Human Digestive System: Anatomy, Function, and Diseases
Human Body Systems: Nutrition and Waste Elimination
The human body relies on several interconnected systems to obtain nutrients and eliminate waste products. These systems include:
Digestive System
The digestive system transforms food into nutrients that are absorbed into the bloodstream. It consists of the digestive tract and accessory glands.
Digestive Tract
The digestive tract is an 8-meter long tube starting at the mouth and ending at the anus. It includes the following parts:
- Oral cavity (mouth)
- Pharynx
- Oesophagus
- Stomach
- Small intestine
- Large intestine
The inner layer of the digestive tract is a mucous membrane protected by mucus and surrounded by muscular layers that contract to move food along.
Accessory Glands
Accessory glands, located outside the digestive tract, produce digestive juices containing enzymes that break down food. These glands include:
- Salivary glands
- Liver
- Pancreas
Respiratory System
The respiratory system takes in oxygen from the air and transfers it to the blood.
Circulatory System
The circulatory system uses blood to carry nutrients and oxygen to cells and transports waste products from cells to excretory organs.
Lymphatic System
The lymphatic system works with the circulatory system to transport substances throughout the body.
Excretory System
The excretory system removes waste products from the blood and expels them from the body.
Anatomy of the Digestive System
Digestive Tract
Mouth
The mouth is the entry point of the digestive tract and contains:
- Teeth: for biting and breaking down food
- Tongue: for mixing and swallowing food and enabling taste
- Salivary glands: for releasing saliva, a watery liquid that starts the digestion of carbohydrates
Pharynx
The pharynx is a cavity shared by the digestive and respiratory systems. The epiglottis, a small flap of cartilage, prevents food from entering the respiratory tract.
Oesophagus
The oesophagus is a 25 cm tube connecting the pharynx to the stomach. Food travels down the oesophagus through muscular contractions.
Stomach
The stomach has strong muscles and glands that secrete gastric juices to mix with food. Two valves regulate the flow of food: the cardia at the entry point and the pylorus at the exit point.
Gastric juices contain:
- Pepsin: an enzyme that starts protein digestion
- Hydrochloric acid: activates pepsin and helps break down food fibers
Small Intestine
The small intestine is a long tube with glands that secrete intestinal juices and folds called villi that absorb nutrients into the bloodstream. It is divided into three parts: the duodenum, jejunum, and ileum.
Large Intestine
The large intestine is wider than the small intestine and has three parts: the caecum, colon, and rectum. The rectum leads to the anus, where faeces are expelled.
Accessory Glands
Salivary Glands
Three pairs of salivary glands secrete saliva into the mouth. Saliva functions include:
- Digesting carbohydrates
- Destroying bacteria
- Lubricating food
Liver
The liver is the largest gland in the body and has several important functions, including:
- Regulating glucose metabolism
- Storing vitamins and minerals
- Processing alcohol and drugs
- Producing bile, which is stored in the gallbladder
Pancreas
The pancreas has both digestive and endocrine functions:
- Secretes pancreatic juice containing enzymes for digestion
- Produces hormones that are released into the bloodstream
Digestion Process
The digestive process consists of four stages:
Mechanical Digestion
Mechanical digestion involves physically breaking down food into smaller pieces. This includes:
- Mastication (chewing)
- Insalivation (mixing with saliva)
- Swallowing
- Peristalsis (wave-like contractions that move food through the digestive tract)
Chemical Digestion
Chemical digestion uses enzymes to break down food into nutrients. This occurs in the mouth, stomach, and small intestine.
Absorption of Nutrients
Nutrients are absorbed through the walls of the small and large intestines and transported to cells via the bloodstream.
Egestion (Defecation)
Undigested material is eliminated from the body as faeces.
Diseases of the Digestive System
Several diseases can affect the digestive system, including:
- Caries (tooth decay)
- Gingivitis (gum inflammation)
- Pyorrhoea (infection of tooth supporting structures)
- Peptic ulcer
- Gastritis (stomach inflammation)
- Gastroenteritis (stomach and intestine inflammation)
- Appendicitis
- Constipation
- Diarrhoea
- Colon cancer