Chapter 16: The Endocrine System: Part A
There are two main classes of hormones
1. Amino acid-based hormones
Amino acid-based hormones are can be synthesized from what?
1. Amino acid derivaties
Steroid based hormones are synthesized from ______?
What kind of hormones act at the receptors outside the target cell? (can not enter the cell)
All amino acid-based hormones, except thyroid hormones, are what type of hormone?
What kind of hormones can enter the cells?
Steroid and thyroid hormones are what type of hormone?
There are two types of hormones that will always be steroid based hormones, what are they?
Hormone action on target cells may be to...?
1. alter plasma membrane permeability and/or membrane potential by opening or closing ion channels
2. stimulate synthesis of enzymes or other proteins
3. activate or deactivate enzymes
4. induce secretory activity
5. stimulate mitosis
When hormones are water soluble they can not enter the cell. How do they act on a target cell then?
1. Act on plasma membrane receptors
2. Act via G protein second messengers
What is target cell specificity?
Target cells must have a specific receptors for specific hormone to bind
Target cell activation depends on what three factors?
1. blood levels of hormone
2. relative number of receptors on or in target cells
3. affinity of binding between receptor and hormone
target cells build more receptors in response to low hormone levels
target cells lose (destoy) receptors in response to high hormone levels
down = destroy
Blood levels of hormones are controlled by which type of feedback system?
negative feedback system
(exception oxytocin - positive feedback system)
Endocrine glands are stimulated to synthesize and release hormones in response to three types of stimuli. List all three.
1. Humoral stimuli
2. Neural stimuli
3. Hormonal stimuli
occurs when blood levels of ions and nutrients get out of normal range and stimualte hormone release
(example - calcium ions are low in the blood so it causes the parathryoid to release PTH)
nerve fibers stimulate hormone release
occurs when hormones stimulate other endocrine organs to release their hormones
(example - anterior pituitary releases thyroid stimulating hormone)
There are two ways hormones circulate in the blood. List them.
1. free circulating
Free circulating hormones are what type of hormones?
water soluble hormones
These hormones attach to plasma proteins and circulate in the blood bound. List two.
2. thyroid hormones
How are hormones removed from the blood?
1. degrading enzymes
one hormone can not exert its effects without another hormone being present
more than one hormone produces same effects on target cell --> amplification
one or more hormones oppose(s) action of another hormone