GNM 1st Year | Anatomy & Physiology
A clear, exam-focused study guide to the digestive system, covering the alimentary canal, digestive organs, digestion, absorption and major digestive glands.
Introduction
The digestive system is responsible for taking in food, breaking it down into smaller substances, absorbing nutrients and water, and removing undigested material from the body.
For GNM students, understanding the digestive system is important because nutrition, digestion, absorption, elimination and many common health conditions are closely related to its normal function.
What Is the Digestive System?
The digestive system consists of the gastrointestinal tract and associated digestive organs. The gastrointestinal tract is a continuous muscular tube extending from the mouth to the anus.
Its major functions include:
- Ingestion of food.
- Mechanical and chemical digestion.
- Movement of food through the gastrointestinal tract.
- Absorption of nutrients and water.
- Elimination of undigested waste.
Main Parts of the Digestive System
The main parts of the alimentary canal are:
- Mouth and oral cavity
- Pharynx
- Oesophagus
- Stomach
- Small intestine
- Large intestine
- Rectum
- Anus
The major accessory digestive organs are:
- Salivary glands
- Liver
- Gallbladder
- Pancreas
Mouth and Oral Cavity
Digestion begins in the mouth. Food is mechanically broken down by chewing and mixed with saliva.
The oral cavity contains the teeth, tongue and openings of the salivary glands.
Functions of the Mouth
- Receives food.
- Chews and mechanically breaks down food.
- Mixes food with saliva.
- Begins carbohydrate digestion.
- Helps form the bolus for swallowing.
Teeth
Teeth are specialized structures used mainly for mechanical digestion.
Different types of teeth perform different functions:
- Incisors: Cutting food.
- Canines: Tearing food.
- Premolars: Crushing and grinding.
- Molars: Crushing and grinding.
Tongue
The tongue is a muscular organ in the oral cavity. It helps move food, mix it with saliva, form the bolus and assist in swallowing.
It also contains sensory structures involved in taste.
Salivary Glands
The major salivary glands are the parotid, submandibular and sublingual glands. They produce saliva, which moistens food and contains enzymes that begin digestion.
Saliva helps lubricate food and contains salivary amylase, which begins the digestion of starch.
Pharynx
The pharynx is a muscular passage that connects the oral cavity with the oesophagus during swallowing. It is also involved in the respiratory pathway.
Oesophagus
The oesophagus is a muscular tube connecting the pharynx to the stomach. It transports swallowed food toward the stomach mainly through coordinated muscular contractions called peristalsis.
Stomach
The stomach is a muscular organ located in the upper part of the abdomen. It receives food from the oesophagus and temporarily stores it while mixing it with gastric secretions.
Functions of the Stomach
- Stores food temporarily.
- Mixes food mechanically.
- Secretes gastric juice.
- Begins significant protein digestion.
- Converts food into a semi-fluid mixture called chyme.
- Regulates the release of gastric contents into the small intestine.
Gastric Juice
Gastric secretions include hydrochloric acid, digestive enzymes and mucus.
Hydrochloric acid creates an acidic environment that supports the activity of pepsin and helps destroy many microorganisms entering with food. The mucus layer helps protect the stomach lining.
Small Intestine
The small intestine is the main site for digestion and absorption of nutrients. It is divided into three parts:
- Duodenum
- Jejunum
- Ileum
Functions of the Small Intestine
- Receives chyme from the stomach.
- Receives bile and pancreatic secretions.
- Completes much of chemical digestion.
- Absorbs nutrients.
- Moves intestinal contents toward the large intestine.
Intestinal Villi
The inner surface of the small intestine contains numerous finger-like projections called villi. Each villus contains blood capillaries and a lymphatic vessel called a lacteal.
Villi greatly increase the surface area available for absorption.
Carbohydrate and protein digestion products are absorbed mainly into blood capillaries, while many products of fat digestion are absorbed through the lymphatic system.
Large Intestine
The large intestine receives the remaining intestinal contents from the small intestine. It consists mainly of the caecum, colon and rectum.
The colon is divided into:
- Ascending colon
- Transverse colon
- Descending colon
- Sigmoid colon
Functions of the Large Intestine
- Absorbs water and electrolytes.
- Helps form and store faeces.
- Contains a large population of intestinal microorganisms.
- Moves faecal material toward the rectum.
Rectum and Anus
The rectum is the terminal part of the large intestine and temporarily stores faeces before defecation.
The anus is the terminal opening of the digestive tract through which faeces are expelled from the body.
Liver
The liver is the largest internal gland and is located mainly in the upper right part of the abdomen. It performs many metabolic and digestive functions.
Important Functions of the Liver
- Produces bile.
- Processes absorbed nutrients.
