ROA 1

Question 1

What are advantages and disadvatages of oral administration?

Answer 1

advantages:

• Simplest, most convenient and safest
• Systemic or local effects
• Needs to be able to survive acidic conditions of stomach so is resistant to enzymatic attack and absorbed across GI tract membrane

Disadvantages:

• Slow onset of actions
• Irregular absorption in interaction with food (tetracycline and calcium), GI secretions and digestive enzymes (oral insulin)

Question 2

Summarise the GIT characteristics and areas.

Answer 2

The GIT is composed of the;

• oesophagus
• stomach
• small intestine
• large intestine/colon

It is a muscular tube approx 6m long and majority of epithelium is covered by a mucous layer. There is a high surface area for absorption, where this is increased by surface roughness

Question 3

Describe the drug movement through the oesophagus and characteristics of this compartment.

Answer 3

A orally ingested drug form with move through the oesophagus in 5-15 seconds.

The oesophagus links the mouth to the stomach, and has a pH level of 5-6.
Material in this area moves by peristaltic motion, and is assisted by gravity.
- swallowing is commonly impared in the elderly (16%)

Question 4

Describe the drug movement through the stomach and characteristics of this compartment.

Answer 4

Drugs will transit through the stomach in ~2hrs.

This is a temporary reservoir and delivers contents to the duodenum at a controlled rate. It has an approx capacity of 1.5L, or in fasting can be less than 50mL of gastric secretions.
Secretions include acid (pH 1 -3.5), gastrin, pepsins (forms pepsinogen) and mucus (protects gastric mucosa).

Question 5

Describe the drug movement through the small intestine and characteristics of this compartment.

Answer 5

The transit time of drugs through the small intestine is ~4-4.5hrs. It is the longest part of the GIT (4-5m) and functions to;
- digest: completes enzymatic degradation
- absorb: major site for drug and nutrient absorption.
Divided into the duodenum, jejnum and ileum.

SA of the small intestine is increased 600 fold by folds of Kerchring, villi, and microvilli.
- microvilli gives the largest increase in SA and is covered by the fibrous substance glycocalyx.

Question 6

Describe the drug movement through the colon and characteristics of this compartment.

Answer 6

Transit time through the colon is ~24hrs.
Last 1.5m of the GIT and is composed of irregularly folded mucosae that increases the SA of the colon by 10-15 fold. The SA is 1/30th that of the small intestine, and functions mainly to:
- absorb
- exchange
- storage and compaction of faeces.

It is colonised by a variety of bacteria, where the pH of the caecum is 6-6.5 and increases to 7-7.5