Ch. 6 Interactions Between Cells and the Extracellular Environment Flashcards
What does the extracellular environment include?
Everything located outside the cell
Cells receive ____ from and release ____ into the extracellular environments.
Nourishment; wastes
How do cells communicate with each other using the extracellular environment?
By secreting chemical regulators into the extracellular environment
How to cells exchange things?
Inside cell –> extracellular
Does diffusion work better over a limited space? Why?
Yes b/c the exchange into extracellular environment occurs faster
What is the extracellular environment in endothelial cells?
The blood running by
True/False: Capillary beds are in close proximity to most cells in the body.
True
__% of our water is within cells in the intracellular compartment; intracellular fluid (ICF).
67% (2/3)
__% of our water is in the extracellular compartment (extracellular fluid, ECF).
33% (1/3)
__% of ECF is in blood plasma.
20%
__% of ECF makes up tissue fluid (or interstitial fluid).
80%
Interstitial fluid
aka tissue fluid
Connects the intracellular compartment with the blood plasma
What does extracellular matrix contain?
Protein fibers (structural support) of collagen and elastin, and ground substance (glycoproteins and proteoglycans)
Foundation to build cells upon; flexible
Protein fibers provide ____ ____.
Structural support
Integrins
Glycoproteins that extend from the cell cytoskeleton and bind to the extracellular matrix; linking cells to the matrix
Selective; different integrins recognize different extracellular matrix
What 3 things to integrins do?
Impart a polarity to cells
Affect adhesion and motility
Affect proliferation
Why is proliferation important? How can it go wrong?
Important: only need once cell covering basement membrane –> proliferation
Tumors are opposite: adding unnecessary cells to cover basement membrane
The plasma membrane is ____ ____.
Selectively permeable
Selectively Permeable plasma membrane
Allows some molecules to cross but not others
What is the plasma membrane generally not permeable to?
Proteins, nucleic acids, or other large molecules
What is the plasma membrane generally permeable to?
Ions, nutrients, and wastes
Non-carrier mediated membrane transport
- Simple diffusion of lipid-soluble molecules
- Simple diffusion of ions through nonspecific channels
- Simple diffusion of water = osmosis
Carrier-mediated membrane transport
- Facilitated diffusion
2. Active transport
Passive Transport
Molecules move from higher to lower concentration w/o using metabolic energy
- -moves down concentration gradient
- -equalize concentration
Active Transport
Molecules move from lower to higher concentration using ATP and specific carrier pumps
- -selective movement
- -move again concentration gradient
Diffusion: Plasma Membrane
Small, nonpolar (or uncharged) lipid-soluble molecules pass easily through the lipid portion of the membrane
- -oxygen, carbon dioxide, and steroid hormones (estrogen, testosterone…)
- -gas exchange: net diffusion of oxygen into cells and CO2 out of cells due to concentration gradients; opposite in lungs (offload CO2 and bring CO2 into lungs)
Aquaporins
Water can pass through these special channels in osmosis
–lipid membrane not water soluble, aquaporins help water move
Where does CO2 build up?
In Krebs cycle and Electron Transport
Osmosis
Diffusion of solvent instead of solute; unique
Why can water pass through the plasma membrane?
Because water molecules do not carry a charge, they can pass slowly
Where are Aquaporins found?
Kidneys, eyes, lungs, salivary glands, and the brain
–glaucoma (occurs from increased eye pressure) can occur b/c of issues w/ aquaporins
Osmotically Active
Solutes that cannot cross and permit osmosis
For osmosis to occur, must there be a solute concentration difference on either side of a membrane permeable to water?
Yes
For osmosis to occur, the membrane must be ____ to the solute, or the concentration difference will not be maintained.
Impermeable
Osmotic Pressure
Force surrounding a cell required to stop osmosis
Osmolality
Total molality of a solution when you combine all of the molecules within it
Pure water has an osmotic pressure of ____.
Zero
A higher solute concentration would require a ____ osmotic pressure.
Higher
Tonicity
The effect of a solute concentration on the osmosis of water
Literally how a cell is going to react in a solution
Hypoosmotic and Hypotonic
Solutions with a lower solute concentration than the cell
Will pull water into the cell; cell will swell and could lyse
Hyperosmotic and Hypertonic
Solutions with a higher solute concentration than the cell
Will pull water out of the cell; cell will shrivel up and crenate
Osmoreceptors
In hypothalamus; detect increases in osmolality (due to dehydration).
Triggers:
- -thirst
- -decreased excretion of water in urine
Decreasing the solute will ____ osmolality.
Increase
Anti-diuretic hormone
Tells kidneys to retain water when dehydrated
Constant osmolality must be maintained, or ____ will be damaged.
Neurons
With a lower plasma osmolality, osmoreceptors are not ____, so more water is excreted in urine.
Stimulated
Gated
Refers to plasma membrane in which things may only be moved at certain times
Opened and closed by a number of stimuli
Channels: Plasma Membrane
Charged ions (small) can pass through ion channels that cross the plasma membrane that may always be open or gated
How do larger polar molecules cross the plasma membrane?
They cannot pass through the membrane by simple diffusion, so they need special carrier proteins in order to cross
Can molecules that are large or polar diffuse across the membrane?
No; carrier proteins within the plasma membrane move these molecules across
What molecules cannot diffuse across the membrane?
AA, glucose, and other organic molecules
What are characteristics of the carriers?
