Name Answer Key


Introduction to Body Fluids


1. What are the fluids in your body composed of?

 Water and dissolved substances, including electrolytes.


2. How are water and electrolytes ingested?

Through the gastrointestinal (GI) tract


3. Where does absorption into the plasma occur?

In the intestine.


4.  How do fluids circulate?

Within the plasma


5. What is responsible for removing excess water and ions?

The kidneys.


6. Give three functions of water in the body, and explain where each function has its primary effect.

Temperature regulation – skin, through sweating; protective cushion – placenta, in a pregnant woman; lubricant – as saliva, in the mouth. 


7. How does water act as a reactant?

Water molecules add to the bonds between the glucose units in starch and hydrolyze the starch.


8. Explain the activity of water as a solvent.

Water is a polar molecule.  When water dissolves ions, the partial negative charge of oxygen attracts positive ions and the partial positive charge on the hydrogen attracts negative ions.  Most ions are dissolved because of water’s ability to act as a solvent, as are proteins and other solutes.


9.  How do the percentages of water in the body differ between a baby, young, athletic woman, an elderly woman, and a man?

Babies have significantly higher percentages of water in their bodies, with roughly 73%, while a young athletic woman has 50%, and a young male has  60%.  The elderly woman has about 45% of her body as water.


10.  List and describe the three main fluid compartments.

Intracellular fluid (ICF) is the fluid in cells, and is  also known as cytosol.  Extracellular fluid (ECF) is the fluid found outside of cells.  There are 2 major kinds of ECF.  Interstitial fluid surrounds cells.  Plasma is the fluid component of the blood.


11.  Give the percentages of body fluid for intracellular fluids, interstitial fluid, and plasma.

62% of the body fluid is intracellular.  30% is interstitial.  8% of body fluid is plasma. 


12.  What does “body fluid” refer to?

Water (solvent) and dissolved substances (solutes).


13.  What may a typical body fluid contain?

Ions, or electrolytes.


14.  What are proteins considered when in body fluids?

Colloids.  They are huge molecules with negative charges, so they are considered electrolytes.


15.  What are nonelectrolytes?  Give an example.

Uncharged molecules found in body fluids.  An example would be glucose.


16.  True or false: blood cells are a part of the body fluid.



17. What are electrolytes?  Give major electrolytes.

Electrolytes are charged particles dissolved in body fluids.  Na+, K+, Ca2+, Mg2+, Cl-, HCO3-, HPO42-, H2PO4-, SO42-, organic acids, and proteins.


18. Why are the compositions of intracellular and extracellular fluids and electrolyte levels important?

They are required for proper functioning of neurons, muscle cells, and other cells of the body.


19.  What is the major extracellular ion?



20.  Give the major intracellular ion.



21.  Which of the major positive ions is found in the extracellular fluid, but not in the intracellular fluid?



22.  Within a fluid compartment, what is the total charge?



23.  Name and describe 7 major electrolyte functions.

Electrolytes can act as cofactors for enzymes.  They serve to speed up reactions in the body.  Contribute to membrane potentials and are responsible for action potentials in neurons and muscle cells.  Calcium is involved in the secretion and action of hormones and neurotransmitters.  Calcium is also involved in the contraction of muscles, including the heart.  Bicarbonate helps maintain acid/base balance.  The sodium potassium pump serves as secondary active transport, helping maintain concentrations.  Electrolytes and proteins function in osmosis as well.


24.  What is osmosis?

Movement of water across a membrane from the side that has more water (less solute) to the side with less water (more solute).  A solution is said to be isotonic when there are equal amounts of water on both sides – they have the same total concentration of solute particles.


25.  What happens to cells when they are in a hypotonic setting?  A hypertonic setting?

They swell and shrink, respectively.


26.  Define osmotic pressure.

External pressure applied to top of a fluid to stop osmosis from occurring.


27.  What is the relationship between concentration and osmotic pressure?

The more solute particles dissolved in solution, the higher the osmotic pressure.


28.  Why do cells crenate?  What is another word for this?

If a cell is placed in hypotonic solution, water will rush into the cell and cause it to burst, or undergo hemolysis.


Electrolyte Homeostasis


29.  How do electrolytes leave the body?

Through urine, skin, and feces.


30.  What is a major function of sodium?

To control movement of fluids across various compartments.


31.  Which compartments does the cell membrane separate?

Intracellular fluid and interstitial fluid.


32.  Compare the rates of movement between potassium and sodium.

Potassium can diffuse quickly, while sodium diffuses slowly.


33.  How do ions and small solutes move between plasma and interstitial fluid?

Freely, through gaps between endothelial cells.


34.  Why do proteins not leave capillaries?

They are too big.


35.  If some proteins do get through the endothelial cells, how are they handled?

Via the lymph system.


