Name: Date: BIO 210: Anatomy and Physiology Text: Fundamentals of Anatomy and Physiology 9ed. Chapter 18 The Endocrine System We typically think of the Nervous System as being the control center for all of our bodily functions. However, very few of our cells are innervated with nerves and those that are receive short-lived commands that are very specific. It is the Endocrine System that continually controls and maintains many important functions of the body for extended periods of time. CELLULAR COMMUNICATION (Table 18-1) Direct communication occurs between two cells of the ; exchange of ions and molecules between ; must be in with each other o Ex. Paracrine communication use of to transfer information from cell to cell within a ; chemicals are called or ; primary effects occur within ; when paracrine factors have a secondary effect in other tissues beyond the tissue of origin, it is then acting as a o Ex. Hormones chemical messengers that are released in one tissue and transported in the to alter activities of cells in another tissue; a substance with effects outside its o Target cells specific cells that can read the message of a and alter its activity accordingly; need specialized for that hormone message FUNCTION OF A HORMONE Stimulate enzyme or protein synthesis Alter transcription or translation to increase or decrease rate of protein and enzyme synthesis Altering channel or membrane enzyme shapes thereby turning it on or off Alter cellular activities of several tissues at the same time Coordinate cell, tissue and organ activities on a long-term basis 1
SYNAPTIC COMMUNICATION Chemical communication using neurotransmitters across synaptic clefts (not in bloodstream) Target cells are close to the synapse and have specific receptors Carries high speed messages which are quick but short-lived Crisis management (fight or flight) CLASSES OF HORMONES Amino Acid Derivatives structures related to amino acids thyroid hormone, and catecholamines (E, NE and dopamine) are derived from the amino acid, melatonin derived from the amino acid, Peptide Hormones thyroid stimulating hormone, LH, and FSH are that consist of long chains of amino acids all hormones from the hypothalamus, heart, digestive tract, thymus, pancreas and posterior pituitary gland are short Lipid Derivatives Eicosanoids commonly have effects; prostaglandins, leukotrines, thromboxanes and prostacyclins Steroid hormones resemble ; secreted by reproductive glands (androgens, estrogens and progestins), by the adrenal glands (corticosteroids), and by the kidneys (calcitriol) DISTRIBUTION OF HORMONES Hormones can circulate freely, or bind to transport proteins Freely circulating hormones are active from only a few minutes up to an hour Freely circulating hormones are inactivated when: o they diffuse out of the blood stream and bind to the target cell receptor o when they are absorbed and broken down by the liver or kidneys o or when enzymes in the cell plasma break it down Thyroid hormones and steroid hormones remain in circulation longer than peptide hormones because they are bound to The bloodstream can have a of bound hormones at any given time 2
Thyroid and steroid hormones last in the blood longer because they attach to a transport protein. This is how hormones maintain equilibrium in the blood stream, free circulating hormones being replaced by bound hormones to a reserve of several weeks supply. MECHANISMS OF HORMONE ACTION Hormone Receptor Is a molecule to which a particular molecule binds strongly Can respond to hormones Different tissues have different combinations of Presence or absence of specific receptor determines hormonal Hormones modify cellular activity. Do they affect all tissues with their receptors the same? Hormones and Plasma Membrane Receptors Catecholamines and Peptide Hormones not and cannot penetrate the plasma membrane; bind to receptor proteins on of plasma membrane called Eicosanoids are so they can diffuse across plasma membrane to reach receptor proteins on the of the plasma membrane called First and Second Messengers Hormones that bind to receptors in the plasma membrane cannot have direct effect on activities inside target cell; they have to use intracellular intermediary to exert effects First Messenger the that binds to the plasma membrane; leads to a second messenger Second Messengers act as,, or resulting in change in rates of metabolic reactions; important second messengers: o Cyclic-AMP (camp) derivative of o Cyclic-GMP (cgmp) derivative of o Calcium ions The Process of Amplification the binding of a small number of hormone molecules to membrane receptors which leads to thousands of in cell; effect of hormone on target cell 3
