Introduction to Endocrine Physiology

1. Prakash Kr. Yadav
Lecturer
Department of Physiology
Chitwan Medical College, Bharatpur.
Introduction to Endocrine Physiology

2. Biological communication
Communication among cells, organisms &
between organisms & their environment is
absolutely central to life & reproduction.

3. II. Endocrine vs. Nervous SysteII. Endocrine vs. Nervous Syste
Major communication systems in the body
Integrate stimuli and responses to changes
in external and internal environment
Both are crucial to coordinated functions of
highly differentiated cells, tissues and
organs
Unlike the nervous system, the endocrine
system is anatomically discontinuous.

4. Nervous systemNervous system
•The nervous system exerts
point-to-point control through
nerves, similar to sending
messages by conventional
telephone.
•Nervous control is electrical in
nature and fast.

5. Hormones travel via the bloodstream to target cellsHormones travel via the bloodstream to target cells
•The endocrine system broadcasts its
hormonal messages to essentially all
cells by secretion into blood and
extracellular fluid.
•Like a radio broadcast, it requires a
receiver to get the message –
•in the case of endocrine messages,
cells must bear a receptor for the
hormone being broadcast in order to
respond.

6. Together, the nervous and endocrine systems coordinate
functions of all body systems.
NERVOUS SYSTEM VS. ENDOCRINE SYSTEM
NERVOUS
neurotransmitters hormones
ENDOCRINE
muscle contractions and glandular
secretions
metabolic activities , growth &
development, reproduction
acts in milliseconds acts in seconds to minutes to
hours to days to months
brief effects long-lasting effects

7. Coordination of body functions by chemical messengers
The multiple activities of the cells, tissues ,and organs of the
body are coordinated by the interplay of several types of
chemical messenger systems:
Neurotransmitters are released by axon terminals of
neurons into the synaptic junctions and act locally to control
nerve cell functions . E.g. Acetylcholine, epinephrine etc
Endocrine hormones are released by glands or specialized
cells into the circulating blood and influence the function of
cells at another location. E.g. thyroid hormones, insulin etc
Neuroendocrine hormones are secreted by neurons into the
circulating blood and influence the function of cells at
another location in the body . Oxytocin, ADH,
hypothalamic releasing hormones.

8. Coordination of body functions by chemical messengers
Paracrines are secreted by cells into the extracellular
fluid and effect neighboring cells of different type . e. g.
GI hormones like histamine, gastrin, somatostatin etc
Autocrines are secreted by cells into the extracellular
fluid and affect the function of the same cells that
produced them. E.g. Interferon
Cytokines are peptides secreted by cells into the
extracellular fluid and can function as autocrines
,paracrine ,or endocrine hormones (interleukins,and
lymphokines) .

11. 5. Neuroendocrine
Interactions between the nervous and endocrine
systems emphasize their coordinated communicative

12. Introduction to endocrine glandsIntroduction to endocrine glands
Endocrine gland:Endocrine gland: A gland that secretes a chemical substance (a hormone)A gland that secretes a chemical substance (a hormone)
into the bloodstream. The endocrine glands are "glands of internalinto the bloodstream. The endocrine glands are "glands of internal
secretion."secretion."

13. Endocrine Glands

14. Hormones:
Specific chemical product secreted by endocrine glands
transported by blood stream to reach target cells to elicit
specific response.
Help regulate total body metabolism, growth, internal
environment and reproduction.
it exerts its effect at very low concentrations.

15. For a chemical substance to be a classical endocrine hormone ,
it must fulfill following characteristics:
Must be synthesized by one or more endocrinal glands;
Must be released directly into the blood (or into lymphatic
channel), without being laid by duct;
Must have a very low blood concentration;
Needs a stimulus for its secretion, and
Acts on distant target cells, containing hormone specific
receptors.
Must have a feedback control system ( regulation)

16. Receptors:
Specific molecular groups of protein present at cell
membrane or inside cell which bind with hormone
specifically with high affinity.
Hormones and their receptor relationship is
expressed – in terms of
Affinity (bind to receptors with high bond strength).
Capacity (quantity of hormone binding)
Hormones binds to the receptor with high specificity
and affinity !!

17. Membrane Receptor Signal Pathways
• Signal molecule (ligand)
• Receptor
• Intracellular signal
• Target protein
• Response

18.  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
General Functions of the Endocrine system

19. V. Properties of the hormone effect
1. Specificity
The special feature of the the target cells is the
presence of receptors which can “attract” and
interact with the hormone.

20. The receptors may be present either on the
plasma membrane, or in the cytoplasm, or in
the nucleus.
These receptor molecules are protein in nature
and may contain carbohydrate or phospholipid
moieties.

21. 2. Signal Transmission
The role of the hormones is to transit the regulatory signals
from the control (endocrine) system to the target cells
(organs or glands).
It could enhance or inhibit some function of the target.

22. 3. High Biological Efficiency
Low plasma concentration (nmol – pmol/L) great
regulatory function

23. Signal
amplification
during the
transmembran
e and
intracellular
transmission

24. 4. Interaction Between the Hormones
(1) Synergistic effects. 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
the heart rate
Complementary: Work on different stages of a
physiological procedure, for example, FSH (initiation) and
testosterone (maintenance) on spermatogenesis

26. (2) Permissive effect. 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

27. (3) Antagonist Effects. 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 milk
secretion and action of prolactin.

28. EFFECTS OF HORMONE ON TISSUE
RESPONSE
28
Receptors are dynamic components
Down–regulation : decrease in the number of target-
cell receptors for a given hormone in response to a
chronic high concentration of that hormone. Cells may
display hyporesponsiveness (Desensitization).
Up–regulation : increase in the number of target-cell
receptors for a given hormone in response to chronic
low concentration of that hormone. Cells may display
hyper responsiveness (Priming effect)

29. Chemical Regulating Systems: Summary
Hormones: cell to cell communication molecules
Made in gland(s) or cells
Transported by blood
Distant or local target tissue receptors
Activates physiological response
Help regulate total body metabolism, growth, internal
environment and reproduction.

30. Types of cell-to-cell signaling (communication system)
1. Neural
Neuron NT synaptic cleft NT(neuron) excitable
or secretory cell
2. Endocrine
Endocrine cell hormone blood hormone target cell
3. Paracrine
Secretory cell secretion IF secretion adjacent cell
4. Autocrine
Secretory cell secretion IF secretion