ch. 16 endocrine system study guide

how do cells communicate?

electrical and chemical signals

what are electrical signals

changes in potential membrane

what are chemical signals

molecules secreted by cells into the extracellular fluid

what are the 4 methods of cell to cell communication through electrical or chemical signals

1. gap junctions

2. contact dependent signals

3. local communication

4. long distance communication

what are the endocrine glands

pituitary gland

thyroid gland

parathyroid gland

adrenal gland

pineal glands

endocrine system

secretes hormones that are transported within blood

widespread effects

slow reaction time

targets any cell in the body with a receptor for hormones

long lasting

nervous system

uses neurotransmitters

targets neurons, muscle cells, and gland cells

rapid reaction time

specific effects

short term

functions of the endocrine system

regulates metabolism, growth, and development; maintains homeostasis; influences reproductive processes.

what is a hormone

chemical messengers that are secreted into the bloodstream and stimulate physiological responses in distant organs

amino acid based hormones

amino acid derivative, peptides, and proteins

are made in many tissues all over the body

steroid hormones

synthesized from cholesterol

they are made in few organs like gonads and adrenal glands

water soluble hormones

mix freely with water, so easily transported in the blood

cannot pass through the plasmatic membrane, so they cannot enter the cell

lipid soluble hormones

do NOT mix freely with water, so they must bind to a transport protein in the blood

they can pass through the plasmatic membrane, so they can enter cells

they act on intracellular receptors in the cytoplasm or in the nucleus and regulate gene expression.

what are target cells

cells with receptors for specific hormone

target cell specificity

target cells must have specific receptors to which hormones bind

what factors influence target cell activation

1. blood levels of hormones

2. relative number of receptors on or in target cells

3. affinity of binding between receptor and hormone

which hormones are lipid soluble

estrogen

progesterone

testosterone

cortisol

aldosterone

thyroid

which hormones are water soluble

norepinephrine, epinephrine, melatonin, antidiuretic, insulin, glucagon, growth, and erythropoietin, oxytocin

what is meant by the half-life of a hormone

time necessary to reduce a hormone’s concentration to half of it’s original life

how do lipid soluble hormones reach their target cells

can diffuse across target cell membrane, their receptors are in the cytosol or nucleus

how do water soluble induce cellular change in their target cells

water soluble hormones uses membrane receptors, these are hormones are polar and cannot diffuse through the membrane

synergistic interactions

one hormone reinforces activity of another hormone, hormones work together to produce greater effect

i.e., estrogen and progesterone effects on a target cell

permissive interactions

one hormone requires activity of another hormone, first hormone allows action of the second hormone

i.e., oxytocin’s milk ejection effect requires prolactin’s milk generating effect

antagonistic interactions

one hormone opposes activity of another hormone, one hormone causes opposite effect of another hormone

i.e., glucagon increases blood glucose, while insulin lowers it

what are junctions

transfers of electrical and chemical signals

what are contact dependent signals

there is a receptor on one cell and a membrane bound signal molecule on another cell. in order for a signal to occur, the cells must be in close contact

local communication

chemicals are produced in one cell and has an effect on another cell

autocrines signals

chemicals produced in one cell and exerts an effect on same cell that it produces

paracrines signals

chemicals produced in one cell and exerts an effect on a different cell than one that secretes them

long distance communications

signals are produced and sent to cells in another location

what are neurohormones

any hormone produced and released by neuroendocrine cells into the blood

endocrine glands

has no glands, produces hormones that are dumped into the bloodstreams

exocrine glands

non-hormonal substances (sweat, saliva, etc). has ducts to carry secretion to membrane surface

examples of amino acid based hormones

epinephrine and norepinephrine which are both synthesized in the medulla of the adrenal glands

examples of steroid hormones

sex hormones - testosterone, aldosterone, cortisol

mechanisms of hormone actions on target cells

• alter plasma membrane permeability and/or membrane potential by opening or closing ion channels

• stimulate synthesis of enzyme or other proteins

• activate or deactivate enzymes

• induce secretory activity

• stimulates mitosis

water soluble hormone mechanisms:

cAMP signaling mechanism

1. hormone (first messenger) binds to receptor

2. receptor activates G protein

3. G protein activates adenylate cyclase

4. adenylate cyclase converts ATP to cAMP (second messenger)

5. cAMP activates protein kinases that phosphorylate proteins

gene activation mechanism of lipid soluble hormones

1. diffuse into target cells and bind with intracellular receptors

2. receptor hormone complex enters nucleus; binds to specific region of DNA

3. prompts DNA transcription to produce mRNA

4. mRNA directs protein synthesis

5. promote metabolic activities, or promote synthesis of structural proteins or proteins for export from cell

three types of endocrine gland stimuli

humoral, neural, and hormonal stimuli

humoral stimuli

changing blood levels on ions and nutrients directly stimulate secretion of hormones

i.e., low Ca 2+ levels in blood can trigger the secretion PTH (parathyroid hormone)

neural stimuli

nerve fibers stimulate hormone release

i.e., action potential causing the release of epinephrine and norepinephrine

hormonal stimuli

hormones stimulate other endocrine organs to release their hormones

i.e., hypothalamus releases hormones into the anterior pituitary gland, causing the release of other hormones

functions of the hypothalamus

• controls the autonomic nervous system

• initiates physical responses to emotions

• regulate body temp

• regulate food intake

• regulate water balance and thirst

• regulate sleep wake cycles

• control endocrine system functions

oxytocin functions

• strong stimulant of uterine contraction released during childbirth

• hormonal trigger for milk ejection

• surges sexual arousal and orgasms

• helps transport sperm up the female reproductive tract

• functions in feelings of sexual satisfaction and emotional bonding between partners

ADH (antidiuretic hormone, vasopressin) functions and stimuli that trigger release

• inhibits or prevents urine formation

• regulates water balance

• targets kidney tubules to reabsorb more water

• release also triggered by pain, low blood pressure, high concentration of solutes in blood, and drugs

• inhibited by alcohol, diuretics, drinking a lot of water

• high concentrations causes vasoconstriction

homeostatic imbalance of ADH

• ADH deficiency can cause insipidus, resulting in extreme thirst and excessive urine output

TSH → thyroid stimulating hormone

also called thyrotropin

growth of thyroid, secretion of thyroid hormone

PRH → prolactin releasing hormone

targets mammary glands, testes

female: milk synthesis

male: increased LH sensitivity and testosterone secretion

GnRH → gondatropin releasing hormone

stimulates the anterior pituitary to release both FSH and LH

CRH → corticotropin releasing hormone

stimulates release of ACTH

FSH → follicle stimulating hormone

targets ovaries and testes

female: growth of ovarian follicles and secretion of estrogen

male: sperm production

ACTH → adrenocorticotropic hormone

targets adrenal cortex

growth of adrenal cortex, secretion of glucocorticoids

GH → growth hormone

targets liver, bone, cartilage, muscle, and fat

widespread tissue growth, especially in the state tissues

LH → luteinizing hormone

targets ovaries and testes

female: ovulation, production and maintenance of corpus luteum

male: testosterone secretion

function of hypophyseal portal system

oxytocin and ADH are produced in the hypothalamus and transported into the posterior pituitary gland where it is stored

hypersecretion of growth hormone

in children, results in gigantism

in adults, results in acromegaly - enlargement of face, hands, and feet

hyposecretion of growth hormone

in children, results in pituitary dwarfism