Water, Membranes and Homeostasis

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Water, Membranes and Homeostasis
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Solute Concentration of Cells
0.9 NaCl
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Hypertonic Solution
3 NaCl
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Cells Crenate in a Hypertonic Solution
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Hypotonic Solution
0.5 NaCl
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Cells in a Hypotonic Solution Swell and May Lyse
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Isotonic Solution
0.9 NaCl
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Isotonic Solutions

• Have the same amount of solutes as body cells
• 300 Milliosmoles
• 0.9 NaCl
• 5 Glucose

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Isotonic IV Solutions

• Normal Saline or Physiological Saline
• 0.9 NaCl
• D5W (Dextrose 5 in Water)
• 5 Glucose
• Lactated Ringers
• Glucose, lactic acid, salt

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Tonicity
Hypotonic
Water
Hypertonic
Sea Water
D5 1/2 NS
Hypertonic
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Which Way Will Fluid Move?
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Fluid Balance

• Fluid leaving body Fluid entering body
• Right amount of fluid in each compartment

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Electrolyte Balance

• Having the right concentration of various ions in
  the body
• Sodium
• Potassium Calcium
• Magnesium

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Fluids and Electrolytes

• Electrolytes attract fluids by osmosis
• Loss of fluids results in a loss of electrolytes
• IV therapy is often needed to restore fluid
  balance, electrolyte balance or both

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Organs that Regulate Fluid and Electrolyte Balance

• Brain
• Adrenal glands
• Kidneys

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Hypothalamus of the Brain
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Adrenal Gland
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Hypothalamus Kidneys
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Application Problem 1

• Richard works as a roofer. He is in the hot sun
  many hours a day. As a result he loses water by
  perspiration. How does his body maintain
  homeostasis?

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Answer to Problem 1

• The hypothalamus will make more ADH causing the
  kidneys to produce less urine.
• His hypothalamus will make him thirsty. This will
  cause him to drink a lot of liquids

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Application Problem 2

• Dawn urinates many times during the day but is
  able to sleep all night without the need to
  urinate. How do you explain this?

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Answer to Problem 2

• The kidneys produce less urine when you are
  asleep because the hypothalamus secretes more ADH
  during sleep.

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Application Problem 3

• Claudia has had diarrhea for the past two weeks.
  Her potassium level is only 25 of the normal
  value. Why is her potassium so low?

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Answer to Problem 3

• Claudia has lost a lot of fluid and with this
  fluid she has lost potassium.
• She will need to be given potassium immediately
  or her heart may develop arrhythmias and stop
  beating.

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Application Problem 4

• Melissa has been unable to eat anything following
  her surgery. Her doctor has ordered an IV of
  D5W. Why did he do this?

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Answer to Problem 4

• The fluid in the D5W will replace fluid she will
  naturally lose.
• The sugar will provide an energy source for her
  body.

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Application Problem 5

• Dr. Quack has told Sally she needs to flush the
  poisons out of her body. He has been giving her
  an IV of distilled water twice a week. What are
  the risks to Sally of this treatment?

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Answer to Problem 5

• Distilled water is hypotonic to blood cells.
• Many of the red blood cells will lyse creating a
  burden on the liver to cleanse the blood.
• Lack of blood cells could make Sally anemic.

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Application Problem 6

• Mike has had a severe head trauma. There is
  swelling on his brain. His doctor has ordered an
  IV of 20 glucose. Why did he do this?

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Answer to Problem 6

• 20 glucose is hypertonic.
• It will attract fluid from the brain into the
  blood.

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Application Problem 7

• Paul has a history of hypertension. His doctor
  has placed Paul on a low salt diet. What is the
  rationale for the low salt diet?

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Answer to Problem 7

• Salt will make Pauls blood hypertonic.
• Fluid will move by osmosis into his blood.
• Increased blood volume will increase blood
  pressure.

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Ion

• Atom or molecule with a charge

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Solution

• A mixture of two or more substances
• Salt water
• salt
• water

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Solvent

• A substance that dissolves solutes in a solution
• Water

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Solute

• Substance that dissolves in a solution
• Salt is a solute in salt water
• Sugar is a solute in sugar water

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Turgor

• Tightness of the skin or a membrane
• Poor skin turgor is a sign of dehydration

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Equilibrium

• When something is balanced with its environment
• A cell in a solution with the same concentration
  of solutes as the cell

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Cell in Equilibrium
0.9 NaCl
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Dehydration

• Condition of excessive water loss

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Osmotic Pressure

• Measure of the tendency of a solution to attract
  water by osmosis
• Osmotic pressure increases when the difference in
  solute concentration between two solutions
  increases

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Which Solution has the Greater Osmotic Pressure?
1 NaCl
3 NaCl
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Milliosmole

• Unit of measurement of all the solutes in a
  solution
• Blood has a concentration of 300 milliosomoles

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Edema

• The accumulation of excess interstitial fluid in
  interstitial spaces (between cells)
• Causes swelling
• May be caused by increased hydrostatic pressure
  in capillaries
• congestive heart failure
• hypertension
• pregnancy

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The End