Chemical Signals in Animals Chapter 45

Chemical Signals: An Intro All animals exhibit coordination by chemical signals –Hormones convey info between organs within the body –Neurotransmitters carry info between cells of the nervous system

Hormones Hormones are chemical signals secreted into body fluids (usually blood) Hormones cause specific responses from selected cells  target cells There are more 50 different hormones in the body!

Endocrine vs. Exocrine Glands Endocrine glands are ductless glands –They secrete hormones into body fluids Exocrine glands secrete their products into ducts (kind of like pipes) –These products go only to certain locations within the body

Pheromones Pheromones are similar to hormones, with one important difference –Pheromones are communication signals between animals of the same species –Function as mate attractants, territorial markers, alarm substances…

Signal-Transduction Pathways A signal transduction pathway links a (mechanical or) chemical stimulus to a cellular response –A hormone binds with a receptor protein in the target cell membrane, which then binds with a G protein, which binds with GTP, which binds with… –“Broken telephone”… but not broken!! –The end result: the desired cellular response

Signal-Transduction Pathway

Major Endocrine Glands Hypothalamus –Integrates the nervous and endocrine systems –The “master chief gland” Pituitary Gland –Obeys the hypothalamus –Posterior and anterior pituitary glands ADH, GH, PRL, FSH, LH, TSH, ACTH

Human Endocrine Glands

Major Endocrine Glands Thyroid Gland –Growth and development –Maintenance of homeostasis –Lowers blood calcium level Parathyroid Glands –Raises blood calcium level

Human Endocrine Glands

Major Endocrine Glands Pancreas –Produces insulin and glucagon –Insulin lowers blood glucose level –Glucagon raises blood glucose level –Hmm… why???

Human Endocrine Glands

Major Endocrine Glands Adrenal Glands –Epinephrine and norepinephrine –Constrict certain blood vessels –Increase metabolic activities Gonads –Testes  androgens –Ovaries  estrogens, progesterone

Human Endocrine Glands

Major Endocrine Glands Pineal Gland –Produces melatonin, which is involved in biological rhythms Thymus –Stimulates T lymphocytes

Human Endocrine Glands

Relationship Between Endocrine and Nervous Systems Structural Relationships –Many endocrine glands are made of nervous tissue Chemical Relationships –Some hormones are also used as signals by the nervous system Functional Relationships –Nervous and hormonal components are arranged in series… –Each system affects the other one