science

• Endocrine system


  A collection of ductless glands scattered around the body that controls various activities of different organs, such as growth and response to stress
• Gland


  An organ that produces and releases chemical substances that perform specific functions in the body
• Structural types of glands

  • Exocrine glands (secrete through ducts or tubes)
  • Endocrine glands (secrete hormones into interstitial fluid)
• Pituitary gland


  A pea-shaped organ about 1.5 cm in diameter, connected to the hypothalamus via the infundibulum
• Hypothalamus


  The true "master" gland that controls the pituitary gland
• Hormones secreted by the pituitary gland

  • Anterior pituitary: somatotropin, thyrotropin, gonadotropin, lactotropin, corticotropin
  • Posterior pituitary: vasopressin (ADH), oxytocin
• Somatotrophs


  Anterior pituitary cells that secrete human growth hormone (hGH)
• Somatotrophs


  • They account for the most numerous cells in the anterior pituitary gland
  • They release bursts of hGH every few hours, especially during sleep
  • They enhance the breakdown of fats in adipose tissues
• Human growth hormone (hGH)


  Stimulates the release of growth factors from the liver, skeletal muscles, cartilage, and bones which cause cells to grow and multiply by increasing the rate of gene expression
• Thyrotrophs


  Anterior pituitary cells that secrete thyroid-stimulating hormone (TSH or thyrotropin)
• Thyrotrophs


  • They are the master regulators of the thyroid gland hormones
  • They control the body's metabolic rate, heat generation, neuromuscular function, and heart rate
• Gonadotrophs


  Anterior pituitary cells that secrete follicle-stimulating hormone (FSH) and luteinizing hormone (LH)
• Gonadotrophs


  • FSH initiates follicular development for menstrual cycle and stimulates estrogen production in females and sperm production in males
  • LH triggers ovulation and progesterone production in females, and stimulates testosterone production in males
• Lactotrophs


  Anterior pituitary cells responsible for secreting prolactin (PRL)
• Prolactin (PRL)


  Initiates and maintains milk production in the mammary glands of females
• Corticotrophs


  Anterior pituitary cells that secrete adrenocorticotropic hormone (ACTH or corticotropin)
• Corticotrophs


  • They secrete ACTH which stimulates the adrenal cortex to secrete cortisol as a response to stress
  • Some also secrete melanocyte-stimulating hormone (MSH) which stimulates the dispersion of the pigment melanin
• Posterior pituitary gland


  Does not synthesize its own hormones, but stores and releases oxytocin and vasopressin (ADH) that are synthesized in the hypothalamus
• Oxytocin


  Stimulates uterine contractions during labor and milk ejection from the mammary glands for suckling by the infant after delivery
• Vasopressin (ADH)


  Stimulates the kidneys to reabsorb more water, decreasing urine output
• Hypothalamic hormones


  Releasing hormones or inhibiting hormones that control the secretions of the anterior pituitary gland
• The interaction between the hypothalamus and the anterior pituitary gland is made possible by the blood vessels' link between them, and their proximity allows the hormones to be delivered immediately
• Disruptions in hypothalamus and pituitary function

  • Hyposecretion (inadequate secretion of hormone)
  • Hypersecretion (excessive secretion of hormone)
• Hypothalamic dysfunction


  General interruption in the functioning of the hypothalamus, which greatly affects the pituitary glands
• Pituitary dwarfism


  Hyposecretion of human growth hormone (hGH) during growth years, slowing down bone growth
• Gigantism


  Hypersecretion of growth hormone (GH) causing the femur to grow very long
• Acromegaly


  Condition in adults where the bones of the face and the hands thicken, caused by hypersecretion of GH
• Neurogenic diabetes insipidus


  Inability to secrete the antidiuretic hormone (vasopressin/ADH), leading to release of large volumes of urine, dehydration and thirst
• Hypothalamus and pituitary gland


  The central endocrine glands since they control the other glands
• The Major Peripheral Endocrine Glands

  • thyroid gland
  • parathyroid glands
  • adrenal glands
  • pancreas
• Thyroid Gland


  • It is a two-lobed endocrine structure that is located just below the larynx
  • The narrow middle portion gives it a butterfly or bow-tie shape
  • Its main hormone is thyroxine
• Follicular cells of the thyroid


  • They are the major secretory cells of the thyroid
  • They are arranged into hollow spheres called follicles
  • These are filled with colloid substances which are storage sites for thyroid hormones
• Thyroid hormones


  • tetraiodothyronine (T4)
  • triiodothyronine (T3)
• Thyroid hormones


  Increase the basal metabolic rate (BMR)
• Basal metabolic rate (BMR)


  The rate at which oxygen is consumed under standard conditions (i.e., awake, at rest, and fasting)
• Increase in BMR


  Increases metabolism of macronutrients
• Thyroid hormones


  • Maintain normal body temperature by stimulating ATP and heat production through sodium-potassium pumps
  • Hasten protein synthesis, and glucose and fatty acid breakdown to produce ATP
• Parathyroid Glands


  • They are endocrine structures that are partially embedded in the thyroid gland
  • Majority of their cells are called chief cells or principal cells
  • They produce the parathyroid hormone (PTH or parathormone)
• Parathyroid hormone (PTH)


  A major regulator of the levels of calcium, magnesium, and phosphate ions in the blood
• PTH


  • Increases the number and activity of osteoclasts
  • These are bone cells that degrade bone to initiate remodeling