This Presentation for all medicos and Basic science students -- Introduction Forms of chemical signaling Posterior pituitary gland Antidiuretic hormone Action of ADH Regulation of ADH Actions of oxytocin Control of oxytocin secretion Factors affecting secretion oxytocin

1. 1
The Endocrine System
Pandian .M
Dept of Physiology
D.Y.P. MEDICAL COLLGE KOP

2. Objectives
• Introduction
• Forms of chemical signaling
• Posterior pituitary gland
• Antidiuretic hormone
• Action of ADH
• Regulation of ADH
• Actions of oxytocin
• Control of oxytocin secretion
• Factors affecting secretion oxytocin

3. 3
Structure and FunctionThe Endocrine System
•Regulates many bodily functions
•Maintains homeostasis by regulating the production of chemicals that affect
most functions of the body
•Secretes substances that aid the nervous system
•Important regulator of growth and development
•Endocrine glands are ductless glands, unlike exocrine glands that secrete
substances into ducts.

4. 4
Glands
glands secrete
hormones
into
bloodstream
to
target tissues
The Endocrine System consist of:-

5. What is Endocrinology?What is Endocrinology?
Endocrinology is about
communication systems &
information transfer
Intercellular Chemical
Communication

6. What are endocrineWhat are endocrine
systems for?systems for?
Endocrine Functions
• Maintain Internal Homeostasis
• Support Cell Growth
• Coordinate Development
• Coordinate Reproduction
• Facilitate Responses to External Stimuli

7. Definitions
• “Study of ductless glands”
• “Study of chemical messengers involved in
homeostasis”
• “Study of cell to cell communication by messenger
molecules traversing an extra cellular space”
• “Hormone is a messenger bio-molecule, which
activates a specific receptor bio-molecule to express
a specific biological response”

8. Hormone
A chemical messenger secreted by one endocrine gland or cell
into the bloodstream and targeted toward cells in another organ.

9. Paracrines and Autocrines
 Local communication
 Signal chemicals diffuse to
target
 Example: Cytokines
 Autocrine–receptor on same
cell
 Paracrine–neighboring cells
Direct and local cell-to-cell communication

10. Long Distance
Communication: Hormones
• Signal Chemicals
• Made in endocrine cells
• Transported via blood
• Receptors on target
cells
Long distance cell-to-cell communication

11. Long distance cell-to-cell communication

12. 12

14. Effects of Hormone Concentration

15. Effects of Hormone Concentration

16. Posterior Pituitary

17. Pituitary gland

18. Posterior Pituitary Gland and Its Relation
to the Hypothalamus
• The PP also called the neurohypophysis, is composed mainly
of glial-like cells called pituicytes.
• The pituicytes do not secrete hormones; they act simply as a
supporting structure for large numbers of terminal nerve
fibers and
• terminal nerve endings from nerve tracts that originate in the
supraoptic and paraventricular nuclei of the hypothalamus

20. •These tracts pass to the neurohypophysis through the
pituitary stalk (hypophysial stalk).
•The nerve endings are contain many secretory granules.
•These endings lie on the surfaces of capillaries,
•where they secrete two posterior pituitary hormones:
(1) antidiuretic hormone (ADH), also called vasopressin,
are formed primarily in the supraoptic nuclei and
(2) oxytocin. is formed primarily in the paraventricular
nuclei.

21. • If the pituitary stalk is cut above the pituitary gland
• But the entire hypothalamus is left intact, the posterior pituitary
• hormones continue to be secreted normally,
• after a transient decrease for a few days;
• they are then secreted by the cut ends of the fibers within the
hypothalamus and not by the nerve endings in the posterior pituitary

23. ANTIDIURETIC HORMONE
• Antidiuretic hormone, as the name indicates,
• Prevents diuresis and is chiefly concerned with the conservation of
body water.
• Since it also causes vasoconstriction, it is also called vasopressin or
more precisely arginine vasopressin.

24. • Biological half-life of ADH is 16–20 min after its release into the
circulation.
• Metabolism - The circulating vasopressin is rapidly inactivated in the
liver and kidney.
VASOPRESSIN RECEPTORS
• Three types of vasopressin receptors are recognized:
• V1–A receptors. These are involved in the vasoconstrictor effect of ADH.
• V1–B receptors. These are involved in the action of ADH on the anterior
pituitary
• V2 receptors. These are involved in the action of ADH on kidney.

25. ACTIONS OF ADH
1. Action on kidney.
2. Vasoconstrictor effect.
3. Action on anterior pituitary.
4. Action on the liver.
5. Action on the brain.

26. Action on kidney.
• The main role of ADH is regulation of water balance in the body by
acting on the kidney,
• where it decreases the excretion of free water (i.e. antidiuretic and
concentrating effect on kidney).
Site of action. The ADH responsive cells line the DCT and CD of the
renal nephron.
• ADH increases the permeability of these cells to water.

