Human Health & Physiology Digestion 6.1

Digestion Why do we digest food? We digest so our cells are provided with the nutrients they need. Basic Format: Ingestion – you eat the food Digestion – a series of chemical reactions that convert the ingested food into smaller and smaller molecular forms Absorption – small molecular forms are absorbed through cells of your digestive system and pass into nearby blood or lymphatic vessels Transport – circulatory system delivers small molecular nutrients to body cells

Molecular Form Ingested Molecular form after Digestion Digestion Solves a Problem of Molecular Size All foods we eat must be chemically digested to suitable size that allows for nutrients to enter the blood stream Molecule Type Molecular Form Ingested Molecular form after Digestion Protein Amino Acids Lipids Triglycerides Glycerol & Fatty Acids Carbohydrates Mono, Di, Poly Saccharides Monosaccharides Nucleic Acids DNA / RNA Nucleotides

Digestion All foods contain either plant or animal cells Plants store carbohydrates as Starch Animals store carbohydrates as Glycogen Each living organism has its own set of proteins Each organism protein has a unique sequence of amino acids DNA and RNA also has a unique sequence Hydrolyse – to undergo a change; become different in essence This is why we digest

Enzymes increase the rate of digestion at body temperature. Enzymes in Digestion As foods enter the alimentary canal digestive enzymes are added to the food Remember: Enzymes are proteins that catalyze reactions Enzymes lower activation energy Which reduces the amount of energy needed in a reaction which is usually heat Enzymes increase the rate of digestion at body temperature.

Enzymes in Digestion We have specific enzymes that break up different types of carbohydrates and proteins Protease – general name for enzymes that break up proteins Remember proteins are large so enzymes digest proteins by individual amino acids starting on the ends Book says 3

Know this!!!! Be able to Diagram this!!

The Role of the Stomach Food is brought to the stomach via the esophagus Peristalsis – a series of smooth muscle contractions that force food down to the stomach. Gastric Juice – a mixture of 3 secretions from cell in the stomach lining Pepsin – a protease enzyme most active in acidic pH Hydrochloric Acid – degrade and breaks down foods and creates the acidic pH necessary for pepsin to be active Mucus – lines the inside of the stomach wall to prevent stomach damage from hydrochloric acid

The Role of the Stomach The stomach wall of the stomach creates a churning motion to mix the food and the gastric juices Then a valve opens and food enters the small intestine

The Role of the Small Intestine Duodenum – first part of the small intestine 3 different organs secrete juices into the small intestine Bile from the liver Bile from the gall bladder Trypsin – ( a protease), lipase, amylase, and bicarbonates from the pancreas

The Role of the Small Intestine Pancreas A multipurpose organ Produces insulin and glucagon (glucose metabolism) Produces three enzymes: Lipase Amylase Protein digesting enzyme known as endopeptidase These are known as Pancreatic Juice All these fluids are released in the beginning of the lumen of the small intestine

The Role of the Small Intestine As digestion continues in the small intestine food is continually broken down into molecules Now they can be absorbed Villi – the inner wall of the small intestines Each villus contains a capillary bed and a lacteal Lacteal – a small vessel of your of your lymphatic system just like a capillary Small intestine lining is smooth Villi increases the surface area to increase absorption rate of molecules

The Role of the Small Intestine The contraction of circular and longitudinal muscle of the small intestine mixes the food with enzymes and moves it along the gut. Need to know

Assimilation Assimilation follows digestion Nutrients that are absorbed into the blood stream are transported to cells throughout the body to perform various functions. Villi absorb monomers formed by digestion as well as mineral ions and vitamins These nutrients are incorporated into the tissues and organs. Starch, glycogen, lipids, and nucleic acids are digested into monomers, cellulose remain undigested

The Role of the Small Intestine Inner lining of the small intestine make up what is called the mucosa. The mucosa has many folds or projections called villi (villus singular) Each villus is composed of may cells whose primary job is selectively absorbing molecules found in the lumen of the small intestine. Absorption occurs through the cells in an epithelial layer that is in direct contact with the nutrients.

The Role of the Small Intestine Epithelial cells have tiny membrane projections called microvilli that extend into the lumen. This greatly increases the surface area The interior of each villus contains a capillary bed for nutrient absorption and transport of digested monomers Small vessel of the lymphatic system, called the lacteal, absorbs some of the nutrients. Monomers are absorbed into the inner capillary bed Larger monomers such as fatty acids are absorbed first into the lacteal

The Role of the Small Intestine Substances Absorbed through the villi: Water Glucose Amino acids Glycerol Fatty acids Mineral ions Vitamins

The Role of the Small Intestine

The Role of the Small Intestine Most of the molecules absorbed are taken into the capillary bed Fatty acids are absorbed by the lacteal Undigested nutrients cannot pass through the villus epithelium

The Role of the Large Intestine Most food is absorbed in the small intestine Enzymes digest most macromolecules in food into monomers in the small intestine Undigested food plus water is passed into the large intestine Primary function of the large intestine is water absorption Water allows food to travel easier through the alimentary canal This is why it is absorbed last Mutualistic bacteria Escherichia coli synthesis vitamin K and maintain a healthy environment in the large intestine Any foods not digested are eliminated

The Role of the Large Intestine

Transport Mechanisms Different methods of membrane transport are required to absorb different nutrients Passive Transport (Mechanisms) Simple diffusion – Direct movement through the cell following the concentration gradient High concentrations to low concentrations Facilitated Diffusion - movement through the cell following the concentration gradient, but the molecule must travel through a protein channel Happens because of polarity Glucose and amino acids

Transport Mechanisms Active Transport (Mechanism) When a cell expends energy to move molecules or ions across a membrane Protein “pumps” a solute across a membrane, usually in the opposite direction to the way it travels in diffusion Requires chemical energy supplied by the mitochondria Active Transport play a vital role in maintaining the cells chemical environment.

Transport Mechanisms Endocytosis – takes in material into the cell within vesicles that bud inward from the plasma membrane.