APII Notes Home Page

Endocrine System:

Hormones and How They Work

glands of the endocrine system

http://biology.clc.uc.edu/courses/bio105/endocrin.htm

I). Definitions

A). Endocrine System:

B). Hormone:

Steroidal or amino acid based molecules released to the blood that act as chemical messengers to regulate specific body functions by influencing the metabolic activities of cells.

Tropic hormones:

C). Endocrine Glands:

            exocrine glands:

II). Summary of Hormonal Effects

A). Alters membrane permeability

B). Stimulates proteins.

C). Activates/deactivates enzymes

D). Secretory activity

E).  Mitosis

III). Hormone Specificity

A). Definitions

i). Target Cells:

ii). Receptor:

B). Are hormones directional?

i). Hormones are not directed to any specific tissue

ii). Hormones are released through out the body.

iii). Some receptors can be found in only certain glands and organs.

C). Factors that affect hormone-receptor interaction

i). Blood levels of the hormone.

ii). Relative number of receptors

iii). The affinity or strength of the bond

 

IV).  Control of Hormone Levels

A).  Duration

 
B).  Hormone release

1).  Hormonal Stimuli

 

2).  Humoral Stimuli

 

3) Neural Stimuli

 

 Endocrine control
C).  Feed back loops

        receptor

        control

        effector

 

  
1).  negative feedback loop

Release of product prevents the release of more product

 
2).  positive feedback loop

Release of product increases the release of more product

 

V).   Hormone Classification (by structure)

LIPOPHOBIC: Lipid ‘fearing’; cannot enter the lipid  membrane

A).  Amines

1. Amino Acid

2.  Peptides

3.  Proteins

4.  glycoproteins (proteins with sugar)

LIPOPHILIC: Lipid ‘loving’; can pass through the lipid membrane

B).  Steroids

C).  Prostaglandins 

 

VI.  Mechanisms Of Hormonal Activity

A). Steroid Hormones

  • Hydrophobic (not water soluble)
  • Receptors in the nucleus and on DNA
  • Function to change protein synthesis
  • Mechanism: Direct Messenger or Direct Gene Activation 
  1. Diffuses through the membrane
  2. Binds & activates nuclear receptor
  3. Activates a gene.
  4. Transcribes and translates into proteins

 

 Steriod Hormones
B). Non Steroid Hormones: Proteins and Peptides
  • Hydrophilic (water soluble)
  • Receptors: on the plasma membrane
  • Mechanism: Second Messenger

Non-steroid hormones-proteins and peptide  (water soluble hormones) do not enter the cell but bind to plasma membrane receptors, generating a chemical signal (second messenger) inside the target cell.

 Five different second messenger chemicals, including cyclic AMP have been identified.
Second messengers activate other intracellular chemicals to produce the target cell response.

Action

  1. Hormone binds with the receptor protein

  2. Activates the G protein which splits GTP->GDP

  3. Activates effector enzymes

  4. Activates Second Messenger

  5. Metabolic Responses Triggered

Non Steroid Hormones: Proteins and Peptides

cyclic AMP mechanism as Second Messenger

PIP-Calcium mechanism as Second Messenger

(Ca++ functions as a third messenger)
Protein Hormones Second Messeinger
C). Prostaglandins

Lipid substances that are present in very small quantities and are not stored in cells but synthesized just before release

effects include:

•Signal nearby cells and tissues and act locally
•Regulate cellular responses to hormone
•Alters a cells response to hormone
•Rapidly inactivate