Digestive System – Anatomy and Physiology
Introduction
The digestive system is responsible for breaking down food into smaller, absorbable substances that the body can use for energy, growth, and repair.
It also helps in eliminating undigested waste from the body. This process involves both mechanical and chemical digestion.
Definition
The digestive system is a group of organs that work together to convert food into nutrients, which can be absorbed into the bloodstream and utilized by body cells.
Original Notes:
Main Parts of the Digestive System
The digestive system consists of the alimentary canal and accessory digestive organs.
1. Alimentary Canal (Gastrointestinal Tract)
It is a continuous hollow tube that extends from the mouth to the anus.
- Mouth: The starting point of digestion. Food is chewed by teeth and mixed with saliva.
- Teeth: Help in mechanical breakdown of food by cutting, tearing, and grinding.
- Tongue: Helps in mixing food with saliva, tasting, and swallowing.
- Salivary Glands: Secrete saliva containing the enzyme amylase, which starts carbohydrate digestion.
- Pharynx (Throat): Connects mouth to esophagus and helps in swallowing.
- Esophagus: A muscular tube that pushes food to the stomach by peristalsis (wave-like movement).
- Stomach: A muscular sac that stores food and secretes gastric juice containing hydrochloric acid (HCl) and pepsin for protein digestion.
- Small Intestine: The main site for digestion and absorption. It has three parts — duodenum, jejunum, and ileum.
- Digestive enzymes from the pancreas and bile from the liver act here.
- The inner lining has villi that increase surface area for absorption.
- Large Intestine (Colon): Absorbs water and minerals, and forms feces.
- Rectum and Anus: Store and expel waste (feces) from the body.
2. Accessory Digestive Organs
These organs help the digestive process by producing enzymes and secretions.
- Liver: The largest gland in the body. It produces bile, which helps digest fats. It also stores glycogen and removes toxins from blood.
- Gallbladder: Stores and releases bile into the small intestine when needed.
- Pancreas: Produces digestive enzymes (amylase, lipase, trypsin) and hormones like insulin and glucagon.
- Salivary Glands: Aid in initial carbohydrate digestion.
Functions of the Digestive System
- Ingestion: Taking in food through the mouth.
- Digestion: Breaking down food physically (chewing) and chemically (enzymes).
- Absorption: Nutrients pass from the intestine into the bloodstream.
- Assimilation: Body cells use absorbed nutrients for energy and repair.
- Egestion: Removal of undigested waste through the anus.
Digestive Juices and Enzymes
| Organ | Juice | Important Enzymes | Function |
|---|---|---|---|
| Salivary glands | Saliva | Amylase | Breaks down starch into maltose |
| Stomach | Gastric juice | Pepsin | Breaks down proteins |
| Liver | Bile | – | Emulsifies fats |
| Pancreas | Pancreatic juice | Amylase, Lipase, Trypsin | Digests carbohydrates, fats, and proteins |
| Small intestine | Intestinal juice | Maltase, Lactase, Sucrase, Peptidase | Completes digestion of carbohydrates and proteins |
Physiology of Digestion
- Mouth: Food is chewed and mixed with saliva to form bolus.
- Esophagus: Bolus is pushed to stomach via peristalsis.
- Stomach: Proteins are digested by pepsin; acid kills bacteria.
- Small Intestine: Bile and pancreatic enzymes act on food; nutrients are absorbed through villi.
- Large Intestine: Water is absorbed, and waste is solidified into feces.
- Rectum and Anus: Waste is expelled from the body.
Common Disorders of the Digestive System
- Indigestion: Incomplete digestion causing discomfort or pain.
- Constipation: Difficulty in passing stool due to hard feces.
- Diarrhea: Frequent loose stools due to infection or irritation.
- Ulcers: Sores in the stomach or intestinal lining caused by acid.
- Jaundice: Yellowing of skin and eyes due to liver malfunction.
- Gastroesophageal Reflux Disease (GERD): Backflow of stomach acid into the esophagus.
