LETS GO TO HELL

What is the endocrine system?

One of the body's two major regulatory systems that uses hormones as chemical messengers to regulate target cells and tissues.

What is a hormone?

A chemical messenger secreted by endocrine cells that travels through body fluids

What is a target cell?

A cell that has receptors for a particular hormone and can therefore respond to that hormone.

What is a target tissue?

A tissue containing cells that have receptors for a particular hormone.

What is a hormone receptor?

A protein that specifically binds a hormone and allows the hormone to influence the target cell's activity.

What is a classic endocrine signal?

A hormone secreted into the blood that travels to and affects distant target cells.

What is endocrine signaling?

Signaling in which hormones enter the bloodstream and travel to distant target cells.

What is paracrine signaling?

Signaling in which a chemical is released into extracellular fluid and affects nearby cells of a different type.

What is autocrine signaling?

Signaling in which a chemical released by a cell affects the same cell or same cell type that secreted it.

What is an endocrine gland?

A ductless gland made of glandular epithelial cells that secretes hormones into interstitial fluid for transport by the blood.

How are endocrine glands different from exocrine glands?

Endocrine glands are ductless and release hormones into interstitial fluid and blood

How quickly can endocrine hormones produce effects?

Hormones can require seconds to several hours or days to produce effects.

How long do endocrine effects generally last compared with nervous system effects?

Endocrine effects are generally longer-lasting than nervous system effects.

What are the three major chemical classes of hormones?

Amino acid-based hormones

What are amino acid-based hormones?

Hydrophilic hormones derived from amino acids

What are steroid hormones?

Lipophilic hormones derived from cholesterol that can diffuse through plasma membranes and bind intracellular receptors.

What does hydrophilic mean?

Water-soluble.

What does lipophilic mean?

Lipid-soluble or fat-soluble.

How are hydrophilic hormones transported in the blood?

They generally travel freely dissolved in the blood plasma.

How are lipophilic hormones transported in the blood?

They generally require transport proteins in the plasma because they do not dissolve well in water.

Where are receptors for hydrophilic hormones usually located?

On the plasma membrane of the target cell.

Where are receptors for lipophilic hormones usually located?

Inside the target cell

Why can steroid hormones cross the plasma membrane?

Because they are lipophilic and the plasma membrane is primarily composed of lipids.

Why can hydrophilic hormones not easily cross the plasma membrane?

Because they are water-soluble and do not readily pass through the lipid bilayer.

What happens when a hydrophilic hormone binds to its membrane receptor?

It activates an intracellular signaling pathway that uses second messengers to change cellular activity.

What is a second messenger?

An intracellular molecule that relays or amplifies a signal after a hormone binds to a cell-surface receptor.

What is the first messenger in a second-messenger pathway?

The hormone that binds to the receptor on the plasma membrane.

What is the general sequence of the cAMP second-messenger pathway?

Hormone binds receptor, receptor activates G protein, G protein activates adenylate cyclase, adenylate cyclase produces cAMP, cAMP activates protein kinase A, and protein kinase A phosphorylates target proteins.

What does a G protein do in hormone signaling?

It relays the signal from an activated membrane receptor to an intracellular effector enzyme.

What is adenylate cyclase?

An effector enzyme that converts ATP into cyclic AMP.

What is cAMP?

Cyclic AMP, a second messenger produced from ATP that helps transmit a hormone signal inside the cell.

What does protein kinase A do?

It phosphorylates target proteins, changing their activity and altering cellular functions.

What does phosphorylation mean?

The addition of a phosphate group to a protein, often changing the protein's activity

What is the general mechanism of direct gene activation by lipophilic hormones?

The hormone crosses the plasma membrane, binds an intracellular receptor, forms a hormone-receptor complex, enters or acts in the nucleus, binds DNA response elements, and alters gene transcription.

What is a hormone-response element?

A specific DNA sequence to which a hormone-receptor complex binds to regulate gene transcription.

How can lipophilic hormones change cell activity?

By changing gene transcription and therefore altering the production of specific proteins.

What is upregulation?

An increase in the number or sensitivity of receptors for a hormone, making a target cell more responsive

What is downregulation?

A decrease in receptor number or sensitivity, making a target cell less responsive to a hormone.

Why can prolonged exposure to high hormone levels cause downregulation?

Continuous stimulation can cause target cells to decrease receptor number or responsiveness.

What is synergism?

An interaction in which two or more hormones act together to produce an effect greater than the sum of their individual effects.

What is antagonism?

An interaction in which one hormone opposes or inhibits the action of another hormone.

What is a complementary hormone interaction?

An interaction in which different hormones produce related effects that contribute to the same overall physiological response.

What is a hormone's half-life?

The amount of time required for the concentration of a hormone in the blood to decrease by half.

What are the three major types of stimuli that trigger hormone secretion?

Hormonal stimuli, humoral stimuli, and neural stimuli.

What is a hormonal stimulus?

A change in hormone levels that causes another endocrine gland to release a hormone.

What is a humoral stimulus?

A change in the concentration of substances in body fluids, such as ions or nutrients, that stimulates hormone secretion

What is a neural stimulus?

Stimulation of hormone secretion by nerve fibers or neurotransmitters.

What is negative feedback?

A regulatory mechanism in which the response to a stimulus reduces or reverses the original stimulus.

Why is negative feedback important in endocrine regulation?

It helps maintain stable internal conditions by preventing hormone levels and their effects from becoming excessive.

What is the hypothalamus?

A brain region that connects the nervous and endocrine systems and regulates many endocrine functions through the pituitary gland.

What is the pituitary gland?

An endocrine gland associated with the hypothalamus that regulates many other endocrine glands and physiological processes.

What is the infundibulum?

The stalk that connects the hypothalamus to the pituitary gland.

