Chapter 17:

AP2 Chapter 17 1

Chapter 17:Functional Organization of

the Endocrine System

Pg 586

AP2 Chapter 17 2

Chapter 17 Outline

I. General Characteristics of the Endocrine System

II. Chemical structure of hormones

III. Control & secretion rate

IV. Transport & distribution in the body

V. Metabolism & Excretion

VI. Interaction of hormones with their target tissue

VII.Classes of Receptors

AP2 Chapter 17 3

I. General Characteristics of the Endocrine System

AP2 Chapter 17 4

I. General Char. of the Endocrine Syst.

Greek:• Endo: within• Krino: to secrete• Hormone: to set in motion

Endocrine System:• Composed of endocrine

glands that typically secrete chemical signals (a.k.a. hormones) into the cardiovascular system– Exocrine glands secrete

their products onto a surface

• Hormones are:a) Prod’d in small amounts

by a collection of cells

b) Secreted in interstitial spaces

c) Enters the cardiovascular system where it is transported some distance

d) Acts on specific tissues (target tissues) at another site in the body to influence the activity of these tissues in some specific fashion

5

I. General Char. of the Endocrine Syst.Endocrine System

• Hormones can be described as Amplitude-modulated Signals

• & in [ ] of hormones in body fluids over periods ranging from minutes to hours

• Responses are also or based on [ ]

Nervous System

• All or none potentials carried along axons can be described as frequency-modulated signals.

• These vary in frequency but not amplitude

• Low frequency weak stimulus• High frequency strong stimulus

• FX last only 1 to a few milliseconds

• Local actions

Regulate activities of structures in body but do so differently Intimate relationship btwn these 2 syst’s is now recognized

As always there are exceptions

AP2 Chapter 17 6

I. General Char. of the Endocrine Syst.Intercellular chemical signals (Table 17.1 pg 588)

1. Autocrine

2. Paracrine

3. Hormones

4. Neurohormones (AKA hormone)

5. NT/Neuromodulator

6. Pheromone

allows 1 cell to communicate w/ another Coordinate & regulate the activities of most cells

NT’s & neuromodulators play essential roles in fxn of the NSHormones are secreted by the Endocrine System

AP2 Chapter 17 7

I. G

ener

al C

har.

of th

e E

ndoc

rine

Sys

t.In

terc

ellu

lar

chem

ical

sig

nals

1. Autocrine

– Secreted by cells in a local area & influences the activity of the same cell type from which it was secreted

2. Paracrine– Prod’d by a wide variety of

tissues & secreted into tissues spaces; usually has a localized effect on others

3. Hormones– Secreted into the blood by

specialized cells; travels some distance to target tissues; influences specific activities

AP2 Chapter 17 8

I. G

ener

al C

har.

of th

e E

ndoc

rine

Sys

t.In

terc

ellu

lar

chem

ical

sig

nals

4. Neurohormones (AKA

hormone)– Produ’d by neurons but

function as hormones

5. NT/Neuromodulator– Prod’d by neurons & secreted

into extracellular spaces by presynaptic nerve terminals; travels short distances; influences postsynaptic cells

6. Pheromone– Secreted into the environment;

modifies the physiology and behavior of other individuals of the same species

AP2 Chapter 17 9

II. Chemical Structure of Hormones

Pg 589

Table 17.2 (Examples listed)

Figure 17.3

AP2 Chapter 17 10

II. Chemical Structure of Hormones

A. Proteins

B. Short sequences of aa’s called polypeptides

C. Derivatives of aa’s

D. Lipids

E. Glycoproteins

AP2 Chapter 17 11

III. Control of Secretion Rate

AP2 Chapter 17 12III. C

on

tro

l of S

ecr

etio

n R

ate

• Negative Feedback loops are used to help maintain the body in a state of homeostasis

• Positive Feedback loops is also used in a very limited capacity

Figure 17.7

AP2 Chapter 17 13


3 major patterns of regulation1. Non-hormonal Regulation of hormone secretion

2. Nervous System regulation of hormone secretion

3. Hormonal regulation of hormone secretion

• As with everything in the body, it can be much more complicated involving multiple mechanisms

• Some hormones:– Are in circulatory system at relatively constant levels– D suddenly in response to stimulation– D in a relatively constant cycle

AP2 Chapter 17 14

III. Control of Secretion Rate3 major patterns of regulation

1. Non-hormonal Regulation of hormone secretion– Changes in the extracellular [ ] of a substance other than a

hormone effect the function of the endocrine gland

AP2 Chapter 17 15

III. Control of Secretion Rate3 major patterns of regulation

1. Neural Control of the endocrine gland– Neuron is synapsed with an endocrine gland and the neuron

influences the activity of the gland

AP2 Chapter 17 16


3 major patterns of regulation3. Hormonal regulation of hormone secretion

– Control of the secretory activity of one gland by a hormone or neurohormone secreted by another gland.

