Chapter 40 The endocrine system

Learning Objectives Define Hormones List and explain the process of the 4 major pathways of endocrine signaling List and define the 4 common classes of chemicals used for endocrine signaling Compare and contrast hydrophilic and hydrophobic hormones Explain the roles of the hypothalamus and the pituitary gland in the body

40.1 Hormones and Their Secretion Endocrine system includes four major types of cell signaling Hormones and local regulators are grouped into four classes based on their chemical structure Hormones are regulated by feedback pathways Body processes are regulated by coordinated hormone secretion

Hormones Substances secreted by cells that control the activities of cells elsewhere in the body Target cells respond to a specific hormone Endocrine system secretes the best-known hormones

4 Major types of signaling Classical Endocrine Neuroendocrine Paracrine Autocrine

4 Major Types of Cell Signaling Classical endocrine signaling: Endocrine glands secrete hormones

4 Major Types of Cell Signaling 2. Neuroendocrine signaling: Neurosecretory neurons release neurohormones into the circulatory system

4 Major Types of Cell Signaling 3. Paracrine regulation: Cells release local regulators that diffuse through extracellular fluid to regulate nearby cells

4 Major Types of Cell Signaling 4. Autocrine regulation: Cells release local regulators that regulate the same cells that produced it

4 Types of Molecules 1. Amines 2. Peptides Based on tyrosine Examples: epinephrine, norepinephrine, thyroxine 2. Peptides Amino acid chains Example: growth factors

4 Types of Molecules 3. Steroids 4. Fatty acids Based on cholesterol Examples: aldosterone, cortisol, sex hormones 4. Fatty acids Paracrine and autocrine regulation Example: prostaglandins

Thyroid-releasing hormone (TRH) Hypothalamus Thyroid-releasing hormone (TRH) Pituitary Thyroid hormones inhibit TSH secretion by pituitary. Thyroid-stimulating hormone (TSH) Figure 40.2: A negative feedback loop regulating secretion of the thyroid hormones. As the concentration of thyroid hormones in the blood increases, the hormones inhibit an earlier step in the pathway (indicated by the negative sign). Thyroid Thyroid hormones Fig. 40.2, p. 912

40.2 Mechanisms of Hormone Action Hydrophilic hormones bind to surface receptors, activating protein kinases inside cells Hydrophobic hormones bind to receptors inside cells, activating or inhibiting genetic regulatory proteins Target cells may respond to more than one hormone, and different target cells may respond differently to the same hormone

Hydrophilic Hormones Bind to receptor proteins embedded in the plasma membrane, activating them Activated receptors transmit a signal through the plasma membrane Signal transduction pathways cause a cellular response

a. Hormone binding to receptor in the plasma membrane Outside cell Hydrophilic hormone Blood vessel 1. Hormone binds to surface receptor and activates it. Signal Reception Cytoplasmic end of receptor Activation Pathway molecule A Activation 2. Activated receptor triggers a signal transduction pathway. Transduction Pathway molecule B Figure 40.3: The reaction pathways activated by hormones that bind to receptor proteins in the plasma membrane (a) or inside cells (b). In both mechanisms, the signal—the binding of the hormone to its receptor—is transduced to produce the cellular response. Activation Molecule that brings about response Pathway molecule C Response 3. Transduction of the signal leads to cellular response. Change in cell Cytoplasm Fig. 40.3a, p. 913

Hydrophobic Hormones Bind to receptors in the cytoplasm or nucleus, activating them Activated receptors control the expression of specific genes Gene products cause the cellular response

Control sequence of gene b. Hormone binding to receptor inside the cell Outside cell Blood vessel Hydrophobic hormone 1. Hydrophobic hormone passes freely through plasma membrane. Reception Steroid hormone receptor 2. Hormone binds to receptor, activating it. Transduction 3. Activated receptor binds to control sequence of a gene, leading to gene activation or inhibition. Figure 40.3: The reaction pathways activated by hormones that bind to receptor proteins in the plasma membrane (a) or inside cells (b). In both mechanisms, the signal—the binding of the hormone to its receptor—is transduced to produce the cellular response. Gene activation or inhibition Response DNA Cytoplasm Control sequence of gene Gene Nucleus Fig. 40.3b, p. 913

Adrenal glands Control sequence 1. Adrenal glands secrete aldosterone into the blood when Na+ concentration falls in the body fluids. Outside cell Adrenal glands Aldosterone 2. Aldosterone enters kidney cell and combines with the aldosterone receptor, activating it. Kidney cell plasma membrane Active hormone- receptor complex 3. Active hormone- receptor complex enters the nucleus, where it activates transcription of the gene coding for aldosterone-induced protein. Aldosterone receptor DNA Control sequence Target gene Nuclear envelope Figure 40.4: The action of aldosterone in increasing Na+ reabsorption in the kidneys when concentration of the ion falls in the blood. mRNA Protein synthesis 4. Aldosterone-induced protein is synthesized in the cytoplasm and inserted into the plasma membrane, where it increases Na+ reabsorption by the kidney cell. Aldosterone-induced protein (an Na+ channel) Cytoplasm Fig. 40.4, p. 914

