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Endocrine system

The body system that secretes hormones into the bloodstream to regulate metabolism, growth, development, and other long-distance processes.

Hormone

A chemical messenger produced by endocrine cells that is secreted in the blood to distant target cells with specific receptors.

Autocrine

Signaling where the secreted molecule acts on the same cell that produced it. (same hormone bind to the same cell)

Paracrine

Signaling where the secreted molecule affects nearby cells within the same tissue. (ex: pancreas - insulin release)

Autocrine vs Paracrine

Autocrine acts on the secreting cell; paracrine acts on neighboring cells.

Endocrine gland

A ductless gland that releases hormones directly into the bloodstream.

Exocrine gland

A gland that secretes products onto surfaces or into cavities via ducts. (smelly and sebaceous)

Neuroendocrine organ

An organ containing nervous tissue that produces hormones (e.g., hypothalamus).

Hypothalamus

The brain region that links nervous and endocrine systems and regulates pituitary function.

Boss (nickname for hypothalamus)

Informal term describing the hypothalamus because it controls many cellular processes via pituitary signaling.

Pituitary gland

The master endocrine gland; releasing hormones that regulate other glands, controlled by hypothalamic signals.

Anterior pituitary

The glandular part of the pituitary that synthesizes and releases tropic and other hormones.

Posterior pituitary

The neural part of the pituitary that stores and releases hormones made in the hypothalamus (ADH, oxytocin).

Adrenal cortex

Outer region of the adrenal gland; produces corticosteroids.

Adrenal medulla

Inner region of the adrenal gland; secretes catecholamines (epinephrine, norepinephrine).

Thyroid gland

Gland that produces thyroid hormones (T3/T4) regulating metabolic rate.

Parathyroid glands

Small glands posterior to the thyroid that secrete parathyroid hormone (PTH) regulating calcium.

Pineal gland

Small gland producing melatonin and regulating circadian rhythms.

Pancreas (islets)

Endocrine tissue producing insulin and glucagon to regulate blood glucose.

Hormone receptor

A protein that binds its specific hormone to elicit a cellular response.

Water-soluble hormone

Hydrophilic hormones that cannot cross the plasma membrane and act on surface receptors and second messengers. Coupled via g-proteins to second messengers

Lipid-soluble hormone

Hydrophobic hormones that diffuse through the plasma membrane and bind intracellular receptors to regulate gene expression.

Amino acid-based hormone

Hormones derived from amino acids; typically water-soluble (with exceptions like thyroid hormones).

Lipid-soluble hormones derived from cholesterol; diffuse into cells and regulate gene transcription.

Lipid-soluble hormones derived from cholesterol; diffuse into cells and regulate gene transcription.

Biogenic amines

Hormones derived from tyrosine or tryptophan; often catecholamines; typically water-soluble.

Prostaglandins (autocrine)

Autocrine lipid mediators derived from arachidonic acid that act on the secreting cell or nearby cells.

Histamine (paracrine example)

Paracrine mediator affecting nearby cells such as parietal cells to regulate acid secretion.

Intracellular receptor

Receptor located inside the cell that binds lipid-soluble hormones and modulates gene expression.

Plasma membrane receptor

Receptor on the cell surface that binds water-soluble hormones to activate second messenger pathways.

Second messenger

A small intracellular molecule that relays and amplifies signals from receptors.

Cyclic AMP (cAMP)

A second messenger produced by adenylyl cyclase that activates protein kinases.

G protein

A heterotrimeric GTP-binding protein that couples receptors to effector enzymes.

Gs protein

Stimulatory G protein that increases adenylyl cyclase activity and cAMP production.

Gi protein

Inhibitory G protein that decreases adenylyl cyclase activity and cAMP production.

Gq protein

G protein that activates phospholipase C, elevating DAG and IP3.

Adenylyl cyclase

Enzyme converting ATP to cyclic AMP in the cAMP signaling pathway.

Phospholipase C

Enzyme cleaving PIP2 into DAG and IP3 to trigger PKC activation and Ca2+ release.

Diacylglycerol (DAG)

Lipid second messenger that activates protein kinase C.

Inositol trisphosphate (IP3)

Second messenger that triggers Ca2+ release from the endoplasmic reticulum.

Protein kinase C (PKC)

Kinases activated by DAG that phosphorylate target proteins to propagate signals.

Calcium (Ca2+) as second messenger

Calcium ions act as intracellular second messengers affecting various cellular processes.

Tyrosine kinase receptor

Receptor with intrinsic kinase activity that autophosphorylates and activates signaling (e.g., insulin receptor).

Insulin receptor

Is a tyrosine kinase enzyme that binds insulin and initiates signaling for glucose uptake.

Insulin

Pancreatic hormone that lowers blood glucose by promoting cellular uptake and storage of glucose.

Diabetes mellitus

Chronic disease with high blood glucose due to insulin deficiency or insulin resistance.

Hyposecretion

Reduced or insufficient secretion of a hormone.

Hyperactivity

Excessive or heightened hormone production or action.

Atrial natriuretic peptide (ANP)

Cardiac hormone that reduces blood volume and pressure by promoting salt and water excretion.