AP2 Chapter 17 17

IV. Transport & Distribution in the body

AP2 Chapter 17 18


1. Unbound Hormones 2. Bound Hormones

2 main ways to transport hormones in the blood

• Water soluble and travel in the blood

• Lipid soluble and do not like the watery environment of the blood thus it must be bound to a transport protein

Pg 594Fig 17.9

AP2 Chapter 17 19


2. Bound Hormones• These are bound in a reversible

fashion• Equilibrium is established btwn

bound and their unbound counterparts

• Bound are also trapped within the confines of the capillary because they are to big to filter thru– These serve as a reservoir. Thus

when one in tissue is used there are replacements that only need to be released from the blood stream

– These can also remain in the blood longer without being destroyed

AP2 Chapter 17 20


a. Lipid soluble hormones

• Pass thru capillary walls readily

• Typically travel bound to binding proteins

• Binding prevents their rapid diffusion from the circulatory system into the tissues

• Reservoir also gives a relatively constant rate of diffusion of the unbound hormone from circ.systm.

b. Water soluble hormones

• Must go thru the pores of the capillary walls (fenestrae)

• The capillaries of the organs regulated by and glands secreting these hormones usually have these large pores.

• These usually get into tissue at a slow rate

Hormones go thru the bld & thus distributed quickly throughout the body They diffuse thru the capillary wall & enter interstitial spaces and the rate of that movement varies by hormone

AP2 Chapter 17 21


AP2 Chapter 17 22

V. Metabolism & ExcretionDestruction & elimination of hormones limit the time that they are active in the body. The body’s activities can or dependent on how long the hormone remains in the body

• Length of time it takes for ½ the dose of a substance to be eliminated from the circulatory system. (RATE)

• Time to eliminate entire amount isn’t helpful b/c it all depends on what you start with.

• Times vary dependent on specific hormone

Ways to lengthen half-life

• Binding them to binding proteins

• Their structures may also protect the hormone– Example– Glycoproteins: their carb

component protects them from proteolytic enzymes in circulatory system

Half-Life

AP2 Chapter 17 23


4 major ways to remove hormones from bld

1. Excretion– Excreted into the urine by the kidney or the bile by the liver

2. Metabolism– Enzymatically degraded in the bld, liver, kidney, lungs, or

target tissues– Byproducts are excreted in the bile & urine

3. Active Transport– Actively transported into cells and used again later as a NT

or hormone

4. Conjugation– Substances are attached to hormones primarily in the liver.

These normally make the hormone less active & increase its rate of excretion

AP2 Chapter 17 24

VI. Interactions of hormones with their target tissues

25

VI. Interactions of hormones w/their target tissues

Hormones (a.k.a. Ligands)• Bind to receptors (proteins or glycoproteins)• Bind at the receptor site (binding site)

Binding Site:• Chemical characteristics of

the site allow only a specific type of chemical signal to bond to it

• “Specificity” can’t get growth hormone to bind to insulin site

• Hormone receptors have a high affinity for the hormones that bind them, thus only a small [ ] results in a significant # of receptors being bound

• Presence or absence of receptor determines wh/cells will react to the hormone’s release, thus it can travel throughout the body, but will only activate the proper cells

AP2 Chapter 17 26


• Drugs can be designed to have a similar structure to a natural hormone & may compete for the receptor’s binding site

• Agonist:– Chemical that will bond to a receptor & activate it (Histamine)

• Antagonist:– Chemical that will bind to a receptor but inhibits its action

(antihistamine)

Taking advantage of hormone

shape to make drugs

AP2 Chapter 17 27


• Can be constant or variable.• Rxns can decrease rapidly with time.

One Explanation:• Fatigue after prolonged stimulation of

targeted cells

Response to Hormone

AP2 Chapter 17 28

VI. Interactions of hormones w/their target tissues1. Down-regulation

– # of receptors can also decrease over time after exposure

– Tissues that down regulate are usually designed to respond to short term hormone increases

– Tissues that respond to constant levels of hormones do not exhibit down-regulation

2. Up-regulation– Periodic increases in

sensitivity of some cells to hormones

– Results from an increase in rate of receptor molecule synthesis

Fig

ure

17.

12 P

g 5

96

AP2 Chapter 17 29

VI. Interactions of hormones w/their target tissuesDown-regulation continued

2 ways of down regulation

1. Synthesis rate of the receptor are reduced

– Most hormone receptor complexes are degraded over time. If they are not replaced because of no synthesis the ultimate result is less cell surface receptors

2. Increased rate of receptor degradation

– Receptor hormone complexes are sometimes degraded more quickly than the receptor alone

AP2 Chapter 17 30

VII. Classes of Receptors

• 2 Major Categories of Hormones• 2 Major Categories of Receptors

(Figure 17.13 pg 597)

AP2 Chapter 17 31

VII Classes of ReceptorsA. Hormones that bind to

membrane bound receptors

• Include large molecules & water soluble molecules both can’t pass thru the plasma membrane

• Examples:– Proteins, glycoproteins,

polypeptides, smaller molecules (epi/norepi)

• When the receptor is bound it initiates a response inside the cell

• Thus they interact w/the outside of the cell with membrane bound receptors– Transmembrane receptors

w/their receptor sites exposed to the outer surface of the plasma membrane

32

VII Classes of ReceptorsB. Hormones that bind intracellular receptors

• These include lipid-soluble and relatively small hormones.

