Animal Hormones PDF

39 Animal Hormones © Oxford University Press Concept 39.1 Hormones Circulate Around the Body and Affect Target Cells (1) Endocrines are chemical signals secreted by epithelial cells directly into the extra...

39 Animal Hormones © Oxford University Press Concept 39.1 Hormones Circulate Around the Body and Affect Target Cells (1) Endocrines are chemical signals secreted by epithelial cells directly into the extracellular fluid (ECF). From the ECF, endocrines can diffuse locally and also into the blood, where they circulate throughout the body. The signals are received only by cells that have appropriate receptors, and responses are determined by the receiving cell’s signal transduction machinery. © Oxford University Press Concept 39.1 Hormones Circulate Around the Body and Affect Target Cells (3) Hormones are endocrine signals that enter the blood and activate target cells, e.g., insulin. Paracrines affect target cells near the release site, e.g., histamine, a mediator of inflammation. Autocrines bind to receptors on the same cells that secrete them. © Oxford University Press Concept 39.1 Hormones Circulate Around the Body and Affect Target Cells (4) Some endocrine cells exist as single cells (e.g., in the digestive tract). Endocrine glands: aggregations of endocrine cells that secrete hormones within the body. Exocrine glands secrete substances through ducts to the outside of the body (e.g., sweat and salivary glands). © Oxford University Press Concept 39.1 Hormones Circulate Around the Body and Affect Target Cells (6) Three classes of hormones: 1. Peptide and protein hormones (e.g., insulin): Water-soluble, easily transported in blood Can be packaged in vesicles and released by exocytosis © Oxford University Press Concept 39.1 Hormones Circulate Around the Body and Affect Target Cells (7) 2. Steroid hormones (e.g., estrogen, testosterone): Synthesized from cholesterol Lipid-soluble; pass easily through cell membranes Usually bound to carrier molecules in the blood © Oxford University Press Concept 39.1 Hormones Circulate Around the Body and Affect Target Cells (8) 3. Amine hormones (e.g., epinephrine): Mostly synthesized from the amino acid tyrosine (e.g., thyroxine) Some are water-soluble; others are lipid- soluble; their modes of release differ accordingly. © Oxford University Press Concept 39.1 Hormones Circulate Around the Body and Affect Target Cells (12) One hormone can trigger different responses in different types of cells. Example: epinephrine and norepinephrine are involved in the fight-or- flight response. The sympathetic nervous system responds to a sudden fright by releasing norepinephrine. © Oxford University Press Concept 39.1 Hormones Circulate Around the Body and Affect Target Cells (13) Endocrine cells in the adrenal glands are stimulated to secrete both epinephrine and norepinephrine, which quickly circulate in the blood. They bind to receptors in the heart, blood vessels, liver, and fat cells. Heart rate increases; some blood vessels constrict to send more blood to muscles. © Oxford University Press Concept 39.1 Hormones Circulate Around the Body and Affect Target Cells (14) Epinephrine stimulates liver cells to break down glycogen and release glucose into the blood as a quick energy supply. In fatty tissue, it stimulates breakdown of fats to fatty acids—another source of energy. © Oxford University Press Concept 39.1 Hormones Circulate Around the Body and Affect Target Cells (15) Chemical signaling was critical for the evolution of multicellular organisms. Even sponges have intercellular chemical communication. Signaling molecules are highly conserved, but their functions differ. As organisms diversified, the same hormone– receptor systems diversified to have different functions, e.g., prolactin. © Oxford University Press Figure 39.4 Prolactin’s Structure Is Conserved, but Its Functions Have Evolved (Part 1) Figure 39.4 Prolactin’s Structure Is Conserved, but Its Functions Have Evolved (Part 2) Figure 39.4 Prolactin’s Structure Is Conserved, but Its Functions Have Evolved (Part 3) Figure 39.4 Prolactin’s Structure Is Conserved, but Its Functions Have Evolved (Part 4) Concept 39.2 The Endocrine System and