Hormones & the Endocrine System A hormone is a chemical signal that is dumped into the bodies circulatory system – Blood or lymph – Effects a great many receptors Target cells are specific to hormone type – Excreted by the endocrine system through endocrine glands Some hormones such as epinephrine are secreted by neurosecretory cells

Control Pathways Efferent Pathway – Stimulus causes the release of the efferent signal (hormone) – The efferent signal acts on the target eliciting a response Controlled by a negative feedback loop – Response reduces the stimulus causing the release of the signal to stop Positive feedback loops are rare and not generally used to maintain homeostasis – Suckling and milk production are an example

Water Soluble Hormones Polypeptides and Amines – Reception depends on binding to a cell surface protein Based on conformation Causes signal transduction

Fat Soluble Hormones Steroids – Pass through the plasma membrane Most receptors are located in the nucleus – Most are non-polar and are responsible for the transduction response » Involves the release of transcription factors in most cases

Paracrine Signaling Creates a local response – Cytokines Immune response – Growth factors Cell division – Prostaglandins Inflammatory response