Define Pharmacokinetics, give the three major mechanisms of drug absorption, and suggest the mechanism of absorption for NaCl in the GIT.

here's the solution to question 2:

2. a) Define Pharmacokinetics.
Pharmacokinetics is the study of how the body affects a drug. It describes the quantitative relationship between drug dose and drug concentration in the body over time, encompassing the processes of Absorption, Distribution, Metabolism, and Excretion (ADME).

$$\boxed{\text{Pharmacokinetics: The study of drug ADME (Absorption, Distribution, Metabolism, Excretion).}}$$

b) Give the three major mechanisms of drug absorption.
The three major mechanisms of drug absorption across biological membranes are:

1. Passive Diffusion: Movement of a drug from an area of higher concentration to an area of lower concentration, directly across the lipid bilayer, without the need for a carrier or energy.
2. Facilitated Diffusion: Movement of a drug across a membrane down its concentration gradient, aided by a specific carrier protein, but without the expenditure of metabolic energy.
3. Active Transport: Movement of a drug across a membrane against its concentration gradient, requiring a specific carrier protein and the expenditure of metabolic energy (ATP).

c) Suggest the mechanism of absorption undergone by the following in the GIT:

• i) Sodium chloride: Sodium ions are primarily absorbed via active transport mechanisms (e.g., Na$^+$-K$^+$ ATPase, Na$^+$-glucose cotransport, Na$^+$-H$^+$ exchange), while chloride ions often follow passively or via specific chloride channels.

  $$\boxed{\text{Sodium chloride: Active transport}}$$

• ii) Glucose: Glucose is absorbed by both facilitated diffusion (via GLUT2 transporters) and secondary active transport (via SGLT1 cotransporters, which use the sodium gradient).

  $$\boxed{\text{Glucose: Facilitated diffusion and secondary active transport}}$$

• iii) Ethanol: Ethanol is a small, lipid-soluble molecule that is readily absorbed across biological membranes primarily by passive diffusion.

  $$\boxed{\text{Ethanol: Passive diffusion}}$$

• iv) Acetyl Salicylic acid: Acetyl salicylic acid (aspirin) is a weak acid. In the acidic environment of the stomach, it exists predominantly in its unionized, lipid-soluble form, allowing it to be absorbed efficiently by passive diffusion.

  $$\boxed{\text{Acetyl Salicylic acid: Passive diffusion}}$$

• v) Water: Water is absorbed across the gastrointestinal tract primarily by osmosis, which is a form of passive movement across semi-permeable membranes, driven by osmotic gradients.

  $$\boxed{\text{Water: Osmosis (passive diffusion)}}$$