Mrs. Jackie

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Homeostasis and excretion

• Mrs. Jackie

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Homeostasis include

• Maintaining a constant interval environment
  despite possible fluctuations in the external
  environment
• Include blood pH
• Carbon dioxide and glucose concentration
• Blood glucose
• Body temperature
• Water balance

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An example of homeostasis in a non biological
system
Detected by thermostat
Heater switched off
Temperature rises
Temperature falls
Desired temperature of bath water
Temperature rises
Temperature falls
Detected by thermostat
Heater switched on
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Examples of homeostasis

• Oxygen and carbon dioxide concentrations
• Maintain in balance due to chemodetectors
• Blood glucose
• Body temperature
• Water balance
• Blood PH
• Main within narrow limits around 7.4
• Contain buffers to minimize fluctuations in pH

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Homeostasis involves monitoring levels of
variables and correcting changes in levels by
negative feedback mechanisms

• Negative feedback
• The control of a process by the result or effect
  of the process in such a way that an increase in
  the results or effects is always reversed.
• Requires
• Sensors require to pass the information to a
  center which knows the desire value and compares
  the current situation to the norm. If the values
  are not the same the center activates a
  mechanisms to bring the current value to normal
  levels
• The center will turn off the mechanisms once it
  reaches the norm

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Nervous and endocrine systems are both involved
in homeostasis

• Thermoregulation is done via nerves
• Blood glucose levels are maintain via hormones

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Nervous system consists of the central nervous
system and peripheral nerves composed of neurons

• Central nervous system (CNS)
• Brain
• Spinal chord
• Peripheral nerves
• Everything else
• Made of neurons
• Transport messages in the form of electrical
  impulses to specific sites

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Control of body temperature

• Thermoregulation
• Body of mammals/birds has thermo-receptors in the
  skin and in the heat center in the brain for
  monitoring temperature changes in the environment
  as well as changes in the blood temperature
• IF the organisms is to hot
• Vasodilatation- blood vessels in the skin become
  wider which increases the flow of blood to the
  skin. Skin becomes warmer which increases heat
  loss to the environment.
• Sweating- evaporation of fluid from the skin
  change of phase(liquid to gas) , requires energy
  which is taken from the body.
• Decreased metabolism- any reaction produces heat
  as a by product
• Behavior adaptations birds-bating, desert
  rodent- retreat into humid burrows, dogs- dig
  holes and allow cool earth to absorb heat from
  belly

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Vasodilation
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Vasoconstriction
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Control of body temperature

• If the organism is too cold
• Vasoconstriction- blood vessels in the skin
  contract which decreases the flow of blood to the
  skin as a result the skin becomes colder
  reducing the heat loss to the environment.
• Shivering- any reaction will produce heat as a by
  product. Muscular contraction produce a lot of
  heat
• Increased metabolism increase production of heat
• Fluffing of hair or feathers increases the
  thickness of the insulating layer of air.
• Thick layer of brown fat or of blubber this is a
  good insulator and reduces radiation and
  convection and generates heat
• Special structure hair (polar bears) which
  absorbs UV light

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Endocrine system

• Consist of glands which release hormones that are
  transported in the blood
• Endocrine glands are ductless- they do not
  release their product into a duct but to the
  blood
• As the hormones passes cells, only those with
  special receptors will react to the presence of
  the hormone- TARGET CELLS

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Control of glucose concentration in blood

• Pancreas is both an exocrine and endocrine gland
• Exocrine cells in the pancreas produce digestive
  enzymes which are released into the small
  intestine via the pancreatic duct.
• Endocrine cells are clustered together in groups
  called the Islets of Langerhans
• Produce hormones which help in regulating the
  blood glucose levels.

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Control of blood glucose

• Islet of Langerhans cells in the pancreas have
  chemoreceptors which are sensitive to levels of
  glucose
• Levels of glucose can go up after a meal and down
  after exercise
• IF glucose levels are to low (see figure 1 page
  138)
• The alpha cells in the islets in the pancreas
  secrete glucagon
• Glucagon- protein hormone whose main target is
  the liver
• Hepatocytes- cells of the liver will respond to
  the presence of glucagon by converting glycogen
  to glucose and releasing it to the blood. Amino
  acids and glycerol are also converted to glucose

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Control of blood glucose

• If blood glucose levels are to high
• Beta cells in the islets of langerhans in the
  pancreas secrete insulin
• Insulin is a protein hormone travel to all parts
  of the body. Its presence will make the muscle
  cells absorbs more glucose
• The muscle cells and hepatocytes converte glucose
  into glycogen
• In adipose tissue glucose is converted into fat
  in the presence of the hormone insulin.
• See diagram on figure 2 page 139

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Excretion
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Excretion

• Removal from an organism of the toxic waste
  products of metabolism

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Role of the kidney

• Main functions
• Maintenance of the water balance in the body and
  the removal of nitrogenous metabolic waste via
  excretion.
• Two basic process
• Ultrafiltration- some components of the blood
  flowing through the kidney are pushed out of the
  blood vessels into kidney tubules. Only plasma
  and small particles can be filtered. Large
  proteins and cells stay in the blood
• Reabsoption- substances useful for the body such
  as glucose and amino acids are reabsorbed and
  send back to the blood. The amount of water and
  salts reabsorbed is regulated to maintain
  homeostasis.
• Unwanted substances become urine and is excreted