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Transcript
Endocrine System The Endocrine System Major controlling system in the body Endocrine system has a slower and more prolonged response (US Mail service) than the nervous system (email) but usually effects last longer Maintains homeostasis by releasing chemicals called hormones into the bloodstream from glands The Endocrine System Hormones Act as messengers by binding to cellular receptors on the plasma membrane of a target cell or organ Alter the activity of body cells that control growth, development, reproduction and maintenance of electrolyte, water and nutrient balance of the blood, regulation of cellular metabolism and energy balance The Endocrine System Glands Organ that produces and releases a substance Exocrine glands Produce substances such as sweat and saliva and have ducts that carry these substances to a membrane surface Endocrine glands (ductless glands) Produce hormones and lack ducts; release their hormones into the bloodstream The Endocrine System Two general groups of hormones Steroid hormones (does enter cell) Produced from cholesterol Binds to a receptor in the cell’s nucleus Activates a gene to transcribe mRNA Non-steroid hormones (doesn’t enter cell) Most hormones are amino acid based Proteins, peptides and amino acids Binds to a plasma membrane receptor Act through a second messenger such as cyclic AMP The Endocrine System All hormones circulate to virtually every tissue but a given hormone influences the activity of only certain tissue cells called target cells Protein receptors are found on the plasma membrane that respond to only a specific hormone When the binding occurs the hormone influences the cell by either turning on specific genes or using a secondary messenger to initiate a response The Endocrine System How are blood levels of all hormones regulated? Negative feedback system Goal is to shut off the stimulus or reduce its intensity back to normal range of functioning Hormone secretion is triggered by a stimulus Hormonal stimulus – stimulated by another endocrine gland Humoral stimulus - stimulated by changes in certain ions and nutrients in the bloodstream Neural stimulus - stimulated by a neuron Endocrine Glands Endocrine organs are usually smaller and unimpressive compared to other organs and scattered throughout the body Pituitary gland Thyroid gland Parathyroid glands Pineal glands Thymus gland Adrenal glands Pancreas Gonads Ovaries and testes Placenta Endocrine Glands Hypothalamus Produces and releases hormones that control other endocrine glands Considered a neuroendocrine organ Endocrine Glands Pituitary gland Seated in the sella turcica of the sphenoid bone Size and shape of a grape Hangs below the hypothalamus by the infundibulum or stalk Secretes eight hormones Two functional lobes controlled by the hypothalamus Anterior pituitary (glandular tissue) releases hormones Posterior pituitary (nervous) releases hormones that are stored here from the hypothalamus Endocrine Glands Anterior Pituitary Gland - “Master endocrine gland” Many of the hormones it produces regulates the activity of other endocrine organs called tropic hormones Thyroid stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), follicle stimulating hormone (FSH) and luteinizing hormone (LH) Endocrine Glands Anterior Pituitary Gland Growth hormone (GH) Promotes most body cells to increase in size and divide Major target is to stimulate the growth of skeletal muscles and bones Endocrine Glands Anterior Pituitary Gland Growth hormone (GH) Hypersecretion in children results in gigantism Abnormally tall often 8 feet with normal body proportions Usually results from an anterior pituitary tumor Hyposecretion in children leads to slowed long bone growth called pituitary dwarfism Abnormally short around 4 feet with fairly normal body proportions Can be corrected with growth hormone replacement therapy On the downside, athletes use the synthetic GH as bodybuilding properties Endocrine Glands Anterior Pituitary Gland Thyroid stimulating hormone (TSH) Regulates the growth and activity of the thyroid gland Endocrine Glands Anterior Pituitary Gland Adrenocorticotropic hormone (ACTH) Stimulates the adrenal cortex gland to release hormones that help resist stressors Stimulated by stress, major surgery, trauma or fever Endocrine Glands Anterior Pituitary Gland Gonadotropins Follicle-stimulating hormone (FSH) and Luteinizing hormone (LH) Regulate the function of the gonads and not present until puberty Follicle-stimulating hormone (FSH) Stimulates gamete (sperm or egg) production Luteinizing hormone (LH) Promotes the production of gonadal hormones Females – LH works with FSH to cause ovarian