AssessmentsGrowth hormone and somatostatin
Growth hormone and somatostatin
USMLE® Step 1 style questions USMLE
A 45-year-old man comes to the clinic because of a recent weight loss of 4.5-kg (9.9-lb) and fatty stools. He has a history of diabetes mellitus and gallstones. Laboratory studies show decreased concentrations of pepsinogen, amylase, lipase, insulin, and glucagon. A CT scan shows a mass in the pancreas, Based on this patient's symptoms, which of the following substances might be secreted by this pancreatic tumor?
The hypothalamus, which is a part of the brain, secretes growth hormone-releasing hormone into the hypophyseal portal system - which is a network of capillaries linking the hypothalamus to the anterior, or front part of the pituitary gland.
In the anterior pituitary, there are many different types of cells, each responsible for producing a type of hormone.
The growth hormone-releasing hormone binds to a surface protein on one of these cells, called somatotroph cells, and stimulates them to release of growth hormone.
Normally, growth hormone releasing hormone is released in a pulsatile manner, throughout the day and peaks one hour after you fall asleep, but it is also secreted in response to various forms of internal and external stimuli.
Now there are a few negative feedback loops that generally control the release of growth hormone.
First, increased levels of growth-hormone-releasing hormone in the blood signals the hypothalamus to stop making more.
Second, when growth hormone reaches tissues like the liver, muscles, and bones, they make somatomedins, which are hormones that signal the anterior pituitary to stop producing growth hormone.
Third, growth hormone and somatomedins together signal to the hypothalamus to produce somatostatin, which is also called the growth hormone inhibiting hormone.
Somatostatin acts like a lawyer that tells other endocrine organs to “cease and desist” in producing more hormones.
- "Medical Physiology" Elsevier (2016)
- "Physiology" Elsevier (2017)
- "Human Anatomy & Physiology" Pearson (2018)
- "Principles of Anatomy and Physiology" Wiley (2014)
- "Growth hormone secretion during sleep" Journal of Clinical Investigation (1968)
- "Growth hormone pulsatility profile characteristics following acute heavy resistance exercise" Journal of Applied Physiology (2001)