Endocrine 1

Features of organs in the Endocrine system

ductless glands, secrete messenger molecules called hormones

Endocrinology

study of hormones and endocrine glands

Pure endocrine organs

pituitary, pineal gland, thyroid gland, parathyroid gland, adrenal gland (adrenal cortex and adrenal medulla)

Organs with a large proportion of endocrine cells

pancreas, thymus, gonads, hypothalamus (neuroendocrine organ)

organs containing some endocrine cells

heart, digestive tract, kidney, skin

Chemical messengers of endocrine system

hormones, autocrines, paracrines

hormones

long distance chemical signals, travel in blood or lymph

autocrines

chemicals that exert effects on same cells that secrete them

paracrines

locally acting chemicals, affects cells other than those that secrete them

classes of hormones

amino acid-based hormones, steroids

basic hormone action

circulate through the body in blood cells, only influence target cells with specific receptors, can have different effects on different target cells

water-soluble hormones

all amino acid based hormones (not thyroid hormone), attach to receptors on plasma membrane, uses intracellular second messengers

lipid-soluble hormones

steroid and thyroid hormones, directly activates genes, uses intracellular receptors

Target cells

tissues with receptors for a specific hormone

effects of hormone action on target cells

alter plasma membrane permeability and/or membrane potential by opening or closing ion channels, stimulate synthesis of enzymes or other proteins, activate or deactivate enzymes, induce secretory activity, stimulate mitosis

main second-messenger systems

Cyclic AMP, PIP2-calcium

cAMP signaling mechanism

hormone binds to receptor, receptor activates G protein, G protein activates/inhibits adenylate cyclase, adenylate cyclase converts ATP to cAMP, cAMP activates protein kinases to phosphorylate other proteins, phosphorylated proteins either activated or inactivated, cAMP degraded by phosphodiesterase (PDE), stops cascade

PIP2-calcium signaling mechanism

G protein activates phospholipase C, activated phospholipase C splits PIP2 into 2 second messengers, Diacylglycerol (DAG) activates protein kinases, Inositol triphosphate (IP3) causes calcium release from intracellular storage sites, calcium then acts another second messenger

Direct gene activation

lipid-soluble steroid hormones and thyroid hormones diffuse into target cells and bind to intracellular receptors, receptor-hormone complex enters nucleus and binds to specific region of DNA, initiates DNA transcription to make mRNA, mRNA is translated into specific protein

Feedback system of hormones

negative feedback system, as hormone effects increase further release of hormone is inhibited

endocrine gland stimuli

humoral, neural, hormonal

humoral stimuli

simplest of endocrine control mechanisms, secretion in response to changing ion or nutrient levels in blood, responds to decline by secretion to reverse decline

humoral stimuli example

parathyroid monitors calcium

neural stimuli

sympathetic nerve fibers stimulate adrenal medulla cells, induces release of epinephrine and norepinephrine

hormonal stimuli

stimuli received from other glands, certain hormones signal secretion of other hormones

hormonal stimuli example

hypothalamus secrets hormones, stimulates pituitary, stimulates other glands

nervous system modulation

nervous system can override normal endocrine controls when needed

nervous system modulation example

“fight or flight”, nervous system overrides insulin to allow blood glucose levels to increase

factors that target cell activation depends on

blood levels of hormone, relative number of receptors on/in target cell, affinity (strength) of binding between receptor and hormone

Up-regulation

target cells form more receptors in response to low hormone levels

down-regulation

target cells lose receptors on response to high hormone levels

bound hormones

steroids and thyroid hormones are attached to plasma proteins

free hormones

circulate without carries, everything except steroids and thyroid hormones

half-life

time required for level of hormone in blood to decrease by half

concentration of circulating hormone reflects

rate of release, speed of inactivation and removal from body

ways hormones can be removed from body

degrading enzymes, kidneys, liver

characteristics of lipid-soluble hormones

all steroid and thyroid hormones, source from adrenal cortex/gonads/thyroid gland, not stored in secretory vesicles. bound to plasma proteins, long half-life, receptors inside cell, direct activation of genes for synthesis of new proteins

water-soluble hormone characteristics

all amino acid-based hormones (except thyroid hormone), sourced in all endocrine glands aside from adrenal cortex/gonads/thyroid gland, stored in secretory vesicles, free in plasma, short half-life, receptors on plasma membrane, acts through second messenger systems

permissiveness

one hormone cannot act without another hormone present

synergism

more than one hormone produces same effects on target cell, causes amplification

antagonism

one or more hormone opposes action of another hormone

permissiveness example

reproductive hormones need thyroid hormones to have effect

synergism example

glucagon and epinephrine both cause liver to release glucose

antagonism example

insulin and glucogon

hypothalamus located

connected to the pituitary gland (hypophysis) by a stalk called the infundibulum

posterior pituitary gland makeup

neural tissue that secretes neurohormones, posterior pituitary and infundibulum makes up neurohypophysis

anterior pituitary gland makeup

glandular tissue, also called the adenohypophysis

hypothalamic-hypophyseal tract

runs through infundibulum, maintains neural connection between posterior pituitary and hypothalamus, arises from neurons in paraventricular and supraoptic nuclei in hypothalamus

neurohormones secreted by posterior pituitary gland

oxytocin, ADH

how does anterior pituitary lobe secrete hormones

hypothalamus secretes releasing and inhibiting hormones to anterior pituitary gland to regulate hormone secretion

hormones released by anterior pituitary gland

growth hormone, thyroid-stimulating hormone, adrenocorticotropic hormone, follicle-stimulating hormone, luteinizing hormone, prolactin

hypophysis makeup

adenohypophysis (anterior pituitary) and neurohypophysis (posterior pituitary)

anterior pituitary gland secretion system

hormones released from the hypothalamus into special blood vessels control release of anterior pituitary hormones

posterior pituitary gland secretion system

action potential travels down axons of hypothalamic neurons, causes hormone release from axon terminals in posterior pituitary

neurons of posterior pituitary gland

paraventricular (PV), supraoptic (SO)

paraventricular neurons

produce oxytocin

supraoptic neurons

produce antidiuretic hormone (ADH)

oxytocin

stimulant of uterine contractions, positive feedback mechanism, uses PIP2-calcium second messenger system

antidiuretic hormone (ADH)

high concentrations of solute triggers ADH secretion, targets kidney tubules to absorb more water to inhibit urine formation, alcohol and drugs inhibit ADH (causes high urine output), high concentrations cause vasoconstriction

anterior pituitary tropic hormones

thyroid-stimulating hormone, adrenocorticotropic hormone, follicle-stimulating hormone, luteinizing hormone

anterior pituitary non tropic hormones

growth hormone, prolactin

hypothalamus hormones released to anterior pituitary gland

corticotropin-releasing hormone, thyrotropin-releasing hormone, growth hormone-releasing hormone, gonadotropic-releasing hormone, somatostatin, prolactin inhibiting hormone (dopamine)

corticotropin-releasing hormone releases

adrenocorticotropic hormone (ACTH)

thyrotropin-releasing hormone releases

thyroid-stimulating hormone (TSH)

growth hormone-releasing hormone releases

growth hormone (GH)

gonadotropic-releasing hormone releases

luteinizing hormone (LH), follicle-stimulating hormone (FSH)

somatostatin releases

thyroid stimulating hormone (TSH), growth hormone (GH)

prolactin inhibiting hormone (dopamine) releases

prolactin (PRL)