KEY Ch 13: Basic Endocrinology

What is a tropic hormone?

A hormone that stimulates another endocrine gland to release hormones.

Give four examples of tropic hormones

TSH, ACTH, FSH, LH

What is a direct effector hormone?

A hormone that acts directly on target tissues rather than another endocrine gland.

Give two examples of direct effector hormones.

Growth hormone (GH) and prolactin

What gland is considered the primary control center of the endocrine system?

Hypothalamus

What structure connects the hypothalamus and pituitary gland?

Pituitary stalk (infundibulum)

What hypothalamic hormone stimulates TSH release?

TRH (thyrotropin-releasing hormone)

What hypothalamic hormone stimulates ACTH release?

CRH (corticotropin-releasing hormone)

What hypothalamic hormone stimulates GH release?

GHRH

What inhibits GH release?

Somatostatin

What is the primary inhibitor of prolactin?

Dopamine

What is another name for the anterior pituitary?

Adenohypophysis

What is another name for the posterior pituitary?

Neurohypophysis

Which pituitary lobe stores and releases hormones made in the hypothalamus?

Posterior pituitary

List all six major anterior pituitary hormones.

• TSH

• ACTH

• FSH

• LH

• GH

• Prolactin

Which hormones are stored and released by the posterior pituitary?

Oxytocin and vasopressin (ADH)

What is negative feedback?

Increased hormone production inhibits further hormone release, stabilizing the system.

What is positive feedback?

Increased product causes further stimulation until a specific endpoint is reached.

Give an example of positive feedback.

Childbirth (parturition) and blood clotting

Which feedback mechanism is the primary means of endocrine regulation?

Negative feedback

What is a primary endocrine disorder?

Failure of the target endocrine gland itself

In primary hypothyroidism, what happens to T4 and TSH?

T4 decreases and TSH increases.

What is a secondary endocrine disorder?

Failure of the pituitary gland.

In secondary hypothyroidism, what happens to T4 and TSH?

Both decrease

What is a tertiary endocrine disorder?

Failure of the hypothalamus.

What endocrine gland is stimulated by TSH?

Thyroid gland

TSH is especially useful for diagnosing what condition?

Adult hypothyroidism.

What gland does ACTH target?

adrenal cortex

Name the three major steroid classes produced by the adrenal cortex.

• Glucocorticoids

• Mineralocorticoids

• Androgens

What is the major glucocorticoid?

Cortisol.

What is the major mineralocorticoid?

Aldosterone.

When are ACTH levels highest?

About 6-8 AM

Which hormone demonstrates significant diurnal variation and is high in the morning?

Cortisol

What is another name for GH?

Somatotropin.

Define amphibolic.

Influences both anabolic and catabolic processes.

What hormone is described as amphibolic?

Growth hormone

Name three actions of GH.

• Stimulates tissue growth

• Stimulates lipolysis

• Enhances protein synthesis

• Promotes IGF production

• Increases gluconeogenesis

What stimulates GH secretion?

Sleep, exercise, meals, hypoglycemia

What inhibits GH secretion?

Glucose loading.

Excess GH before epiphyseal closure causes?

Gigantism

Excess GH after epiphyseal closure causes?

Acromegaly.

Deficiency of GH in childhood causes?

Pituitary dwarfism.

What is the primary function of prolactin?

Milk production and breast development.

What stimulates prolactin release?

TRH

What inhibits prolactin release?

Dopamine

Why is prolactin commonly measured clinically?

Investigation of infertility, galactorrhea, pituitary disorders, and prolactinomas.

Give three names for ADH

ADH, vasopressin, AVP (arginine vasopressin)

What is the major function of ADH?

Promotes water reabsorption in renal tubules and maintains water balance.

What receptors control ADH release?

Hypothalamic osmoreceptors and vascular baroreceptors

ADH deficiency causes what disorder?

Diabetes insipidus.

What symptoms are seen in diabetes insipidus?

Polyuria, polydipsia, dehydration.

What disorder results from excess ADH?

SIADH Syndrome of Inappropriate Antidiuretic Hormone Secretion

What laboratory test is often used to diagnose diabetes insipidus?

Water deprivation test

A postpartum patient has low TSH, ACTH, and prolactin. Which gland is dysfunctional?

Anterior pituitary. (Sheehan syndrome/hypopituitarism)

A patient has polyuria and polydipsia with a normal HbA1c. What endocrine disorder should be considered?

Diabetes insipidus

Small cell lung carcinoma is classically associated with production of what hormone?

ADH (SIADH) or ACTH (ectopic Cushing syndrome).

What suppression test is used to diagnose Cushing syndrome?

Dexamethasone suppression test

Which anterior pituitary hormone stimulates thyroid hormone production?

TSH.

Which anterior pituitary hormone stimulates cortisol production?

ACTH

Which hormone is highest during menopause?

FSH

Which hormone is inhibited by dopamine?

Prolactin

Which hormone is stimulated by hypoglycemia?

GH

Which hormone is suppressed by glucose loading

GH

Which hormone stimulates ovulation?

LH

Which hormone stimulates spermatogenesis?

FSH

Which hormone stimulates milk letdown?

Oxytocin

Which hormone stimulates milk production?

Prolactin

What gland is called the "master gland"?

Pituitary gland

What are the three major chemical classes of hormones?

Peptide/protein hormones, steroid hormones, and amino acid-derived (amine) hormones

List five functions of hormones.

• Maintain homeostasis

• Regulate growth and development

• Promote sexual maturation and reproduction

• Regulate energy production/metabolism

• Help adapt to stress and emergency situations

Which hormone class is water-soluble?

Peptide/protein hormones

Which hormone class is lipid-soluble?

Steroid hormones

Which structural category includes epinephrine and melatonin?

Amines

Which hormone receptors are usually located inside the cell nucleus?

Steroid hormone receptors.

Why do steroid hormones generally have a longer half-life than peptide hormones?

They are lipid soluble and circulate bound to carrier proteins.