follicle to mature LH then triggers ovulation Males - stimulates the testes to produce testosterone Endocrine Glands Anterior Pituitary Gland Prolactin (PRL) Stimulates and maintains milk production in mammary glands of females Function unknown in males Stimulated by the infant’s suckling on the breasts Hypersecretion causes inappropriate lactation, lack of menses and impotence in males Endocrine Glands Posterior Pituitary Gland Stores antidiuretic hormone (ADH) and oxytocin that are made and sent from the hypothalamus Oxytocin Stimulated when cervix or uterus stretches or suckling of infant at breast Causes smooth muscle contractions specifically in the uterus and breasts Initiates labor and milk ejection Released in high amounts during childbirth and nursing women Natural and synthetic oxytocic drugs are used to induce labor Endocrine Glands Posterior Pituitary Gland Antidiuretic Hormone (ADH) Diuresis is urine production An antidiuretic is a substance that inhibits or prevents urine formation Prevents wide swings in water balance helping the body avoid dehydration and water overload Osmoreceptors continually monitor the blood to control ADH release Targets the kidney tubules and causes more water to be reabsorbed Drinking alcohol inhibits ADH secretion and causes lots of urine output Dry mouth and intense thirst of the ‘hangover’ reflect this dehydrating effect of alcohol Endocrine Glands Posterior Pituitary Gland Antidiuretic Hormone (ADH) Hyposecretion of ADH can result in diabetes insipidus (tasteless) (not diabetes mellitus (honey)) Syndrome marked by huge amounts of urine outputs and intense thirst Usually caused by head trauma that damages the posterior pituitary Not serious when the thirst center is operating properly and enough water is drunk Can be life threatening in unconscious or comatose patients Hypersecretion of ADH occurs in children with meningitis, after neurosurgery or secretion from cancer cells Symptoms include retention of fluid, headache, disorientation due to brain edema, and weight gain Endocrine Glands Thyroid Gland Butterfly-shaped; located in the anterior neck on the trachea just inferior to the larynx Largest pure endocrine organ in the body Secretes two hormones Thyroid hormone (TH) and calcitonin Endocrine Glands Thyroid Gland Thyroxine (T4) and Triiodothyronine (T3) make up the thyroid hormone (TH) Regulated by thyroid stimulating hormone (TSH) Stimulates metabolism in every cell in the body Increases the rate at which glucose is burned and body heat production Iodine is essential for formation of the hormones Calcitonin Regulated by blood calcium levels Decreases blood calcium levels Initiates bone resorption Stimulates calcium uptake and deposits into bones Endocrine Glands Thyroid Gland Hypothyroid syndrome, myxedema, can be caused by lack of TSH or lack of iodine in diet Symptoms include low metabolism, chilled, thick, dry skin, puffy eyes, edema, lethargy, obesity and mental sluggishness Goiter - lack of Iodine causes the thyroid gland to enlarge Endocrine Glands Thyroid Gland Hyperthyroidism usually results in an autoimmune disease called Grave’s disease Person makes abnormal antibodies directed against the thyroid cells and cause the TH to be constantly stimulated Symptoms include high metabolic rate, excessive perspiration, irregular heartbeat, nervousness, weight loss, and exophthalmos (protruding eyeballs) Endocrine Glands Parathyroid Gland Four tiny glands nearly hidden from view on the posterior aspect of the thyroid gland Parathyroid hormone (PTH) Stimulated by blood calcium levels Increases blood calcium levels Stimulates bone destruction by osteoclasts Resorption of calcium by the kidneys Uptake from intestines Endocrine Glands Parathyroid Gland Hypoparathyroidism usually follows parathyroid gland trauma or removal Low amounts of calcium in the blood leads to classical symptoms of tetany such as loss of sensation, muscle twitches, and convulsions Endocrine Glands Adrenal Glands Located over the top of the kidneys Structurally two endocrine organs in one Adrenal cortex (hormone) Two major steroid hormones (aldosterone and cortisone) Adrenal medulla (sympathetic nervous system) Two hormones (epinephrine and norepinephrine) Endocrine Glands Adrenal glands Responds to short and long term stress Short term stress response = adrenal medulla Stimulated by the hypothalamus Releases epinephrine and norepinephrine Long term stress response is adrenal cortex Stimulated by ACTH Releases mineralcorticoids and glucocorticoids Endocrine Glands Adrenal Cortex Synthesizes over two dozen steroid hormones called corticosteroids Mineralcorticoids (primarily aldosterone) Regulate the electrolyte concentrations in