Down-regulation the presence of a hormone triggers a in number of ; when levels of particular hormone are high, cells become to it Up-regulation the absence of a hormone triggers an in the number of hormone receptors; when levels of particular hormone are low, cells become to it G Protein middle man between 1st and 2nd messenger. These proteins bind to and are activated when a hormone binds to its at the G Proteins and camp (Figure 18-3) G proteins increase or decrease camp (second messenger) levels in response to peptide hormones, catecholamines, and eicosanoids Increasing camp: 1. Activated G protein activates the enzyme adenylate cyclase 2. Adenylate cyclase converts ATP to camp 3. camp is now a 2nd messenger and activates kinase causing phosphorylation (attaching of a highenergy phosphate group to another molecule) 4. Phosphodiesterase inactivates camp to AMP making increased levels of camp short lived Decreasing camp: 1. Activated G protein stimulates phosphodiesterase activity 2. Adenylate cyclase activity is inhibited 3. camp levels decline 4. without phosphorylation, key enzymes remain inactive G Proteins and Calcium Ions (Figure 18-3) activated G proteins trigger the opening of calcium ion channels in the membrane or the release of calcium ions from intracellular stores 1. G protein activates the enzyme phospholipase C (PLC) 2. Triggers a receptor cascade allowing Ca 2+ release from intracellular reserves (SER) 3. Phosphorylation of calcium channel proteins opens the channel and permits extracellular calcium to enter the cell (positive feedback loop to increase intracellular calcium) 4. Calcium (acting as a second messenger) can bind to calmodulin which activates other enzymes HORMONES AND INTRACELLULAR RECEPTORS (FIGURE 18-4) Alter rate of DNA transcription in nucleus Change patterns of protein synthesis Directly affect metabolic activity and structure of target cell Include steroids and thyroid hormones 4
Steroid hormones diffuse through the plasma membrane and bind to receptors in the or ; the hormone then binds to in the nucleus to activate certain genes Thyroid hormones enter the cytoplasm and bind to receptors on the or in the ; activates or accelerates THE PITUITARY GLAND (Figure 18-6) also called the ; lies within isolated from cranial cavity; hangs inferior to and is connected by the Facts to Know: Releases important peptide hormones Hormones bind to Use as second messenger Anterior Lobe of the Pituitary Gland also called ; hormones turn on endocrine glands or support other organs Hypothalamic Control of the Anterior Lobe two classes of hypothalamic regulatory hormones; rate of secretion is controlled by negative feedback: 1. Releasing hormones (RH) stimulate synthesis and secretion of one or more hormones at anterior lobe 2. Inhibiting hormones (IH) prevent synthesis and secretion of hormones from the anterior lobe HORMONES OF THE ANTERIOR LOBE (7): 5
Points to Note: ACTH targets glucocorticoids (hormones that affect ) Low levels of gonadotropins causes ; FSH is inhibited by Luteinizing hormone prepares the body for in females; in males it stimulates cells of the testes to secrete Prolactin is found in males and might help regulate production Growth hormone stimulates growth directly and indirectly o Indirectly: Liver cells respond to GH by producing compounds that stimulate tissue growth; these peptides bind to receptors on plasma membranes to increase uptake of amino acids for new protein synthesis o Directly: stem cell division and differentiation of epithelial and connective tissues, in adipose tissue: glucose-sparing effect where fatty acids are released from adipose tissue for energy, and in the liver: stimulates the break down of glycogen into glucose from the liver increasing blood glucose levels 6
The Posterior Lobe of the Pituitary Gland also called ; contains unmyelinated axons of hypothalamic neurons; secrete Antidiuretic hormone (ADH) and Oxytocin (OXT) HORMONES OF THE POSTERIOR LOBE (2): Points to Note: Antidiuretic hormone also referred to as ADH responds to a rise in in the blood or fall in blood or by the amount of water loss in the and by causing to increase blood pressure inhibits ADH Oxytocin is responsible for the stimulated by a suckling infant THE THYROID GLAND (Figure 18-10) lies anterior to thyroid cartilage of larynx; consists of two lobes connected by narrow isthmus Points to Note: Thyroid follicles (Figure 18-10c) Thyroxine (T 4 ) also called tetraiodothyronine, contains iodide ions Triiodothyronine (T 3 ) contains iodide ions The absence of Thyroid-Stimulating Hormone (TSH) causes thyroid follicles to become They bind to receptors in: ( ), surfaces of ( ), and the ( ) T4 can be converted to in the liver when needed Thyroid gland contains most of the reserves in the body; needed to synthesize thyroid hormones 7
