●Testosterone causes muscle growth

●When overused (10-100 x normal therapeutic levels) it causes male-pattern muscle development in women...

Chemical Regulation of Homeostasis

1. Pheromones● organism to organism communication

(ex. amoeba, insects, people)

2. Hormones● cell to cell communication molecules● cells that secrete hormones are called

endocrine cells

Hormones

● In multicellular organisms the body communicates through electrical or chemical signals (phone vs. TV signal)

● Hormones are chemical messengers sent to many parts of the body to produce a specific effect on a target cell or organ

●Again, these are regulated using feedback loops

The Endocrine System

● In vertebrates, works in parallel with the nervous system to maintain homeostasis and coordinate function of cells

● Composed of hormone-producing glands and tissues of the body

● Uses chemical signals (hormones) for cell to cell communication

● Response to an endocrine signal occurs within minutes to hours

Endocrine Glands

Hormones can act locally or at a distance1. Circulating Hormones● Travel through the blood to act at a site distant

from the secreting cell or gland● Most hormones

2. Paracrine Hormones ● Act on cells near the secreting cell● local communication

3. Autocrine Hormones

- Act on the secreting cell

4. Neurocrine Hormones

- Secreted by neural cells

Figure 6-2b, c: Long distance cell-to-cell communication

Neurocrine Hormones

● All hormones will travel from their secreting cell, to the target cell

● The target cell will react to the hormone when it binds to a receptor

Receptor locations

Figure 6-4: Target cell receptors

a) intracellular receptors: Cytosolic or Nuclear• Lipophilic hormone enters cell• Often activates gene• Slower response

b) cell membrane receptors• Lipophobic hormone can't enter cell• Outer surface receptor• Fast response

Types of Hormones1. Protein & Polypeptide

- water-soluble, tend to bind surface receptors

2. Amine (amino acid derived)

3. Steroid

- fat-soluble, tend to bind intracellular receptors

1. Protein and Polypeptide Hormones: a) Synthesis and Release

Figure 7-3: Peptide hormone synthesis, packaging, and release

● Same as for any protein that is made for export from the cell

● Because the hormones are water-soluble they are released by exocytosis

● peptide hormones bind to cell surface receptor

● signal from hormone is amplified and sent through the cell (signal transduction)

– open ion channel– activate enzymes

● use second messenger systems

● can lead to protein synthesis

B) mechanism of action

Figure 7-5: Membrane receptors for peptide hormones

...tend to greatly amplify effect, AND have a different effect on different target cells ex. Epinephrine- one molecule of epinephrine in the liver can trigger conversion of glycogen into one million molecules of glucose

- it also leads to vasoconstriction, dilation of airways, suppressed immune function, and elevated heart rate...”fight or flight response”

2. Amine Hormones

● Derived from the amino acid tyrosine

● Includes thyroid hormones and catecholamines (epinephrine, norepinephrine, dopamine)

● Stored until secreted or released, depending on hormone

● Receptors can be on cell surface or intracellular

Amine Hormone Structure

Figure 7-8: Tyrosine-derived amine hormones

● Are made from cholesterol, are lipophilic & can enter target cell

● Are immediately released from cell after synthesis

● Interact with cytoplasmic or nuclear receptors

3. Steroid Hormonesa) structure and receptors

● Activate DNA for protein synthesis

● Are slower acting and have longer half-life than peptide hormones

● Examples: cortisol, estrogen & testosterone

Figure 7-6: Steroid hormones are derived from cholesterol

b) mechanism of action

b) mechanism of action

● Diffuse through lipid bilayer● Bind to intracellular receptor proteins● Activate specific genes, ex. estrogen

can trigger cell growth

Regulating the Regulators: Feedback Loops

Figure 6-26: Negative and positive feedback

● The hypothalamus will release tropic hormones (releasing hormones) to act on the pituitary gland

● The pituitary will release a second tropic hormone that will act on other endocrine glands to stimulate hormone release

● This third hormone will target the specific tissue AND stop further release of the two tropic hormones

Endocrine Feedback Pathways: Overview

Figure 7-9: Hormones may have multiple stimuli for their release

sends signal to pituitary(releasing hormone/tropic hormone)

pituitary releases a tropic hormone

to target adrenal gland/tissue

target gland releases hormone

hypothalamus detects change

hormone has an effectand shuts down

tropic hormone release

Summary of the Endocrine System

Figure 7-2-1: ANATOMY SUMMARY: Hormones

Summary of the Endocrine System

Figure 7-2-2: ANATOMY SUMMARY: Hormones

Summary of the Endocrine System

Figure 7-2-3: ANATOMY SUMMARY: Hormones

● Endocrine glands throughout body are key to chemical integration and homeostasis

● Protein, polypeptide, amine and a few steroid hormones are plasma soluble and target membrane

● Surface receptors transduce signals into cell and activate via second messengers

Summary

● Most steroid and some amine hormones are lipophilic, can pass into cell, bind on cytoplasmic or nuclear receptors and activate DNA for protein synthesis

● The hypothalamus and pituitary hormone pathways coordinate endocrine regulation