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