Homeostasis + Membrane Transport Flashcards
Define Homeostasis and why it is important?
The ability of the body to maintain a relatively stable internal environment. This is important so that cells can function properly.
What are the control systems for homeostasis?
Nervous system (acts quickly) and the endocrine system- hormones (acts slower). Act together or separately. Negative feedback control systems to maintain homeostasis.
What’s an example of positive feedback control?
Birth: oxytocin induce contractions and labour more and more until the women has given birth.
How is the 42 L of our total body water (TBW) divided up?
3 L plasma (fluid components of blood) and 11 L interstitial fluid -both a part of the ECF. 28 L intracellular fluid -ICF distinct.
State whether the following have a higher concentration on the inside or outside of the cell:
Sodium ions, Potassium ions, Calcium ions, Chloride ions, and Proteins.
Sodium ions: outside. Potassium ions: inside. Calcium ions: outside. Chloride ions: outside. Proteins: inside.
SALTY BANANA DIPPED IN CHOCOLATE.
How are ion concentration maintained by the plasma membrane?
Provides physical separation, regulates exchange of substances, and communicates with its environment.
What are the functions of membrane proteins? (5)
Receptors for hormones, neurotransmitters and ligands, enzymes, transporters, cell recognition (antigens) and cytoskeleton anchors (shape).
Membrane transport mechanisms (5)
1.endocytosis/ exocytosis
2. simple diffusion
3. diffusion
4. facilitated diffusion/ transport
5. active transport.
What is simple diffusion?
The movement of molecules due to their random thermal motion. Molecules move from areas of high concentration to low concentration (down gradient) until chemical (dynamic) equilibrium is reached. Lipid soluble substances can move through the membrane without help.
What is Fick’s First Law? Describe the variable we’re calculating for, and the variables in the equation.
Fick’s First Law of Diffusion can be used to predict simple diffusion. Fick’s first law calculates for J = net rate of diffusion in moles or grams per unit time. Using k = boltzmann constant, T = absolute temp, r = molecular radius, and n = viscosity of the medium, A = total surface area of the membrane for diffusion, and dc/dx = concentration gradient of the solute.
What is diffusion?
Polar molecules (ions + water-soluble molecules) cannot diffuse directly through the cell membrane due to the hydrophobic fatty acid region. They require a protein channel/ pore - this is diffusion. The driving force is the concentration gradient still. e.g. water moves through membranes through channels called aquaporins.
What are the factors which affect the rate of diffusion through protein channels? (5) - Can also call this factors affecting the rate of movement through protein leak channel
-Size of the molecule
-Charge of the molecule and channel
-Electrochemical gradient
-Pressure gradient
-Hydration energy (“Hille’s theory of closest fit” - water shell must be removed by the channel without the ion “knowing it” so ion remains “energetically stable”- water re-added on other side)
Describe how these factors affect the rate of diffusion / rate of movement through protein leak channels.
Some of these factors act as filters preventing one ion from passing through another ion’s channel, others act as chemical specificity.
-Filters: size, charge and hydration energy
-Chemical specificity: electrochemical, and pressure gradients
Describe permeability
A measure of how easily an ion can cross a membrane (through pores/ leak channels). -Depends upon the number and type of protein channel in the membrane
A typical cell at rest has the following ion permeabilities:
Na+
K+
Cl-
Which is the most and least permeable?
PNa+ = 2 x 10^-8 cm/sec (least permeable)
PK+ = 2 x 10^-6 cm/sec
PCl- = 4 x 10^-6 cm/sec (most permeable)
What is facilitated diffusion?
This is a form of carrier mediated transport (shape change allows the molecules to cross). Driving force is still concentration gradient. e.g. glucose uniporter - really large molecules.
Characteristics include - chemical specificity, competitively inhibited, and saturation kinetics.
What is active transport?
A form of carrier mediated transport. Moves substances against its concentration gradient. Requires energy (ATP)
e.g. Na+ / K+ ATPase pump
Characteristics include - chemical specificity, competitively inhibited, and saturation kinetics.
What are the functions of the Na+ / K+ pump?
Helps maintain the concentration gradients for Na+ and K+ across the cell membrane. Causes slight increased negativity inside the cell (more positive charge is being removed than replaced). Keeps the cells from swelling and bursting due to osmosis.
What are the inhibitors of the Na+ / K + pump?
Metabolic inhibitors can block the Na+ / K + pump
-Ouabain (from poison arrow tree), die of cardiac arrest
-Digoxin (from foxglove plant), drug for heart failure.
Inhibits the pump by binding to the ion pathway - when the pump is open to the extracellular environment, prevents K + binding.
- These are specific drugs for the isoform of the Na+ / K+ pump. Alpha 2 subtype is in our heart, and Ouabain + digoxin bind more to this subtype.
What is the meaning of electrogenic, what scenario is the term used in?
3 positive charges move out of the cell while only 2 positive charges move in. This is the case with the sodium / potassium channel - 3 sodiums out, 2 potassium in.
Define osmosis
Water movement / diffusion. Water moves down its concentration gradient due to its thermal motion. High solute concentration = low water concentration, low solute concentration = high water concentration - water concentration is determined by the number of solute particles in solution (not on their size). Water moves from low solute to high solute - this net movement of water down concentration gradient is called osmosis.
Define osmol
Unit to describe the # of solute particles in solution that cause osmosis.
Define osmolality
of osmol/Kg of water.
Body fluids (ICF, ECF) are normally 300 mOsmol/ Kg
Define osmolarity
of osmol/ L of water
*osmolality and osmolarity can be considered the same thing in this course
Define tonicity
Ability of a solution to cause osmosis across a cell.
Describe Isotonic solution
No net movement of water. Outside of cell has same osmolarity as inside.
Describe Hypertonic solution
Higher solute outside cell than inside. Water moves out of cell, causes cell to shrivel.
Describe Hypotonic solution
Higher solute inside than outside the cell. Water moves into cell, causes cell to swell.
What are osmo receptors?
Neurons that indicate whether solution is isotonic, hypertonic or hypotonic.
Describe Cystic Fibrosis
Genetic disorder that affects the lungs (+other organs) - Caused by mutation which leads to abnormal protein called CF transmembrane conductance regulator. Part of a special chloride transporter that regulates the compponents of mucus lining the lungs. Without CFTR function, the periciliary liquid becomes more viscous and sticks to cilia and they therefore can’t beat the mucus and debris out of lungs, can get infection easily.
Describe the Darrow-Yannet Diagram
A way to look at relative changes in the volume and concentration of the ICF and ECF compartments. Helps determine the net movement of water across the cell membrane.
Looks at: water load, water loss, solute load and solute loss. Changes always occur to the ECF first, and then the ICF responds.
