6. Absorption Flashcards
Define ‘absorption’.
the process of taking substances into cells and the blood
What are epithelial cells?
single layer of cells forming the inner lining of the mucosa
What is the role of the epithelium in the human digestive system?
absorbing nutrients
What does the rate of absorption (in the epithelium) depend on?
the surface area of this epithelium
Where does absorption of nutrients principally occur?
in the small intesting
How long is the small intestine in an adult? How wide? How is its surface area increased?
- 7m long
- 25-30mm wide
- folds on its inner surface, giving a large surface area of epithelium
How else, apart from folds on the inside of the small intestine, is the surface area of the epithelium increased?
by the presence of villi, which are small finger-like projections of the mucosa on the inside of the intestinal wall
What are villi?
small finger-like projections of the mucosa on the inside of the intestinal wall
How long is a villus? How many villi can there be per square millimetre of small intestinal wall?
- 0.5 - 1.5mm long
- 40 per square millimetre
By how much do the villi increase the surface area of the small intestine?
by about a factor of 10
What do the villi absorb?
- mineral ions and vitamins
- also monomers formed by digestion such as glucose
Draw and label a diagram of a villus. (p73)
outside to in:
- layer of microvilli
- epithelium
- goblet cells (secrete mucus)
- blood capillary
- lacteal (a branch of the lymphatic system)
State 4 different methods membrane transport used in the epithelium to absorb nutrients.
- simple diffusion
- facilitated diffusion
- active transport
- endocytosis
How is ‘simple diffusion’ used by the epithelium cells to absorb different nutrients?
simple diffusion: nutrients pass down concentration gradient between phospholipids in the membrane
example: hydrophobic nutrients such as fatty acids and monoglycerides
How is ‘facilitated diffusion’ used by the epithelium cells to absorb different nutrients?
facilitated diffusion: nutrients pass down the concentration gradient between phospholipids in the membrane
example: hydrophilic nutrients such as fructose
How is ‘active transport’ used by the epithelium cells to absorb different nutrients?
active transport: nutrients are pumped through the membrane against the concentration gradient by specific pump proteins
example: mineral ions such as sodium, calcium and iron
How is ‘endocytosis’ used by the epithelium cells to absorb different nutrients?
endocytosis: small droplets of fluid are passed through the membrane by means of vesicles
example: triglycerides and cholesterol in lipoprotein particles
Give an example of a more complex method of transport used in epithelium cells to absorb nutrients, other than the 4 main types of membrane transport. Explain how this works.
- glucose is absorbed by sodium co-transporter proteins
- which move a molecule of glucose together with a sodium ion across the membrane together into the epithelium cells. Glucose can be moved against its concentration gradient because the sodium ion is moving down its concentration gradient. The sodium gradient is generated by active transport of sodium out of the epithelium cell by a pump protein.
How can we model the absorption be the epithelium of the intestine?
with dialysis tubing
Sketch a dialysis tubing model. (p73)
-
What is expected to happen in the dialysis tubing model?
- cola drink contains mixture of substances which can be used to model digested and undigested foods in the intestine
- water outside bag tested at intervals to see if substances in cola have diffused through dialysis tubing
expected result: glucose and phosphoric acid, which have small-sized particles, diffuse through the tubing but caramel, which consists of larger polymers of sugar, does not
Define a ‘scientific model’.
a theoretical representation of the real world
What do biological models represent?
a structure or process non-mathematically
What happens once a model has been proposed?
predictions are made, and the predictions are tested
How are predictions of a biological model tested? How can a model be trusted more? What happens if predictions are not as close as they could have been?
- with experiments or observations of the real world
- if the predictions based on a model fit experimental data or observations
- the model is modified
What is falsification? What happens when a model or theory is falsified?
- when evidence shows that a model or theory is incorrect
- the model or theory must then be discarded and replaced
Give an example of a physical model.
modelling absorption with dialysis tubing
