Transport Across Cell Membrane
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Transcript of Transport Across Cell Membrane
TRANSPORT ACROSS CELL MEMBRANE
Main Objectives
• Classification • Different Modes, pathways, mechanisms &
their importance• Osmosis
ICF and ECF
CLASSIFICATION
Membrane transportPassive / Diffusion Active Osmosis/
Vesicular
Simple Facilitated Primary Secondary
Countertransport
Cotransport
Basis Of Diffusion
•No need of extra energy •Occurs due to kinetic energy•From high to low concentration•No carrier protein in simple diffusion•Carrier protein for facilitated diffusion
High solute concentration Low solute concentration
Net Diffusion
Equal concentration No net diffusion
Simple Diffusion
Facilitated Diffusion
Active Transport
TRANSPORT PATHWAYSDepends upon lipid solubility
Water soluble
E.g. O2 E.g. Na+, E.g. Glucose
E.g. Ca++
•Channel protein• Selectively permeable • Mostly gated• Na+, K+, Cl-
•Carrier protein• Glucose, amino acids
Channel And Carrier Proteins
Selective Permeability of Protein Channels
Types of gated channels - Voltage gated, Ligand gated, Mechanically stretched
Channel Proteins – Open & gated states
Voltage Gated ChannelsImportant in action potential
Closed Channel Open Channel Inactivated Channel
Ligand Gated channels Neuromuscular junction
Channel closed Channel open
Mechanically Gated channels Pressure or Stretch
Channel closed Channel open
Concentration gradient
Electrical gradient
Pressure gradient
Factors affecting net diffusion
Facilitated Diffusion – Glucose & AA
• No need of energy• From higher to
lower concentration• Needs carrier
proteins• Has Vmax
Due to weak binding and thermal motion
Facilitated Diffusion - Vmax
The rate of transport can not be greater than the rate of back & forth change in carrier protein
Concentration Difference
Molecular weightLipid solubility
Surface area
Membrane thickness
Diffusion – Factors Affecting Permeability
Primary Active Transport
• Against chemical gradient (uphill)• Needs carrier proteins• Needs extra energy• Has Vmax• Types:-
– Primary active e.g. – Na+ - K+ pump, Ca++ pump,– Secondary active
• Co transport – Glucose / AA with Na+ in intestine, kidney• Counter transport - H+ with Na+ in PCT of kidney
Primary Active- E.G. Sodium Potassium Pump
•Maintains sodium-potassium concentration in ICF & ECF•Electrogenic pump•Regulation of cell volume, pressure
Primary Active Transport – Ca++
Secondary Active Transport / UniportSodium Glucose Co-transport
More Na+
Less Na+ More glucose
Less glucose
ECF
ICF
(OR Amino Acid)
Na – Glucose Cotransport
Secondary Active Counter transport /Antiport
Na+
H+
Two ions move in opposite direction
Sodium-Hydrogen counter transport
Osmosis And Osmotic Pressure
Osmotic PressureAmount of pressure required to stop the osmosis
1 osmole = 1gm mol wt of soluteNormal osmolarity of ECF = 300 mOsmol
Osmolality-1 osmole of solute in 1 kg of water
Osmolarity - 1 osmole of solute in 1 lit. of water
The osmotic pressure exerted depends upon the number of particles & not by the mass of the particles
Tonicity
Cell shrinks No change Cell swells
Hypertonic Isotonic hypotonic
Intracellular fluid 300mOsmoleNon penetrating solutes
Normal cell volume
How do they attach to each other?Intercellular attachments
Tight junctions-Kidney, intestine
Gap junctions
Desmosomes-Skin
How do they communicate?Intercellular communications
TARGET ORGAN
How do they take substances in & out?
Endocytosis
Exocytosis
Now the substance is in ICF
Now the substance is in ECF
How do they take larger particles?Pinocytosis – Cell drinking
How do they digest unwanted material?Phagocytosis – Cell eating
How do they move?Amoeboid movements
Ciliary movements
Respiratory passagesFallopian tubes
Summary
Main Study MaterialGuyton – 11th ed. Chap. 4Ganong – 23rd ed. Chap. 1Vander – 9th ed. Chap. 4
Thank You