3.3 absorption

Question 1

adaptations of the ileum

Answer 1

• ileum wall covered in villi which have thin walls surrounded by a network of capillaries and epithelial cells have an even smaller microvilli
• increases surface area for absorption, decrease diffusion distance and maintain conc gradient

Question 2

where are the products of digestion absorbed

Answer 2

across cells lining the ileum

Question 3

outline how molecules diffuse across the ileum

Answer 3

• conc gradient as molecules are constantly digested
• products diffuse from small intestine to blood
• needs to be facilitated diffusion though a channel for large/charged molecules

Question 4

outline why active transport may be used?

Answer 4

• not all glucose can be absorbed by facilitated diffusion as conc in ileum epithelial cells is lower than lumen towards end of digestion
• conc gradient will reach equilibrium

Question 5

process of co-transport

Answer 5

1. ATP used to actively transport sodium ions out of the epithelial cells into the blood using the sodium potassium pump by releasing energy
2. this lowers conc of sodium in the cell compared to the ileum maintaining a diffusion gradient for sodium
3. sodium enters from small intestine by facilitated diffusion down sodium’s conc gradient through a co-transporter protein channel in the plasma membrane. sodium brings with them either glucose or amino acid molecules against their conc gradient
4. resulting high conc off amino acids and glucose in the epithelia cells leads to them entering blood by facilitated diffusion down their conc gradient

Question 6

outline the absorption of lipids

Answer 6

• absorbed by diffusion across cell surface membrane to enter cells of epithelial cells
• this is because fatty acids and monoglycerides are non-polar and lipid soluble
• once in the cell they are converted back into triglycerides by endoplamsic reticulum
• pass to golgi apparatus and are modified by combining with protein to form chlyomicrons
• packaged into vesicles and leave by exocytosis and are removed by lymphatic system

Question 7

describe and explain four features found in a cell specialised for absorption

Answer 7

• folded membrane/microvilli so large s.a
• large number of carrier proteins so fast rate of absorption
• large number of mitochondria so make more ATP to release energy for active transport
• membrane bound digestive enzymes so maintain conc gradient for fast absorption

Question 8

explain why emulsions with small lipid droplets are easier to digest and absorb

Answer 8

• larger SA:V for lipases to work on
• leads to faster rate of digestion of triglycerides to fatty acids and monoglycerides

Question 9

where is maltase found

Answer 9

membrane bound in small intestine

Question 10

name the components of a chlyomicron

Answer 10

• triglycerides
• protein
• cholesterol
• phospholipids