Lecture 1: Body Fluid Compartments and Transport across cell membranes Flashcards
What is total body water?
Total water in the body
The amount of water in the body is __________ related to fat.
Inversely
What are the two major fluid compartments and what percentage of body weight do they comprise?
Intracellular fluid (ICF)- inside cells, 40% BW
Extracellular fluid (ECF)- outside cells, 20% BW
There are two types of extracellular fluid. What are they and what percentage of total body weight do they comprise?
Plasma (inside capillaries)- ~4% total body weight
Interstitial Fluid (bathes cells & tissues)- ~16% total body weight
Total body water is what percentage of body weight?
On average 60%
range of 50-70% depending on species
What is the average blood volume? Important number*
70mL/kg BW
When measuring the AMOUNT of solutes in fluid compartments, you can measure amounts in _________, __________, or _________.
moles, equivalents or osmoles
what is an equivalent?
amount of charged solute that has participated in a chemical reaction or electrical process (ex: 2 Eq of Ca and 2 Eq of Cl)
what is an Osmole?
number of particles into which a solute dissociates in solution (NaCl= 2 osmoles in solution)
What is osmolarity?
osmoles/L
What is electroneutrality?
each body fluid compartment must have the same concentration of cations as of anions
What are the major ions in the ECF?
Cation: Na+
Anions: Cl- and HCO3- (bicarb)
What are the major ions in the ICF?
Cation: K+
Anions: proteins and organic phosphates
What is the normal range of osmolarity?
290-300 mOsm/L
What are the two types of Ca in ICF and ECF?
Total Ca: bound and ionized Ca
Ionized Ca: Free Ca & active form
Cell membranes are selectively permeable, meaning what?
Cell membranes are not freely soluble to all solutes
What are the two transport mechanisms in the cell membrane?
Na+/K+ ATPase pump: pumps Na= out of the cell, K+ pumped into cells (because K+ concentration is higher in cells)
Ca2+/ATPase pump: pumps Ca2+ out of cells (pumps Ca2+ out of cells)
both mechanisms directly use ATP*
Why are ion concentration differences important?
-Allows nerve and muscle cells to have resting membrane potentials (due to K+ difference)
- Upstroke of action potentials in nerve and muscle cells and absorption of nutrients due to Na+ difference
- excitation-contraction coupling in muscle cells depends on Ca2+ difference
Cell membranes are composed of lipids and proteins. What are the three types of lipids that are in cell membranes?
phospholipids
cholesterol
glycolipids
What is the function of lipids in cell membranes?
-allow membrane to be permeable to lipid soluble substances (CO2, O2, fatty acids, steroid hormones
low permeability to H2O soluble substances)
- transporters, enzymes, hormone receptors, antigens, ion& H2O channels
What is the function of proteins in cell membranes?
- transporters, enzymes, hormone receptors, antigens, ion& H2O channels
What is the function of the phospholipid component in cell membranes?
Glycerol backbone (water-soluble) + FA tails (lipid-soluble= amphipathic*
*has both polar and non-polar components in its structure
Cell membranes can contain peripheral proteins. Where can these proteins be found?
Only on one side of the membranes
Transport across cell membranes can occur down an electrochemical gradient. What are these types of transport called?
Simple Diffusion
Facilitated Diffusion (needs a carrier protein to grab and move)
***No input of energy
Transport across cell membranes can occur against an electrochemical gradient. What are these types of transport called?
Primary transport- direct input of energy
Secondary transport- use energy to establish the Na+ gradient, then use Na+ to move other substances
True or False: Simple Diffusion is NOT carrier-mediated.
TRUE
***this is important
When two solutions are separated by a membrane permeable to the solute, the solute will ____________ across the membrane.
equilibrate
What are two additional consequences of charge on an ion that is diffusing?
1) A potential difference across a membrane will alter the rate of diffusion of a charged solute (diffusion of a positively-charged ion will slow down if diffusing to an area with positive charge)
2) A diffusion potential can be created when a charged solute diffuses down its concentration gradient
Movement of solute depends on several factors. Name these factors.
1) Concentration gradient: driving force, the larger the difference in the concentration gradient, the larger the driving force
2) Partition coefficient: based on the lipid solubility of the solvent (greater the solute’s solubility in oil, the higher the partition coefficient, the more easily it can diffise)
3) Diffusion coefficient: based on the size of the solute and the viscosity of solution ( small solutes in non-viscous solution have a higher diffusion coefficient)
4) Thickness of membrane: thicker the membrane, the lower the diffusion
5) Surface area: greater surface area=higher diffusion rate
Facilitated Diffusion: Does it use a carrier protein yes or no? Is there an input of energy yes or no?
Yes, uses a carrier protein
No, no input of energy
Facilitated diffusion will proceed faster or slower at relatively low solute concentrations? Why?
Facilitated diffusion will proceed FASTER at low solute concentrations because there are more carrier proteins available
There are 3 features of carrier-mediated transport. Name the 3 and describe them.
1) Saturation: carrier proteins have a limited number of binding sites for a solute, therefore: the RATE of transport increases at a higher rate at lower solute concentrations
2) Stereospecificity: binding sites for solute on carrier proteins are specific
3) Competition: Although binding sites are specific, carriers may recognize and bind chemically-related solutes
Which type of transport directly uses energy and is carrier-mediated?
A) Primary active transport
B) Secondary active transport
C) Simple Diffusion
D) Facilitated Diffusion
A) Primary Active Transport
Give the definition of primary active transport.
One or more solutes moved AGAINST a concentration gradient directly using ATP
What is the Na+/K+ ATPase pump?
-Present in membranes of ALL cells
- 3 Na+ pumped to ECF and 2 K+ pumped to ICF, this creates a charge separation and potential difference
- Cardiac glycosides inhibit this protein transporter
There are two examples of the Ca2+ ATPase pump. What are they?
1) Plasma-Membrane Ca2+ ATPase (PMCA): one Ca is pumped out of the cell for every ATP consumed
2) Sarcoplasmic and Endoplasmic reticulum Ca2+ATPase (SERCA): takes 2 Ca from ICF into SR or ER for every 1 ATP used
What is the action of the H+/K+ ATPase pump?
Parietal cells of gastric mucosa- pumps H+ into lumen of the stomach
What is the definition of secondary active transport?
Indirectly uses energy by utilizing the Na+ gradient to transport solutes against their concentration gradient
Co-transport (aka symport) is an example of secondary active transport. What does this mean?
- all solutes are transported in the same direction
- Na+/Glucose co-transporter (SGLT 1)
- Na+/Amino acid co-transporter
- Na+/K+/2Cl- co-transporter in renal tube
Counter-Transport (aka antiport) is an example of secondary active transport.
- Solutes move in opposite directions- Na+ moves INTO the cell and other solute moves OUT of the cell
- Ca2+/Na+ exchange
- Na+/H+ exchange
