Pharm 121: Endocrine System - Part 1

Comprehensive vocabulary flashcards covering the introductory anatomy, mechanisms of action, and major hormones of the endocrine system, hypothalamus, and pituitary gland from Pharm 121 Lecture 6.

The second great controlling system of the body that coordinates and directs cellular activity alongside the nervous system, characterized by slower, longer-lasting effects controlling processes such as metabolism, reproduction, and fluid balance.

Endocrine System

A gland that secretes its products into ducts that carry the secretions into body cavities, into the lumen of an organ, or to the outer surface of the body (e.g., sudoriferous, sebaceous, mucous, and digestive glands).

Exocrine Gland

A ductless gland that secretes hormones into the surrounding interstitial fluid, which then diffuse into capillaries and circulate throughout the body in the blood.

Endocrine Gland

A mediator molecule (derived from the Greek $hormon$, meaning 'to excite or get moving') produced and secreted by endocrine glands or hormone-secreting cells that travels through the blood to alter the physiological activity of target cells with specific receptors.

Hormone

Hormones that pass from secretory cells into interstitial fluid and then into the bloodstream to act on distant target tissues, which are eventually inactivated by the liver and excreted by the kidneys.

Circulating Hormones

Local hormones that diffuse through interstitial fluid to act on neighboring target cells rather than entering the bloodstream.

Paracrine Hormones

Local hormones that act directly on the same cell that secreted them.

Autocrine Hormones

A decrease in the number of target-cell receptors or a decrease in cell responsiveness when a hormone is present in excess, resulting in a diminished target-tissue response.

Down-Regulation

An increase in the number of target-cell receptors that makes a target tissue more sensitive to a hormone, typically occurring when a hormone is deficient or continuously inhibited.

Up-Regulation

Hormones—including steroid hormones derived from cholesterol, thyroid hormones ($T_3$ and $T_4$) derived from tyrosine, and eicosanoids—that diffuse freely across plasma membranes to bind cytosolic or nuclear receptors and alter gene transcription.

Lipid-Soluble Hormones

Hormones—including amine, peptide, and protein hormones—that are lipophobic, cannot cross the cell membrane, and bind to cell-surface receptors to trigger intracellular second-messenger cascades (such as $cAMP$).

Water-Soluble Hormones

A type of hormonal interaction where the action of one hormone requires simultaneous or recent exposure to a second hormone to exert its full effect (e.g., catecholamines requiring corticosteroids).

Permissive Effect

A hormonal interaction where the combined effect of two hormones acting together is greater or more extensive than the sum of the effects of each hormone acting alone.

Synergistic Effect

A hormonal interaction where the physiological action of one hormone opposes or reverses the action of another hormone.

Antagonistic Effect

The release of a hormone in direct response to changing levels of specific chemicals, nutrients, or ions in extracellular body fluids (e.g., low blood calcium stimulating $PTH$ release).

Humoral Stimulus

A specialized vascular arrangement wherein blood flows from capillaries in the hypothalamus into portal veins that carry releasing and inhibiting hormones directly to the secondary capillary network in the anterior pituitary.

Hypothalamic-Hypophyseal Portal System

The glandular anterior lobe of the pituitary gland that synthesizes and secretes seven hormones regulated by hypothalamic releasing and inhibiting factors.

Adenohypophysis

The neural posterior lobe of the pituitary gland that stores and releases oxytocin and antidiuretic hormone produced by hypothalamic neurosecretory cells, containing no glandular tissue.

Neurohypophysis

Specialized neuroglial cells located in the posterior pituitary lobe that are associated with the axon terminals of hypothalamic neurosecretory cells.

Pituicytes

A hormone that targets and stimulates another endocrine gland to grow and secrete its own hormones (e.g., $TSH$, $ACTH$, $FSH$, and $LH$).

Tropic Hormone

A major neuroendocrine feedback loop where hypothalamic $CRH$ stimulates anterior pituitary $ACTH$, which triggers adrenal cortex cortisol release; elevated cortisol then exerts negative feedback on both the hypothalamus and anterior pituitary.

Hypothalamic-Pituitary-Adrenal (HPA) Axis

The most abundant hormone of the anterior pituitary (also called somatotropin), produced by somatotrophs, that serves as the primary regulator of body growth and skeletal development.

Human Growth Hormone (hGH)

Small protein hormones (also known as somatomedins) synthesized primarily by the liver in response to growth hormone that mediate the indirect growth-promoting actions of $hGH$ on bones and soft tissues.

Insulin-Like Growth Factors (IGFs)

The anti-insulin metabolic action of human growth hormone characterized by enhanced lipolysis, decreased cellular glucose uptake, and increased hepatic gluconeogenesis, which can lead to insulin resistance and elevated blood sugar.

Diabetogenic Effect

A condition caused by the hyposecretion of human growth hormone during childhood, leading to a maximum adult height of $4\text{ feet}$ while maintaining normal body proportions.

Pituitary Dwarfism

A condition resulting from hypersecretion of human growth hormone during childhood while epiphyseal plates remain open, causing individuals to reach $8\text{ to }9\text{ feet}$ in height with normal body proportions.

Gigantism

A disorder caused by hypersecretion of human growth hormone during adulthood after epiphyseal plate closure, characterized by abnormal body proportions, thickening of facial bones, and enlargement of the hands and feet.

Acromegaly

An anterior pituitary hormone secreted by lactotrophs that stimulates and maintains milk production by the mammary glands following childbirth.

Prolactin (PRL)

An abnormal, inappropriate flow of breast milk that occurs outside of pregnancy or childbirth, commonly caused by hypersecretion of prolactin.

Galactorrhea

A tropic hormone produced by anterior pituitary corticotrophs that stimulates the adrenal cortex to synthesize and release glucocorticoids, particularly cortisol.

Adrenocorticotropic Hormone (ACTH)

A tropic hormone (also called thyrotropin) secreted by thyrotrophs in the anterior pituitary that promotes the growth of the thyroid gland and stimulates the release of $T_3$ and $T_4$.

Thyroid-Stimulating Hormone (TSH)

A gonadotropin from the anterior pituitary that initiates development of ovarian follicles and stimulates estrogen secretion in females, and stimulates sperm production in the testes of males.

Follicle-Stimulating Hormone (FSH)

A gonadotropin that triggers ovulation and corpus luteum formation in females, and acts as interstitial cell-stimulating hormone ($ICSH$) to stimulate testosterone production in males.

Luteinizing Hormone (LH)

A peptide hormone secreted by corticotrophs of the anterior pituitary that increases skin pigmentation by dispersing melanin granules in melanocytes.

Melanocyte-Stimulating Hormone (MSH)

A hypothalamic neurohormone stored in the posterior pituitary that stimulates uterine contractions during labor via positive feedback and induces the milk 'letdown' reflex during breastfeeding.

Oxytocin (OT)

A peptide hormone (also known as vasopressin) produced by the supraoptic nucleus of the hypothalamus and released by the posterior pituitary that stimulates water reabsorption in the kidneys to increase blood volume and decrease urine volume.

Anti-diuretic Hormone (ADH)

A metabolic disorder caused by hyposecretion of antidiuretic hormone, resulting in the excretion of massive amounts of dilute, tasteless urine (polyuria) and extreme compensatory thirst (polydipsia).

Central Diabetes Insipidus