Endocirne (hormone)

• The endocrine system is regulated by feedback

  In much the same way that a thermostat regulates the temperature in a room
• Regulation of hormones by the pituitary gland

  1. Signal sent from hypothalamus to pituitary gland in form of "releasing hormone"

  2. Releasing hormone stimulates pituitary to secrete "stimulating hormone" into circulation

  3. Stimulating hormone signals target gland to secrete its hormone

  4. As hormone level rises, hypothalamus and pituitary gland shut down secretion of releasing hormone and stimulating hormone

  5. This slows secretion by target gland
• This system results in stable blood concentrations of the hormones that are regulated by the pituitary gland
• Types of hormones


  • Steroids
  • Peptides
  • Amines
• Steroid hormones


  • Secreted by gonads, adrenal cortex, and placenta
  • Examples: progesterone and testosterone
• Peptide hormones


  • Examples: oxytocin, luteinizing hormone, thyrotropin releasing hormone
• Amine hormones


  • Examples: epinephrine, norepinephrine, T3, T4
• Hypothalamus


  • Located above the pituitary gland near the base of the brain
  • Links the nervous system to the endocrine system via the pituitary gland
  • Responsible for regulating certain metabolic processes and other activities of the autonomic nervous system
• Follicle-stimulating hormone (FSH)

  Stimulates follicle development in ovaries and sperm development in testes. It regulates the development, growth, pubertal maturation, and reproductive processes of the body.
• Luteinizing hormone (LH)


  Triggers ovulation, causes ruptured follicle to become the corpus luteum and stimulates testosterone production in males.
• Release of FSH and LH


  Controlled by releasing and inhibiting hormones produced by the hypothalamus
• Oxytocin


  Stimulates contractions of the uterus during labor and causes milk ejection
• Antidiuretic hormone (ADH)


  Causes the kidneys to reabsorb solute-free water and return it to the circulation from the tubules of the nephron. It constricts arterioles, which increases peripheral vascular resistance and raises arterial blood pressure (vasopressin).
• Thyroid gland

  • Two lobes located on either side of the trachea or windpipe in the lower part of the neck
  • Consists of many follicles, their shape depends on the stimulating by thyrotrophin (thyroid stimulating hormone, TSH)
• Thyroid hormones


  Triiodothyronine (T3) and Thyroxine (T4) that regulate
• Thyroid gland secretes two types of hormones: the follicular cells which produce thyroid hormones (non-steroid hormones)
• thyroid hormone ( non -steroid hormone ):1-regulate metabolism. , 2- increase protein synthesis , 3- promote glycolysis. , 4- gluconeogenesis & glucose uptake
• Secretion of the two thyroid hormones

  1. Regulated by thyroid-stimulating hormone (TSH)

  2. TSH is secreted from the anterior pituitary gland

  3. TSH is regulated by thyrotropin-releasing hormone (TRH)

  4. TRH is produced by the hypothalamus
• Parathyroid glands


  • Four small ovoid glands smaller than the pea
  • Lie on the posterior surface of the thyroid gland
  • Two pairs: superior and inferior
  • Release parathyroid hormone (PTH)
  • Maintain the level of calcium and phosphorus in the blood
• The Adrenal glands


  • Two small flattened yellowish bodies
  • Situated on the upper of each kidney
  • Outer part is the cortex (yellowish)
  • Inner part is the Medulla (dark)
• The adrenal medulla


  1. Situated directly on the top each kidney

  2. Stimulated by the sympathetic nervous system

  3. Secretes the catecholamines

  4. Catecholamines function to produce a rapid response throughout the body in stress situations

  5. Include epinephrine (adrenaline 80%) and norepinephrine (noradrenaline 20%)

  6. Help maintain blood pressure and stimulate smooth muscles

  7. Adrenaline elicits a fight or flight response, increase blood pressure, increase respiration, increase metabolic rate, increase glycogenolysis and constriction of blood vessels in many parts of the body
• Steroid hormones secreted by the adrenal cortex

  • Mineralocorticoids
  • Glucocorticoids
  • Gonadocorticoids (Androgens)
• Mineralocorticoids


  Such as Aldosterone which maintains electrolyte balance and blood pressure
• Glucocorticoids


  Cortisol and cortisone which functions include the regulation of metabolism of proteins, fats and sugars as well as influence on the immune system
• Gonadocorticoids (Androgens)


  Are converted to fully functional sex hormones (testosterone, estrogen, progesterone) in the gonads and other target organs
• Steroidogenesis


  The production of steroid hormones
• Pancreas


  • Located slightly behind the stomach
  • A mixed gland, has both an endocrine and digestive exocrine function
  • 99% of the pancreas is exocrine and 1% is endocrine
• Endocrine function of the pancreas

  Regulates blood sugar levels, secreting the hormones insulin, glucagon, somatostatin and pancreatic polypeptide
• Maintaining blood glucose levels (homeostasis)

  1. When blood glucose levels are low, alpha cells secrete glucagon, which increases blood glucose levels

  2. When blood glucose levels are high beta cells secrete insulin to decrease glucose in blood

  3. Delta cells in the islet also secrete somatostatin which decreases the release of insulin and glucagon
• Insulin


  Acts to decrease blood glucose levels by facilitating uptake by cells (particularly skeletal muscle)
• Glucagon (to increase blood glucose level )


  • Promotes the creation of glucose and the breakdown of glycogen to glucose in the liver
  • Decreases the uptake of glucose in fat and muscle
  • Release is stimulated by low blood glucose or insulin levels, and during exercise
• Pineal gland


  • Small endocrine gland in the brain of most vertebrates
  • Reddish-gray structure about the size of a pea
  • Situated in the midline of the brain immediately behind the third ventricle
  • Produces melatonin, a serotonin-derived hormone which modulates sleep patterns in both circadian and seasonal cycles
  • Melatonin production is stimulated by darkness and inhibited by light
• Gonads


  • Mixed gland that produces the gametes and sex hormones of an organism
  • Sex hormones include androgens, estrogens, and progestogens
  • Sex hormones secreted from ovaries in female and testes in male
  • Sex hormones play an essential role in reproduction and sexual development, puberty, cholesterol regulation, high growth, distribution of body fat, and inflammatory response