Chapter 16 - The Endocrine System

what is the endocrine system

coordinates activity of body cells using hormones transported in blood

-response is slower but longer lasting than nervous system

endocrine system controls and integrates:

-reproduction

-growth, development

-electrolyte water and nutrient balance in the blood

-cellular metabolism, energy balance

-mobilization of body defenses

what are the endocrine glands

pituitary, thyroid, parathyroid, adrenal, and pineal glands

hypothalamus is _________ organ

neuroendocrine

amino acid based hormones

amino acid derivatives, peptides, and proteins

steroid hormones

synthesized from cholesterol, gonadal and adrenocortical hormones

effects of hormone on target cells:

-alter plasma permeability / mem potential

-stimulate synthesis of enzymes

-activate or deactive enzymes

-induce sectretory activity

-stimulate mitosis

water-soluble hormones

all amino acid-based hormones except thyroid hormone

-binds to receptors on plasma membrane

-act via G protein second messengers

-cannot enter cell

lipid-soluble hormones

steroid and thyroid hormones

-act on intracellular receptors that directly activate genes

-can enter cell

cAMP signaling mechanism (water-soluble hormones)

1. hormone (1st messenger) binds to receptor

2. receptor activates a G protein

3. G protein activates or inhibits effector enzyme adenylate cyclase

4. adenylate cyclase then converts ATP to cAMP (2nd messenger)

5. cAMP activates protein kinases that phosphorylate other proteins

PIP2-calcium signaling mechanism

1. hormone-activated G protein activates a different effector enzyme: phospholipase C

2. activated phospholipase C splits membrane protein, PIP2, into two second messengers:

-diacylglycerol (DAG) activates protein kinases

-inositol trisphosphate (IP3) causes Ca2+ release from intracellular storage sites

3. calcium ions act as another second messenger

-Ca2+ alters enzyme activity and channels, or binds to regulatory protein calmodulin

-calcium-bound calmodulin activates enzymes that amplify cellular response

how do lipid soluble hormones work?

diffuse into target cells and bind with intracellular recpeptors

-helps initiate DNA transcription to produce mRNA

-mRNA -> proteins

humoral stimuli

hormone release caused by altered levels of certain critical ions or nutrients

-eg. low Ca2+ in blood, parathyroid gland secrete PTH to increase Ca2+

**environment says...

neural stimuli

nerve fibers stimulate hormone release

-eg. sympathetic fibers stimulate adrenal medulla to secrete NE

**neurons says...

hormonal stimuli

hormones stimulate other endocrine gland to release their hormones

-eg. hormones from hypothalams allows ant. pituitary to secrete hormones that stimulate other endocrine glands

**hormone says...

target cell activation depends on 3 factors:

1. blood levels of the hormone

2. relative number of receptors on or in the target cell

3. 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 in response to high hormone levels

what hormones circulate in blood freely? which don't?

-steroid hormones and thyroid hormone are attached to plasma proteins

-all other hormones circulate without carriers

hormones can be removed from blood by

-degrading enzymes

-kidneys

-liver

concentration of circulating hormones reflects

1. rate of release

2. speed at which it is inactivated and removed from body

half life

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

hormones have different response times

-some responses are immediate

-some, especially steroid, can take hours to days

-some are inactive until they enter target cells

permissiveness

one hormone cannot exert its effects without another hormone being present

-eg. reproductive hormones need thyroid hormone to have effect

synergism

more than one hormone produces the same effects on a target cell (amplification)

-eg. glucagon and epinephrine both cause liver to release glucose

antagonism

one or more hormones opposes the action of another hormone (opposite effects)

-eg. insulin and glucagon

hypothalamus is connected to pituitary gland via stalk called

infundibulum

pituitary secretes at least ## major hormones

eight

2 lobes of the hypothalamus

-posterior pituitary: secretes neurohormones, makes up the neurohypophysis

-anterior pituitary: (adenohypophysis) consists of glandular tissue

posterior pituitary secretes which neurohormones

oxytocin and ADH (stored in axon terminals and released into blood when neurons fire)

oxytocin

-strong stimulant of uterine contractions for childbirth

-also acts as hormonal trigger for milk ejection

-both positive feedback mechanisms

-acts as neurotrans. in brain (PIP2-calcuim mechanism)

antidiuretic hormone (ADH)

-hypothalamus contains osmoreceptors that monitor solute concentration

-high concentration = posterior pit. release ADH

-tells kidneys to reaborb more water to inhibit or prevent urine formation (prevent water loss by reabsorbing)

anterior pit. and hypothalamic relationships: what does the hypothalamus do?

secretes releasing and inhibiting hormones to anterior pit. to regulate hormone secretion

hypothalamis neurons synthesize releasing and inhibiting hormones. what are they?

