Human Digestive System
From ZuluNotes - Free Leaving Cert Notes
Consists of a number of organs. These organs:
- Mechanically digest food by tearing & crushing food into smaller pieces eg Mouth and Stomach
- Secrete digestive juices to chemically digest and dissolve food eg. Duodenum
- Provide large vascularised surface areas to absorb the products of digestion into the blood eg. Ileum
- Reabsorb water and concentrate unused remains for Egestion eg. Large Intestine
The Alimentary Canal is a term used to describe to continuous tube that begins at the mouth and extends to the anus. It consists of these regions:
- Mouth
- Oesophagus
- Stomach
- Duodenum
- Ileum
- Colon
- Rectum
- Anus
The walls of the canal contain both circular and longitudinal muscles that gradually contract and relax to push the food along it's length.
Contents |
Peristalsis
- The involuntary muscular contractions of the circular & longitudinal muscles that push food through the alimentary canal
Chemical Digestion: Carried out by enzymes which break the large food particles down to single units so that they can be absorbed into the blood
Mechanical Digestion: Begins with the tearing & crushing action of the teeth. The process is continued in the stomach where the muscles gradually contract and relax to further crush the food until it has a liquid consistency.
Teeth
Our teeth play a vital role in the digestion process. They tear and crush food, softening it by mixing it with saliva in the mouth. Teeth are hard surfaces, embedded in the jawbone and adapted to grinding and cutting food. There are 4 different types of teeth. They each have different locations and functions in the mouth:
- Incisors
- Canines
- Premolars
- Molars
Incisors and Canines are at the front of the jaw. They are used for cutting, gripping and tearing food. Premolars and Molars are at the back and are used for crushing and grinding food.
Small Intestine
Is over 5 metres long and consists of the Duodenum, Jejunum and Ileum. The Ileum is the longest part of the small intestine. It's main function is to absorb the products of digestion. The Duodenum provides secretions from 3 sources
- Bile from the gall bladder
- Digestive juices from the walls of the duodenum
- Pancreatic juices from the walls of the duodenum
Functions of the Small Intestine & it's adaptations
- Villi - small finger like projections along the inner lining which increase the surface area
- The surface of each Villus has smaller projections called Microvilli
- Cells at the surface have mitochondria, which provide energy for active transport
- Secretory cells produce large amounts of watery secretions with digestive enzymes
- The blood capillaries are just below the surface to facilitate absorption
Large Intestine
Is approximately 1.5 metres long. It consists of the Caecum, Appendix, Colon and Rectum. Faeces are the remaining mixture of food that enters the large intestine. Faeces consist of fibrous plant materials and large amounts of water from the digestive juices. The large intestine is also a natural habitat for some types of mutualistic bacteria. E. colo is 1 of the most common residential bacteria in the colon. Colon bacteria manufacture some group B vitamins, including Folic Acid and Vitamin K.
Functions of the Large Intestine & it's adaptations
- It is well supplied with blood vessels for re-absorption of valuable materials
- The length provides increased surface area for absorption
- Goblet cells produce large amounts of Mucus to ease the passage of faeces along the intestine
The Liver
Is the most active organ in the body.It is dark red in colour & is found in the abdominal cavity just below the diaphragm close to the stomach. It carries out a number of different functions including storage, detoxification, production and excretion.
- Breaks down and removes poisons from the blood eg. alcohol, nicotine
- Produces bile. Bile salts emulsify fat in the small intestine speeding up their chemical digestion, alkaline salts help neutralise the food from the stomach providing a suitable pH for digestive enzymes
- Main storage site for Carbohydrates in the body (stored in the form of Glycogen). Glycogen is then converted to Glucose by the Liver for energy and it is then released into the blood
- Breaks down excess protein
- Stores fat soluble vitamins (A,D,E,K)
- Produces cholesterol which is essential for the structure of the cell memebrane
- Produces body heat
- Produces Fibrinogen, the protein needed for clotting blood
