L1. Homeostatic Control Systems Flashcards
What is homeostasis?
The maintenance of a relatively constant and optimal environment inside the body for the normal functioning of the cells of the body
Why is homeostasis important?
To keep the cells of the body in an environment that meets their needs and permits them to function normally DESPITE changes in the external environment
Set point?
Optimal value for a homeostatic variable
Normal range?
Range above and below the set point in which the homeostatic variable can fluctuate without the body responding to fix the change
Homeostatic control systems?
Controlled variable –> sensor (that detects changes) –> integration centre (compares the detected level of the homeostatic variable to the set point/normal range) –> effector (tries to restore variable to the set-point/within the normal range)
Negative feedback?
The control system acts to make the deviation from the set point smaller e.g. blood glucose or core temperature
Positive feedback?
The control system acts to make the deviation from the set point bigger to accelerate a process but requires a stop mechanism e.g. blood clotting and childbirth
Where is the central thermoreceptor located and what does it do to restore body temperature?
Hypothalamus; acts to increase cell metabolism, skeletal muscles (shivering), skin blood vessels (vasoconstriction), and piloerector muscles (goosebumps)
Feedforward?
Responses made in anticipation of a likely change in a homeostatic response;
Physiological e.g. smelling or thinking about food causing saliva or insulin release in response to glucose in the mouth
Behavioural (innate and learnt) e.g. putting on more clothes if forecast is cold
If the feedforward system does not prevent changes in the controlled variable, then those changes will be corrected by negative feedback control
Body fluid compartments?
The composition and volume of body fluid are tightly controlled homeostatic variables, as well as the concentration of ions and pH (other properties also tightly controlled)
Can be life threatening if these homeostatic variables are not maintained within the normal range
ICF ions?
Low levels of: Na+, Cl-, and free Ca2+
High levels of: K+,
ECF ions?
High levels of: Na+, Cl-, and free Ca2+
Low levels of: K+
*think of potato example, salty on the outside
Both ICF and ECF hold the same osmolarity; 275-300mosmol/L
Body fluid compartment percentages?
Male TBW = 60%
Female TBW = 55%
ECF = 1/3 of TBW
ICF = 2/3 of TBW
Interstitial fluid = 4/5 of ECF
Plasma = 1/5 of ECF
ECF compartments?
Water is always gained or lost from the ECF first as it’s the transitional compartment, being in contact with the outside of the body
Gain: GI tract
Loss: GI tract, kidneys, lungs
Fluid moving between compartments enables nutrient input and waste output thereby maintaining homeostasis
What separates the ICF and ECF?
Plasma membrane (is the barrier) separating intra- from extracellular compartments
Plasma membrane?
- A selectively permeable barrier that encloses the cells organelles, solutes etc.
- Regulates movement of substances between ECF and ICF
- Is an anchorage site to other cells and extracellular components
- Provide location for proteins that detect the presence of signalling molecules
Plasma membrane structure?
- Composed of a phospholipid bilayer with embedded proteins and cholesterol
- Semipermeable; restricts water soluble (polar) molecules (e.g. ions) but allows lipid soluble molecules (non-polar) (e.g. steroid hormones)
What are the two classes of membrane proteins?
- Integral membrane proteins (integrated into the membrane)
- Peripheral membrane proteins (located on the surface of membrane)
Transmembrane proteins?
Transmembrane proteins are a type of integral protein that can span the cell membrane
- Some form selective channels or pores so water soluble substances can pass into or out of the cell e.g. aquaporins
- Some transmit chemical signals across the membrane
- Some anchor extracellular and intracellular protein filaments to the membrane
Peripheral membrane proteins?
Peripheral membrane proteins are associated with one side of the membrane
- Many have an important role in anchoring the membrane to the cytoskeleton OR to the extracellular environment
- Some are enzymes that mediate metabolism of membrane components
- Some transport small molecules along the membrane or between the membrane and cytosol
