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Passive Transport
✓ Osmosis
✓ Diffusion
✓ Facilitated Transport
Extracellular Fluid contains;
° large amount sodium
° small amount potassium
° large amount chloride ions
intracellular fluid contains;
° phosphates
° proteins
now miscible with either extracellular or intracellular fluid
lipid bilayer
a penetrating protein, interrupt the continuity of the lipid bilayer, constituting an alternative pathway through the cell membrane
transport protein
way through the molecule and allow free movement of water, as well as selected ions or molecules
channel proteins
bind with molecules or ions that are to be transported
carrier proteins
energy that causes diffusion
kinetic motion of matter
random molecular movement of substances molecule by molecule, either through intermolecular spaces in the membrane or in combination with a carrier proteins
diffusion
movement of ions or other substances across the membrane in combination with a carrier proteins in such that the carrier protein causes the substances to move against energy gradient.
active transport
Diffusion through the cell membrane is divided into two subtypes:
° Simple Diffusion
° Facilitated Diffusion
kinetic movement of molecules or ions occur through a membrane opening or through intermolecular spaces without any interaction with carrier proteins in the membrane
Simple Diffusion
requires interaction of a carrier proteins
facilitated diffusion
Simple diffusion can occur through the cell membrane by two pathways;
° through the interstices of the lipid bilayer
° through the watery channels
determines how rapidly a substance diffuses through the lipid bilayer
lipid solubility
are composed of integral cell membrane proteins that form open tubes through the membrane and are always open
pores
the protein channels are distinguished by two important characteristics;
- often selectively permeable to certain substances
- many of the channels can be opened or closed by the gates that are regulated by electrical signals
permit passage of potassium ions across the cell membrane about 1000 times
Potassium Channels
is only 0.3 by 0.5 nanometer in diameter, but more important, the inner surfaces of this channel are lined with amino acids that are strongly negatively charged
sodium channels
controlling ion permeability of the channels
gating of protein channels
the opening and closing of gates are controlled in two principal ways;
° voltage gating
° chemical(ligand) gating
the molecular conformation of the gate or of it’s chemical bonds responds to the electrical potential across the cell membrane
voltage gating
opened by the binding of a chemical substances with the protein; open or closes gate
chemical(ligand) gating
Most important substances that cross cell membranes by facilitated diffusion are;
glucose and amino acids
activated by insulin, which can increase the rate of facilitated diffusion of glucose as much as 10-fold to 20-fold in insulin-sensitive tissues
glucose transporter 4 (GLUT4)
the sum of all the forces of the different molecules striking a unit surface area at a given instant
pressure
most abundant substance that diffuses through the cell membrane
water
the process of net movement of water caused by concentration difference of water
osmosis
the exact amount of pressure required to stop osmosis
osmotic pressure
called to a unit, to express the concentration of a solution in terms of numbers of particles
osmolarity
a process called when a cell membrane moves molecules or ions “uphill” against a concentration gradient
active transport
Active transport is divided into two types according to the source of the energy used to cause the transport
- primary active transport
- secondary transport
the energy derived directly from breakdown of Adenosine triphosphate (ATP) or of some other high-energy phosphate compound
primary active transport
the energy is derived secondarily from energy that has been stored in the form of ionic concentration
secondary active transport
Substances that are transported by primary active transport are;
sodium, potassium, calcium, hydrogen, chloride, and few other ions
the active transport mechanism that has been studied greatest detail
sodium-potassium pump
Three specific features that are important for the functioning of the pump;
° has 3 reception sites for binding sodium ions
° has 2 receptor sites of potassium ions
° the inside portion has ATpase activity
Most important functions of Na+-K pump
to control the volume of each cell
normally maintained at extremely low concentration in the intracellular cytosol of virtually all cells in the body
calcium pump
two places in the body, primary active transport of hydrogen ions is important
✓ in the gastric glands of the stomach
✓ in the late distal tubules and cortical collecting ducts of the chicken
parietal cells have the most potent primary active mechanism for transporting hydrogen ions of many part of the body
gastric glands
are specialized intercalated cells in the late distal tubules and cortical collecting ducts that also transport hydrogen ions by primary active transport
renal tubules
represents a storehouse of energy because the excess sodium outside the cell membrane is always attempting to diffuse to the interior
gradient
sodium ions again attempt to diffuse to the interior of the cell because of their large concentration gradient
counter-transport
are especially important mechanisms in transporting glucose across the renal and intestinal epithelial cells
sodium-glucose co-transport
the action potentials conducted from node to node
saltatory conduction
the process of eliciting the action potential
excitation
period during which a second action potential cannot be elicited, even with a strong stimulus
absolute refractory period
an experimental apparatus which is used to measure flow of ions through the different channels
voltage clamp
the potential difference between the inside and outside
Diffusion potential
