Chapter 17: Endocrine System lecture notes

Vocabulary flashcards covering the mechanisms, categories, and specific glands of the endocrine system based on the Chapter 17 lecture notes.

Endocrine system

A controlling system that exerts control via hormones, which are chemical signals delivered to target cells via the blood stream.

Hormonal stimulation

A mechanism for hormone synthesis and release where one hormone causes the release of another, such as Thyroid-stimulating hormone (TSH) causing the secretion of thyroid hormone ($T_3$ and $T_4$).

Humeral stimulation

A mechanism for hormone synthesis and release where a variable in the blood other than a hormone causes the release, such as $Ca^{++}$ ions triggering parathyroid hormone (PTH) or glucose triggering insulin.

Nervous stimulation

A mechanism for hormone synthesis and release where stimulation by neurons causes a gland to release a hormone, such as sympathetic neurons stimulating the adrenal medulla.

Steroids

A category of lipid-soluble, cholesterol-based hormones that can pass through the cell membrane to bind with intracellular receptors.

Biogenic amines (monoamines)

Hormones derived from modified amino acids (like tyrosine or tryptophan) that are generally water-soluble and bind to cell surface receptors, with the exception of thyroid hormone.

Proteins (peptides)

Hormones consisting of small chains of amino acids (including polypeptides and glycoproteins) that are water-soluble and bind to cell surface receptors.

Autocrine effect

A local hormone effect where the hormone acts on the same cell that produced it.

Paracrine effect

A local hormone effect where the hormone acts on nearby cells.

Eicosanoids

Local hormones produced from arachidonic acid, including prostaglandins, thromboxanes, and leukotrienes.

Half-life

The amount of time required for the level of a circulating hormone to be reduced by $50\%$. Steroids typically have a longer half-life due to carrier proteins.

Hormone-response element

The specific site on DNA where a lipid-soluble hormone-receptor complex binds to initiate transcription and protein synthesis.

Adenylate cyclase

An enzyme activated by a G protein that catalyzes the conversion of ATP into the second messenger cAMP.

Phospholipase C

An enzyme activated by a G protein that produces the second messengers DAG (diacylglycerol) and IP3 (Inositol triphosphate).

IP3 (Inositol triphosphate)

A second messenger that increases intracellular $Ca^{++}$, which then acts as a third messenger to activate protein kinase or alter membrane permeability.

Cascade effect

An amplification process where a single hormone molecule binding to one receptor can cause the activation or inhibition of millions of molecules within a cell.

Up-regulation

An increase in the number of receptors on a cell to alter its response to circulating hormone levels.

Down-regulation

A decrease in the number of receptors on a cell to reduce its response to hormone levels.

Synergistic response

An interaction where one hormone increases the response of a cell to another hormone.

Permissive response

An interaction where one hormone must be present for another hormone to exert its effect.

Antagonistic response

An interaction where hormones have opposite effects on the same target cell.

Hypothalamic-hypophyseal portal system

The blood vessel system connecting the hypothalamus and the anterior pituitary.

Hypothalamic-hypophyseal tract

The axon pathway through which hormones travel from neurosecretory cells in the hypothalamus to the posterior pituitary.

Antidiuretic hormone (ADH)

A hormone produced in the hypothalamus that acts on the kidneys and thirst center to concentrate urine and stimulate water reabsorption when blood osmolarity is too high.

Oxytocin (OT)

A hormone that stimulates smooth muscle contractions in the uterus during childbirth and triggers milk ejection in the breast.

Follicular cells

Cells in the thyroid gland responsible for the synthesis of thyroid hormone ($T_3$ and $T_4$).

Calcitonin

A hormone produced by thyroid parafollicular cells that decreases blood $Ca^{++}$ by reducing GI absorption, kidney reabsorption, and osteoclast activity.

Parathyroid hormone (PTH)

A hormone produced by the parathyroid glands that increases blood $Ca^{++}$ levels by increasing GI absorption, kidney reabsorption, and osteoclast activity.

Chromaffin cells

Cells located in the adrenal medulla that release epinephrine and norepinephrine as part of the sympathetic fight-or-flight response.

Aldosterone

A mineralocorticoid produced by the adrenal cortex that regulates sodium and potassium levels and influences blood pressure.

Cortisol

A glucocorticoid stress hormone from the adrenal cortex that stimulates the release of glucose and fatty acids and has anti-inflammatory and immune-dampening effects.

Alpha cells

Pancreatic cells that secrete glucagon when blood glucose levels are low.

Beta cells

Pancreatic cells that secrete insulin when blood glucose levels are high.