Digestion
Breaking up large organic molecules into smaller, soluble and diffusible molecules
The Digestive System
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Physical Digestion
involves physical break up (chewing, mashing, breaking) of the food, e.g. by teeth
Chemical Digestion
involves the activity of enzymes. Complex molecules are broken down in the process called hydrolysis
What are enzymes?
Biological catalysts made up of proteins that alter the rate of chemical reactions without being chemically changed at the end of the reaction.
Carbohydrases break down...
Carbohydrates into simple sugars
Proteases break down...
Proteins into amino acids
Lipases break down...
Lipids (fats) into glycerol and fatty acids
(Mouth) Mechanical Digestion
Food broken into smaller pieces by chewing
(Mouth) Chemical Digestion
Only Carbohydrate digestion occurs here! → Salivary amylase partially digest starch to maltose
Oesophagus (aka gullet)
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Stomach (1/2)
-Has thick, well-developed muscular walls-Peristalsis in the stomach wall churns and breaks up the food
Stomach (2/2)
-The stomach is distensible-capable of swelling or stretching
Function of hydrochloric acid in stomach
-The HCl secreted kills potentially harmful microorganisms in food.-The pH of the HCl present in gastric juice is about pH2.0 - right condition for action of proteases-Activates the proteases
Small intestine
-Main site for chemical digestion of food-Carbohydrates, fats and proteins are fully digested and absorbed here
Carbohydrate digestion in small intestine
-Remaining undigested starch are broken down to maltose (partially digested carbohydrates by carbohydrase.-They are further digested to glucose (simple sugars) by another carbohydrase in small intestine.
Protein digestion in small intestine
-Remaining undigested proteins are broken down to polypeptides (partially digested proteins by proteases in the small intestine.-They are further digested to amino acids by another protease in small intestine.
Fat digestion in small intestine
Fats are digested to fatty acids and glycerol by lipases in small intestine.
Absorption in small intestine
1. Nutrients absorption-Glucose (simple sugars), amino acids, fatty acids and glycerol are absorbed into the bloodstream2. Water absorption-Most water are absorbed here together with the dissolved nutrients.
Large intestine
Main function is to absorb excess water from the remaining undigested food matter
Rectum
The rectum functions to temporarily store undigested and unabsorbed matter (faeces).
Anus
The anus controls the expulsion of faeces from the body.