27. Mechanism of action.
1.The ADH exerts its antidiuretic effect by binding to plasma membrane
receptor (known as V2 receptor)
2.It present on basal capillary it activates adenylyl cyclase.
3.The increase in intracellular cAMP activates a protein (kinase) on the
opposite (luminal apical) side of the cell.
4.The activated protein kinase leads to rapid insertion of protein water
channels (known as aquaporins) in the plasma membranes of the
principal cells of the collecting ducts.
5.Through these protein water channels (i.e. aquaporin) water rapidly
moves from the tubular lumen into the collecting duct cells.

28. 2. Vasoconstrictor effect. ADH in large doses cause
vasoconstriction and leads to rise in blood pressure.
•Hemorrhage is a potent stimulus to ADH secretion.
3. Action on anterior pituitary. ADH travels to the anterior
pituitary via the portal veins and combines with the V1–B
receptors (also called V3 receptors) and causes increased
ACTH secretion from the corticotrophs.

29. 4. Action on the liver. In the liver, ADH causes
glycogenolysis by combining with the V1–A receptor.
5. Action on the brain. V1–A receptors are also found in
brain, where ADH acts as a neurotransmitter and is involved in
memory, regulation of temperature, regulation of blood
pressure, circadian rhythms and brain development.

30. REGULATION OF
ADH SECRETION
1. Effective osmotic pressure
of plasma or plasma
osmolality

31. 2. Changes in blood volume
• ADH secretion is increased when ECF volume is low
• Decreased when ECF volume is high.

32. Mechanism of action
The changes in blood volume regulate ADH secretion by
following mechanisms :-
•(i) Pressure receptor mechanism.
1.Variations in the discharge from the pressure receptors from
circulatory system are inversely related to rate of ADH
secretion

33. There are two types of pressure receptors in the circulatory
system:
The low and high pressure receptors
1. Low-pressure receptors are located in the great veins, right
and left atria and pulmonary vessels.
2. They monitor mainly respond to volume changes (hence
also called volume receptors).
3. High-pressure receptors are located in the carotid sinuses
and aortic arch (i.e. high pressure portion of the vascular
system) and respond to pressure changes and so are also
called baroreceptors.

34. Mechanism of Afferent impulses from these
receptors
?

35. (ii) Renin–angiotensin mechanism.
• Hypovolaemia also stimulates renin–angiotensin mechanism,
• which reinforces the release of ADH in response to hypovolaemia and
•hypotension by acting on the circumventricular organs.
(iii) Atrial natriuretic peptide (ANP)
•Mechanism also reinforces the release of ADH in response to the
hypovolaemia.
•When circulating volume is increased, ANP is released by the cardiac
myocytes,
•which acts on the hypothalamus to inhibit ADH release.

37. 3. Other factors affecting ADH
secretion• Stress of pain, chronic emotional stress and surgical procedures cause
increase in ADH secretion leading to reduction in urine formation
under these conditions.
• Adrenaline decreases the ADH. Hence one experiences an increased
frequency of micturition during acute emotional stresses such as
interviews, or examinations.
• Alcohol reduces ADH secretion and thus leads to diuresis.
• Age. Elderly individuals secrete more ADH than do younger
individuals.
• Cortisol and thyroid hormones release ADH.
• Some other factors that increase ADH secretion include nausea,
vomiting, standing posture and cytokines.

38. ABNORMALITIES OF ADH
SECRETION
• Abnormalities of ADH secretion include:
• Syndrome of inappropriate hypersecretion of ADH. (SIADH) is also
called dilution syndrome.
• Diabetes insipidus.

40. OXYTOCIN
ACTIONS OF OXYTOCIN
•Mechanism of action
•In human, oxytocin acts mainly on the uterus and
breasts.
•Oxytocin acts through a G protein-coupled serpentine
receptor and increases intracellular Ca2+
levels.
It has a half-life of about 6 minutes.

41. 1. Action on breast. Oxytocin causes contraction of
myoepithelial cells, thus plays an important role in milk
ejection.
2. Action on uterus. Oxytocin causes contraction of uterine
smooth muscles, thus plays an important role during
parturition (labour).
3. Oxytocin also acts on non-pregnant uterus and facilitates
the transport of sperm in the female genital tract.
4. In males, the circulating levels of oxytocin increases during
ejaculation, which causes increased contraction of
5. smooth muscles which helps in propelling the sperms
towards urethra.

42. CONTROL OF OXYTOCIN SECRETION
Stimuli which increase oxytocin release are:
• Oxytocin secretion increases on cholinergic
stimulation
• Suckling stimulates oxytocin release (suckling reflex).
•Genital tract simulation during coitus and labour
increases oxytocin release.

43. Factors which decrease oxytocin release are:
• Emotional stress
• Sympathetic stimulation, and
• Drugs such as ethanol and enkephaline

44. neuroendocrine reflexes.

51. References
•Text book of Medical Physiology
• Guyton & Hall
•Human Physiology
• Vander
•Text book of Medical Physiology
• Indukurana
•Principles of Anatomy and Physiology
• Totora
•Net source

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