Pituitary Gland

Dr. Hany AhmedAssistant Professor of Physiology (MD, PhD).

Al Maarefa Colleges (KSA) & Zagazig University (ARE)Specialist of Diabetes, Metabolism and Obesity Zagazig Obesity Management & Research Unit

Dr. Hany AhmedAssistant Professor of Physiology (MD, PhD).

Al Maarefa Colleges (KSA) & Zagazig University (ARE)Specialist of Diabetes, Metabolism and Obesity Zagazig Obesity Management & Research Unit

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 mech. that control vasopressin secretion.• Describe the general characteristics of hypothalamic releasing

and inhibiting hormones and describe their route of transport from the hypothalamus to the anterior pituitary.

• Identify appropriate hypothalamic hormones that control the secretion of each of the anterior pituitary hormones.

• Diagram short-loop and long-loop negative feedback control of anterior pituitary hormone secretion.

The pituitary is two fused glands

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

Pituitary Gland Secretions

• Anterior Pituitary: secretes1)Growth Hormone (GH)

2)Prolactin (PRL)

3)Thyroid Stimulating Hormone (TSH)

4)AdrenoCorticoTropic Hormone (ACTH)

5)Follicle Stimulating Hormone (FSH)

6)Luteinizing Hormone (LH)

• Posterior Pituitary: secretes

1)Vasopressin (ADH)

2)Oxytocin

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.

Relationship of Hypothalamus & Posterior Pituitary

(Hypothalamo-Hypophyseal Nervous Tract)

1. Vasopressin & oxytocin are synthesized in supraoptic & paraventricular nuclei in the hypothalamus.

2. The hormone travels down the axon to be stored in the neuronal terminals within the posterior pituitary.

3. On excitation of the neuron, the stored hormone is released from these terminals into the systemic blood for distribution throughout the body.

1- ADH (=Vasopressin) Vasopressin receptors: V1 receptors in blood vessels,

and V2 in kidney tubules.

Functions:

1- Anti diuresis (= reabsorption of water by kidneys):

ADH permeability of distal tubules & collecting

ducts to water water reabsorption by passive

diffusion.

Mechanism: cAMP in cells & Formation of

microtubules in cell membrane (Aquaporin 2).

2- Vasoconstrictor effect: in large dose. 10% decrease

in blood volume is sufficient to cause release of ADH.

MECHANISM OF ACTION OF ADH

Regulation of ADH11 Osmolarity of ECF increses ADH release.

11 Blood volume as in hemorrhage frequency of

inhibitory impulses from volume receptors to

supraoptic nuclei release of ADH.

3) Renal ischemia due to hemorrhage Renin

Angiotensin II ADH secretion water

reabsorption.

4) Alcohol inhibits ADH secretion marked diuresis.

5) Anxiety, Pain, Trauma, Morphine, Nicotine & Hot

Weather ADH.

Diabetes Insipidus (DI) ADH secretion or action.• Causes:

1) Central DI: Damage of supraoptic -hypophyseal system by a tumor.

2) 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 (= desmopressin) nasal spray.

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- Vasopressin - 2 receptor antagonists.

3- Water restriction. 4- Demeclocycline.

2- OXYTOCINACTIONS:

• On uterus:

Stimulates pregnant uterus during Labor Powerful contraction and helps delivery.

 • Primary fertilization of ovum:

Sexual Stimulation during intercourse stimulation of paraventricular nuclei oxytocin uterine contractions uterine suction of semen upward toward Fallopian tubes.

• Milk Ejection:

Oxytocin contraction of myoepithelial cells around alveoli of Mammary glands during Lactation.

OXYTOCIN

II. Anterior pituitary (=Adenohypophysis)

Cells:

1)Chromophobes: (50% of cells) = precursor cells.

2)Acidophils (alpha cells): (40% of cells) & secrete: Growth hormone (GH) & Prolactin (PRL).

3)Basophils (Beta cells): (10% of cells) & secrete:

• Thyriod stimulating hormone (TSH) or Thyrotropin.

• Adrenocorticotrophic H. (ACTH) or Corticotropin.

• Follicle stimulating hormone (FSH).

• Luteinizing hormone (LH).

Hypothalamo - Hypophyseal portal system

• Vascular connection between hypothalamus &

anterior pituitary.

• Hypothalamus secretes polypeptide hormones

(= hypothalamic releasing or inhibiting

factors) absorbed into hypothalamic-

hypophyseal portal capillaries to be carried to

anterior pituitary.

Hypothalamic

- hypophyseal

Portal system

Vascular Link Between the Hypothalamus and Anterior Pituitary

Hypothalamic Releasing and Inhibiting Hormones

Anterior Pituitary Hormones

Anterior pituitary hormones

1) Hypothalamus

2) Pituitary stimulation from

hypothalamic trophic hormones

3) Endocrine gland stimulation from

pituitary trophic hormones

Endocrine ControlThree Levels of Integration

Hormones of hypothalamic-anterior pituitary pathway

Negative Feedback Loops• Regulate amount of hormones in blood

• Hormone levels stay within range needed for appropriate responses

• Eliminates waste of hormones.

A) long loop –ve feedback:

1) Direct -ve feedback

• Anterior pituitary hormones stimulate target gland ( TSH Thyroxin).

• E.g. ↓ Thyroxin ↑ TSH from Ant. pituitary

↑ Thyroxin ↓ TSH.

2) Indirect -ve feedback

• When hypothalamus is indirectly involved in regulation of hormone secretion from target gland via releasing or inhibitory factors {TRF TSH Thyroxin}.

E.g. ↑ Thyroxin ↓ TRF. ↓ Thyroxin ↑ TRF.

B) Short loop -ve Feedback:

• Some anterior pituitary hormones e.g. Somatotropin (= GH) can regulate its own release by a short loop -ve feedback on the secretion of its hypothalamic releasing or inhibitory factors. E.g. Somatotropin and Somatotropin RF or Somatostatin.

Negative Feedback LoopsNegative Feedback Loops

Chapter 18 The Central Endocrine GlandsHuman Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning