Biology B4


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Homeostasis is keeping a steady state inside the body

  • This involves:
  • Keeping a constant body temperature
  • keeping the correct levels of water and salt
  • controlling the amount of nutirents such as glucose
  • breathing in enough oxygen for respiration
  • removing waste products from the body
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Control Systems

This is done by control systems. all control systems, both artificial and in the body have:

  • A receptor, which detects the stimuli (change)
  • A processing center, which receives the information
  • an effector which produces an automatic response

An incubator is an artificial control system. it has a thermostat, which detects the temperature (receptor). when the temperature falls to low the heater is turned off (effector)

Negative feedback is a control system where any change is reversed. for example thermostats work by negative feedback; if the temperature drops too low it turns the heater on, if it gets too hot it turns the heater off.

Antagonistic effectors have opposite effects, for example accelerator and breaks on a car. this makes the response more sensitive.

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  • Enzymes are catalysts; They speed up chemical reactions.
  • They are proteins; Proteins are made up of chains of amino acids.
  • Enzymes have an active site, where the reaction takes place, which only matches a particular molecule. this is called lock-and-key model.
  • Important because reactions/digestion would take too long without them
  • 37 degrees Celsius is the optimum temperature for enzymes in the body, if the temperature is too high or too low they do not work efficiently
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  • Your body gains or loses heat according to your environment
  • More heat is lost at your extremities.
  • When cold blood flow is reduced to these areas and is kept in the core of your body to keep you warmer
  • Heat is also gained from respiration; Glucose + oxygen -> carbon dioxide + water (+energy)
  • Your body temperature is lowest at night because you are not moving, and so do not need to respire as quickly.
  • The HYPOTHALAMUS is the processing center in the brain for sleep,water balance body temperature.
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Warming Up

  • Shivering warms up the body by making muscle cells contract quickly, thus respiring faster and producing more energy. It is an automatic response.
  • Hairs stand up on end to trap air, which forms an insulating layer between your body and the environment
  • vasoconstriction is when the muscles in the blood vessel walls contract making the vessels near the skin narrower reducing the amount of heat lost to the environment.
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Cooling Down

  • Sweat glands produce more sweat when we are hot because it cools us down when it evaporates off the skin.
  • water lost through sweating must be replaced otherwise it could lead to dehydration. in humid climates, sweat does not evaporate, so it doesn't help cool you down.
  • Vasodilation is when the blood vessels near the skin fill with blood so more heat energy is transferred to the environment
  • Vasodilation and vasoconstriction are antagonistic effectors
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Heat Stroke

  • Heat stroke occurs when your body cannot lose heat fast enough
  • Core body temperatures of above 42 degrees Celsius effect the hypothalamus, this stops you from sweating.
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Hypothermia occurs when body temperature drops below 35 degrees Celsius.

If core body temperature goes below 30 degrees the patient will go into a coma, and breathing of the patient stops at approximately 28 degrees.

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  • Diffusion is the overall movement of particles from high concentration to low concentration.
  • This occurs because molecules in gases and liquids move about randomly and spread out.
  • diffusion is a passive process; it does not need energy. it occurs through a permeable membrane.
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  • Partially permeable membranes only allow certain molecules to pass through them but not other molecules
  • Osmosis occurs across a partially permeable membrane. This is the overall movement of water molecules from a dilute to a concentrated solution.
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Active transport

When cells need to take in molecules where there is a higher concentration in the cell than outside the cell they use active transport. Glucose is moved into cells using this method.

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Water Balance

The control system for water works by negative feedback

  • Receptors in the hypothalamus ( in the brain ) detect changes in salt concentrations
  • The processing center is the hypothalamus, which triggers the release of ADH from the pituitary gland if salt concentrations are too high.
  • ADH travels to the kidney tubules ( the effectors ), and more water is reabsorbed.
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Kidneys control water balance and excretion.

Small molecules such as water, glucose, ions of salt and urea, are filtered out of the blood as it passes through the kidneys. useful molecules are reabsorbed by diffusion and active transport including all glucose, some water and some salt.

ADH produced by the pituitary gland controls the amount of water that is reabsorbed. waste molecules make urine, which is stored in the bladder for excretion.

The liver cells make urea, which forms part of urine, when they break down amino acids your body cannot use. Urea is poisonous, except in low concentrations, so it is transported to the kidneys via the blood where it is filtered out.

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On a hot day, less urine is produced, because water is needed due to sweating used to cool the body down. salt concentrations of the blood effect the amount of water reabsorbed. also, caffeine and alcohol intake increases the amount of water in the urine by suppressing the production of ADH, causing dehydration, whereas ecstasy reduces the volume of urine a person makes, making their water levels dangerously high.

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