Download Lecture 3 - ISpatula

Physiology
lec 2 Monday
 Revision of last lecture :
- All systems work for general aim which is homeostasis & keep
the internal environment almost constant
- Internal environment is the interstitial space
- Fluids are around 60 % of our body weight
- There are two kinds of fluids :
1. Intracellular fluids (ICF)
2. Extracellular fluids (ECF)
- Extracellular fluids divided into : 1. Vascular 2. Interstitial
- The plasma membrane separates the ICF & ECF with different
constituents .
- Na+ intracellular is 14 millimoles , extracellular 40 millimoles (
the concentrations) the membrane maintains this separation
because one of the important properties of the membrane its
selective permeability. K+ intracellular 20 millimoles ,
extracellular 4.5 millimoles. And apply the same for all ions.
- mole = g\ molecular weight .
- 1 mole of all substances have the same number of molecules
- Membrane is a bilayer of phospholipids that have charged
heads & hydrophobic tails & that’s good (subhan allah )
because both the ECF & ICF are aqueous solutions ( water
environment).
- The bilayer is the main part of the membrane , & the membrane
is not static & move constantly (flip flop) (due to fluid mosaic )
- Other parts of the membrane : proteins
 NEW :
- Membrane proteins are two kinds :
1. Integral proteins (structural) 2.peripheral proteins
- Integral proteins form channels through which substance pass
from one side to the other side if they are open ( according
“with “ concentration gradient )
- The channel may close , not always opened
- The channels are specific , they allow specific substance to
pass through & don’t allow other substances
- Peripheral(surface) proteins are on the surface outside or inside
- Peripheral proteins also beside the integral sometimes form
antigens (ABO) & give specificity for cells & important for giving
cell identity
- Peripheral proteins might form enzymes & they’re on the
surface , not floating
- Ex : enzyme sucrase splits sucrose & lactase splits lactose
(on the surface of GI tract cells ) & maltase splits maltose
- ABO : on the surface of RBC there is A antigen or B antigen or
nothing O
- 3rd constituent of the membrane : carbohydrates , that may bind
to the protein to give glycoprotein or they bind to lipids to give
glycolipids
- Constituents of membrane :
1. Lipid bilayer 2. Proteins 3. Carbohydrates
- Functions of membrane proteins :
1. Ion channel
2. transporter (carrier)
3. Receptor
4. Enzyme
5. Cell identity maker
6. Linker
- If the membrane is broken down then the cell die
- Membrane proteins also move with the lipid bilayer
- Percentage of proteins in the cell membrane depends on the
cell type
 Osmosis & osmotic pressure & Osmolality
- If you have substance in a solution ,this substance might be
dissociated into different molecules
- Ex : 150 mM of Na+Cl- means 150 mM of Na+ + 150 mM of Cl- =
300 mM of molecules
- Number of molecules = osmolality =300 m osm \ L
- If the cell 400 mOsm\L & out 300 mOsm\L , the membrane is
semi permeable (to water ) water will move from lower
osmolality or higher concentration of water to higher osmolality
or lower concentration of water by osmosis until the osmolality
is the same
- 300 mOsm\L is the normal osmolality of our body fluids
- Isotonic solution of NaCl is 150 mOsm\L (2 ions)
- Isotonic solution of glucose 300 mOsm\ L (doesn’t dissociate)
- Isotonic solution of CaCl2 is 100 mOsm\L ( 3 ions )
 Transport of substances
- Two kinds of transport :
1. Passive transport : with concentration gradient (higher to lower)
, no energy needed (downhill transport)
2. Active transport : against concentration gradient (lower to
higher) , energy needed (uphill transport )
- Passive transport has 2 kinds :
1. Simple Diffusion : from higher to lower through the membrane
( the substances are lipid soluble ) ( hydrophilic can’t) (CO2 , O2,
steroids)
- if lipid permeability increases the transported molecules
increase
J= how much transport
Jα
lipid solubility * ▲C
▲C the gradient
√molecular weight * membrane thickness
- The smaller the molecule so it passes easier
- In the lungs the membrane is so thin ( where the exchange
occurs ) , in many diseases like emphysema the membrane is
thicker so the patient has dyspnea because of the exchange
become harder
2. Facilitated diffusion : (carrier mediated diffusion )from
higher to lower concentration , but the molecules are too large
or charged so they need a carrier ( in both directions ) ( no
energy ) (ions)
- They have Tmax transport maximum ( Vmax) ( saturable)
- Osmosis is the transport of water from higher to lower
concentration of water through a membrane
- ‫ فتتوقف حركة الماء‬diffusion ‫يرتفع عمود الماء حتى يمنع الضغط المولد من الماء قوة‬
- Osmotic pressure : pressure that is needed to prevent osmosis
- Solution maybe hyposmotic (less than 300) , hyperosmotic
(more than 300) , isosmotic (280-310)
- Active transport
- Needs ATP , pumps
- Ex : Na+ \ K+ pump , electrogenic pump , primary active ( ATP
delivers directly )(expels 3 Na for 2 K inside)
- Secondary active : you don’t spend the energy directly to move
the substance , you use it indirectly
- Secondary active :
1. Antiporter (countertransporter) (Ca outside & Na inside
)(exchanger)
2. Cotransporter ( symporters) (inside Na & glucose inside )
3. Endocytosis , exocytosis , phagocytosis , pinocytosis
- Active & facilitated all are saturable ( have Tmax)
Done by : Noor Aswad