Human Digestion Topic 6.1 pg 67

What is digestion all about? Ingestion – eating the food (the fun bit) Digestion – series of chem reactions where food is reduced into smaller & smaller molecules Absorption – nutrients pass through cells of digestive system into blood or lymphatic vessels Transport – nutrients enter blood or lymphatic system & are transported around the body

Why is it important to digest large food molecules? Need to be digested in order to be absorbed To be absorbed molecules must be small enough to cross the cells (plasma membranes) lining the gut & eventually get into the bloodstream Macromolecules from animals/veg /fruit etc (polymers) to monomers; we can then make human macromolecules Campbell online act 41.1 pg 1

Why are enzymes required? Speed up breakdown (hydrolysis) of macromolecules by lowering activation energy Temperature cant be used to supply energy needed to activate reaction; enzymes allow reactions to occur at normal body temps Each enzyme is specific for certain food type

Enzyme revision How do enzymes act to lower the activation energy? By holding the substrate in the activate site it puts stress on the bonds holding the substrate molecule together – when bonds are stressed it increases chance that surrounding thermal energy will be sufficient to break the bonds

Campbell online act 41.1 pg 3-5 Amylases  starch Proteases  proteins Lipases  lipids Nucleases  nucleic acids

Enzyme examples Enzyme e.g. Source Substrate Product pH Salivary amylase Pepsin (Protease) Phospholipase A2 Source Saliva (salivary glands) Gastric Juice (stomach cells) Pancreatic Juice (chief cells) Substrate starch proteins phospholipds Product Maltose & glucose Amino acids Glycerol, fatty acids pH 7 2-3 8

Human Digestive System – the alimentary canal

Functions anus - the opening at the end of the digestive system from which feces exit the body. esophagus - the long tube between the mouth and the stomach. It uses rhythmic muscle movements (called peristalsis) to force food from the throat into the stomach. gall bladder - a small, sac-like organ located by the duodenum. It stores and releases bile (digestive chem produced in liver) into the small intestine.

Functions large intestine - the long, wide tube that food goes through after it goes through the small intestine. liver - a large organ located above and in front of the stomach. It filters toxins from the blood, and makes bile (which breaks down fats) and some blood proteins.

Functions mouth - the first part of the digestive system, where food enters the body. Chewing and salivary enzymes in the mouth are the beginning of the digestive process (breaking down the food). pancreas - enzyme-producing gland located below the stomach and above the intestines. Enzymes help in the digestion of carbohydrates, fats and proteins in the small intestine.

Functions small intestine - the long, thin winding tube that food goes through after it leaves the stomach. Main function: chem digestion of carbs, lipids, proteins & absorption. stomach - a sack-like, muscular organ that is attached to the esophagus; food is mixed with acids & enzymes  chemical digestion. Food remains for few hours; peristalsis mixes food until almost fluid – called chyme; pyloric sphincter opens allowing small amounts of acid chyme into duodenum; repeated until stomach empty. Main function: storage; chem digestion of proteins

After food is digested what happens? Nutrients (monomers) are absorbed & then assimilated Absorption is the uptake of monomers across the plasma membranes of cells Assimilation is when the nutrients are converted into protoplasm eg solid or fluid parts of cells/body

How do our bodies maximize the absorption of nutrients? Increasing the surface area over which absorption of nutrients can occur is key Small Intestine is where majority of absorption occurs Villi/microvilli cover the sml intestine lining