Endocrine gland

• Endocrine System


  How the body communicates with itself
• Nerves system


  Impulses travel down nerves in seconds
• Endocrine System


  Hormones released into the blood to target organs to perform functions, can take minutes or hours
• Hormones dictate virtually every part of your body: from your state of mind to your behavior, body shape, eating habits and even your reaction to stress
• Hormonal imbalances can trigger issues like PMS, painful breasts, disrupted monthly cycle, menopausal issues, migraines, mental disorders, acne, cellulite and more
• Endocrine system


  Consists of glands that secrete hormones
• Types of glands


  • Exocrine - release secretions through ducts
  • Endocrine - release secretions directly into the blood
  • Heterocrine - contain both exocrine and endocrine components
• Primary endocrine glands


  • Hypophysis (pituitary gland)
  • Adrenal glands
  • Thyroid gland
  • Parathyroid gland
  • Pancreatic islets
  • Sex glands
• Thyroid


  Located across the trachea, posterior to the larynx
• Adrenal


  Located above the kidney, divided into cortex and medulla
• Pituitary


  Master gland that regulates all other glands, consists of anterior and posterior lobes
• Pancreas


  Consists of islets of Langerhans which secrete insulin
• Ovary


  Female gonad that secretes progesterone
• Hormones


  Chemical substances secreted into body fluid that have a physiological effect on the entire organism
• Types of hormones


  • Polypeptides
  • Steroids
• Hormone inactivation


  Hormones can be inactivated and broken down by processes like oxidation, reduction, etc.
• Positive feedback


  Stimulates or increases the production of the hormone
• Negative feedback


  Inhibits the secretion of the hormone
• Negative feedback loop example (thyroid)

  1. Hypothalamus secretes TRH which stimulates anterior pituitary to secrete TSH

  2. TSH stimulates thyroid to secrete thyroxine

  3. Thyroxine levels above threshold inhibit hypothalamus from secreting TRH, leading to reduced TSH and thyroxine secretion
• Positive feedback mechanisms are rare, they simplify changes rather than expressing hormone secretion
• Positive feedback example (oxytocin during childbirth)

  1. Oxytocin release from pituitary stimulates uterine contractions

  2. Contractions stimulate more oxytocin release

  3. This cycle continues until birth is complete, then oxytocin production stops
• Feedback mechanism


  Monitors hormone concentration in blood and adjusts secretion rate to maintain ideal levels
• Hormones have powerful effects so their levels must be carefully regulated by feedback mechanisms
• Hormones are secreted in small quantities and have a limited time of activity before being inactivated