homeostatsis

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  • homeostasis + cell physiology
    • homeostasis= the adjustment of internal conditions to maintain a near constant internal enviroment
      • negitive feedback loops
        • decrease in conditions due to an increased stimuli or visa versa
      • postive feedback
        • the chnage in conditions in the same direction as the stimuli
          • eg birth and oxytocin
      • feedback loops
        • sensor
        • sensory neurone
        • comparator
        • motor neurone
        • effector
        • failure in any of these can lead to disease
    • body fluids
      • ecf -14l
      • intracellular 28l
      • intersital 10.2
      • plasma 3-5l
      • distribution of Ions
        • high K+ and A- in intracellular compartments
        • Na and CL higher in extra cellular space
      • osmosis = high water pot to low water pot
        • osmotic pressure - movement of water mols can excert pressure on walls
          • eg cap walls - proteins accumulate in ec space causing odema
            • Oncotic pressure, or colloid osmotic-pressure, is a form of osmotic pressure induced by the proteins, notably albumin, in a blood vessel's plasma
        • Osmolarity: • The total number of dissolved particles (ions, molecules or mix of both) per litre of solution.  
        • Osmolality: • The total number of dissolved particles (ions, molecules or mix of both) per Kg of water
    • Action potentials
      • Na and K+ are asymetrically distributed across the membrane - by NA/K ATPase
        • K is greater inside cells - this means it tends to diffuse out = neg charged membrane
        • if K outside were to decrease the less would diffuse out therefore membrane would be more positive
      • VG channels = allow K out and NA in - only open when the membrane is depolaried enough
      • ligand gated = allow NA or K in/out when ligand binds to surface
        • are cation-selective (mainly Na+ flow into the cell). When activated cause depolarisation and make the cell more excitable
        • excitable. • Some ligand-gated channels are anionselective (mainly Cl- flow into the cell). These channels when activated cause hyperpolarisation
      • propergation of an AP
        • myelination- increases conduction velocity as less SA needs to be depolarised
          • salitory conduction
    • nervous system
      • somatic
        • vountary action
        • one neurone
      • autonomic
        • non-voluntray
        • sympathetic
          • pre release acetylcholine binds to nicotinic
          • post release noradrenaline bind to andrgenic
          • adreanal medulla
            • relases catacholine
            • innervated by preganglionic neurones.
        • parasympathetic
          • 'rest and digest'
          • pre and post ganglionic neurones = acetylcholine
          • pre = nicotinic. post = murengic
    • muscles
      • tension length relationships
        • no shortening but increase in passive tension = active twitch
          • isometric
        • starlings law in heart = variation of lengths
        • The functional contractile unit of a striated muscle fibre • The region of the myofibril between two successive Z discs •Composed of myofilaments made up of contractile proteins
          • during contration = migrated to m disk
      • motor unit = the mucles and the nerve its innervated with
      • NM junction
        • ca = faclitates relase of ACH which binds to nitcotinc receptors- ca relased from SR = binds to tropomyosin

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