Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings PowerPoint ® Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Cells communicate with each other through direct contact with other cells or from a distance via chemical signaling. Cell Signaling and the Endocrine System

Overview: The Body’s Long Distance Regulators Animal hormones are chemical signals that are secreted into the circulatory system and communicate regulatory messages within the body – Hormones reach all parts of the body, but only target cells are equipped to respond Two systems coordinate communication throughout the body: the endocrine system and the nervous system – The endocrine system secretes hormones that coordinate slower but longer-acting responses including reproduction, development, energy metabolism, growth, and behavior – The nervous system conveys high-speed electrical signals along specialized cells called neurons; these signals regulate other cells Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Concept 45.1: Hormones and other signaling molecules bind to target receptors, triggering specific response pathways. Chemical signals bind to receptor proteins on target cells, and cells with these receptors are the only ones in the body equipped to respond to the signal. Secreted chemical signals include – Hormones – Local regulators – Neurotransmitters – Neurohormones – Pheromones

Hormones Endocrine signals (hormones) are secreted into extracellular fluids and travel via the bloodstream Endocrine glands are ductless and secrete hormones directly into surrounding fluid Hormones mediate responses to environmental stimuli and regulate growth, development, and reproduction

Fig Blood vessel Response (a) Endocrine signaling (b) Paracrine signaling (c) Autocrine signaling (d) Synaptic signaling Neuron Neurosecretory cell (e) Neuroendocrine signaling Blood vessel Synapse Response

Water and lipid soluble hormones differ in their paths through a body: – Water-soluble hormones are secreted by exocytosis, travel freely in the bloodstream, and bind to cell-surface receptors – Lipid-soluble hormones diffuse across cell membranes, travel in the bloodstream bound to transport proteins, and diffuse through the membrane of target cells Water and Lipid Soluble Hormones

Fig Signal receptor TARGET CELL Signal receptor Transport protein Water- soluble hormone Fat-soluble hormone Gene regulation Cytoplasmic response Gene regulation Cytoplasmic response OR (a) NUCLEUS (b)

Pathway for Water-Soluble Hormones Binding of a water-soluble hormone to its receptor initiates a signal transduction pathway leading to responses in the cytoplasm, enzyme activation, or a change in gene expression Example: cell-surface hormone receptors for epinephrine and the body’s response to short- term stress.

Fig cAMP Second messenger Adenylyl cyclase G protein-coupled receptor ATP GTP G protein Epinephrine Inhibition of glycogen synthesis Promotion of glycogen breakdown Protein kinase A

Pathway for Lipid-Soluble Hormones The response to a lipid-soluble hormone is usually a change in gene expression Steroids, thyroid hormones, and the hormonal form of vitamin D enter target cells and bind to protein receptors in the cytoplasm or nucleus Protein-receptor complexes then act as transcription factors in the nucleus, regulating transcription of specific genes Example: estradiol activates transcription factors that lead to the production of yolk.

Fig Hormone (estradiol) Hormone-receptor complex Plasma membrane Estradiol (estrogen) receptor DNA Vitellogenin mRNA for vitellogenin

Multiple Effects of Hormones The same hormone may have different effects on target cells that have – Different receptors for the hormone – Different signal transduction pathways – Different proteins for carrying out the response A hormone can also have different effects in different species

Fig Glycogen deposits  receptor Vessel dilates. Epinephrine (a) Liver cell Epinephrine  receptor Glycogen breaks down and glucose is released. (b) Skeletal muscle blood vessel Same receptors but different intracellular proteins (not shown) Epinephrine  receptor Different receptors Epinephrine  receptor Vessel constricts. (c) Intestinal blood vessel

Concept 45.2: Negative feedback and antagonistic hormone pairs are common features of the endocrine system. Hormones are assembled into regulatory pathways Hormones are released from an endocrine cell, travel through the bloodstream, and interact with the receptor or a target cell to cause a physiological response A negative feedback loop inhibits a response by reducing the initial stimulus Negative feedback regulates many hormonal pathways involved in homeostasis

Fig PathwayExample Stimulus Low pH in Duodenum: acidic stomach contents released to duodenum serve a stimulus Endocrine S cells of duodenum are stimulated to secrete secretin (red dots) Endocrine cell Blood vessel Pancreas is stimulated to release bicarbonate Target cells Response Bicarbonate release raises pH in duodenum which limits pathway because raise in pH shuts down secretin production Negative feedback – Secretin hormone enters bloodstream and reaches target cells in pancreas

Insulin and Glucagon: Control of Blood Glucose Signals released by one cell type can travel long distances to target cells of another cell type. Endocrine signals are produced by endocrine cells that release signaling molecules, which are specific and can travel long distances through the blood to reach all parts of the body. Insulin and glucagon are antagonistic hormones that help maintain glucose homeostasis The pancreas has clusters of endocrine cells with alpha cells that produce glucagon and beta cells that produce insulin

Fig Homeostasis: Blood glucose level (about 90 mg/100 mL) Glucagon STIMULUS: Blood glucose level falls. Alpha cells of pancreas release glucagon. Liver breaks down glycogen and releases glucose. Blood glucose level rises. STIMULUS: Blood glucose level rises. Beta cells of pancreas release insulin into the blood. Liver takes up glucose and stores it as glycogen. Blood glucose level declines. Body cells take up more glucose. Insulin

Diabetes Mellitus Changes in signal transduction pathways can alter cellular responses. Conditions where signal transduction is blocked or defective can be deleterious. – Diabetes mellitus is perhaps the best-known endocrine disorder – It is caused by a deficiency of insulin or a decreased response to insulin in target tissues – It is marked by elevated blood glucose levels