Fluids Flashcards
What percent of the body is made up of water?
60% in men, 50% in women. The difference is that men have more muscle and muscle contains more water.
Where is the intracellular fluid? Extracellular fluid?
Intercellular fluids are the fluids inside cells. Extracellular fluids are found in two places: blood plasma and the fluids that bathe all body cells (interstitial fluids).
Extracellular fluid is found in two places. What are they?
see above.
Define the term electrolyte:
Nonelectrolyte: Electrolytes dissassociate into ions when placed in water. Nonelectrolytes do not dissassociate in water.
Define the terms isotonic, hypertonic, hypotonic and explain what way water moves in each environment.
Isotonic means that the ratio of solutes to water on each side of the membrane is the same. Hypertonic means that a solution has more solutes to water as compared to another solution. Hypotonic means that a solution has less solutes to water as compared to another solution. In an isotonic environment water and solutes will move across the membrane, but they will move equally - no net movement in either direction. They system is in equilibrium. If you place a cell in a hypertonic environment (meaning that there are more solutes/water in the solution as compared to inside the cell), water will move out of the cell. If you place a cell in a hypotonic environment, water will enter the cell. A basic rule of thumb is that water will always move to the solution that has a higher amout of solutes/water. The goal of the system is to reach the point at which there is an equal ration of solutes to water, or an isotonic condition. This will only happen when the solutes can NOT cross the membrane. This is talking about situations where osmosis is occuring.
Define the term osmolality:
the number of dissolved solutes per unit of water.
Why do electrolytes contribute more to osmolality than nonelectrolytes?
One electrolyte, once it enters water, dissassociates into at least 2 solutes, maybe more. A nonelectrolyte doesn’t dissassociate in water, so it only contributes one molecule, even if it’s bigger than an ion, it is still only one molecule, giving is less power over the osmolality of the solution.
Compare and contrast extracellular and intracellular fluids. How much Na+ is in each? K+? What makes up the bulk of dissolved substances in the body?
In the extracellular fluid the main cation is Na+ and the main anion is Cl-. Intracellular fluids have the main cation of K+ and the main anion of HPO4–. Electrolytes are highest in number in all fluids.
If something needed to move from the blood to a cell, describe the compartments it would travel through and the membranes it would need to cross.
It would first cross the wall of the capillary (simple squamous epithelium), then it would be in the interstitial fluid. Then, it would cross the wall of the cell (phospholipid bi-layer).
What are sources of water intake? Output?
Sources of water input are water from food, water from drinking, water from metabolism. Water outputs are water vapor from our breath, sweat, urine and feces.
How does ADH (anti-diuretic hormone) help maintain the narrow range of solute concentration in the body fluids?
ADH is made by the hypothalamus and stored in the posterior lobe of the pituitary gland. It is released when we are dehydrated. It acts on the principal cells of the collecting duct, causing them to increase manufacturing of aquaporins, transport proteins for water. More water then moves from the filtrate into the principal cells. Then it moves from the principal cells to the blood. In this way, we retain more water and create a concentrated urine.
What three factors govern the thirst mechanism? Briefly explain each.
First there are osmoreceptors. When cells stretch because they take on more water, mechanoreceptors signal the hypothalamus which decreases secretion of ADH. Second, dry mouth occurs when you are dehydrated. There is a lot of water in saliva and decreasing water here to keep blood pressure up is one way your body counters dehydration. You experience a dry mouth. Dry mouth signals the thirst response in the brain. Third, there is a decrease in blood volume/pressure. Baroreceptors pick this up and signal your brain to turn on the thirst response.
Explain why ‘water follows salt’. Give examples.
When Na+ (salt) moves from the blood to the interstitial fluid, the solute concentration in the interstitial fluid increases. Your body is always trying to maintain isotonic conditions across all fluid compartments. If the interstitial fluid becomes hypertonic (more salty), then in order to create an equal ratio of solutes (Na+) to water, more water must enter this compartment. So, water follows the salt from the blood into the interstitial fluid. Then, the salt moves from there into cells. The cells become hypertonic, therefore water follows the Na+ to create isotonic conditions in the cell.
What are the two salts that contain sodium in the ECF?
NaHCO3 and NaCl.
What are the main functions of sodium in the body?
There are two main functions of Na+. First, to control the ECF volume (remmeber that the ECF refers to fluid in two areas - the blood plasma and the interstitial fluids). Second, to control water distribution between fluid compartments (see my answer to #13).
What’s the difference between sodium concentration and sodium content?
Sodium content is the number of Na+ ions in the body. You would count them. The concentration is the ratio of sodium ions to water. The more sodium ions per volume of water, the higher the concentration. If there aren’t many Na+ ions in the same amount of water, there is a lower concentration.
How does water retention work? Why do we retain water when we eat too much salt?
If we eat too much salt the salt is absorbed from our digestive tract into the blood. The sodium concentration of the blood increases. Water enters the blood from the interstitial fluid to bring the conditions to isotonic. The more salt we eat, the more water we need in order to maintain isotonic conditions. The less salt we eat, the less water we need, and any excess is lost in the urine.
Explain how aldosterone works.
When we are dehydrated aldosterone is secreted by the adrenal cortex. Aldosterone works on the principal cells of the collecting duct of the kidney. It affects those cells by increasing the manufacturing of transport proteins for Na+. More Na+ moves from the filtrate inside the tubule to the cells that line the tubule. From there, the Na+ moves into the blood. When we retain Na+, we retain more water, which helps when we are dehydrated.
Explain how Atrial Natriuretic Peptide hormone works.
When blood pressure is high baroreceptors in the atria of the heart are stimulated to secrete ANP. ANP works on the principal cells of the collecting duct in the kidney. It’s effect is to decrease production of these Na+ tranpsort proteins, so more Na+ is excreted in the urine. Less water is retained and more is lost in the urine.
Why is the homeostasis of K+ levels important?
K+ ions directly affect the ability of nerves and muscles to fire and contract.
Explain how the kidneys make sure that there is just the right amount of K+ in the body.
Almost all of the K+ is reabsorbed in the proximal convoluted tubule and loop of henle (nephron loop). The distal convoluted tubule and collecting duct then secrete K+ into the filtrate if necessary. In this way the amount of K+ in the body is very fine tuned.
What is optimal pH in the body?
Optimal blood pH is 7.35-7.45.
Where does the excess of H+ come from when fluids are too acidic?
The excess H+ can come from foods we eat, the breakdown of metabolic products like lactic acid, and other less important sources.
What three ways does the body buffer any excess H+?
Chemical buffers (like bicarbonate and proteins), brain stem respiratory centers (we breath faster when the blood gets acidic), and the kidneys (intersticial cells can secrete H+ into the filtrate or reabsorb H+ if needed).
