ENDO

• Endocrinology


  The scientific study of the function and pathology of endocrine glands

  
• Components of the Endocrine System


  • A network of ductless glands that secrete hormones directly into the blood
  • Considered to be the regulatory system of the body
  • Regulated by means of control of hormones synthesis rather than by degradation

  
• Characteristics of the Endocrine System


  • Cyclicity: production of hormones occur in cycles or in patterns
  • Pulsatility: production of hormones in pulses or periodic intervals
  • Feedback mechanism
• Positive Feedback System


  An increased in the product also increases the activity of the system and the production rate
• Negative Feedback System


  An increased in the product decreases the activity of the system and the production
• Hormones


  Active chemical substances produced by specialized cells, transported by the blood stream to other tissues where they exert specific metabolic regulatory effects affecting the body as a whole
• Functions of Hormones


  • Regulatory: Maintain constancy of chemical component of plasma, interstitial and intracellular fluids
  • Morphogenesis: To control type and rate of growth of an organism
  • Integrative action: The presence of other hormones is important for efficient functioning
• Types of Hormones

  • Endocrine
  • Paracrine
  • Autocrine
  • Neurocrine
• Hormone Actions


  • Proteins/Polypeptides
  • Glycoproteins
  • Steroids
  • Amino acid derivative
• Hormone Composition or Structure


  • Amines
  • Polypeptides
  • Glycoproteins
  • Steroids
  • Eicosanoids
• Hormone Functions


  • Releasing hormones
  • Inhibiting hormones
  • Trophic hormones
  • Effector hormones
• Hormone Properties


  • Lipophilic
  • Hydrophilic
• Regulation of Hormones


  • The majority of endocrine functions are regulated through the pituitary gland, which in turn is controlled by secretions from the hypothalamus
• Hypothalamus


  • Small organ located below the brain, above the pituitary gland
  • Connected to posterior pituitary gland through infundibular stalk
  • Supraoptic and paraventricular nuclei produce vasopressin and oxytocin
  • Neurons in the anterior portion are responsible for the secretion of all Releasing hormones which targets the pituitary gland
• Hormones of the Hypothalamus


  • Releasing: TRH, GHRH, PRF, CRH, GnRH
  • Inhibiting: GHIH, PIH
• Pituitary Gland


  • Also referred to as "hypophysis"- undergrowth
  • Connected to the hypothalamus through the infundibulum or the pituitary stalk
  • Located in a small cavity in the sphenoid bone of the skull called the sella turcica
  • Three distinct parts: Anterior/Adenohypophysis, Posterior/Neurohypophysis, Intermediate lobe

  
• Anterior Pituitary Cell Types


  • Somatotropes
  • Lactotropes or mammotropes
  • Thyrotropes
  • Gonadotropes
  • Corticotropes

  
• Anterior Pituitary Hormones


  • Tropic hormones: TSH, ACTH, GH, FSH, LH
  • Effector hormones: Prolactin
• Growth Hormone


  • Most abundant of all pituitary hormones
  • Vital hormone for normal growth
  • Release is stimulated by GHRH, inhibited by Somatostatin
  • Secreted in pulses
• Actions of Growth Hormone


  • Influences anabolic and catabolic process
  • Indirect effects mediated by insulin-like growth factors (IGFs)
• Growth Hormone Disorders


  • Excess GH: Gigantism, Acromegaly
  • GH Deficiency: Pituitary dwarfism
• Prolactin


  • Otherwise known as the pituitary lactogenic hormone; stress hormone; direct effector hormone
  • Functions in the initiation and maintenance of lactation
  • Acts in conjunction with estrogen and progesterone to promote breast tissue development
• Secretion of Prolactin


  • Controlled primarily by PIF and PRF, which are released by the hypothalamus
  • Gradual increase in PRL secretion appears to occur in the first half of the menstrual cycle with a decline immediately after ovulation
  • Prolactin secretion increases during pregnancy reaching the highest level in the third trimester
• Prolactin Clinical Disorders


  • Prolactin Excess: Hyperprolactinemia
  • Consequence of prolactin excess: Hypogonadism
• Corticotropes


  Cells in the anterior pituitary that secrete adrenocorticotropic hormone (ACTH)
• Prolactin


  Otherwise known as the pituitary lactogenic hormone; stress hormone; direct effector hormone
• Functions of Prolactin


  • It functions in the initiation and maintenance of lactation
  • It also acts in conjunction with estrogen and progesterone to promote breast tissue development
• Secretion of Prolactin


  1. Prolactin secretion is controlled primarily by PIF and PRF, which are released by the hypothalamus

  2. This inhibitory factor has been shown to be dopamine

  3. Gradual increase in PRL secretion appears to occur in the first half of the menstrual cycle with a decline immediately after ovulation

  4. Prolactin secretion increases during pregnancy reaching the highest level in the third trimester
• Hyperprolactinemia


  Prolactin excess
• Causes of Hyperprolactinemia


  • Decrease PIF, increase PRF secretion by the hypothalamus
  • Autonomous production of PRL (pituitary tumor)
• Effects of hyperprolactinemia in females


  • Amenorrhea (cessation of menstrual periods)
  • Galactorrhea (production of milk in any situation other than post partum period)
• Effects of hyperprolactinemia in males

  • Impotence
• Hypoprolactinemia


  Prolactin deficiency
• Consequence of prolactin deficiency


  Lactation does not develop in these patients
• Posterior Pituitary Hormones


  • Extension of the forebrain
  • Represents the storage region for ADH/Vasopressin and Oxytocin
• Anti-Diuretic Hormone (ADH)


  • Otherwise known as vasopressin
  • A nonapeptide that acts on the distal convoluted tubule and collecting tubule of the kidneys
• Functions of ADH


  • It decreases the production of urine by promoting reabsorption of water by the renal tubules
  • It increases blood pressure- a decrease in blood volume or blood pressure will likewise stimulate ADH release
• Mechanism of action of ADH

  1. ADH binds with V2 receptors located in the DCT & collecting ducts

  2. Adenyl cyclase is activated

  3. Cyclic AMP is activated

  4. A cascade of reactions is triggered

  5. Aquaporins are produced

  6. Water is reabsorbed
• Principal Regulators of ADH secretion


  • Increased concentration in plasma osmolality
  • Decrease in blood volume or blood pressure
• Diabetes Insipidus


  Deficient ADH, results in severe polyuria (>3L of urine / day)