Ch. 45: Chemical Signaling in Animals

I. Introduction to Regulatory SystemsA.Hormone: A chemical signal that is secreted

into body fluids; communicate regulatorymessages.

B.Target Cells: Responds to hormones.C.The two systems of internal communcation:

Nervous System & Endocrine System1.Endocrine System: hormone-secreting

cells; endocrine glands are ductless glandsthat secrete their chemical messengersdirectly into body fluids.

2.Neurosecretory cells are specialized nervecells that are a part of endocrine organs.

3.Ex. Of hormone: Epinephrine, acts as the“fight or flight” hormone and also as a neurotransmitter.

D.Invertebrate reguatory systems clearly showendocrine and nervous system interaction:

1.Hormones function in reproduction and development.a. Example: Mollusk Aplysia, secretes a hormone that stimulates the laying of eggsand inhibits the feeding and locomotion,activities that interfere with reproduction.b. Insects and crustaceans molt, triggeredby a hormone called ecdysone.

-Ecdysone is secreted by prothoracic glands-Ecdysone also favors the development of adult characteristics = stimulates metamorphosis

-Ecdysone production is controlled by a hormone called brain hormone (BH).-Ecdysone and BH are controlled by the juvenile hormone (JH).

II. Chemical Signals and Their Modes of ActionA.Growth Factors: peptides and proteins that

stimulate cell proliferation.1.Epidermal Growth Factor (EGF):

Accelerates epidermal development2.Insulinlike Growth Factors (IGF): produced

in the liver; essential to skeletal develop-ment.

B.Nitric Oxide (NO): -Highly reactive and potentially toxic; -acts like a neurotransmitter in neurons;-when released by white blood cells, kills bacteria and cancer cells-dilates walls of blood vessels

C.Prostaglandins (PGs): modified fatty acids-in semen, stimulate contraction of smoothmuscles in the wall of the uterus (helping sperm move towards egg)-secreted by placental cells; can cause laborin childbirth-Defense: induce fever and inflammation,and increase pain-Examples:

a.Prostaglandin E (PGE): causes musclesto relax; dilates blood vessels and promotes oxygenation of the blood

b.Prostaglandin F (PGF): signals musclesto contract; constricts vessels and reducesblood flow to lungs These two are antagonistic

D.Most chemical signals bind to plasmamembrane proteins, initiating signal-transduction pathways (Ch. 11. Also seeActivities for Ch. 45 on the Campbell website)

1.Different signal-transduction pathways indifferent cells can lead to different responses to the same signal.Example: Acetylcholine can producedifferent responses in different target cells.

2.Onehormonecan havea largeeffect.

E.Steroid hormones, thyroid hormones, and some local regulators enter target cells by binding to intracellular receptors.

1.Examples: Estrogen, progesterone, vitamin D, NO See Campbell website, Ch. 45 HormoneActivity

III.The Vertebrate Endocrine System

B.Humans have NINE endocrine glands:

A.Tropic Hormones: target other endocrineglands and are important to understandingchemical coordination.

1.Hypothalamus: releases hormonesthat stimulate andinhibit the anteriorpituitary (adeno-hypophysis).

-Releasing hormones-Inhibiting hormones

Pituitary has 2 parts: 1.Anterior2.Posterior

Hormones from the hypothalamus regulates anterior pituitary hormones, which stimulate many other hormones.

The posterior pituitary (neurohypophysis) is a small bulge of the hypothalamus that stores and secretes hormones made by the hypothalamus: ADH (antidiuretic hormone) and oxytocin.

2.Posterior Pituitary Hormones: a.Oxytocin: acts on muscles of the uterus;

induces contraction of the uterinemuscles during childbirth and causes mammary glands to eject milk during nursing.

b.ADH: regulates osmolarity of the blood;stimulates water reabsorption

3.Anterior Pituitary Hormones:a.Growth hormone (GH):

-protein, about 200 amino acids long;-has a wide variety of target tissues; -stimulates growth of bones and cartilage;-signal the liver to produce insulinlike growth factors (IGFs)

-Too much GH as a child gigantism-Too much GH as an adult abnormal growth of bones in hands, feet, and head = acromegaly -GH deficiencies as a child can be treated with GH from cadavers.

b.Insulinlike growth factors (IGFs):

-Stimulates bone and cartilage growth

c.Prolactin (PRL): -Similar in structure to GH-Diverse effects: Stimulates mammary to produce milk, regulates fat metabolism and reproduction in birds, delays metamorphosis in amphibians, regulates salt and water balance in fish Diversity suggests it’s an “ancient” hormone whose function has evolved

during the evolution of vertebrates.

d.The tropic hormones:1.Follicle-Stimulating Hormone (FSH):stimulate gonads (testes, ovaries)2.Lutenizing hormone (LH):stimulate gonads (testes, ovaries)3.Thyroid-stimulating Hormone (TSH):regulates the release of thyroid hormones 4.Adrenocorticotropic Hormone (ACTH):stimulates the production and secretionof steroid hormones by the adrenal cortex.

