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
Free hormone
Transport
protein
Blood capillary
1 Lipid-soluble
hormone
diffuses into cell
2 Activated
Nucleus
Receptor
receptor-hormone
complex alters
gene expression
Cytosol
3 Newly formed
mRNA directs
synthesis of
specific proteins
on ribosomes
DNA
mRNA
Ribosome
Target cell
Water Soluble Hormones
• Amino acid derivatives, such as
epinephrine, norepinephrine
• Peptides: antidiuretic hormone (ADH),
oxytocin
• Proteins: insulin and growth hormone
Water Soluble Hormones
Blood capillary
1 Binding of hormone (first messenger)
to its receptor activates G protein,
which activates adenylate cyclase
Adenylate cyclase
Water-soluble
hormone
Receptor
Second messenger
G protein
ATP
cAMP
2 Activated adenylate
cyclase converts
ATP to cAMP
6 Phosphodiesterase
Protein kinases
inactivates cAMP
3 cAMP serves as a Activated
second messenger protein
to activate protein kinases
kinases
4 Activated protein
Protein
kinases
phosphorylate
ATP
cellular proteins
ADP
Protein— P
5 Millions of phosphorylated
proteins cause reactions that
produce physiological responses
Target cell
Control of Secretions
Release occurs in short bursts
Regulated 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 development
Also 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; antiinflammatory
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