Chapter 5 The Endocrine System.pdf

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Biology - Biological Sciences
BSC 3096

Chapter 5 The Endocrine System Wednesday, July 10, 2013 5:14 PM 1. Hormone Chemistry a. General hormones are hormones released by the endocrine system i. "general" because they are released into the body fluids, often the blood, and may affect many cell types in a tissue and multiple tissues b. Exocrine glands release enzymes to the external environments through ducts i. Include sweat, oil, mucous and digestive ducts c. Endocrine glands release hormonesdirectly into body fluids i. d. The effects of the endocrine system tend to be slower, less direct and longer lasting than those of the nervous system i. Endocrine hormones can take from seconds to days e. ALL hormones act by binding to proteins called receptors i. Each receptor is highly specific for its hormone ii. Hormones bind to these receptors and initiate biochemical responses inside the cell f. One method of hormone regulation is by increasing or decreasing the number of hormone receptors in the presence of high or low concentrations of the hormone i. Some hormones have receptors on virtually all cells, while others have none g. Very low concentrations are effective h. The endocrine system works WITH the nervous system i. Many endocrine glands are stimulated by neurons i. Peptide hormones i. Derived from peptides ii. Can be large or small and often have carbs attached iii. ALL peptide hormone are manufactured in the rough ER as preprohormone iv. Once inside the ER lumen, the preprohormone is cleaved transported to the Golgi v. In the Golgi, the prohormone is cleaved again and sometimesmodified with carbs vi. The Golgi then packages the hormone into secretory vesicles and upon stimulation by another hormone or nervous signal, the cell releases vii. vii. viii. Peptide hormones are water soluble, so they can move freely through the blood, but have difficulty diffusing through the cell membrane of the target cell (effector) 1) Like started previously, the peptide hormone instead binds to a receptor 2) The receptor may act as an ion channel increasing membrane permeability to a specific ion, or behave like a G protein (which can also active secondary messengers like cAMP) 3) j. Steroid hormones i. Have a similar chemical structures because they are all derived from cholesterol ii. Instead of being stored like peptide hormones, they are synthesized as needed iii. Unlike peptide hormones which are made in tissues all over the body,steroid hormones are only made in a few organs 1) Adrenal cortex, Gonads, placenta iv. v. Formed mainly in the smooth ER and the mitochondria vi. Since they are lipids, require a protein transport molecule to travel through blood but can easily diffuse through membrane 1) k. Tyrosine derivatives i. Hormones that are derived from the AA tyrosine (which has a carbon ring structure on its R group) ii. ALL ARE FORMED BY ENZYMES IN THE CYTOSOL OR ON THE ROUGH ER IN THE ADRENAL MEDULA iii. iv. Catecholamines have one tyrosine molecule and are made by modifying the side chains of tyrosine 1) Neurohormones that bind to cell membrane receptors like peptide hormones 2) Formed in the adrenal medulla v. Thyroid hormones have two tyrosines plus iodine atoms 1) Behave more like steroid hormones 2. Negative Feedback a. Endocrine glands tend to over secrete their hormones b. The response of the pathway usually serves as the negative feedback signal that turns of the production of that hormone i. Hormones respond to conditions, they do not make conditions themselves 3. Anterior Pituitary and Hormones a. Anterior pituitary is located in the brain beneath the hypothalamus i. b. The posterior pituitary (fake pituitary) is thestorage and release site for two hormones: oxytocin and vasopressin i. These peptide hormones are synthesized in the hypothalamus and then transferred down the stalk that connects the posterior pituitary to the hypothalamus where they are stored ii. Once a signal reaches the hypothalamus, it sends an electrical signal down the posterior pituitary which then releases the vesicle 1) iii. Vasopressin, also known as antidiuretic hormone, regulates water balance in the body iv. Oxytocin controls ejection of milk during breast feeding and contractions of the uterus during labor and delivery c. The anterior pituitary secretes six hormones, 5 of which act directly on another endocrine gland (the one being prolactin, which goes directly to the breasts) i. d. The hypothalamus controls the release of these hormones with releasing and inhibitory hormones of its own hormones of its own i. ii. Prolactin controls milk production iii. Growth Hormone, stimulates growth in almost all cells of the body 1) Works by increasing episodes of mitosis, increasing cell size, increasing rate of protein synthesis, mobilizing fat stores, increase use of FA for energy, and decrease use of glucose iv. TSH, thyroid stimulating hormone, stimulates the thyroid to release T and 3 4 1) Also increases thyroid cell size, number and rate of secretion v. ACTH, adrenocorticotropic hormone, stimulates adrenal cortex to release glucocorticoids (stress hormones) 4. Adrenal Cortex a. b. The adrenal glands are located on top of the kidneys and are separated into the adrenal cortex and the adrenal medulla c. Cortex ONLY SECRETES STERIODS d. Mineral corticoids (aldosterone) affect the electrolyte balanse in the blood stream + + i. Increases blood pressure by triggering Na reabsorption and K secretion e. Glucocorticoids increase blood glucose concentration and have an even greater effect on fat and protein metabolism f. The catecholamines are epinephrine and norepinephrine i. Vasoconstrictorsof most internal organs and skin 5. Thyroid a. The general effect of T3 and 4 is to increase basal metabolic rate 6. Parathyroid a. Endocrine cells that are clustered in four small glands behind the thyroid b. Monitor plasma Ca concentrations c. When there is enough Ca around, the receptors on the parathyroid gland are bound, PTH + c. When there is enough Ca around, the receptors on the parathyroid gland are bound, PTH (parathyroid hormone) secretion is inhibited d. If Ca concentration falls below a certain level, inhibition ceases and the parathyroid cells secrete PTH (which increases calcium levels) 7. Pancreas a. Acts as both an endocrine grand and an exocrine gland 8. Male Reproduction a. Male gonads are called testes b. c. Production of sperm occurs in the seminiferous tubules of the testes i. Spermatogonia (the germ cells that undergo meiotic division)located in the seminiferous tubules arise from epithelia tissue to become spermatocytes, spermatids, and then spermatozoa 1) These developing spermatocytes stack in columns from the outer ege of the tubule to the lumen 2) Between each column is a Sertoli cell ii. Sertoli cells 1) Nourish the developing sperm cells 2) Produce androgen-binding protein 3) ABP is secreted into the seminiferous tubule lumen where it binds to
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