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

2019
Views:

164

Pages:

1
Author:

SpaceCadet101

ABSORPTION Purpose of Absorption Absorption involves the movement of fluids or dissolved substances (such as nutrients) across a cellular membrane • The absorbed components then undergo assimilation within the cell in order to become fluid or solid parts of an organism Nutrient absorption occurs within the small intestine, while water and mineral ions are absorbed within the large intestine Membrane Transport Mechanisms Secondary Active Transport • Glucose and amino acids are co-transported across the epithelial membrane with sodium ions (Na+) Endocytosis • Dissolved materials may be rapidly absorbed en masse via the process of pinocytosis (cell ‘drinking’) Facilitated Diffusion • Certain monosaccharides, vitamins and some minerals may be transported by epithelial channel proteins Extracellular Fluid Simple Diffusion • Hydrophobic materials (e.g. lipids) are capable of freely diffusing across the epithelial membrane Cytoplasm Vesicle Small Intestine Structure Longitudinal Cross-Section Transverse Cross-Section Serosa Villi Longitudinal muscle Circular muscle Mucosa Submucosa Muscle layers Mucosa Villi Modelling Absorption Villi are finger-like mucosal projections that increase the surface area of epithelium over which absorption is carried out Dialysis tubing can be used to model the size-specific permeability of a membrane • Large molecules cannot cross (e.g. starch) • Smaller molecules can cross (e.g. glucose) Key features of villi include: • Microvilli (⬆ SA:Vol) • Rich blood network • Single layer epithelium • Lacteals (absorb lipids) • Intestinal crypts (exocrine) • Membrane proteins If large molecules are digested with enzymes, the absorption of the smaller subunits can then be measured in a number of ways: • Via a change in fluid / meniscus levels • Via the presence of specific materials (identified via treatment with a reagent) Sample Experiment: Control Digestion Starch in Water in Maltose exits Water exits