Chapter 45

Chemical Signals in Animals

The endocrine system and the nervous system act individually and together in regulating an

animal’s physiology

• The nervous system– Conveys high-speed electrical signals along

specialized cells called neurons

• The endocrine system, made up of endocrine glands– Secretes hormones that coordinate slower but longer-

acting responses to stimuli

Overlap Between Endocrine and Nervous Regulation

• The endocrine and nervous systems– Often function together in maintaining

homeostasis, development, and reproduction

• Specialized nerve cells known as neurosecretory cells– Release neurohormones into the blood

• Both endocrine hormones and neurohormones– Function as long-distance regulators of many

physiological processes

Control Pathways and Feedback Loops• There are

three types of hormonal control pathways

Pathway Example

Stimulus Low bloodglucose

Receptorprotein

Pancreassecretesglucagon ( )

Endocrinecell

Bloodvessel

LiverTarget

effectors

Response

Pathway Example

Stimulus Suckling

Sensoryneuron

Hypothalamus/posterior pituitary

Neurosecretorycell

Bloodvessel

Posterior pituitarysecretes oxytocin( )

Targeteffectors

Smooth musclein breast

Response Milk release

Pathway Example

Stimulus Hypothalamicneurohormonereleased inresponse toneural andhormonalsignals

Sensoryneuron

Hypothalamussecretes prolactin-releasinghormone ( )

Neurosecretorycell

Bloodvessel

Anteriorpituitarysecretesprolactin ( )

Endocrinecell

Bloodvessel

Targeteffectors

Response

Mammary glands

Milk production

(c) Simple neuroendocrine pathway

(b) Simple neurohormone pathway

(a) Simple endocrine pathway

Hypothalamus

Glycogenbreakdown,glucose releaseinto blood

Figure 45.2a–c

• Three major classes of molecules function as hormones in vertebrates

1. Proteins and peptides

2. Amines derived from amino acids

3. Steroids

• Signaling by any of these molecules involves three key events

1. Reception

2. Signal transduction

3. Response

• Growth factors: proteins and polypeptides that stimulate cell proliferation

• Example: nerve growth factor (NGF) affects certain embryonic cells, developing white blood cells, and other kinds of cells

1. A variety of local regulators affect

neighboring target cells

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Paracrine Signaling by Local Regulators

• In a process called paracrine signaling– Various types of chemical signals elicit

responses in nearby target cells

• Local regulators have various functions and include– Neurotransmitters– Cytokines and growth factors– Nitric oxide– Prostaglandins

• Nitric oxide (NO)– Though a gas, NO is an important local regulator.

– When secreted by neurons, it acts as a neurotransmitter.

– When secreted by white blood cells, it kills bacteria and cancer cells.

– And when secreted by endothelial cells, it dilates the walls of blood vessels.

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•Prostaglandins (PGs): modified fatty acids.

–PGs secreted by the placenta stimulate uterine contractions during childbirth.

–Other PGs play a role in inflammation and the blood flow to the lungs.

Prostaglandins help regulate the aggregation of platelets

– An early step in the formation of blood clots

Figure 45.5

2. Most chemical signals bind to plasma-membrane proteins, initiating signal-transduction pathways.

Fig. 45.3a

hormone protein.mov

Animation 45.1 Peptide Hormo.MOV

• Different signal-transduction pathways in different cells can lead to different responses to the same signal.

Fig. 45.4

• The same hormone may have different effects on target cells that have– Different receptors for the hormone

– Different proteins for carrying out the response

– Different signal transduction pathways

• The hormone epinephrine– Has multiple effects in mediating the

body’s response to short-term stressDifferent receptors different cell responses

Epinephrine

receptor

Epinephrine

receptor

Epinephrine

receptor

Vesselconstricts

Vesseldilates

Glycogenbreaks downand glucose is releasedfrom cell

(a) Intestinal blood vessel

(b) Skeletal muscleblood vessel

(c) Liver cell

Different intracellular proteins different cell responses

Glycogendeposits

Figure 45.4a–c

• Signal- transduction pathways allow for small amounts of a hormone to have a large effect. Cascade effect results in amplificationCopyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig.11.16

• Examples: estrogen, progesterone, vitamin D, NO.– Usually, the intracellular receptor activated by a

hormone is a transcription factor.

