__________________: 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?Fig 7-2

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 post-translational modification to prohormone then hormone

Storage – release?

Short half-life (mins.)

Most common type

Fig 7-4

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 7-6

Fig 7-7

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 6-31/➅

Fig 7-10

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

Hypothalamus

IC1Ant. pituitary

IC2

Endocrine gland

IC3 Target tissue

Negative Feedback Loops in the

Hypothalamic-anterior pituitary axis

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

AntagonismAntagonistic 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

Example: Hyperthyroidism(Review pp. 756 – 761)

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)

Symptoms:

During childhood:stunted growth

retardation

lethargy

low body temp.

In adulthood:Bradycardia

weight gain

lethargy

low body temp.

Hypothyroidism cont.

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?

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

Which of the sets of lab values below would

indicate Grave’s disease? Explain.

Graves’ disease