Chemical signals in animals

KeywordsReading Ch. 45

• Endocrine system• Hormone• Target cell• Neurosecretory cell• Steroid• Amino acid derived

hormone• Surface receptors

• Internal receptors• Action of steroids• Glucose homeostasis• Insulin• Glucagon• Epinephrine• Norepinephrine• ACTH

Chemical signals outside of organisms

• Pheromones

• Prey tracking by rattlesnakes

Pheromone

• A small volatile chemical signal that functions in communication between animals

• Often in mate attraction

Rattlesnakes (research of Dr. Ken Kardong Zoology WSU)

• Bite prey, inject venom, prey runs away, snake can track down the prey

• Follows a scent trail left by bitten prey.

• Doesn’t matter if venom glands have been ligated

• Don’t know what the signal is.

Will focus on chemical signals inside organisms

• Two regulatory systems coordinate internal body functions– Nervous system (will deal with in a later

lecture)– Endocrine system (focus of today’s lecture)

Endocrine system definition

• The internal chemical communication system involving hormones

• Hormone– Chemical signal secreted into body fluids

(usually blood)– Effective in minute amounts

Types of signaling in endocrine system

Hormones act on specific target cells in two ways

• Surface receptors

• Within target cells (internal receptor)

Surface receptor - often amino acid derived hormone

Internal receptor - often steroid hormones

Action of steroids

Two specific examples of hormone action

• Glucose homeostasis

• Stress and the adrenal gland

Glucose homeostasis

• Homeostasis = The steady-state physiological condition of the body

• Glucose = major fuel of cellular respiration

• Normal blood glucose level = 900 mg/L

• How is this regulated?

• First look at when glucose levels are too high

P. 906

• High blood glucose causes beta cells to release insulin

Summary

• Beta cells release insulin

• Insulin causes body cells and liver to take up glucose

• Glucose levels restored

What happens if you need to increase blood glucose?

• Low blood glucose causes alpha cells to release the hormone glucagon

• Glucogon stimulates the liver to break down glycogen releasing glucose

Summary

• Low blood glucose causes alpha cells to release the hormone glucagon

• Glucogon stimulates the liver to break down glycogen releasing glucose

Glucose homeostasis

• Example of use of amino-acid derived hormones: insulin and glucagon are peptides

• Surface receptors on target cells

Diabetes mellitus

• Greek = copious urine, honey

• Type I - autoimmune disorder - cells of pancreas are targeted - no ability to produce insulin - usually occurs during childhood

• Type II (90%) - reduced responsiveness of target cells or insulin deficiency-usually occurs after age 40

Stress and the adrenal gland

• Short-term response - Epinephrine (adrenaline) and norepinephrine

• Long-term response - ACTH and corticosteroids

P. 909

Short-term stress: medulla of the adrenal gland

Some effects of epinephrine and norepinephrine

• Glycogen broken down to glucose

• Increased blood pressure, breathing, metabolic rate

Example of:

• Use of neurosecretory cells

• Amino acid-derived hormones

Long-term stress: cortex of the adrenal gland

Corticosteroids (mineral- and gluco- corticoids) released by

adrenal cortex• Some effects: increased blood volume and

blood pressure, breakdown of protein and fats

Example of:

• Interaction between nervous and endocrine systems

• Use of steroid hormones