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Transcript
Chapter 13: The Endocrine System Communication and Coordination 2 communicating and coordinating systems in the body: Nervous and endocrine systems Nervous system communicates using short term nerve impulses (electrical signals) Endocrine system communicates using longer lasting hormones (chemical signals) o Regulate metabolic processes (carbohydrates, proteins and fats) o Role in growth and reproduction o Regulate water and electrolyte balance o Hunger, thirst and temperature responses o Deal with infection, trauma and stress Endocrine Glands Secrete hormones directly into capillaries and not into ducts Hormones Chemical messengers that influence or control the activities of other tissues or organs Most are transported to areas of the body far from their release site Two classes o Steroids (from the adrenal cortex and sex glands) o Proteins (all other hormones) Hormone Targets Each hormone only binds to its target tissue or target organ Some have many target tissues (insulin) o Widespread, generalized effects Others have fewer target tissues o Specific effects 2 Types of Receptors Membrane receptors located on the outer surface of the cell membrane o Protein hormones bind to receptor sites and a second messenger (cAMP) is produced o cAMP helps activate cellular enzymes Intracellular receptors located within the cell o Steroid hormones (lipid soluable) pass through cell membrane and bind to receptor sites in the nucleus o Steroid-receptor complex stimulates protein synthesis Hormone Control 3 mechanisms to control secretion of hormones o Negative feedback control o Biorhythms o Central nervous system Negative Feedback Information about a hormone of its effects and fed back to the gland that secretes the hormone Insulin production Biorhythms A rhythmic alteration in a hormone’s rate of secretion Female menstrual cycle Circadian rhythm is a 24-hour rhythm o Cortisol levels highest in the morning (peak 8 am) o Lowest levels in the evening (lowest at midnight) Travel and alterations in sleep patterns can disturb these biorhythms Control by The CNS The CNS activates the hypothalamus and stimulates the sympathetic nervous system Stress can cause changes in hormone levels and cause changes in menstrual cycles Pituitary Gland Also called the hypophysis Located under the hypothalamus Attached to the hypothalamus by the infundibulum 2 main parts o Anterior pituitary gland o Posterior pituitary gland Hypothalamus Secretes several hormones and is considered an endocrine gland Secretes releasing hormones and release-inhibiting hormones These hormones stimulate or inhibit secretion of specific anterior pituitary hormones Hypothalamic hormones reach the anterior pituitary gland through the hypothalamic-hypophyseal portal system (network of capillaries) Anterior Pituitary Composed of glandular epithelial tissue Called the adenohypophysis Secretes six major hormones Often called the master gland because the hormones it releases affect so many other glands and organ systems Growth Hormone (GH) Also called somatotropin or somatotropic hormone (STH) Effects o Growth of skeletal muscles and long bones of the body Determines a persons height and size o Causes amino acids to be built into proteins and fats to be broken down and used for energy o Stimulates conversion of protein to glucose, especially between meals Causes blood glucose to rise Secreted during exercise, sleep and hypoglycemia Hypersecretion as a child leads to gigantism o Growth very tall, often 8 or 9 feet Hypersecretion as an adult leads to acromegaly o Enlarged jaw, eyebrow ridges, nose, hands and feet Deficiency in childhood leads to pituitary dwarfism o normal body proportions but short height (4 feet or less) Prolactin (PRL) Also called lactogenic hormone Promotes milk production in women Target tissue is breast tissue Stimulates growth of the mammary glands and stimulates them to produce milk after childbirth Role of PRL in males is unknown Tropic Hormones Hormones that are aimed at and control other glands Thyrotrophin or Thyroid-stimulating hormone (TSH) o Stimulates thyroid to secrete two thyroid hormones Adrenocorticotropic hormone (ACTH) o Stimulates adrenal cortex to secrete three steroids, particularly cortisol Gonadotropic hormones o Target glands are the gonads (overies or testes) o 2 gonadotropins Follicle-stimulating hormone (FSH) Stimulates production of ova or sperm Luteinizing hormone (LH) Causes ovulation and secretion of sex hormones Also called interstitial cell-stimulating hormone (ICSH) in males because it stimulates interstitial cells to synthesize and secrete testosterone Posterior Pituitary An extension of the hypothalamus Composed of nervous tissue Called the neurohypophysis Hormones produced in the hypothalamus and transported to the posterior pituitary where they are stored Nerve impulses from the hypothalamus stimulates secretion of hormones 2 hormones o Antidiuretic hormone (ADH) o Oxytocin Antidiuretic hormone (ADH) Released in an attempt to conserve water Target organ is the kidney Stimulates kidney to reabsorb water Stimulates blood vessel constriction causing elevated blood pressure o Also called vasopressin for this effect Released in response to concentrated plasma (dehydration) Also released in response to stress, trauma, drugs (morphine and nicotine) Alcohol inhibits ADH secretion Diabetes insipidus o Lack of ADH causes profound diuresis o Excretion of up to 25 liters of urine per