Endocrine System: Hormone-Producing Structures and Their Functions - Prof. John R. Cumming, Study notes of Biology

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Lecture Objectives

Hormone-Producing Structures

Identify the hormone producing organs, list the hormones each produces, and discuss the actions of each product.  Thyroid Gland o Thyroid Hormone  Increases basal metabolic rate and heat production (calorigenic effect- breakdown of glucose releasing heat)  Maintains blood pressure (increases number of adrenergenic receptors on the blood vessels; norepinepherine combine with andregernic receptors and cause basal constriction)  Regulates tissue growth and development o Calcitonin  Produced by parafollicular cells  Lowers blood calcium levels  Inhibits the activity of the osteoclasts (which break down bone and release calcium)  Stimulates calcium uptake and deposition (osteoblasts)  Parathyroid Gland o Parathyroid Hormone (PTH)  Control the balance of calcium in the blood  Antagonist to calcitonin  Stimulates osteoclasts to release calcium and phosphates to blood (breaks down bone to release stored minerals)  Enhances reabsorption of calcium by kidneys  Increases absorption of calcium by intestines  Promoyes kidneys to convert vitamin D to its active form- calcitriol (D 3 helps kidneys absorb calcium)  Adrenal Glands o Adrenal Cortex Hormones  Corticosteroids  Mineralocorticoids o Aldosterone o Regulate electrolyte concentrations of extracellular fluids (Sodium and potassium) o Stimulates sodium reabsorption (in kidney tubules) o Helps control blood pressure and blood volume  Glucocorticoids o Cortisol o Regulates energy metabolism of most body cells and resists stressors

o Maintians blood sugar levels (Gluconeogenesis- production of sugar from non-sugar sources) o Maintains blood volume by preventing uptake of water into cells  Gonadocorticoids o Major hormones are week androgens o Contribute to the onset of puberty  Fat soluble  Adrenal medulla hormones  Epinephrine o Increases heart rate o Contracts blood vessels o Dilates air passages o Flight or Flight  Norepinephrine o Fight or Flight o Contracts blood vessels o Dilates air passages o Increases heart rate  Water soluble  Pancreas o Exocrine and endocrine components o Produces digestive enzymes and chemical signaling molecules o Gulcagon  Alpha cells  Functions on liver to release glucose into the blood  Breaks down glycogen into glucose  Synthesizes glucose from lactic acid and noncarbohydrate molecules  Releases glucose into blood  Increases blood glucose levels o Insulin  Lowers blood sugar levels by putting it back into storage  Influences protein and fat metabolism  Enhances membrane transport of glucose into cells  Inhibits breakdown of glycogen into glucose  Inhibits conversion of amino acids or fats to glucose  Inhibits conversion of amino acids or fats to glucose  Inhibits glucoaminogenesis  Promotes the oxidation of glucose (into ATP)  Important in creating the binds between glucose substrates that create glycogen  Insulin promotes the conversion of glucose into fat  High levels of blood sugar or fatty acids increase the release  Parasympathetic

 Testes o Testosterone  Maturation and maintenance of male reproductive organs  Secondary sex characteristics  Sex drive  Sperm production  Ovaries o Estrogen  Maturation of female reproductive organs  Secondary sex characteristics o Progesterone  Functions with estrogen to promote breast development and cyclic changes in uterine lining  Pineal Gland o Melatonin  Promotes drowsiness  Inhibits sexual maturation  Thymus o Thymoprotiens o Thymic factor o Thymosins o All influence the development of T lymphocytes (mature in the thymus) and B lymphocytes (mature in the bone marrow) which are important in immunity  Heart o ANP: causes kidneys to secret a concentrated, salty urine and helps the promotion of aldosterone  Gastrointestinal tract  Placenta o Estrogen o Progesterone o hCG (human corionic gonadotropin) o Helps regulate fetal development  Kidneys o Erythorpoietin: important in increasing RBC production  Skin o Cholecalciferol: inactive form of vitamin D  Adipose Tissue o Leptin: stimulated by fat build up; suppresses appetite and stimulates energy expenditure Describe the histological composition of each of the endocrine glands to illustrate how the hormones are produced.  Thyroid Gland o Composed of follicles made up of epithelial cells

o Around the follicles are cuboidal epithelial (produce thyroglobulin) o Parafollicular cells (produce calcitonin)  Parathyroid Gland o Oxyphil cells (function not known) o Chief cells (secrete PTH)  Adrenal Gland o Cortex  Glandular epithelial  Mineralcorticoids  Glucocorticoids  Gonadocorticoids  3 regions  zona glomerulosa  zona fasiculata  zona reticularis o Medulla  Sympathetic nervous system  Produces epinephrine and norepinephrine  Chromaffin cells are modified ganglionic sympathetic neurons  Pancreas o Acinar cells  Exocrine cells: aid in digestion o Pancreatic islets  Alpha cells: produce glucagon  Beta cells: produce insulin  Gonads  Pineal Gland o Pinealocytes: secrete Melatonin  Thymus  Heart  GI Tract  Placenta  Kidneys  Skin o Epithelial  Adipose Tissue Outline the feedback mechanisms that control endocrine gland activity.  Thyroid Gland o Thyroid Hormone  Increasing levels of T4 inhibit TSH production, while falling levels stimulate it  Increase in body energy needs stimulate the hypothalamus which causes release of TRH, increase in TSH, increase in T1 and T o Calcitonin  High calcium levels are humoral stimuli for C cell activity

 Low calcium levels inhibit C cell activity  Adrenal Gland o Mineral corticoids  Aldosterone secretion stimulated by:  High potassium levels  Low sodium levels  Low blood volume  Low blood pressure o Glucocoirticoids  CRH promotes ACTH which promotes cortisol  Cortisol inhibits both CRH and ACTH o Gonadocorticoids  ACHT stimulates production  Pancreas o Glucagon  Low blood sugar levels and high amino acid levels exert humoral control  Sympathetic stimulation of medulla promotes release  Somatostatin inhibits release  Low blood sugar stimulates glucagon release; high blood sugar inhibits glucagon release o Insulin  High blood sugar levels stimulate production  Parasympathetic release of acetylcholine stimulates release  Hormonal influences also exist  Can be a tropic gland and be stimulated by other hormones  Gonads o Regulated by gonadotropin from the pituitary Discuss four mechanisms of mineralocorticoid secretion.  Renin-angiotensin mechanism o Low blood pressure causes kidneys to produce rennin catalyzes antiotensin (produced by liver) into antinosin II which stimulates adrenal cortex  Plasma concentration mechanism o High in potassium, low in sodium chances medulla membrane and causes production  ACTH mechanism o Stress causes CRH production; CRH causes ACTH to be produced; stimulates adrenal cortex to produce aldosterone  Atrial natriuretic peptide o Produced by the heart when blood pressure goes up o Inhibits rennin-limits aldosterone