HUMAN PHYSIOLOGY
DIGESTION AND ABSORPTION
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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Facilitated diffusion through a membrane transport protein
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Active transport through the membrane pump
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Simple diffusion through the plasma membrane
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Osmosis
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Detailed explanation-1: -a. Glucose enters cells by facilitated diffusion = carrier mediated transport using a GLUT protein.
Detailed explanation-2: -For glucose Since glucose is a large molecule, its diffusion across a membrane is difficult. Hence, it diffuses across membranes through facilitated diffusion, down the concentration gradient. The carrier protein at the membrane binds to the glucose and alters its shape such that it can easily to be transported.
Detailed explanation-3: -Glucose enters the epithelial cells by a process catalyzed by the cotransporter SGLT-1. Intracellular cAMP activates the transepithelial transport by a mechanism possibly involving phosphorylation of SGLT-1. The glucose accumulated intracellularly can diffuse out of the cells by facilitated diffusion through GLUT2.
Detailed explanation-4: -GLUT2 transports glucose from the cell into the extracellular space on the basolateral side, where the glucose diffuses into capillaries. The absorption of glucose is driven by a sodium gradient maintained by basolateral Na-K-ATPase.
Detailed explanation-5: -Meanwhile, it is generally believed that glucose transport across the capillary membrane is mostly carried out by diffusion, and the convective transport is small. The driving force for substrate diffusion is the concentration gradient across the membrane.