Chemical Signals in Animals u 9. c. Students know how feedback loops in the nervous and endocrine systems regulate conditions in the body. u 9. i.* Students know how hormones (including digestive, reproductive, osmoregulatory) provide internal feedback mechanisms for homeostasis at the cellular level and in whole organisms.

Hormone Dysfunction

Feedback Loops u Feedback loops are how the nervous system uses the endocrine system to regulate body conditions. u The presence or absence of hormones in blood brought to the brain by the circulatory system will trigger an attempt to regulate conditions in the body.

Hormone Example u The hormone leptin, which fat cells produce as they become filled with storage reserves. u Leptin is carried by the blood to the brain, where it normally acts to stop hunger u An example of negative feedback. When fat reserves diminish, the concentration of leptin decreases, a phenomenon that in turn causes the appetite center in the brain to start the hunger stimulus and activate the urge to eat.

Hormones work with the Nervous System u For ex-ample, in the digestive system, where insulin released from the pancreas into the blood regulates the uptake of glucose by muscle cells. u The pituitary master gland produces growth hormone for controlling height.

Mode of Action: Chemical Signaling u 1- Plasma membrane reception signal-transduction pathways (neurotransmitters, growth factors, most hormones) u 2- Cell nucleus reception steroid hormones, thyroid hormones, some local regulators

Vertebrate Endocrine System u Tropic hormones ~ a hormone that has another endocrine gland as a target u Hypothalamus~pituitary u Pituitary gland u Pineal gland u Thyroid gland u Parathyroid glands u Thymus u Adrenal glands u Pancreas u Gonads (ovary, testis)

The hypothalamus & pituitary, I u Releasing and inhibiting hormones u Anterior pituitary: u Growth (GH)~bones √gigantism/dwarfism √acromegaly u Prolactin (PRL)~mammary glands; milk production u Follicle-stimulating (FSH) & u Luteinizing (LH)~ovaries/testes u Thyroid-stimulating (TSH)~ thyroid u Adrenocorticotropic (ACTH)~ adrenal cortex u Melanocyte-stimulating (MSH) u Endorphins~natural ‘opiates’; brain pain receptors

The pituitary, II u The posterior pituitary: u Oxytocin ~ uterine and mammary gland cell contraction u Antidiuretic (ADH )~ retention of water by kidneys

Pituitary Hormones u Follicle-stimulating hormone [FSH] and luteinizing hormone [LH] control the gonads u Thyroid-stimulating hormone [TSH] controls the thyroid, and adrenocorticotropic hormone [ACTH] regulates the formation of glucocorticoids by the adrenal cortex). u This master gland is itself controlled by the hypothalamus of the brain.

The pineal, thyroid, & parathyroid u Melatonin ~ pineal gland; biological rhythms u Thyroid hormones: Calcitonin~ lowers blood calcium Thyroxine~ metabolic processes u Parathyroid (PTH)~ raises blood calcium

The pancreas u Beta cells: insulin~ lowers blood glucose levels u Type I diabetes mellitus (insulin-dependent; autoimmune disorder) u Type II diabetes mellitus (non-insulin- dependent; reduced responsiveness in insulin targets)

The adrenal glands u Adrenal medulla (catecholamines): epinephrine & norepinephrine~ increase basal metabolic rate (blood glucose and pressure) u Adrenal cortex (corticosteroids): glucocorticoids (cortisol)~ raise blood glucose mineralocorticoids (aldosterone)~ reabsorption of Na+ and K+

The gonads Ovaries u estrogens (estradiol)~uterine lining growth; female secondary sex characteristics; gonadotropin u progestins (progesterone)~uterine lining growth Testes u Steroid hormones: precursor is cholesterol u androgens (testosterone)~ sperm formation; male secondary sex characteristics; gonadotropin

Regulatory systems u Hormone~ chemical signal secreted into body fluids (blood) communicating regulatory messages u Target cells~ body cells that respond to hormones u Endocrine system/glands~ hormone secreting system/glands (ductless); exocrine glands secrete chemicals (sweat, mucus, enzymes) through ducts u Neurosecretory cells~ actual cells that secrete hormones u Feedback mechanisms ~ negative and positive

Local regulators: cells adjacent to or near point of secretion u Growth factors ~ proteins for cell proliferation u Nitric oxide (NO) ~ neurotransmitter; cell destruction; vessel dilation u Prostaglandins ~ modified fatty acids secreted by placenta and immune system; also found in semen