PHSC1122 Physio II - Chapter 18 The Endocrine System (Intro-18.2)

Endocrine system

made up of endocrine cells and tissues that produce about 30 different hormones (chemical messengers); controls and coordinates body processes

Target cells

have receptors needed to bind and "read" hormonal messages

Hormones

change types, quantities, or activities of enzymes and structural proteins in target cells; can alter metabolic activities of multiple tissues and organs at the same time; and affect long-term processes like growth and development

All endocrine cells and tissues that produce hormones

What does the endocrine system include?

Paracrines

another name for hormones

Amino acid derivatives, peptide hormones, and lipid derivatives

3 classes of hormones

Amino acid derivatives (biogenic amines)

a class of hormones made up of small molecules structurally related to amino acids

Thyroid hormones and catecholamines

hormone derivatives of tyrosine

Tyrosine

Which amino acid do thyroid hormones and catecholamines derive from?

Serotonin and melatonin

hormone derivatives of tryptophan

Tryptophan

Which amino acid do serotonin and melatonin derive from?

Peptide hormones

hormones made up of chains of amino acids; most secreted as prohormones

Prohormones

inactive molecules converted to active hormones before or after they are secreted, common with peptide hormones

Glycoproteins

proteins more than 200 amino acids long that have carbohydrate side chains (ex. TSH, LH, FSH)

TSH, LH, FSH

glycoprotein examples

ADH and OXT

short-chain polypeptide examples; each 9 amino acids long

Insulin, Growth hormone, and Prolactin

small protein examples

Lipid derivatives

class of hormones that includes eicosanoids and steroid hormones

Eicosanoids

hormone derived from arachidonic acid, a 20-carbon fatty acid; paracrines that coordinate cellular activities and affect enzymatic processes (such as blood clotting)

Prostaglandins

coordinate local cellular activities and converted to thromboxanes and prostacyclins in some tissues

Steroid hormones

hormones derived from cholesterol; bound to specific transport proteins in the plasma and remain in circulation longer than peptide hormones

Androgens from testes in males, estrogens and progesterone from ovaries in females, corticosteroids from adrenal cortex, and calcitriol from kidneys

4 steroid hormone examples and locations

Freely or travel bound to special carrier proteins

How can hormones circulate in the body?

Free hormones

remain functional for less than an hour and are inactivated when they diffuse out of bloodstream and bind to receptors on target cells, are absorbed and broken down by liver or kidneys, or are broken down by enzymes in blood or interstitial fluids

Thyroid and steroid hormones

remain functional much longer; more than 99 percent become attached to special transport proteins in blood; equilibrium state exists between free and bound forms and bloodstream contains a substantial reserve of bound hormones

Long time

Are thyroid and steroid hormones functional for a long or short time?

Bound to carrier proteins

Do thyroid and steroid hormones travel freely or bound to carrier proteins?

Alter genetic activity, alter rate of protein synthesis, or change membrane permeability

3 mechanisms of hormone action

Hormone receptor

a protein molecule to which a particular molecule binds strongly; different tissues have different combinations

Presence or absence of a specific receptor

determines hormonal sensitivity of a cell

Down-regulation

presence of a hormone triggers a decrease in the number of hormone receptors; when levels of a particular hormone are high, cells become less sensitive to it

Presence

Would presence or absence of a hormone trigger downregulation?

Up-regulation

absence of a hormone triggers an increase in the number of hormone receptors; when levels of a particular hormone are low, cells become more sensitive to it

Absence

Would presence or absence of a hormone trigger upregulation?

Catecholamines and peptide hormones

non-lipid soluble hormones that are unable to penetrate plasma membrane and bind to receptor proteins on outer surface of plasma membrane (extracellular receptors)

Not lipid soluble

Are catecholamines and peptide hormones lipid soluble or not?

Steroid and thyroid hormones

lipid soluble hormones that can diffuse across plasma membrane and bind to receptors inside cell (intracellular receptors)

Lipid soluble

Are steroid and thyroid hormones lipid soluble or not?

First messenger

hormone that binds to extracellular receptor and promotes release of second messenger in cell

Second messenger

intermediary molecule that appears due to hormone-receptor interaction; may act as enzyme activator, inhibitor, or cofactor and results in change in rates of metabolic reactions

cAMP, cGMP, Ca2+

second messenger examples

Amplification

a process where a small number of hormone molecules bind to extracellular receptors, thousands of second messengers may appear, and magnify the effect of the hormone on the target cell

Nucleus and mitochondria

Where can thyroid hormones bind receptors in a cell?

Negative feedback

main way hormone secretion is controlled; stimulus triggers production of hormone that reduces intensity of the stimulus

Humoral stimuli (change in extracellular fluid), hormonal stimuli (arrival or removal of hormone), or neural stimuli (neurotransmitters)

3 things that can trigger hormone secretion