Chapter 45 ~ Chemical Signals in Animals

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 ~ actual cells that secrete hormones

Feedback mechanisms ~ negative and positive

Local regulators: cells adjacent to or near point of secretion

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 √gigantism/dwarfism √acromegaly

Prolactin (PRL)~mammary glands; milk production

Follicle-stimulating (FSH) &

Luteinizing (LH)~ovaries/testes

Thyroid-stimulating (TSH)~ thyroid

Adrenocorticotropic (ACTH)~ adrenal cortex

Melanocyte-stimulating (MSH)

Endorphins~natural ‘opiates’; brain pain receptors

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

Islets of Langerhans

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

androgens (testosterone)~ sperm formation; male secondary sex characteristics; gonadotropin

estrogens (estradiol)~uterine lining growth; female secondary sex characteristics; gonadotropin

progestins (progesterone)~uterine lining growth

Steroid Hormone Action