm/kg The patient’s condition is most likely caused by inadequate hormone secretion from which of the following locations?

Preoptic nucleus of the hypothalamus

Suprachiasmatic nucleus of the hypothalamus

An investigator studying hormone synthesis and transport uses immunocytochemical techniques to localize a carrier protein in the central nervous system of an experimental animal. The investigator finds that this protein is synthesized together with a specific hormone from a composite precursor. The protein is involved in the transport of the hormone from the supraoptic and paraventricular nuclei to its destination. The hormone transported by these carrier proteins is most likely responsible for which of the following functions?

Upregulation of renal aquaporin-2 channels

Stimulation of thyroglobulin cleavage

Hyperplasia of the adrenal zona fasciculata

Increased insulin-like growth factor 1 production

Maturation of primordial germ cells

A 33-year-old woman presents to her primary care physician for a wellness check-up. She states that recently she has been feeling well other than headaches that occur occasionally, which improve with ibuprofen and rest. She has a past medical history of hypertension and headaches and is currently taking hydrochlorothiazide. Her temperature is 99.2°F (37.3°C), blood pressure is 157/108 mmHg, pulse is 90/min, respirations are 14/min, and oxygen saturation is 98% on room air. Physical exam reveals a young woman who appears healthy. A normal S1 and S2 are auscultated on cardiac exam, and her lungs are clear with good air movement bilaterally. From her previous visit, it was determined that she has an elevated aldosterone and low renin level. Laboratory values are ordered as seen below. Serum: Na+: 139 mEq/L Cl-: 100 mEq/L K+: 3.7 mEq/L HCO3-: 29 mEq/L BUN: 20 mg/dL Creatinine: 1.1 mg/dL Which of the following is the most likely diagnosis?

Narrowing of the renal arteries

A 36-year-old woman presents with thyroid swelling. She has been healthy until now and follows all the healthcare precautions except for missing a flu shot this year. On physical examination, the thyroid gland is diffusely enlarged and tender to palpation. Laboratory findings show a decreased serum TSH level and elevated erythrocyte sedimentation rate. Which of the following histopathologic findings would most likely be found in the thyroid gland of this patient?

Mixed cellular infiltration with multinuclear giant cells

Extensive fibrosis of the stroma

Lymphocytic infiltration with germinal centers

Orphan Annie nuclei with psammoma bodies

Sheets of polygonal cells in amyloid stroma

A 38-year-old man comes to the clinic complaining of recurrent abdominal pain for the past 2 months. He reports a gnawing, dull pain at the epigastric region that improves with oral ingestion. He has been taking calcium carbonate for the past few weeks; he claims that “it used to help a lot but it’s losing its effects now.” Laboratory testing demonstrated increased gastrin levels after the administration of secretin. A push endoscopy visualized several ulcers at the duodenum and proximal jejunum. What characteristics distinguish the jejunum from the duodenum?

Lack of submucosal Brunner glands

A 32-year-old woman presents with amenorrhea and galactorrhea. MRI shows a pituitary adenoma. Histological examination of the surgical specimen shows cells arranged in cords and nests with sinusoidal capillaries. Special staining reveals three distinct cell types: chromophobes (50%), acidophils (40%), and basophils (10%). Immunohistochemistry shows the tumor cells staining strongly for prolactin. Evaluate the relationship between normal pituitary architecture and tumor development to determine which cell type most likely gave rise to this neoplasm.

Lactotrophs (acidophils producing prolactin)

Somatotrophs (acidophils producing growth hormone)

Corticotrophs (basophils producing ACTH)

Gonadotrophs (basophils producing FSH/LH)

Chromophobes (null cells with no secretory granules)

A 65-year-old man with progressive shortness of breath undergoes transbronchial biopsy. Microscopy shows thickened alveolar septa with increased collagen deposition. Type I pneumocytes are decreased, and there is proliferation of type II pneumocytes. Alveolar macrophages are present. The patient has a history of environmental asbestos exposure 30 years ago. Evaluate the histological progression and synthesize the most likely diagnosis considering the temporal relationship and cellular changes.

Asbestosis with interstitial fibrosis and ferruginous bodies

Chronic hypersensitivity pneumonitis with granulomas

Idiopathic pulmonary fibrosis with usual interstitial pneumonia pattern

Sarcoidosis with non-caseating granulomas

Acute respiratory distress syndrome with diffuse alveolar damage

Endocrine gland histology — USMLE Lesson

Pituitary Gland - The Master's Workshop

Feature	Anterior Pituitary (Adenohypophysis)	Posterior Pituitary (Neurohypophysis)
Origin	Oral ectoderm (Rathke's pouch)	Neuroectoderm (neural stalk)
Histology	Cords of epithelial cells; acidophils (GH, prolactin), basophils (FSH, LH, ACTH, TSH), chromophobes	Unmyelinated axons from hypothalamus; pituicytes (glial cells)
Hormones	📌 FLAT PEG: FSH, LH, ACTH, TSH, Prolactin, Endorphins, GH	ADH (vasopressin), Oxytocin

Thyroid & Parathyroid - Neck's Metabolic Engine

Feature	Thyroid Gland	Parathyroid Gland
Main Cells	Follicular cells (cuboidal)	Chief cells (basophilic)
Product	Thyroglobulin → T3/T4	Parathyroid Hormone (PTH)
Other Cells	Parafollicular (C) cells	Oxyphil cells (eosinophilic)
Function	Regulate metabolism	↑ serum Ca²⁺ levels
Key Structure	Follicles with colloid	Dense cell cords

📌 Mnemonic: Parafollicular cells produce calcitonin to put calcium into bone.

Adrenal Gland - Salty, Sweet, & Stressy

Adrenal Gland Histology: Zona Glomerulosa to Reticularis

📌 Mnemonic: “Goes Faster Rushing” (Glomerulosa, Fasciculata, Reticularis) → “Salt, Sweet, Sex” (Aldosterone, Cortisol, Androgens).

Zone	Histology (Cortex)	Primary Product	Regulated By
Glomerulosa	Balls of cells	Aldosterone (mineralocorticoid)	Angiotensin II, K+
Fasciculata	Straight cords, foamy	Cortisol (glucocorticoid)	ACTH, CRH
Reticularis	Net-like (reticular)	DHEA (androgens)	ACTH, CRH
Medulla	Chromaffin cells	Catecholamines (Epi, NE)	Preganglionic sympathetic neurons

Pancreatic Islets - The Sugar Squad

Pancreatic islet cell distribution and secretions

Endocrine cell clusters (Islets of Langerhans) within the exocrine pancreas.
Key Cell Types & Hormones:
- β-cells (center): Insulin (↓ glucose), amylin. Most abundant (~70%).
- α-cells (periphery): Glucagon (↑ glucose).
- δ-cells (interspersed): Somatostatin (inhibits insulin, glucagon, & GH).

⭐ Endogenous insulin release is marked by C-peptide; exogenous insulin lacks it.

High‑Yield Points - ⚡ Biggest Takeaways

Pituitary gland features acidophils (GH, prolactin) and basophils (FSH, LH, ACTH, TSH).

Thyroid follicles contain colloid; parafollicular "C" cells produce calcitonin.

Parathyroid glands have chief cells making PTH and eosinophilic oxyphil cells.

Adrenal cortex zones (GFR): Zona glomerulosa (salt), fasciculata (sugar), reticularis (sex).

Adrenal medulla contains neural crest-derived chromaffin cells that secrete catecholamines.

Pancreatic islets show central beta cells (insulin) and peripheral alpha cells (glucagon).

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