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Chapter 10 The Endocrine System Announcements • Senses lab- Due Wed! • Next Monday- Class cancellation a possibility Lecture Outline • • • • • Function of Endocrine system Hormones and their mechanisms Pituitary gland Pancreas Other glands The Endocrine system Epithelial cells can form glands • A gland- a collection of cells which secrete a product • Exocrine- release substances through ducts or tubes Endocrine glands secrete hormones directly into the body • Hormone- a signalling chemical which is released in one part of the body and affects another part of the body • Examples- Insulin, Follicle stimulating hormone, testosterone The Endocrine System • The endocrine system communicates using chemical messages • Hormones influence growth, development, metabolism, and behavior • Other chemical messengers act locally Endocrine System Communication • Endocrine glands are made up of secretory cells that release their products called hormones directly into the adjacent extracellular fluids where they diffuse directly into the bloodstream • Hormones are one of the chemical messengers of the body Endocrine System Communication Figure 10.1 All signals require a receptor Endocrine System • Main function of the endocrine system is to coordinate body systems and maintain homeostasis • The major endocrine glands are – Pituitary – Thyroid – Parathyroid – Adrenals – Pineal Endocrine System Pineal gland Melatonin • Reduces jet lag and promotes sleep Thymus gland Thymopoietin, thymosin • Promote maturation of white blood cells Adrenal gland (one on each kidney) Adrenal cortex Glucocorticoids (cortisol, corticosterone,cortisone) • Stimulate glucose synthesis and conservation • Inhibit the inflammatory response Mineralocorticoids (aldosterone) • Increase sodium reabsorption by kidneys • Increase potassium excretion by kidneys Gonadocorticoids (androgens, estrogens) • Insignificant effects in adulthood, relative to secretion by gonads Adrenal medulla Epinephrine • Fight-or-flight response to stress Norepinephrine • Fight-or-flight response to stress Parathyroid glands (two of four) Parathyroid hormone (PTH) • Increases blood levels of calcium Heart Kidney Figure 10.2 (1 of 2) Endocrine System Stomach Pancreas Glucagon • Increases blood glucose level Insulin • Decreases blood glucose level Testis (one of a pair) Androgens (testosterone) • Develop male secondary sex characteristics Thyroid gland Thyroid hormone (TH) • Regulates metabolism and heat production • Promotes development and function of nervous, muscular, skeletal, and reproductive systems Calcitonin (CT) • Decreases blood levels of calcium and phosphate Small intestine Uterus (contains the placenta when pregnant) Ovary (one of a pair) Estrogens and progesterone • Develop female secondary sex characteristics Figure 10.2 (2 of 2) Endocrine System Communication • Hormones circulate throughout the body until they reach target cells – They respond to the hormone, influencing growth, development, metabolism, and behavior Target Cells • Target cells have receptors – Protein molecules that recognize and bind to specific hormones • Cells other than target cells lack the correct receptors and are unaffected by the hormone Chemical Composition of Hormones • The mechanism by which hormones influence target cells depend on the chemical makeup of the hormones Chemical Composition of Hormones • Two types of hormones – Lipid-soluble – Water-soluble Lipid-soluble Hormones • Lipid-soluble hormones include steroid hormones – Derived from cholesterol • The main organs that secrete steroid hormones are – Ovaries – Testes – Adrenal glands Lipidsoluble Hormones can freely pass through cell membranes Extracellular fluid Steroid hormone Step 1: The steroid hormone diffuses through the plasma membrane of the target cell. Plasma membrane of target cell (lipid bilayer) Step 7: Enzymes alter the activity of the cell. Step 2: The steroid hormone binds to a receptor in the cytoplasm. Cytoplasm Receptor Nuclear pore Nuclear envelope Step 6: Proteins, including enzymes, are synthesized. Step 5: Certain genes are activated. Step 3: The hormonereceptor complex enters the nucleus. Step 4: The hormonereceptor complex binds to DNA. Nucleus Functional groups can radically change the function of a molecule Estradiol Female lion Testosterone Male lion Water-soluble hormones • Water-soluble hormones are made of amino acids • They cannot pass through the lipid bilayer of the plasma membrane Water-soluble hormones • They exert their effects indirectly by binding to receptors on the surface of the target cell • This stimulates second messengers within the cell that carry out the effect of the hormone • One common second messenger is cyclic adenosine monophosphate (cAMP) cAMP is a common second messenger for watersoluble hormones