Thursday, February 26, 2009



1. What is amphipathic?
Lipids forms the basic structure of the membrane .the lipid molecules are amphipathic, inotherwords they have a hydrophilic polar region at one end of the molecule and hydrophobic hydrocarbon tail at the other end.
The hydrophilic ends of the lipid molecule line up facing the ICF and ECF.
The hydrophobic tail end faces each other in the interior of the bilayer.

2. What is integral and peripheral membrane protein?
1) Integral or intrinsic proteins bind to the hydrophobic center of the lipid bilayer.
Eg: a).transmembrane protein-span the entire bilayer.
They serve as: channels-through which water-soluble substances can diffuse.
  Carriers-transport materials across the bilayer.
  Pumps-actively transport ions across the bilayer.
  Receptors: initiate intracellular process when activated.
 b) Proteins that is present on only one side of the membrane-
  Eg-enzymes-activate or inactivate various metabolic processes.
2) peripheral-or-Extrinsic-bind to hydrophilic polar heads of lipid or integral protein.
Cytoskeleton-peripheral protein binds to intracellular surface of the membrane.
Glycocalyx-bind to extra cellular surface.

3. What is Michaelis-Menten, kinetics?
Unlike simple diffusion the rate of facilitated diffusion rises as the concentration gradient increases until all the binding sites are filled. At this point the rate of diffusion can no longer rise with increasing point of concentration. This is called saturation or Michaelis –Menten, kinetics.

4. How does the membrane potential affect the rate of diffusion of anions and cations?
Electrical potential produce an electrostatic force. A positive charge inside the membrane will attract anions into the cell and repel movement of an ion will depend on the balance of the chemical and electrical gradient acting on it that is the electrochemical gradient.

5. Which ions are most important in the osmotic control of cell volume? Why are they important?
Na ions and Cl ions in the ECF and K ions and inorganic anions (po4and sulphates) inside the cell. These ions are important because,
1. They are osmotically active at cell membrane, which have only limited permeability to them
2. They make the largest contributions to the total osmolality of the relevant solutions.
3. There is a concentration gradient across the cell membrane.
This is maintained both by low membrane permeability and by active transport system (for Na and K)
6. What are cell adhesion molecules? CAMs
Cells are attached to each other by cell adhesion molecules. They also transmit signals into and out of cell. These adhesion proteins (viz.laminin, integrin, IgG, Catherin, selectin) play important role in 
1. Embryonic development
2. Formation of N.S
3. Holding tissues together
4. Inflamation and wound healing
5. Metastasis of tumor

7. What is demarcation potential?
If the axon under one of the electrode is damaged, e.g.-by crushing or cutting the nerve (in damaged area, polarity is abolished) then the damaged area becomes negative relative to the healthy portion at rest. Therefore steady potential difference bn: Two electrodes are recorded at rest, called injury (demarcation) potential.

8. What is Retropulsion?
It is the back and forth movement of the chyme caused by forceful propulsion of food against the closed pyloric sphinter.The wave of peristalsis reaches the pyloric sphinter before the chyme,then when the chyme reaches the sphinter ,it is pushed back in to the body of the stomach.

9. What is receptive relaxation?
When the food enters the stomach, the fundus and upper portion of the body relax and accommodate the food. Peristalsis then begins in the lower portion, mixing and grinding permitting small, semi liquid portion to pass through the pylorus and enter the duodenum. Receptive relaxation is vagally mediated and triggered by movement of esophagus and pharynx.

10. What is haustral shuttling?
Bands of muscles divide the large intestine into saclike segments called haustrations.Although haustrations are present when the colon is empty, the entry of food into the colon cause an increase in colonic contractile activity.
The dynamic formation and disappearance of haustral contractions squeeze the chyme, moving back and forth along the colon similar to S.I segmental contractions.

11. What is antral systole?
The contractions of distal stomach caused by peristaltic wave are called antral systole. In addition, can last up to 10sec.waves occur three-4 times/mt

12. What is Ghrelin?
It is a 28a.a polypeptide. It stimulates growth hormone secretion and has pronounced effect on food intake. It is produced in the stomach and arcuate nucleus. The blood levels of it are decreased after food and increased during fasting.

13. What is paralytic secretion?
Claude Bernard observed that cutting the chorda tympani (parasym) in experimental animals produces scanty secretion of thin turbid saliva, which increases to peak on 7th day and decreases in 3rd week. He called it paralytic bcz it was due to cutting the nerve. However, later on it was observed that the secretion is due to increased sensitivity if the gland to adrenaline after cutting the nerve.

14. What is caloric value? State the caloric value of fat, protein and carbohydrate.
The energy liberated from metabolism of 1gm of substance is known as caloric value of that substance.
Fat-9 calories

15. What is molecular mimicry?
It is a phenomenon that has been discovered as one of the causes for autoimmunity bcz of molecular similarity between foreign and selfpeptides.An example is Rheumatic fever following streptococcal infection. It is due to development of antibodies against streptococcus that cross-react with cardiac myosin and damage the heart. (A portion of cardiac myosin resemble a portion of streptococcal M protein)

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