Basic Introduction to the vast science of the endocrine glands and their interactions. A brief review into the physiological processes that result in endocrine disorders.

1. Introduction to
Endocrinology

2. Course Plan

3. Introduction
• Endocrinology is the understanding of hormone secretion,
hormone action, and principles of feedback control.
• The endocrine system is evaluated primarily by measuring
hormone concentrations.
• Most disorders of the endocrine system are amenable to
effective treatment once the correct diagnosis is
determined.

4. Introduction
• The term endocrine was coined by Starling
• Hormones secreted internally (endocrine)
• Externally (exocrine) i.e. into a lumen, such as the
gastrointestinal tract.
• The term hormone - derived from a Greek phrase meaning
“to set in motion,” aptly describes the dynamic actions of
hormones as they elicit cellular responses and regulate
physiologic processes through feedback mechanisms.

5. Introduction
The Endocrine organs
1. Hypothalamus
2. Pituitary gland
3. Thyroid gland
4. Parathyroid glands
5. Adrenal glands
6. Pancreatic islet cells (Endocrine Pancreas)
7. Gonads
8. Others – Eg. The gastrointestinal tract
The classic
endocrine
organs

6. Introduction
Other hormones
 Kidney (Erythropoietin, Renin)
 Heart (ANP)
 Lungs (PG, ACE)
 GIT (Many GI hormones)
 Placenta (Many hormones during Pregnancy)

7. Hormones
5 major classes

8. Hormones
A variety of peptide growth factors , most of which act locally,
share actions with hormones.

9. 9
(a) Humoral: in
response to
changing
levels of ions
or nutrients in
the blood
(b) Neural:
stimulation by
nerves
(c) Hormonal:
stimulation
received from
other
hormones
Mechanisms of
hormone release

10. Endocrine glands
Sites of hormone
action
Exocrine glands

11. Autocrine glands
Sites of hormone
action
Neurotransmission

12. Functions
• Maintenance of growth & development – Growth
hormone, Thyroxine, insulin, Glucocorticoid, & Gonadal
hormones
• Maintenance of internal environment – ADH,
Mineralocorticoids, PTH
• Regulation of energy balance and metabolism –Insulin,
glucagon , Leptin & Ghrelin
• Reproduction & species propagation – Gonadal & Pituitary
hormones

13. Interactions between
hormones
• When two or more hormones work together to produce
particular result their effects are said to be synergistic.
• These effects may be additive or complementary.
• Additive: Same effect of the hormones on one target organ,
for example, epinephrine and norepinephrine on heart rate
• Complementary: Work on different stages of a physiological
procedure, for example, FSH (initiation) and testosterone
(maintenance) on spermatogenesis
1. Synergistic effects

14. Interactions between
hormones
1. Synergistic effects

15. Interactions between
hormones
A hormone is said to have a permissive effect on the action of a
second hormone when it enhances the responsiveness of a target
organ to the second hormone or when it increases the activity of the
second hormone.
• Estrogen – Expression of progesterone receptors on uterus –
progesterone effect on the uterus.
• Glucocorticoids – effects of catecholamines on cardiovascular
system
• Thyroid hormones- effects of catecholamines on
cardiovascular system
2. Permissive effect

16. Interactions between
hormones
In some situations the actions of one hormone antagonize the effects
of another.
Lactation during pregnancy is prevented because the high
concentration of estrogen in the blood inhibits the action of prolactin
and hence milk secretion.
2. Antagonistic effect

17. Example of an
endocrinal axis
Regulation by negative feedback and direct
control is shown, along with the equilibrium
between active circulating free hormone
and bound or metabolized hormone.

18. Endocrinal axes

19. Regulation
• Feedback control , both negative
and positive, is a fundamental
feature of endocrine systems.
• Each of the major hypothalamo-
pituitary-hormone axes is governed
by negative feedback, a process
that maintains hormone levels
within a relatively narrow range

20. Regulation
• As an example, a small reduction of
thyroid hormone triggers a rapid
increase of TRH and TSH secretion, 
thyroid gland stimulation and increased
thyroid hormone production.
• When thyroid hormone reaches a
normal level, it feeds back to suppress
TRH and TSH.
• Feedback regulation also occurs for
endocrine systems that do not involve
the pituitary gland, Eg. glucose
inhibition of insulin secretion

21. Overview of Endocrine
disorders

22. Overview of Endocrine
disorders

23. Presentation

24. Investigations