Biopharmaceutics Part A - Aulton Chapters 19, 20

The process of absorbing nutrients (e.g., drugs) from the small intestine.

Finger-like projections in the small intestine that increase surface area for absorption.

A creamy mixture of partially digested food in the stomach, ready to move to the small intestine.

The stomach's role is primarily to mix and churn food, not to absorb it.

The small intestine is the primary site for drug absorption due to its large surface area and specialized structures like villi.

The large intestine is inhabited by a diverse population of bacteria which play a vital role in various bodily processes.

The time it takes for a drug to pass through the stomach and into the small intestine.

A series of muscular contractions in the empty stomach that help clear the digestive system.

The rhythmic contractions of the stomach muscles that mix and move food towards the small intestine.

A ring of muscle that controls the flow of food from the stomach into the small intestine.

A process where the digestive tract pushes partially digested food back into the stomach for further mixing and breakdown.

The pH of the stomach can significantly affect the absorption of certain medications, impacting their effectiveness.

The digestive tract contains enzymes that can break down drugs before they are absorbed, potentially affecting their efficacy.

A drug that is inactive in its original form but becomes active after being metabolized by the body.

The process of breaking down and changing a drug into its active form. This usually occurs in the liver.

A drug that is absorbed through the lining of the gastrointestinal tract, entering the bloodstream.

The process of substances like drugs being taken up into the circulatory system from the site of administration.

The movement of a substance across a membrane from an area of high concentration to an area of low concentration.

The process of a drug being taken up by the gastrointestinal membrane and then transported to the bloodstream.

The movement of a drug across the GI membrane through the spaces between cells rather than through them.

A drug that dissolves readily in fats and oils, making it easier to cross cell membranes.

A type of membrane transport that requires energy to move molecules against their concentration gradient, from a region of low concentration to high concentration.

Substances that are actively transported across cell membranes, including nutrients like amino acids, sugars, essential vitamins, and electrolytes.

Facilitated diffusion is a type of carrier-mediated transport that doesn't require energy but relies on protein carriers to facilitate movement across the membrane.

The process of the cell membrane folding inwards to enclose material, forming small vesicles that transport substances into the cell.

A type of endocytosis where the cell engulfs fluids and small particles in a non-specific manner.

A type of endocytosis that uses specific receptors to bind and internalize targeted molecules.

A type of endocytosis where the cell engulfs large particles like bacteria or debris.

The movement of substances through tiny gaps between cells, bypassing the cell membrane. It's important for the absorption of small, water-soluble molecules.

Tight junctions are like seals between cells, controlling what passes through. They are not equally tight everywhere in the body, with the small intestine being more 'leaky' for absorption.

The paracellular pathway's importance decreases as you move along the digestive tract. This is because the gaps between cells become smaller and less numerous.

P-glycoprotein acts like a doorman, kicking out specific drugs back into the gut, reducing their absorption. It requires energy and works against the concentration difference.

The presence of food in the gut can influence how well a drug is absorbed. It might increase, decrease, or have no effect on the absorption process.

The oral route of drug administration offers several benefits, including convenience for the patient, ease of administration, high patient acceptance, and potential for sustained release formulations.

The mucus layer lining the GI epithelium plays a crucial role in protecting the underlying cells from damage, acting as a barrier to harmful substances and facilitating the movement of food through the digestive tract. It's made up of mucins and other components, and its turnover time is approximately 2-3 hours.

The stomach is a muscular organ with a volume that varies depending on the state of fullness. In the fasting state, the stomach holds about 50 ml, while in the fed state, it can expand to hold up to 1.5 liters. Its primary roles include mechanical digestion, chemical digestion (with the help of gastric acid and enzymes), and limited absorption. The pH of the stomach is typically acidic (around 1-3), and gastric secretions include hydrochloric acid, pepsinogen, mucus, and intrinsic factor. Phase III of the Migrating Myoelectric Complex (MMC), also known as the 'housekeeper wave', occurs during the fasting state when the stomach is empty, helping to clear the digestive tract.

The small intestine is the primary site for nutrient and drug absorption. It is approximately 6 meters long and has a slightly alkaline pH (around 7-8). The colon, on the other hand, is responsible for absorbing water and electrolytes. It is about 1.5 meters long and has a neutral pH (around 7). Drug absorption in both the small intestine and the colon can be influenced by factors like surface area, blood flow, and the presence of food.

Gastric motility refers to the patterns of muscular contractions within the stomach. In the fasted state, the stomach undergoes rhythmic contractions called the Migrating Myoelectric Complex (MMC) to clear the digestive tract. In the fed state, peristalsis (wave-like contractions) mixes food and propels it towards the small intestine. The gastric residence time of a dosage form, the time it spends in the stomach, is primarily influenced by two factors: the size of the dosage form (larger forms tend to stay longer) and the presence of food (food slows down gastric emptying). The pyloric sphincter, a circular muscle at the junction of the stomach and small intestine, regulates the passage of food from the stomach into the small intestine.

The gastric residence time of a drug, the time it spends in the stomach, is directly related to the size of the dosage form and the presence of food. Larger dosage forms tend to stay in the stomach longer, while the presence of food slows down gastric emptying. Drugs administered with water typically reach the intestine faster than those administered with food or on an empty stomach because they don't need to be broken down and move through the stomach more quickly.

The GI membrane is a complex barrier that separates the intestinal lumen from the bloodstream. Drug transport across this membrane can occur via passive diffusion, active transport, or facilitated diffusion. Passive diffusion, the most common mechanism for drug absorption, involves the movement of molecules from an area of high concentration to low concentration, without the need for energy. This mechanism is particularly efficient for small, lipophilic molecules. Factors that affect the rate of passive diffusion include the drug's concentration gradient, its lipid solubility, the surface area of the membrane, and the thickness of the membrane.

Active transport involves the movement of molecules across the membrane against their concentration gradient, from an area of low concentration to high concentration, requiring the investment of energy by the cells. This process is mediated by specific carrier proteins and is saturable, meaning that there is a limit to the amount of substance that can be transported at a given time. Active transport allows cells to maintain specific concentrations of molecules within themselves, even if those concentrations are different from those in the surrounding environment.