Active and vesicular Transport

By Dr Nazish

A four-year-old boy severely dehydrated child presented with one day history of severe diarrhea and vomiting and a temperature up to 40°C (104°F).

Over the previous 12 hours the child had watery, bowel movements every 20 Minutes .

Mother gave the history that vommitting is now settled but diarrhea is still there.

On physical examination, the patient's temperature was 39.6°C , his respiratory rate was 28 and his pulse rate was 140 .

The patient weighed 15 kg (33 lb) and had a blood pressure measurement of 90/60 mm Hg. He was alert but irritable, with a dry mouth . Bowel sounds were

increased, and the abdominal examination was otherwise normal.The child was admitted to the peadriatic OPD and was given an intravenous

antibiotic as well as intravenous saline.

Condition of the child improved and was discharged in the morning. Along with an oral antibiotic cover for 5 days the doctor also advised that the child

should be continued with ORS for atleast 2 days.

Active transport

• It is the movement of the molecules against the electrical, concentration or the pressure gradient with the use of energy.

Active transport is a type of assisted transport.• A substance moves against its concentration

gradient.

• It requires a carrier molecule.

• Primary active transport requires the direct use of ATP to drive a sodium-potassium pump.

• Secondary active transport is driven by a concentration gradient of ions established by primary active transport.

PRIMARY ACTIVE TRANSPORT

ICF

ECF

(Passive)Na+–K+

pump (Active)

(Active)(Passive)K+ channelNa+ channel

Figure 3.29 Page 92

= Sodium (Na+) = Potassium (K+) = Phosphate

When open to the ECF, the carrier drops off Na+ on its high-concentration side and picks up K+ from its low-concentration side

Phosphorylated conformation Yof Na+–K+ pump has high affinityfor Na+ and low affinity for K+ when exposed to ICF

When open to the ICF, the carrier picks up Na+ from its low-concentration side and drops off K+ on its high-concentration side

Dephosphorylatedconformation X of Na+–K+ pump has high affinity forK+ and low affinity for Na+when exposed to ECF

ICF

ECF

Figure 3.22Page 82

Importance of Na+-K+ Pump

• Establish Na+-K+ concentration gradient across membrane generation of membrane potential.

• Regulate cell volume by controlling concentration of solutes inside the cells

• Pump energy is used indirectly for co-transport of other materials, i.e., glucose, amino acids

What would be the effect on cell volume, if the sodium

pottasium pump is damaged?

SECONDARY ACTIVE TRANSPORT

Secondary active transport

• Energy is required in the entire process but not directly

• Transportation against conc gradient

• Using carrier with more than one binding site

Lumen ofintestine

No energyrequired

Cotransport carrier Luminal border

Epithelial cell liningsmall intestine

Basolateralborder

Energyrequired

Tightjunction

Na+–K+ pump

Blood vessel

= Sodium = Potassium = Glucose = Phosphate

Figure 3.23

Page 84

No energyrequired Glucose

carrier

CO TRANSPORT

• Sodium glucose co transport in intestinal and renal cells

COUNTER TRANSPORT

SODIUM HYDROGEN COUNTER TRANSPORT

SODIUM CALCIUM COUNTER TRANSPORT

A four-year-old boy severely dehydrated child presented with one day history of severe diarrhea and vomiting and a temperature up to 40°C (104°F).

Over the previous 12 hours the child had watery, bowel movements every 20 Minutes .

Mother gave the history that vommitting is now settled but diarrhea is still there.

On physical examination, the patient's temperature was 39.6°C , his respiratory rate was 28 and his pulse rate was 140 .

The patient weighed 15 kg (33 lb) and had a blood pressure measurement of 90/60 mm Hg. He was alert but irritable, with a dry mouth . Bowel sounds were

increased, and the abdominal examination was otherwise normal.The child was admitted to the peadriatic OPD and was given an intravenous

antibiotic as well as intravenous saline.

Condition of the child improved and was discharged in the morning. Along with an oral antibiotic cover for 5 days the doctor also advised that the child

should be continued with ORS for atleast 2 days. What would be the effects on tonicity of the body fluids of this child?Explain the effects of change of tonicity on the size and shape of body cells.What type of IV fluid is given to the child and why?

How does ORS therapy works? Explain the physiological basis of mechanism of action of ORS in treatment of dehydration..

VESICULAR TRANSPORT

Other kinds of assisted transport are:

• Vesicular transport - Materials move in or out of the cell wrapped in a membrane.

• Need energy

• Examples of vesicular transport are endocytosis and exocytosis.

• By endocytosis substances move into the cell.

• Exocytosis is the reverse process.

Particularprotein

Nucleusof cell

Surface receptor site

Endocytoticpouch

Endocytoticvesicle

Receptor-mediated endocytosis

White blood cell

Pseudopod Bacterium

Phagocytic vesicle

Lysosome

Phagocytosis

Click to view animation.

Phagocytosis

Animation

Click to view animation.

Secretion

Animation

Exocytosis

Characteristics of methods of membrane transport: DIFFUSION

Until Steady state, or stopped by opposing hydrostatic pressure, or cell dies

Passive Water onlySpecial case of osmosis

Until Steady state reached

Passive Specific small ions, Na,K,Cl

Through protein

Continues until gradient is abolished

Passive Nonpolar molecules of any size

O2, CO2, FA

Through lipid bilayer

Limits to transport

Energy requirements & force producing movements

Substances involved

Method of transport

Characteristics of methods of membrane transport: CARRIER MEDIATED TRANSPORT

Transport maximum Cotransport carrier saturation

Active Specific polar molecules and ions for which cotransport carriers available

Secondary ACTIVE TRANSPORT

Transport maximum. Saturation

Active Specific small ions, Na,K,Cl

PRIMARY ACTIVE TRANSPORT

Displays a Transport maximum (Tm). Saturation

Passive Specific polar molecules

glucose

Facilitated DIFFUSION

Limits to transport

Energy requirements & force producing movements

Substances involved

Method of transport

Characteristics of methods of membrane transport: VESICULAR TRANSPORT

Secretion triggered by neural or hormonal stimuli

ATP required Increase in cytosolic Ca induces fusion

Secretory products Large molecules passing through Membrane recycling

EXOCYTOSIS

Necessitates binding to specific receptor site

ATP required

Active

Multimolecular particles

Phagocytosis

Control poorly understood

ATP requiredSmall volume of ECF may be bound with proteins

ENDOCYTOSIS

Pinocytosis

Limits to transport

Energy requirements & force producing movements

Substances involved

Method of transport