Growth hormone responsive condition

pituitary gland

called the "master gland," plays a central role invregulating many endocrine functions. It is located at the base of the brain, just below the hypothalamus, and is connected to it via the pituitary stalk.

anatomical structure

• anterior pituitary

• posterior pituitary

anterior pituitary

Made up of glandular cells, this section produces and secretes several key hormones in response to signals from the hypothalamus.

posterior pituitary

Composed of neural tissue, it stores and releases hormones that are produced in the hypothalamus

MRI imaging and tumour identification

MRI scans are used to visualise the pituitary gland and detect abnormalities. In

the images:

•A normal pituitary gland appears as a small, well-defined structure.

•A pituitary tumour may appear as an enlarged mass, often pushing

upwards against the optic chiasm, which can be seen displaced in the

scan.

This displacement can lead to visual disturbances, such as blurred vision

or loss of peripheral sight, due to pressure on the optic nerves

pituitary tumours: characteristic and effects

Most pituitary tumours are:

•Benign (non-cancerous)

•Slow-growing, but still clinically significant due to their location and

hormonal impact

They can cause:

•Hormone overproduction (hypersecretion) – leading to

conditions like acromegaly, Cushing’s disease, or hyperprolactinemia

•Hormone underproduction (hyposecretion) – resulting in

deficiencies such as hypothyroidism or adrenal insufficiency

hypothalamus and pituitary gland: hormonal control centre

The hypothalamus and pituitary gland form a central regulatory system that controls many endocrine functions. They work together to coordinate hormone release throughout the body

anterior pituitary

Releasing hormones from the hypothalamus travel through the hypothalamic- hypophyseal portal system to reach the anterior pituitary. These signals

stimulate specific endocrine cells to release hormones into the bloodstream.

endocrine cells in anterior pituitary

• somatotrophs

• lactotrophs

• corticotrophs

• thyrotrophs

• gonadotrophs

somatotrophs

release growth hormone (GH), which promotes growth

and metabolism.

lactotrophs

release prolactin, which supports milk

production.

corticotrophin

release ACTH, which stimulates cortisol production from

the adrenal glands.

thytrophs

release TSH, which stimulates the thyroid gland.

gonadotrophs

release LH and FSH, which regulate reproductive

functions.

SHypothalamic Releasing Hormones

GnRH (Gonadotropin-releasing hormone) – stimulates release of LH

and FSH.

•GHRH (Growth hormone-releasing hormone) – stimulates GH release.

•TRH (Thyrotropin-releasing hormone) – stimulates TSH and prolactin

release.

•CRH (Corticotropin-releasing hormone) – stimulates ACTH release.

•Dopamine – inhibits prolactin release.

anterior pituitary tropic hormones

In response to hypothalamic signals, the anterior pituitary releases tropic

hormones that act on peripheral glands:

• LH and FSH

• GH

• TSH

• prolactin

• ACTH

LH and FSH

act on the gonads to stimulate production of sex hormones

(oestrogen, progesterone, testosterone

GH

acts on the liver, which produces IGF-1 to

promote growth.T

TSH

acts on the thyroid gland to

produce thyroid hormones (T3 and T4)

prolactin

acts on breast tissue to support lactation.

ACTH

acts on the adrenal cortex to stimulate cortisol production.

Growth Hormone (GH / Somatotropin): Function and Regulation

Growth hormone (GH), also known as somatotropin, is a key hormone involved

in linear growth and metabolic regulation. It is secreted by acidophilic cells in

the anterior pituitary gland.

GH regulatory pathways

The release of GH is controlled by the hypothalamus, which secretes GHRH (Growth Hormone-Releasing Hormone). This stimulates the anterior pituitary to release GH.

Once released, GH acts as a tropic hormone, primarily targeting the liver. In the liver, GH stimulates the production of somatomedins, also known as insulin-like growth factors (IGFs). IGFs then act on target cells throughout the body to promote growth, especially in bones and tissues.

GH direct and indirect function

Growth hormone (GH) plays a vital role in both metabolism and growth. Its

effects can be divided into direct actions on metabolic processes and indirect

actions mediated through insulin-like growth factors (IGFs), also known

as somatomedins.

direct effects on metabolism

•Increasing blood glucose levels by opposing insulin’s action (anti-insulin

effect).

•Stimulating gluconeogenesis in the liver, which produces glucose from

non-carbohydrate sources.

•Enhancing protein synthesis, contributing to muscle growth and repair.

•Reducing glucose uptake in peripheral tissues, helping preserve glucose

•Promoting lipolysis, which breaks down fat stores to release energy.

These metabolic effects support energy availability during growth and

stress, and they help maintain lean body mass

indirect effects on growth

Hypertrophy – an increase in cell size, supported by enhanced protein

synthesis.

•Hyperplasia – an increase in cell number, driven by cell division.

•Skeletal growth – especially in long bones, contributing to linear height

increase during childhood and adolescence.

These effects also support the enlargement of organs and overall body

development

regulatory pathways

GH release begins in the hypothalamus, which secretes GHRH

GH then acts on the liver, prompting the production of somatomedins, also

known as insulin-like growth factors (IGFs). These IGFs act on target cells to

promote growth, especially in bones and tissues.

influencing factor

GH then acts on the liver, prompting the production of somatomedins, also

known as insulin-like growth factors (IGFs). These IGFs act on target cells to

promote growth, especially in bones and tissues.

causes of GH deficiency

Congenital – due to genetic mutations or structural abnormalities in the

brain present at birth.

•Acquired – resulting from damage to the pituitary gland caused by injury,

infection, or radiation.

•Idiopathic – where the cause is unknown despite clinical evidence of

deficiency.

treatment of growth hormone deficiency

Growth hormone deficiency can significantly affect growth, metabolism, and

quality of life. Treatment involves hormone replacement therapy, most

commonly using Somatropin, a recombinant form of human growth

hormone

Growth Hormone (GH) Excess: Gigantism and Acromegaly

Excessive secretion of growth hormone (GH) can lead to two distinct clinical

conditions depending on the age of onset: gigantism in children

and acromegaly in adults. Both result from prolonged exposure to high GH

levels, often due to a pituitary tumour

Gigantism (in Children)

Gigantism occurs when GH excess begins before the closure of growth

plates in bones. This leads to excessive linear growth and other systemic

effects.

Acromegaly (in Adults)

Acromegaly develops when GH excess begins after growth plates have closed so it does not cause increased height but leads to tissue and bone thickening.

surgical treatment

Surgery is often the first-line treatment, especially when a pituitary adenoma is

the cause of GH excess. If the tumour is small and accessible, surgical removal

can completely cure acromegaly.

However, large adenomas pose a challenge due to their proximity to critical brain

structures. In such cases, surgery may only partially reduce GH levels, requiring

additional therapies.

radiation therapy

When surgery is not fully effective or feasible, radiation therapy may be used.

This includes:

•Stereotactic radiation – a precise, targeted method

•Conventional radiation – broader but less targeted

Radiation requires extreme care, as it can damage surrounding tissues and impair

the function of other pituitary hormones. Patients often need lifelong hormone

replacement therapy to compensate for these losses.

drug therapy

Pharmacological options are available to either reduce GH secretion or block its

effects. These include:

•Somatostatin analogues (e.g., octreotide, lanreotide) – inhibit GH release.

•GH receptor antagonists (e.g., pegvisomant) – block GH action at target tissues.

•Dopamine agonists (e.g., cabergoline) – may help in some cases, especially

when prolactin is also elevated