Growth Hormone

BCH 120 — Metabolic & Endocrine Biochemistry · Dr. Radi

build Jul 17 · 11:11 · CC BY-NC-SA 4.0 · owned figures (RDKit / matplotlib / PyMOL)
Dr. Radi

By the end of this unit, you can…

  • Describe GH production (somatotropes) and its regulation (GHRH/ghrelin push; somatostatin/IGF-1 brake; pulsatile, sleep-linked), plus the CJD history and the IGF-1 mediator
  • Explain that GH acts largely through liver-made IGF-1 (JAK-STAT receptor), its metabolic effects (anabolic but anti-insulin/diabetogenic), and the IGF-1 negative-feedback loop
  • Analyze GH disorders (deficiency; gigantism vs acromegaly by growth-plate timing) and the lifestyle factors (sleep, exercise, fasting, stress/cortisol) that modulate GH
Dr. Radi

Today's route 🗺️

  1. Growth Hormone — Production & Regulation
  2. GH's Metabolism & IGF-1 Feedback
  3. GH Disorders & Lifestyle
Dr. Radi

1 · Growth Hormone — Production & Regulation

"Growth hormone is the pituitary's most abundant product, and its story has a dark chapter (CJD from cadaver extracts). But the biochemistry is elegant: a push-pull control panel, a nightly pulse, and a hidden middleman that does the actual growing."

Dr. Radi

GH — the most abundant pituitary hormone

Growth hormone (GH) is made by somatotropes, which make up about half of all anterior-pituitary cells — it's the most abundant pituitary hormone. Its job is to drive you to adult height (indirectly) and to run a metabolic program: mobilize fat, spare glucose, and build protein. It also carries a cautionary history: early hGH was extracted from cadaver pituitaries, and prion contamination caused fatal Creutzfeldt-Jakob disease — so it was banned in 1985. Today we use safe recombinant rhGH made in bacteria.

Dr. Radi

The somatotroph's control panel

GH release is a push-pull system. Two signals push: GHRH from the hypothalamus (working through cAMP/PKA) and ghrelin from the gut (through PLC/IP₃/Ca²⁺). Two signals brake: somatostatin (shuts off adenylyl cyclase and calcium) and IGF-1 (turns off the GH gene). (Dopamine and other neurotransmitters tune the signal too.) And the output isn't steady — GH comes in pulses, with the biggest surge during deep sleep. So "you grow in your sleep" is literally true, once again.

Dr. Radi

The secret: GH works through IGF-1

Here's the twist that surprises everyone: GH barely touches your muscles and bones directly. Instead, GH tells the liver to make IGF-1 (insulin-like growth factor-1), and it's IGF-1 that reaches the tissues and does the growing. GH is the command; IGF-1 is the courier that carries it out. And the GH receptor signals through JAK-STAT — the very same pathway you met for leptin and erythropoietin. One relay, reused across the whole endocrine system.

Dr. Radi

2 · GH's Metabolism & IGF-1 Feedback

"Growth hormone is a paradox: it's anabolic (builds muscle and bone through IGF-1) but also diabetogenic (it fights insulin and raises blood sugar). And like every axis in this course, IGF-1 closes a tidy negative-feedback loop."

Dr. Radi

Anabolic, but diabetogenic

GH's metabolic program has three parts, and one is a trap. Protein: it boosts amino-acid uptake and protein synthesis (with IGF-1) — building muscle and bone. Fat: it drives lipolysis, burning fat for fuel. Glucose: here's the catch — GH is anti-insulin, cutting glucose uptake in muscle and fat so blood sugar stays up. That "spare glucose for the brain" effect makes GH useful in fasting, but chronically high GH causes insulin resistance — about 30% of acromegaly patients develop type 2 diabetes. Anabolic and diabetogenic at once.

Dr. Radi

IGF-1 closes the loop

Growth can't run away, because it self-limits — through the same courier that carries it out. When GH drives the liver to make IGF-1, that IGF-1 does two jobs: it grows the tissues, and it feeds back to inhibit GH release (acting on both the hypothalamus and pituitary). So more growth signal → more IGF-1 → less GH. It's the identical three-tier axis with negative feedback you've seen for the thyroid, adrenal, and gonads — just with IGF-1 as the feedback messenger.

Dr. Radi

3 · GH Disorders & Lifestyle

"Too little growth hormone stunts kids and drains adults; too much does very different things depending on one thing — whether your growth plates have fused yet. And day to day, GH is swayed by sleep, exercise, fasting, and stress."

Dr. Radi

GH disorders — and why timing decides the picture

GH disease comes in three forms, and the excess ones hinge on timing. Deficiency stunts kids (short stature, delayed puberty) and saps adults (fatigue, low bone density, more fat) — treated with recombinant rhGH. Excess before the growth plates fuse → gigantism: excessive height and enlarged limbs. Excess after they fuse (adult) → acromegaly: the bones can't lengthen, so they thicken — enlarged hands, feet, face, joint pain, and organ overgrowth (usually from a pituitary adenoma). Same excess, opposite shape — all about when. Treat excess with surgery, somatostatin analogs, or GH-receptor blockers.

Dr. Radi

What moves GH day to day

GH isn't fixed — it swings with how you live. It rises with deep sleep (the big nightly pulse), resistance exercise and HIIT, fasting/hypoglycemia, and ghrelin. It falls with age (it steadily declines through adulthood), high blood glucose or obesity, and its own brakes, somatostatin and IGF-1. The sneaky one is chronic stress: sustained cortisol suppresses GH and IGF-1 — which is exactly why prolonged stress can stunt growth in children. Sleep, move, and manage stress, and your GH takes care of itself.

Dr. Radi

Can you…?

  • ☐ describe GH production (somatotropes) and its regulation (GHRH/ghrelin push; somatostatin/IGF-1 brake; pulsatile, sleep-linked), plus the CJD history and the IGF-1 mediator?
  • ☐ explain that GH acts largely through liver-made IGF-1 (JAK-STAT receptor), its metabolic effects (anabolic but anti-insulin/diabetogenic), and the IGF-1 negative-feedback loop?
  • ☐ analyze GH disorders (deficiency; gigantism vs acromegaly by growth-plate timing) and the lifestyle factors (sleep, exercise, fasting, stress/cortisol) that modulate GH?

If any box stays empty, the practice site has a drill for it. 🧪

Dr. Radi