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• Endocrine System


  A collection of glands that produce hormones directly into the circulatory system to be carried to distant target organs

  
• Endocrine System


  • No duct system
  • Secretion is directly drained into the bloodstream and the secretion is carried to the different target organs
• Hormone


  • Chemical substances that regulate cellular or organ activity
  • Chemical messengers
  • Regulate growth and metabolism, sexual development and function
  • Released into the bloodstream and affects one or several organs throughout the body
  • Regulated by feedback mechanism to maintain homeostasis
• Major Glands


  • Hypothalamus
  • Pituitary
  • Thyroid
  • Parathyroid
  • Adrenals
  • Pineal Body
  • Reproductive Organs (Ovaries, Testes)
  • Placenta (during pregnancy)

  
• Functions of Endocrine System

  • Water Balance: ADH, Aldosterone
  • Uterine contraction, and milk release: Oxytocin, Prolactin
  • Growth, metabolism, and tissue maturation: Growth Hormone, Thyroid Hormone, Cortisol, Catecholamines
  • Ion Regulation: Aldosterone
  • Heart rate and blood pressure regulation: Cortisol, Catecholamines
  • Blood glucose control: Glucagon, Insulin
  • Reproductive function control: Testosterone, Estrogen, FSH, LH/ICSH
  • Sleep: Melatonin
• Neurotransmitters


  Released by axon terminals of neurons into synaptic junctions, act locally to control nerve cell functions
• Neuroendocrine Hormones


  Secreted by neurons into blood, influence function of target cells in another location in the body
• Paracrines


  Secreted into the extracellular fluid, affect neighboring target cells of a different type
• Autocrines


  Secreted by cells into the extracellular fluid, affect the function of same cells that produce them
• Pituitary Gland


  • A tiny organ at the base of the brain, weighs about 0.5 g
  • Often referred to as the master gland because the hormones that it produces influence the activities of many other endocrine glands
  • Vital to life
  • Controlled in large part by the hypothalamus

  
• Pituitary Gland


  • Female pituitary gland is larger than male by 20%
  • Increases by 10% during pregnancy due to increase production of prolactin
• Anatomical Relations of Pituitary Gland

  • Anterior: Sphenoid sinus
  • Posterior: Dorsum sellae, Basilar artery, Pons
  • Superior: Diaphragma sellae, Optic chiasma
  • Inferior: Body of sphenoid bone, with its air sinuses
  • Lateral: Cavernous sinus and its contents

  
• Sella Turcica


  • A depression on the body of the sphenoid, the pituitary gland is lodged in this fossa
  • Inferior to the sella turcica/depression is the air sinus - the sphenoid sinus
  • Diaphragma Sellae is part of the dura mater that covers the pituitary gland and is the roof of the sella turcica

  
• Anterior Pituitary


  • AKA adenohypophysis
  • Origin: Rathke's Pouch
  • Highly vascularized
  • Makes up about 80% of the pituitary gland
  • Regulates growth, metabolism, and reproduction through the hormones that it produces
  • Made up of 3 distinct parts: Anterior part, Tuberal part, Intermediate part

  
• Role of Hypothalamus


  • Secreted into the bloodstream and sent to the adenohypophysis via the hypophyseal portal system
  • Secretory activity of the hypothalamus and hypophysis is regulated by the negative feedback mechanism

  
• Posterior Pituitary


  • Origins: Epidermal Diverticulum / Infundibulum
  • Does not produce hormones
  • Hormones are transmitted by nerve impulse through the nerve tract in the infundibulum
  • Further divided into: Pars nervosa, Median eminence, Infundibulum, Pituitary / Infundibular Stalk

  
• Role of Hypothalamus


  • Travel by the axons from the hypothalamus directly into the posterior pituitary
  • Glial cells (pituicytes) envelope these axons completely and form the hypothalamohypophyseal tract
• Blood Supply and Venous Drainage of Pituitary Gland

