Chapter 45Chapter 45

Hormones and theHormones and theEndocrine SystemEndocrine System

The Body’s Long-Distance RegulatorsThe Body’s Long-Distance Regulators An animal hormoneAn animal hormone

Is a chemical signal that is secreted into Is a chemical signal that is secreted into the circulatory system and communicates the circulatory system and communicates regulatory messages within the bodyregulatory messages within the body

Hormones may reach all parts of the Hormones may reach all parts of the bodybody But only certain types of cells, target But only certain types of cells, target

cells, are equipped to respondcells, are equipped to respond

Animals have two systems of internal Animals have two systems of internal communication and regulationcommunication and regulation The nervous system: Conveys high-speed The nervous system: Conveys high-speed

electrical signals along specialized cells electrical signals along specialized cells called neuronscalled neurons

The endocrine system: Secretes The endocrine system: Secretes hormones that coordinate slower but hormones that coordinate slower but longer-acting responses to stimulilonger-acting responses to stimuli

A common feature of control A common feature of control pathwayspathways Is a feedback loop connecting the Is a feedback loop connecting the

response to the initial stimulusresponse to the initial stimulus Negative feedbackNegative feedback

Regulates many hormonal pathways Regulates many hormonal pathways involved in homeostasisinvolved in homeostasis

Hormones and other chemical Hormones and other chemical signals bind to target cell receptors, signals bind to target cell receptors, initiating pathways that culminate in initiating pathways that culminate in specific cell responsesspecific cell responses

Hormones convey information via Hormones convey information via the bloodstreamthe bloodstream To target cells throughout the bodyTo target cells throughout the body

Three major classes of molecules Three major classes of molecules function as hormones in vertebratesfunction as hormones in vertebrates Proteins and peptidesProteins and peptides Amines derived from amino acidsAmines derived from amino acids SteroidsSteroids

Signaling by any of these molecules Signaling by any of these molecules involves three key eventsinvolves three key events ReceptionReception Signal transductionSignal transduction ResponseResponse

Cell-Surface Receptors for Cell-Surface Receptors for Water-Soluble HormonesWater-Soluble Hormones

The receptors for most water-The receptors for most water-soluble hormonessoluble hormones Are embedded in the plasma Are embedded in the plasma

membrane, projecting outward from membrane, projecting outward from the cell surfacethe cell surface

Binding of a hormone to its Binding of a hormone to its receptorreceptor Initiates a signal transduction Initiates a signal transduction

pathway leading to specific pathway leading to specific responses in the cytoplasm or a responses in the cytoplasm or a change in gene expressionchange in gene expression

SECRETORYCELL

Hormonemolecule

VIABLOOD

Signal receptor

TARGETCELL

Signaltransductionpathway

Cytoplasmicresponse

Nuclearresponse

NUCLEUS

DNA

OR

(a) Receptor in plasma membrane

The same hormone may have The same hormone may have different effects on target cells that different effects on target cells that havehave Different receptors for the hormoneDifferent receptors for the hormone Different signal transduction pathwaysDifferent signal transduction pathways Different proteins for carrying out the Different proteins for carrying out the

responseresponse

The hormone epinephrineThe hormone epinephrine Has multiple effects in mediating the Has multiple effects in mediating the

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

Epinephrine

receptor

Epinephrine

receptor

Epinephrine

receptor

Vesselconstricts

Vesseldilates Glycogen

breaks 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

Intracellular Receptors Intracellular Receptors for Lipid-Soluble for Lipid-Soluble

HormonesHormones Steroids, thyroid hormones, and Steroids, thyroid hormones, and

the hormonal form of vitamin Dthe hormonal form of vitamin D Enter target cells and bind to Enter target cells and bind to

specific protein receptors in the specific protein receptors in the cytoplasm or nucleuscytoplasm or nucleus

The protein-receptor The protein-receptor complexescomplexes Then act as transcription Then act as transcription

factors in the nucleus, factors in the nucleus, regulating transcription of regulating transcription of specific genesspecific genes

SECRETORYCELL

Hormonemolecule

VIABLOOD

TARGETCELL

Signalreceptor

Signaltransductionand response

DNA

mRNA

NUCLEUS

Synthesis ofspecific proteins

The hypothalamus and pituitary The hypothalamus and pituitary integrate many functions of the integrate many functions of the vertebrate endocrine systemvertebrate endocrine system

The hypothalamus and the pituitary The hypothalamus and the pituitary glandgland Control much of the endocrine systemControl much of the endocrine system

