Gastrointestinal tract (GIT) medications Flashcards
Oral cavity
Substances enter the digestive system through the mouth. As food enters, the salivary glands release saliva, which mixes with the food to form a bolus (a wet mass). The mouth is the first site of chemical digestion, while chewing (mastication) breaks down food into smaller pieces for swallowing.
Drugs can enter the mouth as tablets, capsules, or liquids and are usually swallowed to enter the digestive tract. However, not all drugs are swallowed. Some, given by the buccal (inside the cheek) or sublingual (under the tongue) routes, are absorbed quickly through the mouth lining, bypassing the rest of the digestive system.
Oesophagus
The pharynx connects to the stomach through the esophagus, a long tube. Two muscular sphincters, at the top and bottom of the esophagus, open during swallowing to let food pass from the pharynx to the stomach.
The esophagus doesn’t play a big role in drug absorption. However, if the upper sphincter is weak or relaxed, stomach acid can flow back into the esophagus, causing heartburn or acid reflux. Some gastrointestinal medications are designed to neutralize this acid and relieve symptoms of reflux.
Stomach
When the bolus reaches the stomach, it is mixed with stomach secretions and broken down into chyme, a semifluid mass. While some protein and fat digestion happens here, very little absorption occurs in the stomach. After 2-6 hours, the chyme is slowly released into the small intestine.
The stomach lining has five types of cells that aid digestion. Four of them (surface mucous cells, mucous neck cells, parietal cells, and chief cells) produce gastric secretions, which include mucin (protects the stomach), intrinsic factor (helps absorb vitamin B12), hydrochloric acid, and pepsin. The fifth cell type, G cells, releases gastrin, which helps with stomach movement and secretion.
Though the stomach doesn’t absorb much food, it can absorb drugs, especially acidic ones like aspirin. To prevent disintegration in the stomach’s acidic environment, some drugs are enteric coated so they dissolve in the intestines instead. The speed at which the stomach empties can also impact how quickly a drug is absorbed, with faster emptying leading to quicker absorption.
Small intestine: Duodenum, jejunum and ileum
Chyme leaves the stomach in small amounts and enters the duodenum, the first part of the small intestine. In the small intestine, it mixes with bile and pancreatic juices from the gallbladder and pancreas. These secretions are controlled by two hormones, CCK and secretin. The chyme then moves to the jejunum for digestion and absorption, and this continues in the ileum, the last part of the small intestine.
Most drugs are absorbed in the intestines due to their large surface area. Food in the gut can affect drug absorption, which is why some drugs are taken before meals (for faster absorption) and others with food (to prevent stomach irritation). Gastrointestinal issues like vomiting, diarrhea, or constipation can also affect how well drugs are absorbed.
Large intestine
The watery chyme moves from the small intestine into the large intestine, which extends from the ileum to the anus. The large intestine includes the caecum, ascending colon, transverse colon, descending colon, sigmoid colon, rectum, and anus. Its main job is to absorb water and electrolytes (like sodium and chloride), turning the chyme into faeces. Bacteria in the large intestine help break down leftover carbohydrates, proteins, and fats.
Inflammation can change the structure and function of the gut wall, which may affect drug absorption, depending on the affected area. The GIT also plays a role in drug excretion, with some drugs being excreted in bile and removed with faeces.
Introducing solids/liquids into the oral cavity
Ingestion
Mixing and moving material through the GIT
Motility
Manufacturing and releasing substances that facilitate digestion
Secretion
Breaking down (mechanically or chemically) ingested food into smaller structures
Digestion
Transporting digested molecules, electrolytes, vitamins, water from the GIT into the blood or lymph
Absorption
Expelling indigestible or unabsorbed material
Elimination
An introduction to gastrointestinal tract conditions
Good bowel function relies on a diet with enough fiber, proper fluid intake, and regular physical activity, which may also help prevent some gastrointestinal diseases. Some GIT issues, like nausea, vomiting, diarrhea, and constipation, are temporary and linked to infections or diseases, while others are chronic and need ongoing treatment.
Nausea and vomiting
Definition
Nausea is an uneasiness of the stomach
Vomiting is the forcible voluntary or involuntary emptying of stomach contents through the mouth
Processes at play
Causes include food allergies, seasickness, morning sickness, GIT infections, and some medications, including cancer treatments
Gastric reflux (Heartburn)
Definition
Excessive activity of the stomach acid
Processes at play
Stomach produces hydrochloric acid or HCl and this acid flows up into the oesophagus
If prolonged is referred to as gastro-oesophageal-reflux disease (GORD)
Peptic ulcers
Definition
An erosion or break in the stomach mucosa - allows contacts between eroded area and the stomach’s acid (HCl)
Processes at play
Erosions may be caused by bacteria e.g. Helicobacter pylori (a spiral-shaped bacteria)
May occur from overproduction of acid (rare) e.g. from gastrin-producing tumours
