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)

Describe the endocrine glands not associated with the hypothalamus & pituitary glands

• pineal gland

• pancreas

• parathyroid/thyroid

• thymus

• pineal gland - helps regulate circadian rhythms

• pancreas - regulates blood glucose

• parathyroid/thyroid - regulates blood calcium

• thymus - regulates lymphocyte production/maturation

What does the pineal gland do in the endocrine system?

helps regulate circadian rhythms

What does the pancreas do in the endocrine system?

regulates blood glucose

What does the parathyroid/thyroid do in the endocrine system?

regulates blood calcium

What does the thymus do in the endocrine system?

regulates lymphocyte production/maturation

Describe the structure of the thyroid gland

• contains colloid-filled follicle with thyroglobulin inside (where t3 and t4 are attached); thyroid hormone made in here

• surrounded by follicular cells that make thyroid hormone

• parafollicular cells in between follicles make calcitonin for Calcium homeostasis

What does the thyroid do?

• produces T3 and T4

• metabolic actions: stimulate ATPase pumps (affects nearly all cells in body); promotes glucose and lipid breakdown for energy

• Growth and development: essential for normal CNS development, promotes normal muscle and skeletal growth

• permissive effects for other hormones (ex. epinephrine, GH, steroids)

How is thyroid hormone synthesized?

1. thyroid follicular cells stimulated by TSH to make thyroglobulin protein and thyroid peroxidase to secrete into follicle

2. thyroid peroxidase attaches iodine to tyrosine (amino acid) on thyroglobulin to make T3 and T4

3. T3 and T4 still attached to thyroglubin

4. when TSH arrives, enzymes cleave off T3 and T4

5. T3 and T4 (lipid-soluble) diffuse out of cell

What kind of hormones are T3 and T4 and are they hydrophobic or hyrdophilic?

• amino acid derivates

• hydrophobic

Why does an iodine insufficiency cause a goiter?

low iodine prevents making of T3 and T4, causing high TSH/TRh levels

What hormones does the adrenal MEDULLA produce? What class of molecules are they? How are they stimulated?

• norepinephrine and epinephrine (neural tissue)

• amino acid derivative

• nerually stimulated

Describe the structure of the adrenal glands

• above kidneys

• cortex (outside) of gland made of epithelial tissue

• medulla (inside) of gland made of nervous tissue

What hormones does the adrenal CORTEX produce? What class of molecules are they? How are they stimulated?

• cortisol (follows circadian rhythm), aldosterone, androgen

• steroids

• hormonally stimulated by ACTH

  • stress/circadian —> CRH —> ACTH —→ cortisol

What releases cortisol? What does cortisol do?

• released by adrenal cortex

• increases plasma glucose

• permissive for many metabolic and developmental functions

• anti-inflammatory/anti-immune

• promotes bone breakdown

Describe the pathway that leads to the release of cortisol

• stress or circadian rhythm

• CRH released from hypothalamus

• ACTH released from anterior pituitary gland

• cortisol released from adrenal cortex

describe the 2 stress responses mediated by the adrenal gland

• fast: neurally stimulated adrenal medula, releases NE and epinephrine to act throughout body (increase HR, BP, metabolic rate, etc.) ; effect goes away faster

• slow: hormonally stimulated adrenal cortex, releases steroid cortisol to increase blood glucose levels, suppress immune system; longer lasting effects