A2 Unit BY4: Metabolism, Microbiology and Homeostasis

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Topic 4.6 CONTROL SYSTEMS CO-ORDINATE AND REGULATE PROCESSES – Page 1

From the syllabus:

l. Control Systems Coordinate and Regulate Processes

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  1. The term homeostasis is used to describe the mechanisms by which a constant internal environment is achieved.

  1. Understand why homeostasis is important and appreciate that all homeostatic processes include a detector, coordinator and effector.

  1. Most biological systems operate a negative feedback system.

  1. Osmoregulation is the control of water content and solute composition of body fluids.

  1. Unlike the digestive products of carbohydrates and fats, the amino acids cannot be stored. Surplus amino acids, not used for the synthesis of proteins and other nitrogen molecules, are deaminated in the liver.

  1. Label a diagram of a mammalian urinary systems; renal artery, renal vein, kidney, ureter, bladder and urethra.

  1. Label the gross structure of the liver (L.S.) to include cortex, medulla and pelvis and include the position of a nephron.

  1. Draw and label the structure of a single nephron; afferent arteriole, efferent arteriole, glomerulus, Bowman’s capsule, proximal convoluted tubule, loop of Henlé, distal convoluted tubule and collecting duct.

  1. Ultrafiltration is filtration under pressure, which separates small soluble molecules from the plasma.

  1. The structure of the glomerulus and capsule allows ultrafiltration. The basement membrane of the capillary forms a selective barrier between the blood and the nephron and it acts as a molecular sieve.

  1. A high filtration pressure is achieved in the glomerulus due to a difference in diameter between afferent and efferent arterioles and high blood pressure in the renal artery.

  1. Selective reabsorption of glucose and Na+ (active) and Cl- and water (passive) in the proximal convoluted tubule.

  1. Relate the structure of a proximal convoluted tubule cell to its function of reabsorption: large surface area due to microvilli and basal channels, numerous mitochondria, closeness of blood capillaries.

  1. The loop of Henlé allows a counter current multiplier system to operate.

  1. Na+ ions and Cl- ions are actively pumped into the descending limb into the tissue fluid of the medulla and diffuse into the descending limb. The ascending limb is relatively impermeable to water while the descending limb is permeable. Water leaves the filtrate osmotically and the contents of the descending limb become more concentrated. The ascending limb receives a filtrate rich in Na+ and Cl- ions.

  1. The maximum concentration occurs at the tip of the loop of Henlé, both inside and outside in the extracellular fluid.

  1. The length of the loop is related to the environment of mammals.

  1. The distal convoluted tubule and the collecting duct have restricted permeability, which is subject to hormonal control.

  1. Further water absorption occurs through the walls of the collecting duct.

  1. ADH makes walls of the duct permeable so that water is reabsorbed and the urine has a concentration of the tissues near the bottom of the loop, that is, hypertonic to the general body fluids.

  1. The part of the osmoregulatory system which regulates water content; detector-hypothalamus, coordinator – posterior lobe of the pituitary gland (ADH), effector – collecting ducts of kidney.

  1. Understand the mechanism of osmoregulation through ADH secretion to show how negative feedback restores the normal osmotic concentration if blood is diluted or becomes more concentrated.

  1. The environment in which an animal lives plays a part in the nitrogenous waste produced and different animals deal with its disposal in different ways.

  1. Aquatic animals produce ammonia, birds and reptiles produce uric acids and mammals produce urea.