Erythropoietin (EPO)

Kidney-produced hormone that stimulates red blood cell production.

Leptin

Adipose-derived hormone that regulates appetite and energy balance.

Why should you understand the endocrine system?

enables you to monitor & advise patients with diseases such as diabetes mellitus.

the nervous system

Endocrine system acts with "____________” to regulate major processes

growth & development, reproduction, maintenance of electrolyte, water & nutrient balance of blood, regulation of cellular metabolism, mobilization of body defenses

Examples of metabolic activities via hormones (controls and integrates)

Target cells

Include most body cells and have receptors for a specific hormone

produce a response

Cells that do not have a receptor or hormone, is not a target cell will NOT _____

Nervous System

System that has a direct connection, effect is local and specific

Endocrine System

System has a long duration of responses, the effect is general and widespread

Gland

A specialized cell, groups of cells, or an organ of “epithelial origin” that secretes a product = a secretion

yes

can a gland be an organ?

no (hypothamalus - made up of nervous tissue)

are all organs gland?

saliva, sweat

“Extracellular effects” (nonhormonal)

Pancreas, gonads (ovaries & testes) & placenta

Organs that contain “endocrine tissue”

stomach, heart, kidneys, small intestine

Other tissues and organs that produce hormones are adipose cells, thymus and cells in the “walls” of the ______

possible 3rd class. not classified as hormones because they ahve short distance signals

Autocrine examples 

Prostaglandins and smooth muscle 

Gonadal & adrenocortical hormones

Steroids (lipid-soluble hormones) synthesized from cholesterol and the main places where you find them is the

.

Summary of Hormones by Chemical class 

Calcitriol (active form of vitamin D)

Name lipid soluble hormone (Secreted in Kidney)

Testosterone

Name lipid soluble hormone (Secreted in Testes)

Estrogens, Progesterone

Name lipid soluble hormone ( Secreted in ovaries)

Aldosterone, cortisol, androgens

Name lipid soluble hormones (Secreted in adrenal cortex)

T3 (triiodothyronine), T4 (thyroxine)

Name lipid soluble hormones (secreted in thyroid gland) (follicular cells) 

target cell type

Hormone action increases or decreases “normal cellular processes” of the target cell. response depends on ____

Lipid-soluble hormones (lipophilic)

Act on intracellular receptors that directly activate genes - induce protein synthesis (can enter cells)

whether the hormonal molecule is hydrophobic or hydrophilic

A major determinant of a hormones mechanism of action is 

DAG (Diacylgycerol) & IP3 (Inositol triphosphate)

PIP2 involves G-protein (Gq) and Phospholipase C (PLC) PLC is a membrane-bound effector enzyme that splits PIP2 (phosphatidyl inositol biphosphate) into two messengers: ______ and _____

Insulin receptor

is a tyrosine kinase enzyme (receptor-enzyme) (ex: growth factors, insulin)

Chemical signaling

A chemical messenger (hormone, neurotransmitter, or drug) that binds to a receptor to initiate a cellular response.

Receptor

A binding site—often a protein—that recognizes and binds a specific ligand to trigger signal transduction.

Ligand-receptor complex

The bound form of ligand and receptor that activates downstream cellular responses.

Second messenger

Intracellular chemical that relays signals from membrane receptors to intracellular targets (e.g., cAMP, DAG, IP3, Ca2+).

cAMP

Cyclic adenosine monophosphate; a common second messenger produced by many receptor pathways.

DAG

Diacylglycerol; second messenger produced from PIP2 that activates protein kinase C.

IP3

Inositol triphosphate; second messenger that triggers Ca2+ release from intracellular stores.

Ca2+

Calcium ion; versatile second messenger in many signaling pathways.

PIP2

Phosphatidylinositol 4,5-bisphosphate; plasma membrane lipid cleaved to yield DAG and IP3.

Lipid-soluble hormone

Hormone that can diffuse through the plasma membrane and binds intracellular receptors.

Intracellular receptor

Receptor located inside the cell; binds lipid-soluble hormones to regulate gene activity.

Receptor enzyme

An enzyme-linked receptor; hormone binding activates the receptor’s enzymatic activity (e.g., tyrosine kinase).

Tyrosine kinase pathway

Signaling cascade activated by receptor tyrosine kinases that phosphorylate substrates to propagate the signal.

Phosphorylation

Addition of a phosphate group to a protein, often activating signaling proteins.

G protein-coupled receptor (GPCR)

Membrane receptor that activates G proteins to modulate second messenger systems.

Promoter region

DNA region upstream of a gene where transcription factors bind to regulate transcription.

Hormone response element (HRE)

DNA sequence in a gene promoter recognized by hormone-receptor complexes to control transcription.

Transcription

Process of synthesizing messenger RNA from DNA.

Translation

Process of protein synthesis from mRNA at ribosomes.

Upregulation

Increase in receptor density on a cell in response to low hormone levels, increasing sensitivity.

Downregulation

Decrease in receptor density in response to high hormone levels, reducing sensitivity.

Affinity

Strength of binding between receptor and its ligand; high affinity means greater receptor occupancy.