Overview of Chemical Messengers in the Endocrine System

Chemical messenger

A substance secreted by the endocrine system that communicates regulatory messages within the body.

Signaling pathway

The process by which a chemical signal is transmitted through a series of molecular events.

Hormone classification

The categorization of hormones based on their chemical structure and solubility.

Lipid hormones

Hormones that are soluble in lipids and can easily pass through cell membranes.

Non-lipid hormones

Hormones that are not soluble in lipids and typically require receptors on the cell surface to exert their effects.

Up-regulation

The process by which a cell increases the number of receptors for a hormone, enhancing its sensitivity.

Down-regulation

The process by which a cell decreases the number of receptors for a hormone, reducing its sensitivity.

Primary messengers

Molecules that bind to receptors on target cells to initiate a signaling pathway.

Secondary messengers

Intracellular molecules that relay signals received from receptors on the cell surface to target molecules inside the cell.

Hormone interactions

The ways in which different hormones can influence each other's effects on target cells.

Hypothalamus

A region of the brain that regulates many bodily functions, including the release of hormones from the pituitary gland.

Anterior pituitary gland

The front portion of the pituitary gland that produces and secretes various hormones.

Posterior pituitary gland

The back portion of the pituitary gland that stores and releases hormones produced by the hypothalamus.

Target cells

Specific cells that have receptors for a particular hormone and can respond to its signal.

Homeostasis

The maintenance of stable internal conditions in the body despite changes in the external environment.

Nervous system

The system of the body that transmits signals between different parts of the body and regulates physiological functions.

Endocrine system

The system of glands that secrete hormones directly into the bloodstream to regulate various bodily functions.

Mediator molecules

Substances, such as hormones and neurotransmitters, that facilitate communication between cells.

Reception

The first step in the signaling pathway where a hormone binds to a receptor on the target cell's membrane.

Signal transduction

The process by which a signal is converted into a functional response within the cell.

Response

The final outcome of a signaling pathway, which can vary depending on the type of target cell.

Lipid-soluble hormones

Hormones that are hydrophobic and include steroids, thyroid hormones, and nitric oxide.

Steroids

Lipids derived from cholesterol on the smooth endoplasmic reticulum, with different functional groups providing uniqueness.

Thyroid hormones

Hormones that consist of a tyrosine ring plus attached iodines, specifically T3 and T4.

Nitric oxide

A molecule that functions as both a hormone and a neurotransmitter.

Water-soluble hormones

Hormones that are hydrophilic, including amine, peptide, and protein hormones.

Amine hormones

Hormones that are modified amino acids.

Peptide hormones

Hormones that are grouped amino acids.

Examples of water-soluble hormones

Insulin, serotonin, melatonin, histamine, and epinephrine.

Eicosanoid hormones

Hormones derived from arachidonic acid, including prostaglandins and leukotrienes.

Hormone transport in blood

Protein hormones circulate in free form, while lipid hormones attach to transport proteins synthesized by the liver.

Mechanisms of hormone action

Hormones must bind to appropriate receptors to trigger a response.

Receptors for water-soluble hormones

Located on the cell membrane of target cells.

Receptors for lipid-soluble hormones

Located inside the target cells.

Effects of lipid hormones

Lipid hormones diffuse across the cell membrane and attach directly to receptors, altering gene expression.

Effects of non-lipid hormones

Binding to receptors causes a chain reaction within the cell, often activating a G-protein cascade.

First messenger

The hormone that binds to the receptor to initiate a response.

Second messenger

Cyclic AMP (cAMP), which is produced as a result of the first messenger's action.

cAMP

Activates protein kinases, which add phosphate groups to other molecules, leading to activation or inactivation.

Control of hormone secretions

Regulated by signals from the nervous system, chemical changes in blood, and other hormones.

Negative feedback systems

Most hormonal regulatory systems operate through this mechanism.

Positive feedback systems

A very few hormonal regulatory systems operate through this mechanism.

Hormone activity

Hormones affect only specific target tissues with specific receptors.

Down-regulation

Occurs when an excess of a hormone is present, reducing receptor number and sensitivity.

Up-regulation

Occurs when too little hormone is present, increasing receptor production and sensitivity.

Hormone interactions

Responsiveness of target cells depends on hormone concentration, number of receptors, and influences of other hormones.

Permissive effects of hormones

When the presence of one hormone alters the effect of another, which can be synergistic or antagonistic.

Master endocrine glands

The pituitary gland, considered the master controller gland, is regulated by the hypothalamus.

Hypothalamus

The brain region that links the nervous system and endocrine system, synthesizing nine hormones.

Pituitary gland

Lies in the sella turcica of the sphenoid bone and has two portions: anterior pituitary and posterior pituitary.

