Learning Objectives
- By the end of lectures, students should be able to:
- State the location of pituitary gland and hypothalamus
- Enumerate the hormones secreted by pituitary gland
- Enumerate the hormones/factors secreted by hypothalamus
- Summarize the functions of hormones of pituitary gland
- Summarize the functions of hormones/factors secreted by
hypothalamus - Explain the interrelationships of functions of the hypothalamus
and the posterior and anterior lobes of the pituitary gland - Highlight the effects of lesions of pituitary gland
Key Terms
- Pituitary Gland: An endocrine gland, about the size of a pea, that sits
in a small, bony cavity at the base of the brain whose secretions
control the other endocrine glands and influence growth,
metabolism, and maturation. - Hypothalamus: A region of the forebrain located below the thalamus,
forming the basal portion of the diencephalon, that regulates body
temperature, some metabolic processes, and governs the autonomic
nervous system. - Hypophyseal Portal System: The system of blood vessels that link the
hypothalamus and the anterior pituitary in the brain.
Physiological Anatomy
- Master gland
- Pituitary gland or hypophysis, an endocrine gland about pea size and
weighing 0.5 g - Protrusion off the bottom of the hypothalamus at the base of the
brain, and rests in a small, bony cavity (sella turcica) covered by a
dural fold (diaphragm sellae)
Physiological Anatomy
- The pituitary fossa, in which the pituitary gland sits, is situated in the
sphenoid bone in the middle cranial fossa at the base of the brain. - The pituitary gland secretes hormones regulating homeostasis,
including tropic hormones that stimulate other endocrine glands. - It is functionally connected to the hypothalamus by the median
eminence via a small tube called the Pituitary Stalk.
Physiological Anatomy
Physiologically, the pituitary gland is divided into two portions
- Anterior pituitary– adenohypophysis
- Posterior pituitary– neurohypophysis
- Small, avascular zone is present in between called pars intermedia
- Embryologically
- Anterior pituitary originates from rathke’s pouch, an embryonic
invagination of the pharyngeal epithelium– epitheloid nature - Posterior pituitary from neural tissue outgrowth from
hypothalamus, justifies large numbers of glial cells in this gland
Anterior Pituitary Hormones
- Secretes five endocrine hormones from different types of epithelial
endocrine cells. - Release of anterior pituitary hormones is regulated by hypothalamic
hormones (releasing or inhibitory)
- Growth hormone promotes growth of the entire body by protein
formation, cell multiplication, and cell differentiation. - Adrenocorticotropin (corticotropin) controls secretions of
adrenocortical hormones– metabolism of glucose, proteins, and
fats.
- Thyroid-stimulating hormone (thyrotropin) controls the rate of
secretion of thyroxine and tri-iodothyronine by the thyroid gland–
regulates most intracellular chemical reactions in the body. - Prolactin promotes mammary gland development and milk
production and influences the secretion of estrogen/progesterone. - Two separate gonadotropic hormones, FSH & LH, control growth of
the ovaries and testes and control their hormonal and reproductive
activities respectively. - Beta-endorphin is a polypeptide that effects the opioid receptor,
whose effects include the inhibition of the perception of pain.
- Posterior pituitary is neural in origin
- The hormones are stored in neurosecretory vesicles (Herring bodies)
before being released by the posterior pituitary into the bloodstream. - Two hormones stored by posterior pituitary and are secreted by
hypothalamus.
- Antidiuretic hormone (also called vasopressin) secreted by
paraventricular nucleus– regulates water excretion, helping to control
the concentration of water in the body fluids - Oxytocin secreted by supraoptic nucleus– express milk from the glands of
breast during suckling and helps in parturition at the end of gestation
Hypothalamic Controls
- Pituitary secretions are controlled by hormonal or nervous signals
from hypothalamus - Secretion of anterior pituitary by hormonal signals
- Secretion of posterior pituitary by nerve signals
- Hormones from hypothalamus can be releasing as well as inhibitory
- Hypothalamo-hypophyseal portal system transport these hormones
to pituitary gland to control its secretions
- Hypothalamic Hormones– secreted into Median Eminence
- Thyrotropin-releasing hormone (TRH), which causes release of TSH
- Corticotropin-releasing hormone (CRH), which causes release of
ACTH - Growth hormone–releasing hormone (GHRH), which causes release
of GH, and growth hormone inhibitory hormone (GHIH), also called
somatostatin, which inhibits release of GH
- Gonadotropin-releasing hormone (GnRH), which causes release of
the two gonadotropic hormones, LH & FSH - Prolactin inhibitory hormone (PIH), which causes inhibition of
prolactin secretion - Antidiuretic hormone (also called vasopressin) secreted by
paraventricular nucleus– regulates water excretion, helping to
control the concentration of water in the body fluids - Oxytocin secreted by supraoptic nucleus– express milk from the
glands of breast during suckling and helps in parturition at the end
of gestation
Posterior Pituitary Gland
- Composed mainly of cells
called ‘Pituicytes’, which
act as packing & supporting
cells - Stores & releases hormones into
the close capillaries. - These hormones are produced in
hypothalamus.
