Why is the upper part of small intestine used (duodenum near stomach? What are t

Question

Why is the upper part of small intestine used (duodenum near stomach? What are the effects and mechanisms of action of 25 degree C Tyrode's solution on the movements of gastrointestinal smooth muscle? What are the effects and mechanisms of action of Ach on the movements of gastrointestinal smooth muscle? What are the effects and mechanisms of action of NE on the movements of gastrointestinal smooth muscle? What are the effects and mechanisms of action of 1 mol/L HCI on the movements of gastrointestinal smooth muscle? What are the effects and mechanisms of action of 1 mol/L NaOH on the movements of gastrointestinal smooth muscle?

Explanation / Answer

1. Duodenum is a part of the body where mnost of the chemical reactions of digestion takes place. Duodenum receives partially digested food from the stomach and further processes the same to be absorbed by the body.Certain hormone secreted in the duodenum stimulates the secretion of digestive enzymes by the pancreas.

A secretion called secretin aids in neutralising the strong acid in the stomach by stimulating pancreas and bile to produce sodium bicarbonate.

Another hormone gastric inhibitory peptide produced in the duodenum aids in the slower rate of transfer of food into duodenum and thus small intestine has adequate time to digest complex food molecules like carbohydrates, proteins and fats.

3. Acetylcholine is a neurotranmitter that aids in the contraction of smooth muscles of gastrointestine. This is done by activation of 2 receptors of M2 and M3. Once activated calcium is released that increases the internal calcium concentration and inturn causes the potassium channels to open. Tha calcium activated potassium channels open that results in the contraction of whole muscle.

4.Norepinephrine derived from extrinsic sympathetic neurons are involved in neurotransmission in gastrointestinal tract. In cointrast to ACh, NE decreases or inhibits the movement of smooth muscles and these are shortened.

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