GHRH, GHIH, TRH, CRH, GnRH, PIH

hyopophyseal portal system contists of

-primary capillary plexus

-hypophyseal portal veins

-secondary capillary plexus

are the anterior pituitary hormones peptide or steroid?

peptide (amino-acid based / water soluble)

what are the 8 anterior pituitary hormones? which uses cAMP 2nd messenger? which are tropic?

-growth hormone (GH) (does not use cAMP 2nd msg)

-thyroid-stimulating hormone (TSH) (tropic)

-adrenocorticotropic hormone (ACTH) (tropic)

-follicle-stimulating hormone (FSH) (tropic)

-luteinizing hormone (LH) (tropic)

-prolactin (PRL)

hypersecretion of GH

gigantism in children (heights of 8 feet)

acromegaly in adults (overgrowth of hands, feet, face)

hyposecretion of GH

pituitary dwarfism in children (height of only 4 feet)

usually no problems in adults

what does TSH do and how is it released

stimulates normal development and secretory activity of thyroid

-hypothalamus releases thyrotropin-releasing hormone (TRH) which tells anterior pit. to release TSH

what does ACTH do

stimulates adrenal cortex to release cortisol / corticosteroids

what regulates ACTH release

hypothalamic corticotropin-releasing hormone CRH (highest levels in morning)

-fever, hypoglycemia and stressors can alter release of CRH

what are the 2 gonadotropins

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

how is gonadotropin release regulated

-by the gonadotropin-releasing hormone (GnRH) during and after puberty

-suppressed by gonadal hormones (feedback)

what does FSH do

stimultes production of gametes (egg or sperm)

what does LH do (males vs females)

promotes production of gonadal hormones

-female: helps mature follicles of egg, triggers ovulation, releases estrogen and progesterone

-male: stimulates production of testosterone

when are LH and FSH present

absent in blood of girls and boys until puberty

what is PRL and how it is released

stimulates milk production in females

-increased estrogen stimulate PRL (cause breast swelling and tenderness during menstral cycle)

-suckling stimulates PRL release and promotes continued milk production

how is PRL regulated

regulation controlled by prolactin-inhibiting hormone (PIH), which is dopamine

-PIH prevents release of PRL until needed

what is the thyroid hormone (TH)

body's major metabolic hormone

-2 forms: T4 (thyroxine ; 2 iodine) and T3 (triiodothyronine ; 3 iodine)

-affects every cell in body

calorigenic effect of TH

increases basal metabolic rate and heat production

synthesis of thyroid hormone

1. hyroglobulin is synthesized and discharged into the follicle lumen

2. iodides (I-) is trapped (actively transported in)

3. iodide is oxidized to iodine

4. iodine attaches to tyrosine, forming DIT and MIT

5. iodinated tyrosines link together to form T3 and T4

6. thyroglobuli colloid is endocytosed and combined with a lysosome

7. lysosomal enzymes cleave T4 and T3 from thyroglobulin and hormones diffuse into bloodstream

T4 and T3 transported by

thyroxine-binding globulins (TBGs)

T4 vs T3: which is more active

T3 by 10 times

falling TH levels stimulate release of

thyroid stimulating hormone (TSH)

myxedema

hypothyroidism (hyposecretion of TH in adults)

-low metabolic rate, thick / dry skin, puffy eyes, chilly, constipation, edema, mental sluggishnes, legarthy

goiter

enlargement of the thyroid gland due to lack of iodine

-lack of iodine (hypo), triggers increased TSH secretion, triggering thyroid to synthesize more unuseable thyroglobulin

congenital hypothyroidism

usually caused by poor development of thyroid gland (bc TH is critical for normal skeletal growth and brain development)

-pituitary problems or maternal medication may sometimes affect baby's ability to make TH

-may be asymptomatic or present w weak cry, poor feeding, constipation, jaundice

Graves' disease

hyperthyroidism (hypersecretion of TH)

-antibodies mimic TSH and stimulates TH release

-elevated metabolic rate, sweating, rapid and irregular heartbeats, nervousness, weight loss

-exophthalmos may occur

exophthalmos

bulging eyes

what is calcitonin

produced by parafollicular cells of thyroid gland that lowers blood Ca2+ levels

-antagonistic to PTH

-stimulates Ca2+ uptake and incorporation into bone matrix

what is the parathyroid gland and what does it do

4-8 tiny yellow glands embedded in thyroid

-contain oxyphil, and parathyroid cells that secrete PTH

what does PTH do

increases blood Ca2+ levels

-target organs: skeleton, kidneys, intestine

what is the adrenal gland and where is it

paired, pyramid shaped organs on top of kidneys

-aka suprarenal glands

-2 glands in one

adrenal gland: what are the adrenal cortex and medulla

cortex: synthesize and secrete several different hormones

medulla: part of sympathetic nervous system

what does the adrenal cortex produce

corticosteroids

-not stored in cells

-rate of release depends on rate of synthesis

3 layers of cortical cells produce the different corticosteroids

-zona glomerulosa -> mineralocorticoids

-zona fasciculata -> glucocorticoids

-zona reticularis -> gonadocorticoids

what is aldosterone and what does it do

mineralocorticoid hormone of adrenal cortex

-stimulates Na+ reabsorption by kidneys (increased BP and volume)

