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71Homeostasisandcontrolsys74Urinarysys

71Homeostasisandcontrolsys74Urinarysys - Unit 3 Homeostasis...

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Unit 3. Homeostasis   7.1. Homeostasis and Control Systems (pp. 334-336)    Homeostasis:   “process to keep the internal environment constant despite changes in the      external environment”   aka.  dynamic equilibrium:   condition remaining stable within fluctuating limits   e.g.s.  blood glucose levels @ 0.1%     (low - exercising, high - eating)      body temperature   @ 37 0 C     (low - sleeping,      high - exercising)      systolic blood pressure @ 120 mmHg  (low - sleeping,     high – exercising)      blood pH @ 7.35     (low – eating,   high – exercising)   body maintains a constant balance by many monitored adjustments   three components:  Monitor  (sensors)    - sends a signal (chemical/hormones) to the    in organ                coordinating centre when organ operates         outside limits   Coordinating centre - brain Regulator    - restores the balance Homeostasis and Feedback     negative feedback:   process by which a mechanism is activated to restore conditions to their original state  (Fig. 3, p. 336)   * designed to resist change:  changes trigger the coordinating centre to counteract       any further change in the same direction      prevent any small changes from becoming too large      positive feedback:   process by which a small effect is amplified   * designed to reinforce the change:  moves the variable away from the steady state   - e.g.   birth process:      decrease            small           increase         larger               expel             decrease progesterone     contractions   oxytocin contractions          newborn       oxytocin                (no contractions) 7.4. The Urinary System (pp. 346-348)   aorta   renal arteries   kidneys
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  Kidneys:   organs that filter wastes from blood   - can hold 25% of body’s blood at a time        Urine flow:   kidneys      (Fig. 1, p. 346) ureter (tubes)     bladder   urinary sphincter urethra (tube)          outside body       Three parts:   Cortex   - outer connective tissue     (Fig. 1, p. 346) Medulla - midlayer Pelvis - inner hollow chambers, joining kidney with uterer tubes Nephrons:   tubules within kidneys  (Fig. 2, p. 347)      Cortex        *  site of filtration      *  high pressure     renal     afferent            glomerulus         efferent   * peritubular   renal     artery    arterioles        (capillary bed)         arterioles      capillaries  venule                       surrounded by             * 
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