HUMAN BODY SYSTEM

                                              HUMAN BODY SYSTEM

                                              DIGESTION IN HUMANS

What food is?

 Food is anything solid or liquid, which when taken into the body provides the body with energy and

promotes growth.

 Food nutrients are the chemical substances found in food, which give energy to the body.

 The major nutrients found in food are carbohydrates, proteins, vitamins, fats and oils, mineral salts and sometimes water.

Importance of feeding in humans

 Feeding is important because food gives us energy.

 Food contains vitamins which fights against diseases in the body.

 Food promotes growth in our bodies.

Food follows a said pattern in our body. Ingestion → Digestion → Absorption → Assimilation → Egestion.

Digestion In Humans

 Digestion is the breakdown of complex food substances into simple forms the body can absorb by the activity of enzymes. (Enzymes are biological catalysts that speed up the rate of reactions).

 Digestion of food starts in the mouth and ends in the anus through the digestive tract or alimentary

canal.

 When we eat food, the path that the food takes is Mouth→ Oesophagus (Gullet) → Stomach → Small Intestine → Large Intestine → Rectum → Anus.

 To easily remember that, we use the acronym “M O S S L R A”

Below is a diagram showing the alimentary canal as observed in humans.

THE PROCESS OF DIGESTION

Mouth:

 The teeth break food into smaller forms known as mastication.

 The salivary gland secretes saliva to moisten and soften the food.

 The saliva secreted contains an enzyme called salivary amylase which digests starch or carbohydrates in

food into maltose.

 The tongue rolls the food into a bolus and pushes it into the oesophagus or gullet.

Oesophagus or Gullet:

 The bolus moves slowly through the 20 – 30 cm long tube through a process called peristalsis.

Peristalsis is the contraction and relaxation of the walls of the oesophagus to move the food into the

stomach.

Stomach:

 The food hits the walls of the stomach and it secretes juices which contain proteases (protein – digesting enzymes: (pepsin and rennin) and hydrochloric acid.

 The hydrochloric acid reduces the pH of the stomach region to aid the activity of the proteases.

 The proteases digest the proteins in the food into amino acids.

 The food changes into a semi-liquid form, known as chyme.

Small intestine:

 The small intestine is made up of two parts: duodenum and ileum.

 In the duodenum, digestion of fats occur.

 The liver secretes bile which is stored in the gall bladder. Immediately food reaches the duodenum, the gall bladder releases the bile to emulsify or breakdown the fats in the food into tiny droplets.

 The pancreas also secretes pancreatic juice which contains enzymes called lipase (responsible for the

digestion of fats into fatty acids and glycerol) and ptyalin (which further breakdown carbohydrates from

maltose to glucose).

 The duodenum again contain a protein digesting enzyme called trypsin.

 In the ileum, there are thousands of finger – like projections which are highly vascularised called the

villi. These villi increase the surface area of the ileum for maximum absorption of nutrients from the

digested food.

Large intestines:

 The large intestine, also known as colon, absorbs water and salts from the food.

Rectum:

 The undigested food substances(faeces) are stored in the rectum.

Anus:

 The anus opened to allow for release of the faeces in a process known as egestion.