together behind the retina due to their photoreceptors facing forward instead of
backwards as in vertebrates.
The most advanced mollusks are the cephalopods… ex. octopus and squids with
some of the best vision on the planet
Hormones-
the signals of the endocrine system are transmitted to the appropriate target organ
via blood
Types of chemical messengers
o
Neurotransmitters
- jump synapses; local
o
Hormones
affect cells at a distance; involve blood. “Endocrine”
o
Exocrine
refers to secretion to the outside of the body. Pheromomes signal between
organisms
o
Paracrine
refers to localized effects. Ex: organ growth and repair, cell positioning
Lipophilic hormones:
o
Non-polar; and fat soluble
o
Need to use transport proteins to travel through blood
o
Enter cells and bind to transcription factors to effect DNA transcription; and are slow-
acting (hours to days)
Hydrophilic hormones:
o
Often polar; and blood plasma (water) soluble
o
Do not need transport proteins to travel through blood
o
Bind to cell receptors and activate protein kinases/induce signal transduction; and are
fast-acting (minutes to hours)
Lipophillic hormone exampes
o
Steroids, thyroid hormones, retinoids, vitamin D, and vitamin A
o
Work more slowly over a longer time period for changes that need to be gradual such as
steroids/menstrual cycle
Hydrophilic hormone examples
o
Peptide, protein, glycoprotein hormones, and catecholamines
Work much faster but for a short period of time
Example: sugar homeostasis (insulin and glucagon) or in an emergency system
(adrenalin)
Type I diabetes is due to the pancreas’ inability to produce the hydrophilic hormone, insulin, and
is treated by insulin injections. What is true?
o
Insulin binds to cell receptors and signal transduction occurs so that glucose can either
be moved out the blood and into cells for energy needs or stored as glycogen for later
use.
Lipophilic: binds to intracellular receptors thus regulating gene expression
Hydrophilic: binds to cell membrane receptors to stimulate signal transduction pathways
How could blocking hormone production or binding decrease cancerous tumor growth?
o
By blocking estrogen binding to that disuse it can slow the growth rate and or decrease
the cancerous growth.
o
By blocking estrogen production, one may be able to slow the growth of tumors.
How does tamoxifen work to help reduce growth of breast cancer?
o
Blocks the action of estrogen thereby slowing the growth rate of the cancerous cells
ADH- Antidiuretic Hormone
o
Involved in osmotic balance.
o
Synthesized in the hypothalamus
o
Released by posterior pituitary (neurohypophysis)
o
Increased blood solute concentration (dehydration) cases the release of ADH
o
In the PRESENCE of ADH, the kidneys reabsord water before forming urine.
