Fig 7-2

__________________: the study
of hormones, their receptors,
the intracellular signaling
pathways they invoke, and the
diseases and conditions
associated with them.

What are hormones?

Major endocrine glands?

Physiological processes
controlled by hormones?
Hormones

Known since ancient times

Secreted by cells into the blood

Transported to distant targets

Effective at very low concentration

Bind to receptors

Hormone action must be of limited
duration
Classification of Hormones

3 main types:
–Peptides and proteins
–Steroids
–Amines
Differ on basis of synthesis, storage,
release, transport and cellular
mechanism of action (review Table 7-1)
Peptide (Protein) Hormones

Synthesis as preprohormone  posttranslational modification to
prohormone  then hormone
Fig 7-4

Storage – release?

Short half-life (mins.)

Most common type
Fig 7-3
Cellular Mechanism of Action for
Peptide Hormones

Lipophobic  how
does message get into
cell?

Usually rapid cellular
response because
existing proteins are
modified

cAMP 2nd messenger
system most common
Steroid Hormones

All derived from cholesterol

Where synthesized?

Storage – release?

Transport in blood?

Longer half-life

Mechanism of action
Fig 7-7
Fig 7-6
Amine Hormones


Derived from one or two amino acids
3 groups
– Tryptophan  Melatonin
– Tyrosine
 Catecholamines
behave like peptide hormones
– Tyrosine
 Thyroid hormones
behave like steroid hormones
Fig 7-8
Control of Hormone Release
All endocrine reflex pathways have
similar components
– Stimulus / input signal
– Integration (where?)
– Output signal (hormone / neurohormone)
– Physiological action
– Negative feedback – turns off reflex
One Hormone may follow > 1 reflex pathway pattern
Fig 7-9
Simple Endocrine Reflex
Endocrine cell acts as sensor AND
integrating center  no afferent
pathway  responds by secreting
hormone
Example: PTH  increases [Ca2+] in
plasma
Fig 7-10
Fig 6-31/➅
Neurohormone
Reflex
NH release by modified
neurons upon NS
signal

3 major groups of Neurohormones:
– Catecholamines from adrenal medulla
– Hypothalamic neurohormones from
posterior pituitary
– Hypothalamic neurohormones acting on
anterior pituitary
Fig 6-31/②
Neurohormones of Posterior Pituitary

Other name of
gland?

2 neurohormones

Both are peptides
(9 aa) transported
in secretory
vesicles via axonal
transport
Fig 7-12
Anterior Pituitary

Secretes 6 Hormones (names?)

A Trophic (tropic) hormone controls the
secretion of another hormone

Hypothalamic trophic hormones and the
hypothalamic-hypophyseal portal system
Fig 7-13
Negative Feedback Loops in the
Hypothalamic-anterior pituitary axis
Hypothalamus
IC1
Ant. pituitary
IC2
Endocrine gland
IC3
Target tissue
Hormones serve as negative feedback signals:
Short-loop vs. long-loop negative feedback.
Feedback patterns important in diagnosis of
ES pathologies
Hormone Interactions
Multiple hormones can affect a single
target simultaneously
Three types of hormone interactions:
 Synergism
 Permissiveness
 Antagonism
Synergism

Combined action of hormones is
more than just additive!

Example: Blood glucose levels &
synergistic effects of glucagon,
cortisol and epinephrine
Fig 7-18
Permissiveness
Hormone A will not exert full effect without
presence of hormone B.
Example: Thyroid hormone & growth hormone
Antagonism
Antagonistic hormones have opposing
physiological actions – Hormone B
diminishes the effect of hormone A
(mechanisms?)
Hormone Antagonists and Cancer: Tamoxifen
Endocrine Pathologies
“Unbalance leads to disease”
Due to:
1. Hypersecretion (excess)
2.
Hyposecretion (deficiency)
3.
Abnormal target tissue response
Hypersecretion:

Due to ?
– Iatrogenic (could lead to gland atrophy)
– ________

Symptoms: Exaggerated Effects
Examples:
 Cushing’s Syndrome
 Gigantism
 Graves disease
Hyperthyroidism
(Review pp. 756 – 761)
Example:
Most common cause:
Graves' disease
Autoantibodies (TSI) bind to
TSH receptor and stimulate
thyroid hormone production
This activation by TSI is not
subject to the normal
negative feedback loop.
Left exophthalmus in Graves disease
Hyposecretion:

Due to ?

Symptoms: Normal effects of
hormone diminished or absent
Examples:
 Addison’s disease
 Dwarfism
 Hypothyroidism
Example: Hypothyroidism
Most common cause in US: chronic
autoimmune thyroiditis
(Hashimoto's thyroiditis = Chronic
thyroiditis )
Other causes
 surgical removal of the thyroid gland
 radioactive iodine treatment
 external radiation
 a deficiency in dietary iodide
consumption (=endemic or primary
goiter)
Hypothyroidism
cont.
Symptoms:
During childhood:
stunted growth
retardation
lethargy
low body temp.
In adulthood:
Bradycardia
weight gain
lethargy
low body temp.
Abnormal Tissue Responsiveness
Hormone levels normal, target
unresponsive
Due to:
– Abnormal hormone / receptor
interaction
– Abnormal signal transduction
Diagnosis of Endocrine Pathologies

Primary Pathology
– Defect arises in last integration center
in the reflex
– Examples?

Secondary Pathology
– Defect arises in one of the trophic
integration centers
– Examples?
Which of the sets of lab values below would
indicate Grave’s disease? Explain.
Patient
Serum T4
Serum TSH
A
6 µg/dl
1.5 µU/ml
B
14 µg/dl
.25 µU/ml
C
2.5 µg/dl
20 µU/ml
D
16 µg/dl
10 µU/ml
Normal
4.6-12 µg/dl
0.5 - 6 µU/ml
Graves’ disease