Physiology Gi Tract

INTRODUCTION

Give a brief description in your own words of the objectives and aims of this practical.

The aim of this practical was to understand how the autonomic nervous system has an effect

In the ileum. Through this, we can delve deeper by understanding how nerves, through the actions

Of various neurotransmitters affect the motility of the gastrointesital tract. Furthermore, we can investigate

The effects of drugs, and their uses in replicating effects of autonomic neurotransmitters as well as

The way certain drugs can interfere with autonomic neurotransmitters and how they interact with

Their target tissues.

A. RESPONSES TO NERVE STIMULATION

 Attach a copy of your experimental recordings showing a period of spontaneous contractions and the response to stimulating the nerves at 20 Hz with both a voltage that produced only a modest response and the voltage that produced the maximal response.

1) Briefly describe the response of the ileum when it is unstimulated and during stimulation of the nerves.

When the ileum is unstimulated, the contraction peaks at around 8mV and goes down to around

1 mV. This is repeated steadily. During Stimulation, the ileum contractility depends on the voltage and

Frequency. For 5v stimulation, the contractility of the ileum rapidly declines.

2) What is the frequency of the regular spontaneous contractions of the ileum? What causes these spontaneous contractions?

14Hz. The longitudinal muscle layers cause these spontaneous contractions.

 Attach a copy of your experimental recordings showing the response to stimulating the nerves with the maximal voltage at both 5 Hz and 50 Hz.

3) Explain the effect of altering stimulus frequency on the response of the ileum to nerve stimulation.

Increasing the stimulus frequency decreases the ileum contractility (Mv) At 5hz there was a minimal

Decrease in contractility. However, when the frequency was increased to 50Hz, there was a large

Decrease in ileum contractility, a larger response.

B. MIMICKING THE ACTION OF THE AUTONOMIC NERVOUS SYSTEM USING DRUGS

 Attach copies of your experimental recordings showing the response of the ileum to the direct addition of noradrenaline and of acetylcholine to the tissue bath.

1) What was the final bath concentration of noradrenaline you used? Briefly describe the response of the ileum to the direct addition of noradrenaline.

C1v1=c2v2------30x10^-6 x 0.25 = 50.25 x c2 ----------- c2=1.49x10^-7 M

Upon addition of noradrenaline, there was a gradual decrease in ileum contractility.

2) What was the final bath concentration of acetylcholine you used? Briefly describe the response of the ileum to the direct addition of acetylcholine.

C1v1=c2v2------30x10^-6 x 0.25 = 50.25 x c2 ----------- c2=1.49x10^-7 M

Upon addition of acetylcholine, there was a rapid increase in ileum contractility.

3) Since an inhibitory response to nerve stimulation was observed in all (or most) of the tissues studied in the practical, how is differential control (i.e., both inhibition and excitation) of gut contraction achieved in the body? Is it always inhibitory in vivo? What happens in the intact animal?

Waves of contractions which allows contents to travel through the gut. The smooth muscle

Contractions generate enough force to push the contents through the gut and toward

The rectum. This occurs when the intestinal wall is stretched.

C. BLOCKING AUTONOMIC NERVOUS SYSTEM TRANSMITTER TARGETS

Effect of phentolamine on the responses to nerve stimulation and added transmitter substances

 Attach copies of your experimental recordings showing the response of the ileum