T1L4 - Cell physiology Flashcards by Mohamed Yusuf

Solvent [3]

fluid present
Biological systems - it is water
Organic fluids in lab

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Solute [3]

particles dissolved in solvent
Can be atoms & molecules
DNA, sugars, proteins & H+ ions

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Important ions

Na+, K+, Ca2+, H+, Mg2+, OH-, Cl-, HCO3_, SO4-, PO4-& charged proteins

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PO4-

is important for reactions involving ATP (enzyme) & structurally in bone

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SO4-

is important structurally in glycosaminoglycan (connective tissue )

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Ionic imbalance causes [8]

Trauma 
Haemorrhage
Diabetes
Hormonal imbalances
Dehydration
Kidney dysfunction
Poisons 
Extensive D &amp; V

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Fluid compartments: plasma

Na+ based

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Fluid compartments: interstitial

~ plasma & lacks blood proteins

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Fluid compartments: Intracellular

K+ based & lots of protein

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Fluid compartments: Transcellular

In the lumen of tubes and organs

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Methods of transport

Channels 
Pumps 
Transporters
Exchangers
Leak

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Role of ions

Start cellular processes and act as secondary messengers - transmit information across cell membrane

Second messengers are molecular mechanisms for transmitting chemical signals from outside cell (usually a hormone or neurotransmitter)
Create energy (as ATP), activate enzymes (protein kinase C),  move water (kidney) &amp; control transmembrane voltage (voltage = information in neurones)

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Wrong ion concentration of ions can lead to

cardiac arrhythmias, bone deformities, oedema & seizures

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Voltage

The difference in potential energy between 2 points in an electric field. The electric potential or driving force for charged particles (ions) to move.

V= IR 
V = I/G

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Chemical force

Called diffusional force
Based upon the difference in concentration across membrane
10X as much Na+ outside, 30X as much potassium in intracellular fluid than extracellularly

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Electrical force

Based on Vm (membrane potential -> varies over time)

Based on a few positive charges

Blood fluids and ions

• Na+ gets pumped or moves through ion channels
• Cl- tends to follow Na+
Water follows Cl-

Plasma and ions

• Highest in Na+ concentration

Slightly more negative in electric potential than extracellular fluid

Intracellular Fluid and ions

Highest in Highest in proteins
Highest electrolyte concentration (milliEquivalents)
Most negative voltage

Extracellular space and ions

Highest chloride concentration (lac

Excitable

• Cells that can propagate an action potential
• An action potential is a specific kind of amplified voltage response
Neurons and muscle cells are excitable

Non-excitable

Cells without action potentials
Not muscle or nerve
Skins & liver (especially epithelial cells

Hypocalcaemia

(insufficient free calcium in blood) leads to paraesthesia -> over-reactive tendon reflexes

ECG abnormalities and risks of arrhythmia of heart

Free calcium

Calcium ions that are ionised and in solution -> free to activate enzymes

Calcium found in bone -part of an insoluble solid that will not react with enzymes

It can be bound to proteins
It can be sequestered inside cellular organelles

Free calcium concentration

○ ~ 100 nanoM (that is, one tenth of a micromolar conc) | Cf. extracellular free Ca2+ = 1.2 milliM, > 10,000X

Actin & Myosin

Myosin = a golf-club shaped motor protein with a hinge. The myosin head bends (and generates force) by breaking ATP Actin = a structural protein that myosin grabs onto

Second messenger

Calcium, kinases, phospholipases

Rules

The concentration of positive and negative ions must “nearly” balance Any ion that leaves the cell must be replaced soon by another ion of that type coming into the cell Energy is always being used to re-establish the ionic gradients across membranes

The concentration of positive and negative ions must “nearly” balance

○ If a positive ion moves across the membrane, the charge imbalance must be corrected Either a negative ion will shortly follow to correct the imbalance, or another positive charge must go in the opposite direction “Nearly” means that there can be tiny amounts of unbalanced cations on one side of a membrane that are near to anions on the other side of the membrane

Any ion that leaves the cell must be replaced soon by another ion of that type coming into the cell

This is fundamental to homeostasis, otherwise the salivary cells would run out of K+ ions Often the replacement happens at opposite ends of the cell, so when chloride enters the cell at the basolateral membrane, it may leave the cell at the apical membrane

Energy is always being used to re-establish the ionic gradients across membranes

``` Example: Na+ / K+ pump (ATPase) exchanges 3 Na+ outward for 2 K+ inward, and consumes ATP to pump these ions against their concentration gradients Without energy (eg after death) the ionic gradients dissipate and equalise. This is an example of entropy. ```