Digestive System: Organs, Processes, and Essential Nutrients
Digestive System
Index
- Digestive Organs
- Digestion
- Indigestion
- Intestinal Digestion and Absorption
- Substances Found in Food
1. Digestive Organs
Types of Digestive Systems in Invertebrates
- Annelida
- Molluscs
- Arthropoda
Annelida
Annelids have a tube-like tract with two openings. These include:
- Mouth
- Muscular pharynx
- Crop (for storing food)
- Gizzard (with small grains of sand for crushing food)
- Intestine (runs through the body and ends at the anus)
Extracellular digestion occurs almost entirely along this tube.
Molluscs
The gastrointestinal tract in most molluscs (except bivalves like clams and oysters) consists of:
- Mouth (with a radula for chewing food)
- Esophagus
- Stomach
- Intestine (leading to the anus)
They have a hepatopancreas gland that aids in the digestive process. Bivalves have a primitive filter-feeding system.
Arthropods
Arthropods are a diverse group with varied feeding habits. Their digestive systems generally include:
- Oral cavity (with appendages for capturing and ingesting food)
- Pharynx
- Esophagus, crop, and gizzard
- Midgut (secretes digestive enzymes)
- Hindgut (leading to the anus)
Various glands secrete digestive enzymes specific to each type of arthropod.
Digestive Tract of Vertebrates
- Oral cavity
- Pharynx
- Esophagus
- Stomach
- Intestine
Oral Cavity
The mouth is surrounded by lips. Inside are teeth for cutting, chopping, and grinding food (mechanical digestion). The tongue, covered in taste buds, mixes food and facilitates its passage to the esophagus. Salivary glands secrete saliva, which:
- Acts as a lubricant
- Destroys some ingested bacteria
- Begins carbohydrate digestion with amylase (breaks down starch into maltose)
Pharynx
The pharynx connects the digestive and respiratory tracts. The epiglottis closes the airway during swallowing, preventing food from entering the respiratory system.
Esophagus
The esophagus is a muscular tube. Peristaltic movements push the food bolus toward the stomach.
Stomach
The stomach stores food temporarily. It consists of:
- Cardiac region (borders the esophagus)
- Body (middle region)
- Pyloric region (connects to the intestine)
Muscular contractions aid mechanical digestion. Gastric juices contribute to chemical digestion. Water, alcohol, and some salts are absorbed in the stomach. Food becomes chyme before entering the intestine.
Intestine
The intestine has two sections:
- Small Intestine: Duodenum, jejunum, and ileum. Performs chemical digestion and absorption.
- Large Intestine: Cecum, colon, rectum, and anus. Absorbs water, stores waste, and houses intestinal flora.
2. Digestion
Digestion involves transforming and absorbing ingested food. Mechanical processes (e.g., chewing) break down food. Chemical processes convert complex molecules into simpler ones for absorption. Carbohydrates become sugars, fats become fatty acids and glycerol, and proteins become amino acids. Hydrolysis, facilitated by enzymes in digestive juices, is the primary chemical reaction.
3. Indigestion
Indigestion refers to upper gastrointestinal discomfort after eating or drinking. Symptoms include heartburn, belching, bloating, nausea, and vomiting. Self-medicating for extended periods is discouraged, as some symptoms mimic serious diseases.
4. Intestinal Digestion and Absorption
The small intestine (duodenum, jejunum, and ileum) completes digestion and absorbs nutrients. The large intestine absorbs water and prepares waste for elimination.
5. Substances Found in Food
Proteins: Found in meat, milk, eggs, and vegetables. Broken down into amino acids for building and repairing tissues.
Carbohydrates: Found in fruits, vegetables, and milk. Provide energy.
Lipids (Fats): Found in milk, meat, oils, and nuts. Provide energy and support various bodily functions.
Minerals: Regulate body processes.