Download Posterior pituitary

PITUITARY GLAND
Dr. Amel Eassawi
OBJECTIVES
The student should be able to:
 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.
ENDOCRINE CONTROL: THREE LEVELS
OF INTEGRATION
• Hypothalamus
• Pituitary stimulation–from hypothalamic trophic
hormones
• Endocrine gland stimulation–from pituitary
trophic hormones
PITUITARY GLAND
 Hypophysis
 Regulating the activity of most the other endocrine glands(so
called master gland).
 Consists of:
 Neurohypophysis – posterior lobe (neural tissue)
 Receives, stores, and releases hormones from the
hypothalamus.
 Adenohypophysis – anterior lobe, made up of glandular
tissue
 Synthesizes and secretes a number of hormones
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ANTERIOR PITUITARY GLAND
• Anterior Pituitary: 6 hormones
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Growth hormone (GH)
Thyroid stimulating hormone (TSH)
Adrenocorticotropic hormone (ACTH)
Follicle stimulating hormone (FSH)
Luteinizing hormone (LH)
Prolactin (PL)
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CONTROL OF ANTERIOR PITUITARY
SECRETION
1. The Hypothalamic Control:
– Through the hypothalamic releasing and inhibitory factors
secreted by hypothalamus and carried to the anterior pituitary
through the hypothalamic hypophyseal portal circulation
2. Feed Back Control:
blood levels of adrenocortical hormones, thyroid hormones and
gonad steroid influence the pituitary secretion of ACTH, TSH
and gonadotropins respectively. The influence in mainly
inhibitory in nature ( negative feedback mechanism )
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Negative Feedback Controls:
Long and Short Loop Reflexes
Short
long
Negative feedback loops in
the hypothalamicanterior
pituitary pathway
Control pathway for cortisol secretion
NEGATIVE FEEDBACK LOOPS
• Regulate amount of hormones in blood
• Hormone levels stay within range needed for
appropriate responses
• Eliminates waste of hormones
Hypothalamic-hypophyseal
Portal system
Posterior 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
Neurohormones: secreted into the Blood by
Neurons
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.
Relationship of the Hypothalamus and Posterior
Pituitary gland
POSTERIOR PITUITARY HORMONES
1. 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)
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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 FINDING
• 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
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Aims to:
Replace ADH
Ensure adequate fluid replacement
Identify and correct the underlying cause
POSTERIOR PITUITARY HORMONES
2. 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:
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suckling by a nursing infant
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crying sounds from a baby
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fear and stress inhibit release
REGULATION OF SECRETION OF OXYTOCIN THROUGH POSITIVE FEEDBACK MECHANISM
Uterine Contractions Force the Baby's Head into the
Cervix
Stretch Receptors in Cervix
(Detector)
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Nerve Impulses
Hypothalamus and Posterior Pituitary
(Control Center)
Release of Oxytocin
Uterine Smooth Muscle Contraction
(effector)
Stronger Contractions Force the Baby's
Head Further into the Cervix
Inhibition Occurs After Delivery When is no Uterine
Contractions
Stimulation
REFERENCES
 Human physiology, Lauralee Sherwood, seventh
edition.
 Text book physiology by Guyton &Hall,11th
edition.
 Physiology by Berne and Levy, sixth edition.
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