Homeostasis Flashcards
Definition of homeostasis?
The ability or tendency of the body or a cell to seek and maintain a condition of equilibrium – a stable internal environment — as it deals with external changes.
Basically… Staying the same
Note ‘the same’ is with reference to a time period that is short relative to the human life, as for example the a body changes over time…
Baby - teenager - adult - elderly - dead
Why is understanding homeostasis important in the context of medicine?
Disease often occurs when there is a failure to maintain homeostasis
Your job, as physicians or surgeons, will be to try to maintain homeostasis in your patients and, when there is a departure, to help them get as close to normal again
How can we divided the function of homeostasis in to two sub-categories?
Homeostasis is used to…
Avoid change caused by internal processes inherent to the body –> internal changes that occur when we start excercising - e.g. elevated blood CO2 and decreased O2
Avoid change driven by external factors - e.g. changes in external temperature
What changes occur in the body when it is exposed to warm and cold temperaturs?
In order to maintain internal temperature the body will…
Warm temperature - Dilate capillaries, blood vessels are brought closer to the skin surface and we start sweating (hidrosis)
Cold temperature - contraction of capillaries, blood vessels move further away from skin surface, shivering and a closed stance to minimize exposure.
Note - there are also behavioural changes, like wearing warm clothing, moving into a shelter area and having a external heat source.
What are some common diseases that are caused by a failure of maintaining homeostasis?
Many common diseases are failures of homeostasis
1. Infection
2. Diabetes
3. Hypertension
4. Cancer
5. Alzheimer’s disease
6. Ageing?
What can the second law of thermodynamics teach us about bodily homeostasis?
Firstly, the bodily is heavily ordered oragnisms with many layers of complexity.
As stated by the the second law of thermodynamics, everything tends to move towards a state of disorder/increased entropy over time.
Furthermore, a disordered stated requires an input of energy to move back to an ordered state.
Hence, this gives us a quick explanation as to why the body has to invest a significant amount of energy into maintain order as it is fighting the second law of thermodynamics
Example - maintaining ion gradients across a membrane
This energy is derived from the food we eat (cellular respiration), which ultimately derives its energy from the sun (photosynthesis)
From an energetics perspective, how does the body perform/fuel desired chemical reactions?
Couple a downhill reaction (reaction that releases energy) with an uphill reaction - bond energy from one reaction fuels a second reaction
Note - Reactions in biology almost always run ‘downhill’ in energy terms from a net perspective - when two reactions are coupled the change in downhill energy needs to exceed the uphill loss as energy transfer is not 100% efficient
Why is ATP used as a packet of energy instead of glucose?
Typical biochemical reactions involve energy changes of about 0.2eV
But oxidizing a molecule of glucose releases 29eV of energy - too much…
Hence, reactions are instead driven by 0.3eV ‘packets’ of energy donated by the energy carrier ATP
Why is this important for homeostasis - ATP is the main form of energy currency used to failure the 2nd law of thermodynamics!
How does the body extract the energy from glucose?
The energy that is stored in a single glucose molcule is extracted via the process of aerobic respiration - involves multiple small steps (glycolysis and TCA cycle) that allow for energy stored in glucose to be converted into 36 ATP molecules.
Note…
- Some steps pass this energy direct to ATP – phosphorylation
- Some steps pass it to intermediate carriers such as NADH – electron transport
Why does phase seperation occur - i.e. the seperation of polar and non-polar molecules?
When adding non-polar molecules into a polar solution (i.e. water) the water molecules will be unable to reach their lowest energy state as their hydrogen bonding will be disrupted.
Hence, polar and non-polar molecules separate in an attempt to reduce the energy state
What is one of the main examples of phase seperation in the body?
Formation of the plasms membrane - phospholipid bilayer
In order to minimize the free energy state, hydrophilic heads align with the aqueous internal and external environment.
Whereas, the hydrophibic tails face eachother, creating a hydrophobic space/region in the middle of the bilayer.
What is one problem with the phosphophilid bilayer and how is it solved?
The tails pack so regularly the bilayers would be solid (like ‘2D ice’) even at body temperature
Cell adds cholesterol to lipid bilayers to mess up their packing and stop them freezing/becoming solid at 37ºC
Cholesterol = increases fluidity of the membrane
What are some examples of molecules that can and can’t diffuse across the bilayer?
