Posterior Pituitary hormones-5.ppt- endocrine physiology

1. Posterior Pituitary
Hormones
Dr. Sai Sailesh Kumar G
Professor
Department of Physiology
NRIIMS
Email: dr.goothy@gmail.com

2. Case study
 A 35 years old woman presents with a history of acne, oily skin, mild
hirsutism with elevated testosterone levels. The patient also complains of
excessive sweating and enlargement of her hands and feet, such that she
recently had to resize a ring that she had worn for years. Her menstrual
cycle became more irregular. She has a protruding jaw with an enlarged
tongue, and kyphosis. She has head ache and visual disturbances.

3. Case study
1. What is your probable diagnosis?
2. What is the pathophysiology of this disease?
3. What is the physiological basis of elevated fasting blood glucose?
4. What is physiological basis of visual disturbance?

4. Case study
 The tumor produces excessive amounts of growth hormone,
causing many of the signs and symptoms of acromegaly. Some
of the symptoms of acromegaly, such as headaches and
impaired vision, are due to the tumor pressing on nearby brain
tissues.

5. Physiological basis?
 What is the advantage of hormones secretion into the portal system?

6. Posterior pituitary hormones
 The posterior pituitary gland 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.

8. Posterior pituitary hormones
 These tracts pass to the neurohypophysis through the pituitary stalk
(hypophysial stalk).
 The nerve endings are bulbous knobs that 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, and (2) oxytocin.

9. Posterior pituitary hormones
 If the pituitary stalk is cut above the pituitary gland but the entire
hypothalamus is left intact?

10. Posterior pituitary hormones
 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

11. Posterior pituitary hormones
 The reason for this is that the hormones are initially synthesized in the
cell bodies of the supraoptic and paraventricular nuclei
 then transported in combination with “carrier” proteins called
neurophysins down to the nerve endings in the posterior pituitary
gland, requiring several days to reach the gland.

12. Posterior pituitary hormones
 ADH is formed primarily in the supraoptic nuclei, whereas oxytocin is
formed primarily in the paraventricular nuclei.
 Each of these nuclei can synthesize about one sixth as much of the
second hormone as of its primary hormone

13. Posterior pituitary hormones
 When nerve impulses are transmitted downward along the fibers from
the supraoptic or paraventricular nuclei,
 the hormone is immediately released from the secretory granules in
the nerve endings
 by the usual secretory mechanism of exocytosis
 and is absorbed into adjacent capillaries.

14. Chemical Structures
 Both oxytocin and ADH (vasopressin) are polypeptides, each
containing nine amino acids.
 Vasopressin: Cys-Tyr-Phe-Gln-Asn-Cys-Pro-Arg-GlyNH2
 Oxytocin: Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-GlyNH2

15. Chemical Structures
 these two hormones are almost identical except that in vasopressin,
phenylalanine and arginine replace isoleucine and leucine of the
oxytocin molecule

16. PHYSIOLOGICAL FUNCTIONS OF
ANTIDIURETIC HORMONE
 The injection of extremely minute quantities of ADH
 as small as 2 nanograms
 can cause decreased excretion of water by the kidneys
 Antidiuresis

17. PHYSIOLOGICAL FUNCTIONS OF
ANTIDIURETIC HORMONE
 in the absence of ADH,
 the collecting tubules and ducts become almost impermeable to
water,
 prevents significant reabsorption of water
 therefore allows extreme loss of water into the urine,
 causing extreme dilution of the urine.

18. PHYSIOLOGICAL FUNCTIONS OF
ANTIDIURETIC HORMONE
 In the presence of ADH,
 the permeability of the collecting ducts and tubules to water increases
greatly
 allows most of the water to be reabsorbed as the tubular fluid passes
through these ducts,
 thereby conserving water in the body
 producing very concentrated urine

19. PHYSIOLOGICAL FUNCTIONS OF
ANTIDIURETIC HORMONE
 Without ADH, the luminal membranes of the tubular epithelial cells of
the collecting ducts are almost impermeable to water

20. PHYSIOLOGICAL FUNCTIONS OF
ANTIDIURETIC HORMONE
 immediately inside the cell membrane are a large number of special
vesicles that have highly water-permeable pores called aquaporins.
 Aquaporins (AQP) are integral membrane proteins that serve as
channels in the transfer of water
 more than 13 isoforms (AQP0-AQP12) have been identified so far.
 AQP1,2,3 is expressed in the kidney collecting ducts

21. PHYSIOLOGICAL FUNCTIONS OF
ANTIDIURETIC HORMONE
 When ADH acts on the cell,
 it first combines with membrane receptors (V2 receptors)
 activate adenylyl cyclase
 formation of cAMP inside the tubular cell cytoplasm
 phosphorylation of elements in the
 special vesicles

22. PHYSIOLOGICAL FUNCTIONS OF
ANTIDIURETIC HORMONE
 causes the vesicles to insert into the apical cell membranes,
 providing many areas of high water permeability
 All this occurs within 5 to 10 minutes.