3. Steroid hormones, thyroid hormones, and some local regulators enter target cells

and bind to intracellular receptors

Fig. 45.3b

Intracellular Receptors for Lipid-Soluble Hormones

• Steroids, thyroid hormones, and the hormonal form of vitamin D– Enter target cells and bind to specific protein

receptors in the cytoplasm or nucleus

Animation 45.2 Steroid Hormo.MOV

Tropic hormonestarget other endocrineglands and areimportant tounderstandingchemicalcoordination.

• Humans havenine endocrineglands.

Introduction

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin CummingsFig. 45.5

Memorize chart on p899!!!

Memorize chart on p899!!!

• Concept 45.3: The hypothalamus and pituitary integrate many functions of the vertebrate endocrine system

• The hypothalamus and the pituitary gland– Control much of the endocrine system

Relation Between the Hypothalamus and Pituitary Gland

• The hypothalamus, a region of the lower brain– Contains different sets of neurosecretory cells

Posterior Pituitary Hormones

• The two hormones released from the posterior pituitary– Act directly on nonendocrine tissues

• Oxytocin– Induces uterine contractions and milk ejection

• Antidiuretic hormone (ADH)– Enhances water reabsorption in the kidneys

Girls put on fantastic lingerie that arouse men easily

Fat metabolism and reproduction in birdsDelays metamorphosis in amphibiansRegulates larval growth and salt balance in fish

Table 45.1 (continued)

Anterior Pituitary Hormones

• The anterior pituitary– Produces both tropic and nontropic hormones

Tropic Hormones

• The four strictly tropic hormones are– Follicle-stimulating hormone (FSH)

– Luteinizing hormone (LH)

– Thyroid-stimulating hormone (TSH)

– Adrenocorticotropic hormone (ACTH)

• Each tropic hormone acts on its target endocrine tissue– To stimulate release of hormone(s) with direct

metabolic or developmental effects

Nontropic Hormones

• The nontropic hormones produced by the anterior pituitary include

1. Prolactin

2. Melanocyte-stimulating hormone (MSH)

3. -endorphin

• Prolactin stimulates lactation in mammals– But has diverse effects in different vertebrates

• MSH influences skin pigmentation in some vertebrates– And fat metabolism in mammals

• Endorphins– Inhibit the sensation of pain

Growth Hormone

• Growth hormone (GH)– Promotes growth directly and has diverse

metabolic effects– Stimulates the production of growth factors by

other tissues

Growth hormones can increase yield and in cows, increase milk production

Growth hormones can increase yield and in cows, increase milk production

• Concept 45.4: Nonpituitary hormones help regulate metabolism, homeostasis, development, and behavior

• Many nonpituitary hormones– Regulate various functions in the body

Thyroid Hormones• The thyroid gland

– Consists of two lobes located on the ventral surface of the trachea

– Produces two iodine-containing hormones, triiodothyronine (T3) and thyroxine (T4)

• The hypothalamus and anterior pituitary– Control the secretion

of thyroid hormones through two negative feedback loops

Hypothalamus

Anteriorpituitary

TSH

Thyroid

T3 T4+Figure 45.9

• The thyroid hormones– Play crucial roles in

stimulating metabolism and influencing development and maturation

• The thyroid glandof mammals consistsof two lobes locatedon the ventral surfaceof the trachea.– Triiodothyronine (T3)

and thyroxine (T4): amines.

– Stimulates and maintainmetabolic processes.

– Secretion regulated by TSHhormones.

3. Thyroid hormones function in develop-ment, bioenergetics, and homeostasis

Fig. 45.8

Hyperthyroidism is the excessive secretion of thyroid hormones, exhibited by high body temperature, profuse sweating, weight loss, irritability, high blood pressure.

An insufficient amount of thyroid hormones is known as hypothyroidism. Infants: cretinism. Adults: weight gain, lethargy,

cold intolerance. Goiter: often associated with

iodine deficiency.