The major human endocrine glandsThe major human endocrine glands

Hypothalamus

Pineal gland

Pituitary gland

Thyroid glandParathyroid glands

Adrenal glands

Pancreas

Ovary(female)

Testis(male)

Figure 45.6

Major human endocrine glands and Major human endocrine glands and some of their hormonessome of their hormones

Table 45.1

Table 45.1

Insulin and Glucagon: Insulin and Glucagon: Control of Blood GlucoseControl of Blood Glucose

Two types of cells in the pancreasTwo types of cells in the pancreas Secrete insulin and glucagon, Secrete insulin and glucagon,

antagonistic hormones that help antagonistic hormones that help maintain glucose homeostasismaintain glucose homeostasis

GlucagonGlucagon Is produced by alpha cellsIs produced by alpha cells

InsulinInsulin Is produced by beta cellsIs produced by beta cells

Maintenance of glucose homeostasisMaintenance of glucose homeostasis

Beta cells ofpancreas are stimulatedto release insulininto the blood.

Insulin

Liver takesup glucoseand stores itas glycogen.

Body cellstake up moreglucose.

Blood glucose leveldeclines to set point;stimulus for insulinrelease diminishes.

STIMULUS:Rising blood glucose

level (for instance, aftereating a carbohydrate-

rich meal)

Homeostasis:Blood glucose level

(about 90 mg/100 mL)

Blood glucose levelrises to set point;

stimulus for glucagonrelease diminishes.

STIMULUS:Dropping blood glucoselevel (for instance, after

skipping a meal)

Alpha cells of pancreasare stimulated to releaseglucagon into the blood.

Liver breaksdown glycogenand releasesglucose intoblood.

GlucagonFigure 45.12

Target Tissues for Target Tissues for Insulin and GlucagonInsulin and Glucagon

Insulin reduces blood glucose levels Insulin reduces blood glucose levels byby Promoting the cellular uptake of Promoting the cellular uptake of

glucoseglucose Slowing glycogen breakdown in the Slowing glycogen breakdown in the

liverliver Promoting fat storagePromoting fat storage

High blood glucose High blood glucose levelslevels

Low blood glucose Low blood glucose levelslevels

1. pancreas (beta) 1. pancreas (beta) produces produces

insulininsulin

2. Insulin stimulates 2. Insulin stimulates muscle muscle

and liver to take glucose and liver to take glucose

from blood and convert to from blood and convert to

glycogen.glycogen.

3. resulting in lowering 3. resulting in lowering the the

glucose level in the blood.glucose level in the blood.

1. pancreas (alpha) 1. pancreas (alpha) produces produces

glucagonglucagon

2. Glucagon stimulates 2. Glucagon stimulates liver liver

to convert glycogen back to convert glycogen back

into glucose.into glucose.

3. releasing of glucose 3. releasing of glucose intointo

blood blood

Glucagon increases blood glucose Glucagon increases blood glucose levels bylevels by Stimulating the conversion of glycogen Stimulating the conversion of glycogen

to glucose in the liverto glucose in the liver Stimulating the breakdown of fat and Stimulating the breakdown of fat and

protein into glucoseprotein into glucose

Diabetes mellitus, perhaps the best-known Diabetes mellitus, perhaps the best-known endocrine disorderendocrine disorder Caused by a deficiency of insulin or a decreased response Caused by a deficiency of insulin or a decreased response

to insulin in target tissuesto insulin in target tissues Is marked by elevated blood glucose levelsIs marked by elevated blood glucose levels

Type I diabetes mellitus (insulin-dependent Type I diabetes mellitus (insulin-dependent diabetes)diabetes) Is an autoimmune disorder in which the immune Is an autoimmune disorder in which the immune

system destroys the beta cells of the pancreassystem destroys the beta cells of the pancreas JuvenileJuvenile

Type II diabetes mellitus (non-insulin-Type II diabetes mellitus (non-insulin-dependent diabetes)dependent diabetes) Is characterized either by a deficiency of insulin or, Is characterized either by a deficiency of insulin or,

more commonly, by reduced responsiveness of target more commonly, by reduced responsiveness of target cells due to some change in insulin receptorscells due to some change in insulin receptors

AdultsAdults Body produces insulin, pancreas either cant produce Body produces insulin, pancreas either cant produce

enough or body cant use it adequately (glucose cant get enough or body cant use it adequately (glucose cant get into cells so there is a build up of glucose in blood)into cells so there is a build up of glucose in blood)