digestion in the ileum Flashcards
what is the ileum
second part of the small intestine
adaptions of the ileum
-long- allowing time for digestion and absorption
-having villi- increases surface area
-lining of a single layer of the epithelium cells- decrease diffusion distance
-good blood supply- many capillaries to maintain a concentration gradient
how are columnar epithelial cells adapted to help absorption in the ileum
-microvilli- increase cell surface area for diffusion
-high density of mitochondria- provides ATP as a source of energy for the absorption of nutrients by active transport
what does the cell surface membrane of the epithelial cells contain
intrinsic and extrinsic membrane proteins
what are some intrinsic and extrinsic membrane proteins made out of
disaccharidases and dipeptidases
what do some intrinsic membrane proteins acts as
channels or carriers which allow small molecules and ions to be absorbed from the lumen into the cell by the process of facilitated diffusion.
how do other carriers work if not by facilitated diffusion
use ATP to transport ions across the membrane by active transport
can be carried out against the concentration gradient
what are absorbed by facilitated diffusion alone
some amino acids and monosaccharides
why might the epithelium have the concentration to drive absorption
contains a high concentration of glucose
facilitated diffusion would be too slow
so co transport is used
explain co transport
-sodium ions are moved by active transport out of the epithelium cells and into the blood. Sodium ions are also actively transported out of the epithelium cells into the lumen
-This means there is a concentration gradient of sodium ions which are less concentrated in the epithelial cell than in the lumen. Sodium ions will therefore have a tendency to diffuse from the lumen to the epithelial cells
-there is a protein carrier in the membrane that transports one sodium ion and one glucose molecule at the same time
-the concentration gradient of sodium ions therefore drives the absorption of both these and glucose molecules from the lumen into the epithelial cells
as glucose concentration increases on the epithelial cells it passes by facilitated diffusion through protein carriers in the membrane and enters the blood
what consequences with the absorption of water soluble nutrients have
lowers the water potential in the epithelial cells and blood
its lower than the water potential in the lumen
so water will move from the lumen into the epithelial cells and blood by osmosis
what’s different with the absorption of lipids
they are hydrophobic and miscible with the phospholipid bilayer in the membrane of epithelial cells
how are lipids absorbed
lipase usually digests triglycerides in the micelles by removing 2 fatty acids leaving one attached to the glycerol as a monoglyceride
the micelles now contain monoglyceride, fatty acids and other lipids as well as bile salts (micelles help make more soluble)
this produces a higher concentration of fatty acids outside compared to inside so fatty acids and lipids cross by simple diffusion
-inside the cell the monoglycerides and fatty acids combine into triglycerides and are enclosed into a vesicle and transported to the lymph
