Gastrointestinal tract and mechanism of drug absorption

Biopharmaceutics and Pharmacokinetics

1. Presented by K. Bhanu Sri Chandana B. Chandrakala M. Pharmacy 1st Gastrointestinal Tract and Mechanism of Drug Absorption Under the Guidance of Dr. R. Nagaraju M. Pharma, Ph. D. Dept of Pharmaceutics

2. Contents : Gastro Intestinal Tract Mechanism of Drug Absorption References

3. Gastro Intestinal Tract GIT is also known as “Gut” It consists of a hollow muscular tube which starts from the oral cavity to the rectum and anus Gut consists of 3 parts: Foregut Midgut Hindgut

4. Layers of Gut Serosa Muscularis Externa Sub – Mucosa Mucosa

5. Foregut It consists of : Mouth Pharynx Oesophagus Stomach

6. Stomach : Stomach has 4 portions Cardiac portion Fundic Portion Body Pyloric portion Secretions – HCl, Intrinsic factors, Histamine, Serotonin, Mucous

7. Midgut It consists of : Small Intestine Large Intestine Hindgut It consists of : Rectum Anus

8. Small Intestine It consists of : Duodenum Jejunum Ileum

9. Large Intestine It consists of 3 parts : Appendix Caecum Colon

10. Physiological conditions that effect Bioavailability in GIT Transit of Pharmaceuticals in GIT Gastrointestinal pH Enzymes Presence of food or liquids in GIT

11. Mechanism of Drug Absorption Drug Absorption : The process of movement of unchanged drug from the site of administration to the systemic circulation . Bioavailability : The rate and extent of drug entering into the systemic circulation

12. Mechanism The three broad categories of drug transport mechanisms involved in absorption are : A. Transcellular/intracellular transport B. Paracellular/intercellular transport C. Vesicular transport

13. A. Transcellular/Intracellular Transport Passive Transport Processes 2. Active Transport Processes    a. Passive diffusion. b. Pore transport. c. Ion-pair transport. d. Facilitated diffusion . a. Primary active transport b. Secondary active transport i . Symport (co-transport) ii. Antiport (counter-transport)

14. a. Passive diffusion Fick’s first law of diffusion: It states that  the drug molecules diffuse from a region of higher concentration to lower concentration until equilibrium is attained and that the rate of diffusion is directly proportional to the concentration gradient across the membrane .

15. b. Pore transport. It is also called as convective transport, bulk flow or filtration. This mechanism is responsible for transport of molecules into the cell through the protein channels present in the cell membrane.

16. c. Ion-pair transport

17. d. Facilitated diffusion

18. 2. Active Transport Processes    Primary active transport  : Here, there is direct ATP   requirement. T he process transfers only one ion or molecule and in only one direction, and hence called as uniporter ( i ) Ion transporters (ii)  ABC (ATP-binding cassette) transporters 

19. b. Secondary active transport Symport Antiport

20. B. Paracellular/intercellular transport It is defined as the transport of drugs through the junctions between the GI epithelial cells. Permeation through tight junctions of epithelial cells Persorption  

21. C. Vesicular transport It involves transport of substances within vesicles into a cell Vesicular transport of drugs can be classed into two categories: 2. Phagocytosis 1. Pinocytosis

22. References: Ross and Wilson Anatomy and Physiology in Health and Illness Biopharmaceutics and Pharmacokinetics – A Treatise by D. M. Brahmankar and Sunil B. Jaiswal Structural organization and function of Gastrointestinal tract by Suman and Taman