ENDOCRINOLOGY

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ENDOCRINOLOGY
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• All the physiological actions are regulated by
  the two major systems in the body
• Nervous system
• Endocrine system

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• Endocrine system functions by secreting chemical
  substances called chemical messengers.
• These are of two types
• Classical hormones by endocrine glands
• Local hormones secreted by tissues

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Another classification

• Endocrine messengers
• Neurocrine messengers
• Paracrine messengers
• Autocrine messengers

• Transported by the blood to the target
• Neurotransmitters are released from nerve
  endings, carry the message from the nerve
  endings
• Diffuse through the interstitial fluides
• It controlls the source cells which secrete them

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Methodes of study

• Anatomy
• Functions
• Regulation of the activity
• Applied physiology
• Hormones
• Source
• Secretion chemistry
• Synthesis
• Action

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Hormones

• Steroid
• Proteins
• Derivatives of aminoacids called tyrosine

• Cholesterol or its derivatives-adrenal
  cortex,gonads and placenta
• Secreted by pituitary gland,parathyroid,pancreas
  and placenta
• Thyroid and adrenal medullary hormones

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HORMONAL ACTION

• Hormone does not act directly on the cellular
  structures .First they combines with the
  transmembrane receptores present on the target
  tissues to form hormone receptor complex.
• This hormone receptor complex induces various
  changes or reactions in the target tissues
• Any hormone can act on the target cells only if
  the target cell has the receptor for that hormone
  

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• The hormone receptors are situated in the cell
  membrane cytoplasm , or nucleus
• Cell membrane receptors of protein hormones and
  adrenal medullary hormones are situated in the
  cell membrane
• Cytoplasm receptors of steroid hormones are
  situated in the cytoplasm
• Nucleus receptors of thyroid hormones are
  situated in the nucleus

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Mechanism of hormonal action

• By altering the permeability of cell membrane
  neurotransmitters act by this mechanism
• By activating intracellular enzyme proteins and
  catecholamines Act by this mechanism
• By actuvating the gene thyroid hormones and
  steroid hormones act by this mechanism

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PITUITARY GLAND
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ANATOMY

• It is a small gland of diameter of 1cm and
  weight 0.5-1 gm
• It lies at the base of the brain in sella turcica
  and bridged over by a fold of duramater called
  the diaphragmasella
• Above it is optic chiasma and below sphenoidal
  sinuses and laterally the cavernus sinuses
• It is connected with the hypothalamus by
  pituitary stalk or hypophyseal tract

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• Pituitary gland is also known as hypophysis
  Physiologically gland is divided into
• 1.anterior pituitary -adenohypophysis
• 2.posterior pituitary-neuro hypophysis
• Between the two portions there is small
  avascular zone called pars intermedia ,it forms a
  part of anterior pituitary

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• Posterior pituitary consists of three portions
• Parsnervosa or infundibular process
• Neural stalk or infundibular sem
• Median eminence
• The pars tuberalis of anterior pituitary and the
  neural stalk of posterior pituitary forms the
  hypophyseal stalk

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HISTOLOGY

• Posterior pituitary is made up of neural type of
  cells called pituitocytes and unmylinated nerve
  fibres
• Pituitocytes
• These are also called glial cells or fusiform
  cells
• These cells are have several process and brown
  pigment granules
• They act as supporting cells and do not secrete
  any hormone
• UNMYLINATED NERVE FIBRES
• This is coming from supra optic and para
  ventricular nuclei of the hypothalamus through
  through the pituitary stalk

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DEVELOPMENT

• Anterior pituitary is ectodermal in origin
• It arises from pharyngeal epithelium as an upward
  growth known as Rathkes pouch
• Posterior pituitary is neuroectodermal in origin
  .
• It arises from the base of the brain as downward
  growth .the Rathkes pouch and the downward
  diverticulam from hypothalamas meet midway
  between the roof of the buccal cavity and the
  base of the brain and lie close together

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HORMONES OF POSTERIOR PITUITARY

• ADH
• OXYTOCIN
• posterior pituitary does not secrete hormone.
  ADH and
• OXYTOCIN is secreted by hypothalamus and carried
  to the posterior pituitary through the
  hypothalamo hypophyseal tract

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ADH

• ADH is secreted by supra optic nucleus of the
  hypothalamas and in small quantity by para
  ventricular nucleus
• Adh is a polypeptide cotaining 9 amino acids
• Main function of ADH is retension of water by
  acting on kidneys . It increases the water
  reabsorption from distal convoluted tubule and
  collecting duct in the kidneys

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MODE OF ACTION OF ADH IN RENAL TUBULE

• ADH increases water absorption through the renal
  tubule
• That is by regulating the water channel proteins
  called the aquaporins through the V2receptors

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VASOPRESSOR EFFECT OF ADH

• ADH has action on blood vessels
• It causes constriction of the blood vessels in
  all parts of the body
• The blood pressure increases
• The amount of ADH required to cause the
  vcasopressor effect is greater than the amount
  required to cause the anti diuretic effect

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REGULATION OF SECRETION OF ADH

• Decrease in the extra cellular fluid volume
• Increase in the osmolar concentration in th ECF

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ROLE OF OSMORECEPTORS

• THE OSMORECEPTORES are the receptors which give
  response to change in the osmolar concentration
  to the blood
• These receptores are situated in the supra optic
  nucleus and paraventricular nuclei
• When osmolar concentration increase the
  osmoreceptores are activated
• The release of adh causes resorption of water
  from the renal tubules
• So only a small amont of water with usual solute
  is secreted through the urine
• This increase the volume of the ECF and restores
  the normal osmolarity

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OXYTOCIN

• oxytocin is secreted mainly by the
  paraventricular nucleus and asmall quantity by
  the supra ventricular nucleus of hypothalamus
• It is transported to the posterior pituitary
  through the nerve fibres of the hypothalamo
  hypophyseal tract
• When suitable stimuli reach the hypothalamus
  oxytocin is released into the blood

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• Oxytocin is a polypeptide having 9 aminoacids
• Oxytocin acts on the mammary gland and uterus

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Action on uterus

• On pregnant uterusexpulsion of the foetus
• On non pregnant uterusenhancing the sperm
  motility

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Action on mammary gland

• Milk ejection reflex
• Neuroendocrine mechanism

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Applied physiology of posterior pituitary
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Hyper activity of posterior pituitary

• SIAD-syndrome of inappropriate hyper secretion of
  antidiuretic hormone
• Loss of sodium through urine due to hyper
  secretion of ADH
• Main cause is due to cerebral tumors lung tumors
  , because the cancer cells secrete ADH

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Signs and symptoms

• Excess of ADH decreases the urine output
• Increase in the volume of ECF
• secondary increase in urine output with increased
  concentration
• There is reduction in the sodium in extra
  cellular fluids
• The patients die due to convulsion and coma

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Hypoactivity of posterior pituitary

• Diabetes insipedus
• Excess excretion of water through urine
• Causes
• Lesion of the supra optic and para ventricular
  nuclei of hypothalamus
• Lesion in the hypothalamo hypophyseal tract
• Atrophy of post pituitary
• Inability of renal tubules to respond into ADH

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Signs andsymptoms

• Polyurea
• Polydipsea
• dehydration