● Testosterone causes muscle growth ● When overused ( 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 distance 1. 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 Hormones 1. 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 Hormones a) 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

● 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 effect and 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