Endocrine System PDF

ENDOCRINE SYSTEM Hormones arouse cells, or alter cellular activity. Typically, one or more of the following occurs: Second controlling system of the body...

ENDOCRINE SYSTEM Hormones arouse cells, or alter cellular activity. Typically, one or more of the following occurs: Second controlling system of the body — Nervous system is the fast-control system 1.) Changes in plasma membrane permeability or electrical state Uses chemical messengers (hormones) that are released into the blood 2.) Synthesis of proteins, such as enzymes Hormones control several major processes: 3.) Activation or inactivation of enzymes — Reproduction — Growth and development 4.) Stimulation of mitosis — Mobilization of body defenses — Maintenance of much of homeostasis 5.) Promotion of secretory activity — Regulation of metabolism Hormones act by two mechanisms: HORMONE OVERVIEW 1.) Direct gene activation Hormones are produced by specialized cells 2.) Second-messenger system Cells secrete hormones into extracellular fluids DIRECT GENE ACTIVATION (STEROID HORMONE ACTION) Blood transfers hormones to target sites 1.) Steroid hormones diffuse through the plasma These hormones regulate the activity of other cells membrane of target cells Endocrinology is the scientific study of hormones and 2.) Steroid hormones enter the nucleus endocrine organs 3.) Steroid hormones bind to a specific protein within THE CHEMISTRY OF HORMONES the nucleus Hormones are classified chemically as 4.) Hormone-receptor complex binds to specific sites * Amino acid–based, which includes: on the cell’s DNA — Proteins — Peptides 5.) Certain genes are activated that result in… — Amines 6.) Synthesis of new proteins ▪ Steroids —made from cholesterol ▪ Prostaglandins —made from highly active lipids that act as local hormones HORMONE ACTION Hormones affect only certain tissues or organs (target cells or target organs) ▪ Target cells must have specific protein receptors ▪ Hormone binding alters cellular activity #ninerarie SECOND-MESSENGER SYSTEM (NONSTEROID HORMONE ACTION) 1.) Hormone (first messenger) binds to a membrane receptor 2.) Activated receptor sets off a series of reactions that activates an enzyme 3.) Enzyme catalyzes a reaction that produces a second- messenger molecule (such as cyclic AMP, or cAMP) 4.) Oversees additional intracellular changes to promote a specific response in the target cell 2.) HUMORAL STIMULI OF ENDOCRINE GLANDS Changing blood levels of certain ions and nutrients stimulate hormone release Humoral indicates various body fluids, such as blood and bile Examples: CONTROL OF HORMONE RELEASE — Parathyroid hormone and calcitonin are produced in Hormone levels in the blood are maintained mostly by response to changing levels of blood calcium levels negative feedback — Insulin is produced in response to changing levels of A stimulus or low hormone levels in the blood triggers the blood glucose levels release of more hormone Hormone release stops once an appropriate level in the blood is reached ENDOCRINE GLAND STIMULI The stimuli that activate endocrine glands fall into three major categories: 1. Hormonal 2. Humoral 3. Neural 1.) HORMONAL STIMULI OF ENDOCRINE GLANDS Most common stimulus Endocrine organs are activated by other hormones Example: — Anterior pituitary hormones travel to target glands, such as the thyroid gland, to prompt the release of a particular hormone, such as thyroid hormone 3.) NEURAL STIMULI OF ENDOCRINE GLANDS Some glands are purely endocrine — Anterior pituitary, thyroid, adrenals, parathyroids Nerve impulses stimulate hormone release Endocrine glands are ductless glands Most are under the control of the sympathetic nervous system Hormones are released directly into blood or lymph Examples: Other glands are mixed glands, with both endocrine and exocrine functions (pancreas, gonads) — The release of norepinephrine and epinephrine by the adrenal medulla PITUITARY GLAND AND HYPOTHALAMUS Pituitary gland is the size of a pea — Hangs by a stalk from the hypothalamus in the brain — Protected by the sphenoid bone — Has two functional lobes Anterior pituitary—glandular tissue Posterior pituitary—nervous tissue Often called the “master endocrine gland” Hypothalamus produces releasing and inhibiting hormones — These hormones are released into portal circulation, which connects hypothalamus to anterior pituitary Hypothalamus also makes two hormones: oxytocin and antidiuretic hormone — Carried to posterior pituitary via neurosecretory cells for storage MAJOR ENDOCRINE ORGANS Pituitary gland Thyroid gland