Nervous System Work Together (1) Neural signals are very fast, can be turned off quickly, and can rapidly communicate complex information. Endocrine signals are slow: they must diffuse and circulate; often act through cellular process such as protein synthesis; but responses are sustained. Thus it is advantageous for these systems to work together. © Oxford University Press Concept 39.2 The Endocrine System and Nervous System Work Together (3) The pituitary gland is attached to the hypothalamus of the brain; it connects the nervous and endocrine systems. Anterior pituitary is controlled by hypothalamic neurohormones that travel via the blood. Posterior pituitary contains axons of hypothalamic neurons that release neurohormones. © Oxford University Press Concept 39.2 The Endocrine System and Nervous System Work Together (4) Hypothalamic neurons secrete 2 neuro-hormones into the posterior pituitary: 1. Antidiuretic hormone (ADH) increases the water retained by the kidneys when necessary. Also called vasopressin—it causes the constriction of peripheral blood vessels to elevate blood pressure. © Oxford University Press Concept 39.2 The Endocrine System and Nervous System Work Together (5) 2. Oxytocin stimulates uterine contractions in childbirth and milk flow. The baby’s suckling stimulates neurons in the mother’s brain that cause secretion of oxytocin. An example of how the nervous system integrates information that regulates hormonally mediated processes. © Oxford University Press Concept 39.2 The Endocrine System and Nervous System Work Together (6) The anterior pituitary secretes tropic hormones that control other endocrine glands. Thyrotropin (thyroid-stimulating hormone) Luteinizing hormone Follicle-stimulating hormone Corticotropin © Oxford University Press Concept 39.2 The Endocrine System and Nervous System Work Together (7) Growth hormone (GH) stimulates cells to take up amino acids, and liver cells to produce signals to stimulate growth of bone and cartilage. Endorphins and enkephalins: neuro- transmitters in the brain; natural painkillers. Melanocyte-stimulating hormone (MSH) stimulates production of melanin in skin and hair. © Oxford University Press Figure 39.7 The Anterior Pituitary Is Controlled by the Hypothalamus (Part 1) Concept 39.2 The Endocrine System and Nervous System Work Together (9) Anterior pituitary cells are also under negative feedback control by hormones of the target glands they stimulate. © Oxford University Press Concept 39.2 The Endocrine System and Nervous System Work Together (10) Hormones also influence the nervous system in other ways: Oxytocin plays a role in the birth process and stimulating milk flow; it also promotes bonding between mother and baby, and pair bonding in many animals, including humans. Sex hormones have a strong influence on behavior. © Oxford University Press Concept 39.3 Hormones Play Important Roles in Development (7) In insects with complete metamorphosis, larvae molt into larger instars as long as juvenile hormone is present in large amounts. When the level falls, the insect enters the pupal stage. Pupae do not produce juvenile hormone, so they molt into adults. © Oxford University Press Concept 39.3 Hormones Play Important Roles in Development (8) Hormones also control development in vertebrates, e.g., anterior pituitary growth hormone affects growth. The gonads (testes and ovaries) produce steroid hormones that determine whether a fetus develops into a phenotypic female or male. © Oxford University Press Concept 39.3 Hormones Play Important Roles in Development (9) Androgens: male; dominant form is testosterone. Estrogens and progesterone: female; dominant form is estradiol, which is synthesized from testosterone. Males and females both synthesize testosterone, but females have an enzyme (aromatase) that converts testosterone to estradiol. © Oxford University Press Concept 39.3 Hormones Play Important Roles in Development (11) At puberty, production of sex hormones increases. Gonad activity is controlled by gonadotropins from the anterior pituitary: Luteinizing hormone (LH) Follicle-stimulating hormone (FSH) © Oxford University Press Concept 39.3 Hormones Play Important Roles in Development (12) Gonadotropins are controlled by hypothalamic gonadotropin-releasing hormone (GnRH)—its release increases at puberty. Increase in gonadotropins leads to increased levels of sex steroids and development of secondary sex characteristics. © Oxford University Press Concept 39.4 Hormones Regulate Metabolism and the Internal Environment (1) The thyroid gland secretes 2 hormones: Thyroxine regulates metabolism; produced by follicle epithelial cells. Calcitonin is produced by cells between the follicles and is involved in blood calcium regulation. © Oxford University Press Concept 39.4 Hormones Regulate Metabolism and the Internal Environment (2) Thyroglobulin (a polymer of tyrosine) is produced and secreted into the lumen of the follicle, where it is iodinated and stored until processed by the epithelial cells to generate T3 and T4. © Oxford University Press Figure 39.13 Cleavage of Thyroglobulin Yields Two Active Hormones T3 is a more active form; difference in the activities of T3 and T4 makes it possible to control the effects of thyroxine in different tissues. Concept 39.4 Hormones Regulate Metabolism and the Internal Environment (3) thyrotropin releasing hormone (TRH) thyrotropin/thyroid stimulating hormone (TSH) thyroid gland thyroxine © Oxford University Press Concept 39.4 Hormones Regulate Metabolism and the Internal Environment (6) A goiter is an enlarged thyroid gland; associated with either hyperthyroidism (excess thyroxine) or hypothyroidism (thyroxine deficiency). The most common cause of hypothyroid goiter is iodine deficiency—follicle cells cannot produce thyroxine. Without thyroxine in the blood, TSH levels remain high, and the thyroid continues to produce thyroglobulin. © Oxford University Press Concept 39.4 Hormones Regulate Metabolism and the Internal Environment (7) Regulation of calcium levels in the blood is critical to body function. Mechanisms for changing blood calcium levels: Deposition or absorption of bone Excretion or retention of Ca by kidneys Absorption of Ca from digestive tract © Oxford University Press Concept 39.4 Hormones Regulate Metabolism and the Internal Environment (8) These mechanisms are controlled by 3 hormones: 1. Calcitonin is released by the thyroid; lowers blood Ca by regulating bone turnover. Bone is continuously remodeled: osteoclasts break down bone and release Ca into the blood; osteoblasts take up Ca and deposit it in new bone. Turnover of bone in adult humans is not very high; calcitonin is more important in young people whose bones are growing © Oxford University Press Concept 39.4 Hormones Regulate Metabolism and the Internal Environment (10) 2. Parathyroid hormone (PTH); secreted by the parathyroid glands. Blood Ca levels control synthesis and release of PTH—when low, PTH is released, which stimulates bone turnover by osteoclasts and osteoblasts and increases blood Ca levels. PTH also stimulates kidneys to reabsorb Ca. © Oxford University Press Concept 39.4 Hormones Regulate Metabolism and the Internal Environment (11) 3. Vitamin D (calciferol) is synthesized from cholesterol when skin cells receive ultraviolet light. In the liver and kidneys, PTH activates conversion of calciferol to calcitriol. Calcitriol promotes absorption of calcium from food in the gut. Thus the combined actions of PTH and calcitriol raise blood calcium levels. © Oxford University Press Concept 39.4 Hormones Regulate Metabolism and the Internal Environment (12) Small increases in Ca and phosphate in the blood can result in precipitation of calcium phosphate salts. This can result in kidney stones and hardening of the arteries (Ca deposits). PTH acts on kidneys to eliminate phosphate in the urine. © Oxford University Press Concept 39.4 Hormones Regulate Metabolism and the Internal Environment (13) Diabetes mellitus (type I) is caused by lack of the protein hormone insulin. Glucose transporters are controlled by insulin. When insulin binds to cell receptors, transporters move to the cell membrane and facilitate glucose uptake. When glucose is not present, transporters are returned to the cytoplasm, and glucose uptake is inhibited. © Oxford University Press Figure 39.16 Glucose Transporters Are Controlled by Insulin Concept 39.4 