USMLE® Step 1 style questions USMLE
USMLE® Step 2 style questions USMLE
A 24-year-old man comes to the clinic because a protruding forehead and mandible as well as hypertrichosis. The patient's mother is concerned because he has not stopped growing and is over a foot taller than everyone else in his family. Blood tests reveal an elevated serum IGF-1 as well as a failure to suppress serum growth hormone following an oral glucose tolerance test. The physician recommends magnetic resonance imaging (MRI) of the brain, which would most likely reveal a lesion in which of the following bony structures?
Content Reviewers:Rishi Desai, MD, MPH
Contributors:Sam Gillespie, BSc
Acromegaly can be broken down into “acro” which refers to extremity and “megaly” which refers to enlargement.
So acromegaly is a hormonal disorder in adults where there is an excess of growth hormone or somatotropin, and causes continued growth of the extremities in adults, leading to large hands, feet and face.
As examples, the French wrestler André the Giant who played Fezzik in the movie The Princess Bride and actor Richard Kiel who played Jaws in the James Bond movies both had acromegaly.
In children, excess growth hormone causes a different disorder, called gigantism, because their long bones haven’t stopped growing yet.
So let’s talk about how growth hormone is made.
Normally, the hypothalamus which is at the base of the brain, secretes growth hormone-releasing hormone in bursts throughout the day - every couple hours, and this can increase based on things like low blood glucose levels, lack of food, increased exercise, increased sleep, and increased stress like trauma.
The growth hormone-releasing hormone goes into the hypophyseal portal system - which is a network of capillaries linking the hypothalamus to the anterior pituitary which is smaller in size than a pea.
The growth hormone-releasing hormone binds to a surface protein on somatotroph cells of the anterior pituitary gland, and in response, they release growth hormone.
The body uses three main ways to help limit the amount of growth hormone that gets made.
First, too much growth-hormone-releasing hormone signals the hypothalamus to stop making more.
Second, when growth hormone reaches tissues like the liver, bones, and muscles, they make somatomedins, which are small protein hormones.
These somatomedins signal the anterior pituitary to stop producing growth hormone.
Third, growth hormone and somatomedins together signal to the hypothalamus to produce somatostatin, another hormone, whose role is also to signal the anterior pituitary to stop producing growth hormone.
Now, growth hormone affects lots of tissues directly and indirectly throughout the body.
Direct effects occur in certain tissues where growth hormone stimulates cellular metabolism and leads to organ growth.
The liver releases more glucose into the blood, the body retains nitrogen leading to more muscle growth, and osteoblasts get stimulated which causes the bones to thicken.
Another direct effect of growth hormone is to increase insulin resistance - making it harder for cells to take in glucose - which leads to an increase in blood insulin levels.