Download posterior pituitary hormones

Pituitary Gland
Dr. Hany Ahmed
Assistant 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: secretes
1) 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 childbirth 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 ADH
1)  Osmolarity of ECF increses ADH release.
2)  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- OXYTOCIN
ACTIONS:
• 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
factors)
releasing
absorbed
into
or
inhibiting
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
Endocrine Control
Three Levels of Integration
1) Hypothalamus
2) Pituitary stimulation from hypothalamic
trophic hormones
3) Endocrine
gland
stimulation
pituitary trophic hormones
from
Hormones of hypothalamic-anterior
pituitary pathway
Negative Feedback Loops
• Regulate amount of hormones in blood
• Hormone levels stay
appropriate responses
within
range
needed
for
• 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 Loops
Chapter 18 The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning