2.1 Explain the anatomy and physiology of the gastrointestinal tract in relation to extended feeding

This guide will help you answer 2.1 Explain the anatomy and physiology of the gastrointestinal tract in relation to extended feeding.

The gastrointestinal tract (GI tract or digestive system) moves food, absorbs nutrients and eliminates waste. In extended feeding, such as tube feeding or parenteral nutrition, understanding how each part functions helps keep people healthy and safe.

The GI tract is a long, muscular tube running from the mouth to the anus. Each section has a distinct role in digestion, even when some or all natural feeding is bypassed.

Key parts include:

Mouth
Pharynx (throat)
Oesophagus
Stomach
Small intestine (duodenum, jejunum, ileum)
Large intestine (colon)
Rectum and anus

Accessory organs—like the liver, gallbladder, and pancreas—support digestion by producing or storing enzymes and fluids, although they do not form part of the tract itself.

Mouth and Oral Cavity

The mouth is where food enters and the process of digestion starts. Teeth break up food (chewing or mastication), while saliva moistens and begins to break down starches using an enzyme called amylase.

In people who need extended feeding, food often bypasses the mouth. Even though this step is missed, keeping the mouth clean remains important to prevent infections and discomfort.

Key facts:

Enzymes in the saliva start digestion of carbohydrates.
Swallowing shapes food into a bolus (soft mass) for easy passage.
Problems at this stage (like swallowing difficulty) may require tube feeding.

Pharynx and Oesophagus

The pharynx, or throat, guides chewed food or fluid from the mouth to the oesophagus. The oesophagus is a muscular tube carrying food to the stomach using wave-like muscle actions called peristalsis.

Important details:

Peristalsis moves food or nutrients downwards, even with a feeding tube inserted into the stomach or intestine.
An oesophageal sphincter at the lower end prevents acid reflux.
If the swallowing reflex is impaired, feeding tubes may be used to protect the airway and support nutrition.

Stomach

The stomach is a muscular, pouch-like organ. It mixes food with gastric juices, containing hydrochloric acid and digestive enzymes (like pepsin), to form a semi-liquid called chyme.

Main functions:

Breaking down proteins.
Mixing and churning food.
Acting as a reservoir, slowly releasing contents to the small intestine.
Killing many germs due to acidity.

For tube feeding (enteral nutrition), the stomach is often used. A gastrostomy tube (PEG tube) may be sited directly into the stomach through the abdominal wall.

Points to remember:

Large volumes too quickly can cause stomach discomfort or vomiting.
The pyloric sphincter at the lower end controls release into the duodenum (first part of the small intestine).
Acid and enzymes may irritate tissues if tubes are not properly sited.

Small Intestine

The small intestine has three main parts: duodenum, jejunum, and ileum. It is the longest section of the GI tract, about 6-7 metres in adults.

Functions:

Digests and absorbs most nutrients.
Breaks down proteins, fats, and carbohydrates with help from digestive juices from the pancreas and bile from the liver.
Transfers nutrients into the bloodstream through the intestinal wall.

For some tube feeding, a jejunostomy (feeding tube into the jejunum) is used, especially if the stomach cannot be accessed directly or is not working properly. Feeding is often slower and more frequent to match the intestine’s capacity.

Special points:

The lining (mucosa) is covered in tiny finger-like projections called villi, which increase the surface area for absorption.
Damage or disease (e.g., in Crohn’s disease) affects nutrient absorption.

Large Intestine (Colon)

The large intestine starts at the ileocaecal junction and ends at the anus. It absorbs water and salts from the remaining undigested material, turning it into faeces.

Main parts:

Caecum
Ascending, transverse, descending, and sigmoid colon
Rectum

Functions:

Absorbs remaining water to form solid stool.
Houses bacteria that help break down some fibres.
Short-term storage of waste before expulsion.

In extended feeding, less use of the upper GI tract or changes in gut bacteria may affect bowel movements. Faecal output may change with longer periods on tube feeds, sometimes leading to constipation or diarrhoea.

Rectum and Anus

The rectum stores faeces until they are passed out. The anus has two sphincters—internal (involuntary) and external (voluntary)—that control bowel movements.

Extended feeding may affect this process if the GI tract is underused or bowel movements are less regular.

Accessory Organs: Liver, Gallbladder, and Pancreas

Though not part of the GI tract, three major organs assist digestion:

Liver: Produces bile, helps process nutrients, and detoxifies chemicals.
Gallbladder: Stores and releases bile to help break down fats.
Pancreas: Releases digestive enzymes and hormones (like insulin to control blood sugar).

Problems in these organs can affect digestion, absorption, and the type of feeding support needed.

