Endocrine System Physiology and Disorders

Vocabulary practice flashcards covering endocrine signaling, hormone mechanics, hypothalamic-pituitary control, feedback loops, and disorders of the pituitary, thyroid, adrenal, and endocrine pancreas from Chapters 40 and 41.

Endocrine action

A mode of hormone delivery where the chemical messenger enters the bloodstream to travel a fair distance to target tissues, likened to international air mail.

Paracrine action

A local mode of hormone delivery where the hormone acts nearby where it was released without entering the bloodstream, such as sex hormones acting locally within the ovary.

Autocrine action

A form of signaling where a hormone exerts its effects on the exact same cell that produced and secreted it, such as insulin.

Entocrine action

An intracellular mechanism where a hormone is produced and acts in a contained manner entirely within the same cell.

Neurocrine action

A delivery mechanism where a neuron synthesizes and secretes a hormone that enters the bloodstream instead of acting locally like a neurotransmitter, exemplified by $ADH$ and epinephrine.

Steroid hormones

Lipid-based hormones derived from cholesterol, including estrogen, glucocorticoids, and testosterone.

Lipid-soluble hormones

Hormones, such as steroids and thyroid hormones, that cannot circulate freely in plasma and must bind to carrier proteins produced by the liver, shielding them from water and extending their half-life.

Water-soluble hormones

Hormones that circulate freely in plasma without protein carriers, undergo rapid metabolism, and bind to surface cell receptors to trigger intracellular second messenger systems.

Thyroxine ($T_4$)

A thyroid hormone that is $99\%$ bound to carrier proteins, granting it a long half-life of approximately $6\text{ days}$.

Angiotensin

A rapid-acting hormone with a half-life of less than $1\text{ minute}$ that quickly executes blood pressure control and is rapidly cleared.

High affinity receptor binding

The ability of a receptor to bind tightly to its specific hormone even when the circulating hormone concentration is low.

Hypothalamic-hypophyseal portal system

The vascular connection between the hypothalamus and the anterior pituitary that delivers tiny amounts of releasing and inhibiting chemical signals.

Posterior pituitary

An extension of the hypothalamus connected by nerve axons that stores and directly releases the hypothalamic-synthesized hormones $ADH$ and oxytocin into the bloodstream.

Negative feedback

A homeostatic control mechanism operating like a thermostat, where rising hormone levels inhibit further secretion from upstream glands to maintain normal physiological ranges.

Positive feedback

A rare control mechanism that accelerates hormone secretion, exemplified by rising estradiol triggering an $LH$ surge necessary for ovulation.

Stimulation test

A diagnostic procedure used for suspected hypofunction where a tropic hormone, such as synthetic $ACTH$, is administered to evaluate whether the target gland can respond by elevating its hormone output.

Suppression test

A diagnostic test used for suspected hyperfunction where a synthetic hormone is administered to check if negative feedback successfully shuts off endogenous gland production.

Hormone resistance

A condition in which normal or elevated levels of a hormone are present, but target tissues fail to respond, such as in Laron syndrome dwarfism with Growth Hormone.

Primary endocrine disorder

An endocrine dysfunction originating directly within the final hormone-producing target gland itself, such as Addison's disease or post-surgical thyroid removal.

Secondary endocrine disorder

An endocrine dysfunction where the primary target gland is intact, but the regulatory gland one step above—typically the pituitary gland—fails to supply proper stimulation.

Tertiary endocrine disorder

An endocrine dysfunction originating at the highest regulatory level within the hypothalamus.

Pituitary functional reserve

The extensive compensatory capacity of the pituitary gland, requiring approximately $75\%$ of tissue loss before clinical signs and symptoms of hypopituitarism emerge.

Anti-insulin effect of Growth Hormone

The metabolic action of Growth Hormone that promotes the burning of fats over glucose and induces cellular resistance to insulin, predisposing to glucose intolerance.

Triiodothyronine ($T_3$)

The highly potent thyroid hormone that increases oxygen consumption, drives metabolic rate, and is essential for infant brain development.

Hashimoto's thyroiditis

An acquired autoimmune hypothyroid disorder causing slowed metabolism, cold intolerance, weight gain, constipation, bradycardia, and non-pitting myxedema with a coarse voice.

Graves' disease

An autoimmune hyperthyroid condition where stimulating antibodies bind thyroid receptors, continuously overproducing $T_3$ and $T_4$, often presenting with a bulging, staring gaze.

Thyroid storm

A severe hyperthyroid crisis triggered by stressors or abrupt medication cessation, manifesting with high fever, rapid heart rate, heart failure, and delirium.

Addison's disease

Primary adrenal insufficiency characterized by destruction of the adrenal cortex, deficiency of cortisol and aldosterone, potassium retention, sodium/water wasting, and skin hyperpigmentation from excessive $ACTH$.

Cushing syndrome

A state of hypercortisolism characterized by a rounded moon face, buffalo hump, thin limbs with muscle wasting, hyperglycemia, hypokalemia, and immunosuppression.

Congenital Adrenal Hyperplasia (CAH)

An inherited defect in cortisol synthesis that causes the pituitary to produce compensatory excess $ACTH$.

Type 1 Diabetes Mellitus

An autoimmune disorder that destroys pancreatic insulin-producing beta cells, leading to an absolute lack of insulin, lipolysis, and high vulnerability to diabetic ketoacidosis.

Type 2 Diabetes Mellitus

A metabolic disorder characterized by peripheral insulin resistance in muscle, liver, and fat, followed by eventual beta-cell exhaustion.

Hemoglobin $A_1C$

A diagnostic blood test reflecting glucose attachment to red blood cells over their $120\text{-day}$ lifespan, providing a long-term glycemic overview.

Diabetic Ketoacidosis (DKA)

An acute metabolic complication seen mainly in Type 1 diabetes, presenting with hyperglycemia, urinary ketones, low pH metabolic acidosis, and Kussmaul respirations.

Hyperosmolar Hyperglycemic State (HHS)

An acute complication typically seen in Type 2 diabetes marked by extreme hyperglycemia, concentrated hyperosmolar blood, profound dehydration, and neurological deficits without ketoacidosis.

Hypoglycemia

A state of low blood sugar defined as glucose $< 70\,\text{mg/dL}$, producing counterregulatory adrenergic symptoms like shakiness and neuroglycopenic signs such as seizures or coma.

Somogyi effect

Rebound morning hyperglycemia resulting from an undetected episode of hypoglycemia during the night that triggers compensatory hepatic glucose dumping.

Dawn phenomenon

Early morning hyperglycemia that is not preceded by nocturnal hypoglycemia, caused by normal circadian morning hormone surges occurring in the setting of impaired insulin regulation.