What are the two major divisions of the pituitary gland?

The anterior pituitary and the posterior pituitary.

What is the anterior pituitary also called?

The adenohypophysis.

What is the posterior pituitary also called?

The neurohypophysis.

How is the anterior pituitary connected to the hypothalamus?

It is connected through the hypothalamic-hypophyseal portal system, a specialized blood vessel network.

What is the hypothalamic-hypophyseal portal system?

A blood vessel network that carries hypothalamic hormones directly to the anterior pituitary.

Why is the hypothalamic-hypophyseal portal system important?

It allows small amounts of hypothalamic hormones to rapidly reach and regulate anterior pituitary cells.

What are hypothalamic tropic hormones?

Hormones released by the hypothalamus that stimulate or inhibit hormone secretion by the anterior pituitary.

What is TRH?

Thyrotropin-releasing hormone, a hypothalamic hormone that stimulates the anterior pituitary to release TSH.

What is CRH?

Corticotropin-releasing hormone, a hypothalamic hormone that stimulates the anterior pituitary to release ACTH.

What is GHRH?

Growth hormone-releasing hormone, a hypothalamic hormone that stimulates the anterior pituitary to release growth hormone

What is somatostatin?

A hypothalamic hormone that inhibits growth hormone secretion by the anterior pituitary.

What is GnRH?

Gonadotropin-releasing hormone, a hypothalamic hormone that stimulates the anterior pituitary to release LH and FSH.

What is PRH?

Prolactin-releasing hormone, a hypothalamic signal that promotes prolactin secretion.

What is dopamine or PIH?

Prolactin-inhibiting hormone, a hypothalamic signal that inhibits prolactin secretion.

How is the posterior pituitary different from the anterior pituitary?

The posterior pituitary stores and releases hormones made by the hypothalamus, while the anterior pituitary produces and secretes its own hormones in response to hypothalamic signals.

What are the two major hormones released by the posterior pituitary?

Antidiuretic hormone and oxytocin.

Where are ADH and oxytocin actually produced?

They are produced by neurons in the hypothalamus and transported to the posterior pituitary for storage and release.

What is ADH?

Antidiuretic hormone, a hormone that promotes water retention by increasing the permeability of the kidneys' collecting ducts to water.

What is another name for ADH?

Vasopressin.

Where is ADH produced?

In neurons of the hypothalamus, particularly in the supraoptic and paraventricular nuclei.

Where is ADH stored and released?

It is stored and released from the posterior pituitary.

What stimulates ADH release?

Increased plasma solute concentration, decreased blood volume, or decreased blood pressure can stimulate ADH release.

What do hypothalamic osmoreceptors monitor?

The concentration of solutes in the blood or plasma osmolarity.

How does ADH affect the kidneys?

It increases water permeability of the collecting ducts, allowing more water to be reabsorbed into the blood.

What are aquaporins?

Water channels inserted into the membranes of kidney collecting duct cells in response to ADH, allowing water to move into the cells.

What happens to urine when ADH levels increase?

More water is reabsorbed, producing a smaller volume of more concentrated urine

What happens when ADH levels decrease?

Less water is reabsorbed, producing a larger volume of more dilute urine

What is diabetes insipidus?

A condition involving insufficient ADH activity or response that causes excessive water loss in the urine and increased thirst.

What is oxytocin?

A posterior pituitary hormone involved in uterine contractions and milk let-down during breastfeeding.

What stimulates oxytocin release during labor?

Stretch of the cervix caused by the baby's movement through the birth canal.

Why is oxytocin during labor an example of positive feedback?

Cervical stretching stimulates oxytocin, oxytocin increases uterine contractions, and stronger contractions cause more cervical stretching

What does oxytocin do during breastfeeding?

It causes milk let-down by stimulating contraction of cells surrounding mammary gland structures.

What are the major anterior pituitary hormones?

TSH, ACTH, prolactin, LH, FSH, and GH.

What is TSH?

Thyroid-stimulating hormone, an anterior pituitary hormone that stimulates the thyroid gland to produce and release thyroid hormones

What stimulates TSH secretion?

TRH from the hypothalamus stimulates TSH secretion.

What hormones provide negative feedback to reduce TSH secretion?

Thyroid hormones, especially T3 and T4, inhibit the hypothalamus and anterior pituitary

What is the thyroid axis?

The pathway TRH from the hypothalamus stimulates TSH from the anterior pituitary, which stimulates the thyroid to release T3 and T4.

What is ACTH?

Adrenocorticotropic hormone, an anterior pituitary hormone that stimulates the adrenal cortex to produce glucocorticoids, especially cortisol

What stimulates ACTH secretion?

CRH from the hypothalamus.

What is the HPA axis?

The hypothalamic-pituitary-adrenal axis in which CRH stimulates ACTH, which stimulates cortisol secretion from the adrenal cortex.

What provides negative feedback in the HPA axis?

Cortisol inhibits both CRH release from the hypothalamus and ACTH release from the anterior pituitary.

What is prolactin?

An anterior pituitary hormone that promotes milk production by the mammary glands.

What regulates prolactin secretion?

Hypothalamic signals regulate prolactin, with dopamine acting as an important inhibitor.

What are gonadotropins?

Anterior pituitary hormones that act on the gonads (sex hormones), specifically LH and FSH.

What is LH?

Luteinizing hormone, an anterior pituitary gonadotropin that regulates reproductive functions in the ovaries and testes

What is FSH?

Follicle-stimulating hormone, an anterior pituitary gonadotropin involved in ovarian follicle development and sperm production

What stimulates LH and FSH secretion?

GnRH from the hypothalamus.

What is GH?

Growth hormone, an anterior pituitary hormone that promotes growth and influences metabolism