💙 3.3.3 Absorption Flashcards
What are some adaptations of villi and the gut for absorption?
- large surface area
- very thin wall (a single layer of epithelial cells) to reduce the diffusion distance
- Epithelial cells lining the villi have microvilli
- good moving blood supply so that blood can carry away absorbed nutrients so that a steep concentration gradient is maintained
- muscles are able to move which helps with mixing the contents of the small intestine to help maintain a steep concentration gradient
- lacteal is present to absorb lipids
There are five steps to the absorption of lipids. What is step number one?
Monoglycerides and fatty acids combine with bile salts to form micelles. These transport the monoglycerides and fatty acids from the lumen of the gut to the epithelial cell membrane.
What is step number two in the absorption of lipids?
The bile salts and triglycerides/fatty acids separate and the latter cross the epithelial cell membrane by simple diffusion
What is step three in the absorption of lipids ?
Monoglycerides and fatty acids recombine in the SER to make triglycerides
What is step four in the absorption of lipids?
The triglycerides are packaged in the Golgi apparatus along with protein and cholesterol to form chylomicrons
What is step five in lipid absorption?
The chylomicrons move to the membrane of the cell and into the lacteal by exocytosis
Describe the method of co-transport of absorption of glucose and amino acids
- sodium potassium pump (via active transport) Na+ out of the epithelial cells and into the blood/capillaries
- this creates a concentration gradient of Na+ between epithelial cells and the gut
- Na+ enters the epithelial cells of villi by facilitated diffusion
- co transporter proteins carry glucose/amino acids into epithelial cells at the same time as Na+
- glucose/amino acids enter capillaries/blood by facilitated diffusion