-stimulates K+ elimination by kidneys

factors that regulate aldosterone secretion

1. renin-angiotensin-aldosterone mechanism

2. plasma concentration of K+

3. ACTH

what are glucocorticoids of adrenal cortex

keep blood glucose levels relatively constant, influence metabolism, and helps resist stressors

-main one is cortisol

-released in response to CRH/ACTH

-causes increase in blood glucose, fatty acids, amino acids

gluconeogenesis

formation of glucose from fats and proteins

Cushing's syndrome

hypersecretion of cortisol

-depresses cartilage / bone formation amd immune system

-inhibits inflammation

-disrupts neural, crdiovascular, and gastrointestinal function

-seen with "moon" face and "buffalo hump"

-due to tumor on pituitary, lungs, kidney, adrenal cortex

Addison's disease

hyposecretion of cortisol

-decrease in plasma glucose and Na+ levels

-involves deficits in glucocorticoids and mineralocorticoids

-weight loss, severe dehyration, hypotension

-seen with bronzing of skin (high ACTH = melain production)

what are gonadocorticoids of adrenal cortex

adrenal sex hormones

-weak androgens (male sex hormones) converted to testosterone, some estrogens

what do gonadotropins do

-onset of puberty and appearance of secondary sex characteristics

-sex drive in women

-source of estrogens in postmenopausal women

medullary chromaffin cells synthesize

catecholamines epinephrine (80%) and norepinephrine (20%)

effects of catecholamines

-vasoconstriction

-increased HR

-increased blood glucose levels

-blood diverted to brain, heart and skeletal muscle

stress in adrenal medulla vs cortex

medulla: short term stress ; involved with NE and epinephrine for fight or flight

cortex: long term stress ; involved with glucocorticoids and some mineralocorticoids

if long term stress response is prolonged...

it can become detrimental, leading to high BP, muscle loss, altered immune function, etc.

what is the pineal gland

small endocrine gland in the brain (3rd ventricle)

-pinealocytes secrete melatonin

melatonin may affect

-timing of sexual maturation and puberty

-day/night cycles

-physiological processes that show rhythmic variations (body temperature, sleep, appetite)

-production of antioxidant and detoxification molecules in cells

acinar cells (exocrine) in pancreas...

produce enzyme-rich juice for digestion

pancreatic islets (islets of Langerhans) contain endocrine cells. what cells

-alpha cells -> produce glucagon (hyperglycemic hormone)

-beta cells -> produce insulin (hypoglyceminc hormone)

glucagon

triggered by decreased blood glucose levels, rising amino acid levels, sympathetic nervous system

!! increases blood glucose !!

insulin

secreted when blood glucose levels increase

!! decreases blood glucose !!

3 ways insulin lowers blood glucose levels

-enhances membrane transport of glucose into fat and muscle cells

-inhibits breakdown of glycogen to glucose

-inhibits conversion of amino acids or fats to glucose

diabetes mellitus (DM) can be due to...

-hyposecretion of insulin: type 1

-hypoactivity of insulin: type 2

3 cardinal signs of DM

-polyuria—huge urine output

-polydipsia—excessive thirst

-polyphagia—excessive hunger and food consumption

lipidemia

high levels of fatty acids in blood

-occurs when sugars cannot be used as fuel, so in DM, fats are used

ketoacidosis

excessive production of ketones, making the blood acidic

-due to fatty acid metabolism (which forms ketones)

ovaries produce...

estrogen and progesterone

what does estrogen do

-maturation of reproductive organs

-appearance of secondary sexual characteristics

-with progesterone, causes breast development and cyclic changes in uterine mucosa

testes produce....

testosterone

what does testosterone do

-initiates maturation of male reproductive organs

-causes appearance of male secondary sexual characteristics and sex drive

-necessary for normal sperm production

-maintains reproductive organs in functional state

placenta

secretes estrogens, progesterone, and human chorionic gonadotropin (hCG)

adipose tissue release...

-leptin - appetite control; stimulates increased energy expenditure

-resistin - insulin antagonist

-adiponectin - enhances sensitivity to insulin

GI tract: gastrin

stimulates release of HCl

GI tract: ghrelin

stimulates food intake

GI tract: secretin

stimulates liver and pancreas

GI tract: cholecystokinin (CCK)

activates pancreas, gallbladder, hepatopancreatic sphincter