In order to fully gain the nutrients attained from the food we ingest, the body must absorb it. In this IBDP Biology post, we will understand:
- The different ways in which the body absorbs different molecules
- Villi and Microvilli
- Modes of absorption
Absorption
Absorption happens using the Villi and Microvilli
Villi are:
- finger-like projections
- increase
- surface are
- a for absorption
- Epithelial cells with many
mitochondria
Villi: Many folds of the inner cells lining the small intestine
Each villus contains:
- Capillary
Bed for absorption and transportation
- Lacteal
(vessel of lymphatic system) to absorb larger monomers (fatty acids)
Adaptations for absorption:
- Many villi potrude into the lumen greatly increasing the surface area for absorption
- Single cell layer of epithelial cells - short path for diffusion
- Micro villiof the surface of each cell increase surface area even more
- Capiliries are close to epithelium - short path for diffusion, rich supply of blood
- Rich blood supply maintains concentration gradient between lumen and blood
Transport mechanisms for Absorption
Lipids
- Simple Diffusion:
- Nutrients pass down the concentration gradient between phospholipids in the membrane
- Hydrophobic nutrients fatty acids and monoglycerides
Fructose and Vitamins
- Facilitated Diffusion:
- Nutrients pass down the concentration gradient through specific channel proteins in the membrane
- Hydrophillic nutrients fructose
Mineral ions
- Active Transport:
Nutrients are pumped through the membrane against the concentration gradient by specific pump proteins eg. Sodium, calcium and iron
Tryglycerides and cholesterol in lipoprotein particles
- Endocytosis:
In which small droplets of fluid are passed through the membrane by means of vesicles
Dialysis tubing to model Absorption
In IBDP Biology, Dialysis tubing can be used to model absorption by the epithelial cells of the small intestine
The tubing is semi-permeable and contains pores 1 - 10 nm in diameter
Cola drinks contain a mixture of substances that models digested and undigested food in the intestine
The water surrounding the bag is tested at different intervals to see if substances in the cola have diffused through the dialysis tubing
Test solutions inside and outside dialysis tubing for starch and glucose before and after 15 minutes
Expected Result: Glucose and phosphoric acid [contain small-sized particles] diffuse through the tubing but caramel [contains larger polymers of sugar] does not
And that's the end!
References:
https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.sciencelearn.org.nz%2Fimages%2F2259-villi-in-the-small-intestine&psig=AOvVaw0fLAFUZPaY7Qg7dcBiHCH-&ust=1625294823137000&source=images&cd=vfe&ved=0CAoQjRxqFwoTCNDbh5flw_ECFQAAAAAdAAAAABA3
Drafted by Venetia (Biology)