Specific to a given molecule
–e.g. Glucose transporter moves glucose only
May be competition for similar carriers or molecules
–e.g. Antibiotics: must figure out which ones are going to be eliminated in urine and which ones won’t
Saturation - number of carriers is limited
–eventually all the carriers are being used and we can’t move anything else
Facilitated Diffusion
Powered by the random movement of molecules - no ATP used
Move from high to low concentration
Requires specific carrier-mediated proteins
Transport proteins may always exist in the plasma membrane or be inserted when needed
Active Transport
Molecules must be moved from an area of low concentration to an area of high concentration
–against concentration gradient
Requires expenditure of ATP
also called pumps
Primary Active Transport
Occurs when hydrolysis of ATP is directly responsible for carrier protein function
Transport protein is also an ATPase enzyme that will hydrolyze ATP
Pump activated by phosphorylation using a phosphate from ATP
Na+/K+ Pump
Found in all body cells
ATPase enzyme pumps 3 NA+ out of the cell and 2 K+ into the cell
What 3 functions does the Na+/K+ Pump serve?
- Provides energy for coupled transport of other molecules
- Produces electrochemical impulses in neuron and muscle cells
- Maintains osmolality
Discuss Na+ and K+ concentrations inside and outside of the cell.
High K+ concentration in cell, low K+ concentration outside cell
Low Na+ concentration in cell, high Na+ concentration outside cell
Secondary Active Transport
Aka coupled transport
Energy needed to move molecules across their concentration gradient is acquired by moving sodium back into the cell
Secondary Active Transport: Cotransport or Symport
Other molecule is moved with sodium. Common way of transporting glucose
Secondary Active Transport: Countertransport or Antiport
Other molecule is moved in the opposite direction from sodium.
e. g. Sodium hydrogen antiport
- -kidneys move sodium in, we move hydrogen out
Absorption
Transport of digestive products across intestinal epithelium into the blood
–pulling things in from gut
Reabsorption
Transport of molecules out of the urinary filtrate back into the blood
–referring to renal fxn; kidneys filter blood, reabsorb water and sodium
Transcellular Transport
Movement of molecules through the cytoplasm of the epithelial cells
–moving things through cell
Paracellular Transport
Movement across tiny gaps between cells
–moving things between cells
Transport usually involves what type of cells?
Epithelial cells
What are the 3 types of cell-cell adhesion?
- Tight junctions
- Adherens junctions
- Desmosomes
All 3 hold epithelial cells together
Tight Junctions
Do not allow easy diffusion
Limit paracellular transport
Adherens Junctions
Cell patterning/cell recognition
–space between plasma membrane
Desmosomes
Lots of skin movement
–space between plasma membrane
Bulk Transport: Exocytosis
Large molecules such as proteins, hormones, and neurotransmitters are secreted
Requires ATP
Involves fusion of vesicle w/ plasma membrane
–we can dump out a lot of molecules at once
Bulk Transport: Endocytosis
Movement of large molecules such as cholesterol into the cell
Can be receptor-mediated (selective)
Usually a transport protein interacts with plasma membrane proteins to trigger endocytosis
Why is there a difference in charge on each side of the plasma membrane?
- Permeability of the membrane
- Action of Na+/K+ pumps
- Negatively charged molecules (lot of proteins) inside cell
Potential Difference
Difference in charge [of plasma membrane]
Makes inside of cell negative compared to outside
Why does K+ accumulate at high concentrations in the cell?
- Na+/K+ pumps actively bring in K+
- Membrane is very permeable to K+
- Negative anions inside cell attract cations outside the cell
- Limited by strong concentration gradient
K+ concentration inside is 150 mEq/L and out is 5 mEq/L
How do we measure the potential difference?
Measured as voltage
K+ Equilibrium
Inside of cell has a voltage 90mV lower than the outside; this is the voltage needed to maintain 150 mM K+ inside and 5mM K+ outside
Is the resting potential for our cells on the negative or positive side?
Negative side
Na+ Equilibrium
Concentration of sodium in a normal cell is 12mM inside and 145mM outside
To keep so much sodium out, inside would have to be positive to repel sodium ions
Equilibrium potential for sodium is +66mV
The membrane is less permeable to ____, so the actual membrane potential is close to that of the more permeable ____.
Na+; K+
Resting Membrane Potential
Membrane potential of a cell not producing any impulses
Depends on:
- ratio of concentrations of each ion on either side of the membrane
- specific permeability to each ion
Which ions contribute to the resting potential? Which ion has the greatest influence?
K+, Na+, Ca2+, and Cl- contribute
K+ has greatest influence b/c it’s most permeable
T/F: A change in the permeability of the membrane for any ion will change the resting potential.
True
T/F: A change in the concentration of any ion inside or outside the cell will change the resting potential.
True
Does every cell have a resting membrane potential?
Yes
Occurs when there are no impulses: no neurons firing, no muscles contracting…
What are the 4 types of cell signaling?
- Gap junctions
- Paracrine signaling
- Synaptic signaling
- Endocrine signaling
Gap Junctions
Allow adjacent cells to pass ions and regulatory molecules through a channel between cells
Cardiac cells, muscle cells
Paracrine signaling
Cells w/in an organ secrete molecules that diffuse across the extracellular space to nearby target cells; often called local signaling
One cell signals another w/in the same organ
Synaptic signaling
Involves neurons secreting neurotransmitters across a synapse to target cells
Endocrine Signaling
Involves glands that secrete hormones into bloodstream; these can reach multiple target cells
Receptors
Allows cells to recognize signals, cells must have the specific receptor proteins either on the plasma membrane (outside cell) or inside the cell
Nonpolar Regulator
Receptors on inside
Steroid hormones, thyroid hormone, and nitric oxide gas
Polar Regulator
Receptors on outside (plasma membrane)
Epinephrine, acetylcholine, and insulin
cAMP
Cyclic adenosine monophosphate
Signaling molecule; common second messenger
How does cAMP work?
- Signaling molecule binds to a receptor
- Activates an enzyme that produces cAMP from ATP
- cAMP activates other enzymes
- Cell activities change in response
