Lecture 15-17

the endocrine system

endocrine system

the second major regulatory system of the body that uses hormones secreted into the blood

endocrine signaling

type of signaling that secretes hormones into the bloodstream to impact distant tissues (ex. growth hormone and insulin)

paracrine signaling

type of signaling where cells secrete chemicals into extracellular fluid to impact nearby but different cell types (some hormones may function as paracrine signals)

autocrine signaling

type of signaling where cells secrete chemicals into the interstitial fluid to impact the same types of cells (some hormones may function as autocrine signals)

endocrine glands

organs made from ductless glandular epithelial cells that release hormones into the bloodstream

primary endocrine organs

anterior pituitary, thyroid, parathyroid, adrenal cortex, pancreas, thymus

secondary endocrine organs

testes, ovaries

hormones

chemical messengers that regulate the functions of other cells

protein hormones

hydrophilic hormones (ex. growth hormone, insulin, glucagon)

peptide hormones

hydrophilic hormones made from several amino acids (ex. oxytocin, ADH)

amine hormones

generally hydrophilic hormones (ex. epi and norepi) or hydrophilic (ex. thyroid hormone)

steroid hormones

hydrophobic hormones based on cholesterol (ex. cortisol, aldosterone)

hydrophilic hormones

hormones that cannot cross the plasma membrane but bind to it’s receptors; removed faster than hydrophobic hormones

hydrophobic hormones

hormones that can cross the plasma membrane and bind to receptors in the cytosol or nucleus; long lasting effects

upregulation

target cells increase receptor number when hormone levels are low

downregulation

target cells decrease receptor number when hormone levels are high

synergists

two hormones act on the same target cell for an amplified effect

complementary actions

different hormones act on different target cells to achieve a common goal

antagonists

hormones act on the same cell to produce opposite effects

hydrophilic hormone signaling (first messenger system)

1) hormone binds to receptor on plasma membrane

2) receptor activates a peripheral protein (G protein)

3) G protein activates enzyme

4) enzyme catalyzes formation of second messenger

cAMP pathway (ex of second messenger)

hormone → receptor → G protein → adenylate cyclase → cAMP → protein kinases

hydrophobic hormone mechanism

1) hydrophobic hormone diffuses into target cell

2) hormone binds to intracellular (cytoplasmic or nuclear) receptor

3) hormone-receptor complex binds DNA

4) DNA is altered to regulate gene transcription, mRNA, and protein synthesis

humoral stimulation

hormone secretion that is triggered by changes in blood levels (ex. glucose → insulin)

neural stimulation

hormone secretion that is triggered by nerve impulses

hormonal stimulation

hormone secretion that is triggered by another hormones release

hypothalamus

part of the brain that works with the pituitary gland to control homeostatic functions

pituitary gland

endocrine gland split into anterior pituitary and posterior pituitary

posterior pituitary

part of the pituitary gland that stores and releases neurohormones made in the hypothalamus (ADH and oxytocin)

ADH

hormone released by posterior pituitary to control water retention through vasoconstriction of arteries

diabetes insipidus

when ADH is low causing excessive peeing, dehydration, and extreme thirst

oxytocin

hormone released by posterior pituitary that controls contractions and lactation

hypothalamic hormones

TRH, CRH, GnRH, somatostatin, and dopamine

tropic hormones

hormones that regulate secretion from other endocrine glands

examples of tropic hormones

TSH - stimulated by TRH and stimulates thyroid development/secretion

ACTH - stimulated by CRH and stimulates adrenal gland

LH - stimulated by GnRH and stimulates testosterone, estrogen, and progesterone production

FSH - stimulated by GnRH and LH; stimulates testosterone concentration and follicle maturation

prolactin

non tropic hormone that stimulates mammary gland tissue growth and initiates lactation after birth

growth hormone (GH)

non tropic hormone produced by anterior pituitary gland, stimulated by GHRH, and inhibited by somatostatin; promotes growth and metabolism regulation

thyrotropin releasing hormone (TRH)

triggers release of TSH from anterior pituitary

corticotropin releasing hormone (CRH)

triggers release of adrenocorticotropic (ACTH) from anterior pituitary

gonadotropin releasing hormone (GnRH)

triggers release of luteinizing (LH) and follicular stimulating hormone (FSH)

growth hormone releasing hormone (GHRH)

triggers release of GH from anterior pituitary

somatostatin

inhibits GH secretion

prolactin inhibitory factor (dopamine)

inhibits PRL

tiers of hormone regulation

1) first tier - hypothalamus secretes tropic hormones

2) second tier - tropic hormones regulate anterior pituitary secretion

3) third tier - anterior pituitary hormones act on target tissues to stimulate glands

short term effects of growth hormone

1) promotes fat breakdown (lipolysis)

2) stimulates gluconeogenesis (new glucose production in liver)

3) inhibits glucose uptake by muscle fibers

4) net effect (increases blood glucose and fatty acids fuels growth)

long term effects of growth hormone

stimulation of IGF which stimulates protein synthesis, promotes cell division, enhances bone and muscle growth, regulates body mass in adults, and decreases blood glucose

gigantism

GH disorder where there is GH hypersecretion before epiphyseal plate closure causing abnormal height increase

acromegaly

GH disorder where there is GH hypersecretion after epiphyseal plate closure causing tissue growth in firth (bones ad soft tissue)

dwarfism

GH disorder where there is GH hyposecretion before epiphyseal plate closure causing stunted growth

adrenal glands

three layered endocrine gland located on top of the kidneys that produces steroid hormones

zona glomerulosa

outer layer of adrenal cortex that secretes mineralcorticoids (ex. aldosterone)

zona fasiculata

middle layer of adrenal cortex that secretes glucocorticoids (ex. cortisol) and androgenic steroids

zona reticularis

inner layer of adrenal cortex that secretes glucocorticoids (ex. cortisol) and androgenic steroids

inner adrenal medulla

secretes epi and norepi to act as messengers of the sympathetic nervous system (increase HR, dilate bronchioles, increase BP, dilate pupils)

aldosterone

hormone secreted by adrenal glands that…

1) maintains sodium potassium balance in ECF

2) regulates ECF volume via Na/Cl reabsorption in kidney tubule cells

3) maintains BP via renin angiotensin- aldosterone system (RAAS)

