Honours Unit 1

Endocrine system

• Acts with nervous system to coordinate/integrate activity of body cells

• Influences metabolic activities via hormones transported in blood

• Responses lslower but longer lasting than nervous system reponses

Endocrinology

Study of hormones and endocrine organs

Exocrine glands

Produces nonhormal substances

ex: sweat, saliva

Have ducts to carry secretion to membrane surface

Endocrine glands

Produces hormones

Lacks ducts

Hypothalamus

Neroendocrine organ and master regulator

In charge of other endocrine organs

Hormones

Long-distance chemical signals; travel in blood or lymph

Amino acid-based hormones

Amino acid dervatives, peptides, and protein

Steroids

Synthesized from cholesterol

Water-soluble hormones

• Act on plasma membrane receptors

• Act via G protein second messengers

• Cannot enter cell

• All amino acid-based hormones except thyroid hormone

Lipid-soluble hormones

• Act on intracellular receptors that directly activate genes

• Can enter cell

Second-messenger systems

Amino acid-based hormones, except thyroid hormone, exert effects through __.

Cyclic AMP signaling mechanism

1. Hormone (first messenger) binds to receptor

2. Receptor activates a G protein

3. G protein activates or inhibits effector enzyme adenylate cyclase

4. Adenylate cyclase converts ATP to cAMP (second messenger)

5. cAMP activates protein kinases that phosphorylate (add a phosphate) other protein

Phosphorylated proteins are either activated or inactivated

First messenger

Hormone

Intracellular Receptors

Inside the cell’s cytoplasm and binds to hydrophobic molecules

Lipid-soluble steroid hormones and thyroid hormone can diffuse into target cells and bind with __.

Acts as a transcription —> binds specific region of DNA to initiate transcription to produce mRNA

negative feedback systems

Blood levels of hormones is controlled by __.

Humoral Stimulus

Hormone release caused by altered levels of certain critical ions or nutrients

Changing blood levels of ions and nutrients directly stimulate secretion of hormones

Neural Stimulus

Hormone released caused by neural input

Nerve fibers stimulate hormone release

Hormonal Stimulus

Hormone release caused by another hormone (a tropic hormone)

Hormones stimulate other endocrine organs to release their hormones

Up-regulation

Target cells from more receptors in response to low hormone levels

Down-regulation

Target cells lose receptors in response to high hormone levels