Endocrine glands

• Endocrine system


  The system of glands that secrete hormones directly into the bloodstream to regulate the body's growth, metabolism, and sexual development
• Major endocrine glands in man

  • Pituitary gland
  • Thyroid gland
  • Parathyroid glands
  • Pancreas
  • Adrenal glands
  • Gonads
• Exocrine gland


  A gland that secretes a substance out through a duct, either inside the body or on a surface of the body
• Pituitary gland


  The master gland that controls the activity of other endocrine glands
• Pituitary gland


  • Attached to the hypothalamus
  • About the size of a pea
  • Consists of two distinct lobes: anterior and posterior
• Anterior lobe of pituitary gland


  • Affects, regulates and maintains the development and functions of the endocrine glands
  • Secretes many hormones including thyroid stimulating hormone, growth hormone, and hormones that influence gonads and adrenal glands
• Less growth hormone produced during childhood


  Individual becomes pituitary dwarf
• Overproduction of growth hormone in adults


  Condition called acromegaly results, where only the feet, hands and face can respond and become overly large
• Posterior lobe


  It secretes two hormones, oxytocin and antidiuretic hormone
• Oxytocin causes powerful contractions of uterus during birth. It causes the ejection of milk
• Antidiuretic hormone


  It causes reabsorption of water from the nephrons. It's under secretion results in large quantity of dilute urine. This disease is called diabetes insipidus
• Thyroid gland


  • Located in the neck and fits closely around and sides of trachea just be larynx
  • Has two lobes
  • Secretes thyroxin and calciton
• Thyroxin


  Regulates basic metabolism. It regulates process of growth especially maturatio mental and skeletal development in children
• Goitre


  Enlargement of thyroid gland caused by iodine deficiency in diet, common in mountain areas
• Calcitonin


  Secreted when blood calcium level is high, stimulates the deposition of extra calcium in bones, and thus mainlains the of neck level of calcium in blood
• Parathyroid glands


  • Located on the thyroid glands, two pairs of very small structures
  • Secrete parathormone
  • Parathormone has function opposite to calcitonin, controls the balance of calcium ions and phosphate in body
• Pancreas


  • Present in the abdominal cavity near the stomach
  • Endocrine as well as exocrine gland
  • Contains Islets of Langerhans with alpha and beta cells
  • Alpha cells secrete glucagon, beta cells secrete insulin
• Insulin


  Secreted when blood sugar rises, facilitates glucose transport across cell membrane, enhances conversion of glucose to glycogen
• Glucagon


  Increases glucose concentration by stimulating the liver to convert glycogen to glucose
• Diabetes Mellitus


  Caused when beta cells do not produce enough insulin, glucose accumulates in blood and is excreted with urine, requires insulin injections or medicines
• Adrenal glands


  • Two glands resting on top of kidneys
  • Adrenal cortex secretes corticosteroids
  • Adrenal medulla produces adrenaline and nor-adrenaline
• Adrenaline


  Secreted to meet emergency situations, increases heart rate, blood pressure, and blood flow to limbs to prepare body to face emergency
• Noradrenalin


  Raises blood pressure and is responsible for the constriction of blood vessels
• Hormone testosterone


  Secreted by the testes of males, responsible for the appearance of secondary sexual characters at puberty e.g., appearance of beard, coarseness of voice etc.
• Female hormone oestrogen


  Secreted by the ovaries, stimulates the development of secondary sexual characteristics
• Gonads


  Testes and ovaries, their hormones are required for reproduction ,testosterone is secreted by testes of male, female hormone estrogen is secreted by ovaries ,these hormones stimulates development of secondary sexual characteristics
• Feedback Mechanism


  1. Secretion of hormones is regulated through feedback mechanism

  2. Regulation of a process by the output of that process is called feedback

  3. Feedback mechanism is of two types: Negative Feedback and Positive Feedback
• Negative Feedback


  If output of a process inhibits the process it is called negative feedback, maintains homeostasis by returning conditions to the normal, more common in living organisms
• Negative Feedback Mechanism


  1. When blood glucose level is raised, insulin is secreted

  2. Insulin stimulates the absorption and storage of glucose as glycogen in liver and skeletal muscles

  3. Blood glucose level returns to normal

  4. Normal blood glucose level inhibits further insulin secretion
• Negative Feedback


  • Maintains homeostasis
  • Returns conditions to the normal
• Positive Feedback


  1. If output of the process further enhances the process, it is called positive feedback

  2. It is non-homeostatic as it diverts condition from normal

  3. Less common in living system

  4. Suckling action by infants stimulates milk production through hormonal secretion, more suckling will result in more milk production