day Oxytocin Target organs are the uterus and the mammary glands Stimulates muscles of the uterus to contract o Helps in initiation of labor and delivery of a baby Released in response to breastfeeding Stimulates the contraction of smooth muscles around the mammary ducts in the breasts releasing breast milk o Called the milk let-down reflex Pituitary Gland and MSH Small third lobe of the pituitary gland secretes melanocyte-stimulating hormone (MSH) MSH stimulates melanocytes to increase pigmentation of the skin Structure of MSH is similar to ACTH Hypersecretion of ACTH causes skin to darken and become bronzed Thyroid gland Located in the anterior neck on the front and sides of the trachea just below the larynx Two lobes connected by the isthmus 2 types of cells o Follicular cells Located within the thyroid follicle o Parafollicular cells Located between the follicles Thyroid Follicle Thyroid gland is composed of secretory units called follicles Follicular cavity lined with cuboidal cells and filled with clear viscous substance called colloid Secretes triiodothyronine (T3) and tetraiodothyronine (T4 or thyroxine) T3 and T4 Regulate the metabolism of carbohydrates, proteins and fats Increase the rate of metabolism of most cells Needed for normal maturation of the nervous system and normal growth and development Hypothyroidism Infants born with no thyroid can develop cretinism o Infant fails to develop physically and mentally o Short and stocky with abnormal skeletal development and severe mental retardation o Early diagnosis (in first 2 months) and treatment with T3 can prevent further developmental delays In an adult low thyroid function leads to myxedema, a slowed metabolic state o Slow heart rate o o o o o o Sluggish peristalsis resulting in constipation Low body temperature Low energy Loss of hair Weight gain Skin becomes thick and puffy from thick fluid accumulating under the skin Hyperthyroidism Over production of thyroid hormones leads to a sped-up metabolic state Common type is Grave’s disease o Increased heart rate o Increase in peristalsis resulting in diarrhea o Elevation in body temperature o Hyperactivity o Weight loss o Wide emotional swings o Bulging eyes called exophthalmia due to enlarged fat pads behind the eyeballs Regulation of Thyroid Gland Hypothalamus secretes ad releasing hormone This hormone stimulates the anterior pituitary to secrete TSH TSH stimulates thyroid gland to release T3 and T4 When T3 and T4 increase sufficiently negative feedback stops production of TSH Iodine and Thyroid Tetraiodothyronine or thyroxine contains four iodine atoms (T4) Triiodothyronine contains three iodine atoms (T3) Iodine comes from dietary sources and is actively pumped into the follicular cells of the thyroid gland Iodine Deficiency When iodine is deficient in the diet T3 and T4 production decreases Secretion of TSH is continuous because there isn’t a high enough concentration of T3 and T4 in the blood to shut it off Persistent stimulation of the thyroid gland by TSH causes thyroid to enlarge (goiter) Calcitonin Secreted by the parafollicular cells Works with parathyroid hormone to help regulate the plasma levels of calcium Parathyroid Glands Four tiny parathyroid glands lie on the posterior surface of the thyroid gland Secretes parathyroid hormone (PTH) Secretion stimulated by low plasma level of calcium 3 target organs o Bone o Digestive system o kidneys Calcium Regulation Low calcium o PTH released o PTH increases release of calcium from bone tissue o PTH stimulates kidneys to reabsorb calcium form urine and excrete phosphate o PTH (with vitamin D) increases absorption of calcium by the digestive tract High calcium o Calcitonin released o Calcitonin stimulates bone production o Calcitonin increases excretion of calcium in the urine Adrenal Glands Two small glands located above the kidneys Also called the suprarenal glands 2 regions o Inner medulla Hormones secreted not essential for life o Outer cortex Hormones secreted are essential for life Adrenal Medulla Inner region of the adrenal gland An extension of the sympathetic nervous system Secretes epinephrine (adrenaline) and norepinephrine Exert effects similar to the sympathetic nervous system so they are called sympathomimetic hormones Epinephrine & Norepinephrine Secreted in emergency or stress situations Elevate blood pressure Increase heart rate Convert glycogen to glucose Increase metabolic rate of most cells Cause bronchodilation Cause dilation of blood vessels to the heart and muscles Constrict blood vessels to the digestive tract Adrenal Cortex Outer region of the adrenal gland Secretes 3 steroids o Glucocorticoids o Mineralocorticoids o Sex hormones Glucocorticoids Converts amino acids into glucose and help maintain blood glucose levels between meals Also cause protein and fat to be utilized for energy production Essential for life Death will occur if adrenal cortex function is lost unless steroid are administered Cortisol Chief glucocorticoid A stress hormone secreted in greater amounts during times of physiological stress o Disease, physical injury, hemorrhage, infection, pregnancy, extreme temperature and emotional stress (anger or rage) Has an anti-inflammatory effect Used as a drug to prevent inflammation in the treatment of arthritis, sever allergic responses and swelling associated with head trauma Cortisol Secretion Hypothalamus secretes a releasing hormone Anterior pituitary stimulated to release adrenocorticotropic hormone (ACTH) ACTH stimulates