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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