Chapter 45 ~ Chemical Signals in Animals

Internal regulation Interstitial fluid: internal fluid environment of vertebrates; btw cells exchanges nutrients and wastes Homeostasis: “steady state” or internal balance – Regulator (moderates internal temp) vs Conformer (int. temp varies w/ external) Control System – 3 components Receptor (sensor) - detects change Control center - directs response Effector - carries out response

Negative feedback: change in a physiological variable that is being monitored triggers a response that counteracts the initial fluctuation Maintaining body temperature, blood sugar Positive feedback: physiological control mechanism in which a change in some variable triggers mechanisms that amplify the change Uterine contractions at childbirth

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

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

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

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

The hypothalamus & pituitary, I Releasing and inhibiting hormones Anterior pituitary: Growth (GH) ~ bones Prolactin (PRL) ~ mammary glands; milk production Follicle-stimulating (FSH) & Luteinizing (LH) ~ ovaries/testes Thyroid-stimulating (TSH) ~ thyroid Melanocyte-stimulating (MSH) Endorphins ~ natural ‘opiates’

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

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

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

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

The gonads Steroid hormones: precursor is cholesterol Regulated by FSH and LH Androgens (testosterone) sperm formation; male secondary sex characteristics Estrogens (estradiol) uterine lining growth; female secondary sex characteristics Progestins (progesterone) uterine lining growth