5- Hypothalamus & Pituitary

What is the difference between tropic and non-tropic hormones?

Tropic hormones target another gland and affect the secretion of other hormones. Non-tropic hormones target non-endocrine tissue directly and do not affect the secretion of other hormones.

What are the posterior pituitary hormones?

Oxytocin and ADH.

Where are oxytocin and ADH made?

They are made in the hypothalamus and sent to the posterior pituitary.

What is the FLAT PEG acronym for?

It represents the anterior pituitary hormones: FSH, LH, ACTH, TSH, PRL, Endorphins, GH.

What does "PIG on Acid" refer to?

It refers to the acidophil hormones: Prolactin and GH.

What is unique about insulin compared to other hormones in terms of receptor usage?

Insulin is the only hormone that doesn't use a G coupled protein receptor. It uses tyrosine kinase instead.

What does oxytocin do?

Oxytocin stimulates contraction of myoepithelial cells within breast tissue for milk ejection (let-down) and works through a positive feedback loop.

Where is ADH synthesized and what is its function?

ADH is synthesized in the hypothalamus and increases water retention/resorption in the nephron, concentrating urine.

What happens in SIADH?

Too much ADH causes water retention, dilute blood, concentrated urine, and hyponatremia. Symptoms include nausea, vomiting, confusion, fatigue, and seizures.

What is long-loop negative feedback?

Long-loop negative feedback occurs when the bottom hormone level inhibits the secretion of the top-level hormones (hypothalamus and anterior pituitary).

What is short-loop negative feedback?

Short-loop negative feedback occurs when anterior pituitary hormones inhibit hypothalamic hormone secretion.

How does cross-talk occur in hormone regulation?

Cross-talk occurs due to hormone similarities. For example, GHIH may inhibit TSH secretion, TRH may stimulate PRH secretion, and PRL may inhibit GnRH.

What is prolactin (PRL) and how is it regulated?

PRL is produced by the anterior pituitary and is negatively controlled by PIH (dopamine) and positively controlled by TRH, suckling, and increased estrogen. It is the only non-tropic hormone of the anterior pituitary and produces milk.

How are thyroid hormones controlled?

Thyroid hormones are controlled by TRH and TSH.

What are gonadotropins and how are they regulated?

GnRH from the hypothalamus controls the secretion of LH and FSH from the anterior pituitary. LH and FSH affect ovaries and testes. Sex steroid feedback can be positive or negative depending on the reproductive cycle.

How is GnRH released?

GnRH is released in a pulsatile fashion.

How does LH feedback to the hypothalamus?

LH feedback negatively inhibits GnRH release from the hypothalamus.

What factors inhibit GnRH?

GnRH is negatively inhibited by opioids, stress, and prolactin.

How are corticosteroids regulated?

CRH from the hypothalamus controls ACTH secretion from the anterior pituitary. ACTH can feedback negatively to the hypothalamus. Corticosteroids can feedback negatively or positively.

What are the effects of cortisol?

Cortisol promotes gluconeogenesis, protein metabolism, fat mobilization, and suppresses the immune system.

How does growth hormone (GH) act?

GH acts opposite of insulin by stimulating the release of FFA, AA absorption, protein synthesis, IGF secretion, and glucose secretion. GH can decrease body fat.

What are the stimulators and inhibitors of growth hormone production?

GH is stimulated by decreased glucose, FFA, fasting, hormones of puberty, exercise, and stress. It is inhibited by increased glucose, FFA, obesity, senescence, somatostatin, somatomedins (IGF-1), and GH.

What does IGF-1 do?

IGF-1 increases with protein intake and decreases with fasting. It acts like insulin by promoting synthesis and storage when plenty full and breakdown and mobilization when fasting.

What is growth hormone deficiency (GHD)?

GHD leads to growth failure in childhood and puberty, delayed puberty, hypoglycemia, and can be treated with subcutaneous GH injections.

What are the effects of growth hormone (GH) on insulin?

GH causes insulin resistance by decreasing glucose uptake, increasing blood glucose levels, lipolysis, and blood insulin levels.

What are the effects of GH on protein synthesis and growth?

GH increases protein synthesis and growth via IGF-1, promoting amino acid uptake, DNA/RNA/protein synthesis, and lean body mass/organ size.

What happens when there is excess GH?

Excess GH can cause acromegaly, often due to a pituitary tumor. This may cause bitemporal hemianopsia.

What are the types of anterior pituitary adenomas?

Prolactin-secreting adenomas (~45%), GH-secreting adenomas (~20%), ACTH-secreting adenomas (~15%), Gonadotropin-secreting adenomas (~15%), TSH-secreting adenomas (rare ~1-2%).

What causes anterior pituitary deficiencies?

Anterior pituitary deficiencies can be caused by head trauma or genetics, leading to hormone deficiencies.

What is the pattern of HPA axis disorders?

Primary disorders affect the endocrine gland (thyroid, adrenal cortex), secondary disorders affect the pituitary, and tertiary disorders affect the hypothalamus. GH and PRL do not follow this pattern.

What are the values in hypothyroidism?

In primary hypothyroidism: TRH = high, TSH = high, T4 = low. In secondary hypothyroidism: TRH = high, TSH = low, T4 = low. In tertiary hypothyroidism: TRH = low, TSH = low, T4 = low.

What are the values in hyperthyroidism?

In primary hyperthyroidism: TRH = low, TSH = low, T4 = high. In secondary hyperthyroidism: TRH = low, TSH = high, T4 = high. In tertiary hyperthyroidism: TRH = high, TSH = high, T4 = high.

What is Diabetes Insipidus (DI)?

DI is characterized by unregulated ADH (neurogenic) or unresponsiveness to ADH (nephrogenic). Neurogenic DI is fixed by giving ADH, while nephrogenic DI is not responsive to ADH.

How is DI diagnosed?

DI is diagnosed by dehydration stimulus followed by the inability to concentrate urine.

What are pituitary tumor types?

Cushing's Disease (ACTH-secreting adenoma), Hyperthyroidism (TSH-secreting adenoma), Hypogonadism (FSH/LH-secreting adenoma), Pituitary Failure (null cell adenoma).

What is Sheehan Syndrome?

Sheehan Syndrome is postpartum hypopituitarism characterized by symptoms such as inability to lactate, amenorrhea, weight retention, skin/voice changes, and fatigue. The posterior pituitary may be relatively unaffected due to a different blood supply.

What is prolactinoma?

Prolactinoma is an adenoma of lactotropes, with PRL >200 ng/mL.

What is prolactinemia?

Prolactinemia is characterized by PRL levels between 100 and 200 ng/mL.