Human Digestive System: Ingestion to Egestion
The Alimentary Canal
The alimentary canal is a long tube that forms part of the digestive system, along with the liver and pancreas. Key features include:
- Peristalsis: The movement of muscles that contract and relax to propel food along the canal.
- Sphincter Muscles: Specialized muscles that close off sections of the tube.
- Mucus: A substance produced in goblet cells that helps food slide easily.
Ingestion
The process begins in the mouth with the teeth, lips, and tongue. Saliva plays a crucial role:
- Water dissolves substances.
- Mucus binds food together, forming a bolus.
- Amylase digests starch into maltose.
The bolus then travels down the esophagus, a tube that connects the mouth to the stomach.
The Stomach
The stomach contains cells that produce:
- Mucus (goblet cells)
- Rennin (for milk digestion)
- Protease enzymes (pepsin) to digest proteins into polypeptides
- Hydrochloric acid, creating acidic conditions and forming chyme
Digestion and Absorption in the Small Intestine
Duodenum
The pancreas secretes pancreatic juice containing:
- Amylase: Starch to maltose
- Trypsin: Proteins to polypeptides
- Lipase: Fats to fatty acids and glycerol
- Sodium hydrogen carbonate: Reduces acidity
The liver produces bile, which is stored in the gall bladder. Bile contains:
- Bile salts: Emulsify fats (break them into smaller droplets)
- Bile pigments: Excretory products
Ileum
Enzymes are found on the cells covering the villi:
- Maltase: Maltose to glucose
- Sucrase: Sucrose to glucose and fructose
- Lactase: Lactose to glucose and galactose
- Peptidase: Polypeptides to amino acids
- Lipase: Fats to fatty acids and glycerol
Egestion
In the large intestine, indigestible food, bacteria, and some dead cells from the alimentary canal are passed out at intervals through the anus as feces.