USMLE® Step 1 style questions USMLE
A 14-year-old boy presents to his family physician accompanied by his parent due to concerns regarding delayed puberty. The patient’s parent expresses concern about a lack of secondary male sex characteristics compared to his sibling of the same age. The patient has a reserved demeanor and answers questions with one-word answers. The patient gets mostly C’s and some D’s in school. He has been picked on since starting school for his inability to smell when other students intentionally break wind in his presence. On physical examination, height and weight are near the 60th percentile for his age. The patient has absent pubic hair and small testes. A deficiency of which of the following hormones is most directly responsible for this patient’s clinical presentation?
Contributors:Sam Gillespie, BSc
Kallmann syndrome is an endocrine disorder caused by a decrease in sex hormones, either testosterone in males or estrogen and progesterone in females. That decrease leads to a failure to start or complete puberty.
The syndrome is named after Dr. Franz Kallmann, the geneticist who first described it.
Normally, during fetal development there’s a region of the brain called the olfactory placode. Two groups of neurons emerge from that region.
The first group contains olfactory neurons that eventually help with sensing smells.
These neurons migrate down from the olfactory placode and get embedded in the cribriform plate, which is a bone plate that separates the nasal cavity from the brain, forming the olfactory bulb.
The second group contains neurons that release gonadotropin-releasing hormone.
And these neurons migrate through the cribriform plate, and settle in the hypothalamus.
The hypothalamic-pituitary-gonadal axis is a system of hormone signaling between the hypothalamus, pituitary gland, and gonads, either the testes or ovaries, to control sexual development and reproduction.
When gonadotropin-releasing hormone reaches the pituitary gland, it stimulates cells in the anterior pituitary, called gonadotrophs, to release gonadotropin hormones, luteinizing hormone and follicle-stimulating hormone into the blood.
These gonadotropin hormones then stimulate the gonads to produce sex specific hormones.
In females, the theca cells respond to luteinizing hormone by producing progesterone and androstenedione.
Then, follicle stimulating hormone causes the granulosa cells to convert the androstenedione into estrogen.
During puberty, waves of estrogen and progesterone regulate primary sex characteristics, like monthly changes to the ovary stroma to promote egg maturation and ovulation, and changes to the uterine wall lining as part of the menstrual cycle.
They also direct secondary sex characteristic development like increased height, growth of pubic hair and breasts.
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