Usually small apolar hydrophobic molecules can diffuse across - CO2, testosterone, aspirin
Whereas, larger polar/hydrophilic molecules can not diffuse across - ions, glucose, amino acids, water, urea, etc –> channels or pumps
Hence, this is why the membrane is considered to be selectively permeable
How protein is used to faciliate the transport of water across a membrane?
Aquaporin channels – water channel that allows for the selective movement of water (bidirectional movement)
What are the four types of channel transport?
- Direct free diffusion
- uniporter - transport of one molecule/ion
- Symporter - transport two or more molecules/ions in the same direction
- Antiporter - transport two or more molecules/ions in the opposite direction
Note - Symporter and antiporters are both considered co-transporters
It is important to note that in all of these, net transport is down a concentration gradient, and will reduce differences in concentration - relies on passive diffusion
None of these mechanisms can create order on its own.
What is active transport?
Movement of ions/molecules against their concentration using energy in the form of ATP
Unvirsal example maintaining sodium (high outside/ low inside) and potassium concentration (high inside/ low outside) - relies a Na+ K+ ATPase pump –> that pumps out 3 Na+ ions while simulatenously pumping in 2 K+ ions.
Explain how Na+ is used to pump glucose from the urinary space of the kidney (selective reabsorption) back into the body?
Firstly, the body setups of a Na+ concentration gradient outside the cell by using the Na+K+ ATPase active transporter.
Subsequently, this Na+ concentration gradient (higher outside the cell) will favour the passive diffusion of Na+ into the cell –> Hence, the cell couples this downward Na+ movement with glucose trasnport, using a Na+/glucose symporter (SLC5A2), to move glucose into the cell even though it is moving up it’s gradient
Common method employed to drive active transport - hundreds of co-transporters that use this trick, some of which are used as drug targets - e.g. canagliflozin limits glucose reabsorption in diabetes patients.
Form of active transport that relies on setting up a Na+ concentration gradient.
How is NADH and FADH2 used to create ATP?
NADH and FADH2 are both electron carriers that are reduced during glycolysis and the TCA cycle.
These carriers become oxidized/donate their electrons to the electron transport chain, which is where the electrons pass through complexes, known as cytochromes, which drive the movement of H+ into the intermembrane space, which sets up a electro-chemical gradient of H+ ions.
These ions then diffuse through a large complex known as ATP synthase, which is able to convert the energy from H+ movement into chemical energy stored in ATP molecules.
Process known as oxidative phosphorylation
Note - Cyanide is poisonous because it interrupts this chain - binds to Cytochrome C oxidase
Why are cytochromes medically important?
Cytochromes medically important because they can be important in metabolizing drugs
Liver has many different types of cytochromes -used for drug metabolism – explains high level of drug liver toxicity
How to define a signal? What is important to keep in mind when thinking about signalling?
A “signal” is a communication that conveys meaning
A “signal” and its meaning are defined from the point of view of the receiver - scientific view
E.g. Bacteria don’t intend to present ‘destroy me’ signals on their surface but macrophages interpret the bacteria antigens in this way.
Hence, the same signal can have different meanings to different receivers - main example - action of hormones/endocrine system
Link between signalling and energetics?
Making and transmitting information has to be paid for with ATP - information and energy are heavily interlinked
Example - converting the genetic code into functional protein
Definition of signal bandwidth?
The amount of information that can be passed per unit time is the bandwidth.
High bandwidth is expensive - use the minimal amount in order to acheive the desired goal
How does the body attempt to mimimize the level of signal bandwidth used? Why is this relevant for medicine?
By using simple signals but ensuring that the receivers have the right amount of information in order to interpret these signals.
Analogy - Traffic light - we know and can interpret what a green, yellow and red light mean.
Medical application - allows us to change the messages by making alterations to how well these simple signals are received, or by making simple signals of our own –> this is how most drugs work
What are the four different types of signalling present in the body?
Autocrine - cells signaling to themselves
Juxtacrine - signaling to immediate neighbor (direct contact of cellular components)
Paracrine - signaling to cells within a proximal vicinity (short lasting)
Endocrine - signaling that occurs via the bloodstream