Download Slide 1

Pituitary Gland
Dr. Shaikh Mujeeb Ahmed
Lecture Objectives
• Explain the hypothalamus as the major integrative site for the
neuroendocrine system.
• Contrast the anterior and posterior pituitary lobes with respect to cell
types, vascular supply, development, and innervations.
• Describe the general characteristics of hypothalamic releasing and
inhibiting (hypophysiotropic) 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.
• List the target tissues for oxytocin and describe its effects on each.
• Name the stimuli for oxytocin release during parturition or lactation.
• Describe the stimuli and mechanisms that control vasopressin secretion.
The pituitary is two fused glands
Pituitary Gland
• Hypophysis
• Small gland (0.5 – 1 gm)located in bony cavity just below
hypothalamus
– Thin stalk connects pituitary gland to hypothalamus
• Consists of two anatomically and functionally distinct
lobes
– Posterior pituitary (neurohypophysis)
• Composed of nervous tissue
– Anterior pituitary (adenohypophysis)
• Consists of glandular epithelial tissue
Anatomy of the Pituitary Gland
Anterior/Posterior pituitary gland secretions
• Anterior Pituitary: 6 hormones
• Growth hormone (GH)
• Thyroid stimulating hormone (TSH)
• Adrenocorticotropic hormone (ACTH)
• Follicle stimulating hormone (FSH)
• Luteinizing hormone (LH)
• Prolactin (PL)
• Posterior Pituitary: 2 hormones
• Vasopressin (ADH)
• oxytocin
Terminology
• Tropic hormone:
• A hormone that controls the secretion of
another hormone is known as a trophic
(tropic) hormone.
Pituitary Gland
• Release of hormones from both anterior and posterior
pituitary is controlled by hypothalamus
• Posterior pituitary
– Along with hypothalamus forms neuroendocrine
system
– Does not actually produce any hormones
– Stores and releases two small peptide hormones
• Vasopressin (ADH)
– Conserves water during urine formation
• Oxytocin
– Stimulates uterine contraction during
childbirth and milk ejection during breastfeeding
Relationship of the Hypothalamus and Posterior
Pituitary
1. The hormone, vasopressin
and oxytocin are
synthesized in supraoptic
and 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.
Neurohormones: secreted into the Blood
by Neurons
Figure 7-12: Synthesis, storage, and release of posterior pituitary hormones
Oxytocin
vasopressin
Prolactin
Growth hormone
TSH
ACTH
FSH
LH
Anterior Pituitary Hormones
Regulation of pituitary hormones
secretion by the hypothalamus


secretion of anterior pituitary hormones: a typical
endocrine regulatory mechanism
important releasing/inhibiting hormones
produced in hypothalamus:
- Corticotropin-releasing hormone (CRH)
- Thyrotropin-releasing hormone (TRH)
- Gonadotropin-releasing hormone (GnRH)
- Growth-hormone-releasing hormone (GHRH)
- Prolactin-releasing hormone (PRH)
- Prolactin-inhibitory hormone (PIH)
Hypothalamic Releasing and Inhibiting
Hormones
• Secretion of each anterior
pituitary hormone is
stimulated or inhibited by
one or more
hypothalamic
hypophysiotropic
hormones
Hypothalamic-hypophyseal
Portal system
Endocrine Control: Three Levels of
Integration
• Hypothalamus
• Pituitary stimulation–from hypothalamic trophic
hormones
• Endocrine gland stimulation–from pituitary
trophic hormones
Endocrine Control: Three Levels of
Integration
Figure 7-13: Hormones of the 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
Negative Feedback Controls:
Long & Short Loop Reflexes
Short
long
Negative feedback loops in
the hypothalamicanterior
pituitary pathway
Negative Feedback Controls:
Long & Short Loop Reflexes
Control pathway for cortisol secretion
Vascular Link Between the Hypothalamus and
Anterior Pituitary
Posterior pituitary hormones
•
Antidiuretic hormone (ADH, vasppressin)
- chemistry: 9 amino acid peptide, produced
primarily by supraoptic nucleus and small
amount by paraventricular nucleus
- actions:
1) water retention by the kidney 
urine volume and  ECF
2) vasoconstriction (in large amounts)
- regulation/stimuli:
1) blood (or ECF) osmolality/osmoreceptors
2) blood volume
3) others: alcohol, nicotine, barbiturates, etc.
- abnormality: Diabetes Insipidus
Vasopressin Secretion
Diabetes Insipidus
• Diabetes insipidus is a disorder of the posterior lobe
of the pituitary gland.
• ADH is deficient.
• Causes could be head trauma, brain tumor, or
irradiation of the pituitary gland, infections of the
CNS (meningitis, encephalitis, tuberculosis) or
tumors (eg, metastatic disease, lymphoma of the
breast or lung). Another cause is failure of the renal
tubules to respond to ADH; this may be related to
hypokalemia,hypercalcemia, and a variety of
medications (eg, lithium,Declomycin).
Clinical Manifestations
• Enormous daily output of very dilute, water-like
urine.
• Intense thirst: The patient drinks 2 to 20 liters of fluid
daily.
• Fluid intake cannot be limited; otherwise the patient
will experience crave for fluid and would develop
hypernatremia and severe dehydration.
Assessment and Diagnostic Findings
• Fluid deprivation test for 8 to 12 hours.
• The patient is weighed frequently during the test.
• Perform plasma and urine osmolality studies before
and after the test.
• Low specific gravity and weight loss, rising serum
osmolality, and elevated serum sodium levels.
• Terminate the test if tachycardia, excessive weight
loss, or hypotension develops.
• Plasma levels of ADH (vasopressin) and plasma and
urine osmolality.
Medical Management
Aims to:
• Replace ADH
• Ensure adequate fluid replacement
• Identify and correct the underlying cause

Oxytocin
- chemistry: 9 amino acid peptide, produced
primarily by paraventricular nucleus and small
amount by supraoptic nucleus
- actions: 1) regulating breast milk release
2) contraction of pregnant uterus
- regulation/stimuli:
suckling by a nursing infant
crying sounds from a baby
fear and stress inhibit release
References
 Human physiology, Lauralee Sherwood, seventh
edition.
 Text book physiology by Guyton &Hall,11th
edition.
 Physiology by Berne and Levy, sixth edition.
31
THANK YOU