The Endocrine System

INTRODUCTION

Endocrine v Nervous

Endocrine system Releases hormones into interstitial fluid blood general circulation

Effectors: virtually any type of body cell; can have widespread effects on diverse aspects of metabolism

Slower, longer-lasting responses as hormones linger in blood

Hormone Action

• Hormones are carried in blood stream • Only certain cells can be affected by

hormones– These target cells have 1000’s of receptors

specific for a particular hormone.– Response determined by target cell:

different cells may respond differently to the same hormone.

Location of Endocrine Glands

HORMONE CHEMISTRY

Lipid-Soluble Hormones

• Steroids, such as testosterone, estrogens• Thyroid hormones: T3 and T4 • Nitric oxide (NO)

Lipid-Soluble Hormones

1Lipid-solublehormonediffuses into cell

Blood capillary

Activatedreceptor-hormonecomplex altersgene expression

NucleusReceptor

mRNANewly formedmRNA directssynthesis ofspecific proteinson ribosomes

DNACytosol

Target cell

Transportprotein

Free hormone

Ribosome

2

3

Water Soluble Hormones

• Amino acid derivatives, such as epinephrine, norepinephrine

• Peptides: antidiuretic hormone (ADH), oxytocin

• Proteins: insulin and growth hormone

Water Soluble Hormones

Water-solublehormoneReceptor

cAMP serves as asecond messengerto activate proteinkinases

G protein

Protein kinases

cAMP

Activatedproteinkinases

Protein—

Second messenger

Phosphodiesteraseinactivates cAMP

Activated adenylatecyclase convertsATP to cAMP

Activated proteinkinasesphosphorylatecellular proteins

Millions of phosphorylatedproteins cause reactions thatproduce physiological responses

Blood capillary

Binding of hormone (first messenger)to its receptor activates G protein,which activates adenylate cyclase

Adenylate cyclase

Target cell

P

ADP

Protein

ATP

ATP

1

2

6

4

3

5

Control of Secretions

Release occurs in short burstsRegulated by• Signals from nervous system

– Example: epinephrine• Chemical changes in blood

– Example: blood Ca2+ affects PTH• Other hormones

– Example: ACTH from pituitary stimulates release of cortisol from adrenal cortex

HYPOTHALAMUS & PITUITARY

Anterior Pituitary

Also called the adenohypophysis; it produces:• hGH (somatotropin)• IGF (Insulinlike Growth Factor)• TSH – Thyroid Stimulating Hormone• FSH – Follicle Stimulating Hormone

Anterior Pituitary

• LH – Luteinizing Hormone• PRL – Prolactin• ACTH – Adrenocorticotropic Hormone• MSH – Melanocyte Stimulating Hormone• These are all regulated by release factors

made in the hypothalamus

Posterior Pituitary

Also called the neurohypophysis; it stores and releases:

• Oxytocin• ADH – Antidiuretic Hormone• These substances are produced by the

hypothalamus

GLANDS OF THE BODY

The Thyroid Gland

Produces thyroxin (T4) and triiodothyronine (T3)

• Actions: Increases BMR (rate of O2 consumption) → body temp

• Body growth and developmentAlso produces calcitonin• Lowers blood levels of Ca, P

The Parathyroid Glands

Produces Parathyroid Hormone (PTH)• Increases blood levels of Ca, P, Mg

The Pancreas

Pancreas is both endocrine and exocrine (digestive enzymes)

Islets of Langerhans produce glucagon and insulin

• Glucagon increases blood levels of glucose• Insulin decreases blood glucose levels

The Adrenal Glands

Adrenal Cortex• Mineralocorticoids such as Aldosterone –

regulates Na+ (reabsorption) and K+ (excretion)• Glucocorticoids such as Cortisol – breaks down

proteins and triglycerides; anti-inflammatory

The Adrenal Glands

Adrenal Medulla• Produces epinephrine and norepinephrine• Stress response;• Fight-or-flight

The Pineal Gland

Produces melatonin• Biological clock• Levels increase in darkness and during sleep• Levels high in infants and young children;

lower in adults