The Endocrine System

Exocrine vs Endocrine Classified by location of secretion Exocrine- through tube or duct to a surface Endocrine- secrete into internal environment

Endocrine Glands Can be cell, tissue, or organ (gland) Hormone- messenger secreted by gland Target cell- receives the message –Receptor for hormone –Hormone creates a response Tropic hormones- hormone whose target cell is another endocrine gland

Other Messengers “Local Hormones”- never reach bloodstream –Paracrine- affect neighboring cells –Autocrine- affect secreting cell Prostaglandins- lipids messenger usually affecting organ secreted in

Hormone Action Steroid HormoneSteroid Hormone (derivative of cholesterol) Steroid Hormone –Must be carried by plasma proteins through bloodstream –Diffuse into any cell –Binds to receptor in cell –Activates specific area of DNA –Protein synthesis is end result –Example Example

Hormone Action (cont) Nonsteriod hormoneNonsteriod hormone (amines, peptides, proteins) Nonsteriod hormone –Hormone (primary messenger) binds to receptor on outside of cell –Binding causes activity center inside cell to activate a messenger (sometimes cAMP) –This second messenger cause the change in the target cell

Hormonal Control Stimulation of hormone release –Hypothalamus –Nervous system –Changing internal environment Inhibition of hormone release –Negative feedback loop

Hypothalamus Located deep inside the brain Releasing and inhibiting hormone secretion to anterior pituitary Direct innervation to posterior pituitary

Pituitary Gland Located deep within the brain Divided into two sections Anterior Pituitary- glandular epithelium with many blood vessels Posterior Pituitary- nerve fibers and neuroglial cells

Tropic Hormones of the Anterior Pituitary Thyroid-stimulating hormone (TSH) Adrenocorticotropic hormone (ACTH) Gonadotropins –Follicle-stimulating hormone (FSH) –Lutenizing hormone (LH)

Thyroid-stimulating hormone (TSH) Thyroid-stimulating hormone (TSH) Stimulation: Thyrotropin-releasing hormone (TRH) from hypothalamus Inhibition: Circulating thyroid hormones decrease TSH and TRH secretion Target Cell: Thyroid Action: Increase thyroid secretions

Adrenocorticotropic hormone (ACTH) Stimulation: Corticotropin-releasing hormone (CRH) from hypothalamus Target Cell: Adrenal cortex Action: Increase adrenal cortex secretions

Follicle-stimulating hormone (FSH) Stimulation: Gonadotropin-releasing hormone from hypothalamus Target Cell: Gonads (testes in males and ovaries in females) Action: –Female- maturation of egg; secretion of estrogen –Male- development of sperm

Lutenizing hormone (LH) Also called Interstitial cell stimulating hormone (ICSH) Stimulation: Gonadotropin-releasing hormone from hypothalamus Target Cell: Gonads (testes in males and ovaries in females) Action: –Female- release of mature egg from ovary (ovulation) –Male- development of interstitial cell; secretion of male sex hormones

Other hormone of the Anterior Pituitary Growth Hormone (GH) –Stimulation: GH-releasing hormone from hypothalamus –Inhibition: GH release-inhibiting hormone –Target Cell: Somatic cells –Action: enhances movement of amino acids across cell membrane; speeds up rate of carbohydrate utilization

Other hormone of the Anterior Pituitary (cont) Prolactin (PRL) –Stimulates breast development necessary for lactation –Stimulates breast to secrete milk after birth

Posterior Pituitary Antidiuretic hormone (ADH) –Stimulation: Nerve Impulse from hypothalamus when osmoreceptors sense dehydration –Target Cell: kidneys –Action: kidneys produce less urine to conserve water Oxytocin (OT) –Stimulates contraction of the pregnant uterus –Stimulates “let-down” of milk

Thyroid Location: attached to front of trachea Contains follicles Follicles have hollow center cavity filled with colloid

Thyroid (cont) Follicular cells secrete two hormones –Thyroxine (tetraiodothyronine)- T 4 –Triiodothyronine- T 3 (much more potent) –Increases metabolism of carbohydrates, lipids, and proteins Extrafollicular cells secrete calcitonin –Lowers blood calcium level by inhibiting osteoclasts and making kidney secrete more calcium in urine

Parathyroid glands Located on the thyroid in four patches of highly dense secretory cells Secrete Parathyroid hormone (PTH) –Raises blood calcium levels –Inhibits osteoblasts, stimulates osteoclasts, makes kidneys conserve calcium, increase absorption of calcium in intestine

Adrenal glands

Adrenal Cortex Three layers: outer, middle, and inner Closely packed masses of epithelial tissue

Outer Layer of Cortex Outer (glomerulosa) –Mineralocorticoid (MC)- regulate mineral electrolytes Aldosterone –Stimulated by decrease in blood levels of sodium, increase in potassium in blood levels, or decrease in blood pressure –Cause kidneys to retain sodium and secrete potassium into urine –Indirectly water will be retained as well

Adrenal Cortex (cont) Middle (fasciculata) –Glucocorticoids- affects glucose metabolism Cortisol or hydrocortisone –Increase gluconeogenisis –Inhibition of protein synthesis –Promotion of fatty acid release from adipose tissue –Produce state of stress

Adrenal Cortex (cont) Inner (reticularis) –Sex hormones Produces androgen hormones Can be used to synthesize female sex hormones like estrogens

Adrenal Medulla Composed of modified neurons Secrete epinephrine (adrenaline) and norepinephrine (noradrenaline) “Fight or Flight” response Directly innervated by sympathetic nervous system

Pancreatic Islets (Islets of Langerhans) Alpha cells –Glucagon Accelerates process of gylcogenolysis Beta cells –Insulin Increeases movement of glucose inside of cells for metabolism Stimulates liver to produce glycogen

Thymus Located in mediastinum cavity Hormones called thymosins Important function in development of immune system

Pineal gland Releases melatonin –Regulates body clock and sleep cycle

Female Sex Glands Ovaries Ovarian follicles Corpus luteum

Male sex glands Testes –Interstitial cells produce testosterone –Testosterone stimulates sperm production

Placenta Chorionic gonadotropins Pregnancy tests test for this hormone Prevents dissolution of corpus luteum

Other hormones Wall of Atria in Heart –Atrial Natriuretic hormone- regulates fluid and electrolyte balance by increasing removal of sodium and water Various Digestive Glands Kidneys –Erythropoietin- red blood cell growth hormone