Endocrine Control Chapter 26

Endocrine System Major Components Hypothalamus Pituitary gland Pineal gland Thyroid gland Parathyroid glands Thymus gland Adrenal glands Pancreatic islets Ovaries Testes

hypothalamus (part of the brain) pineal gland pituitary gland, anterior lobe pituitary gland, posterior lobe thyroid gland parathyroid glands (four) thymus gland adrenal gland (one pair) cortex medulla pancreatic islets ovaries (one pair of female gonads) testes (one pair of male gonads) Fig. 26-1, p.449

Hormones Secreted by endocrine glands, endocrine cells, and hypothalmic neurons Travel through bloodstream to target cells Bind to receptors on target cells

Other Signaling Molecules Neurotransmitters From axon endings of neurons Local signaling molecules Prostaglandins Nitric oxide (NO)

Three-Step Hormonal Action Activation of a receptor as it binds the hormone Transduction of signal into a molecular form that can work inside the cell Functional response of target cell signal reception signal transduction cellular response

Responses to Hormones Vary Different hormones activate different responses in the same target cell Not all types of cells respond to a particular hormone

Main Hormone Types Steroid hormones Peptide hormones Amine hormones Lipids derived from cholesterol Peptide hormones A few amino acids Amine hormones Modified amino acids Protein hormones Longer amino acid chains

Receptors Intracellular Plasma membrane Steroid hormones Diffuse across plasma membrane Plasma membrane Peptides and proteins Too big or polar to diffuse Second messengers (cAMP)

hormone-receptor complex Steroid Hormones hormone Most diffuse across the plasma membrane and bind to a receptor Hormone-receptor complex acts in nucleus to inhibit or enhance transcription receptor hormone-receptor complex gene product

hormone-receptor complex A steroid hormone molecule moves from the blood into interstitial fluid that bathes a target cell. 1 2 Being a lipid-soluable molecule, the steroid hormone diffuses across the target cell’s plasma membrane. The hormone diffuses through the cytoplasm, then on through the nuclear envelope. Inside the nucleus, it will bind with a receptor molecule. 3 5 The mRNA transcript moves from the nucleus into the cytoplasm. There it becomes translated into a gene product that is required for the response to the hormone signal. receptor Now the hormone-receptor complex triggers transcription of gene regions in the DNA. 4 hormone-receptor complex gene product Fig. 26-2a, p.451

Peptide Hormone Hormone binds to a receptor at cell surface glucagon Hormone binds to a receptor at cell surface Binding triggers a change in activity of enzymes inside the cell glucagon receptor cyclic AMP + Pi ATP The cAMP activates protein kinase A. Protein kinase A converts phosphorylase kinase to active form and inhibits an enzyme required for glucagon synthesis.

unoccupied glucagon receptor at target cell’s plasma membrane A glucagon molecule diffuses from blood into the interstitial fluid that bathes the plasma membrane of a liver cell. 1 unoccupied glucagon receptor at target cell’s plasma membrane cyclic AMP +Pi ATP Glucagon binds with the receptor, and the binding activates adenylate cyclase. This enzyme catalyzes the formation of cAMP inside the target cell. 2 The cAMP now activates protein kinase A. 3 Protein kinase A converts phosphorylase kinase to active form. This enzyme activates a different enzyme, which breaks down glycogen to its glucose monomers. 4 Protein kinase A also inhibits an enzyme required for synthesis of glycogen. 5 Fig. 26-2b, p.451

Hypothalamus and Pituitary Glands in brain Structurally and functionally linked Master integrating center for endocrine and nervous systems Hypothalmic neurons produce Neurotransmitters Hormones

Pituitary Gland Pea-sized gland at base of hypothalamus Two lobes Posterior lobe stores and releases hormones made in hypothalamus Anterior lobe produces and secretes its own hormones

Posterior Pituitary Secretions cell body in hypothalamus Antidiuretic hormone (ADH) Oxytocin (OCT) axons to the general circulation

Cell bodies in hypothalamus synthesize ADH or oxytocin cell body axon capillaries Cell bodies in hypothalamus synthesize ADH or oxytocin ADH, oxytocin move down axons, accumulate in axon endings Action potentials cause release of hormones, which capillaries pick up Small vessels carry hormones to general circulation Stepped Art Fig. 26-3, p.452

a muscles in uterus wall b c nephrons in kidneys d Cell bodies of secretory neurons in hypothalamus synthesize ADH or oxytocin. a muscles in uterus wall The ADH or oxytocin moves downward inside the axons of the secretory neurons and accumulates in the axon endings. b oxytocin mammary glands Action potentials trigger the release of these hormones, which enter blood capillaries in the posterior lobe of the pituitary. c ADH nephrons in kidneys Small blood vessels deliver the hormone molecules to the general circulation. d Fig. 26-3, p.452