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e.Melanocyte-Stimulating Hormone (MSH):regulates the activity of pigment-containing cells in the skin.It also regulates fat metabolism.

f. Endorphins: Class of molecules called“natural opiates,” giving a natural highbecause they inhibit the perception ofpain. Exercise releases endorphins.Opiate drugs mimic endorphins.

4.Pineal Gland hormones: Involved inbiorhythmsa.Melatonin: Modified

amino acid

Melatonin is secreted at night, and the amount secreted depends on the lengthof the night.Winter: more melatonin secretedSummer: less melatonin secreted

b.Affects skin pigmentation (more =darker skin)

c.Associated with biological rhythms biological clocks

5.Thyroid hormones:a.Two lobes around the tracheab.Produces Calcitonin:hormone that

controls Ca2+ levels in blood

c.Produces T3 & T4

hormones T4 converts to T3

in target cellsd.T3 and T4 are

derived from amino acid tyrosine.

d.Tyroid gland plays a crucial role in development and maturation. Tadpole into a frog Cretinism in humans: thyroid deficiency causes retarded skeletal

growth and mental development.

e.Tyroid gland helps maintain homeostasis:-Blood pressure-Heart rate-Muscle tone-Digestion-Reproductive functions

f. Hyperthyroidism: excess secretion of thyroid hormones

g.Hypothyroidism: shortage of thyroidhormones

h.Goiterism: shortage of thyroid hormones

Great website to visit!:http://www.biosbcc.net/barron/physiology/endo/thyr.htm

i. Feedback control loops regulating the secretion of T3 and T4.

6.Parathyroid hormones:a. Four parathyroid glands embedded in

the surface of the thyroid, function inthe homeostasis of calcium ions (Ca 2+ ).

-They secrete parathyroid hormone (PTH), which raises blood levels of Ca2+

(opposite of calcitonin).

7.Endocrine tissues:a.Pancreas: two tissue -Exocrine: produces bicarbonate ions and digestive enzymes that are carried to the small intestines via the pancreatic duct.

-Endocrine (1-2% of pancreas): 1. Islets of Langerhans:

secretes glucagon from its alpha cells secretes insulin from its beta cells -Insulin and glucagon are antagonistic hormones that regulate the concentration of glucose in blood.

-Type I diabetes mellitus: autoimmune disorder; immune system attacks the cells of the pancreas.• Occurs in childhood• person cannot produce insulin• treatment: daily injections of insulin-Type II diabetes mellitus: non-insulin dependent diabetes• characterized by deficiency in insulin or reduced responsiveness in target cells due to changes in insulin receptors• usually occurs after age 40• 90% of diabetics are type II• can be managed by exercise and dietary control• heredity and obesity are major factors

8.Adrenal medulla and Adrenal cortex hormones:a.Adrenal glands: adjacent to the kidneys

-Medulla: central part-Cortex: outer part

b.Catecholamines:1. Epinephrine (aka adrenaline)2. Norepinephrine (aka noradrenaline)Released due to positive and negative stress.Produces a rapid bioenergetic boost; increasing basal metabolic rateProduces the “fight or flight responseIncreases the rate of glycogen break- down and glucose release into bloodStimulate the release of fatty acids from fat cellsIncreases rate and stroke volume of heart rateIncreases rate of oxygen delivery to body

Moves blood away from skin, digestive organs, and kidneys, while increasing blood supply to heart, brain, and skeletal muscles.

c.What causes the release of epinephrineand norepinephrine? -adrenal medulla is under control of

nerve cells from the sympathetic division of the autonomic nervous system-Under stress, the nerve cells are excited and release the neurotransmitter acetylcholine. Acetylcholine stimulates the release of epinephrine.

-Adrenal cortex secretes steroids called corticosteroids when acted upon by ACTH (from the anterior pituitary gland).-Three types of corticosteroids: 1.Glucocorticoids (ex. Cortisol): promotes the synthesis of glucose from noncarbohydrate sources (protein). Glucocorticoids act on skeletal

muscles to break down protein to be converted to glucose.

2.Mineralocorticoids (ex. Aldosterone):effects salt and water balance. Aldosterone stimulates the kidney toreabsorbe sodium and water from thefiltrate, raising blood pressure and volume.

3.Sex hormones, androgen (“male hormones”) estrogen, and progesterone (“female hormones”).

9. Gonadal steroids:a.Gonads produce and secrete androgens,

estrogens, and progestins.b.All 3 are found in both males and

females but in different proportions.c.All are produced in testes and ovaries.d.Affect growth and development and also

regulate reproductive cycles and sexualbehavior.

e.Testes primarily produce androgens, themain such hormone being testosterone.

f. Estrogen maintain and develop femalereproductive system.

g.Progestins (progesterone) are primarilyinvolved in preparing and maintaining the uterus, which supports the growthand development of the embryo.

h.Synthesis of estrogens and androgensare controlled by gonadotropins FSH andLH. FSH and LH are controlled by thehormone GnRH (gonadotropin-releasinghormone) released by the hypothalamus.