endocrine system

• Thyroid-stimulating hormone (TSH) is released when thyroxine levels are low, causing the thyroid gland to secrete more T3 and T4.
• The posterior pituitary gland stores two hormones, oxytocin and antidiuretic hormone (ADH).
• The hypothalamus secretes releasing factors that stimulate the anterior pituitary to release its own hormones.
• Adrenocorticotropic hormone (ACTH) stimulates the adrenal cortex to produce glucocorticoids such as cortisol, which regulate metabolism and suppress immune responses.
• Endocrine means that ductless glands secrete hormones directly into the bloodstream, which then delivers them to their specific target cells and organs
• Exocrine means that the glands secrete their products through tiny ducts onto an interior or exterior body surface
• Exocrine examples: sweat glands, tear duct, hair follicles secreting hair oils
• Endocrine organ examples: thyroid, pituitary, adrenal (x2), pineal and parathyroid
• Endocrine and exocrine organ examples: pancreas, thymus, gonads (ovaries and testes) and hypothalamus
• The endocrine system is made up of several different types of glands that release hormones into the bloodstream, where they travel throughout the body to affect various functions.
• A hormone is a chemical messenger molecule that is produced by a gland and is transported by blood in the bloodstream to a target organ
• A target cell is only a particular group of cells a hormone may affect
• A target organ is a specific organ that a hormone may affect
• The hypothalamus secretes inhibiting and releasing factors that control the pituitary gland
• Inhibiting factor stops the secretion of certain hormones from the anterior lobe of the pituitary gland
• Releasing factor stimulates the secretion of certain hormones from the anterior lobe of the pituitary gland
• The pituitary gland is known as the master gland because it secretes hormones that control the function of other endocrine glands
• A paracrine hormone is a secretion (by endocrine cells) into the adjacent cells or surrounding tissue rather than the bloodstream.
• The anterior pituitary lobe consists of nerves connected to a complex network of blood vessels laying in the infundibulum. The nerves are connected to the hypothalamus.
• What hormones are released by the anterior pituitary lobe?

  • Adrenocorticotropic hormone (ACTH)
  • growth hormone (GH),
  • thyroid-stimulating hormone (TSH),
  • Gonadotropins: follicle-stimulating hormone (FSH) and luteinising hormone (LH)
  • prolactin
• The posterior pituitary lobe is

  joined to the hypothalamus by nerve fibres that come from nerve cell bodies in the hypothalamus and pass through the infundibulum
• The posterior pituitary lobe is not considered to be an endocrine gland because it does not secrete hormones
• The posterior lobe releases and stores hormones
• The hormones that are released by the posterior pituitary lobe are oxytocin and antidiuretic hormone
• Oxytocin and ADH are produced in the hypothalamus nerve cells and have have long extensions that pass through the infundibulum to the lobe where they are stored for release into the bloodstream
• How are hormones released in the posterior pituitary lobe?

  The release is triggered by nerve impulses initiated in the hypothalamus and conducted along the cell extension
• Gonadotropins


  hormones that affect the gonads
• Follicle Stimulating Hormone (FSH) 


  Stimulates the development of the follicles that contain eggs in the ovaries (ovulation) (females). Stimulates the production and maturation of sperm in testes (males)
• What does FSH stimulate in females?


  FSH stimulates the development and maturation of eggs, which is known as ovulation
• Luteinising Hormone (LH)


  Works with FSH in females to bring about ovulation and to form the corpus luteum after ovulation. Acts on ovaries to stimulate oestrogen production. In Males it stimulates interstitial cells in the testes to secrete male sex hormones. Acts on testes to stimulate testosterone production.
• Growth Hormone - GH (somatotropin)


  Stimulates and regulates body growth (particularly skeletal growth). GH increases the rate at which amino acids are taken up by cells and built into proteins. It is secreted throughout life as it maintains organ sizes once maturity is reached.
• Thyroid-Stimulating Hormone - TSH (thyrotropin)


  Stimulates the production and secretion of thyroxine from the thyroid gland
• Adrenocorticotropic Hormone -ACTH (adrenocorticotropin)


  Controls the production and release of some hormones (cortisol) from the adrenal cortex glands
• Prolactin (lactogenic)


  Works with other hormones to initiate and maintain milk production in mammary glands for lactation
• Indundibulum


  Stalk-like structure that joins the pituitary gland to the hypothalamus
• Anterior Pituitary lobe


  Regulates various bodily functions through hormones released by the gland. The secretions are controlled by releasing and inhibiting factors secreted by the hypothalamus.
• Hormones in the posterior pituitary lobe are produced in the hypothalamus‘ nerve cells. The hormones travel through the infundibulum to the lobe, where they are stored ready until released into the bloodstream.
• The nerve cells in the in the hypothalamus have long extensions. The hormones then move down the extensions.
• The release in the posterior lobe in triggered by nerve impulses initiated in the hypothalamus and are conducted along the cell extension.
• Oxytocin -OT


  Stimulates contractions in the uterine muscles. It is released in large quantities during labour. Also stimulates the contraction of the lobules (cells in mammary glands), releasing milk during breastfeeding.