PNB 2774 block 1

homeostasis

a state of maintaining consistent internal conditions. multiple response loops provide input and result in stabilizing outputs.

feedback

the process in which some part of the output of a system is returned to its input in order to regulate the system’s further output. only occurs in closed loop control systems.

negative feedback loops

occurs when the output of a system acts to oppose changes to the input of the system. These shut off the original input and maintain homeostasis. these can self-terminate.

examples: body temp., blood pressure, blood glucose levels.

positive feedback loops

occurs when the output of a system acts to increase changes to the input of the system. these require outside factors to shut down the system. these are NOT homeostatic.

examples: lactation, uterine contractions, blood clotting (?)

coronal plane

divides the body into anterior (front) and posterior (back) parts

transverse plane

divides the body into superior (upper) and inferior (lower) parts

midsagittal plane

divides the body into left and right halves

functions of plasma membrane

structure: lipid bilayer

physical barrier

gateway for exchange (selective permeability)

communication

site of attachment to: other cells, extracellular proteins, intracellular proteins (cytoskeleton, etc.)

membrane transport

the movement of ions or molecules across a cell membrane.

passive transport

does NOT require energy from cell. materials spontaneously move FROM a region of HIGH concentration TO a region of LOW concentration. downhill movement. all types of this type of transport involve diffusion and permit transmembrane flow. has 4 types: simple diffusion, osmosis, facilitated diffusion, and bulk flow.

active transport

DOES require energy input. materials are actively moved TO a region of HIGH concentration FROM a region of LOW concentration. uphill movement.

simple diffusion

the random motion of molecules in solution. results in the spread of molecules from areas of high concentration to low concentration.

properties of simple diffusion

passive and RANDOM process

high concentration to low

net movement until concentrations are uniformly equal

rapid over short distances

directly related to temperature

inversely related to molecular size and fluid viscosity

can occur in an open system or across a partition

fick’s law of diffusion

Jnet = -Ds (dCs/dx) or in simpler terms: rate of diffusion = ((temp x area x membrane perm.) / membrane thickness) x concentration gradient.

flux equals the negative of the product of solute diffusion coeffcient and solute concentration gradient. changing the composition of the lipid bilayer can either increase or decrease membrane permeability. since surface area is a term in Fick’s equation, structures that maximize diffusional flux tend to show expanded surface area and thin epithelia

Flux is

proportional to temperature & concentration gradient and INVERSELY proportional to friction (molecule size, fluid viscosity.)

osmosis

the diffusion of water across a selectively permeable membrane

aquaporins

membrane transport proteins providing a facilitated pathway for water flow through the membrane.

osmolarity

refers to concentrations in units of osmoles/L. depends on concentrations of ALL solutes in cell or solution.

tonicity

refers to the effects of solutions on cells - it’s a relative descriptor. depends on concentrations only of non-permeable solutes.

facilitated diffusion (to be edited)

membrane proteins provide a path for diffusion

bulk filtration

the concentrated movement of large groups of molecules including water. everything moves in the same direction. occurs most often in response to pressure.

channels

membrane proteins that act as a passive conduit for ions through the membrane. when open, provides a continuous pathway through the bilayer, allowing flux of many ions, permitting passive diffusion. may have high selectivity.

channelopathies

diseases or disorders associated with ion channel dysfunction. example: Dravet Syndrome.

Transporter

allows transport of solutes across a cell membrane. can facilitate active or passive transport. in general, these are not designed for speed. examples: carriers and exchangers.

alternating access model

carrier proteins cycle between multiple conformations in which a solute binding site is accessible on one side of the membrane or the other.

occlusion state

a state where in the solute may not access either inside or outside. with carrier proteins, there is never an open channel all the way through the membrane.

primary active transport (pumps)

directly requires ATP. the movement of (one or more) solutes against their concentration gradient using chemical energy. example: Na+/K+ pump.

secondary active transport

utilizes energy stored in pre-existing gradient. the movement of one or more solutes down their concentration gradients provides energy for the movement of other solutes AGAINST their concentration gradient. example: Na+/glucose transporter.