Hormones and the Endocrine system Chapter 45 Hormones 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. Insect metamorphosis and many other processes are regulated by hormones. P.S. – Plants have hormones too

Overview: continued… 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.

Hormones trigger specific responses Chemical signals bind to receptor proteins on target cells. Only target cells respond to the signal.

Types of Secreted Signaling Molecules Secreted chemical signals include: Hormones Local regulators Neurotransmitters Neurohormones Pheromones

What is a Hormone? Endocrine chemicals secreted into extracellular fluids and travel in 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.

(a) Endocrine signaling Fig. 45-2a Blood vessel Response (a) Endocrine signaling Response Figure 45.2 Intercellular communication by secreted molecules (b) Paracrine signaling Response (c) Autocrine signaling

Not all Glands are Endocrine. Exocrine glands have ducts and secrete substances onto body surfaces or into body cavities (for example, tear ducts).

Local Regulators Local regulators are chemical signals that travel over short distances by diffusion. Local regulators help regulate blood pressure, nervous system function, and reproduction. Local regulators are divided into two types: Paracrine signals act on cells near the secreting cell Autocrine signals act on the secreting cell itself

(a) Endocrine signaling Fig. 45-2a Blood vessel Response (a) Endocrine signaling Response Figure 45.2 Intercellular communication by secreted molecules (b) Paracrine signaling Response (c) Autocrine signaling

Neurotransmitters and Neurohormones Neurons (nerve cells) contact target cells at synapses. Neurons secrete chemical signals called neurotransmitters that diffuse a short distance across the synapse to bind to receptors on the target cell.

(d) Synaptic signaling Fig. 45-2b Synapse Neuron Response (d) Synaptic signaling Neurosecretory cell Figure 45.2 Intercellular communication by secreted molecules Blood vessel Response (e) Neuroendocrine signaling

Neurohormones: Are a class of hormones that originate from neurons in the brain and diffuse through the bloodstream. Endorphins are an example.

(d) Synaptic signaling Fig. 45-2b Synapse Neuron Response (d) Synaptic signaling Neurosecretory cell Figure 45.2 Intercellular communication by secreted molecules Blood vessel Response (e) Neuroendocrine signaling

Pheromones Pheromones - chemical signals that are released from the body and used to communicate with other individuals in the species. Pheromones are “outside” the body. Pheromones - mark trails to food sources, warn of predators, and attract potential mates.

Chemical Classes of Hormones Three major classes of molecules function as hormones in vertebrates: Polypeptides (proteins and peptides) Amines derived from amino acids Steroid hormones

Classes and properties of hormones The solubility of a hormone correlates with the location of receptors inside or on the surface of target cells. Lipid-soluble hormones (steroid hormones) pass easily through cell membranes, while water-soluble hormones (polypeptides and amines) do not.

Polypeptide: Insulin Amine: Epinephrine Amine: Thyroxine Fig. 45-3 Water-soluble Lipid-soluble 0.8 nm Polypeptide: Insulin Steroid: Cortisol Figure 45.3 Hormones differ in form and solubility Amine: Epinephrine Amine: Thyroxine

Cellular Response Pathways 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.

Cell Signaling: Signaling by any of these hormones involves three key events: Reception Signal transduction Response

Water- soluble hormone Fat-soluble hormone Transport protein Fig. 45-5-1 Water- soluble hormone Fat-soluble hormone Transport protein Signal receptor TARGET CELL Signal receptor Figure 45.5 Receptor location varies with hormone type (a) NUCLEUS (b)

Water- soluble hormone Fat-soluble hormone Transport protein Fig. 45-5-2 Water- soluble hormone Fat-soluble hormone Transport protein Signal receptor TARGET CELL OR Signal receptor Figure 45.5 Receptor location varies with hormone type Cytoplasmic response Gene regulation Cytoplasmic response Gene regulation (a) NUCLEUS (b)

Water soluble example: The hormone epinephrine has multiple effects in mediating the body’s response to short-term stress. Epinephrine binds to receptors on the plasma membrane of liver cells. This triggers the release of messenger molecules that activate enzymes and result in the release of glucose into the bloodstream.

G protein-coupled receptor Fig. 45-6-1 Epinephrine Adenylyl cyclase G protein G protein-coupled receptor GTP ATP Second messenger cAMP Figure 45.6 Cell-surface hormone receptors trigger signal transduction

Epinephrine Adenylyl cyclase G protein GTP G protein-coupled receptor Fig. 45-6-2 Epinephrine Adenylyl cyclase G protein G protein-coupled receptor GTP ATP Second messenger cAMP Figure 45.6 Cell-surface hormone receptors trigger signal transduction Protein kinase A Inhibition of glycogen synthesis Promotion of glycogen breakdown

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.

Hormone (estradiol) Estradiol (estrogen) receptor Plasma membrane Fig. 45-7-1 Hormone (estradiol) Estradiol (estrogen) receptor Plasma membrane Hormone-receptor complex Figure 45.7 Steroid hormone receptors directly regulate gene expression

Hormone (estradiol) Estradiol (estrogen) receptor Plasma membrane Fig. 45-7-2 Hormone (estradiol) Estradiol (estrogen) receptor Plasma membrane Hormone-receptor complex Figure 45.7 Steroid hormone receptors directly regulate gene expression 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.

Negative feedback and antagonistic hormone pairs are common features of the endocrine system Hormones are assembled into regulatory pathways. Feedback loops are commonly used. Hormones are often arranged in pairs that work against each other. Blood sugar regulation and calcium deposition in bones are common test examples.