What role do hormones play in transforming a caterpillar into a butterfly? Figure 45.1 For the Discovery Video Endocrine System, go to Animation and Video Files.

Intercellular communication by secreted molecules Blood vessel Response (a) Endocrine signaling Response (b) Paracrine signaling Response (c) Autocrine signaling Synapse Neuron Figure 45.2 Response (d) Synaptic signaling Neurosecretory cell Blood vessel Response (e) Neuroendocrine signaling

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

Receptor location varies with hormone type 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)

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

Steroid hormone receptors are inside the cell and directly regulate gene expression Hormone (estradiol) Estradiol (estrogen) receptor Plasma membrane Hormone-receptor complex Figure 45.7 DNA Vitellogenin mRNA for vitellogenin

Same receptors but different intracellular proteins One hormone, different effects Same receptors but different intracellular proteins Different receptors Epinephrine Epinephrine Epinephrine Epinephrine  receptor  receptor  receptor  receptor Glycogen deposits Vessel dilates. Vessel constricts. Glycogen breaks down and glucose is released. Figure 45.8 (a) Liver cell (b) Skeletal muscle blood vessel (c) Intestinal blood vessel

Specialized role of a hormone in frog metamorphosis (b) Figure 45.9

Major endocrine glands: Hypothalamus Pineal gland Pituitary gland Organs containing endocrine cells: Thyroid gland Thymus Parathyroid glands Heart Liver Adrenal glands Stomach Figure 45.10 Major human endocrine glands Pancreas Testes Kidney Kidney Small intestine Ovaries

A simple endocrine pathway Example – Stimulus Low pH in duodenum S cells of duodenum secrete secretin ( ) Endocrine cell Negative feedback Blood vessel Figure 45.11 Target cells Pancreas Response Bicarbonate release

Maintenance of glucose homeostasis by insulin and glucagon Body cells take up more glucose. Insulin Beta cells of pancreas release insulin into the blood. Liver takes up glucose and stores it as glycogen. STIMULUS: Blood glucose level rises. Blood glucose level declines. Homeostasis: Blood glucose level (about 90 mg/100 mL) Figure 45.12 Maintenance of glucose homeostasis by insulin and glucagon STIMULUS: Blood glucose level falls. Blood glucose level rises. Alpha cells of pancreas release glucagon. Liver breaks down glycogen and releases glucose. Glucagon

Hormonal regulation of insect development Brain Neurosecretory cells Corpus cardiacum PTTH Corpus allatum Low JH Prothoracic gland Ecdysone Juvenile hormone (JH) Figure 45.13 EARLY LARVA LATER LARVA PUPA ADULT

Endocrine glands in the human brain Cerebrum Thalamus Pineal gland Hypothalamus = brain Cerebellum Pituitary gland Spinal cord Endocrine glands in the human brain Figure 45.14 Hypothalamus Posterior pituitary Anterior pituitary

Table 45.1

Table 45.1

A simple neurohormone pathway Example Stimulus Suckling + Sensory neuron Hypothalamus/ posterior pituitary Neurosecretory cell Posterior pituitary secretes oxytocin ( ) Positive feedback Blood vessel Figure 45.16 Target cells Smooth muscle in breasts Response Milk release

Liver, bones, other tissues Production and release of anterior pituitary hormones Tropic effects only: FSH LH TSH ACTH Neurosecretory cells of the hypothalamus Nontropic effects only: Prolactin MSH Nontropic and tropic effects: GH Hypothalamic releasing and inhibiting hormones Portal vessels Endocrine cells of the anterior pituitary Posterior pituitary Pituitary hormones Figure 45.17 HORMONE FSH and LH TSH ACTH Prolactin MSH GH TARGET Testes or ovaries Thyroid Adrenal cortex Mammary glands Melanocytes Liver, bones, other tissues

A hormone casade pathway Figure 45.18 A hormone cascade pathway Example A hormone casade pathway Stimulus Cold Sensory neuron – Hypothalamus secretes thyrotropin-releasing hormone (TRH ) Neurosecretory cell Blood vessel – Anterior pituitary secretes thyroid-stimulating hormone (TSH or thyrotropin ) Negative feedback Figure 45.18 A hormone cascade pathway Thyroid gland secretes thyroid hormone (T3 and T4 ) Target cells Body tissues Increased cellular metabolism Response

Falling blood Ca2+ level Blood Ca2+ level (about 10 mg/100 mL) Antagonistic Hormone Pairs control blood calcium levels Active vitamin D Stimulates Ca2+ uptake in kidneys Increases Ca2+ uptake in intestines PTH Parathyroid gland (behind thyroid) Stimulates Ca2+ release from bones Figure 45.20 The roles of parathyroid hormone (PTH) in regulating blood calcium levels in mammals STIMULUS: Falling blood Ca2+ level Blood Ca2+ level rises. Homeostasis: Blood Ca2+ level (about 10 mg/100 mL)

Summary: Stress and the Adrenal Gland Nerve signals Hypothalamus Spinal cord Releasing hormone Nerve cell Anterior pituitary Blood vessel ACTH Adrenal medulla Adrenal cortex Adrenal gland Kidney (a) Short-term stress response Figure 45.21 Stress and the adrenal gland (b) Long-term stress response Effects of epinephrine and norepinephrine: Effects of mineralocorticoids: Effects of glucocorticoids: 1. Glycogen broken down to glucose; increased blood glucose 2. Increased blood pressure 3. Increased breathing rate 4. Increased metabolic rate 1. Retention of sodium ions and water by kidneys 1. Proteins and fats broken down and converted to glucose, leading to increased blood glucose 5. Change in blood flow patterns, leading to increased alertness and decreased digestive, excretory, and reproductive system activity 2. Increased blood volume and blood pressure 2. Possible suppression of immune system

Signal Transduction Pathway Example – Stimulus Low blood glucose Pancreas alpha cells secretes glucagon Endocrine cell Negative feedback Blood vessel Target cells Liver Glycogen breakdown, glucose release into blood Response

You should now be able to: Distinguish between the following pairs of terms: hormones and local regulators, paracrine and autocrine signals. Describe the evidence that steroid hormones have intracellular receptors, while water-soluble hormones have cell-surface receptors. Explain how the antagonistic hormones insulin and glucagon regulate carbohydrate metabolism. Distinguish between type 1 and type 2 diabetes.

Explain how the hypothalamus and the pituitary glands interact and how they coordinate the endocrine system. Explain the role of tropic hormones in coordinating endocrine signaling throughout the body. List and describe the functions of hormones released by the following: anterior and posterior pituitary lobes, thyroid glands, parathyroid glands, adrenal medulla, adrenal cortex, gonads, pineal gland.