- Stores glycogen and certain vitamins and minerals.
- Participates in metabolism of carbohydrates, fats and proteins.
- Helps detoxify and process various substances.
- Synthesizes important plasma proteins.
Bile
Bile is produced by the liver and stored and concentrated in the gallbladder. It is released into the small intestine and helps in the digestion and absorption of fats by emulsifying fat into smaller droplets.
Bile does not contain digestive enzymes.
Gallbladder
The gallbladder is a small pear-shaped organ located beneath the liver. Its main functions are to store and concentrate bile and release it into the small intestine when required.
Pancreas
The pancreas is an organ located behind the stomach. It has both digestive and endocrine functions.
Exocrine Function
The exocrine pancreas produces digestive enzymes and bicarbonate-rich fluid that are released into the duodenum.
Pancreatic secretions contribute to the digestion of carbohydrates, proteins and fats.
Endocrine Function
The endocrine pancreas produces hormones such as insulin and glucagon, which help regulate blood glucose levels.
Digestion of Carbohydrates
Carbohydrate digestion begins in the mouth with salivary amylase. Further digestion occurs mainly in the small intestine through pancreatic and intestinal enzymes.
The final products of carbohydrate digestion are mainly simple sugars such as glucose, which can be absorbed through the intestinal lining.
Digestion of Proteins
Protein digestion begins mainly in the stomach with the action of pepsin in an acidic environment. Digestion continues in the small intestine through pancreatic and intestinal enzymes.
The final products are mainly amino acids and small peptides that can be absorbed through the intestinal lining.
Digestion of Fats
Fat digestion occurs mainly in the small intestine. Bile helps emulsify fats, increasing their surface area for enzyme action.
Pancreatic lipase helps break down dietary fats into smaller molecules that can be absorbed by the intestinal lining.
Absorption
Absorption is the movement of digested nutrients, water and electrolytes from the gastrointestinal tract into the blood or lymph.
The small intestine is the principal site of nutrient absorption.
Major Absorption Sites
| Substance | Main absorption site |
|---|---|
| Glucose and other simple sugars | Small intestine |
| Amino acids | Small intestine |
| Fat digestion products | Small intestine; many enter lymphatic lacteals initially |
| Water | Mainly small intestine, with additional absorption in large intestine |
Movement of Food Through the Digestive Tract
The gastrointestinal tract uses coordinated muscular activity to move its contents.
Peristalsis is a series of coordinated muscular contractions that propels food and intestinal contents forward through the digestive tract.
Segmentation consists of localized contractions that mix intestinal contents and assist contact with the intestinal lining.
Stages of Digestion
- Ingestion: Taking food into the mouth.
- Digestion: Mechanical and chemical breakdown of food.
- Absorption: Movement of nutrients and other substances into blood or lymph.
- Elimination: Removal of undigested material from the body as faeces.
Clinical and Nursing Relevance
Knowledge of the digestive system is important in nursing because changes in digestion, absorption and elimination can affect nutrition, hydration and overall health.
During assessment, nurses may observe symptoms such as abdominal pain, nausea, vomiting, diarrhoea, constipation, abdominal distension and changes in appetite or bowel habits.
Nurses also monitor nutritional intake, hydration status, bowel function and relevant symptoms according to the patient's condition.
Quick Revision
- Alimentary canal: Mouth → pharynx → oesophagus → stomach → small intestine → large intestine → rectum → anus.
- Main site of digestion and absorption: Small intestine.
- Three parts of small intestine: Duodenum, jejunum and ileum.
- Three major salivary glands: Parotid, submandibular and sublingual.
- Liver: Produces bile and performs many metabolic functions.
- Gallbladder: Stores and concentrates bile.
- Pancreas: Produces digestive secretions and important hormones.
- Villi: Increase the absorptive surface area of the small intestine.
- Lacteals: Lymphatic vessels within intestinal villi that help absorb dietary fat.
- Peristalsis: Propels gastrointestinal contents forward.
Frequently Asked Questions
Where does most digestion and absorption occur?
Most chemical digestion and nutrient absorption occur in the small intestine.
What are the three parts of the small intestine?
The small intestine consists of the duodenum, jejunum and ileum.
What is the function of bile?
Bile helps emulsify dietary fats, making them easier for digestive enzymes to act upon.
Does bile contain digestive enzymes?
No. Bile does not contain digestive enzymes. Its bile salts help with the digestion and absorption of fats.
What is peristalsis?
Peristalsis is coordinated muscular activity that moves food and other contents through the gastrointestinal tract.
Related GNM Study Resources
After studying this chapter, use the Important Questions on Digestive System for GNM 1st Year for examination preparation.
You can also test your understanding with the Digestive System MCQs for GNM 1st Year.