adrenal cortex to secrete cortisol Cortisol inhibits further secretion of ACTH through negative feedback loop Mineralocorticoids Chief mineralocorticoid is aldosterone Important role in regulation of blood volume and blood pressure and in concentration of electrolytes in the blood Target organ is the kidney Causes conservation of sodium and water and elimination of potassium Sex Hormones Estrogens and androgens secreted in small amounts from the adrenal cortex In females the sex hormones secreted by the ovaries usually mask the effects of adrenal sex hormones After menopause adrenal androgens can cause increased body hair and other affects once production of estrogens from the ovaries decreases Hyposecretion of Cortical Hormones Insufficient production of adrenal cortical hormones Called Addison’s disease o General weakness o Muscle atrophy o Bronzing of the skin o Severe loss of fluids and electrolytes Is life threatening and must be treated with steroids and replacement of fluids and electrolytes Hypersecretion of Cortical Hormones Oversecretion of adrenal cortical hormones Caused by oversecretion of either ACTH (anterior pituitary) or cortisol (adrenal cortex) Often caused by administration of steroids as drugs o Must taper off dosage o Can’t just stop taking them all at once Causes Cushing’s syndrome o Obesity o o o o o Rounded facial apperance (moon face) Thin skin that bruises easily Bone loss Muscle weakness Salt and water retention cause blood volume and blood pressure to increase Pancreas Long slender organ that lies transversely across the upper abdomen from the curve of the duodenum to the spleen Exocrine and endocrine gland o Exocrine function concerned with digestion of food o Endocrine function secretes insulin and glucagon Hormone-secreting cell called the islets of Langerhans Pancreas Hormone-secreting cell called the islets of Langerhans Two types of cells o Alpha cells Secrete glucagon (increase blood glucose) o Beta cells Secrete insulin (lower blood glucose) Insulin Secreted by the beta cells of the islet of Langerhans Released in response to increased blood glucose levels Secretion decreases as blood glucose levels decrease Has many target tissues (liver, skeletal muscle, adipose tissue) 2 main effects o Helps transport glucose into cells o Helps control carbohydrate, protein and fat metabolism in the cell Stimulates the breakdown of glucose for energy Increases the transport of amino acids into cells and then stimulates the synthesis of proteins Promotes the synthesis of fats from fatty acids Insulin deficiency – diabetes mellitus Glucagon Secreted by the alpha cells of the islet of Langerhans Released in response to decreased blood glucose levels Increases blood glucose levels Stimulates conversion of glycogen to glucose in the liver Stimulates the conversion of proteins into glucose Diabetes Mellitus Hyperglycemia o Excess glucose in the blood Glucosuria or glycosuria o Glucose in the urine o Kidneys can’t reabsorb excess glucose and it is excreted in the urine Polyuria o Excretion of large amounts of urine o Caused by glucosuria Acidosis o Excess of acidic substances in the blood o Cells can’t utilize glucose as fuel so they fatty acids instead o Rapid, incomplete breakdown of fatty acids produces strong acids called ketoacids o Causes diabetic ketoacidosis Fruity odor to the breath o Acetone (ketone) produced by fatty acid breakdown o Acetone smells like bananas and makes the patient’s breath smell fruity o Fruity odor is a sign of ketoacidosis Gonads Sex glands Ovaries o Produce ova (eggs) Testis o Produce sperm Also secrete hormones making them glands Ovaries Located in the pelvic cavity on each side of the uterus Secrete estrogen and progesterone Help development and functioning of the female reproductive organs and expression of female sex characteristics o Breast development o Fat in hips, thighs, and breasts o Body hair growth o Maturation of reproductive organs o Closure of the epiphyseal discs of long bones Excretion controlled by hypothalamic-releasing hormones and the gonadotropins (FSH and LH) Testes Located in the scrotum Interstitial cells of the testes secrete testosterone Stimulated by anterior pituitary hormone LH Testosterone helps in maturation of sperm and is responsible for male sex characteristics o Growth and development of the male reproductive organs o Musculoskeletal growth o Body and facial hair growth o Enlargement of the larynx and voice changes Thymus Gland Lies in the thoracic cavity behind the sternum Much larger in children than in adults Involutes, gets smaller, as a child enters puberty Secretes thymosins which play a role in the immune system Pineal Gland Cone shaped gland located close to the thalamus in the brain Called the bodies “biological clock” because it controls many of the bodies biorhythms Secretes melatonin Melatonin Affects the reproductive cycle by influencing the secretion of hypothalamicreleasing hormones Plays important role in sexual maturation Plays a role in sleep/wake cycle o Lowest secretion during daylight hours o Highest secretion at night o Elevated levels in people with seasonal affective disorder (SAD) Prostaglandins Hormones derived from the fatty acid arachidonic acid Produced by many tissues and generally act near their site of secretion Important role in regulation of smooth muscle contraction and the inflammatory response Increases the sensitivity of pain nerve endings Aspirin, ibuprofen and acetaminophen block synthesis of prostaglandins