Endocrine System (BIOLOGY)

A communication system that uses hormones as its signalling molecules- in the bloodstream
1. Hormones are chemical messengers- carry signal from endocrine glands to target cells
  1. Amino-acid derived
    1. E.g. adrenaline, insulin & glycagon
    2. Polar- not soluble in the phospholipid bilayer of their target cells
      1. Binds to complementary receptors on target cell
        Uses 1st + 2nd messengers
        1st messenger= non-steroid hormone
        2nd messenger= cAMP
        Activates G protein
        Activates adenyl cyclase
        converts ATP to cAMP
        cAMP brings about response in the cell
        e.g. activation of enzyme, opening a channel protein or protein synthesis
  2. Steroid
    1. e.g. oestrogen + testosterone
    2. Non-polar- soluble in the phospholipid bilayer
      1. Diffuses into target cell + has a direct effect on DNA in nucleus
        e.g. activation of an enzyme, opening channel protein or protein synthesis
2. Endocrine glands
  1. Ductless glands, that manufacture and release hormones directly into the bloodstream
  2. Exocrine glands- produces + secrete other substances into ducts (e.g. pancreatic duct, salivary duct)
Adrenal Gland
1. A pair of glands, above the kidneys
  1. Manufacture + secrete adrenaline (+ other hormones)
2. Adrenal Cortex
  1. 3 distinct layers of cells
    1. ZONA GLOMERULOSA
    2. ZONA FASCICULATA
    3. ZONA RETICULARIS
  2. uses cholesterol to produce a range of hormones
    1. So steroid based + can have a direct effect on DNA of target cell
3. Cortex + Medulla: well supplied w/blood to secrete hormones into
4. Adrenal Medulla
  1. Manufactures and secretes adrenaline (+ nonadrenaline) into the bloodstream
    1. Adrenaline is an amino acid derived hormone- so polar
      1. It uses a 1st + 2nd messenger; that brings about a response in the cell
    2. The effects of adrenaline are widespread + prepare the body for activity
      1. Pupil dilation, increased heart + breathing rate, decreased digestion, vasoconstriction- raises blood pressure
The Pancreas
1. Small organ below the stomach
  1. Endocrine Function
    1. Islet of Langerhans contain alpha and beta cells
      1. If beta & alpha cells detect blood glucose levels as too high...
        Beta cells release insulin
        target cells are liver, muscle and brain cells
        look at 'ACTIONS OF INSULIN'
        look at 'RELEASE OF INSULIN FROM BETA CELLS'
      2. Is beta and alpha cells detect blood glucose levels as too low...
        Alpha cells release glucagon
        target cells are hepatocytes
        look at 'ACTIONS OF GLUCAGON'
  2. Exocrine Function
    1. Manufactures + secretes digestive juices into the small intestine via, the pancreatic duct
      1. Exocrine cells are grouped into...
        acini
        Acini are grouped into small lobules, separated by connective tissue
        Acini cells secrete digestive juices into the tiny tubules in the centre
        Tubules join to form intralobular ducts, which make up the pancreatic duct
        Pancreatic duct- carries digestive enzymes into the small intestine
      2. Digestive juices contain the enzymes...
        Trypsinogen
        inactive protease converts into trypsin
        Lipases
        Amylases
        Contains sodium hydrogencarbonate (alkali)

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Endocrine System (BIOLOGY)

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