Digestion.pptx

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Digestive System

Sports Nutrition

Stephen Williams

Digestive system - Functions

• Three main things occur in the digestive system:

• Foods are broken down into their individual nutrients.

  • These nutrients are then absorbed into the blood stream.

  • Any waste is excreted.

Digestive system - functions

These things are achieve in a number of ways:

• Ingestion – the action of putting food and drink into your mouth is known as ingestion.

• Propulsion – this is the movement of food from one area of the digestive system to the next. It occurs by strong waves of involuntary muscle contraction called peristalsis

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Digestive system - functions

Mechanical digestion

• Starts outside the mouth – food is cooked and cut up.

• In the mouth food is chewed.

• In the stomach food is churned and mixed.

Digestive system - functions

Chemical digestion

• Digestive juices are present in the mouth and other digestive organs.

• Digestive juices contain digestive enzymes that break down the large molecules of the nutrients in food into smaller ones that can be absorbed into the blood.

Digestive system - functions

Digestive system - functions

Absorption

• The products of digestion are mainly absorbed in the small intestine

Excretion / defecation

• Expulsion of any waste matter not needed by the body

Digestive System Structure

• The digestion and absorbtion of nutrients and the elimination of waste takes place in the gastrointestinal tract or gut.

• This is a long tube running from the mouth to the anus.

• It includes the mouth, pharynx, oesophagus, stomach, small intestine, large intestine (colon) and the anus.

• There are three other organs important in the digestive system the pancreas, the liver and the gall bladder.

Gastrointestinal Tract

Mouth (Buccal cavity)

• Teeth and jaws grind and mash the food.

• Salivary gland release saliva.

• Saliva softens food.

• Saliva also contains the digestive enzyme amylase which starts the breakdown of carbohydrates.

• The tongue helps mix the food and then produce the swallowing action.

Oesphagus

• Once swallowed food enters the oesophagus.

• This delivers food to the stomach helped by gravity and peristalsis (contractions of the muscular wall of the gut).

• Amylase continues to break down carbohydrate.

Stomach

• Stomach continues chemical digestion, but no absorption takes place here as further digestion is needed.

• Only alcohol is absorbed in the stomach!

• The stomach is made up of layers of smooth muscle.

• The contractions help mix food and more digestive enzymes.

Stomach

• Pepsinogen is released, a protein digesting enzyme.

• The stomach also secretes hydrochloric acid which kills off some bacteria and helps break down of food.

• The stomach takes around four hours to empty completely after a meal.

Pancreas

• Although not part of the gut the pancreas is a very important digestive organ.

• It secretes digestive juices containing three digestive enzymes.

• Amylase which acts to break down carbohydrates.

• Lipase which breaks down fats

• Proteases (like trypsin) to digest protein.

Small intestine

• Most digestion takes place in the top two thirds of the small intestine.

• The small intestine is 5-6m long.

• It is folded to fit in a small area.

• It has three parts

  • Duodenum – top 25cm

  • Jejunum – next 2m

  • Ileum – 3-4m

Small intestine

• The partly digested food, called chyme moves through the small intestine helped by gravity and peristalsis.

• The inside walls of the small intestine have lots of small folds called villi and micro villi.

• These increase the surface area so more nutrients can be absorbed.

• Any waste is passed on to the large intestine.

Liver

• Like the pancreas, liver is also separate from the gut (the food does not pass through the liver or pancreas) but is still important.

• The liver makes bile.

• Bile is important as it helps in the digestion of fats.

• Bile is stored in the gall bladder (just below the liver) before release into the small intestine.

Large intestine

• The large intestine (colon) performs the following functions:

  • Storage of waste before elimination

  • Absorbs water from waste

  • Breakdown of any toxins that might damage the colon

  • The colon contains many millions of bacteria which work to keep the colon healthy through detoxifying the waste and producing vitamins.

Rectum and anus

• Semi solid waste is stored in the rectum before being eliminated through the anus