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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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Topic
1. The term homeostasis is used to describe the
mechanisms by which a constant internal environment
is achieved.
2. Understand why homeostasis is important and
appreciate that all homeostatic processes include a
detector, coordinator and effector.
3. Most biological systems operate a negative feedback
system.
4. Osmoregulation is the control of water content and
solute composition of body fluids.
5. 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.
6. Label a diagram of a mammalian urinary systems; renal
artery, renal vein, kidney, ureter, bladder and urethra.
7. Label the gross structure of the liver (L.S.) to include
cortex, medulla and pelvis and include the position of a
nephron.
8. 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.
9. Ultrafiltration is filtration under pressure, which
separates small soluble molecules from the plasma.
10.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.
11.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.
12.Selective reabsorption of glucose and Na+ (active) and
Cl- and water (passive) in the proximal convoluted
tubule.
13.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.
14.The loop of Henlé allows a counter current multiplier
system to operate.
15.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
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concentrated. The ascending limb receives a filtrate rich
in Na+ and Cl- ions.
16.The maximum concentration occurs at the tip of the
loop of Henlé, both inside and outside in the
extracellular fluid.
17.The length of the loop is related to the environment of
mammals.
18.The distal convoluted tubule and the collecting duct
have restricted permeability, which is subject to
hormonal control.
19.Further water absorption occurs through the walls of
the collecting duct.
20.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.
21.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.
22.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.
23.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.
24.Aquatic animals produce ammonia, birds and reptiles
produce uric acids and mammals produce urea.