Key concepts Hormones are compounds produced in one part of the body and

transported to another location to produce specific responses; small amount s can induce substantial responses.

Chemical signals produced by the body are mostly produced by glands.

Hormones either affect a target effector organ directly or via the signal transduction pathway.

Effects of hormones vary depending on whether they bind to a receptor in the plasma membrane or within the nucleus of a cell.

Action of hormones is controlled by feedback mechanisms. Hormones are classified by mode of transport or through chemical

composition. Diseases in the endocrine system occur when levels of hormones

released are at an abnormal level or when receptors of that particular hormone are damaged.

Endocrine system

Hormone-secreting cells

Chemical signals secreted into body fluids, eliciting responses in target cells

Functions with NS in maintaining homeostasis

Effects are slower and longer-lasting

Maintenance of Homeostasis by the ES and NS Neurosecretory cells Neurosecretory cells

– nerve cells that – nerve cells that secrete hormones into secrete hormones into bloodstream (eg. bloodstream (eg. epinephrineepinephrine))

Feedback regulationFeedback regulationPositive feedbackPositive feedback

○ Suckling Suckling release of release of oxytocin oxytocin milk milk secretionsecretion

Negative feedbackNegative feedback○ Control of blood Control of blood

calcium and glucose calcium and glucose levelslevels

Invertebrate Endocrine Systems Hydra –control method

of reproduction Mollusks –controls egg-

laying Arthropods – extensive

endocrine systems for molting and maturity Ecdysone molting and

promotion of adult features

Brain hormone (BH) regulates production of ecdysone

Juvenile hormone (JH) retention of larval characteristics

Chemical signals and their modes of actionChemical signals and their modes of action

most peptides, proteins and glycoproteins

steroids and thyroid hormones

Importance of signal transduction Importance of signal transduction pathwayspathways

1) Different pathways in different cells different responses to the same signal

2) Amplification of the single signal allows small amounts of hormones to have a large effect

Vertebrate endocrine systems Hypothalamus

integrates endocrine and nervous functions

Neurosecretory cells of hypothalamus produce trophic/tropic hormones Stored and secreted

by posterior pituitary

Affect anterior pituitary’s release of own hormones

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Table 45.1 (continued)

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Feedback control loops: a closer Feedback control loops: a closer looklook

Regulation of Regulation of thyroid hormonesthyroid hormones

Regulation of glucose in the Regulation of glucose in the bloodblood

Hormones and the female reproductive cycleHormones and the female reproductive cycle

Hormones control Hormones control the reproductive the reproductive cycle of human cycle of human femalesfemales

PerformanPerformance-ce-enhancing enhancing drugsdrugs