Drugs are small molecules that often occur in either a neutral or a charged form, depending on pH. For example, aspirin can be either neutral or lose a proton to be negatively charged. When aspirin is charged, it does not diffuse well into the body. pH varies in the gastrointestinal track. Since the stomach has a low pH (pH=3), it has a larger concentration of neutral aspirin (10-3 M), while the small intestine (pH=6) has a smaller neutral aspirin concentration (10-6 M). For the following, assume that the neutrally charged aspirin molecule has a diffusion coefficient through the cell of 1 x 10-6 cm2/s. C) We’d like to figure out where in the body aspirin is absorbed as determined by its diffusion rate. If the small intestine has a surface area 50 times that of the stomach, what is the ratio of the diffusion rates in the stomach compared to the small intestine? D) In which part of the GI tract is most of the aspirin absorbed?
Drugs are small molecules that often occur in either a neutral or a charged form, depending on pH. For example, aspirin can be either neutral or lose a proton to be negatively charged. When aspirin is charged, it does not diffuse well into the body. pH varies in the gastrointestinal track. Since the stomach has a low pH (pH=3), it has a larger concentration of neutral aspirin (10-3 M), while the small intestine (pH=6) has a smaller neutral aspirin concentration (10-6 M). For the following, assume that the neutrally charged aspirin molecule has a diffusion coefficient through the cell of 1 x 10-6 cm2/s.
C) We’d like to figure out where in the body aspirin is absorbed as determined by its diffusion
rate. If the small intestine has a surface area 50 times that of the stomach, what is the ratio
of the diffusion rates in the stomach compared to the small intestine?
D) In which part of the GI tract is most of the aspirin absorbed?
- Since pH affects the solubility of the molecule, which determines the stability of pharmaceuticals, the biological tolerability of the formulation, and the activity of the molecule, pH is a crucial component for all medications manufactured as aqueous liquid forms.
- Ionized drugs cannot pass across biological membranes. Aspirin is mostly unionized in low pH environments like the stomach (pH = 2) and easily penetrates membranes into blood vessels.
- A portion of the nutrients are absorbed by diffusion via the small intestinal wall.
Aspirin does not diffuse well into the body when it is charged. The gastrointestinal tract has varying pH. The concentration of neutral aspirin (10-3 M) is higher in the stomach because of its low pH (pH=3), whereas it is lower in the small intestine (pH=6) (10-6 M).
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