ch 7 endocrine system

hormones

chemical messengers, secreted by epithelial tissue, that travel through the bloodstream, and act on target tissues

hormones function

control rates of enzymatic reactions, ion transport,
gene expression

classic hormones

hormones of the pancreas, thyroid, adrenal glands, pituitary, parathyroid, and gonads

variations on classic hormones: secreted by cells/groups of cells

hormones can also be isolated (ex. immune )

variations on classic hormones: secreted into blood

hormones can also be secreted into surrounding tissue

variations on classic hormones: transport to distal target

some hormones can be paracrine in nature (localized response)

similarity between all hormones

hormones are secreted in low concentrations

hormone receptors

binding sites on target cells; binding elicits varied cellular responses (ex. insulin)

termination of hormone action

3 ways: mechanisms, half-life, or receptor-hormone complexes

mechanisms of hormone termination

reduced secretion (negative feedback); endocytosis; enzymatic degradation into inactive metabolites

half-life

amount of time to reduce the concentration by one-half

Receptor-hormone complex

enters nucleus and binds to specific region of DNA and helps initiate DNA transcription to produce mRNA which is translated into specific protein

How are hormones classified?

by chemical synthesis/structure

peptide and protein hormones

linked amino acids

steroid hormones

derived from cholesterol

amine hormones

a modified single amino acid molecule of tyrosine or tryptophan

The majority of hormones in the body are

peptide hormones

preprohormones

inactive precursor with signal sequence, directing to ER

prohormones

inactive precursor with signal sequence removed; packaged into vesicles; stored until needed

storage, synthesis and release of peptide hormones

1. preprohormone: inactive precursor with signal sequence
2. signal sequence is cleared, becomes pro hormone that is still biologically inactive
3. prohormone is packaged in Golgi into vesicles with enzymes
4. biologically active molecule hormone Is stored in vesicle until needed

why do peptide hormones have short half lives

they are easily degraded because they are water soluble and can dissolve in plasma
they are not bound or protected by carrier proteins; no protective mechanisms in blood

peptide hormones bind to

cell surface receptors

signal transduction pathway

The process by which a signal on a cell's surface is converted into a specific cellular response.

GPCR-cAMP Pathway

Stop signaling pathway
1. hormone binds to receptor (GPCR)
2. GPCR activates G protein
3. G protein separates and activates or inhibits effector enzyme (adenylate cyclase)
4. adenylate cyclase converts ATP to cAMP
5. cAMP activates protein kinases that modify other proteins
6. cAMP is degraded by phosphodiesterase to stop signaling pathway

tyrosine kinase receptors

membrane receptors that attach phosphates to protein tyrosines

steroid hormones are derived from

cholesterol

Where are steroid hormones produced?

gonads, adrenal cortex, skin, placenta

adrenal cortex (kidneys) hormones

cortisol and aldosterone

Gonads hormones

estrogen, progesterone, testosterone

skin hormones

Vitamin D

How are steroid hormones synthesized?

synthesized on demand from cholesterol; needs signal, but is not waiting in vesicles

How are steroid hormones transported?

since steroid hormones are lipid-soluble they require transport proteins in plasma

lipophilic steroid hormones

move easily through membranes

how do carrier proteins affect steroid hormones

carrier proteins increase solubility and extend half lives of steroid hormones

steroid hormones transport

most steroid hormones have cytoplasmic and/or nuclear receptors to diffuse through the cell membrane

The binding of lipophilic messengers, such as steroid hormones, to their receptors triggers

gene transcription (synthesizing RNA from DNA)

amine hormones

melatonin, catecholamines, thyroid hormones

melatonin

synthesized from tryptophan in pineal gland
regulates circadian rhythm (sleep cycle) and immune function

catecholamines

dopamine, norepinephrine, epinephrine
synthesized from tyrosine

thyroid hormones

synthesized from tyrosine and iodine
involved in metabolism, growth, development

simple endocrine reflex

involves only one hormone
cell acts as sensor, integrator;
hormone is output signal
response is usually negative feedback

parathyroid hormone (PTH)

secreted from parathyroid glands and is regulated by blood calcium levels
parathyroid cell detects low Ca2+, increases PTH
PTH acts on bone (bone reabsorption), kidneys and intestines to raise blood Ca2+

insulin secretion

regulated by negative feedback when high blood sugar levels trigger its release from beta cells to reduce blood levels of glucose

neurohormones

chemicals released by neurons into the blood for action at distant targets
include catecholamines, hypothalamic hormones from posterior and anterior pituitary

anterior pituitary

epithelial tissue, endocrine organ
aka adenohyphysis

posterior pituitary

extension of the brain that releases hormones produced by the hypothalamus;
aka neurohypophysis

2 hormones of the posterior pituitary

ADH and oxytocin

antidiuretic hormone (ADH)

regulates water balance in the kidneys by inserting aquaporin water channels (reabsorption)

oxytocin

controls milk ejection during breastfeeding and uterine contraction during childbirth

posterior pituitary hormone release

1. neurohormone made+packaged in cell body of neuron in hypothalamus
2. vesicles transported down the cell
3. vesicles w/ neurohormone are stored in posterior pituitary
4. neurohormone released out vein and into bloodstream

what is anterior pituitary controlled by

releasing hormones from hypothalamic neurons

trophic hormones

hormones that stimulate other endocrine glands to release hormones; those released from the anterior pituitary= FSH, LH, ATCH,TSH

anterior pituitary hormone release

1. in hypothalamus, neurons synthesizing trophic neurohormones release them into capillaries of portal system
2. portal veins carry neurohormones to anterior pituitary, where they act on endocrine cells
3. endocrine cells release their peptide hormones into second set of capillaries to distribute out to body

hypothalamic-hypophyseal portal system

two sets of capillaries connecting hypothalamus to anterior pituitary

6 anterior pituitary hormones

Growth hormone (GH)
Thyroid-stimulating hormone (TSH)
Adrenocorticotropic hormone (ACTH)
Follicle-stimulating hormone (FSH)
Luteinizing hormone (LH)
Prolactin

prolactin

stimulates milk production

Thyroid Stimulating Hormone (TSH)

stimulates thyroid gland, increases prod of T3 and T4
endocrine target= thyroid gland
hormones secreted= T3 T4

Adrenocorticotropic hormone (ACTH)

controls cortisol release
endocrine target= adrenal cortex
hormones secreted= cortisol

Growth Hormone (GH)

promotes skeletal and muscular growth
endocrine target = liver
hormones secreted= IGFs (insulin like growth factors)

Gonadotropin-releasing hormone (GnRH)

Promotes secretion of follicle-stimulating hormone (FSH) and luteinizing hormone (LH)

luteinizing hormone (LH)

secreted by the pituitary gland to promote ovulation

Follicle-stimulating hormone (FSH)

secreted by the pituitary gland to stimulate maturation of the egg cell (ovum)

hypothalamic-pituitary-adrenal (HPA) axis

a body system involved in stress responses

short loop feedback

pituitary hormones feed back to decrease hormone secretion by the hypothalamus

long loop feedback

hormones of target endocrine gland feeds back on hypothalamus and anterior pituitary gland