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:
1. Foregut
2. Midgut
3. Hindgut

4. Layers of Gut
1. Serosa
2. Muscularis Externa
3. Sub – Mucosa
4. Mucosa

5. Foregut
 It consists of :
1. Mouth
2. Pharynx
3. Oesophagus
4. Stomach

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

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

8. Small Intestine
 It consists of :
a. Duodenum
b. Jejunum
c. Ileum

9. Large Intestine
 It consists of 3 parts :
a. Appendix
b. Caecum
c. Colon

10. Physiological conditions that
effect Bioavailability in GIT
1. Transit of Pharmaceuticals in GIT
2. Gastrointestinal pH
3. Enzymes
4. 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
1. 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
a. Primary active transport :
 Here, there is direct ATP requirement.
 The 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.
1. Permeation through tight junctions of epithelial cells
2. 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