36.  What is oncotic pressure?  What is another term for it?

The osmotic effect of protein in the plasma – also called colloid osmotic pressure.


37.  What two pressure forces oppose one another in bulk flow?

Osmotic effect of pressure and hydrostatic pressure.


38. What is the net result of bulk flow?

Fluid moves into the capillary at the venous end, and moves out of the capillary at the arterial end.


39.  What is edema?

An accumulation of fluid in the interstitial compartment that can occur locally in a specific area, or can be systemic.


40.  Why does it occur?

Usually a result of electrolyte imbalance.  It can be caused by decreased colloid osmotic pressure, increased hydrostatic pressure, increased capillary permeability, or lymphatic obstruction.


41.  What protein is secreted into the plasma by the liver?  What effect does it have?

Plasma.  An osmotic effect called colloid osmotic pressure – maintains blood volume by pulling water into the plasma.


42.  Briefly explain why liver failure causes edema.

Albumin production decreases, so colloid osmotic pressure decreases.  Water moves into the interstitial fluid, causing accumulation in the interstitial compartment.


43.  What effect does this have on blood pressure?  Why?

Blood pressure decreases as blood volume decreases.  Blood flow is also reduced due to the impingement of increased fluid volume in the interstitial compartment.


44.  How does local edema occur?

Injury or inflammation causes permeability of capillaries close to the area of injury, and proteins move more freely into the interstitial compartment.


45.  What is the normal concentration range of sodium in the plasma?

136-145 mEq/L.


46.  What happens in a hypernatremic situation?

Cells will shrink.


47.  What happens in hyponatremic situations?

Cells will swell as water moves into cells.

48.  Give 2 major roles of sodium.

Primary regulator of water movement, and nerve impulse conduction and muscle contraction.


49.  What are the two possible causes of hypernatremia?

Water loss from the plasma without a corresponding loss of sodium, or too much sodium added to the plasma without adding water.


50.  List symptoms of hypernatremia.

Non-specific signs of CNS dysfunction including confusion, lethargy, seizures, and possibly death.


51.  Why do these occur?

Neurons shrink.


52.  What regulates sodium levels in the plasma?

The kidney – more specifically, sodium is filtered at the glomerulus.


52.  Where is sodium resorbed?  What percent is recovered?

85-90% is reabsorbed at the PCT and Loop of Henle.


53.  What happens in absence of aldosterone?  What does aldosterone do?

Remaining sodium will remain in filtrate and end up in urine.  Aldosterone causes collection of sodium in the DCT and collecting ducts.


54.  What other ion does aldosterone affect?



55.  What can cause a potassium deficiency?

Diuretics can do this by promoting urine formation.


56.  What is one major role of potassium in the body?

Responsible for intracellular fluid volume through osmosis.


57.  What would an increase in potassium levels in the ECF do to cells?

Cause them to shrink.


58.  How does potassium aid in acid-base balance?

As hydronium ions move in one direction, potassium moves in the opposite direction to counterbalance the charge movement and maintain electroneutrality.


59.  What can occur in hypercalcemia?

Dysrhythmias – the heart can stop if the calcium levels get too high.


60.  What happens in hypocalcemia?

Muscle spasms can occur.  When it gets very low, a person can go into tetanus.  Breathing will stop when this affects the diaphragm.


61.  Where is most calcium found?

About 99% is in bone as a salt, and 1% is dissolved in the extracellular fliuds.


63.  What gland regulates calcium levels via calcitonin?

The thyroid gland.


62.  What is the target tissue of calcitonin?



63.  How does calcitonin work?  What is its ultimate effect? [May need to turn up the volume here.]

Inhibits osteoclasts, which break down bone, and stimulates osteoblasts, which stimulate bone formation.  This  stimulates the uptake of calcium into the bone matrix.  Osteocytes maintain bone tissue.  Net effect is a decrease in calcium concentrations.


64.  What gland senses low calcium concentrations and works to rectify the levels?  What hormone does it produce?

The parathyroid, via PTH (parathyroid hormone).


65.  Name two target tissues of this hormone.

Bone and the kidney.


66.  How does it work in the target tissues?

Increases uptake of calcium and inhibits phosphate absoroption (causing greater phosphate exertion in urine.)  It also promotes activity of dietary Vitamin D into the hormone calcitrol in the kidney.  Calcium increases the rates of calcium absorption from the GI tract.


67.  What is the net effect of PTH?

To increase calcium levels.


Water Homeostasis


68.  How much water does the body contain?

About 40 liters.


69.  When does hypervolemia occur?

When too much water and solute are taken in at the same time.  Plasma osmolarity may remain normal although ECF increases.


70.  Explain hypovolemia.

It occurs when water and solute are lost concurrently.  This usually indicates loss of plasma volume.  Plasma osmolarity remains normal.


71.  Explain overhydration.


72.  Explain dehydration.