Parathyroid glands Adrenal glands Pineal gland Thymus gland Pancreas Gonads (ovaries and testes) Hypothalamus POSTERIOR PITUITARY AND HYPOTHALAMIC HORMONES 1.) Oxytocin — Stimulates contractions of the uterus during labor, sexual relations, and breastfeeding — Causes milk ejection (let-down reflex) in a breastfeeding woman 2.) Antidiuretic hormone (ADH) 1.) Growth hormone (GH) — Inhibits urine production (diuresis) by promoting water — General metabolic hormone reabsorption by the kidneys — Major effects are directed to growth of skeletal muscles and — In large amounts, causes vasoconstriction of arterioles, long bones leading to increased blood pressure (the reason why ADH is known as vasopressin) — Plays a role in determining final body size — Alcohol inhibits ADH secretion — Causes amino acids to be built into proteins — Diabetes insipidus results from ADH hyposecretion — Causes fats to be broken down for a source of energy HORMONES OF THE ANTERIOR PITUITARY Growth hormone (GH) disorders Six anterior pituitary hormones — Pituitary dwarfism results from hyposecretion of GH during childhood — Two affect nonendocrine targets: — Gigantism results from hypersecretion of GH during 1. Growth hormone childhood 2. Prolactin — Acromegaly results from hypersecretion of GH — Four stimulate other endocrine glands to release during adulthood hormones (tropic hormones): 2.) Prolactin (PRL) 1. Thyroid-stimulating hormone (thyrotropic hormone) 2. Adrenocorticotropic hormone — Stimulates and maintains milk production following 3. Follicle-stimulating hormone childbirth 4. Luteinizing hormone — Function in males is unknown Characteristics of all anterior pituitary hormones — Protein (or peptides) structure 3.) Adrenocorticotropic hormone (ACTH) — Act through second-messenger systems — Regulated by hormonal stimuli — Regulates endocrine activity of the adrenal cortex — Regulated mostly by negative feedback 4.) Thyrotropic hormone (TH), also called thyroid- stimulating hormone (TSH) — Influences growth and activity of the thyroid gland GONADOTROPIC HORMONES — Regulate hormonal activity of the gonads 5.) Follicle-stimulating hormone (FSH) — Stimulates follicle development in ovaries — Stimulates sperm development in testes 6.) Luteinizing hormone (LH) — Triggers ovulation of an egg in females — Stimulates testosterone production in males THYROID GLAND Thyroid hormone disorders — Found at the base of the throat A.) Goiters — Consists of two lobes and a connecting isthmus — Thyroid gland enlarges because of lack of iodine — Salt is iodized to prevent goiters Produces two hormones: 1. Thyroid hormone B.) Cretinism 2. Calcitonin — Caused by hyposecretion of thyroxine — Results in dwarfism during childhood C.) Myxedema — Caused by hypothyroidism in adults — Results in physical and mental sluggishness D.) Graves’ disease — Caused by hyperthyroidism — Results in increased metabolism, heat intolerance, rapid heartbeat, weight loss, and exophthalmos ____________________________________________________ 2.) Calcitonin — Decreases blood calcium levels by causing calcium deposition on bone 1.) Thyroid hormone — Antagonistic to parathyroid hormone — Major metabolic hormone — Produced by parafollicular cells found between the follicles — Controls rate of oxidation of glucose to supply body heat and chemical energy PARATHYROID GLANDS — Needed for tissue growth and development Tiny masses on the posterior of the thyroid Secrete parathyroid hormone (PTH) Composed of two active iodine-containing hormones — Stimulates osteoclasts to remove calcium from bone — Thyroxine (T4)—secreted by thyroid follicles — Hypercalcemic hormone (increases blood calcium levels) — Triiodothyronine (T3)—conversion of T4 at target — Stimulates the kidneys and intestine to absorb more calcium tissues ADRENAL GLANDS Sit on top of the kidneys Two regions: 1.) Adrenal cortex — outer glandular region has three layers that produce corticosteroids — Mineralocorticoids are secreted by outermost layer — Glucocorticoids are secreted by middle layer — Sex hormones are secreted by innermost layer 2. ) Adrenal medulla —inner neural tissue region 2.) Glucocorticoids (including cortisone and cortisol) — Produced by middle layer of adrenal cortex — Promote normal cell metabolism — Help resist long-term stressors by increasing blood glucose levels (hyperglycemic hormone) — Anti-inflammatory properties — Released in response to increased blood levels of ACTH 3.) Sex hormones HORMONES OF THE ADRENAL CORTEX — Produced in the inner layer of the adrenal cortex 1.) Mineralocorticoids (mainly aldosterone) — Small amounts are made throughout life — Produced in outer adrenal cortex — Mostly androgens (male sex hormones) are made, — Regulate mineral content in blood, particularly sodium but some estrogens (female sex hormones) are also and potassium ions formed — Regulate water and electrolyte balance ADRENAL GLANDS — Target organ is the kidney Adrenal cortex disorders Release of aldosterone is stimulated by: A.) Addison’s disease — Humoral factors (fewer sodium ions or too many — Results from hyposecretion of all adrenal cortex hormones potassium ions in the blood) — Bronze skin tone, muscle weakness, burnout, susceptibility to infection — Hormonal stimulation (ACTH) B.) Hyperaldosteronism — Renin and angiotensin II in response to a drop in blood — May result from an ACTH-releasing tumor pressure — Excess water and sodium are retained, leading to high blood pressure and edema Aldosterone production is inhibited by atrial natriuretic peptide (ANP), a hormone produced by the heart when blood pressure is too high C.) Cushing’s syndrome PANCREATIC ISLETS — Results from a tumor in the middle cortical area of the adrenal cortex Pancreas — “Moon face,” “buffalo hump” on the upper back, high — Located in the abdomen, close to stomach blood pressure, hyperglycemia, weakening of bones, — Mixed gland, with both endocrine and exocrine functions depression The pancreatic islets produce hormones D.) Masculinization * Insulin—produced by beta cells — Results from hypersecretion of sex hormones * Glucagon—produced by alpha cells — Beard and male distribution of hair growth ▪ These hormones are antagonists that maintain blood sugar HORMONES OF THE ADRENAL MEDULLA homeostasis Produces two similar hormones: (catecholamines) 1. Epinephrine (adrenaline) 2. Norepinephrine (noradrenaline) These hormones prepare the body to deal with short-term stress (“fight or flight”) by: — Increasing heart rate, blood pressure, blood glucose levels — Dilating small passageways of lungs 1.) Insulin — Released when blood glucose levels are high — Increases the rate of glucose uptake and metabolism by body cells 2.) Glucagon — Released when blood glucose levels are low — Stimulates the liver to release glucose to blood, thus increasing blood glucose levels HOMEOSTATIC IMBALANCE Diabetes mellitus — Occurs in the absence of insulin — Blood sugar levels increase dramatically — Blood glucose is lost in the urine; water follows Three cardinal signs: 1. Polyuria 2. Polydipsia 3. Polyphagia PINEAL GLAND Located posterior to the third ventricle of the brain Secretes melatonin — Helps establish the body’s sleep/wake cycles as well as biological rhythms — Believed to coordinate the hormones of fertility in humans THYMUS GLAND Located posterior to the sternum Largest in infants and children Produces thymosin — Matures some types of white blood cells — Important in developing the immune system GONADS Ovaries — Produce eggs — Produce two groups of steroid hormones: 1. Estrogens 2. Progesterone Testes — Produce sperm — Produce androgens, such as testosterone HORMONES OF THE OVARIES Estrogens — Stimulate the development of secondary female characteristics — Mature female reproductive organs With progesterone, estrogens also — Promote breast development — Regulate menstrual cycle Progesterone — Acts with estrogen to bring about the menstrual cycle — Helps in the implantation of an embryo in the uterus — Helps prepare breasts for lactation HORMONES OF THE TESTES Produce several androgens Testosterone is the most important androgen — Responsible for adult male secondary sex characteristics — Promotes growth and maturation of male reproductive system — Required for sperm cell production OTHER HORMONE-PRODUCING TISSUES AND ORGANS Parts of the small intestine Parts of the stomach Kidneys DEVELOPMENTAL ASPECTS OF Heart THE ENDOCRINE SYSTEM Many other areas have scattered endocrine cells In the absence of disease, efficiency of the endocrine PLACENTA system remains high until old age Produces hormones that maintain pregnancy Decreasing function of female ovaries at menopause leads to such symptoms as osteoporosis, increased Some hormones play a part in the delivery of the baby chance of heart disease, and possible mood changes Produces human chorionic gonadotropin (hCG) in Efficiency of all endocrine glands gradually decreases addition to estrogen, progesterone, and other with aging, which leads to a generalized increase in hormones incidence of: — Diabetes mellitus — Immune system depression — Lower metabolic rate — Cancer rates in some areas