Endocrine online

Copyright © 2011 Pearson Education, Inc.

Chapter 15 Part I Overview

Hormone types

Hormone activity


Endocrine System Function

• Control cell activity

• metabolism

• Release hormones

• Slower control than CNS/PNS

• Endocrine glands: pituitary, thyroid, parathyroid, adrenal, and pineal glands


Endocrine System: Overview

• Some organs have endocrine and exocrine function

• pancreas and gonads

• adipose cells, thymus, small intestine, stomach, kidneys, and heart

• Hypothalamus has neural and endocrine functions

Copyright © 2011 Pearson Education, Inc. Figure 15.1

Pineal glandHypothalamus

Pituitary gland

Parathyroid glands(on dorsal aspectof thyroid gland)Thymus

Thyroid gland

Adrenal glands

Pancreas

Ovary (female)

Testis (male)


Chemical Messengers

• Hormones: Long ranging chemical signals, travel through blood or lymph

• Autocrine: chemicals affect the cells that secretes them

• “self stimulating”

• Paracrine: locally acting chemicals that affect other cells


Hormone Action

• How hormones cause change:

1. Open or close ion channels

2. Stimulate synthesis of proteins

3. Activate or deactivate enzymes

4. Induce secretion

5. Stimulate mitosis


Chemistry of Hormones

• Two main classes

1. Amino acid-based hormones

• Water soluble

• ex. Proteins… such as tryptophan

2. Steroids

• Non-water soluble

• Made from cholesterol

• ex. Estrogen & testosterone


Mechanisms of Hormone Action

Two mechanisms, depends on chemical makeup

1. Water-soluble hormones (amino acid–based)

• Cannot enter target cells

• Can’t pass through plasma membrane

• Bind to receptors on cell surface

• Initiate chain reactions inside cell


Membrane Receptors and Second-Messengers

• Hormone signaling mechanism

1. Hormone (primary messenger) binds to surface receptor

2. Receptor activates internal signals(secondary messengers)

3. Triggers change in the cell

• Increased mitosis

• Protein production

Copyright © 2011 Pearson Education, Inc. Figure 15.2, step 1

Hormone (1st messenger)binds receptor.

Receptor

Hormones thatact via cAMPmechanisms:

EpinephrineACTHFSHLH

Extracellular fluid

Cytoplasm

GlucagonPTHTSHCalcitonin

1

Figure 15.2, step 2


Receptoractivates Gprotein (GS).

Receptor

G protein (GS)



Extracellular fluid

Cytoplasm

GDP


1

2

Figure 15.2, step 3


Receptoractivates Gprotein (GS).

G proteinactivatesadenylatecyclase.

Receptor

G protein (GS)

Adenylate cyclase



Extracellular fluid

Cytoplasm

GDP


1

2 3

Figure 15.2, step 4


Receptor

G protein (GS)

Adenylate cyclase



Extracellular fluid

Cytoplasm

GDP


1

2 3 4

Figure 15.2, step 5


cAMP acti-vates proteinkinases.Receptor

G protein (GS)

Adenylate cyclase

Triggers responses of target cell (activates enzymes, stimulates cellular secretion, opens ion channel,etc.)



Inactiveprotein

Extracellular fluid

Cytoplasm

Activeprotein

GDP


1

4

5

• cAMP is a common second messenger.


Mechanisms of Hormone Action

2. Lipid-soluble hormones (steroids)

• Can pass through plasma membrane

• Bind to intracellular receptors

• Directly activates gene

• Receptor + hormone binds to DNA

• Promotes transcription of mRNA

• mRNA then translated into protein

Copyright © 2011 Pearson Education, Inc. Figure 15.3, step 1

Receptor-hormonecomplex

Receptorprotein

Cytoplasm

Nucleus

Extracellular fluid

Steroidhormone

The steroid hormonediffuses through the plasmamembrane and binds anintracellular receptor.

Plasmamembrane

1

Figure 15.3, step 2


Receptorprotein

Cytoplasm

Nucleus

Extracellular fluid

Steroidhormone


The receptor-hormone complex entersthe nucleus.

Plasmamembrane

1

2

Figure 15.3, step 3

DNA

Hormoneresponseelements


Receptorprotein

Cytoplasm

Nucleus

Extracellular fluid

Steroidhormone



The receptor- hormonecomplex binds a hormoneresponse element (aspecific DNA sequence).

Plasmamembrane

1

2

3

Figure 15.3, step 4

mRNA

DNA



Receptorprotein

Cytoplasm

Nucleus

Extracellular fluid

Steroidhormone




Binding initiatestranscription of thegene to mRNA.

Plasmamembrane

1

2

3

4

Figure 15.3, step 5

mRNA

New protein

DNA



Receptorprotein

Cytoplasm

Nucleus

Extracellular fluid

Steroidhormone




Binding initiatestranscription of thegene to mRNA.

The mRNA directsprotein synthesis.

Plasmamembrane

1

2

3

4

5


Target Cell Activation

• Target cell activation depends on:

1. Presence of receptor

• Target cells must have specific hormone receptors

• Receptors are often limited to specific tissues

2. Hormone concentration

3. Number of receptors on cell

4. binding of receptor and hormone


Target Cell Activation

• Hormones can influence receptor numbers

• Up-regulation —more receptors

• Down-regulation — lose receptors


Control of Hormone Release

• Negative feedback loops

• Help control hormone release

• Hormones produced inhibit upstream glands

• ex. To make hormone 3 you need hormones 1 and 2.

• Negative feedback loop is hormone 3 inhibits production of hormones 1 and 2.

• Prevents overproduction of hormones

Copyright © 2011 Pearson Education, Inc. Figure 15.4c

Hypothalamus

Thyroidgland

Adrenalcortex

Gonad(Testis)

Pituitarygland

1 The hypothalamus secreteshormones that…

2 …stimulatethe anteriorpituitary glandto secretehormonesthat…

3 …stimulate other endocrineglands to secrete hormones

Neg

ativ

e fe

edba

ckNegative Feedback Loop

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