Mechanical vs. Chemical Digestion

Mechanical Digestion Larger pieces of food get broken down into smaller pieces while being prepared for chemical digestion; this process starts in the mouth and continues into the stomach.  Occurs in the following locations: 1. Mouth via Mastication by teeth, tongue and palates 2. Esophagus via Peristalsis - the wave like contractions move food through the system 3. Stomach via the muscular churning action of stomach 4. Small Intestine via the Emulsification (breakdown) of Fats

Why do we need Mechanical Digestion? Mastication (chewing) begins the process of breaking down food into nutrients. chewing creates smaller pieces are more readily digested through chemical digestion Movement of substance through digestive tract Peristalsis moves the food through the rest of the digestive tract Absorption the nutrients that come from food in the SI NOTE: Mechanical digestion only deals with the physical breakdown of substances

Chemical Digestion Involves the breaking down large, insoluble molecules into small, soluble ones. Enzymes speed up the process and work efficiently at body temperature and at a suitable pH level Chemical Digestion happens Mouth Stomach Small Intestine

Chemical Digestion Lubricants – Mucus found throughout our digestive system (saliva, stomach, SI) plays a major role in lubricating food as it passes through the digestive system. Secretions – a substance produced by a gland or tissue and released into the organism for special use by the organism or for excretion Examples: digestive juices, hormones, and perspiration

Chemical Digestive Enzymes The Salivary Glands, Gastric Glands, Liver, Gallbladder and Pancreas all play different roles in chemical digestion: Enzymes secreted from these sources, break down large food molecules by the process of hydrolysis HYDROLYSIS The process by which a water molecule is added at the site where a bond is broken This in turn breaks down the molecules into smaller molecules (easier to digest)

Chemical Digestive Enzymes

Chemical Digestive Enzymes 1. Mouth: salivary glands produce the enzyme salivary amylase which breaks down starch (Glucose) into maltose. 2. Stomach: is lined with Gastric glands Secrete 400-800 mL of gastric juice each meal Stomach has a pH of >2, which helps break down food and kill bacteria. PARIETAL CELLS Secrete Hydrochloric Acid (HCl) GASTRIC LIPASE From Chief Cells, speeds up digestion CHIEF CELLS Pepsinogen  Pepsin (protein  peptides) MUCUS SECRETING CELLS Protective Mucus coating of stomach lining

*Note: Lactose intolerance results from a lack of the enzyme lactose.* Chemical Digestion 3. Small Intestine: Final digestion of Proteins and Carbohydrates. Fats begin to break down (be Emulsified) Villi cells produce enzymes that complete digestion of peptides and sugars. *Note: Lactose intolerance results from a lack of the enzyme lactose.* Enzymes Break Down Results Maltase  Maltose 2 Glucose Lactase  Lactose 1 Glucose & 1 Galactose  Sucrase  Sucrose 1 Glucose & 1 Fructose  Peptidase  Tripeptide Dipeptide & 1 Amino Acid Nuclease  Nucleic Acid Nucleotides

Chemical Digestion 3. Small Intestine: Final digestion of Proteins and Carbohydrates. INTESTINAL JUICES Intestinal juice contains the following substances: water, mucin and enzymes. The glands that secrete intestinal juice are called the “CRYPTS OF LIEBERKUHN”. These glands are located at the base of the villi that line the SI.

Chemical Digestion 3. Small Intestine: Final digestion of Proteins and Carbohydrates. PANCREATIC JUICES Pancreatic juice contains water, mucin, sodium bicarbonate and enzymes. Pancreatic juice is produced by and released from the pancreas and flows by way of a tube called the pancreatic duct into the duodenum. The Sodium Bicarbonate that is present in pancreatic juice is important in that it acts as a buffer to change the pH of the chyme from 2 to a pH of 8.

Absorption A very important part of the digestive process as it allows digested food to be transferred to the bloodstream and transported to cells in the body. Most absorption occurs in the small intestine. Villi and micro villi greatly increase the surface area. Absorption through the intestinal walls occurs by ________________ and ____________________. Fat, however, enter the _________________ (vessel) which is part of the lymphatic system and takes the fat to fat tissue where it is stored.