3 - Endocrine System

What are endocrine glands?

• epithelial tissue

• secrete hormones into blood vessel from basal surface

• may or may not have lumen

• slower signalling, but often larger effects, than nervous system signalling

What are hormones?

signalling moleucles that affect metabolic processes by traveling through blood to a target tissue

What are the endocrine organs?

• Pineal

• Hypothalamus

• Pituitary Gland

• Thyroid

• Parathryoid

• Thymus - create immune structures to help develop T cells

• Adrenal Glands - secrete 4 hormones, dual function

• Pancreas - dual function (hormones and exocrine secretion to GI tract)

• gonads - ovary/tests, make gametes as well

What two systems communicate together to maintain homeostasis? Which is faster?

• nervous and endocrine system

• nervous system is faster

What are the chemical classes of hormones, including their hydrophillicity?

• amino acid based hormones - usually hydrophilic

• steroids - usually hydrophobic

Describe the amino acid based class of hormones

• small amino acid derivatives - slightly modified single aa; ex. adrenalin

• small peptides - ex. oytocin

• large polypeptide chains - ex. insulin

• usually hydrophilic - dissolve easily in blood/H20, but can’t get through cell lipid bi layer

• stored in vesicles

• faster release then steroids (already made)

Describe the steroid class of hormones

• cholesterol derived

• made on demand, so slower release then amino acid based hormones

• hydrophobic - can diffuse across cell membrane, so can’t make ahead of time; lipid soluble

• ex. testosterone, estrogen, progesterone, cortisol

Describe free vs bound hormone concentratinos

• hydrophobic hormones are bound to plasma proteins to help keep them in the blood (like a raft)

• only so much availability to bind to receptors

What are the different ways to stimulate the release of a hormone? Describe them

1. humoral stimulus - responds to amount of a substance in the blood, causing a gland to secrete/stop secreting hormones

2. Neural stimulus - brain detects signal/change, stimulates a neuron to stimulate endocrine glands to release hormones

3. Hormonal Stimulus - hormones trigger hormone release; hormone travels through blood to stimulate release of a another hormone form a gland

Describe humoral stimulus of a hormone. Include an example

• gland responds to amount of a substance in the blood, causing a gland to secrete/stop secreting hormones

• ex. pancreas detects high glucose, releases insulin, which tells body to lower blood glucose

Describe neural stimulus of a hormone. Include an example

• brain detects signal/change, stimulates a neuron to stimulate endocrine glands to release hormones

• ex. stress signal, brain signals adrenal gland to release adrenalin

Describe hormonal stimulus of a hormone. Include an example

• hormones trigger hormone release; hormone travels through blood to stimulate release of a another hormone form a gland

• ex. Hypothalamus releases F- inhibiting hormone into portal system, travels to anterior pituitary, tells anterior pituitary to release less FSH

How do peptide/protein hormones signal target cells?

• dissolve freely into blood (hydrophilic)

• bind to membrane receptors that bring them to the target cell

• second messengers inside cell act (can amplify and cause many effects in one cell)

How do steroids/lipid-soluble hormones signal target cells?

• carried by proteins in blood

• travel through cell membrane and bind to intracellular receptors

• affects gene inscription directly inside cell (ex. bind to DNA)

What can hormones affect in target cells?

• membrane permeability of a cell

• protein synthesis

• enzyme activity

• secretory activity

• mitotic activity

What kind of hormone interactions are there? Describe them.

• permissiveness - permissive hormone has no effect on target molecule, but allows OTHER hormone to have a large (instead of usual small) effect

• synergism - both hormones have an effect on a cell, but have much larger overall effects when combines

• antagonism - hormones have opposite effects

What is a permissive hormone and an example?

• hormone that has no affect on a target molecule, but allows other hormones to have a large effect

• ex. Thyroid hormones

Describe the hypothalamus and pituitary glands from most superior to inferior

• hypothalamus

• infundibulum

• anterior pituitary gland (epithelial tissue)

• posterior pituitary gland (neural tissue)

What is the hypothalamus?

• main control center for maintaining homeostasis

• integrates info from brain

• neurally signals posterior pituitary gland, hormonally signals anterior pituitary gland

What hormones does the posterior pituitary gland produce and what do they do?

• oxytocin - affects mammary glands and uterus, affects brain (ex. mother-child bond); hydrophilic peptides

• vasopressin (ADH) - constricts blood vessels to raise blood pressure, signals kidneys to lower urine production; hydrophilic peptides

How are oxytocin and ADH signalled/released?

• neural signalling in posterior pituitary

• hypothalamic neurons produce oxytocin or ADH

• hormones transported down axon to axon terminal in posterior pituitary gland

• oxytocin/ADH released into blood vessel in posterior pituitary gland when neurons fire

How are hormones in the anterior pituitary gland signalled/released?

• hormonal signalling

• hypothalamic neurons produce either releasing or inhibiting hormones

• hormones released into portal system

• hormones travel through portal system directly to anterior pituitary gland

• RH/IH affect cells in anterior pituitary gland to make hormones (FLAT PG)

What is the portal system and how is it used in endocrinology?

• A specialized vascular arrangement in which blood passes through two capillary beds in sequence

• Allows substances to be transported directly and efficiently from one organ or tissue to another without dilution in the systemic circulation.

• Capillaries in the hypothalamus collect releasing and inhibiting hormones.

• Blood flows through portal veins to a second capillary bed in the anterior pituitary.

What hormones are released by the Anterior Pituitary Gland and what do they do?

• Follicle Stimulating Hormone (FSH) - affects gonads to produce testosterone and estrogen

• Luteinizing Hormone (LH) - affects gonads to produce testosterone and estrogen

• Adrenocorticotropic Hormone (ACTH) - affects adrenal glands release cortisol

• Thyroid stimulating hormone (TSH) - affects thyroid gland to produce TH

• Prolactin (PRL) - affects mammary glands/uterus, usually constantly secreting unless told not to

• Growth Hormone (GH) - affects bones, muscle, liver, etc. to produce Growth Factor (GF)