Extended Feeding Methods and the GI Tract

Extended feeding is often needed when a person cannot maintain adequate nutrition by mouth. Main options:

Enteral feeding uses a tube placed in the stomach, duodenum, or jejunum. Examples: nasogastric tube (via the nose), gastrostomy tube (direct to stomach), and jejunostomy tube (direct to jejunum).
Parenteral nutrition is given intravenously, bypassing the GI tract completely. Mainly used if the gut cannot be used at all.

Enteral Feeding (Through the GI Tract)

Nasogastric tubes (NGT) pass through the nose and oesophagus to the stomach.
Gastrostomy tubes (such as PEG) are inserted through the skin directly into the stomach.
Jejunostomy tubes (PEG-J or PEJ) go further into the small intestine.

These methods deliver nutrition, fluid, and medication when normal feeding is not possible or safe.

Key facts for enteral feeding:

Nutrients must be in a form the intestine can absorb.
Feeds can be bolus (large amounts at intervals) or continuous (slow and steady).
The functioning mucosa absorbs nutrients if healthy.
Feeding tubes must be well cared for to prevent infection, blockage, or movement.

Parenteral Nutrition (Bypassing the GI Tract)

Total parenteral nutrition (TPN) delivers nutrients directly into a vein, often a large one near the heart. Used if the gut is non-functioning or has been removed, such as after major surgery, severe Crohn’s disease, or bowel obstruction.

Key differences:

No digestion or absorption by the gut.
All nutrition is formulated to provide precise amounts of calories, protein, fat, vitamins, and minerals.
Careful monitoring is needed, as risks include infection and imbalances in blood nutrients or fluids.

Physiology in Relation to Extended Feeding

Muscle Movement (Peristalsis)

Muscles throughout the GI tract contract in waves called peristalsis. This pushes contents along, from mouth to anus.

If tubes are inside the GI tract, peristalsis helps move tube feeds or flush fluids.
Sick or immobile people may have slower peristalsis, risking constipation.

Enzyme Action

Enzymes are chemicals that break food into nutrients:

Salivary enzymes begin breaking down starchy food in the mouth.
Gastric enzymes and acids attack proteins and help kill bacteria.
Pancreatic enzymes released into the small intestine finish breaking down protein, fats, and carbohydrates.
Bile from the liver emulsifies fats, making absorption easier.

For feeding tubes, pre-digested or special feeds may be needed if natural enzyme action is inadequate.

Absorption

Most nutrients are absorbed in the small intestine. The structure of villi and microvilli increases the contact area, maximising absorption.

Water and some minerals are absorbed in the large intestine.
Damage to the mucosa (lining) may reduce absorption, needing adjustments to feeding.

Prevention of Infection

Natural feeding maintains the integrity of mouth and gut tissues. With extended feeding, oral and gut linings may be more prone to infection, especially if feeds or equipment are not kept clean.

Regular mouth care remains important.
Feeding tubes and site hygiene are necessary to prevent complications.

Impact of Long-Term Tube Feeding

When the GI tract is not used for normal eating and drinking, some parts may change or become less active.

Potential effects:

Muscle tone in the gut may decrease, slowing transit and leading to constipation.
The gut’s natural defences against infection may weaken.
Reduced saliva flow may lead to oral infections.
Gut bacteria balance can change, affecting bowel function.

Extended feeding often requires monitoring for:

Tube position and function
Signs of leaks, infection, or blockages
Weight and hydration
Regular bowel function

Complications Related to GI Anatomy and Physiology

Awareness of complications is key for those working in health and social care. Some risks linked to extended feeding and the GI tract include:

Reflux or aspiration (food/fluid entering lungs) if the stomach does not empty well or if the person cannot protect their airway.
Blockages in the tube or tract, sometimes due to thick feeds or kinks.
Diarrhoea if feeds are too fast, concentrated, or poorly absorbed.
Constipation if movement is reduced or water intake is low.
Infections at tube sites or within the gut.

These complications link closely to the anatomy (structure) and physiology (function) of the GI tract.

Care Approaches Based on Anatomy and Physiology

Health and social care workers use knowledge of anatomy and physiology for:

Checking placement and function of tubes.
Selecting appropriate feeding methods (e.g., stomach feeding if there is normal stomach function, or jejunal feeding if there is delayed stomach emptying).
Monitoring bowel health and addressing issues early.
Educating and reassuring the individual receiving extended feeding.
Reporting signs of infection or tube problems.

Regular assessment aids in maintaining health and improving comfort.

Final Thoughts

Understanding the GI tract’s structure and working principles supports safe and effective extended feeding. Each section of the tract has its own role, even if feeds bypass one or more sections.

Skilled support ensures individuals needing extended feeding stay as healthy and comfortable as possible.