Chapter 45 Chemical Signals in Animals

The endocrine system and the nervous system are structurally, chemically, and functionally related.

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

Feedback mechanisms ~ negative and positive (feature that is also common in the nervous system)

Local regulators: cells adjacent to or near point of secretion

Growth factors ~ proteins for cell proliferation

Nitric oxide (NO) ~ (highly reactive& potentially toxic) neurotransmitter; cell destruction (bacteria, cancer cells); vessel dilation

Prostaglandins ~ modified fatty acids secreted by placenta (induce labor) and immune system (fever, pain); also found in semen (contract smooth muscle in uterus helping convey sperm to egg.

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 Page 961

Tropic hormones ~ a hormone that has another endocrine gland as a target

Hypothalamus: causes release of hormones produced by posterior pituitary and regulates anterior pit.

Pituitary gland Pineal gland Thyroid gland Parathyroid glands Thymus Adrenal glands Pancreas Gonads (ovary, testis)

The hypothalamus & pituitary 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 (pigment cells)

(MSH) Endorphins~natural ‘opiates’; brain

pain receptors

The pituitary

The posterior pituitary: Oxytocin~

uterine and mammary gland cell contraction

Antidiuretic (ADH)~ retention of water by

kidneys, increase permiability of epithelium to water, amplifies water reabsorption

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 (clusters of endocrine cells that secrete hormones) Alpha cells:

•glucagon~ raises blood glucose levels Beta cells:

•insulin~ lowers blood glucose levels Type I diabetes mellitus (insulin-

dependent; autoimmune disorder, attack mounted on pancreas cells)

Type II diabetes mellitus (non-insulin-dependent; reduced responsiveness in insulin targets)

The adrenal glands Adrenal medulla (catecholamines-synthesisized from AA

tyrosine): •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

Signal Transduction Pathway

Signal- transduction pathways allow for small amounts of a hormone to have a large effect.

Endocrine System

How are chemical signals in the body transmitted from cell to cell?

Chemical signals called transmitters include amino acids, polypeptides, and gases that can be received by other cells via a protein receptor on the surface of the receiving cell or by entering the cell directly.

What are some of the sources of the body’s chemical signals? Neurotransmitters from nerve cells. Endocrine signals from endocrine glands.

How are endocrine signals different from nerve cell signals? Neurotransmitters are usually small, nitrogen-

containing compounds that are conveyed from one specialized nerve cell to another along specific nerve highways throughout the body and are designed to elicit immediate responses

Endocrine signals are usually hormones secreted from glands that use blood vessels to disperse their signal molecules, to elicit a slower response.

How are endocrine signals similar to neurotransmitters? Some molecules, such as epinephrine, serve as

both neurotransmitters and endocrine signals;some specialized nerve cells called neurosecretory cells are located in the endocrine glands and secrete hormones into the bloodstream.

Hormones

Hormones, the most common class of signal molecule used by endocrine glands, affect every cell in the body. How is it possible that very diverse types of cells can respond to these signals?

While some hormones require surface receptors, most hormones because they are small and non-polar, can pass through the cell membranes without a channel or receptor and proceed directly to a receptor in the cytoplasm or go into the nucleus to act as a gene activator.

Trophic Hormones

Some endocrine signals target other glands, stimulating them to secrete their own signals. What is this type of domino effect called?

These signals are called trophic hormones.

Endocrine Review

Brain: hypothalamus, pituitary, pineal Pituitary: Anterior Posterior

Endorphines ADH GH (Growth Hormones) Oxytocin ACTH (adrenal cortex TSH (thyroid stimulating) PRL (prolactin) LSH,FSH (gonads) MSH (Melanocyte cells-melatonin (skin pigment)

Thyroid Metabolism (throxine)-metabolism, (calcitonin) decrease

Ca+ Parathyroid (PTH)-Increase Ca+ A dramatic drop in calcium would cause convulsive

contractions of skeletal muscles Adrenal Glands (top of kidneys)- fight or flight Medulla

norepinephrine and epinephrine increase metabolism, increase glucose (breakdown of glycogen)& pressure

-Cortex- increase glucose, reabsorption of k+, Na+

Pancreas- Alpha cells (glucagon)-increase glucose Beta cells (insulin) decrease

Gonads- steroids, testosterone, estrogens, progestins