a&p II endocrine system key notes/terms

endocrine system

a system composed of ductless endocrine glands that synthesize and secrete hormones

ligands

chemical messengers (signals)

nervous system vs endocrine system

endocrine system:

• targets any cells w correct receptors

• relatively slow process (secs, minutes, hours)

• widespread effects (typically)

• long-lasting responses (days - weeks, can continue even after stimulus is removed)

major endocrine glands

pituitary, pineal, thyroid, parathyroid, adrenal

additional endocrine organs

hypothalamus, skin, thymus, heart, liver, stomach, pancreas, small intestine, adipose connective tissue, kidneys, and gonads

hormonal stimulation

a gland cell releases its hormones when some other hormone binds to it

humoral stimulation

a gland cell releases its hormone when there is a certain change in levels of a nutrient or ion in the blood

nervous system stimulation

a gland cell releases its hormone when a neuron stimulates it

steroids (circulating-hormones)

aka lipid-soluble molecules synthesized from cholesterol

includes:

• gonadal steroids (estrogen)

• steroids synthesized by the adrenal complex (cortisol)

• calcitriol (more accurately called sterol)

biogenic amines (monoamines)

modified amino acids

water-soluble (except for thyroid hormone (TH))

includes:

• catecholaminos, thyroid hormone, melatonin

proteins (aka peptides)

most hormones fit in this category

water-soluble chains of amino acids

lipid soluble transport

• typically small, non polar, and lipophilic

• can diffuse across lipid cell membrane (receptors are in nucleus or cytosol)

• need a carrier protein (binding is temporary)

  • carriers are water-soluble proteins made by the liver

• do not readily dissolve in blood

• majority of the hormone is unbound (90% or more) but only the unbound protein can exit blood and bind to target cell receptors

water soluble proteins

• bind to surface cell receptors

• polar (can’t diffuse across the cell membrane)

• travel freely across the blood (do not require a carrier protein)

• however, some use carrier proteins to extend their half-life

hormone release

positively correlated

• an increase in release results in higher blood concentrations (and vice versa)

hormone elimination

can occur in multiple ways

• enzymatic degradation in liver cells

• removal from blood via kidney excretion or target cell uptake

  • the faster the elimination rate, the lower the blood concentration (and vice versa)

biological half-life

time necessary to reduce hormone concentration to half of its original level

signal transduction pathway

ex. activation of the g-protein

actions of water-soluble hormones

• activation/inhibition of enzymatic pathways

• growth through cellular division

• release of cellular secretions

• changes in membrane permeability

• muscle contraction/relaxation

degrees of cellular responses

1) its number of receptors for the hormone

2) its simultaneous response with other hormones

up-regulation

increase in # of receptors

• increase sensitivity to hormone

  • sometimes occurs when blood levels of a hormone are low

  • sometimes occurs with changes in development, cell cycle, or cell activity

down-regulation

decreased number of receptors

• decreased sensitivity to hormone

  • sometimes occurs when blood levels of a hormone are high

  • sometimes occurs with changes in development, cell cycle, or cell activity

synergistic interactions

one hormone reinforces activity of another hormone

• ex. estrogen and progesterone effects on a target cell

permissive interactions

one hormone requires the activity of another hormone

• ex. oxytocin’s milk ejection effect requires prolactin’s milk generating effect

antagonistic interactions

one hormone opposes activity of another hormone

• ex. glucagon increases blood glucose when insulin lowers it

primary plexus

porous capillary network associated with the hypothalamus

secondary plexus

capillary network associated with the anterior pituitary

hypophyseal portal veins

drain primary plexus to the secondary plexus

posterior pituitary

a storage and release site for antidiuretic hormone (ADH) and oxytocin (OT) hormones made in the hypothalamus

antidieretic hormone (vasopressin)

made in supraoptic nucleus

functions:

• decrease urine production, stimulates thirst, constrict blood vessels

oxytocin

made in paraventricular nucleus

functions:

• uterine contractions, milk ejection, emotional bonding

hypothalamus releases….

regulatory hormones

anterior pituitary releases…

hormones into general circulation

common releasing hormones (increases secretion of anterior pituitary)

• thyrotropin- releasing hormones

• prolactin- releasing hormones

• gonadotropin- releasing hormone

• corticotropin- releasing hormone

• growth hormone- releasing hormone

common inhibiting hormones (decreases secretion of anterior pituitary)

• prolactin- inhibiting hormone

• growth- inhibiting hormone

hormones of the anterior pituitary

• thyroid- stimulating hormone (TSH); thyrotropin

• prolactin (PRL)

• adrenocorticotropin hormone (ACTH; corticotropin)

