A 37-year-old man presents with dull, continuous epigastric pain that radiates to the back in a circumscribing fashion. The history is significant for 3 episodes of acute pancreatitis that were managed conservatively. He reports no history of such episodes in his relatives and denies a family history of any cardiovascular or gastrointestinal disorders. The vital signs include: blood pressure 105/70 mm Hg, heart rate 101/min, respiratory rate 17/min, and temperature 37.4℃ (99.3℉). The physical examination reveals epigastric tenderness, slight muscle guarding, a positive Mayo-Robson’s sign, and abdominal distention. Laboratory studies show the following findings: Complete blood count Erythrocytes 4.5 x 106/mm3 Hgb 14.7 g/dL Hct 43% Leukocytes 12,700/mm3 Segmented neutrophils 65% Bands 4% Eosinophils 1% Basophils 0% Lymphocytes 27% Monocytes 3% Biochemistry Serum amylase 170 U/L ALT 21 U/L AST 19 U/L Total serum cholesterol 139 mg/dL (3.6 mmol/L) Serum triglycerides 127 mg/dL (1.4 mmol/L) The magnetic resonance cholangiopancreatography findings are shown in the exhibit. What embryogenic disruption could cause such anatomic findings?

Failure of fusion of dorsal and ventral pancreatic duct anlages

Duplication of the pancreatic bud of the midgut

Ectopy of the developing bile duct

Duplication of the embryonic pancreatic duct

Improper rotation of the ventral pancreatic bud

You have been asked to deliver a lecture to medical students about the effects of various body hormones and neurotransmitters on the metabolism of glucose. Which of the following statements best describes the effects of sympathetic stimulation on glucose metabolism?

Epinephrine increases liver glycogenolysis.

Norepinephrine causes increased glucose absorption within the intestines.

Without epinephrine, insulin cannot act on the liver.

Peripheral tissues require epinephrine to take up glucose.

Sympathetic stimulation to alpha receptors of the pancreas increases insulin release.

A 21-year-old college student comes to the emergency department because of a two-day history of vomiting and epigastric pain that radiates to the back. He has a history of atopic dermatitis and Hashimoto thyroiditis. His only medication is levothyroxine. He has not received any routine vaccinations. He drinks 1–2 beers on the weekends and occasionally smokes marijuana. The patient appears distressed and is diaphoretic. His temperature is 37.9°C (100.3°F), pulse is 105/min, respirations are 16/min, and blood pressure is 130/78 mm Hg. Physical examination shows abdominal distention with tenderness to palpation in the epigastrium. There is no guarding or rebound tenderness. Skin examination shows several clusters of yellow plaques over the trunk and extensor surfaces of the extremities. Hemoglobin concentration is 15.2 g/dL and serum calcium concentration is 7.9 mg/dL. Which of the following is the most appropriate next step in evaluation?

Obtain an upright x-ray of the abdomen

Perform a pilocarpine-induced sweat test

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 55-year-old woman comes to the physician because of a 2-week history of painful swelling on the right side of her face. The pain worsens when she eats. Examination of the face shows a right-sided, firm swelling that is tender to palpation. Oral examination shows no abnormalities. Ultrasonography shows a stone located in a duct that runs anterior to the masseter muscle and passes through the buccinator muscle. Sialoendoscopy is performed to remove the stone. At which of the following sites is the endoscope most likely to be inserted during the procedure?

Opposite the second upper molar tooth

Lateral to the lingual frenulum

Lateral to the superior labial frenulum

An 87-year-old male presents to his neurologist for a follow-up visit. He is being followed for an inoperable tumor near his skull. He reports that he recently noticed that food has started to lose its taste. He also notes increasing difficulty with swallowing. He has a history of myocardial infarction, diabetes mellitus, hyperlipidemia, hypertension, and presbycusis. He takes aspirin, metoprolol, metformin, glyburide, atorvastatin, lisinopril, and hydrochlorothiazide. On examination, the patient is a frail-appearing male sitting in a wheelchair. He is oriented to person, place, and time. Gag reflex is absent on the right side. A taste evaluation is performed which demonstrates a decreased ability to detect sour and bitter substances on the right posterior tongue. The nerve responsible for this patient’s loss of taste sensation also has which of the following functions?