4) maintains acid base balance by stimulating H+ secretion in kidney tubules to lower blood acidity

hyperaldosteronism

aldosterone disorder that leads to hypokalemia, hypernatremia, hypertension, and metabolic alkalosis

cortisol

hormone secreted by adrenal glands that…

1) increases blood glucose (gluconeogenesis)

2) regulates protein breakdown in skeletal muscle for amino acids for gluconeogensis

3) regulates lipolysis for fatty acids for fuel and glucose production

4) decreases certain leukocytes

5) immunosuppressive (stress response)

cortisol production

hypothalamus releases CRH → CRH stimulates anterior pituitary to create ACTH → ACTH stimulates cortisol secretion

cushing’s disease

disease where adrenal tumor causes excess cortisol (symptoms include moon face, muscle wasting, hyperglycemia, increased appetite, osteoporosis)

addison’s disease

hyposecretion of cortisol and aldosterone causing adrenal damage, enzyme deficiency, and adrenal destruction

thyroid

butterfly gland above the larynx that secretes thyroid hormones (regulate growth and metabolism) and secretes calcitonin (regulates Ca2+ metabolism)

thyroid gland structure

thyroid follicles (produce thyroid hormones), colloid (stores thyroid hormone precursors), and parafollicular cells (produce calcitonin)

T3 and T4

hormones that regulate temperature and metabolism, essential for bone, muscle and nervous system development

T3

thyroid hormone that is more active with a short half life of 2.5 days

T4

thyroid hormone with a longer half life of 6.5 days; usually stored for conversion to T3

high T3 and T4

supresses TRH and TSH

hyperthyroidism

overproduction of thyroid hormones causing heat intolerance, weight loss, increased HR, and hypertension

hypothyroidism

underproduction of thyroid hormones causing cold intolerance, weight gain, slow HR, and hypotension

parathyroid hormone (PTH)

hormone secreted by chief cells in the parathyroid glands; increases blood calcium

PTH process

1) stimulates osteoclasts by releasing Ca2+ from bone

2) stimulates production of calcitrol (active vitamin D) to increase Ca2+ absorption from small intenstine

calcitonin

hormone secreted by parafollicular cells in thyroid; released in response to hypercalcemia (inhibits osteoclast activity, allows osteoblast to continue building bone, overall decreases blood calcium)

pancreas

endocrine organ behind the stomach that produces insulin and glucagon to maintain blood glucose levels

pancreas cell groups

acinar (exocrine) which secrete digestive enzymes into the GI tract and islets of langerhans (endocrine) which secrete alpha, beta, and delta cells

alpha cells

islets of langerhans that secrete glucagon

beta cells

islets of langerhans that secrete insulin

delta cells

islets of langerhans that secrete somatostatin

glucagon

pancreatic hormone that regulates glucogenolysis (glycogen breakdown into glucose) and gluconeogenesis (new glucose formation in liver)

glucagon stimulators

low BG, sympathetic stimulation, ingested proteins

glucagon inhibitors

high BG, somatostatin

insulin

pancreatic hormone that promotes uptake of glucose, amino acids, and lipids into the cell (lowers BG, increases fat storage, stimulates protein synthesis, promotes satiety)

hypoglycemia causes

excess insulin, starvation, tumors, alcohol

hyperglycemia causes

chronic BG elevation due to diabetes

type I diabetes

autoimmune destruction of beta cells leading to no insulin production

effects of type I diabetes

1) target cells cannot uptake glucose

2) liver overproduces glucose (unopposed glucagon)

3) elevated ketone bodies (risk of ketoacidosis)

4) glucose and ketones in urine cause excessive peeing and thrist

type II diabetes

target tissues become insulin resistant

effects of type II diabetes

1) obesity

2) hyperglycemia

3) glucosuria

4) polyuria and polydipsia

BG increases (eating)

high BG → beta cells detect rise → beta cells increase insulin and alpha cells decrease glucagon → glucose uptake and storage is increased

BG deceases (fasting or exercise)

low BG → alpha cells detect decrease and ingested protein → alpha cells increase glucagon and beta cells decrease insulin → glycogenolysis and gluconeogenesis restore glucose

pineal gland

endocrine hormone that secrets melatonin to regulate the sleep wake cycle

thymus

endocrine gland that is the site of T lymphocyte maturation

testosterone

steroid hormone that drives sperm production, bone growth, muscle mass, and male secondary sex traits

estrogen

steroid hormone that stimulates female secondary sex traits and regulates the menstrual cycle

progesterone

steroid hormone that prepares body for pregnancy, supports fetal development, and affects smooth muscle, blood clotting, and metabolism

leptin

protein hormone that targets hypothalamic neurons (crosses BBB) and induces satiety

ANP

vasodilates blood vessels and promotes natriuresis to decrease blood volume and lower BP

erythropoetin

hormone produced by kidneys in response to low blood oxygen to stimulate RBC production