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
• Portions of the pituitary gland

  • Anterior pituitary glands
  • Posterior pituitary glands
• Hormones secreted by the pituitary gland

  • Somatotropin
  • Thyrotropin
  • Gonadotropin
  • Lactotropin
  • Corticotropin
  • Vasopressin
  • Oxytocin
• Somatotrophs


  Anterior pituitary cells that secrete human growth hormone (hGH)
• 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
• Somatotrophs also release bursts of hGH every few hours, especially during sleep, and enhance the breakdown of fats in adipose tissues
• Thyrotrophs


  Secrete thyroid-stimulating hormone (TSH or thyrotropin) which controls the secretions of the two thyroid hormones: triiodothyronine (T3) and thyroxine (T4)
• Thyrotropin


  Controls the body's metabolic rate, heat generation, neuromuscular function, and heart rate
• Gonadotrophs


  Secrete follicle-stimulating hormone (FSH) and luteinizing hormone (LH), which act on male and female gonads
• Follicle-stimulating hormone (FSH)


  Initiates follicular development for menstrual cycle and stimulates the production of estrogen in females and sperm production in the testes of males
• Luteinizing hormone (LH)


  Triggers female ovulation and progesterone production, and stimulates the production of testosterone in males
• Lactotrophs


  Anterior pituitary cells responsible for secreting prolactin (PRL), which initiates and maintains milk production in the mammary glands of females
• Corticotrophs


  Secrete adrenocorticotropic hormone (ACTH or corticotropin), which stimulates the adrenal cortex to secrete cortisol as a response to stress
• Some corticotrophs also secrete melanocyte-stimulating hormone (MSH), which stimulates the dispersion of the pigment melanin
• Hormones secreted by the posterior pituitary gland

  • Oxytocin
  • Vasopressin (antidiuretic hormone, ADH)
• Oxytocin


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


  Stimulates the kidneys to reabsorb more water, decreasing urine output and water loss through perspiration
• The hormones of the hypothalamus serve as major controls to the secretions of the anterior pituitary gland, acting as releasing hormones or inhibiting hormones
• 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 the functions of the hypothalamus and pituitary glands

  • Hyposecretion (inadequate secretion of hormone)
  • Hypersecretion (excessive secretion of hormone)
• Pituitary dwarfism


  Caused by hyposecretion of hGH during growth years, slowing down bone growth
• Gigantism


  Caused by hypersecretion of GH, can cause 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


  Caused by the inability to secrete the antidiuretic hormone, resulting in the 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
• Adrenal Glands


  • They are paired and pyramidal endocrine structures located above each kidney
  • They have two functional regions: Adrenal cortex is the outer region, Adrenal medulla is the inner region