Functions of Thyroid Hormones (T 3 and T 4 ) thyroid hormones enter target cells by transport system and affect most cells in body In children they are essential to normal development of skeletal, muscular, and nervous systems Responsible for, where the cell consumes more energy resulting in increased and is responsible for strong, immediate, and short-lived increase in rate of ; in, these hormones increase in to help them adapt Elevates rates of consumption and consumption; in children, may cause a rise in Increases and ; generally results in a rise in blood pressure Increases sensitivity to stimulation Maintains normal sensitivity of respiratory centers to changes in and concentrations Stimulates formation and thus enhances delivery Stimulates activity in other endocrine tissues Accelerates turnover of in bone The C Cells of the Thyroid Gland and Calcitonin (Figure 18-10c) C (clear) cells also called parafollicular cells Produce (CT) Helps regulate concentrations of in body fluids Inhibits, which slows the rate of Ca 2+ release from bone Stimulates Ca 2+ excretion by the Most important during to stimulate bone growth Reduced bone loss during and PARATHYROID GLANDS (Figure 18-12) four Parathyroid Glands embedded in the posterior surface of the thyroid gland Parathyroid Hormone (PTH) produced by parathyroid (chief) cells respond to low concentrations of ihibits and indirectly increases numbers for calcium release enhances reabsorption of calcium by the, reducing increases secretion by the kidneys which increases Ca 2+, PO 4 3 absorption by Antagonist for 8
HORMONES OF THE THYROID AND PARATHYROID GLANDS (4): ADRENAL GLANDS (Figure 18-14) lie along superior border of each ; subdivided into the adrenal cortex and the adrenal medulla superficial adrenal cortex, especially cholesterol and fatty acids and manufactures Inner adrenal medulla has secretory activities controlled by sympathetic division of ANS; produces and whose metabolic changes persist for several minutes Adrenal Cortex (Figure 18-14c) outer region of adrenal cortex; produces mineralocorticoids (aldosterone)! Aldosterone stimulates conservation of and elimination of increases sensitivity of in taste buds to increase desire for salty foods Causes of sodium ions by affecting the kidneys, sweat glands, salivary glands, and pancreas Secretion responds to: drop in,, or and a rise in concentration produces glucocorticoids (cortisol (hydrocortisone) with corticosterone)! Glucocorticoids accelerate and, show effects (slow phagocyte activity at injury site) and inhibit release of (cortisone creams) 9
Cortisol liver converts to cortisone; secretion regulated by negative feedback; has inhibitory effect on production of Corticotropin-releasing hormone (CRH) in hypothalamus and ACTH in adenohypophysis produces under stimulation by ACTH stimulate growth in adolescents, and muscle mass, blood cell formation, and sex drive in only The Adrenal Medulla contains two types of secretory cells: One produces epinephrine (adrenaline) 75% to 80% of medullary secretions The other produces norepinephrine (noradrenaline) 20% to 25% of medullary secretions Epinephrine and Norepinephrine activation of the adrenal medullae has the following effects: In skeletal muscles, epinephrine and norepinephrine trigger mobilization of reserves and accelerate the breakdown of to provide In adipose tissue, stored are broken down into fatty acids which are released into the bloodstream for other tissues to use for production In the liver, molecules are broken down and the resulting glucose molecules are released into the bloodstream In the heart, the stimulation of beta 1 receptors triggers an in the rate and force of HORMONES OF THE ADRENAL GLAND 10
