The Endocrine System

• ENDOCRINE GLAND

  • gland that produces hormones directly into the bloodstream
  • hormones are signalling molecules that enable systems of the body to communicate with each other.
  • this is done by the hormones travelling in general circulation in the bloodstream until it affects the target tissue
  • does not have a duct. ductless. the hormones secrete directly into the bloodstream
• EXOCRINE GLAND

  • gland that secretes through a duct
• Endocrine system


  The endocrine system is a complex network of glands that produce and secrete a variety of chemical messengers known as hormones. It uses hormones to control and regulate distant organs. Hormones travel in general circulation in the bloodstream
• Hormones


  • Slower responses
  • Longer-lasting effects
  • Less specific (since hormones reach every cell in the body but only some cells actually respond)
  • chemical messengers
  • after exerting their effect, they are broken down and excreted
  • influence the growth and development of body parts, cellular metabolism, reproduction, and behaviour
  • can be amino acids, peptides,, proteins, fatty acids of steroids
  • maintains homeostasis, a constant internal environment, within narrow limits despite changes to the external environment.
  • 3 types
• Endocrine vs Nervous System

  Messages are transmitted through nervous tissue as an action potential or electrical impulse. thus, nervous impulses are lightning-fast, very specific (in terms of what tissue they stimulate), and their effects are short-lived.

  in contrast, hormones travel in general circulation in the bloodstream. As a result, the responses they produce in tissue are slower, longer-lasting and less specific (since hormones reach every cell in the body but only some cells actually respond).
• Main endocrine glands- brain

  • Hypothalamus
  • Pineal gland
  • Pituitary gland (master gland)
• Hypothalamus produces...

  • Antidiuretic hormone (ADH)
  • regulates the reabsorption of water in the collecting ducts of the nephrons. they will make more aquaporins.
  • if the level of water in your body is too low, the hypothalamus will produce more ADH. it travels all around the body but only the nephrons will respond. more aquaporins are made, more water gets reabsorbed, and less is wasted.
  • Oxytocin
  • important reproductive hormone
  • Thyrotropin-releasing hormone
  • stimulates the pituitary gland to release more thyroid-stimulating hormones (TSH)
• Pineal gland


  Produces melatonin, which regulates aspects of the circadian rhythm
• Pituitary gland produces...

  • Growth hormone (GH)
  • controls the body's growth and structure
  • Adrenocorticotrophic hormone (ACTH)
  • regulates the release of cortisol from adrenal glands
  • Thyroid-stimulating hormones (TSH)
  • regulates the release of thyroid hormones
  • Luteinising hormones (LH)
  • regulates the release of sex hormones from gonads
  • Prolactin (PRL)
  • Stimulates milk production
• Main endocrine glands (cont)

  • thyroid gland
  • parathyroid glands
  • thymus gland
  • adrenal glands
  • gonads
  • ovaries
  • testes
  • pancreas
• Thyroid gland produces...

  • thyroxine
  • regulates metabolism in the body. increases metabolic rate by stimulating all cells of the body to convert glucose into ATP more quickly
  • calcitonin
  • reduces blood calcium levels
• Parathyroid gland produces...

  • parathyroid hormone (PTH)
  • increases blood calcium levels
  • on the other side of the thyroid gland
• Thymus gland produces...

  • thymosin
  • stimulates the production of T lymphocytes
• Adrenal glands produces...

  • adrenaline
  • promotes 'flight' or 'fight' responses
  • cortisol
  • released in response to stress, increases blood sugar levels, suppresses the immune system, and aids in the metabolism of fats, proteins and carbohydrates.
• Ovaries produce...

  • oestrogen
  • the primary female sex hormone
  • progesterone
  • plays important roles in the menstrual cycle, pregnancy and other functions
• Testes produce...

  • testosterone
  • primary male sex hormone
• Pancreas produce...

