Download Lecture 5: Endocrine System

Lecture 5: Endocrine System
Silverthorn Chapter 7
There are two different control systems in the human body, responsible for coordinating communication between the body systems.
Cells must communicate with each other in order to coordinate actions that maintain homeostasis, because as we’ll see, the majority of
homeostatic mechanisms involve more than one organ system.
Comparing Control Systems
ENDOCRINE SYSTEM
Target specificity
Signal type
Speed of signal
transmission
Speed of effect
Duration of effect
Control of effect
intensity
NERVOUS SYSTEM
General
Any cell with the correct receptor can be affected
by a hormone.
Specific
Only cells that synapse with a neuron can be affected.
Hormone
Action potential (AP) and neurotransmitter (NT)
This is a chemical signal
AP is electrical, NT is chemical
Slow
Fast
Hormones pass through the blood to reach target
and initiate response.
Slow
Some neurons relay information at 120 m/s. This is
equal to 268 mph
Often hormones initiate protein synthesis in a cell,
which takes time.
Long
As soon as NT is released, the effect occurs
Fast
Instantaneous
The effect can last a very long time
Multiple signals can increase the duration
Quantity of hormone
Number and speed of AP
Ultimately, the two systems WORK TOGETHER (see fig 6.31-5th ed; 6.19- 6th ed)
The Endocrine System
A regulatory system that produces hormones. The endocrine system is not truly a distinct system (though it does have specific organs
that are identified as “endocrine players”) because it plays a role in everything.
1. Hormone: a substance secreted by a gland (or single cell) into the blood that acts on a distant target tissue.
A. Hormones can initiate an effect at very low concentrations. In other words, you don’t need very much hormone to make a
big impact.
B. They are very specific in their action, because they bind to a certain RECEPTOR on the TARGET CELL (if the cell has no
receptor for the hormone, then the cell is not a target cell of that hormone).
C. Hormones initiate signal transduction…in which chemical reactions are initiated (or halted) within the target cell.
2. Examples of hormone-receptor interactions
A. (initiate/block) protein synthesis
B. (activate/inactivate) enzymes
C. (open/close) ion channels in cell membrane
3. Hormone action is terminated by enzymes that break down the hormone
4. Hormone in the blood is degraded, usually in liver or kidney and then excreted in urine or bile
5. There are 3 primary types of hormones:
A. Steroid hormones
B. Peptide hormones
C. Amino acid derivatives
Steroid Hormones
Steroids are lipid soluble hormones. What is another word to describe something that is lipid soluble?
1. Steroid hormones are all derived from cholesterol. That means they have a similar structure that is relatively easy to identify.
2. They are produced in the adrenal cortex, gonads, or placenta
3. Often they have –sterone in the name
Bio 7: Human Physiology
15
Spring 2014: Riggs
4. Mechanism of action:
A. The are transported in blood, but must be attached to a CARRIER (why???)
B. After being released from the carrier, they can diffuse into the target cell. (How did you know they could diffuse into the
cell?)
C. Usually they attach to a mobile receptor in the nucleus…(though some actually do attach to membrane receptors, or floating
cytoplasmic receptors…)
D. The hormone-receptor complex then attaches to a specific GENE, and stimulates TRANSCRIPTION of that gene.
E. Resulting mRNA travels to the ribosome in the cytoplasm for TRANSLATION, and new proteins are produced.
F. All of this is initiated by the binding of the hormone to the floating mobile receptor.
5. Key Features
A. Amount of steroid hormone directly impacts amount of protein produced (and consequent metabolic activity of the cell).
There is no amplification is possible with steroid hormones
B. The mechanism of these molecules is very SLOW. Takes a while to do all these steps…between 45min-several days!
Amino Acid Derivatives
1. Some hormones are derived from single amino acids. Examples:
A. Tryptophan is used to produce only melatonin
i. Note: serotonin is a NT that is also derived from tryptophan
B. Tyrosine is used to produce all other amino acid derivative hormones.
2. There are two categories of tyrosine based hormones:
A. Catecholamines (made from 1 tyrosine) are neurohormones
i. Epinephrine
ii. Norepinephrine (produced in adrenal medulla)
iii. Dopamine (produced in hypothalamus…also produced in other places in the brain where it acts as a NT)
iv. All of these guys act like peptide hormones
B. Thyroid hormones (made from 2 tyrosines and iodine)
i. Produced in thyroid
ii. Act like steroid hormones
Peptide Hormones
If a hormone is not an AA derivative and it is not steroid, then it must be a peptide hormone.