Figure 10.4 This type of hormone characteristically requires a second messenger. • • • • A) Lipid-soluble B) Steroid C) Water-soluble D) Prostaglandins Feedback Mechanisms • Feedback mechanisms regulate the secretion of hormones The regulation of blood sugar is an example of hormones in action to maintain homeostasis Figure 10.18 (1 of 2) Feedback Mechanisms • Control is usually by a negative feedback mechanism whereby the increased blood level of the hormone inhibits its further release Feedback Mechanisms • Some hormones are regulated by a positive feedback mechanism in which the outcome of a process further stimulates the process Positive and negative feedback systems regulate reproduction Figure 10.5 The Pituitary gland The pituitary gland is a master control gland • Controls other glands • Secretes many hormones that affects systems directly Hormones • The anterior pituitary is connected to the hypothalamus, which synthesizes and secretes releasing and inhibiting hormones Hormones • The anterior pituitary gland synthesizes and secretes – Growth hormone (GH) – Prolactin (PRL) – Thyroid-stimulating hormone (TSH) – Adrenocorticotropic hormone (ACTH) – Follicle-stimulating hormone (FSH) – Luteinizing hormone (LH) Hormones Hypothalamus Nerve cells in the hypothalamus produce antidiuretic hormone (ADH) and oxytocin (OT). ADH and OT travel to the ends of the cells in the posterior pituitary, where they are released into the bloodstream to influence target tissues. Posterior pituitary Nerve cells in the hypothalamus secrete releasing hormones and inhibiting hormones. Anterior pituitary Releasing and inhibiting hormones travel by way of the bloodstream to the anterior pituitary and cause it to modify secretion of its six hormones (FSH, LH, GH, PRL, ACTH, and TSH). Antidiuretic hormone (ADH) Follicle-stimulating hormone (FSH) and Luteinizing hormone (LH) Growth hormone (GH) Oxytocin (OT) Ovaries, testes Prolactin (PRL) Kidney tubules Thyroidstimulating hormone (TSH) Smooth muscle in uterus Mammary glands Adrenocorticotropic hormone (ACTH) Bones, muscles Mammary glands Thyroid gland Cortex of adrenal gland Figure 10.6 Human Growth Hormone • Two hormones of the hypothalamus regulate the synthesis and release of GH – Growth hormone-releasing hormone (GHRH) stimulates the release of GH – Growth hormone-inhibitory hormone (GHIH) inhibits the release of GH Human Growth Hormone • Growth hormone (GH) stimulates an increase in cell size and the rate of cell division in target cells • Gigantism – Abnormally high production of GH in childhood when the bones are still capable of growing in length Human Growth Hormone Figure 10.7 Human Growth Hormone • Acromegaly – High levels of GH in adulthood when the bones can thicken but not lengthen Human Growth Hormone Human Growth Hormone • Pituitary dwarfism – Insufficient production of GH in childhood – A genetic disorder treated with growth hormone produced by recombinant DNA Human Growth Hormone Figure 10.9 Prolactin • Prolactin (PRL) – Stimulates the mammary glands to produce milk – Produced during lactation • Excess may cause infertility and lactation when there is no pregnancy • In men – PRL is involved with the production of mature sperm in the testes – Overproduction can lead to sterility Tropic Hormones • TSH, ACTH, FSH, and LH are tropic hormones – Hormones that influence the secretion of hormones by other glands Thyroid-Stimulating Hormone • Thyroid-stimulating hormone (TSH) – Acts on the thyroid gland to stimulate the synthesis and release of thyroid hormones Adrenocorticotropic Hormone • Adrenocorticotropic hormone (ACTH) – Controls the synthesis and secretion of glucocorticoid hormones from the adrenal cortex Follicle-Stimulating Hormone • Follicle-stimulating hormone (FSH) – Promotes development of egg cells and secretion of estrogen in females • In males – FSH promotes the production of sperm Luteininzing Hormone • Luteinizing hormone (LH) – Causes ovulation and the secretion of estrogen and progesterone – Prepares the uterus for implantation of a fertilized ovum and the breasts for the production of milk • In males – LH stimulates the production and secretion of testosterone Posterior Pituitary • Cells within the posterior lobe of the pituitary do not produce any hormones – Neurons of the hypothalamus manufacture antidiuretic hormone (ADH) and oxytocin (OT) – They travel down the nerve cells into the posterior pituitary, where they are stored and released Posterior Pituitary Hypothalamus Nerve cells in the hypothalamus produce antidiuretic hormone (ADH) and oxytocin (OT). ADH and OT travel to the ends of the cells in the posterior pituitary, where they are released into the bloodstream to influence target tissues. Nerve cells in the hypothalamus secrete releasing hormones and inhibiting hormones. Posterior pituitary Anterior pituitary Releasing