Anterior pituitary

Synthesizes and secretes hormones that regulate a wide range of bodily activities.

Posterior pituitary

Stores and releases two hormones made in the hypothalamus but does not synthesize any hormones.

Water soluble

(hydrophilic)

Lipid soluble

(hydrophobic)

Steroids

Lipids derived from cholesterol on SER with different functional groups attached to core of structure providing uniqueness.

Thyroid hormones

Hormones consisting of a tyrosine ring plus attached iodines (T3 and T4).

Nitric oxide

A hormone and a neurotransmitter (NT).

Amine, peptide, and protein hormones

Hormones that are modified amino acids or grouped amino acids, including insulin, serotonin, melatonin, histamine, and epinephrine.

Hormone Transport in Blood

Protein hormones circulate in free form in blood, while lipid hormones must attach to transport proteins synthesized by the liver.

Mechanisms of hormone action

Hormones must bind to an appropriate receptor to trigger a response.

Receptors for water soluble hormones

Located on the cell membrane of the target cell.

Receptors for lipid soluble hormones

Located inside the target cells.

Effects of lipid hormones

Lipid hormones diffuse across cell membrane and attach directly to a receptor, altering gene expression of the target cell.

Effects of non-lipid hormones

The binding of non-lipid hormones to receptors causes a 'chain-reaction' of events within the cell.

First messenger

The hormone that binds to the receptor, initiating a response.

Second messenger

Cyclic AMP (cAMP), produced as a result of a G-protein cascade activated by hormone binding.

cAMP

Activates one or more protein kinases, enzymes that add a phosphate group to other molecules.

Phosphorylation

The addition of a phosphate group that can lead to activation or inactivation of molecules.

Negative feedback systems

Most hormonal regulatory systems work via this mechanism.

Positive feedback systems

A very few hormonal regulatory systems work via this mechanism.

Hormone interactions

Responsiveness of target cell depends on hormone concentration, number of hormone receptors, and influences of other hormones.

Permissive effects of hormones

When the presence of one hormone alters the effect of another.

Synergistic effects

Effect is greater when both hormones are present than when each hormone acts alone.

Antagonistic effects

One hormone opposes the action of another hormone.

Master endocrine glands

The pituitary gland was considered the master controller gland, regulated by the hypothalamus.

Pituitary gland

Lies in the sella turcica of the sphenoid bone, with anterior and posterior portions.

Checkpoint Questions Part 1

What is a mediator molecule?

Chemical messenger

A substance secreted by endocrine glands that communicates regulatory messages within the body.

Signaling pathway

The process through which a chemical messenger transmits a signal to elicit a response in target cells.

Hormone classification

The categorization of hormones into lipid-soluble and water-soluble types based on their chemical properties.

Lipid hormones

Hormones that are hydrophobic and can diffuse across cell membranes.

Non-lipid hormones

Hormones that are hydrophilic and bind to receptors on the cell membrane of target cells.

Up-regulation

The process by which a cell increases the number of hormone receptors in response to low hormone levels.

Down-regulation

The process by which a cell decreases the number of hormone receptors in response to high hormone levels.

Primary messengers

Hormones that bind to receptors on target cells to initiate a signaling pathway.

Secondary messengers

Molecules like cyclic AMP (cAMP) that relay signals inside the cell after the primary messenger binds to its receptor.

Mediator molecules

Substances such as neurotransmitters and hormones that facilitate communication between cells.

Hormone transport in blood

The mechanism by which hormones circulate in the bloodstream, either free or bound to transport proteins.

Protein kinases

Enzymes that add phosphate groups to other molecules, often leading to activation or inactivation of proteins.

Negative feedback systems

Regulatory mechanisms that reduce the output or activity of a system when a certain level is reached.

Positive feedback systems

Regulatory mechanisms that enhance or amplify changes in a system.

Hypothalamus

A brain region that links the nervous system and endocrine system, controlling the pituitary gland.

Pituitary gland

An endocrine gland that secretes hormones regulating various bodily functions, divided into anterior and posterior parts.

Lipid-soluble hormones

Hormones that can easily pass through cell membranes and typically alter gene expression.

Water-soluble hormones

Hormones that cannot pass through cell membranes and require receptors on the cell surface.

Synergistic effects

When the combined effect of two hormones is greater than the sum of their individual effects.

Antagonistic effects

When one hormone opposes the action of another hormone.

G-protein cascade

A series of biochemical events triggered by the binding of a hormone to its receptor, leading to the production of second messengers.

cAMP

Cyclic adenosine monophosphate, a common second messenger involved in signal transduction pathways.

Receptor synthesis

The process by which cells produce hormone receptors, which can be increased or decreased based on hormone levels.