  • insulin
  • stimulates the liver, skeletal muscles and most body cells to take glucose from the blood and store it as glycogen
  • secreted by specialised beta cells
  • glucagon
  • stimulates the liver and skeletal muscles to convert glycogen to glucose and release it into the blood
  • secreted by specialised alpha cells
• 2 main kinds of hormones

  • Lipid Hormones (steroids)
  • Amino acid-based hormones
• Lipid Hormones (steroids)

  • are derived from cholesterol.
  • hydrophobic but lipid soluble, which means they can easily diffuse across a phospholipid bilayer (they can go straight into a cell)
  • examples: testosterone, progesterone, cortisol

  ​
• Amino acid-based hormones

  • hydrophilic and cannot diffuse through a phospholipid bilayer (polar and is repelled by the nonpolar fatty acid tails)
  • usually have to bring to a receptor outside the cell
  • divided into 2 main groups
  • Amine hormones - derived from tyrosine
  • Peptide (and protein) hormones - a polymer of amino acids.
• Amine Hormones

  • any of a class of chemical compounds that contain a single amino acid that has been modified into a hormone
  • adrenaline, thyroxine
• Peptide and protein hormones

  • the difference between a peptide and a polypeptide is length. peptide hormones usually have less than 50 amino acids whereas protein hormones (polypeptides) usually have more than 100 amino acids
  • ADH (29 aa) is a peptide hormone, Insulin (51 aa) is a peptide hormone, FSH (111 aa) is a protein hormone.
• ENDOCRINE SIGNAL TRANSDUCTION - how hormones communicate

  • AMINO ACID BASED
  • a signalling molecule from outside the cell, coming from the brain, travels in the bloodstream. it binds to an extracellular receptor (complementary in shape and size). It sets off a cascade of molecular changes along the membrane, producing another signalling molecule inside the cell. Initiates a response
  • LIPID-BASED
  • able to diffuse through the phospholipid bilayer and thus can bind directly to an intracellular receptor.
• ENDOCRINE SIGNAL TRANSDUCTION - defintion

  • transduction - converting a signal from one form to another
• TRANSDUCTION EXAMPLE (lipid)

  • testosterone (a lipid-based hormone) can diffuse straight through the plasma membrane (hydrophobic and non-polar). it does not need to bind to a transmembrane protein such as GPCR
• HOW HORMONES WORK

  • although hormones travel in general circulation in the body and so are less specific than nerve impulses, they are still specific to particular cell types. only some cells will respond to a particular hormone. Which cells respond and how they respond depends on the receptor involved and the signal transduction pathway initiated by it.
  • one cell can have many different receptors, which bind to a specific hormone.
  • Cells a and b may share the same receptors, thus, they transduce the signal carried by a hormone
  • however, a hormone can have a different effect on each cell.
• Types of Hormones

  • autocrine
  • cell releases a hormone which acts on itself
  • paracrine
  • cell releases a hormone which acts on a neighbouring cell
  • endocrine
  • acts on cells further away
• Hypothalamus

  • coordinates the nervous system and endocrine system
  • constantly surveying the conditions of an organism's internal environment. regulates heartbeat, body temperature and water balance
  • secretes releasing hormones, which regulate the hormones of the anterior pituitary
  • its other hormones (eg ADH) are transported to, stored in, and released from the posterior pituitary
• Pituitary gland

  • responds to information from the hypothalamus by secreting a range of hormones that will act on other endocrine glands to restore balance if conditions change
  • 2 lobes
  • Anterior pituitary
  • prl, gh, acth, tsh, lh
  • actually secretes hormones, but it's regulated by the hypothalamus
  • Posterior pituitary
  • oxytocin, adh
  • doesn't secrete hormones. these are the stored hormones from the hypothalamus
• Pancreas

  • made from 2 types of tissue
  • exocrine tissue
  • responsible for the production and release of pancreatic juice into the duodenum via the pancreatic duct to aid digestion
  • endocrine tissue
  • the islets of langerhans. responsible for the production and release of the protein-based hormones insulin and glucagon into the bloodstream.