The Digestive System

DIGESTION

• Is the process, which breaks down food into substances that can be absorbed and used by the body for energy, growth, repair and heat

ANATOMY

• Alimentary Canal (mouth – anus) which consists of:  Teeth, tongue, salivary glands, oesophagus, stomach, small and large intestine, rectum and anus

ACCESORY ORGANS

• Liver, gall-bladder, pancreas

DIGESTIVE PROCESSES

• Ingestion
• Movement of food
• Digestion
• Absorption
• Elimination 

DIGESTION IS CARRIED OUT 

• Mechanically e.g. chewing
• Chemically through enzymes and acids 

DIGESTION IN THE MOUTH 

• Mechanically by chewing
• Chemically – enzyme in saliva o Amylase – initiates break down of starch 

OESOPHAGUS 

• Secretes mucous  
• Transports food to stomach by peristalsis 

DIGESTION IN THE STOMACH 

• Mucous secreted to protect stomach lining  
• Mechanical – breaks down food and mixes it with digestive juices until it becomes thin liquid called chyme
• Chemical - enzyme Pepsin to break down proteins  - hydrochloric acid – activates pepsin

SMALL INTESTINE 

• Duodenum    25cm  
• Jejunum       2.5m  
• Ileum   3.6m

DIGESTION IN THE SMALL INTESTINE 

•   Duodenum - Pancreatic juices from Pancreas: Trypsin, Lipase and Amylase       + Bile from gall bladder enters Duodenum
•  Jejunum and Ileum – Secrete intestinal juices (2-3 litres a day): Lactase, Maltase, Sucrase Have mucous membranes arranged in folds, which are covered with VILLI – finger like projections that absorb fatty acids, monosaccharides and amino acids 90% of absorption takes place in the small intestine. 
• Ileum – Studded with lymphatic nodes – PEYERS PATCHES

LARGE INTESTINE also known as the Colon 

• Completion of Absorption (water)  
• Manufacture of certain vitamins
• Formation and expulsion of faeces 

ACCESSORY ORGANS:

Pancreas

• Secretes pancreatic juices into the duodenum
• Islets of Langerhans – secretes hormones – insulin/glucagon 

 Liver (weighs 3lb)

• Made up of right and left lobes
• Function: o
  • Formation of bile – 1 litre/day (made of disintegrated red blood cells). Responsible for breaking down fats
  • Detoxifying organ – parcels up toxins for elimination  
  • Stores vitamins and glycogen o Manufactures enzymes, cholesterol, vitamin A and clotting factors
  • Activates vitamin D

Gall Bladder

• Stores and concentrates bile 

Additional Information for VTCT Qualification 
 

Salivary Glands 
 
There are 3 pairs of salivary glands: ? Sublingual – found underneath and either side of the tongue ? Submandibular – under the angle of the jaw ? Parotid – found just near the masseter muscle on each side of the face Saliva helps to lubricate food, making it easier to swallow and also stimulates the taste buds. It plays an important role in keeping the tissues of the mouth moist and clean. There is an enzyme called amylase present in saliva which is important for beginning the chemical breakdown of starches 
 
Body Fat 
 
Body fat is made from carbohydrates and proteins and fats eaten in excess of the body‘s needs and stored in the fat deposits mainly under the skin but also around organs such as the kidneys and liver. When required the stored fat can be converted into energy. In order to release these stores the energy output has to be greater than the calorie intake.

DIGESTION SNIPPETS 
 
Nutrients provide the energy necessary to drive the chemical reactions required in living organisms. In addition nutrients supply the chemicals necessary for building and maintaining the body tissues. Nutrients are obtained as food and are not in a suitable state for immediate use. The digestive system is designed to perform two major functions. Food particles are broken down into molecules of small enough size to cross the plasma membrane in the process called digestion. The passage of these particles into the blood and lymphatic system is called absorption. 
 
The digestive system organs are divided into two groups: the gastro-intestinal tract and the accessory organs. The g.i. tract (sometimes called the alimentary canal) is essentially a continuous tube from the mouth to the anus. The mouth, pharynx, oesophagus, stomach, small intestine and large intestine are all considered structures of the g.i. tract. Food is digested inside the lumen of this tract.  The accessory structures aid mechanical and chemical digestion and include the teeth, tongue, salivary glands, liver, gallbladder and pancreas. The tongue and teeth function in ingestion and mechanical digestion while the other accessory structures provide secretions necessary for chemical digestion. 

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