Hormone Producing Structures Thyroid Gland Two lobes connected by isthmus Largest pure endocrine gland Histological Composition Gland composed of epithelial tissue surrounding follicles made up of epithelial cells Cells produce thyroglobulin thyroid hormone plus iodine Stored in follicals as colloid Thyroid hormone derived from colloid Also contain parafollicular fells Produce calcitonin Thyroid Hormone Actually 2 separate hormones T3 T4 Functions Increases basal metabolic rate and heat production increases oxidation of glucose exergonic production Calorigenic effect Maintains blood pressure Increases number of adrenergic receptors receptors associated with ANS causes increase of basorestriction which cause increase in BP Regulates tissue growth and development Synthesis Anterior pituitary secretes TSH result of TRH produced by pituitary which travels to thyroid gland via blood vessels TSH triggers production of and uptake of thyroglobulin by promoting protein synthesis in cell which accumulates in follicles TSH triggers active transport of iodine into follicles Thyroglobulin is iodized to form T1 and T2 T1 and T2 link to form T3 and T4 T3 and T4 are packaged into lysosomes Lysosomal enzymes free T3 and T4 and release them into bloodstream Diurnal Cycle Thyroid unique in that it can store hormone TSH peaks before sleep and remains high at night Produced TH stored in extracellular colloid Transport T3 and T4 bind to transport proteins in bloodstream Esp TBG thyroxin binding globulin Delivered to target cells and bind to intracellular receptors Transcription results Feedback Increasing levels of T4 inhibit TSH production Falling levels of T4 stimulate it TSH Increase in body energy needs stimulate release of TRH which will promote TSH which will promote thyroid hormone production Calcitonin Produced by parafollicular cells Called C cells Function Lowers blood calcium levels Most important in periods of rapid skeleton growth and reformation Action Inhibits osteoclast breakdown of bone activity Stimulates calcium uptake and deposition Feedback High calcium levels are humoral stimuli for C cell activity Low calcium levels inhibit C cell activity Parathyroid Gland Embedded in in posterior portion of thyroid gland Histological Composition Two types glandular cells Oxyphil cells not sure what they do Chief cells secrete parathyroid hormone PTH Parathyroid Hormone PTH Most important hormone in controlling calcium balance of blood Action Stimulates osteoclasts to release calcium and phosphates to blood Enhances reabsorption of calcium by kidneys Increases absorption of calcium by intestines Promotes kidneys to convert vitamin D to its active form calcitriol D3 Adrenal Glands Paired glands located atop each kidney Each comprised of cortex and medulla Adrenal Cortex Hormones Secretes Corticosteroids Mineralocorticoids Glucocorticoids Gonadocorticoids Histological Composition Zona glomerulosa Zona fasiculata Zona reticularis Mineralocorticoids Major hormone is aldosterone Function to regulate electrolyte concentrations of extracellular fluids Action Stimulates sodium reabsorption In distal parts of kidney tubules Also from sweat saliva and gastric juice Other ions and water linked to sodium Therefore controls blood pressure and blood volume Feedback Aldosterone secretion stimulated by High potassium levels Low sodium levels Low blood volume Low blood pressure Mechanisms of Secretion Renin angiotensin mechanism Mechanisms of Secretion Renin angiotensin mechanism Plasma concentration mechanism Mechanisms of Secretion Renin angiotensin mechanism Plasma concentration mechanism ACTH mechanism Mechanisms of Secretion Renin angiotensin mechanism Plasma concentration mechanism ACTH mechanism Atrial natriuretic peptide ANP Glucocorticoids Major hormone is cortisol Function to regulate energy metabolism of most body cells and resist stressors Action Maintain blood sugar levels Gluconeogenesis production of new glucose molecules from non carbon Maintain blood volume by preventing uptake of water by cells Feedback CRH promotes ACTH which promotes cortisol Cortisol inhibits both CRH and ACTH Effects of Stress Increase cortisol Increase gluconeogenesis Liberate fatty acids for energy Break down proteins into amino acids Assist in vasoconstriction Gonadocorticoids Major hormones are weak androgens male sex hormones however its precursor DHEA can become testosterone or estrogen These converted to testosterone and estrogen Contribute to onset of puberty Provide sex drive to women Anatomy Joke of the Day Feedback ACTH stimulates production of gonadotropin Inhibition not noted Adrenal Medulla Hormones Epinephrine Norephinephrine Histological Composition Chromaffin cells are modified ganglionic sympathetic neurons Action Stress promotes release by stimulating sympathetic nervous system Blood sugar levels rise so that glucose becomes available to cells Blood vessels constrict Heart beat increases Blood pressure rises Blood is diverted to brain heart skeletal muscles and preganglionic sympathetic nerve endings in adrenal medulla fight or flight Pancreas Located in abdomen behind stomach Has both exocrine and endocrine components Histological Composition Acinar cells exocrine portion Pancreatic islets Islets of Langerhans endocrine Alpha cells Beta cells Glucagon Functions on liver to release glucose into blood Actions Breaks down glycogen into glucose Synthesizes glucose from lactic acid and noncarbohydrate molecules Releases glucose into blood Feedback Low blood sugar levels and high amino acid levels exert humoral control And reverse Sympathetic stimulation of medulla promotes release Somatostatin also inhibits release Insulin Lowers blood sugar levels Influences protein and fat metabolism Actions Enhances membrane transport of glucose into cells Inhibits breakdown of glycogen into glucose Inhibits conversion of amino acids or fats to glucose Feedback High blood sugar levels stimulate production Also high levels of fatty acids and amino acids Parasympathetic release of acetylcholine stumlates release Hormonal influences also exist Gonads Testes Ovaries Sex Hormones Female Male Testosterone Estrogen Progesterone Actions Testosterone Maturation and maintenance of male reproductive organs Secondary sex characteristics Sex drive Sperm production Estrogen Maturation of female reproductive organs Secondary sex characteristics Progesterone Functions with estrogen to Promote breast development Cause cyclic changes in