the potential difference required, with negativity inside the fiber membrane
94 millivolts
rises high enough within the milliseconds to block further net diffusion ions to the inside
membrane potential
positive inside the fiber
61 millivolts
the diffusion potential level across the a membrane that exactly opposes the net diffusion of a particular ion through the membrane
nernst potential
is placed in the extracellular fluid, and the potential difference between the inside and outside of the fiber is measured using an appropriate voltmeter
indifferent electrode
recording electrode passes through the voltage change area at the cell membrane
electrical dipole layer
resting potential
-90 millivolts
more positive chargers are pumped to the outside than to the inside
electrogenic pump
causes large concentrations gradients sodium and potassium across the resting nerve membrane
sodium potassium pump
Sodium
° 142 mEq/L (outside)
° 14 mEq/L (inside)
Potassium
° 4 mEq/L (outside)
° 140 mEq/L (inside)
ratio of sodium ions from inside to outside the membrane
0.1
transmit nerve signal which are rapid changes in the membrane potential that spread rapidly along the nerve fiber membrane
action potentials
resting membrane potential before the action potential begins
resting stage
permeable to sodium ion
depolarization stage
permeable to potassium ions
repolarization stage
two types of transport channels through the nerve membrane
° voltage-gated sodium
° potassium channels
one near the outside of the channel
activation gate
another near the inside
inactivation gate
during this state, sodium ions can pour inward through the channel, increasing the sodium permeability of the membrane as much as 500- to 5000- fold
activated state
composed of numerous fibers ranging from 10-80 micrometer diameter
skeletal muscles
is a thin membrane enclosing a skeletal muscle fiber
sarcolemma
are composed of actin and myosin filaments
myofibrils
are larged polymerized protein molecules that are responsible for the actual muscle contraction
myosin filaments and actin filaments
a light bands contain only actin filaments
I bands (isotropic)
dark bands contain myosin filaments, as well as as the ends of the actin filaments where they overlap the myosin
A bands (anisotropic)
the portion of the myofibril that lies between two successive Z discs
sacromere
keep the myosin and actin filament ls in place
thin filamentous molecules
achieved by a large number of filamentous molecules of a protein
titin
act as a framework that holds the myosin and actin filaments in place so that the contractile machinery of the sarcomere will work
springy titin molecules
is a specialized ER of skeletal muscle
Sarcoplasmic Reticulum
are composed of multiple myosin molecules
myosin filaments
composed of six polypeptide chains two heavy chains and four light chains
myosin molecules
actin filaments are composed of;
actin, tropomyosin, troponin
a double stranded, the backbone of the actin filaments and represented by two lighter-colored strands
F-actin protein molecule
a polymerized strand of double F-actin helix, having a molecular weight of about 42000
G-actin molecules
another actin filaments has a molecular weight of 70000 and la length of 49 nanometers
tropomyosin molecules
one hypothesis for which considerable evidence exist
walk along (ratchet theory)
tilt of the head
power stroke
the greater the amount of work performed by the muscle, the greater the amount of ATP is cleaved
Fenn effect
at a sarcomere length of about 2 micrometers, it attracts upon activation with the approximate maximum force of attraction
resting length
increase in tension that occurs during contraction, decreases as the muscle is stretched beyond its normal length
active tension
energy is transferred from the muscle to the external load
work
first source of energy that is used to reconstrate ATP, carries a high phosphate bond, similar to the bonds of ATP
phosphocreatine
second source of energy that is used to reconstitute both ATP and phosphocreatine
glycolysis
third and final source of energy
oxidative metabolism
many features of muscle contraction can be demonstrated by eliciting single what?
muscle twitches
when the muscle does not shorten during contraction
isometric
when it does not shorten but the tension on the muscle remains constant throughout the contraction
isotonic
muscles reacts rapidly, including anterior tibialis are composed of mainly of this
fast fibers
muscle such as soleus that respond slowly but with prolonged contraction are composed of this fibers
slow fibers
iron-containing protein similar to hemoglobin in RBC
myoglobin
deficit of red myoglobin in fast muscle
white muscle
all muscle fibers wre innervated by a single nerve fiber
motor unit
adding together of individual twitch contractions to increase the intensity of overall muscle contraction
summation
increasing the frequency of contraction. can lead to tetanization
frequency summation
when the frequency reaches a critical level, the successive contraction eventually is rapid so that they fuse together
tetanization
a phenomenon which strength of contraction increases to a plateau
staircase effect/treppe
even when muscle are at rest, a certain amount of tautness usually remains
muscle tone
prolonged and strong contraction of a muscle
muscle fatigue
when the total mass of muscle decreases
muscle atrophy
enlargement of individual muscle fibers
fiber hypertrophy
pathway that appears to account for much of the protein degradation in a muscle undergoing atrophy
ATP-dependent ubiquitin-proteasome pathway
chemical reaction that breaks peptide bonds
proteolysis
regulatory protein that basically label which cells will be targeted for proteasomal degradation
ubiquitin
increase in fiber number
fiber hyperplasia
the fibrous tissue that replaces by the muscle fibers during denervation atrophy alse has a tendency to continue shortening for many months
contracture
causes large motor units
macro motor units
muscles that contract and become rigid, even without potentials
rigor mortis
