Lecture #4 Cell Environment & Membranes

homeostasis

the ability of the body to rapidly adjust & adapt to fluctuating environmental conditions while maintaining a constant "milieu inetieur" (essential for proper cell & organ function)

negative feedback, positive feedback, & feed-forward

what are the 3 feedback systems?

negative feedback

responds to an altered output by RESTORING itself towards a PREDETERMINED set point (balance what changed)

positive feedback

responds to a disturbance by moving variable FARTHER AWAY from the INITIAL set point (amplify what changed)

feed-forward

can ANTICIPATE changes & prompt the system to ACT BEFORE the alterations begin to affect it

homeostatic systems

network of feedback loops, hierarchy of feedback loops, redundancy, & adaptability

homeostasis

to maintain a constant internal environment (____________________), you must be able to control it!

control

refers to the direct manipulation of a variable

regulation

refers to the achievement of an end result

integrating

homeostasis generates a response by giving an input signal to the _______________ center, which generates an output signal

decrease

when blood pressure increases, blood vessels do what?

negative

baroreceptor reflex (response to mild hemorrhage) is what type of feedback system since it promotes stability of the environment?

baroreceptor reflex pathway

increased firing when baroreceptors stretch & increased HR, vessel constriction, & cardiac contractibility cause PA to be normal; blood loss: decreased PA, decreased stretch, & decreased firing of carotid sinus nerve

positive feedback

hemorrhagic shock (leads to progressive instability) is what kind of feedback system?

hemorrhagic shock pathway

severe hemorrhage decreases venous return, decreases cardiac output, decreases blood pressure, decreases coronary blood flow, & decreases cardiac contractility (situation heightens)

positive

childbirth is what kind of feedback system?

childbirth pathway

cervical stretch stimulates oxytocin release, which causes contractions, which pushes baby against the cervix

stop the cycle

positive feedback requires an interruption to

negative

what feedback promotes stability?

positive

what feedback promotes a change in one direction, leading to instability (disease & death sometimes)?

blood clotting cascade, childbirth (cervico-uterine feedback), & generations of nerve signals (action potentials)

examples of positive feedback

counteracts

negative feedback: the response ____________ the stimulus, shutting OFF the response loop (initial stimulus->response->decreased stimulus)

reinforces

positive feedback: the response _____________ the stimulus, sending the variable FARTHER from the set point (initial stimulus->response->increased stimulus)

shut off the feedback cycle

positive feedback requires an outside factor to

feed-forward

what feedback anticipates change?

HR increase in anticipation of exercise

what is an example of feed-forward system?

living organism

complex, self-replicating, self-assembling, dynamic, open system, maintained at or very nearly at the steady-state by the continual entry/exit of matter & energy

open system

matter and/or energy can be exchanged with the environment

steady state

the inputs (of matter & energy) equal the outputs; time invariant (a condition stays the same with time)

equilibrium

the lowest free energy state of a system; no gradients of electrochemical potential energy within the system

no

is a steady-state system always in equilibrium?

no net change

steady-state & equilibrium mean

no energy required for that state

equilibrium means

60:40:20 rule

60% of the body is water; 40% of that is ICF & 20% ECF

80% ISF & 20% PV

the ECF is composed of

0.6

total body water is weight in kg times

0.4

ICF is weight in kg times

0.2

ECF is weight in kg times

0.8

interstitial fluid is ECF times

0.2

plasma volume is ECF times

osmotic

the ECF & ICF are in _____________ equilibrium

interstitial fluid

lies between the circulatory system & the cells

blood plasma

liquid matrix of blood

plasma

fluid of blood in RBC (has anticoagulant)

serum

plasma minus the clotting factors (no anticoagulant)

hematocrit

RBC vol/whole blood vol x 100 (percentage of red cells)

Na ion

plasma: ~140 mmol/l

ICF: 9 mmol/l

K ion

plasma: 3.5-5 mmol/l

ICF: 135 mmol/l

Ca ion

plasma: 1-2 mmol/l

ICF: 10^-4 mmol/l

HCO3-

plasma: 24 mmol/l

ICF: 9 mmol/l

pH

plasma: 7.4 mmol/l

ICF: 7.1-7.2 mmol/l

hydrostatic pressure, osmotic pressure, & colloid osmotic pressure

fluid exchange between compartments is driven by a combination of what forces (starling forces)?

