1. Pituitary Gland

2. Lecture Objectives
Explain hypothalamus as the major integrative site for the neuroendocrine system.
Contrast anterior and posterior pituitary lobes with respect to cell types, vascular supply, development, and innervations.
Identify posterior pituitary hormones (oxytocin & vasopressin).
List target tissues for oxytocin and describe its effects on each.
Describe stimuli and mechanisms that control vasopressin secretion.
Disorders of secretion of ADH

3. The pituitary is two fused glands

5. Pituitary Gland (Hypophysis)
Pea sized mass of glandular tissue
Lies in sella turcica
Slender stalk: Infundibulum connects pituitary gland to hypothalamus
2 parts:
Posterior pituitary (=neurohypophysis)
Composed of nervous tissue
Anterior pituitary (=adenohypophysis)
Consists of glandular epithelial tissue

6. Pituitary Gland Secretions
Anterior Pituitary: secretes
Growth Hormone (GH)
Prolactin (PRL)
Thyroid Stimulating Hormone (TSH)
AdrenoCorticoTropic Hormone (ACTH)
Follicle Stimulating Hormone (FSH)
Luteinizing Hormone (LH)
Posterior Pituitary: secretes
Vasopressin (ADH)
Oxytocin

8. I. Posterior Pituitary (=Neurohypophysis)
Along with hypothalamus forms neuroendocrine system.
Does not actually produce any hormones.
ADH & Oxytocin are formed mainly in supraoptic and paraventricular nuclei in hypothalamus respectively.
Transported as granules by Hypothalamo-Hypophyseal Nervous Tract.
Stores & releases two small peptide hormones (9 A.A.):
1- Vasopressin (ADH): conserves water during urine formation.
2- Oxytocin: stimulates uterine contraction during child-birth and milk ejection during breast-feeding.

9. Relationship of Hypothalamus & Posterior Pituitary (Hypothalamo-Hypophyseal Nervous Tract)
Vasopressin & oxytocin are synthesized in supraoptic & paraventricular nuclei in the hypothalamus.
The hormone travels down the axon to be stored in the neuronal terminals within the posterior pituitary.
On excitation of the neuron, the stored hormone is released from these terminals into the systemic blood for distribution throughout the body.

11. 1- ADH (=Vasopressin)
Vasopressin, also known as arginine vasopressin (AVP) or antidiuretic hormone (ADH), is a neurohypophyseal hrmone.
Site of production: mainly supraoptic and paraventericular nuclei in hypothalamus.
Site of storage: posterior pituitary (=neurohypophysis)
Vasopressins are peptides consisting of nine amino acids (nonapeptides). 
Its two primary functions are to retain water in the body and to constrict blood vessels.

12. 1- ADH (=Vasopressin) Vasopressin receptors: Functions:
1- Antidiuresis (=  reabsorption of water by kidneys):
ADH  increased urine osmolarity (increased urine concentration) and decreased water excretion by  the permeability of distal tubules & collecting ducts to water   water reabsorption by passive diffusion.
V1A receptors
V1B receptors
V2 receptors
Site
Blood vessels
Anterior Pituitary
Collecting Ducts of Nephrons
Mechanism
 intracellular Ca++
 cAMP
Function VC
ACTH secretion
Antidiuretic effect

13. Mechanism of action of ADH on kidney tubules
Mechanism:  cAMP in cells & Formation of microtubules in cell membrane (Aquaporin 2).

14. Effect on Cardiovascular system
10% decrease in blood volume is sufficient to cause release of ADH.
Vasopressin increases peripheral vascular resistance (vasoconstriction) in large amounts only, and thus increases arterial blood pressure.
This effect appears small in healthy individuals; however it becomes an important compensatory mechanism for restoring blood pressure in hypovolemic shock such as that which occurs during hemorrhage.

15. Effect on Central nervous system
ADH stimulates ACTH via V1B receptors.
It is likely that vasopressin acts in conjunction with corticotropin-releasing hormone (CRH) to modulate the release of corticosteroids from the adrenal gland in response to stress, particularly during pregnancy and lactation in mammals.

16. Regulation of ADH
1)  Osmolality of ECF (e.g.  salt intake)  increases ADH release to dilute ECF again to normal
2)  Blood volume (e.g. hemorrhage)   frequency of inhibitory impulses from volume receptors in heart to supraoptic nuclei   release of ADH.
3) Renal ischemia due to hemorrhage   Renin   Angiotensin II   ADH secretion   water reabsorption.

17. Regulation of ADH 4) Alcohol inhibits ADH secretion  marked diuresis.
5) Atrial natriuretic peptide inhibits ADH secretion, in part by inhibiting Angiotensin II-induced stimulation of ADH secretion.
5) Anxiety, Pain & Trauma   ADH
6) Morphine & Nicotine   ADH
7) Hot Weather   ADH.

20. Diabetes Insipidus (DI)
 ADH secretion or action.
Causes:
Central DI: Damage of supraoptic -hypophyseal system by a tumor.
Nephrogenic DI: Lack of kidney response to ADH (V2 receptor defect).
Manifestations:
Polyuria (4-6 L/day & may be 15 L/day)  loss of fluid in urine  dehydration  Polydipsia (constant thirst due to dehydration).
Treatment: Synthetic vasopressin (nasal spray).

22. Syndrome of Inappropriate ADH Secretion (SIADH)
Causes:
1-  ADH from brain tumors & lung tumors.
2-  ADH from posterior pituitary in T.B. & pneumonia.
Manifestations:
 ECF volume (= water intoxication),  Na+ concentration & osmolality (= dilutional hyponatraemia)  intracellular edema  convulsions & coma  sudden death.
Treatment:
1- Loop diuretics with saline.
2- V2 receptor antagonists.
3- Water restriction.
4- Demeclocycline.

23. OXYTOCIN
The word oxytocin was coined from Greek “oxys” and “tokos” meaning "quick birth“.
Oxytocin became the first peptide hormone to be sequenced or synthesized. Vigneaud was awarded the Nobel Prize in 1955 for his work.
Oxytocin is normally produced in the hypothalamus (paraventricular nuclei) and stored in the posterior pituitary gland.
Oxytocin is a peptide consisting of nine amino acids (=nonapeptide).
It helps Labour, Lactation & Love.

24. 2- OXYTOCIN
ACTIONS: 1) On uterus: Stimulates pregnant uterus during Labor  Powerful contraction and helps delivery. 2) Primary fertilization of ovum: Sexual Stimulation during sexual intercourse  stimulation of paraventricular nuclei   oxytocin   uterine contractions  uterine suction of semen upward toward Fallopian tubes.

25. 3) Milk Ejection: Oxytocin  contraction of myoepithelial cells around alveoli of Mammary glands during Lactation (Letdown reflex).
4) Increasing Maternal behavior
5) Increasing trust, reducing fear and suppressing appetite.
6) As a medication, it is used to cause contraction of the uterus, which is used to start labor, increase the speed of labor, and to stop bleeding following delivery.

26. OXYTOCIN

27. Chapter 18 The Central Endocrine Glands Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning