The Endocrine System Anatomy & Physiology

The Endocrine System The “other” great controlling system of the body What’s the first?

Endocrine vs. Nervous Endocrine Nervous Slower Uses hormones Responses are continuous or long-term Nervous Faster Uses nervous impulses Responses are immediate

What Are Hormones? Chemical substances, secreted by cells into extracellular fluids, that regulate the metabolic activity of other cells of the body

Target Cells/Hormones The specific cells or organs a hormone is meant to affect Each hormone must have a receptor protein present on a cell’s plasma membrane in order to work

Types of Hormones Non-steroidal or amino-acid based: made from proteins, peptides or amines) Steroidal: made from cholesterol Includes all sex hormones and hormones made in adrenal cortex

How Do They Work? First Mechanism Direct Gene Activation a. Steroid hormones diffuse through plasma membrane (why?) b. Enters nucleus c. Binds to a specific receptor inside nucleus—hormone-receptor complex (HRC) d. HRC binds to cell’s DNA— causes transcription of mRNA e. mRNA translated in cytoplasm—makes new proteins

How Do They Work? Second Mechanism Second Messenger System a. Non-steroidal hormones bind to receptors on plasma membrane (why?) b. Reactions go off inside cell activating an enzyme c. Enzyme sets off reactions to create a second messenger (cAMP) d. Second messenger instills changes in cell

Controlling Hormone Release Negative Feedback Mechanisms Hormone released triggered by internal or external stimuli Rising hormone levels in blood inhibits further release Blood levels of hormones vary within a very narrow range

Controlling Hormone Release Hormone Stimuli 1. Humoral: changing blood levels of different ions and nutrients example: PTH in response to calcium levels 2. Hormonal: endocrine organs stimulated to work due to presence of other hormones example: TSH stimulates thyroid

Controlling Hormone Release 3. Neural: nerve fibers stimulate hormone release example: epinephrine and nor-epinephrine

Major Endocrine Organs Pituitary gland (anterior & posterior) Pineal Gland (body) Thymus Thyroid & Parathyroid Pancreas Adrenal glands (cortex & medulla) Gonads (testes or ovaries)

Anterior Pituitary Gland Secretes 6 Hormones Found at base of hypothalamus “Master Endocrine Gland” Actually regulated by hypothalamus All non-steroidal All respond to hormonal stimuli from hypothalamus http://www.becomehealthynow.com/images/organs/nervous/glakgar_pit_hypothalamus.jpg

Anterior Pituitary Gland 1. Growth Hormone Target cells: skeletal muscles & bones Function: to stimulate growth of target cells Cause fat metabolism, sparing glucose Hyposecretion disorder: dwarfism Hypersecretion: kids = gigantism adults = acromegaly

Anterior Pituitary Gland 2. Prolactin Target cells: the breasts of females Function: stimulates & maintains milk production after birth No associated disorders

Anterior Pituitary Gland 3. Adrenocorti-cotropic Hormone (ACTH) Target cells: adrenal cortex Function: regulates release of hormones 4. Thyroid-Stimulating Hormone (TSH) Target cells: thyroid Function: regulates growth & activity of gland

Anterior Pituitary Gland 5. Follicle-stimulating Hormone (FSH) Target cells: gonads Functions: Females: stimulates follicle development Males: stimulates sperm development Hyposecretion: sterility

Anterior Pituitary Gland 6. Luteinizing Hormone (LH) Target cells: gonads Functions: Females: triggers ovulation Males: stimulates testosterone production Hyposecretion: sterility

Posterior Pituitary Gland Stores 2 hormones made by hypothalamus Non-steroidal hormones 1. Oxytocin Target cells: uterus & breasts of pregnant women Functions: stimulates contractions & breast milk ejection

Posterior Pituitary Gland 2. Antidiuretic Hormone (ADH) Target Cells: kidneys Functions: causes kidneys to reabsorb water—decrease urine volume/ increases blood volume Hyposecretion: diabetes insipidus ** diuretics inhibit ADH

Adrenal Glands 2 bean shaped glands Sit on top of kidneys Steroidal hormones 2 parts: Adrenal cortex: outside layer Adrenal medulla: center

Adrenal Cortex 1. Corticosteroids: mineralocorticoids, glucocorticoids, sex hormones A. Mineralocorticoids: aldosterone Target cells: kidneys Function: Regulates water & electrolyte balance Causes uptake of sodium (and water), release of potassium by kidneys

Adrenal Cortex B. Glucocorticoids: cortisol and cortisone Target cells: all body cells Function: promote normal cell metabolism Assist body in coping with long-term stress—increasing blood glucose Can decrease edema and pain

Adrenal Cortex C. Sex Hormones: aka androgens; released in both males & females all through life.

Adrenal Cortex Hormones Hyposecretion of any adrenal cortex hormone: Addison’s Disorder Hypersecrretion of any adrenal cortex hormone: Cushing’s Syndrome

ADRENAL CORTEX DISORDERS Addison’s Disorder Cushing’s Syndrome

Adrenal Medulla Located in center of adrenal gland Stimulated by sympathetic nervous system 1. Catecholamines: epinephrine & norepinephrine Target cells: all body cells Function: assists body in coping with short-term stressors increase glucose levels, increase breathing rate “fight or flight” response

Thyroid Gland Located at base of throat Makes 2 hormones both non-steroidal 1. Calcitonin Target cells: bones Function: causes absorption of calcium by bones decreases blood calcium levels

Thyroid Gland 2. Thyroid Hormone (thyroxine, T4, & tri-iodothyronine, T3) requires iodine Target cells: all body cells Function: controls rate of glucose metabolism Needed for normal tissue growth & development Hyposecretion: Kids: cretinism, adults: myxedema Hypersecretion: graves disease

Parathyroid Gland Tiny masses of tissue on posterior thyroid 1. Parathyroid Hormone (PTH) Target cells: bone cells, kidneys & intestines Function: regulates blood calcium levels Causes release of calcium from bones Hyposecretion: tetany Hypersecretion: massive bone loss

Pancreas Located close to stomach in abdominal cavity Part exocrine gland/ part endocrine gland Pancreatic Islets—endocrine portion

Pancreas 1. Insulin: stimulated by high glucose Target cells: all body cells Function: allows for uptake of glucose by cells Hyposecretion: diabetes mellitus 2. Glucagon: stimulated by low glucose Target cells: liver Functions: calls for breakdown of glucogen to glucose.

Pineal Gland aka pineal body Small, cone-shaped Located in diencephalon of brain 1. Melatonin Target cells: ?? Function: day-night cycle Peak levels occur at night– drowsiness Low levels around noon—alertness “Biological Clock” ???

Thymus Located in upper thorax, posterior to sternum Large in infants and kids—decreases and converts to fat in adults 1. Thymosin Target cells: t-cells of immune system Function: assists in maturation of t-cells

Gonads Females: ovaries Males: testicles A. Ovaries 1. Estrogen Target cells: female sex organs Function: stimulate development of secondary sex characteristics Assists in preparing uterus for fertilized egg Help maintain pregnancy and produce milk

Gonads 2. Progesterone Target cells: uterus Function: assists in preparation of uterus for fertilized egg During pregnancy—quiets contractions of uterine muscle Hyposecretion of either hormone—inability to conceive and bear children

Gonads B. Testes 1. Testosterone (made by interstitial cells) Target cells: male sex organs Function: development of male secondary sex characteristics Growth and development of sex organs Male sex drive Production of sperm Hyposecretion: sterility