I Endocrine System A) Function 1) control systems, maintain homeostasis a) control chemical and water balance in body b) control growth and metabolism c) control embryonic development and preparation for nurturing a newborn d) influence sexual behavior, stimulate growth and maturation of the gonads e) feedback to the nervous system f) early studies on insect molt B) How does it work? - Basic Overview of the Feedback System 1) Nervous systems monitors environment 2) If aberrations are detected - nervous system sends message to endocrine glands 3) Endocrine glands produce and secrete hormones into blood 4) Hormones hit target organ 5) Target organ produces substance 6) Substance is picked up by receptors and brain stops sending message to endocrine glands II Endocrine System - Components A) Components 1) Endocrine glands 2) Chemical messages = hormones 3) works intimately in conjunction with the nervous and circulatory systems Example: Hypothalamus - Anterior Pituitary Example: Hypothalamus - Posterior Pituitary 4) Disorders - homeostatic imbalances Hyposecretion of hormones by glands - low levels of hormones being produced Hypersecretion of hormones by glands - high levels of hormones being produced B) Humans as an example of typical vertebrate endocrine system 1) Anterior pituitary gland and its hormones (base of the brain) a) GH - growth hormone, stimulates muscle and skeletal growth, 1) Target organ - liver, stimulates liver to produce growth factors that stimulate bone and cartilage growth 2) disorders Hypo (pituitary dwarfism) Hyper (early development leads to gigantism; abnormal growth of hands and feet - acromegaly in adulthood) b) TSH - Thyroid stimulating hormone, stimulates Thyroid Gland to produce hormones Disorder: Hyper - Goiter (overstimulation of thyroid) c) FSH - follicle stimulating hormone, stimulates development of follicles d) LH - luteinizing hormone, stimulates development of testes and ovaries e) ACTH - stimulates adrenal glands to produce hormones f) PRL (prolactin) - stimulates mammary gland growth and milk production 2) Posterior Pituitary a) Oxytocin - stimulates uterine contractions, milk ejection reflex in the mammary glands b) ADH - antidiuretic hormone, stimulates retention of water action blocked by alcohol and caffeine 3) Thyroid Gland (neck) a) Thyroxine Target organs - primarily skeletal, muscle tissue stimulates metabolic rate for growth increases oxygen consumption and cell metabolism Disorders Hyper - hyperthyroidism (increases temperature and BP, weight loss, irritability) Hypo - lethargy, weight gain, cretinism in children (abnormal skeletal growth and retardation) b) Calcitonin - regulates Ca++ levels in the blood (decreases concentration) Target organs - kidney, bone, digestive system 4) Adrenal Glands (on top of kidneys) - hormones in the fight/fright response a) Glucocorticoids - raises glucose levels in the blood, stimulates glucose production by cells b) Epinephrine - complement supply from the sympathetic system function is to give the body an energetic boost, increase metabolic rate, dilates bronchioles in the lungs, increases heart rate, etc. Target - most systems of the body c) Mineralocorticoids - retention of ions 5) Pancreas (at junction of stomach and small intestine) a) Insulin - lowers blood sugar levels (secreted by beta cells) Target organs - liver, skeletal, adipose (fat) tissues Diabetes - Hypo Type I - autoimmune disorder (destroys ability to produce insulin) Type II - due to aging, lifestyle, heredity and other lifestyle (diet) factors decreased responsiveness by cells of target organs to insulin b) Glucagon - increases blood sugar levels (secreted by alpha cells) Target organs - liver, skeletal, adipose (fat) tissues 6) Male gonads - testes (pelvic region on men) a) testosterone, maintain secondary sexual characteristics, stimulate sperm production 7) Female gonads - ovaries (pelvic region of women) a) estrogen and progesterone, maintain secondary sexual characteristics, regulate reproductive cycle C) How do hormones work? 1) 2nd messenger system - most hormones attach to receptors on the cell membrane, they never enter the cell, the receptor delivers the message, usually in the form of cAMP 2) Direct system - only steroids (sex hormones) can pass through the cell membrane and directly affect DNA or chemical reactions in the cell
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