  1. Hypothalamic-Hypophyseal Portal System

  2. Originates from the superior and inferior hypophyseal arteries, which are the branches of the internal carotid artery

  3. The superior hypophyseal arteries form a primary plexus within the infundibulum and median eminence

  4. The portal veins divide and form another plexus in the anterior pituitary; the secondary plexus

  
• Pineal Gland


  • Approx. 6 mm long, weighs approx. 0.1 gram
  • Consists of pinealocytes (hormone-secreting cells) and glial cells (supports the pinealocytes)
  • Innervated by postganglionic sympathetic nerve fibers

  
• Functions of Pineal Gland

  • Secretes melatonin, which influences the activities of pituitary gland, islets of Langerhans in the pancreas, parathyroids, adrenals, and gonads
  • Actions are mainly inhibitory
• Gross Features of Pineal Gland

  • Pineal Stalk: Attaches the gland to the brain, specifically, to the posterior wall of the roof of the 3rd ventricle
  • Pineal recess of the 3rd Ventricle: Space between the laminae, filled with the cavity of the 3rd ventricle
  • Corpora Arenacea: "Brain sand", deposits of calcium, phosphates, and carbonates, accumulates with age

  
• Hormone Secretion of Pineal Gland

  • Melatonin: Main secretion of pinealocytes, regulates the circadian rhythm of the body (sleep-wake cycle)
  • Production of melatonin is stimulated by little to no light (night) and inhibited by bright light (morning)
• Posterior commissure


  Contains the habenular commissure
• Superior lamina


  Contains the habenular commissure
• Pineal recess of the 3rd Ventricle


  • Space between the laminae
  • Filled with the cavity of the 3rd ventricle
• Corpora Arenacea


  • Brain sand
  • Deposits of calcium, phosphates, and carbonates
  • Form the multilaminar corpuscles
  • Accumulates with age
• Corpora Arenacea

  Mostly a by-product of secretory activity
• Corpora Arenacea


  • Sometimes used as landmarks during radiologic examinations
  • Helps in identifying the pineal gland microscopically and histologically

  
• Melatonin

  • Main secretion of pinealocytes
  • Regulates the circadian rhythm of the body (sleep-wake cycle)
• Melatonin production


  1. The pineal gland gathers information about the day-night cycle from the environment and the information is used to modulate the release of melatonin

  2. Little to no light (night): production is stimulated

  3. Bright light (morning): production is inhibited
• Pineal gland


  • Has regulatory importance in influencing the activity of other endocrine glands
  • Mostly inhibitory to the other endocrine glands by inhibiting the production of their hormones or indirectly by inhibiting the secretion of releasing factors by the hypothalamus
• Other hormones produced by the pineal gland

  • Serotonin
  • Indolamines and Polypeptide Hormones
• Serotonin


  Neurotransmitter; regulates mood and social behavior, appetite, digestion, sleep, memory, and sexual desire and function
• Indolamines and Polypeptide Hormones

  Reduces the activity of the adenohypophysis (AP)
• Arterial Supply


  • Posterior Choroidal Arteries
  • Main blood supply
  • Arise from the posterior cerebral artery
• Venous Drainage

  • Internal Cerebral Veins
  • Flow mainly into the cerebral vein of Galen
• Innervation


  Postganglionic sympathetic nerve fibers
• The thyroid gland is the largest gland with pure endocrine function

  
• Thyroid gland


  • Butterfly-shaped vascular organ
  • Surrounded by a thin fibrous capsule
  • Surrounded by a sheath derived from the pretracheal layer of deep fascia
  • Normal weight varies from 15-20 g to 25-30 g in adults
  • Slightly heavier in females
  • Enlarges during pregnancy and menstruation
  • Physiologic enlargement (homogenous and equal in size) during the period of rapid growth, but will not be visible after 25 y/o. If it persists, it is no longer physiologic

  
• Location of thyroid gland

  • Middle of the lower neck, below the larynx, just above the clavicle and anterior to the trachea
  • Lies deep to the sternothyroid and sternohyoid muscles
  • Extends from C5 to T1 and lies anterior to the thyroid and cricoid cartilages of the larynx and the first five or six tracheal rings
  • Found in the muscular triangle of the neck