Introduction to Endocrinology and Pituitary Hormones

Vocabulary-style flashcards covering the basic principles of endocrinology, hormone messenger systems, hypothalamic-pituitary regulation, and pathologies associated with Growth Hormone.

Hormones

Chemical substances released by a cell or group of cells into body fluids that exerts some type of physiological "control."

Proteins and polypeptides

A class of hormones composed of long or short chains of amino acids.

Steroids

A class of hormones derived from lipid cholesterol.

Amine hormones

A class of hormones derived from tyrosine.

Negative feedback

A regulatory mechanism that prevents over activity of the hormonal system; used by most hormones.

Positive feedback

A regulatory mechanism that offers surges of the required hormone, such as Luteinizing hormone (LH).

Metabolic clearance rate

Calculated as the rate of disappearance of hormone from plasma divided by the Concentration of hormone in each milliliter of plasma.

cAMP Signaling Mechanism

A second messenger system where a hormone binds to a receptor, activates a G protein ($GDP \rightarrow GTP$), and the $G \alpha$ subunit binds with adenylyl cyclase to convert $ATP$ to $cAMP$. Examples include $TSH$, $ACTH$, $LH$, and Somatostatin.

Cell Membrane Phospholipid 2nd Messenger System

A mechanism where a hormone activates phospholipase C, causing breakdown of $PIP_2$ (phosphatidyl inositol 4,5-bisphosphate) into $IP_3$ (inositol triphosphate) and $DAG$ (diacylglycerol).

IP3 (inositol triphosphate)

A molecule that binds to its receptor on the mitochondria or endoplasmic reticulum to mobilize $Ca^{2+}$.

DAG (diacylglycerol)

A molecule that activates protein kinase C (PKC) to phosphorylate proteins and elicit cell responses.

Calcium-Calmodulin Second Messenger System

A system where hormone-receptor binding alters membrane permeability to $Ca^{2+}$ ions; the entering $Ca^{2+}$ binds with calmodulin, leading to a conformational change that activates or inhibits target proteins and kinases.

Transcriptional Pathway

A mechanism used by steroid hormones where the hormone-receptor complex binds to a specific site known as the Hormone response element on $DNA$ to initiate transcription of $mRNA$.

Adenohypophysis

The anterior pituitary gland, which is connected to the hypothalamus by the superior hypophyseal artery and contains five types of secretory cells.

Neurohypophysis

The posterior pituitary gland, which is a neural outgrowth of the hypothalamus that supports the axons of hypothalamic secreting neurons.

Somatotropes

Secretory cells in the anterior pituitary that produce Growth Hormone (GH).

Corticotropes

Secretory cells in the anterior pituitary that produce Adrenocorticotropin (ACTH).

Thyrotropes

Secretory cells in the anterior pituitary that produce Thyroid-Stimulating Hormone (TSH).

Gonadotropes

Secretory cells in the anterior pituitary that produce both Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH).

Lactotropes

Secretory cells in the anterior pituitary that produce Prolactin.

Hypophyseal portal system

The vascular system through which hypothalamic releasing and inhibitory hormones travel to the adenohypophysis to control secretion.

Somatostatin

A hypothalamic hormone that inhibits the secretion of Growth Hormone (GH) and other hormones.

PIH (Prolactin inhibiting hormone / dopamine)

A hypothalamic substance that inhibits the secretion of Prolactin (PRL).

Growth Hormone (GH) Structure

A single polypeptide containing $200\,aa$ and $2$ disulfide bridges, with a molecular weight of approximately $22,000$, synthesized as a prehormone.

Diabetogenic effect

A metabolic effect of Growth Hormone characterized by increased plasma glucose (decreased uptake and oxidation) and overstimulation of insulin secretion.

Dwarfism

A condition caused by hypopituitarism during childhood, resulting in growth inhibition and sexual immaturity.

Gigantism

A condition caused by an increase in Growth Hormone (GH) before adolescence, leading to growth exceeding $8\,\text{ft}$ because the epiphyses are not closed.

Acromegaly

A condition caused by an acidophilic tumor after adolescence, resulting in enlargement of soft tissues and the lower jaw bone.

Supraoptic nucleus

The specific hypothalamic site where Antidiuretic hormone (ADH) is synthesized.

Paraventricular nucleus

The specific hypothalamic site where Oxytocin is synthesized.

Pituicytes

Cells in the posterior pituitary that provide structural support for terminal nerve fibers and nerve endings.

V2 receptors

Receptors in the distal convoluted tubules and collecting ducts of the renal medulla where $ADH$ binds to enhance water permeability.

V1 receptors

Receptors on arteriolar smooth muscle cells where $ADH$ binds to cause vasoconstriction and increase blood pressure.

Oxytocin Functions

Stimulates myoepithelial contractions in the breast for "milk let down" upon suckling and contracts the uterus during the birthing process.