Exophthalmia

Graves’ Disease

Exophthalmia

Graves’ Disease

GoiterGoiter

Calcitonin: a peptide. Lowers blood calcium levels. Secretion regulated by calcium in blood.

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• The four parathyroid glands are embedded in the surface of the thyroid gland.

• PTH raises blood calcium levels

• PTH takes Ca++ from bones, causes more absorption form intestines and more reabsorption form the kidneys.

• Underfunction can result in TETANY.

4. Parathyroid hormone and calcitonin regulate blood calcium

level

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tetany

InsulinInsulin

CCK

• The adrenal glands are located adjacent to the kidneys.– The adrenal cortex is the outer portion.– The adrenal medulla is the inner portion.

6. The adrenal medulla and adrenal cortex help the body manage stress

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ABC NEWS// 4/5/01Marriage and HormonesScientists Say the Body’s Hormones Detect Divorce FirstBut when the researchers took a close look at the failed marriages, they were in for a surprise. Although such things as aggression and a negative attitude are generally thought of as the best predictors of divorce, the researchers found a more tantalizing clue in the blood samples collected more than a decade earlier. Those same three hormones — epinephrine, norepinephrine and ACTH — were "consistently and significantly elevated in the couples" who later divorced, Kiecolt-Glaser says.These are "stress hormones," the "fight or flight" chemical messengers that are supposed to tell us whether to hang around and duke it out or run for cover. "If those hormones stay up, you're probably going to have higher blood pressure, higher heart rate, and it's not good for your body," she says. The elevated hormone level didn't just appear in the blood drawn during the discussion of marital problems, she adds, it was present in later samples, even those drawn while the participants were asleep.

ABC NEWS// 4/5/01Marriage and HormonesScientists Say the Body’s Hormones Detect Divorce FirstBut when the researchers took a close look at the failed marriages, they were in for a surprise. Although such things as aggression and a negative attitude are generally thought of as the best predictors of divorce, the researchers found a more tantalizing clue in the blood samples collected more than a decade earlier. Those same three hormones — epinephrine, norepinephrine and ACTH — were "consistently and significantly elevated in the couples" who later divorced, Kiecolt-Glaser says.These are "stress hormones," the "fight or flight" chemical messengers that are supposed to tell us whether to hang around and duke it out or run for cover. "If those hormones stay up, you're probably going to have higher blood pressure, higher heart rate, and it's not good for your body," she says. The elevated hormone level didn't just appear in the blood drawn during the discussion of marital problems, she adds, it was present in later samples, even those drawn while the participants were asleep.

• Testes.

– Androgens (example: testosterone): steroids.• Supports sperm formation.• Promote development and maintenance of male sex

characteristics.• Secretion regulated by FSH and LH.

7. Gonadal steroids regulate growth, development, reproductive

cycles, and sexual behavior

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• Ovaries secrete estrogens and progesterone.– Estrogens: steroids.

• Stimulate uterine lining growth.

• Promote development and maintenance of female sex characteristics.

• Secretion regulated by FSH and LH.

– Progestins (example: progesterone): steroids.• Promotes uterine lining growth.

• Secretion regulated by FSH and LH.

Gonadal Sex Hormones

• The gonads—testes and ovaries–Produce most of

the body’s sex hormones: androgens, estrogens, and progestins

• The testes primarily synthesize androgens, the main one being testosterone– Which stimulate the development and

maintenance of the male reproductive system

• Testosterone causes an increase in muscle and bone mass–And is often taken

as a supplement to cause muscle growth, which carries many health risks

Figure 45.14

Mr. Chee - before he started working out

• Estrogens, the most important of which is estradiol– Are responsible for the maintenance of the female

reproductive system and the development of female secondary sex characteristics

• In mammals, progestins, which include progesterone– Are primarily involved in preparing and maintaining

the uterus

Melatonin and Biorhythms• The pineal gland,

located within the brain–Secretes

melatonin

• Release of melatonin– Is controlled by light/dark cycles

• The primary functions of melatonin– Appear to be related to biological rhythms

associated with reproduction

• Insect metamorphosis– Is regulated by hormones

Figure 45.1