• Examples:– Thyroid hormones, steroid

hormones (testosterone, estrogen, progesterone, aldosterone, & cortisol)

• Diffuse thru the plasma membrane & bind to Intracellular Receptors.– These are receptors in the

cytoplasm or even the nucleus of the cell

• Thus the hormone-receptor complex interacts with the DNA directly to prod. a response.

AP2 Chapter 17 33

VII. Classes of Receptors2 Major Categories

Membrane Bound Receptors Intracellular Receptors

AP2 Chapter 17 34

VII. Classes of ReceptorsMembrane Bound Receptors

1. Receptors that activate G-proteins

2 major categories

Mechanisms for membrane bound receptors

2. Receptors that directly alter the activity of intracellular enzymes

AP2 Chapter 17 35


• These have 3 subunits: , , a b& g

• Called G-proteins because a binds to guanine nucleotides

• Result #1:• Activated a-

subunit can alter the activity of molecules inside the cell prod’ing cellular responses

Fig 7.14 pg 599

AP2 Chapter 17 36

1. Receptors that activate G-proteins• Result #2:

• Activated a-subunit can combine w/ion channels causing them to open & close

• Some ions or molecules can act as intracellular modulators

• Enter or are synthesized w/in the cell that regulate enz activity in the cell

Fig 7.15 pg 600

AP2 Chapter 17 37


• Result #3:• Activated a-subunit can also alter the activity of enz’s

inside the cell

Fig 7.16 pg 601

AP2 Chapter 17 38


• Result #4:• Alter the [ ] of

intracellular mediators other than Ca2+ & cAMP

Fig 7.17 pg 602

AP2 Chapter 17 39


1. Receptors that activate G-proteins– When the hormone separates from the receptor

additional G-proteins are no longer activated– Inactivation of a-subunit occurs when phosphate

is removed from the GTP-leaving GDP with the a-subunit

– Then the subunits of the G-protein recombine

• Membrane Bound Receptors

AP2 Chapter 17 40

VII. Classes of ReceptorsMembrane Bound Receptors


2 major categories

Mechanisms for membrane bound receptors


AP2 Chapter 17 41


• These receptor when bound directly alter the activity of an intracellular enzymes (mediators) w/no 2nd messenger needed

• Altered enz’s can be membrane bound or not

• Mediator enz’s act as chemical signals that move from where they are altered into the cytoplasm where they activate processes that prod a cellular response

Fig 7.18 pg 602

AP2 Chapter 17 42


• Altered enzyme activity can:a) or the activity of

intracellular mediator molecules

b) Results in the phosphorylation of intracellular proteins

c) Intracellular mediators (Phosphoylated proteins) activate processes that prod the response of the cell

Fig 7.18 pg 602

43


• Some are bound & a portion of the receptor on the inner surface of the membrane acts as a phosphorylase enzyme that phosphorylates several specific proteins– Phosphorylated proteins:

• Can be part of the membrane bound protein or not

• Influence the activity of other enzymes in the cell

AP2 Chapter 17

Fig 7.19 pg 603

44


Cascade Effect– Most hormones act

exponentially causing a pyramid effect that result in rapid responses

– Few mediator molecules activate several enz’s & each enz activates several other enz’s that prod a response

– An amplification system exists in wh/a few molecules can control the activity of many enz’s w/in the cell

AP2 Chapter 17

Fig 7.20 pg 604

AP2 Chapter 17 45

VII. Classes of Receptors2 Major Categories

Membrane Bound Receptors Intracellular Receptors

AP2 Chapter 17 46


• Lipid soluble hormones cross the plasma membrane into the cytoplasm or nucleus & bind to intracellular receptors by the process of diffusion

• Thus receptor location is in the cytoplasm or nucleus

Fig 7.21 pg 605

AP2 Chapter 17 47

VII. Classes of Receptors• Fxns of receptor-

hormone complex:a. Alter the activity of enz’s

of the cell

b. Bind to DNA to prod a response:• Via gene expression• DNA is transcribed into

mRNA then translated into a protein

• Thus it increases the synthesis of a specific protein.

Fig 7.21 pg 605

AP2 Chapter 17 48


• These types of rxns are not instant, they usually take several hours btwn hormone release & response is observed– To make mRNA & protein

• Hormone influence is limited via hormone-receptor complex degradation Fig 7.21 pg 605

AP2 Chapter 17 49

VII. Classes of ReceptorsIntracellular Receptors

Fig 7.21 pg 605

Documents

Chapter 17: