Endocrine System Biology 211: Anatomy & Physiology 1 Tony Serino, Ph.D. Biology Department Misericordia University

Endocrine System Controls and modifies the internal environment by releasing chemicals (hormones) into the blood Slower response time but longer duration of action compared to nervous system

Chemical Messengers (hormones) Hormone –secreted by cell into blood and acts on another cell some distance away Neurohormone –secreted by neuron into blood to affect a target cell some distance away Local hormones –secreted by cell into interstitial fluid to affects cells nearby Paracrines –affect neighboring cells Autocrines –affect the secreting cell Pheromones –secreted by cell onto body surface to affect cells of another individual

Hormones Chemical Classification Amines –single or few amino acids, most water soluble Epinephrine, Thyroxine (but water insoluble), Melatonin Proteins –short to long chains of amino acids; water soluble GH, FSH, LH, Insulin, Glucagon, ADH, etc. Steroids –derivatives of cholesterol; water insoluble Estrogen, Testosterone, Progesterone, Cortisol, Aldosterone

Steroid Hormones

Characteristics Common to all Hormones Must have target cell with appropriate receptor molecules Receptor-hormone complex must trigger events in target cell that changes its physiology Mechanisms for deactivating the hormone response must be present

Controlling Hormone Response Half-life of the hormone Physiological range Modifying target cell response Up and down regulation Turning off secretion Negative feedback Control by other hormones, neurons and metabolites

Control of Hormone Secretion

Mechanisms of Hormone Action 2nd messengers Water Soluble Water Insoluble Carrier protein

2nd Messengers: cAMP

2nd Messengers: IP3 and Ca++-Calmodulin

Steroid Hormone Transduction

Different Styles of Secretion Prohormone –a hormone that is made as a larger (inactive form) that must be changed prior to secretion (allows for storage of hormone in secreting cell) Ex.: proinsulin, pro-opiomelanocortin Prehormone –a hormone that is secreted in an inactive form that must be changed near or in the target cell Ex.: Thyroxine, Angiotensinogen

Proinsulin

Types of Endocrine Disorders Hypersecretion Too much secretion of the hormone Hyposecretion Too little secretion of hormone Hyporesponsiveness Normal secretion, but little to no response by target cells

Endocrine Glands

Hypothalamus Control of Pituitary

Posterior Pituitary

Anterior Pituitary

Control of Growth Growth periods: prenatal and postnatal (consists of pre-puberal (especially the first 2 years –infancy) and puberty Several factors influence growth: genetics, diet, health, and hormonal balance Prenatal growth dominated by insulin secretion, post-natal dominated by GH, thyroxine, and sex hormones

GH secretion and effects GH secretion stimulated by exercise, fasting, sleep (diurnal rhythm), stress, decreased plasma glucose, increased plasma AA (such as after a high protein meal) Increase protein synthesis Increase differentiation (increase mitosis)

GH interactions with other Hormones Thyroxine: essential and permissive for GH Needed to maintain energy levels for growth Increases sensitivity of target cells to GH effects Insulin: essential for GH effects Dominant hormone for pre-natal growth Estrogen and Testosterone: surge at puberty stimulates GH release, synergistic with GH anabolism; also trigger epiphyseal closure Cortisol: anti-growth effects; decrease GH secretion, cell division, and increase catabolism

GH pathologies Hypersecretion: Gigantism –in children with responsive epiphyseal plates Acromegaly –in adults, with closed epiphyseal plates

GH pathologies Hypofunction: Dwarfism –in children Pituitary –decreased GH secretion Laron –decreased responsiveness due to lack of GH receptors 28 yo woman with pituitary dwarfism; 45” tall Achondroplastic Dwarfism (genetic dwarf) due to failure of cartilage to form in epiphyseal plate

Thyroid Location

Thyroid Follicle Parafollicular cells  calcitonin (follicular cells  thyroxine) Parafollicular cells  calcitonin

T3 & T4 Formation and Secretion

T3 & T4

Control of Thyroxine Secretion Short loop Long loop

Thyroid Malfunction Hypothyroidism Endemic goiters –due to iodine deffeicency Cretinism –i thyroxine in child results in igrowth (dwarf) and severe mental retardation Myxedema –i thyroxine in adult, leads to swelling of tissues plus other symptoms

Cretinism

Thyroid Malfunction Hyperthyroidism Toxic goiters (Graves disease) –Ab may stimulate thyroid without negative feedback control Exophthalmos –symptom present in many hyperthyroid patients

Parathyroid Location

Parathyroid

PTH Actions Stimulates resorption of bone  hCa+ and PO4- in blood Stimulates Ca+ absorption in intestine (active Vit. D3 necessary for Ca+ absorption) Stimulates Ca+ reabsorption and PO4- excretion in kidney Stimulates Vit. D3 formation (skin) and activation (kidney) Vital for life

Adrenal Location and Structure

Adrenal Layers (Epinephrine (adrenalin)) (Androgens) (Glucocorticoids (cortisol)) (Mineralocorticoids, (Aldosterone))

GAS (General Adaptation Syndrome)

Adrenal Malfunction Hypersecretion Cushing’s syndrome –increase in glucocorticoids Usually due to over secretion of ACTH by pituitary or from adrenal cortex tumors stimulating an increase in glucocorticoids. Characteristic obesity of trunk only and development of “buffalo hump” (a fat pad behind the shoulders). Will develop hypertension, atherosclerosis, muscular weakness and fatigue. Conn’s syndrome –excess amount of aldosterone Salt imbalance, water retention, hBP, muscle weakness Adrenogenital syndrome –too much androgen Premature sexual development in children or masculinization in women

Cushings (buffalo hump) Obesity of trunk

Adrenogenital syndrome A 15 yo girl, note typical masculine build, under developed breasts, and excessive body hair

Adrenal Cortex Malfunction Hyposecretion –Addison’s disease Due to decrease amounts of mineral and glucocorticoids Can be due to over use of steroids or an autoimmune mechanism resulting in destruction of the gland Dehydration, K+ loss, iBP, fatigue, pigmentation deepening (bronzing of skin) may be symptom of loss of negative feedback

Pineal Gland Plays a major role in circadian rhythm control through its sympathetic connection to the hypothalamus Melatonin increases at night and decreases during daylight Implicated in the control of major life changes (such as the onset of puberty and adulthood

Thymus Gland Bilobed organ that is largest in children, but begins to regress sharply at the onset of puberty (around age 11) It is the site of T-cell lymphocyte production and produces hormones (such as, thymosin) that modifies their physiology