6.1 Digestion Topic 6: Human health & physiology

On your human body outline, sketch in and name the organs of the digestive system.

Large food molecules need to be digested before the nutrients can be absorbed. Large molecules are: usually insoluble too large to diffuse across membranes and into the blood Products of digestion are: usually soluble small enough for absorption into the bloodstream and assimilation into the tissues * Remember! Hydrolysis is the reaction used to break down large organic molecules. Enzymes are needed in these reactions.

AmylaseProteaseLipase Macromolecule CarbohydratesProteinsLipids/fats Example Salivary amylaseTrypsinPancreatic lipase Substrate StarchPolypeptidesTriglycerides Product MaltoseAmino acidsFatty acids and glycerol Source Mouth (salivary glands) Duodenum (small intestine) Pancreas Optimal pH 7 – – 7.5 Question: Where would an enzyme with an optimum pH of 2 be found?

nb This is NOT to scale oesophagus stomach small intestine anus mouth & salivary glands large intestine pancreas liver rectum duodenum ileum gall bladder

Stomach o muscular contractions continue mechanical digestion. o acid kills bacteria. o pepsin begins digestion of proteins. Ileum (small intestine) o lower half of small intestine. o absorbs nutrients into the blood via the villi. Duodenum (small intestine) o bile from the liver and gall bladder neutralises acid and emulsifies fats. o pancreatic amylase and lipase digest carbohydrates and fats. o trypsin digests polypeptides to amino acids. Large intestine o water is reclaimed and returned to the blood, leaving semi-solid faeces which are stored in the rectum.

Mouth o ingestion o chewing begins mechanical digestion. o saliva moistens food to make a bolus for swallowing. o salivary amylase begins chemical digestion of starch. Egestion o faeces (containing undigested food, dead cells and other wastes) is moved out of the anus.

o The villi (singular is villus) are finger-like projections in the small intestine which absorb the products of digestion. o The large number of these villi creates a huge surface area for the absorption of digested food molecules. o Epithelial (surface) cells have microvilli – tiny finger-like hairs to increase the surface area even more (only label these on a diagram if you can see them). o Each villus has a thin epithelium, only one cell thick, to make diffusion fast and more efficient. o A rich blood supply maintains a concentration gradient down which nutrients can diffuse across the membranes. o Lymph vessels (lacteals) close to the surface allow lipids to be easily absorbed.