Homeostasis Flashcards
What is homeostasis?
Homeostasis is about us ‘staying the same’ - the body being at ease and in resting, functional state.
As a doctor, help cope with altering from homeostasis - disease is broadly failure of homeostasis.
We do this by;
1. avoiding change caused by internal processes inherent to the body (mitigating internally-generated change; reaction to high energy demand; heart rate and respiration increase to respond to high energy demand).
2. avoiding change driven by external factors (at higher temperature vs comfortable temperature skin looks red due to high blood flow in surface capillaries and profuse hidrosis (sweating))
Behavioural responses are for homeostasis as well; wearing warm clothes, building fire, shelter…
What is the failure of homeostasis?
Disease - infection, diabetes melitus, hypertension (high b.p.), cancer (basal cell carcinoma), Alzheimer’s disease…
Also aging to an extent - how much is damage, how much is normal?
What is the second law of thermodynamics?
How does it relate to the human body?
In a closed system entropy increases with time.
This means ordered things become more disordered/disorganised with time and once order is lost, it’s pretty much irreversible.
The living body is a highly structured, living thing, so cells have to resist entropy to keep concentrations of ions stable and keep them right when concentration is different out of cell.
How does the body maintain it’s organisation against the action of the 2nd law of thermodynamics?
We are not a closed system - the body constantly expands energy just to survive. We gain this energy from glucose.
How do we drive biochemical reactions?
In biochemical processes, the net direction of energy is always ‘downhill’ as an ‘uphill’ change in energy must be compensated for. Often ATP is the high energy molecule that gets broken down and the chemical reaction requires less than it releases, so overall energy in system is decreased.
Most require an energy change of about 0.2eV, driven by the 0.3eV packets of ATP decomposition.
Lots of steps in biochemical reactions provide for the overall energy supply - lots of intermediates allow for recovery of small energy amounts along the way so it’s not overwhelmed by happening all at once.
How do cellular membranes work?
Phase separation.
Temporary interactions mean atoms of similar charges are attracted to each other so hydrophobic phospholipid tails of membranes group together and the hydrophilic heads group on the outside of the lipid sandwich which can interact with the hydrophilic bodily fluid. This allows for the stable phospholipid bilayer structure of the membrane.
How do membranes maintain flexibility?
Cholesterol is embedded in them which prevents them seizing.
What types of molecules can cross the phospholipid bilayer membrane directly by passive diffusion?
Hydrophobic molecules can cross; steroids (like testosterone), CO2…
Some drugs can cross (like aspirin) as are hydrophobic enough but also hydrophilic enough to dissolve in bodily fluid.
Hydrophilic molecules (like glucose) cannot cross.
What do selective channels (uni-porters) allow to cross the membrane?
Hydrophilic molecules - food (glucose), raw materials (amino acids), waste products (urea), ions, water…
Signals and information like hormones
What is aquaporin?
A uni-porter allowing only water to pass through passively, by diffusion (in both directions).
What are co-transporters?
Membrane proteins that allow for diffusion of multiple molecules together (like K+, Na+, 2Cl- that diffuse together through SLC12A2 in kidney).
What are anti-porters?
Membrane channels that transport molecules together but in the opposite direction (like H+, Ca2+ anti-porter YkFE).
What does active transport allow for?
Non-equilibriums/differences in concentration to be maintained.
Like the non-equilibrium of Na+ and K+, achieved and maintained by Na+-K+-ATPase. As unequal amounts of charged ions move, so too do unequal charges so it is therefor a ‘electrogenic’ pump.
ATP is needed to change the conformation of the protein so the ions can be transported.
What can the high concentration of Na+ outside the cell allow for?
Co-transporters/anti-porters can use the gradient to move other molecules across the membrane ‘uphill’ while sodium flows ‘downhill’ (like glucose symport in urinary tube - Na+ gradient pushed glucose through at same time).
How does the electron transport chain work?
NADH gives up electrons to the transport chain.
The electrons get passed along connected complexes in a series of small manageable energy steps.
These are coupled to redox reactions (using oxygen and the ‘H’ of the NADH to make water), and also to the pumping of electric charge (H+) across the membrane.
The H+ gradient is itself an energy store.
An enzyme, ATPsynthase, includes a channel that allows H+ to flow back and feed the energy released to phosphorylate ADP to make new ATP.