Major Endocrine Cells and Glands of Vertebrates Hypothalamus Pituitary gland Thyroid gland Parathyroid gland Adrenal medulla Adrenal cortex Testes and ovaries Islets of Langerhans (pancreas) Pineal gland

Produces hormones that regulate pituitary secretions Hypothalamus Produces hormones that regulate pituitary secretions Pineal gland Secretes melatonin Anterior pituitary Secretes ACTH, TSH, FSH, and LH, prolactin, GH, MSH, and endorphins Thyroid gland thyroxine and triiodothyronine, calcitonin Posterior pituitary ADH and oxytocin Adrenal cortex cortisol and aldosterone Parathyroid glands Secrete parathyroid hormone Adrenal medulla Secretes epinephrine and norepinephrine Figure 40.6 The major endocrine cells and glands of the human body. Islets of Langerhans (in pancreas) Secrete insulin and glucagon Ovaries (female gonads) Secrete estrogens and progestins Testes (male gonads) Secrete androgens Fig. 40.6, p. 917

40.3 The Hypothalamus and Pituitary Under regulatory control by hypothalamus, the anterior pituitary secretes eight major hormones Posterior pituitary secretes two hormones into the circulatory system

The Hypothalamus and Pituitary Hypothalamus and pituitary together regulate many endocrine cells and glands in the body Pituitary gland has 2 major lobes Posterior pituitary (contains neurosecretory nerve endings from hypothalamus) Anterior pituitary (nonneuronal endocrine cells)

Neurosecretory neuron that secretes releasing and inhibiting hormones Hypothalamus Capillaries in hypothalamus Releasing and inhibiting hormones Blood in Portal vein Figure 40.7: The hypothalamus and pituitary. Hormones secreted by the anterior and posterior pituitary are controlled by neurohormones released in the hypothalamus. Endocrine cells secreting hormones Posterior pituitary Capillaries of anterior pituitary Anterior pituitary Blood out Fig. 40.7b, p. 920

Fig. 40.7c, p. 920 Figure 40.7: The hypothalamus and pituitary. Hormones secreted by the anterior and posterior pituitary are controlled by neurohormones released in the hypothalamus. Fig. 40.7c, p. 920

Gonadotropins (FSH and LH) Thyroid- stimulating hormone (TSH) Prolactin (PRL) Gonadotropins (FSH and LH) Thyroid- stimulating hormone (TSH) Adrenocorticotropic hormone (ACTH) Growth hormone (GH) Mammary glands Testes in males Ovaries in females Thyroid gland Adrenal cortex Muscle, bone and other tissues Figure 40.7: The hypothalamus and pituitary. Hormones secreted by the anterior and posterior pituitary are controlled by neurohormones released in the hypothalamus. Produces milk Produce gametes and hormones Increases rate of metabolism Helps regulate fluid balance; helps body cope with stress Promotes growth Fig. 40.7d, p. 920

Melanocyte- stimulating hormone (MSH) Endorphins Antidiuretic hormone (ADH) Oxytocin Melanocytes in skin of some vertebrates Pain pathways of PNS Nephrons in kidneys Uterus Mammary glands Figure 40.7: The hypothalamus and pituitary. Hormones secreted by the anterior and posterior pituitary are controlled by neurohormones released in the hypothalamus. Promotes skin darkening Inhibit pain perception Increases permeability Stimulates contraction Stimulates milk release Fig. 40.7e, p. 920

Hormones of the Hypothalamus Hypothalamus produces tropic hormones (releasing hormones and inhibiting hormones) that control secretion of anterior pituitary hormones

8 Major Hormones of the Anterior Pituitary 1. Prolactin (PRL) Breast development, milk secretion 2. Growth hormone (GH) Bone and tissue growth, glucose metabolism Stimulates IGF release in liver 3. Thyroid-stimulating hormone (TSH) Thyroid hormones, thyroid growth

8 Major Hormones of the Anterior Pituitary 4. Adrenocorticotropic hormone (ACTH) Glucocorticoid secretion in adrenal cortex 5. Follicle-stimulating hormone (FSH) Egg development, female sex hormones Sperm production 6. Luteinizing hormone (LH) Ovulation Male sex hormones

8 Major Hormones of the Anterior Pituitary 7. Melanocyte-stimulating hormone (MSH) Produces a darkening of the skin 8. Endorphins Neurotransmitters that affect pain pathways in the PNS, inhibiting perception of pain

Hormones of the Posterior Pituitary Antidiuretic hormone (ADH) Regulates body water balance Oxytocin Childbirth: Stimulates contraction of smooth muscle in the uterus Triggers milk release from mammary glands