Anterior Pituitary Responds to hypothalmic signals Releasers Stimulate secretion of pituitary hormones Inhibitors Inhibit release of pituitary hormones

Anterior Pituitary Secretions Adrenocorticotropin (ACTH) Thyroid stimulating hormone (TSH) Follicle-stimulating hormone (FSH) Luteinizing hormone (LH) Prolactin (PRL) Growth hormone (GH)

most cells (growth-promoting effects) Cell bodies of different secretory neurons in the hypothalamus secrete releasing and inhibiting hormones. a The hormones are picked up by a capillary bed at the base of the hypothalamus. b Bloodstream delivers hormones to a second capillary bed in anterior lobe of pituitary. c Hormones secreted from anterior lobe cells enter small blood vessels that lead to the general circulation. e Molecules of the releasing or inhibiting hormone diffuse out of capillaries and act on endocrine cells in the anterior lobe. d ACTH TSH FSH LH PRL GH (STH) most cells (growth-promoting effects) adrenal glands thyroid gland testes in males ovaries in females mammary glands Fig. 26-4, p.453

Abnormal Pituitary Output Pituitary gigantism Pituitary dwarfism Acromegaly

Abnormal Pituitary Outputs

Thymus, Thyroid and Parathyroid Immune function Thyroid Development and metabolism Regulated by feedback loops Parathyroid Calcium levels

Negative Feedback and Thyroid Function Stimulus Response Hypothalamus – Blood level of thyroid hormone falls below a set point. + TRH – Anterior Pituitary Rise in the blood level of thyroid hormone inhibits secretion of TRH and TSH. TSH Thyroid Gland Thyroid hormone is secreted

Thyroid Function Requires mineral iodine Deficiency causes goiter

Parathyroid and Calcium Parathyroid hormone (PTH) regulates blood calcium secreted when calcium levels drop causes bone cells to release calcium from bone tissue stimulates calcium reabsorption by kidneys

Calcium and Vitamin D Without vitamin D, not enough calcium is absorbed Low blood calcium causes oversecretion of PTH Breaks down existing bone Causes rickets

Adrenal Glands and Stress Adrenal cortex secretes cortisol and aldosterone Negative feedback maintains blood cortisol levels

Negative Feedback Control of Adrenal Glands – Stimulus Hypothalamus Response Blood level of cortisol falls below a set point a + CRH b – Anterior Pituitary adrenal cortex ACTH adrenal medulla Both the hypothalamus and pituitary detect rise in blood level of cortisol and slow its further secretion. f Adrenal Cortex Cortisol is secreted, with these effects: Cellular uptake of glucose from blood slows in many tissues, especially muscles (not the brain). c d Proteins degraded in many tissues, especially in muscles. The free amino acids are converted to glucose and used in the assembly or repair of cell structures. kidney e Fats in adipose tissue degraded to fatty acids that enter blood as an alternative energy source, indirectly conserving glucose for the brain.

Stress Response Stress can cause nervous system to override feedback loop Cortisol levels rise above normal, suppress inflammation Persistent high cortisol levels may harm health

The Pancreas and Glucose Homeostasis stomach pancreas small intestine

Pancreatic Hormones and Glucose Balance Glucagon Secreted by alpha cells in islets Raises blood glucose level Insulin Secreted by beta cells in islets Lowers blood glucose level Somatostatin Secreted by delta cells Blocks insulin and glucagon secretion

Increase in blood glucose Decrease in blood glucose Stimulus a f Stimulus Increase in blood glucose Decrease in blood glucose PANCREAS b alpha cells c beta cells g alpha cells h beta cells – + + – insulin glucagon glucagon insulin LIVER Cells in liver break down glycogen faster. The released glucose monomers enter blood. i MUSCLE FAT CELLS Body cells, especially in muscle and adipose tissue, take up and use more glucose. Cells in skeletal muscle and liver store glucose in the form of glycogen. d j Response Increase in blood glucose e Response Decrease in blood glucose Fig. 26-9, p.456

Excess glucose accumulates Diabetes Mellitus Excess glucose accumulates Type 1 Autoimmune disease Usually appears in childhood Insulin injections Type 2 Target cells don’t respond Usually appears in adults Diet, drugs

Table 26-2, p.457

Sex Hormones Testes and ovaries synthesize the same sex hormones in different amounts Estrogens Progesterone Testosterone Influence sexual traits

The Pineal Gland Photosensitive gland embedded in brain In absence of light, secretes melatonin Influences seasonal behaviors Affects human biological clock sleep-wake cycles seasonal affective disorder

Deformed Frogs Something in water triggers deformities Problem thyroid function? Tadpoles from “hotspots” developed normally when given extra thyroid hormones UV, parasites also play a role

Effects of Pollution on Frogs

Table 26-3, p.459