Nutrition and Digestion

Lynsey Cleaver                                                 Human Nutrition and Digestion


Virtually all nutrients from our diet are absorbed into blood across the mucosa of the small intestine. In addition, the intestine absorbs water and electrolytes, thus playing a critical role in maintenance of body water and acid-base balance. One of the processes that takes place in the small gut is of extreme importance, which makes absorption possible is the establishment of an electrochemical gradient of sodium across the epithelial cell boundary of the lumen.

Th remain viable all cells are required to maintain a low intracellular concentration of sodium. In polarised epithelial cells like electrolytes, low intracellular sodium is maintained by a large number of Na+/K+ ATPases-called sodium pumps, embedded in the basolateral membrane. These pumps export 3 sodium ions from the cell in exchange for 2 potassium ions, thus establishing a gradient of both charge and sodium concentration across the basolateral membrane. (McGuiness, H. 2010).

Dietary sources of protein, carbohydrate and fat must all undergo the final stages of chemical digestion prior to absorption of, amino acids, glucose and fatty acids.There are two ways in which substances can enter or leave a cell, passively, by simple diffusion, facilitated diffusion or osmosis (water only), actively, molecules and particles.

Diffusion is the net passive movement of particles (atoms, ions or molecules) from a region in which they are in higher concentration to regions of lower concentration. It continues until concentration of substances is uniform throughout.

Facilitated diffusion is the movement of specific   molecules down a concentration gradient, passing through the membranes via a specific carrier protein. Similar to enzymes, each carrier has its own shape and only allows one molecule (or one group of closely related molecules) to pass through. Selection is by size, shape and charge....