PINEAL GLAND (Figure 18-15) lies in posterior portion of roof of third ventricle; contains pinealocytes and synthesizes the hormone melatonin Functions of Melatonin: Inhibits functions; slows maturation of sperm, oocytes, and organs; levels decrease after Protects against damage by ; serves as an protecting neural tissue from and Influences PANCREAS (Figure 18-16) lies between inferior border of stomach and proximal portion of small intestine; contains exocrine and endocrine cells Exocrine Pancreas Consists of clusters of gland cells called pancreatic and their attached ducts Takes up roughly of pancreatic volume Gland and duct cells secrete alkaline, enzyme-rich fluid called ; serves as digestive enzymes in the break down of food Endocrine Pancreas consists of cells that form clusters known as pancreatic islets, or Alpha cells produce Beta cells produce Delta cells produce identical to GH IH F cells secrete Blood Glucose Levels When levels rise: When levels decline: Insulin is a peptide hormone released by beta cells when glucose concentrations exceed normal levels Cells that have insulin receptors are Cells of the brain, kidney, digestive tract lining, and RBC s lack insulin receptors; termed ; can take up glucose without the aid of insulin Affects on target cells: Accelerates by increasing Accelerates glucose utilization and enhances production Stimulates formation when glucose is in excess Stimulates absorption and synthesis 11
Stimulates formation in adipose tissue and the absorption of which is used to make more tryglycerides Glucagon released by alpha cells; mobilizes energy reserves Affects on target cells: Stimulates breakdown of in skeletal muscle and liver cells Stimulates breakdown of in adipose tissue Stimulates production of in liver (gluconeogenesis) End result is the reduction in glucose use and the release of glucose into the HORMONES OF THE PANCREAS Hyperglycemia abnormally glucose levels in the blood in general; glucose appears in the, and urine volume generally becomes excessive Diabetes Mellitus characterized by glucose concentrations high enough to overwhelm the reabsorption capabilities of the kidneys Type 1 (insulin dependent) diabetes is characterized by inadequate insulin production by the pancreatic beta cells; persons with type 1 diabetes require insulin to live and usually require multiple injections daily, or continuous infusion through an insulin pump or other device; this form of diabetes accounts for only around 5% 10% of cases; it often develops in childhood Type 2 (non-insulin dependent) diabetes is the most common form of diabetes mellitus; most people with this form of diabetes produce normal amounts of insulin, at least initially, but their tissues do not respond properly, a condition known as insulin resistance; associated with obesity; weight loss through diet and exercise can be an effective treatment 12
Complications of untreated, or poorly managed diabetes mellitus include: Diabetic nephropathy degenerative changes in the kidneys, can lead to kidney failure Retinal Damage diabetic retinopathy ; the proliferation of capillaries and hemorrhaging at the retina may cause partial or complete blindness Early Heart Attacks degenerative blockages in cardiac circulation can lead to early heart attacks; for a given age group, heart attacks are three to five times more likely in diabetic individuals than in nondiabetic people Peripheral Nerve Problems abnormal blood flow to neural tissues is probably responsible for a variety of neural problems with peripheral nerves, including abnormal autonomic function; these disorders are collectively termed diabetic neuropathy Peripheral Nerve Damage blood flow to the distal portions of the limbs is reduced, and peripheral tissues may suffer as a result; example, a reduction in blood flow to the feet can lead to tissue death, ulceration, infection, and loss of toes or a major portion of one or both feet ENDOCRINE TISSUE OF OTHER SYSTEMS The Intestines produce hormones important to coordination of digestive activities The Kidneys produce the hormones calcitriol (calcium and phosphate absorption on the digestive tract), erythropoietin (EPO) (stimulates RBC formation when oxygen levels are low), and renin (elevates blood volume by retaining water in the kidneys) The Heart produces natriuretic peptides (ANP and BNP) when blood volume becomes excessive; action opposes angiotensin II resulting in reduction in blood volume and blood pressure; suppresses thirst The Thymus produces thymosins (blend of thymic hormones) that help develop and maintain normal immune defenses The Testes produce androgens in interstitial cells; testosterone is the most important male hormone; also secretes inhibin in nurse cells; supports differentiation and physical maturation of sperm The Ovaries produce estrogens, principal estrogen is estradiol; after ovulation, follicle cells reorganize into corpus luteum and release estrogens and progestins, especially progesterone Adipose Tissue Secretions leptin, the feedback control for appetite; controls normal levels of GnRH, gonadotropin synthesis 13
HORMONES OF OTHER SYSTEMS 14