extracellular fluids Glucocorticoids (primarily cortisol) Influence the energy metabolism of most body cells and help us to resist stressors Gonadocortocoids Adrenal sex hormones Endocrine Glands Adrenal Cortex Aldosterone (mineralocorticoids) Regulated by a decrease in sodium levels or elevated potassium levels Promotes reabsorption of sodium and excretion of potassium in the kidneys Hypersecretion usually results from tumors Symptoms include hypertension and edema due to excessive sodium and water retention Endocrine Glands Adrenal Cortex Cortisone (glucocorticoids) Stimulated by adrenocorticotropic hormone (ACTH) Increases blood glucose Endocrine Glands Adrenal Cortex Addison’s disease Hyposecretory disease of the adrenal cortex Deficits in glucocorticoids and mineralocorticoids Symptoms include weight loss, decrease levels of glucose and sodium, increase in potassium levels, severe dehydration and hypotension are common Endocrine Glands Adrenal Medulla Neural stimulus by the sympathetic nervous system Two hormones secreted epinephrine (adrenaline) and norepinephrine Blood glucose levels rise, blood vessels constrict, heart beats faster, blood is diverted from nonessential organs to the heart and skeletal muscles Epinephrine is used as a heart stimulant in heart attack patients and a bronchodilator in asthma attacks Endocrine Glands Adrenal Medulla Hypersecretion of epinephrine and norepinephrine are usually caused by a tumor Produces symptoms of uncontrolled sympathetic nervous system activity Hyperglycemia (elevated blood glucose), increased metabolic rate, rapid heartbeat and palpitations Endocrine Glands Pineal gland Tiny, pine cone shaped; located in the third ventricle in the brain Function is still somewhat a mystery Major secretory product is melatonin Involved in rhythmic activities (daily and seasonal) Levels in the blood rise and fall in a daily cycle Highest at night making us drowsy and lowest occurring around noon Regulated by visual cues of daylight Endocrine Glands Pancreas Located partially behind the stomach in the abdominal cavity Mixed gland composed of both endocrine and exocrine gland cells Exocrine cells produce enzyme rich juice for digestion Endocrine cells called islets of Langerhans secrete glucagon and insulin that help regulate blood glucose levels Endocrine Glands Pancreas Glucagon (hyperglycemic hormone) Major target is the liver Humoral stimulation due to blood glucose levels falling Raises blood glucose levels from the breakdown of glycogen to glucose, makes glucose from lactic acid and releases glucose to the blood by liver cells Endocrine Glands Pancreas Insulin (hypoglycemic hormone) Humoral stimulation due to blood glucose levels rising Lowers blood glucose levels by enhancing membrane transport of glucose into body cells, inhibiting the breakdown of glycogen to glucose, inhibiting the conversion of amino acids or fats to glucose and promoting protein synthesis or fat storage Endocrine Glands Pancreas Hyposecretion or hypoactivity of insulin results in diabetes mellitus When insulin is absent blood sugar levels remain high after a meal because glucose is unable to enter the cells Eventually excess of glucose begins to be lost from the body in the urine (glycosuria) Three cardinal signs of diabetes are polyuria (huge urine outputs), polydipsia (excessive thirst), and polyphagia (excessive hunger and food consumption) Can be treated with synthetic insulin Endocrine Glands Pancreas Hyperinsulinism results in low blood glucose levels or hypoglycemia Triggers the release of hyperglycemic hormones like glucagon Causes anxiety, nervousness, tremors, and weakness Insufficient glucose in the brain causes disorientation, convulsions, unconsciousness and even death Treated with ingesting sugar Endocrine Glands Gonads Produce steroid sex hormones testosterone and estrogen/progesterone Regulated by gonadotropins (FSH and LH) Endocrine Glands Ovaries (women) Found in the pelvic cavity of the female Produce estrogen and progesterone Estrogen Maturation of the reproductive organs Development of the secondary sex characteristics at puberty Stimulates uterine lining Prepare uterus to receive fertilized egg Progesterone Acts with estrogen to bring about the menstrual cycle Promotes the growth of uterine lining Endocrine Glands Placenta Temporary endocrine organ Secretes estrogen, progesterone and human chorionic gonadotropin (hCG) that influence the course of the pregnancy Endocrine Glands Testes (men) Paired glands suspended in the scrotum Produce testosterone Maturation of the male reproductive organs during puberty Development of secondary sex characteristics Stimulates the male sex drive Needed for normal production of sperm