Chapter 4_Macronutrient Uptake, Absorption, Transport

.pdf

School

Arapahoe Community College *

*We aren’t endorsed by this school

Course

100

Subject

Biology

Date

Dec 6, 2023

Type

pdf

Pages

Uploaded by UltraEnergy12630

From The Kansas State University Human Nutrition (HN 400) Flexbook by Brian Lindshield is in the public domain in the United States. 4 Macronutrient Uptake, Absorption & Transport The term absorption can have a number of different meanings. Not everything that is taken up into the enterocyte from the lumen will be absorbed, so the term uptake refers to compounds being transported into the enterocyte. Absorption means that a compound is transported from the enterocyte into circulation. Under most circumstances, compounds that are taken up will then be absorbed. After this chapter, hopefully this distinction between these terms will be clear. After later micronutrient chapters, hopefully you will understand the reason for emphasizing this distinction. Sections: 4.3 Types of Cell Uptake/Transport 4.4 Carbohydrate Uptake, Absorption, Transport & Liver Uptake 4.5 Glycemic Response, Insulin & Glucagon 4.6 Protein Uptake, Absorption, Transport & Liver Uptake 4.7 Lipid Uptake, Absorption & Transport

4.3 Types of Cell Uptake/Transport There are a number of different forms of uptake/transport utilized by your body. These can be classified as passive or active. The difference between the two is whether energy is required and whether they move with or against a concentration gradient. Passive transport does not require energy and moves with a concentration gradient. Active transport requires energy to move against the concentration gradient. The energy for active uptake/transport is provided by adenosine triphosphate (ATP), which is the energy currency in the body. Tri- means three, thus ATP is adenosine with three phosphate groups bonded to it. Phosphorylation is the formation of a phosphate bond. Dephosphorylation is removal of a phosphate bond. Overall phosphorylation is a process that require energy. The net effect of dephosphorylation is the release of energy. Thus, energy is required to add phosphates to ATP, energy is released through removing phosphates from ATP. Subsections: 4.31 Passive Uptake/Transport 4.32 Active Uptake/Transport

4.31 Passive Uptake/Transport There are three forms of passive uptake/transport: 1. Simple Diffusion 2. Osmosis 3. Facilitated Diffusion 1. Simple Diffusion Simple diffusion is the movement of solutes from an area of higher concentration (with the concentration gradient) to an area of lower concentration without the help of a protein, as shown below. Figure 4.311 Simple diffusion 2. Osmosis Osmosis is similar to simple diffusion, but water moves instead of solutes. In osmosis water molecules move from an area of lower concentration to an area of higher concentration of solute as shown below. The effect of this movement is to dilute the area of higher concentration. Figure 4.312 Osmosis

The following videos do a nice job of illustrating osmosis. Web Links: Video: Osmosis (0:47) Video: Osmosis in the Kitchen (0:58) Another example illustrating osmosis is the red blood cells in different solutions shown below. Figure 4.313 Effect of salt solution concentration on red blood cells 1 We will consider the simple example of salt as the solute. If the solution is hypertonic, that means that there is a greater concentration of salt outside (extracellular) the red blood cells than within them (intracellular). Water will then move out of the red blood cells to the area of higher salt concentration, resulting in the shriveled red blood cells depicted. Isotonic means that there is no difference between concentrations. There is an equal exchange of water between intracellular and extracellular fluids. Thus, the cells are normal, functioning red blood cells. A hypotonic solution contains a lower extracellular concentration of salt than the red blood cell intracellular fluid. As a result, water enters the red blood cells, possibly causing them to burst. 3. Facilitated Diffusion The last form of passive absorption is similar to diffusion in that it follows the concentration gradient (higher concentration to lower concentration). However, it requires a carrier protein to transport the solute across the membrane. The following figure and video do a nice job of illustrating facilitated diffusion. Figure 4.314 Facilitated diffusion examples 2

Web Link: Video: Facilitated Diffusion (0:27) References 1. http://en.wikipedia.org/wiki/File:Osmotic_pressure_on_blood_cells_diagram.svg 2.https://en.wikipedia.org/wiki/Facilitated_diffusion#/media/File:Scheme_facilitated_diffusion_in_cell_membrane -en.svg Videos 1. Osmosis - http://www.youtube.com/watch?v=sdiJtDRJQEc 2. Osmosis in the Kitchen - http://www.youtube.com/watch?v=H6N1IiJTmnc&NR=1&feature=fvwp 3. Facilitated Diffusion - http://www.youtube.com/watch?v=s0p1ztrbXPY

4.32 Active Uptake/Transport There are two forms of active uptake/transport: 1. Active Carrier Transport 2. Endocytosis 1. Active Carrier Transport Active carrier transport is similar to facilitated diffusion in that it utilizes a protein (carrier). However, energy is also used to move compounds against their concentration gradient. The following figure and video do a nice job of illustrating active carrier transport. Figure 4.321 Sodium-potassium ATPase (aka sodium-potassium pump) an example of active carrier transport 1 2. Endocytosis Endocytosis is the engulfing of particles, or fluids, to be taken up into the cell. If a particle is endocytosed, this process is referred to as phagocytosis. If a fluid is endocytosed, this process is referred to as pinocytosis as shown below. Figure 4.322 Different types of endocytosis 2 References 1. https://en.wikipedia.org/wiki/File:Scheme_sodium-potassium_pump-en.svg 2. http://commons.wikimedia.org/wiki/File:Endocytosis_types.svg

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version