Posterior pituitary gland releases 2 hormones:
- Antidiuretic hormone (ADH), or arginine vasopressin
(AVP).
- Oxytocin
- Both hormones are produced in hypothalamic nuclei:
- paraventricular nucleus → (ADH + 1/6 oxytocin)
- Supraoptic nucleus → (Oxytocin + 1/6 ADH)
- ADH (vasopressin):
- Antidiuretic hormone (ADH), or arginine vasopressin
(AVP), is produced mainly in Supra Optic Nucleus of
hypothalamus.
ADH activates (2) second messenger systems:
- cAMP
- IP3
/Ca2+
Actions of ADH
- water reabsorption (retention) by distal tubules &
collecting ducts of the kidneys → decrease osmotic
pressure of the blood.
- Regulated by V2
receptors, through the action of cAMP.
- Contraction of vascular smooth muscles → generalized
vasoconstriction.
- Regulated by V1
receptors, through the action of IP3
/Ca2+
Control of ADH Release
in osmotic pressure of the ECF ( in plasma osmolality), as in
dehydration which will stimulate osmoreceptors in the
hypothalamus → ADH.
blood volume ( 10%) → stimulate mechanoreceptors in the great
arteries (aorta & carotids) & right atrium → ADH.
Hyposecretion of ADH
- Lack of ADH → Diabetes insipidus.
2 types of DI:
a. Neurogenic (central or cranial) - Problem in Hypothalamus or Post pituitary gland
- Could be primary or secondary
b. Nephrogenic (renal) - Resistance of V2
receptors in collecting ducts of the kidney
Diabetes Insipidus
Symptoms:
Polyurea 20 L/day (N 1.5 L/d),
Polydypsia,
specific gravity of urine (diluted urine),
plasma osmolarity
Treatment
- ADH will be given in neurogenic Diabetes insipidus
- No ADH will be given in nephrogenic Diabetes insipidus
Hypersecretion of ADH
• ADH, ‘Schwartz-Bartter Syndrome
- Adenoma, Ectopic Kidney
- Bronchial carcinoma
Signs & Symptoms: - Hyponatremia i.e. [Na+]extracellular to 110 mM(140mM) resulting
in - Mental confusion.
- Coma
- Death
Posterior Pituitary Gland
- Oxytocin:
- Produced mainly in the paraventricular nucleus of the
hypothalamus
Oxytocin
- Oxytocin has a major contribution in parturition
- In a hypophysectomized animal, the duration of labor is
prolonged - Amount of oxytocin in plasma increases during labor– last
stage - Stimulation of the cervix in a pregnant animal send
nervous signals hypothalamus– increased secretion of
oxytocin
Action of Oxytocin
- Contraction of smooth muscles of the uterus → enhances
labor. - Contraction of mammary gland myoepithelial cells of the
alveoli & the ducts → Ejection of milk as a reflex in
lactating women - In men → ejaculation.
- Oxytocin is concerned with releasing or ejection of milk,
while prolactin is concerned with synthesis & production of
milk
Oxytocin– Role in Milk Ejection
- Suckling stimulus on nipple
- Sensory signals transmitted to hypothalamus
- Release of oxytocin by posterior pituitary gland
- Reaches the breast by blood– contraction of
myoepithelial cells - Milk begins to flow after suckling
- Milk letdown or milk ejection
Sheehan Syndrome
• Sheehan syndrome is a condition that happens when the pituitary
gland is damaged during childbirth. It’s caused by excess blood loss
(hemorrhage) or extremely low blood pressure during or after labor. A
lack of blood deprives the pituitary of the oxygen it needs to work
properly.
Pituitary Adenomas
• Pituitary adenomas arise from the pituitary gland account for 15% of
primary brain tumors and are the third most common intracranial
tumor after meningiomas and gliomas.
• The great majority (over 90%) of pituitary adenomas are benign slow
growing tumors, approximately 5-10% are somewhat more aggressive
(atypical) and less than 1% qualify as pituitary carcinoma.
• Symptoms and signs of a mass lesion: headaches, altered appetite,
thirst, visual field defects—particularly bitemporal hemianopia
• Treatment– surgical removal and radiotherapy