Human Digestive System: Functions and Organs
Functions of the Digestive System
- Digestion of Food: Breakdown of food into smaller particles.
- Mechanical Digestion: Changes the physical form of food.
- Chewing in the mouth
- Churning in the stomach.
- Chemical Digestion: Enzymes change the chemical composition of food.
- Lipids to fatty acids
- Proteins to amino acids
- Carbohydrates into simple sugars
- Absorption of Nutrients: Transport of nutrients to the blood.
- Assimilation of Nutrients: Transport of nutrients into the cells.
- Egestion of Faeces: Semi-solid waste material passes out of the body.
Mouth
Salivary Glands
Produce saliva to break up the food. Enzymes in saliva convert starch into glucose.
The Tongue
Helps to crush the food and mixes it with the saliva (forming a bolus). It also helps deglutition and is covered with taste buds.
The Teeth
Cut and chew the food.
- Crown: This is the part we can see.
- Root(s): This is the part embedded in the jaw bone.
- Incisors: Cut the food.
- Canines: Tear the food.
- Premolars and Molars: Crush and grind the food.
- Adults have 32 teeth, children have 20.
The Pharynx (Throat)
It belongs to both the digestive and respiratory tracts. It connects the mouth with the esophagus.
Swallowing
The bolus is pushed into the pharynx by the tongue. The soft palate closes off the nose. The larynx rises and the epiglottis (cartilage) closes the trachea (respiratory system). The bolus is pushed into the esophagus.
The Esophagus
It is a muscular tube that connects the pharynx with the stomach and takes food down to the stomach due to peristaltic movements (wave-like movement of the walls of the alimentary canal that helps to move food through the canal and contributes to physical digestion).
The Pancreas
It is a glandular organ with two main functions:
- It produces hormones that regulate the quantities of glucose.
- It secretes pancreatic juice that is released into the duodenum and contains juices that attack all the molecules found in chyme: carbohydrates, lipids, and proteins.
The Liver
It is an organ that produces bile, that is stored in the gallbladder and is released when food enters the intestine. Bile does not contain digestive enzymes. Bile contains bile salts that emulsify fats (enzymes found in digestive juices break down fats. Fats are transformed into very small drops).
Assimilation of Nutrients in the Liver
Assimilation is the movement of nutrients into the cells of the body where they are used. The hepatic portal vein delivers blood from the small intestine to the liver. This blood contains nutrients absorbed during digestion (glucose, amino acids, fatty acids) that are transported to the liver for assimilation.
The Stomach
Muscular organ important for the digestion of proteins. The stomach is connected with valves to:
- The esophagus through the cardia.
- The small intestine through the pylorus.
The stomach has three parts (fundus, body, and antrum).
Gastric Juice
The stomach produces gastric juice that is mixed with the bolus inside the stomach.
Gastric juice contains:
- Gastric proteases (enzymes) that digest proteins into amino acids.
- Hydrochloric acid that creates an acidic environment:
- To kill bacteria.
- Necessary for proteases to develop their activity.
The walls of the stomach contract to break the bolus (physical digestion). The digested food that leaves the stomach is called chyme.