Communication among cells - may occur between adjacent cells or cells located in different areas of body

Local regulator - substance that influences cells in its immediate vicinity - e.g., growth factors

Hormone - substance that influences specific cells throughout body

Internal system of chemical communication

Hormones secreted by ductless glands - travels via bloodstream to target cells

Signal molecule binds to receptor of target cell - elicits cellular response

Works in concert with nervous system in regulation of cellular processes and homeostasis

Reception - target cell detects signal coming from outside cell

Signal transduction - converts signal to a form that can bring about a specific cellular response

Response - cell responds to signal

Molting triggered by ecdysone - secreted by prothoracic glands - favors development of adult characters

Brain hormone - secreted by neurosecretory cells - stimulates ecdysone production

Juvenile hormone - promotes retention of juvenile characters - balances brain hormone and ecdysone

Numerous hormones

Some specific - others affect most tissues

Trophic hormones - regulate other endocrine glands

Located in brain

Hypothalmus - secretes releasing & inhibiting hormones - regulates activity of pituitary

Pituitary - secretes growth hormone, prolactin, trophic hormones - functions in growth, metabolism, water retention, reproduction

Located in center of brain

Secretes melatonin - regulates functions related to light and photoperiod - skin pigmentation, biological rhythms related to reproduction

Located on pharynx or trachea

Produces iodine-containing hormones - controlled by hypothalmus & pituitary

Influences numerous processes - important in development - maintains normal blood pressure, heart rate - important in metabolism & reproduction

Embedded in thyroid

Parathyroid hormone elevates blood calcium levels

Located in abdominal cavity - mostly exocrine tissue & functions

Islets of Langerhans - endocrine tissue - Secrete the antagonistic hormones insulin & glucagon - interact to regulate blood glucose level

Deficiency of insulin results in diabetes

Adjacent to kidneys

Adrenal medulla - responds to nervous input - positive or negative stress - releases epinephrine and norepinephrine - "fight or flight response"

Adrenal cortex - responds to endocrine signals - releases several hormones - glucose metabolism, sex hormones, salt & water balance

Secrete androgens, estrogens, progestrins - - proportions vary in males vs females

Regulate growth, development & sexual behavior