University:
Felician University
Course:
BIO-102 | Human Biology
Academic year:

2020
Views:

23

Pages:

1
Author:

larbiwxcvbn

DIGESTIOn Purpose of Digestion The main purpose of the digestive system is to break large molecules down into smaller subunits due to the fact that: • Large molecules are typically chemically inert and need to be broken down and reassembled into usable products • Large molecules are typically insoluble and cannot be easily absorbed into cells, whereas smaller subunits are soluble Digestive System Structure Digestive System Components The digestive system is composed of the alimentary canal and a variety of supporting accessory organs Salivary Glands Oesophagus Liver Stomach Gall Bladder Pancreas Small Intestine Rectum Large Intestine Alimentary Canal (directly transfers food) • Oesophagus – Food tract from mouth to stomach • Stomach – Storage tank with low pH (protein digestion) • Small intestine – Site of nutrient absorption • Large intestine – Absorbs water and dissolved minerals Accessory Organs (supports digestive processes) • Salivary glands – Moistens food bolus (starch digestion) • Pancreas – Secretes key enzymes into small intestine • Liver – Metabolises absorbed nutrients (produces bile) • Gall bladder – Stores and secretes bile (emulsifies fats) Digestive Movement Peristalsis • Unidirectional movement of food along alimentary canal • Caused by contraction of sequential longitudinal muscles Segmentation • Bidirectional mixing of food within the small intestine • Caused by contraction of non-sequential circular muscles Types of Digestion Starch Hydrolysis Food can be digested by one of two ways: Starch is composed of glucose monomers • Is linear (amylose) or branched (amylopectin) Mechanical Digestion The breakdown of food via physical actions • Chewing (grinding food using teeth) • Churning (squeezing stomach contents) • Segmentation (intestinal contractions) Chemical Digestion The breakdown of food via chemical agents • Stomach acids (low pH environment) • Bile (emulsification of fats into droplets) • Enzymes (catalyse hydrolysis reactions) Liver Mouth Amylase (salivary or pancreatic) digests starch • It digests amylose into maltose disaccharides • It digests amylopectin into dextrin chains The pancreas regulates the uptake of glucose • Insulin increases glucose uptake by cells • Glucagon decreases glucose uptake by cells The liver is responsible for glucose storage • Glucose is stored as glycogen (polysaccharide) Stomach Pancreas Small Intestine