• gonadotropins: follicle- stimulating (FSH) and luteinizing hormone (LH)

• growth hormone (GH): somatotropin

tropic hormones

hormones released from the anterior pituitary are… (except prolactin)

thyroid stimulating hormone (TSH)

release triggered by TRH from hypothalamus

causes: release of thyroid hormone (TH) from thyroid gland

prolactin (PRL)

release triggered by PRH, inhibited by PIH from hypothalamus

causes: milk production, mammary gland growth

adrenocorticotropic hormone (ACTH); corticotropin

release triggered by CRH from hypothalamus

causes: release of corticosteroids by adrenal cortex

gonadotropins: follicle-stimulating hormones (FSH) and luteinizing hormones (LH)

release triggered by GnRH from hypothalamus

causes:

• in females: regulate ovarian development and secretion of estrogen and progesterone

• in male: sperm development and secretion of testosterone

growth hormone (GH; somatotropin)

causes liver to secrete insulin- like growth factors 1 & 2 (IGF-1 and IGF- 2)

• GH and IGFs function synergistically to stimulate cell growth and division

half life

IGFs have similar functions to GH but a longer ______

gluconeogensis

conversion of nutrients to glucose (stimulated)

glycogenesis

synthesis of glycogen (inhibited)

lipolysis

breakdown of triglycerides (stimulated)

lipogenesis

formation of triglycerides (inhibited)

anterior pituitary is….

MASTER GLAND!

• directs the functions of numerous other glands (thyroid, adrenals, etc)

follicular cells

cuboidal epithelial cells that surround a central lumen, synthesize thyroglobulin (TGB)

• produce and release thyroid hormones (T3 and T4)

parafollicular cells

cells between follicles, make calcitonin

• hormone that decreases blood calcium

calorigenic

generates heat/raises temp

glucose-sparing effect

body shifts away from using glucose as a main form of energy

hyperthyroidism

results from excessive prod. of T3 or T4

• caused by T4 ingestion, excessive stimulation, excessive stim. by the pituitary gland, or loss of feedback control in the thyroid (Graves disease)

results in: increased metabolic rate, weight loss, hyperactivity, heat intolerance

can be treated by removing the thyroid

hypothyroidism

results from decreased prod. of TH

• caused by decreased iodine intake, loss of pituitary stim. of thyroid, postsurgical, or immune system destruction

results in: low metabolic rate, weight gain, lethargy, cold intolerance

treated with thyroid hormone replacement

calcitonin

• synthesized and released from parafollicular cells of thyroid gland

• acts to decrease blood calcium levels

adrenal glands

soft, sit just on top of the kidneys

embedded in fat and fascia

adrenal medulla

forms inner core of each adrenal gland

red-brown color due to extensive blood vessels

release epinephrine and norepinephrine with sympathetic stim.

adrenal cortex

synthesizes more than 25 corticosteroids

yellow due to lipids within cells

three regions producing different steroid hormones:

• zona glomerulosa

• zona fasciculata

• inner zona reticularis

catecholamines (made in adrenal medulla)

• epinephrine (EPI) (80%)

• norepinephrine (NEPI) (20%)

• dopamine (pre-req for NEPI and EPI)

acetylecholine

true neurotransmitter

• spark from the nerve, making chromaffin cells release in the rich blood vessels (pouring out EPI and NEPI)

• EPI and NEPI are already produced and readily stored, they just need a signal to be released

mineralocotricoids

regulate electrolyte levels

• made in zona glomerulosa: thin, outer cortical layer

• aldosterone fosters Na+ retention and K+ secretion

glucocorticoids

hormones that regulate blood sugar

• made in zona fasciculata: larger, middle cortical layer

• cortisol increases blood sugar

gonadocorticoids

sex hormones

• made in zona reticularis: thin, inner cortical layer

• adrenal androgens are sex hormones made by adrenals

  • amt produced by adrenals is less than amt from testes

cortisol regulation

1) stimuli regulating release of CRH

• negative feedback by an increase in cortisol

• time of day: CRH, ACTH, cortisol increases at night and peaks in morning

• stress: CRH, ACTH, cortisol released with increased stress (cortisol nicknamed the stress hormone)

effects of cortisol

• cortisol targets cells to increase blood nutrient levels

• liver cells increase glycogenesis and gluconeogenesis (decrease glycogenesis)

• adipose cells increase lipolysis and decrease lipogenesis

• many body cells break down proteins (protein catabolism); liver cells use the amino acids for gluconeogenesis

• most cells decrease their glucose uptake, sparing it for the brain

hypothalamus initiates neuroendocrine respones

three stages:

1) alarm reaction

• initial response involving sympathetic nervous system activation, epinephrine/norepinephrine

