Rev Sci Summary Digestion

Maris Stella High School GCE O Level Science Biology

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Nutrition in Mammals Revision Summary Digestive System

Muscles of the gut Peristalsis: Contraction and relaxation of circular and longitudinal muscles cause wave-like contractions that help move the food along the gut. Circular muscles will act in the opposite way to the longitudinal muscles. Sphincters: The rings of muscle that controls the openings at the entry to the stomach, duodenum and anus.

Digestion Oesophagus

Amylase Starch → Maltose

Amylase Starch → Maltose (From saliva, oesphagus does not secrete amylase)

Processes

Physical Digestion

Chemical Digestion

Fluids (source)

Buccal Cavity Saliva: pH ~7 (Salivary glands) Contains salivary amylase

Mastication: Chewing action (due to movement of jaws + teeth) Saliva is mixed with food through action of jaws, teeth and tongue. Tongue helps to roll food into boli to be swallowed.

Peristalsis enables food to be pushed down into the stomach.

Stomach Gastric juice: pH ~2 (Gastric glands) Contains pepsinogen, prorennin, HCl

Pepsin Protein → Peptones

Churning: Stomach contents are churned around with gastric juice (due to contractions of stomach wall) Rennin: Caseinogen (Soluble milk protein → Casein (Insoluble milk protein) (Increase time in stomach for digestion.) Pepsinogen: Activated by HCl. Acid also helps to cause unfolding (denaturation) of dietary protein which increases surface area for digestion.

Small Intestine Bile (Liver, stored temp in gall bladder) Contains bile pigments & bile salts Pancreatic juice (Pancreas) Contains amylase, trypsinogen, lipase Intestinal juice (Intestinal glands) Contains enterokinase, maltase, lactase, sucrase, erepsin, lipase Fluids have pH~8 in ileum, lower pH in duodenum as chyme must be neutralized. Amylase Maltase Starch → Maltose → Glucose Sucrase Sucrose → Glucose + Fructose Lactase Lactose → Glucose + Galactose Trypsin Erepsin Protein → Peptones → Amino acids Lipase Fat → Fatty Acids + Glycerol Emulsification: Bile causes fats to emulsify into smaller fat globules (increases surface area for action of lipase) Peristalsis enables food to be pushed along small intestine. Trypsin is secreted in inactive form (trypsinogen), which is only activated by the enzyme enterokinase from the intestinal glands.