hydrostatic pressure

blood pressure (most important)

osmotic pressure

exerted by solutes in the plasma or fluid

colloid osmotic pressure

pressure due to the presence of protein in the fluid (ISF)

D2O, antipyrine

injectable markers for TBW

mannitol, inulin, & sulfate

injectable markers for ECF

labeled albumin (RISA), Evans blue

injectable markers for plasma

TBW-ECF

injectable markers for ICF

ECF-plasma

injectable markers for ISF

amount

amount of marker injected & consumed - amount excreted (mg)

concentration

concentration of marker in plasma (mg/L)

volume

volume of the compartment (L)

volume of the compartment (L)

amount/concentration

classes of lipids

phospholipids, glycolipids, & cholesterol

cell membrane functions

-containment (barrier, protection)

-communications (receptors, signals)

-customs (transporters, channels)

membranes

-separate the cell from the outside world (plasma membrane)

-separate compartments inside the cell (organellar membrane)

-general functions common to all cellular membranes (regulation of solute movement)

-diverse functions (dependent on cell type, organelles, or regions)

bilayer

membranes all have one thing in common: they consist of lipids arranged as a ____________

phospholipids, glycolipids, & cholesterol

3 classes of lipids contribute to the lipid bilayer

phosphate

phospholipids contain glycerol, non-polar fatty acid chains, _________________ group, & polar head group

hydrophilic; hydrophobic

phospholipids are amphipathic- possess both _____________(water-loving) & ______________ (water-fearing) properties

hydrophobic

non-polar end is water insoluble or

hydrophilic

polar end is water soluble

inward

phospholipids can self-assemble to form bilayers: polar heads face water while non-polar ends face

outer leaflet

phosphatidylcholine has choline polar head group & membrane is located on

inner leaflet

phosphatidylethanolamine has ethanolamine polar head group & membrane is located on

inner leaflet

phosphatidylserine has serine polar head group & membrane is located on

outer leaflet

sphingomyelin has choline polar head group & membrane is located on

both inner & outer leaflets

phosphatidylinositol has inositol polar head group & membrane is located on

C16-18

fatty acid chains typically have an even number of carbons in the range C14-24, with _______ being the most common; lipid chains can be saturated or unsaturated

outer leaflet

glycolipids are lipid molecules with sugar moieties found predominantly in the PM, mainly in the

glycolipids

work as cell-cell recognition, receptors, antigens, & protection

galactosylcerebroside

an important component of the myelin sheath

steroids

what is derived from cholesterol?

polar; non-polar

cholesterol has the ______ region to the hydrophilic side & ___________ region to the hydrophobic side of the membrane

cholesterol

occupies both inner & outer leaflets of the membrane

increasing

plants, animals, & bacteria adapt to DECREASING temperatures by ______________ the proportion of unsaturated fatty acids in the membrane

decreasing

plants, animals, & bacteria adapt to INCREASING temperatures by _____________ the proportion of unsaturated fatty acids in the membrane (& increase the saturated fatty acid content)

unsaturated fatty acids

low temps favor

saturated fatty acids

high temps favor

kinked (stops close packing)

unsaturated tails appear

straight (packed together)

saturated tails appear

reduces membrane fluidity

cholesterol does what at moderate temperatures, but hinders solidification at low temps?

this reduces the effects of temperature

cholesterol has a rigid nucleus (it can work as a fluidity buffer for membranes)

eukaryotes

cholesterol is only found in the membranes of

increases fluidity

how does cholesterol effect the membrane at low temps?

acyl chains

at low temps: cholesterol disrupts the close packing of _____________ that would make inflexible membrane

reduces fluidity

how does cholesterol effect the membrane at high temps?

acyl chains

at high temps: cholesterol constrains the mobility of the

more, less

cholesterol makes the membrane (more/less) fluid at cold temps & (more/less) fluid at warmer temps