A 15-year-old female presents to her family physician for an annual school physical exam and check-up. She is accompanied by her mother to the visit and is present in the exam room. The patient has no complaints, and she does not have any past medical problems. She takes no medications. The patient reports that she remains active, exercising 5 times a week, and eats a healthy and varied diet. Which of the following would be the best way for the physician to obtain a more in-depth social history, including sexual history and use of alcohol, tobacco, or recreational drugs?

Ask the mother to step outside into the hall for a portion of the visit

Disallow the mother to be present in the examination room throughout the entirety of the visit

Give the patient a social history questionnaire to fill out in the exam room

Ask the patient the questions directly, with her mother still in the exam room

Speak softly to the patient so that the mother does not hear and the patient is not embarrassed

A 5-year-old girl accompanied by her mother presents to the emergency department after suffering a fall on the elementary school playground. Her mother reports that a child on the playground pushed her daughter who fell on her right side, after which she screamed and was found clutching her right leg. The girl's past medical history is significant for a fracture of the left femur and right radius over the past 2 years and an auditory deficit requiring hearing aid use starting 6 months ago. Inspection reveals a relatively short girl in moderate distress. She has brown opalescent teeth. She refuses to bear weight on her right lower extremity. Radiography of the right lower extremity reveals a femoral midshaft fracture. Which of the following is the most likely etiology of the patient's condition?

Defective type I collagen production

Decreased cystathionine beta synthase activity

A 5-year-old boy is brought to the emergency room by his parents after slipping on a rug at home and experiencing exquisite pain and swelling of his arms. Radiographs reveal a new supracondylar fracture of the humerus, as well as indications of multiple, old fractures that have healed. His parents note that an inherited disorder is present in their family history. A comprehensive physical exam also reveals blue-tinted sclera and yellow-brown, discolored teeth. What is the etiology of the patient’s disorder?

Defect in the glycoprotein that forms a sheath around elastin

Deficiency of type 3 procollagen

Defect in the hydroxylation step of collagen synthesis

A 4-year-old boy is brought to the physician for a well-child examination. He started walking at 20 months of age. He can use a cup to drink but cannot use silverware. He speaks in 2-word sentences and can build a tower of 4 blocks. He can scribble but cannot draw a circle. He is above the 99th percentile for height and at the 15th percentile for weight. Vital signs are within normal limits. Examination shows bilateral inferior lens dislocation. His fingers are long and slender. He has a high-arched palate. The thumb and 5th finger overlap when he grips a wrist with the opposite hand. The skin over the neck can be extended and stretched easily. Which of the following is the most likely cause of these findings?

Cystathionine synthase deficiency

Hypoxanthine-guanine-phosphoribosyl transferase deficiency

Connective tissue cells and fibers for USMLE Step 2 CK: High-Yield Anatomy Lessons

CT Overview - The Body's Glue

Provides structural/metabolic support, binding tissues into organs. Derived from mesoderm.
Composed of three main elements:
- Cells: Fibroblasts, adipocytes, immune cells
- Fibers: Collagen, elastin, reticular
- Ground Substance: Amorphous gel-like material
Fibers + Ground Substance = Extracellular Matrix (ECM).

⭐ All connective tissues originate from mesenchyme, an embryonic tissue.

Loose Areolar Connective Tissue Components

CT Cells - The Resident Crew

Connective tissue proper contains a variety of resident cells, each with a specialized role. These cells are non-migratory and remain within the tissue.

Cell	Key Function(s)	Identifying Feature(s)
Fibroblast	Synthesizes ECM (collagen, elastin) & ground substance	Spindle-shaped, prominent RER
Adipocyte	Stores triglycerides for energy, insulation, cushioning	Large, empty-looking cell (signet ring); nucleus pushed to periphery
Macrophage	Phagocytosis of debris/pathogens; antigen presentation	Irregular shape, kidney-bean nucleus, abundant lysosomes
Mast Cell	Mediates local inflammatory & allergic responses	Large, central nucleus; cytoplasm filled with basophilic granules (histamine, heparin)
Plasma Cell	Produces & secretes antibodies (immunoglobulins)	Eccentric "clock-face" nucleus, perinuclear halo (Golgi)

CT Fibers - Strength and Stretch

Fiber Type	Composition	Key Function	Locations	Staining
Collagen	Type I Collagen (most abundant)	Tensile strength, resists stretch	Bone, skin, tendons, ligaments	Eosin (pink)
Reticular	Type III Collagen	Delicate supportive mesh	Spleen, lymph nodes, liver	Silver stain (black)
Elastic	Elastin & Fibrillin	Stretch & recoil	Aorta, lungs, skin, vocal cords	Verhoeff stain (black)

⭐ Ehlers-Danlos Syndrome is a group of hereditary connective tissue disorders caused by defective collagen synthesis or processing. It classically presents with joint hypermobility, skin hyperextensibility, and tissue fragility.

Connective tissue cells and fibers

CT Pathologies - When Fibers Fray

Ehlers-Danlos Syndrome: Defective collagen synthesis (e.g., Type V/III). Results in joint hypermobility and hyperextensible, fragile skin.
Osteogenesis Imperfecta: Brittle bone disease from Type I collagen defects (COL1A1/A2). Presents with multiple fractures, blue sclerae, and hearing loss.
Marfan Syndrome: Fibrillin-1 gene (FBN1) defect, weakening elastin. Leads to arachnodactyly, aortic root dilation, and upward lens dislocation.
Scurvy: Vitamin C deficiency impairs collagen hydroxylation. Causes bleeding gums, poor wound healing, and perifollicular hemorrhage.

Clinical manifestations of Marfan syndrome

⭐ Exam Favorite: Differentiate Marfan's upward (superotemporal) lens dislocation from homocystinuria's downward (inferonasal) dislocation.

High‑Yield Points - ⚡ Biggest Takeaways

Fibroblasts are the main producers of extracellular matrix (ECM), including collagen and elastin.

Remember key collagen types: Type I (Bone), Type II (Cartilage), Type III (Reticulin), Type IV (Basement Membrane).

Alport syndrome is a Type IV collagen defect; vascular Ehlers-Danlos syndrome is a Type III defect.

Marfan syndrome is caused by a defect in fibrillin, a key component of elastic fibers.

Mast cells release histamine granules, mediating Type I hypersensitivity reactions.

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