Hormones Regulate Metabolism and the Internal Environment (14) Adult onset or type II diabetes is associated with obesity, high carbohydrate consumption, and lack of exercise. Caused either by low production of insulin or insensitivity to insulin. © Oxford University Press Concept 39.4 Hormones Regulate Metabolism and the Internal Environment (15) In both types, glucose builds up in the blood and increases in the urine. Urine output increases: water moves from cells to blood by osmosis, and increased glucose in kidney tubules pulls more water in by osmosis. Diabetic person suffers dehydration and lack of metabolic fuel. © Oxford University Press Concept 39.4 Hormones Regulate Metabolism and the Internal Environment (16) Insulin replacement therapy allows people with type I diabetes to lead almost normal lives. Type II diabetes can be treated with a combination of dietary changes and weight loss. © Oxford University Press Concept 39.4 Hormones Regulate Metabolism and the Internal Environment (17) Islets of Langerhans: endocrine cells in the pancreas that produce 3 hormones: Beta (b) cells produce insulin. Alpha (a) cells produce glucagon Delta (d) cells produce somatostatin © Oxford University Press Concept 39.4 Hormones Regulate Metabolism and the Internal Environment (18) When blood glucose rises after a meal, beta cells produce insulin. When blood glucose falls, insulin production stops and most cells shift to using glycogen as a fuel source. If blood glucose falls substantially below normal, alpha cells release glucagon, which stimulates liver to convert glycogen to glucose. © Oxford University Press Concept 39.4 Hormones Regulate Metabolism and the Internal Environment (19) Somatostatin has paracrine functions; inhibits release of both insulin and glucagon. Also slows digestive activities to extend the period of nutrient absorption. © Oxford University Press Concept 39.4 Hormones Regulate Metabolism and the Internal Environment (20) © Oxford University Press Concept 39.4 Hormones Regulate Metabolism and the Internal Environment (21) Adrenal cortex produces steroid hormones called corticosteroids: Mineralocorticoids influence salt and water balance. Aldosterone stimulates kidneys to conserve Na and excrete K. Glucocorticoids influence blood glucose concentration. Sex steroids (produced in negligible amounts in adults). © Oxford University Press Concept 39.4 Hormones Regulate Metabolism and the Internal Environment (22) Cortisol, the main glucocorticoid, mediates metabolic stress responses. Responses are similar to those of epinephrine in the fight-or-flight response, but are slower and last longer. Inhibits the immune system. Adaptive in responding to acute stress, but cause problems if sustained over time. © Oxford University Press Concept 39.4 Hormones Regulate Metabolism and the Internal Environment (23) Anterior pituitary controls cortisol release by adrenocorticotropic hormone (ACTH). ACTH release is controlled in turn by corticotropin-releasing hormone (CRH) from the hypothalamus. Acute stress response is turned off by negative feedback of cortisol to brain. © Oxford University Press Concept 39.4 Hormones Regulate Metabolism and the Internal Environment (24) With chronic or prolonged stress, cortisol must exert negative feedback through the hippocampus decreasing the ability to turn off the stress response. Prolonged stress can lead to digestive system problems, cardiovascular problems, strokes, impaired immune system, and increased susceptibility to cancers and other diseases. © Oxford University Press Concept 39.4 Hormones Regulate Metabolism and the Internal Environment (25) Adrenal medulla releases epinephrine and norepinephrine in response to stress. Drugs called beta blockers inhibit b-adrenergic receptors, and thus can blunt the fight-or-flight response without disrupting physiological processes. Beta blockers are used to reduce symptoms of anxiety. © Oxford University Press Concept 39.4 Hormones Regulate Metabolism and the Internal Environment (27) The pineal gland, located between the cerebral hemispheres, secretes the hormone melatonin in a daily rhythm. Coordinates daily rhythms of physiological functions. © Oxford University Press