and inhibiting hormones travel by way of the bloodstream to the anterior pituitary and cause it to modify secretion of its six hormones (FSH, LH, GH, PRL, ACTH, and TSH). Antidiuretic hormone (ADH) Follicle-stimulating hormone (FSH) and Luteinizing hormone (LH) Growth hormone (GH) Oxytocin (OT) Ovaries, testes Prolactin (PRL) Kidney tubules Thyroidstimulating hormone (TSH) Smooth muscle in uterus Mammary glands Adrenocorticotropic hormone (ACTH) Bones, muscles Mammary glands Thyroid gland Cortex of adrenal gland Figure 10.6 Posterior Pituitary Hormones • Antidiuretic Hormone (ADH) – Also called vasopressin – Causes the kidneys to remove water from the fluid destined to become urine • A deficiency of ADH results in diabetes insipidus – Characterized by excessive urine production and dehydration Posterior Pituitary Hormones • Oxytocin (OT) – Stimulates uterine contractions of childbirth and milk ejection from the mammary glands • In men – OT may facilitate the transport of sperm and be involved in male sexual behavior Posterior Pituitary Hormones Figure 10.5 Posterior Pituitary Hormones Figure 10.10 Thyroid Gland Hormones • Hormones secreted by the thyroid gland regulate metabolism and decrease blood calcium – Thyroxine (T4) and triiodothyrinine (T3), collectively known as thyroid hormone (TH), regulate metabolic rate – Calcitonin • Decreases blood calcium Thyroid Gland Hormones Opening to trachea Larynx Thyroid gland Parathyroid glands Trachea Back view Front view (a) The thyroid gland lies over the trachea, just below the larynx. Figure 10.11a Thyroid Gland Hormones Figure 10.11b Thyroid Gland Hormones • Thyroid hormone (TH) – Produced in the follicular cells – Stimulates protein synthesis, the breakdown of lipids, and the use of glucose for the production of ATP Thyroid Gland Hormones • Simple goiter – An enlarged thyroid gland – May be produced by a diet deficient in iodine, which is needed for the production of TH – Can be treated by iodine supplements or administration of TH Thyroid Gland Hormones Figure 10.12a Thyroid Gland Hormones • Cretinism – Too little TH during fetal development or infancy – Characterized by dwarfism and delayed mental and sexual development • Myxedema – Too little TH in adulthood – Causes a condition in which fluid accumulates in facial tissues and a decrease in alertness, body temperature, and heart rate Thyroid Gland Hormones Figure 10.12b Thyroid Gland Hormones • Graves’ disease – Oversecretion of TH – Results in an autoimmune disorder due to the production of antibodies that mimic the action of TSH • Symptoms include – Increased metabolic rate and heart rate accompanied by sweating, nervousness, and weight loss – Many also have exopthalmos Thyroid Gland Hormones Figure 10.12c Thyroid Gland Hormones • Calcitonin (CT) – Helps regulate calcium concentration in the blood by either • Stimulating the absorption of calcium by bone • Increasing the excretion of calcium in the urine Thyroid Gland Hormones Figure 10.13 Thyroid Gland Hormones Figure 10.13 (1 of 2) Thyroid Gland Hormones Figure 10.13 (2 of 2) Parathyroid Gland Hormones • Parathyroid glands – Four small round masses lateral to the thyroid gland – Secrete parathyroid hormone (PTH), or parathormone, which increases the blood calcium level Parathyroid Gland Hormones • PTH – Stimulates • Osteoclasts to break down bone-releasing calcium into the blood • Removal of calcium from the urine, returning it to the blood • Rate calcium is absorbed from the gastrointestinal tract – Inhibits • Osteoblasts Parathyroid Gland Hormones • Undersecretion of PTH – Can result in nervousness and muscle spasms • Oversecretion – Pulls calcium from bone tissue, causing weakened bones and elevated blood calcium levels • Might lead to kidney stones, calcium deposits in the soft tissue, and decreased activity of the nervous system Adrenal Gland Hormones • The adrenal glands – Located at the top of the kidneys – Composed of two regions • Adrenal cortex • Adrenal medulla Adrenal Gland Hormones • The adrenal cortex (outer region) secretes – Gonadocorticoids – Glucocorticoids – Mineralcorticoids • The adrenal medulla (inner region) secretes – Epinephrine (adrenaline) – Norepinephrine (noradrenaline) Adrenal Gland Hormones Figure 10.14a cortex Adrenal GlandAdrenal Hormones Adrenal gland • Mineralocorticoids • Gonadocorticoids • Glucocorticoids Adrenal medulla • Epinephrine • Norepinephrine (b) A section through the adrenal gland reveals two regions, the outer adrenal cortex and the inner adrenal medulla. These regions secrete different hormones. Figure 10.14b Adrenal Gland Hormones • Gonadocorticoids – Androgens and estrogens – Secreted by the adrenal cortex in both males and females Adrenal Gland Hormones • Mineralocorticoids – Affect mineral homeostasis and water balance • Aldosterone – Acts on cells of the kidneys to • Increase reabsorption of sodium ions into the blood • Promote the excretion of potassium ions in the urine Adrenal Gland Hormones • Addison’s disease – Caused by the undersecretion of cortisol and aldosterone – Appears to be an autoimmune disorder in which the cells of the adrenal cortex are perceived as foreign – Results in bronzing of the skin, weight loss, fatigue, electrolyte imbalance, poor appetite, and resistance to stress – May be caused by inadequate secretion of ACTH Adrenal Gland Hormones Figure 10.15 Adrenal Gland Hormones • Glucocorticoids – Affect glucose homeostasis – Act on the liver to promote the conversion of fat and protein into intermediate substances available to the body’s cells – Inhibit the inflammatory response Adrenal Gland Hormones • Cushing’s syndrome – May be caused by the oversecretion of glucocorticoids or a tumor on either the adrenal cortex or anterior pituitary – Results in redistribution of body fat and accumulation of fluid in the face, fatigue, high blood pressure, and elevated glucose levels Adrenal Gland Hormones Figure 10.16 Adrenal Gland Hormones • The adrenal medulla – Produces epinephrine (adrenaline) and norepinephrine (noradrenaline) – Both of these hormones are used in our response to danger, preparing us for fight-or-flight Pancreas Gland Hormones • Hormones of the pancreas – Secreted from the pancreatic islets – Regulate blood glucose levels through glucagon and insulin Pancreas Gland Hormones Stomach Common bile duct (from gallbladder and liver) Pancreas Pancreatic duct Duodenum (first part of small intestine) (a) Structure of the pancreas and associated ducts. Exocrine cells of the pancreas secrete digestive enzymes into the pancreatic duct, which unites with the common bile duct before entering the small intestine. Figure 10.17a Pancreas Gland Hormones Figure 10.17b Pancreas Gland Hormones • Glucagon – Increases glucose in the blood by converting glycogen to glucose in the liver Pancreas Gland Hormones Figure 10.18 (2 of 2) Pancreas Gland Hormones • Insulin – Decreases blood glucose levels – Stimulates transport of glucose into muscle cells, white blood cells, and connective tissue cells – Inhibits the breakdown of glycogen to glucose – Prevents conversion of amino and fatty acids into glucose Pancreas Gland Hormones • Diabetes mellitus – A group of metabolic disorders characterized by an abnormally high level of glucose in the blood Pancreas Gland Hormones • Type 1 diabetes mellitus – Usually develops in people younger than 25 years of age – An autoimmune disease – A person’s own immune system attacks the cells of the pancreas responsible for insulin production Pancreas Gland Hormones • Type 2 diabetes mellitus – Usually develops after age 40, but has begun showing up in younger people recently – Characterized by a decreased sensitivity to insulin (insulin resistance) Thymus Gland Hormones • Thymus gland – Secretes hormones, such as thymopoietin and thymosin, which are involved in the maturation of T lymphocytes – These hormones and the thymus gland play a very important role in immunity Pineal Gland Hormones • The pineal gland – Contains secretory cells that produce melatonin – Levels of circulating melatonin are greater at night than during daylight hours • Due to the input the pineal gland receives from the visual pathways Pineal Gland Hormones Pineal gland Cerebrum Hypothalamus Skull Pituitary gland Figure 10.19 Pineal Gland Hormones • Melatonin is linked to sleep, fertility, and aging • Too much melatonin can result in seasonal affective disorder (SAD), which is associated with winter • Treatment includes repeated exposure to very bright light Pineal Gland Hormones PLAY Animation—The Hypothalamus and the Pituitary Other Chemicals Act Locally • Local signaling molecules act very quickly on adjacent cells – Neurotransmitters – Growth factors – Nitric oxide (NO) – Prostaglandins Other Chemicals Act Locally • Prostaglandins – Lipid molecules continually released by the plasma membranes of most cells – At least 16 different prostaglandin molecules function within the human body Other Chemicals Act Locally • Although they act locally, prostaglandins can have very diverse effects including – Actions on the reproductive system – Fertility – Blood clotting – Body temperature Hormonal Response to Stress • General adaptation syndrome (GAS) – A series of physiological adjustments made by our bodies in response to extreme stress – Has three phases • Alarm • Resistance • Exhaustion Hormonal Response to Stress • Alarm – Fight-or-flight response • Resistance – Glucocorticoids from adrenal cortex are the main hormones – Body’s protein and fat reserves mobilized – Body fluids conserved • Exhaustion – Organs are unable to meet the heavy demands of the resistance phase, and they begin to fail Hormonal Response to Stress PLAY | Fighting Stress