24. V1 receptors
 Located in the smooth muscles of blood vessels
 Cause constriction of blood vessels

25. V2 receptors
 Located in the renal tubules
 Increases permeability of tubules to water

26. Regulation of ADH
 When a concentrated electrolyte solution is injected into the artery
 that supplies the hypothalamus,
 the ADH neurons in the supraoptic and paraventricular nuclei immediately
transmit impulses into the posterior pituitary
 to release large quantities of ADH into the circulating blood,
 sometimes increasing the ADH secretion to as high as 20 times normal..

27. Regulation of ADH
 Conversely,
 injection of a dilute solution into this artery
 causes cessation of the impulses
 and therefore almost total cessation of ADH secretion.

28. Regulation of ADH
1. Somewhere in or near the hypothalamus are modified neuron receptors
called osmoreceptors.
2. When the extracellular fluid becomes too concentrated,
3. fluid is pulled by osmosis out of the osmoreceptor cell,
4. decreasing its size
5. initiating appropriate nerve signals in the hypothalamus
6. to cause additional ADH secretion

29. Regulation of ADH
 Conversely,
 when the extracellular fluid becomes too dilute,
 water moves by osmosis in the opposite direction, into the cell,
 which decreases the signal for ADH secretion

30. Regulation of ADH
 Although some researchers place these osmoreceptors in the
hypothalamus (possibly even in the supraoptic nuclei),
 others believe that they are located in the organum vasculosum,
 a highly vascular structure in the anteroventral wall of the third
ventricle.

31. Regulation of ADH
 higher concentrations of ADH have a potent effect of constricting the
arterioles throughout the body
 and therefore increasing the arterial pressure.
 For this reason, ADH has another name, vasopressin

32. Regulation of ADH
1. Increased blood volume
2. the atria have stretch receptors
3. excited by overfilling
4. they send signals to the brain
5. inhibit ADH secretion

33. Regulation of ADH
1. Decreased blood volume
2. the atria have stretch receptors
3. Underfilling
4. Inhibited
5. No signals to the brain
6. Stimulates ADH secretion

34. Diabetes insipidus
1. Deficiency of ADH
2. Production of abnormally high volume of diluted urine
3. Dysfunction of the hypothalamus or posterior pituitary
4. Poly uria – water diuresis promoted due to deficiency of ADH
5. Polydipsia –secondary to dehydration

35. Diabetes insipidus
1. How to differentiate DM from DI?

36. Diabetes insipidus
 In DI – pure water loss – osmolality is less than 300 mOsm/L
 In DM- water+ glucose lost – osmolality is more than 1200
mOsm/L
 In DI- urine is tasteless ( Insipidus- tasteless)
 In DM– Sweet urine (Mellitus-sweet )

37. Diabetes insipidus
1. Two types of DI
2. Nephrogenic DI (Kidney fails to respond to ADH)
3. Neurogenic/ Central DI (deficiency of ADH secretion)

38. Nephrogenic DI
1. ADH secretion is normal
2. But kidneys do not respond to ADH
3. Receptors deficiency or abnormality
4. Acquired or genetic
5. Chlorpropamide is used – increases renal response to ADH

39. Neurogenic DI
1. Disease of CNS
2. Tumors or head injury or infections-meningitis
3. Desmopressin is used to treat
4. Acts selectively on V2 receptors
5. The brand name of this medication is DDAVP®.

40. Syndrome of inappropriate ADH secretion
1. Excessive secretion of ADH
2. Excessive water reabsorption
3. Increase in ECF
4. Decreased aldosterone secretion
5. Loss of sodium in urine
6. Natriuresis

41. Physiological functions of oxytocin
 The hormone oxytocin, in accordance with its name,
 powerfully stimulates contraction of the pregnant uterus,
 especially toward the end of gestation
 Neuro-endocrine reflex
 Parturition reflex

43. Oxytocin Aids in Milk Ejection by the Breasts
 In lactation, oxytocin causes milk to be expressed from the alveoli into
the ducts of the breast so that the baby can obtain it by suckling
 Lactation reflex
 Neuro-endocrine reflex

45. Oxytocin actions in non-pregnant women
 Following deposition of sperms into the female genital tract
 Oxytocin causes contraction of uterus
 Facilitates sperm transport to fallopian tube

46. Oxytocin actions in males
 Contraction of smooth muscles of vasdeferens
 During orgasm
 Helps for ejaculation

47. Oxytocics
 Preparation of oxytocin
 Used to induce labor
 Injected immediately following delivery of the placenta
 To prevent excessive postpartum hemorrhage
 Uterus contracts severely
 Compress the blood vessels

48. THANK YOU