2) stage of resistance

• after depletion of glycogen stores, adrenal secretes cortisol to raise blood sugar and help meet energy demands

3) stage of exhaustion

• after weeks or months, depletion of fat stores results in protein breakdown for energy, leading to weakening of the body and illness

pancreas

located posterior to stomach, between duodenum and spleen

insulin is a main hormone- short amino acid peptide (compared to others)

• has endocrine AND exocrine (able to transfer hormones to nearby organs in a medium that is NOT blood) functions

acinar cells

generate exocrine secretions for digestion

• make up vast majority of pancreas as saclike acini

pancreatic islets

contain clusters of endocrine cells

• alpha cells secrete glucagon

• beta cells secrete insulin

• delta cells- somatostation and F cells- pancreatic peptide (not discussed)

pancreatic hormones

help maintain healthy blood glucose

• 70-110 mg of glucose/deciliter

high levels damage blood vessels and kidneys

low levels cause lethargy, mental/physical impairment, or death

steps to regulate insulin release

• after food intake, beta cells detect a rise in glucose and respond by secreting insulin (humoral stim)

• insulin travels through blood to encounter target cells

• net effect is blood glucose/other nutrients decrease

• regulated by neg. feedback: when blood glucose falls, beta cells stop releasing insulin

ex. oral glucose tolerance tests

effects of insulin

• decreases levels of all nutrients (glucose, fatty acids, amino acids)

• hepatocytes remove glucose from blood and store it as glycogen

• adipose cells decrease fatty acid levels in blood; store fat

hepatocytes

entry point of sugar into cell for storage

diabetes mellitus

inadequate uptake of glucose in blood

chronically elevated glucose, blood vessels damaged

leading cause of retinal blindness, kidney failure, and non-traumatic amputations in the US

associated w heart disease and stroke

type- 1 diabetes (born w this)

absent or diminished release of insulin by pancreas; cause may have autoimmune component

tends to occur in children/younger ind.

requires daily injections of insulin

type-2 diabetes (lifestyle disease)

caused from decreased insulin release or insulin effectiveness

obesity major cause in development

tends to occur in older ind., but can occur in young adults

treatment w diet, exercise, and medications

gestational diabetes

seen in pregnant women

if untreated, causes risk to fetus and increases delivery complications

increases chance of later developing type 2 diabetes

(can go away on its own)

hypoglycemia

glucose levels below 60 mg/DL

numerous causes:

• insulin overdose (hypothetical bodybuilder), prolonged exercise, alcohol use, liver or kidney dysfunction

• deficiency of glucocorticoids or GH or genetics

symptoms: hunger, dizziness, confusion, sweating, and sleepiness

glucagon can be given to unconscious ind if unable to eat (more severe)

steps in regulation of glucagon release

1) alpha cells detect drop in blood glucose and release glucagon

2) glucagon causes target cells to release stored nutrients into blood

3) glucagon release regulated by negative feedback: as nutrient rises, glucagon release decreases

effects of glucagon

effector cells release stored nutrients into the blood

• hepatocytes release glucose

• adipose cells release fatty acids and glycerol

glucagon does not affect protein comp (like cortisol does)

pineal gland

small, unpaired body in the epithalamus of diencephalon

• secretes melatonin at night

  • causes drowsiness

  • regulates circadian rhythm and mod

• melatonin influences GnRH secretion

parathyroid glands

on posterior of thyroid gland in neck

• usually between 2 or 6 of them (typically 4)

contains chief cells and oxyphil cells

• chief (principal) cells make parathyroid hormone (PTH)

• function of oxyphil cells are unknown

parathyroid hormone (PTH)

increases blood calcium

• if this is chronically high then there may be issues w bone density long- term (getting calcium from the breakdown of bone)

thymus epithelial cells

secrete thymic hormones

• located anterior to top of heart

• grows during childhood but then begins to shrink

• maturation site for T-lymphocyte while blood cells

endrocrine tissue in heart

secretes atrial natriuretic peptide (ANP)

• ANP is the final defense for lowering bp

• kidneys increase urine output and blood vessels dilate

kidney endocrine cells

release erythropoietin (EPO)

• secretion occurs in response to low blood oxygen

• EPO causes increased red blood cell prod (humoral stim)

liver secretions

include insulin-like growth factors and inactive hormone angiotensinogen (reg. of bp coming from the liver)

• angiotensinogen is converted to active angiotensinogen II by enzymes from the kidney and lung blood vessels

• angiotensinogen II raises bp

  • causes vessel constriction, decreases urine output, stimulates thirst

stomach

secretes gastrin

• gastrin increases secretion and motility in stomach for digestion