Parasympathetic innervation to the parotid gland

Somatic sensory innervation to the roof of the pharynx

Parasympathetic innervation to the trachea

Somatic sensory innervation to the lower lip

Parasympathetic innervation to the submandibular gland

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)

Pancreas and salivary gland histology for USMLE Step 3: High-Yield Anatomy Lessons

Pancreas - The Double-Duty Gland

Pancreatic islet of Langerhans and acini histology

Exocrine Pancreas (~85%): Synthesizes and secretes digestive enzymes.
- Acinar cells: Arranged in serous acini; contain basophilic RER at the base and eosinophilic zymogen granules at the apex.
- Ductal cells: Transport secretions; start as centroacinar cells, progressing from simple cuboidal to columnar epithelium.
Endocrine Pancreas (~2%): Consists of Islets of Langerhans, which secrete hormones directly into the bloodstream.

Cell Type	Approx. %	Location in Islet	Secretion
β (Beta)	60-70%	Central	Insulin
α (Alpha)	15-20%	Peripheral	Glucagon
δ (Delta)	5-10%	Peripheral	Somatostatin

Salivary Glands - The Spit Syndicate

📌 Mnemonic: Parotid is Purely serous. SubMandibular is Mixed. Sublingual has lots of mucous.

General Histology:
- Acini: Secretory units (serous, mucous, or mixed).
- Myoepithelial cells: Contractile cells surrounding acini that expel saliva.
- Duct System: Saliva flows from intercalated ducts to larger, eosinophilic striated ducts (which modify saliva to become hypotonic) and finally to excretory ducts.
Major Gland Comparison:
- Parotid Gland:
  - Purely serous acini.
  - Well-developed intercalated and striated ducts. Often has significant adipose tissue.
- Submandibular Gland:
  - Mixed, but predominantly serous acini.
  - Key feature: serous demilunes (serous cells capping mucous tubules).
- Sublingual Gland:
  - Mixed, but predominantly mucous acini.
  - Ducts are less prominent.

⭐ The submandibular gland, while not the largest, is the workhorse, producing approximately 70% of unstimulated saliva.

Histo-Path Hits - When Glands Go Rogue

Pancreas: Exocrine acini (zymogen granules) and endocrine islets (hormone producers).
- Acute Pancreatitis: Acinar cell injury causes premature enzyme activation, leading to autodigestion and fat necrosis with saponification (calcium deposits).
- Type 1 Diabetes: Autoimmune T-cell-mediated destruction of β-cells within the Islets of Langerhans.
Salivary Glands: Composed of serous and mucous acini with a ductal system.
- Sjögren's Syndrome: Dense lymphocytic infiltrate (autoimmune) destroys the glandular tissue, causing dry mouth/eyes.
- Pleomorphic Adenoma: Benign mixed tumor showing epithelial (ductal) and myoepithelial (stromal, often chondromyxoid) differentiation.

Pleomorphic Adenoma Histology: Ducts and Myxoid Stroma

⭐ Pleomorphic adenoma is the most common salivary gland tumor, nicknamed "benign mixed tumor" due to its biphasic appearance. It most frequently arises in the parotid gland.

High‑Yield Points - ⚡ Biggest Takeaways

Pancreatic islets (pale endocrine clusters) are embedded within darker exocrine acini.

The exocrine pancreas has zymogen granules in acini and unique centroacinar cells starting the ducts.

Parotid glands are almost purely serous, while sublingual glands are predominantly mucous.

Submandibular glands are mixed, featuring characteristic serous demilunes capping mucous tubules.

Salivary striated ducts have prominent basal striations (mitochondria) for ion transport.

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