A 7-year-old girl presents to her primary care physician for a routine check-up. The physician allows the medical student to perform a physical examination. The medical student notes hearing impairment as well as the findings show in Figures A and B. Radiographs show indications of multiple old fractures of the humerus that have healed. After questioning the girl’s parents, the medical student learns that in addition, the patient is extremely picky with her food and eats a diet consisting mainly of cereal and pasta. What is the most likely etiology of the patient’s disease?

Dietary deficiency of ascorbic acid

Defective mineralization of cartilage

A 42-year-old woman comes to the physician with acute, severe pain in the middle of her lower back. She also complains of constipation and trouble sleeping recently. Menses occur regularly at 28-day intervals. Examination shows localized tenderness to palpation over the lumbar spine. Serum calcium is 14 mg/dL and serum phosphorus is 1.5 mg/dL. An x-ray of the lumbar spine shows a compression fracture of the L4 vertebral body and osteopenia. Which of the following is the most likely underlying cause of this patient's decreased bone mineral density?

Increase in parathyroid hormone secretion

Decrease in osteoblast activity

Increase in calcitonin secretion

Decrease in estrogen production

An investigator is studying the structural integrity of collagen. Human fibroblasts are cultured on a medium and different enzymes are applied. One of the cultures is supplemented with an enzyme that inhibits lysyl oxidase, preventing the formation of covalent cross-links between collagen α-chains. Which of the following processes is most likely to be impaired as a result?

Internal elastic lamina formation

Cartilaginous growth plate mineralization

A 28-year-old male presents to his primary care physician with complaints of intermittent abdominal pain and alternating bouts of constipation and diarrhea. His medical chart is not significant for any past medical problems or prior surgeries. He is not prescribed any current medications. Which of the following questions would be the most useful next question in eliciting further history from this patient?

"Can you tell me more about the symptoms you have been experiencing?"

"Does the diarrhea typically precede the constipation, or vice-versa?"

"Is the diarrhea foul-smelling?"

"Please rate your abdominal pain on a scale of 1-10, with 10 being the worst pain of your life"

"Are the symptoms worse in the morning or at night?"

Specialized connective tissues for USMLE Step 2 CK: High-Yield Anatomy Lessons

Cartilage - The Flexible Framework

Avascular & aneural tissue. Composed of chondrocytes housed in lacunae, surrounded by a gel-like extracellular matrix (ECM) they secrete. The perichondrium provides blood supply (absent in articular cartilage & fibrocartilage).

Micrographs of hyaline, fibro-, and elastic cartilage

Type	Key Matrix Component	Primary Locations
Hyaline (Type II)	Glassy, smooth ECM	Articular surfaces, costal cartilage, nose, trachea
Elastic (Type II)	Elastic fibers for flexibility	Epiglottis, external ear, Eustachian tube
Fibrocartilage (Type I & II)	Dense collagen for shock absorption	Intervertebral discs, pubic symphysis, menisci

Bone - Rigid Scaffolding

Composition: A specialized connective tissue with a mineralized matrix.
- Inorganic Matrix (~65%): Primarily Hydroxyapatite crystals, $Ca_{10}(PO_4)_6(OH)_2$, providing compressive strength and rigidity.
- Organic Matrix (Osteoid, ~35%): Mostly Type I collagen, granting tensile strength and slight flexibility.
Cellular Cast:
- Osteoblasts: Synthesize osteoid. 📌 Blast = Build.
- Osteocytes: Trapped in lacunae; mechanosensors that regulate remodeling.
- Osteoclasts: Multinucleated cells that resorb bone. 📌 Clast = Chew.
Architectural Types:
- Compact (Cortical): Dense, forms the outer shell. Organized into Osteons (Haversian systems).
- Spongy (Cancellous): Trabecular meshwork, contains bone marrow.

⭐ In osteoporosis, osteoclast activity outpaces osteoblast activity, leading to reduced bone mass and ↑ fracture risk, especially in trabecular bone of the vertebrae and femoral neck.

Adipose & Blood - Metabolic Movers

Adipose Tissue: Stores lipids & secretes hormones.
- White (WAT): Unilocular. Stores energy (triglycerides). Secretes leptin (satiety) & adiponectin (↑ insulin sensitivity).
- Brown (BAT): Multilocular, many mitochondria. For thermogenesis via UCP-1 (thermogenin). Common in newborns.
Blood: Fluid connective tissue; plasma is the matrix.
- Cells: Erythrocytes (O₂), Leukocytes (immunity), Platelets (clotting).
- Function: Transports gases, nutrients, waste, hormones.

⭐ High-Yield: Active Brown Adipose Tissue (BAT) shows high uptake on FDG-PET scans due to metabolic activity, which can be mistaken for malignancy in supraclavicular and paravertebral areas.

High‑Yield Points - ⚡ Biggest Takeaways

Cartilage is avascular and gets nutrients via diffusion; its type varies by location: Hyaline (Type II collagen) in joints, Fibrocartilage (Type I & II) in discs.

Brown fat generates heat via UCP-1 (thermogenin) in its many mitochondria, unlike the energy-storing white fat.

Bone is a mineralized connective tissue constantly remodeled by osteoblasts (build) and osteoclasts (resorb).

Blood is a fluid connective tissue with a plasma matrix.

Continue reading on Oncourse

CONTINUE READING — FREE

or get the app

App Store|Google Play