1. Characteristics of peptide hormones
A. Soluble in blood
B. Many still use carrier proteins so they don’t get degraded en route to their target
2. Mechanism of action: second messenger mechanism (see visual analogy guide pg 242-243)
A. The hormone is “FIRST MESSENGER” and binds to a receptor on cell membrane
B. Receptor changes and activates a cascade of chemical reactions (proteins)
C. End product of the cascade is cAMP- cyclic adenosine monophosphate
D. cAMP is the “SECOND MESSENGER” that activates the specific enzymes that produce the cellular RESPONSE to the
original hormone
E. cAMP either diffuses out of the cell (stopping rxn) OR is deactivated by the cell…
3. Key Features
A. Because an activated cAMP keeps working in the cell, the action of a non-steroid hormone can be amplified greatly (small
amts of hormone can have BIG effects)
B. VERY VERY FAST reaction…
Pituitary and Hypothalamus
mm Anatomy link!
The hypothalamus is a portion of the brain that developed from the embryological diencephalon. It is the
priary integration center for the Autonomic Nervous System. The hypothalamus is physically attached to
the pituitary gland via a thin stalk called the infundibulum. The pituitary “gland” is actually composed of
two parts. The anterior pituitary gland is true endocrine tissue. The posterior pituitary gland is actually an
extension of neural tissue from the hypothalamus.
The pituitary gland sits in the sphenoid bone of the skull, in the depression called the sella turcica.
Bio 7: Human Physiology
16
Spring 2014: Riggs
Hypothalamus
1. Considered the “center for homeostasis”
A. Controls body temp
B. Thirst and urine output
2. Food intake
3. Autonomic integrating center (impacts smooth muscle, heart and exocrine glands)
4. Produces hormones stored in posterior pituitary (neurohypophysis)
A. oxytocin
B. vasopressin (antidiruretic hormone)
5. Produces hormones that stimulate the release of hormones produced in the anterior pituitary (adenohypophysis)
Note! A tropic (or trophic, according to your text) hormone is one that stimulates the release of another hormone somewhere else.
Therefore, the hypothalamus produces many TROPIC hormones.
A. These hormones travel through the hypothalamic-hypophyseal portal system (portal system: 2 sets of capillaries connected
by larger vessels)
B. Hormone isn’t diluted when it travels through the portal system
C. There are only 3 portal systems in the body...do you know where they are?
D. Tropic hormones produces in hypothalamus:
i. Prolactin RF(s) (releasing factors)
ii. Thyrotropin RH
iii. Corticotropin RH
iv. Growth hormone RH
v. Somatostatin
vi. Gonadotropin RH
Pituitary
1. Considered “master gland” of body
2. Secretes more hormones than any other gland
3. Consists of two parts.
A. Anterior (adenohypophysis)
i. True endocrine gland
ii. Produces 6 hormones
a. Prolactin
b. Thyrotropin (TSH)
c. Adrenocorticotropin
d. Growth hormone (somatotropin)
e. Follicle-stimulating hormone
f. Leuteinizing hormone
iii. Hypothalamus neurohormones regulate the secretion of these hormones.
B. Posterior (nuerohypophysis)
i. Extension of neural tissue from the hypothalamus
ii. Stores and releases 2 hormones (produced by the hypothalamus)
a. oxytocin
b. vasopressin (antidiruretic hormone)
iii. Neuron makes the hormone in the hypothalamus, then transports it down into the post.pit where it is STORED
iv. Nervous stimulation causes secretion
Bio 7: Human Physiology
17
Spring 2014: Riggs
External Brain 5: Endocrine System
Study Guide
1. Compare and contrast the endocrine system and the nervous system.
2. Define and describe the word HORMONE.
3. Compare and contrast the three different types of hormones.
4. Briefly compare and contrast catecholamines and thyroid hormones.
5. Clearly describe the general mechanism of action for a peptide (protein) hormone.
6. Clearly describe the general mechanism of action for a steroid hormone
7. Describe the anatomical relationship between the hypothalamus and the pituitary. (How are they related structurally? How
are they “connected”?)
8. Describe the anatomy of the pituitary gland.
9. What is a tropic (trophic) hormone? Be able to identify whether or not a hormone is considered “tropic”.
10.What is a “portal system”?
11. Describe the hypothalamic-hypophoseal portal system. What is the advantage of having a portal system in this location?
Bio 7: Human Physiology
18
Spring 2014: Riggs