ANBI 420

• Endocrinology: the study of the endocrine glands and their secretions.
• Endocrine glands: Ductless glands that secrete hormones into the blood.
• Preprohormone: precursor protein to one or more prohormones. Prohormones: precursors to peptide hormones.
• Prohormones: secreted by endocrine glands and are inactive until they are converted to their active form within target cells. They are cut in the gland
• Hormone: a substance secreted by specialized cells and released into a vascular system (blood stream) or tissue fluid for transport to target tissues in distant organs causing a response.
• Hormones are response mediated by receptors specific to the hormone in target tissues.
• Hormones are synthesized by endocrine cells.
• Hormones can be secreted by small groups of cells, ductless glands, or individual cells.
• Most hormones have more than one production site.
• Hormones can be released into the lymph, extracellular fluids, or the bloodstream.
• Major functions of hormones:

  • Maintaining homeostasis.
  • Reproduction.
  • Growth and development.
  • Behavior.
• The evolution from unicellular to multicellular organisms made it necessary to have coordinating systems to regulate and integrate the function of different cells.
• The endocrine system includes: Endocrine glands/cells, hormones, and the target organ.
• Some synthesized hormones may not be secreted but stay where they were produced.
• Exocrine glands: releases secretion via a duct into an epithelial surface (sweat glands, tear glands/ ducts).
• Exocrine glands go compounds -> lumen -> epithelial surface.
• Endocrine glands: ductless and release substances directly to the bloom/lymph depending on solubility.
• Water soluble substances move through vesicles. Lipid-soluble substances move through diffusion.
• Types of hormone signaling: Autocrine, Paracrine, and endocrine.
• Endocrine: when hormones enter the bloodstream/lymph and bund to hormone receptors in target cells in distant organs.
• Examples of endocrine signaling are:

  • High blood glucose levels cause signaling to the Beta cells in the islets of Langerhans in the pancreas to produce and release insulin into the blood where it travels to many tissues, including the liver which signals it to store glucose in the form of glycogen instead of releasing it.
  • Cortisol produced from the adrenal glands goes into the blood stream to the heart, lungs and metabolic system
  • Epinephrine released from adrenal glands into the blood due to fight or flight.
• Paracrine signaling: when hormones bind to cells near the cells that released them (within the same organ or tissue).
• Hormones released by paracrine signaling are often degraded or taken up rapidly.
• An example of paracrine signaling is when Testosterone is secreted from the Leydig cells in and testes acts as a paracrine agent to stimulate spermatogenesis in the adjacent seminiferous tubules.
• Autocrine signaling: when a hormone produces a biological effect on the same cell that has released it.
• An example of autocrine signaling is the lining in a mammalian endometrium responds to oxytocin in an autocrine/paracrine manner to cause production of prostaglandins which cause uterine contractions.
• Intracrine signaling: when a hormone is synthesized and acts within the same cell (does not leave the cell).
• An example of intracrine signaling is when precursor sex steroid hormones are synthesized and then are converted by enzymes to activate androgens/ estrogens which bind to receptors within the same cell.
• Neuroendocrine signaling: a chemical is produced by a neuron or nervous tissue and is released into the bloodstream to act on another cell type.
• Neurohormone: when the cell at one end of the communication is not a neuron.
• Neurotransmitter: when communication is a neuron on neuron.
• Exocrine signaling: released externally to initiate response in to communication with another organism.
• Examples of exocrine signaling is: pheromones released for identification within species, repelling predators, and reproductive attractants.
• Types of pheromones:

  • Primer: cause change in the endocrine system of the receiving animal (menstrual synchrony)
  • Signaler: relays information (newborn able to smell its mother)
  • Modulator: Influences mood or emotion (andesternone in pigs)
  • Releaser: changes behavior (aggression, maternal behavior, suckling)
• Hormones can be categorized into 4 main structures: Peptides and proteins, amino acids, steroids, and eicosanoids.
• Peptides and proteins are amino acid based and constitutes most hormones.
• Peptide and proteins are synthesized as preprohormones and undergo post-translational processing (enzymes cut away extras, possible further cutting after release). They are then held in vesicles which fuse with the cellular membrane and contents gets dumped outside of the cell.
• Cells with type 1 diabetes will not produce C-peptides, whereas cells with type 2 diabetes produce the C-peptide, they do not response.
• Peptide/protein hormones can be secreted by one of two pathways: regulated secretion and constitutive secretion.
• Regulated secretion: stored in vesicles.